阅读说明：本技术 全固态二次电池及其制造方法 (All-solid-state secondary battery and method for manufacturing same ) 是由 今井真二 小泽信 铃木秀幸 于 2020-03-16 设计创作，主要内容包括：本发明提供一种全固态二次电池的制造方法、以及利用该制造方法制造的全固态二次电池,所述全固态二次电池具有含有无机固体电解质的粒子的固体电解质层及在固体电解质层的一个表面上的正极活性物质层,所述全固态二次电池的制造方法具备：使用含有正极活性物质及负极活性物质前体的正极用组合物,在固体电解质层的一个表面形成正极活性物质层的工序；对包含所形成的正极活性物质层及固体电解质层的层叠体进行充电的工序；及至少对正极活性物质层进行加压来压缩的工序。(The present invention provides an all-solid-state secondary battery having a solid electrolyte layer containing particles of an inorganic solid electrolyte and a positive electrode active material layer on one surface of the solid electrolyte layer, and a method for manufacturing the all-solid-state secondary battery manufactured by the manufacturing method, the method including: forming a positive electrode active material layer on one surface of the solid electrolyte layer using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor; charging a laminate including the formed positive electrode active material layer and solid electrolyte layer; and a step of compressing the positive electrode active material layer by applying pressure thereto.)

1. A method of manufacturing an all-solid-state secondary battery, the all-solid-state secondary battery having: a solid electrolyte layer containing an inorganic solid electrolyte and a positive electrode active material layer on one surface of the solid electrolyte layer,

the method for manufacturing an all-solid-state secondary battery includes:

forming a positive electrode active material layer on one surface of the solid electrolyte layer using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor;

charging a laminate including the positive electrode active material layer and the solid electrolyte layer; and

and a step of compressing at least the positive electrode active material layer by applying pressure after the step of charging.

2. The manufacturing method of an all-solid secondary battery according to claim 1,

in the step of compressing, the laminate is pressurized at a pressure of 10 to 1000 MPa.

3. The manufacturing method of an all-solid secondary battery according to claim 2,

the pressure is above 80 MPa.

4. The manufacturing method of an all-solid secondary battery according to any one of claims 1 to 3,

and a step of charging the laminate while the laminate is pressed and restrained in the laminating direction.

5. The manufacturing method of an all-solid secondary battery according to any one of claims 1 to 4,

the compressing step is performed so that no voltage is applied to the laminate.

6. The manufacturing method of an all-solid secondary battery according to any one of claims 1 to 5,

the negative electrode active material precursor is at least one compound selected from the group consisting of alkali metal or alkaline earth metal, carbonate, oxide, and hydroxide.

7. The manufacturing method of an all-solid secondary battery according to any one of claims 1 to 6,

the all-solid-state secondary battery has a negative electrode active material layer on the other surface of the solid electrolyte layer.

8. The manufacturing method of an all-solid secondary battery according to claim 7,

the method further comprises a step of forming the negative electrode active material layer using a negative electrode composition containing silicon or an alloy containing a silicon element, prior to the step of charging.

9. An all-solid secondary battery obtained by the method for manufacturing an all-solid secondary battery according to any one of claims 1 to 8.

Technical Field

The present invention relates to an all-solid-state secondary battery and a method for manufacturing the same.

Background

A lithium ion secondary battery is a storage battery that has a negative electrode, a positive electrode, and an electrolyte interposed between the negative electrode and the positive electrode, and can perform charging and discharging by reciprocating lithium ions between the two electrodes. Conventionally, in a lithium ion secondary battery, an organic electrolytic solution is used as an electrolyte. However, the organic electrolytic solution is liable to cause liquid leakage, and short-circuiting may occur inside the battery due to overcharge and overdischarge, and therefore further improvement in reliability and safety is required.

Under such circumstances, development of all-solid-state secondary batteries using an incombustible inorganic solid electrolyte instead of an organic electrolytic solution is under way. In all-solid-state secondary batteries, all of the negative electrode, electrolyte, and positive electrode are made of solid, and therefore, the safety and reliability of batteries using an organic electrolytic solution, which are problems, can be greatly improved, and the life can also be extended.

In general, a secondary battery in which metal ions are reciprocated between two electrodes generally has an irreversible capacity, and when the battery is charged for the first time after manufacture, the amount of metal that becomes a metal ion source (the amount of lithium in the case of an all-solid lithium ion secondary battery) is reduced (loss of discharge capacity is concerned), and a desired battery capacity may not be exhibited.

As one of the measures for reducing the amount of metal by the first charging, there is a technique of replenishing the corresponding metal ion separately from the active material forming the negative electrode active material layer or the positive electrode active material layer. For example, patent document 1 describes a method of predoping lithium ions into a negative electrode in a lithium ion secondary battery using a nonaqueous electrolyte by applying a voltage between a positive electrode precursor and a negative electrode under specific conditions to a laminate composed of the positive electrode precursor containing a positive electrode active material and a specific lithium compound, the negative electrode, and a separator, thereby decomposing the lithium compound. This method describes that the high load charge-discharge cycle characteristics of the lithium ion secondary battery can be optimized by retaining the nonaqueous electrolyte solution in the holes generated by the decomposition of the lithium compound in addition to the preliminary doping of the lithium ions.

Prior art documents

Patent document

Patent document 1: japanese patent No. 6251452

Disclosure of Invention

Technical problem to be solved by the invention

However, in all-solid-state secondary batteries, since the electrolyte is also a solid, it is difficult to hold or fill the solid electrolyte layer in the holes generated in the positive electrode active material layer as in patent document 1. On the other hand, in order to compensate (compensate) the decrease in the amount of metal (the amount of loss of discharge capacity), the more the amount of preliminary doping of metal ions is increased, the more the energy density is decreased.

The present invention addresses the problem of providing an all-solid-state secondary battery that achieves not only a high battery capacity but also a high energy density, and a method for manufacturing the same.

Means for solving the technical problem

The present inventors have found that an all-solid-state secondary battery having higher performance with respect to battery capacity and energy density can be manufactured by preparing a laminate of a positive electrode active material layer containing a negative electrode active material precursor and a solid electrolyte layer, and compressing the positive electrode active material layer after charging the laminate. The present invention has been completed by further conducting a study based on these findings.

That is, the above problem is solved by the following means.

< 1 > a method for manufacturing an all-solid-state secondary battery having a solid electrolyte layer containing an inorganic solid electrolyte and a positive electrode active material layer on one surface of the solid electrolyte layer, comprising:

forming a positive electrode active material layer on one surface of the solid electrolyte layer using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor;

charging a laminate including a positive electrode active material layer and a solid electrolyte layer; and

and a step of compressing at least the positive electrode active material layer by applying pressure after the step of charging.

< 2 > the method for manufacturing an all-solid-state secondary battery according to < 1 >, wherein the step of compressing is performed by pressurizing the laminate at a pressure of 10 to 1000 MPa.

< 3 > the method for manufacturing an all-solid-state secondary battery according to < 2 >, wherein the pressure is 80MPa or more.

< 4 > the method for manufacturing an all-solid-state secondary battery according to any one of < 1 > to < 3 >, wherein the step of charging is performed in a state in which the laminate is constrained under pressure in the lamination direction.

< 5 > the method for manufacturing an all-solid-state secondary battery according to any one of < 1 > to < 4 >, wherein the step of compressing is performed without applying a voltage to the laminate.

< 6 > the method for manufacturing an all-solid secondary battery according to any one of < 1 > to < 5 >, wherein the anode active material precursor is at least one compound selected from the group consisting of alkali metal or alkaline earth metal, carbonate, oxide and hydroxide.

< 7 > the method of manufacturing an all-solid-state secondary battery according to any one of < 1 > to < 6 >, wherein the all-solid-state secondary battery has an anode active material layer on the other surface of the solid electrolyte layer.

< 8 > the method of manufacturing an all-solid-state secondary battery according to < 7 >, wherein the method comprises a step of forming a negative electrode active material layer using a negative electrode composition containing silicon or an alloy containing silicon element before the step of charging.

< 9 > an all-solid-state secondary battery obtained by the method for manufacturing an all-solid-state secondary battery as defined in any one of the above < 1 > to < 8 >.

Effects of the invention

The method for manufacturing an all-solid-state secondary battery according to the present invention can manufacture an all-solid-state secondary battery exhibiting high battery capacity and high energy density. The all-solid-state secondary battery of the present invention exhibits high battery capacity and high energy density.

The above and other features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings where appropriate.

Drawings

Fig. 1 is a longitudinal sectional view schematically showing a preferred embodiment of the all-solid secondary battery of the present invention.

Detailed Description

In the description of the present invention, the numerical range represented by "to" means a range in which the numerical values before and after "to" are included as the lower limit value and the upper limit value.

[ all-solid-state secondary battery ]

First, an all-solid secondary battery manufactured by the method for manufacturing an all-solid secondary battery according to the present invention (also referred to as an all-solid secondary battery according to the present invention) will be described.

The all-solid-state secondary battery of the present invention has a positive electrode active material layer, a negative electrode active material layer facing the positive electrode active material layer, and a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer. The all-solid-state secondary battery of the present invention preferably has a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer adjacent to each other.

In the present invention, unless otherwise specified, the negative electrode active material layer includes not only a preliminarily formed negative electrode active material layer (negative electrode active material layer in the embodiment where the negative electrode active material layer is preliminarily formed) but also a layer containing a metal precipitated by charging (negative electrode active material layer in the embodiment where the negative electrode active material layer is not preliminarily formed).

In the present invention, each layer constituting the all-solid-state secondary battery may have a single-layer structure or a multi-layer structure as long as it exerts a specific function.

The all-solid-state secondary battery of the present invention is not particularly limited as long as it has the above-described structure (solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer), and other structures may be adopted, for example, a known structure relating to all-solid-state secondary batteries.

Fig. 1 is a cross-sectional view schematically showing a stacked state of respective structural layers constituting a battery for one embodiment of an all-solid secondary battery. The all-solid-state secondary battery 10 of the present embodiment has a structure in which the negative electrode current collector 1, the negative electrode active material layer 2, the solid electrolyte layer 3, the positive electrode active material layer 4, and the positive electrode current collector 5 are stacked in this order when viewed from the negative electrode side, and adjacent layers are in direct contact with each other.

The charge and discharge of the all-solid secondary battery of the present invention having such a structure are the same as those of a general all-solid secondary battery except for the predoped metal ions, and the following description will be briefly made.

I.e. electrons (e) during charging^-) The alkali metal or alkaline earth metal that is supplied to the negative electrode side and constitutes the positive electrode active material layer is ionized and moves to the negative electrode side through the (conductive) solid electrolyte layer 3, and ions of the alkali metal or alkaline earth metal are (reduced and) accumulated. For example, in the case of a lithium ion secondary battery, lithium ions (Li)⁺) Is accumulated in the negative electrode.

As will be described in detail later, when the first charge is performed after the production of the all-solid-state secondary battery, the negative electrode active material precursor in the positive electrode active material layer is decomposed (oxidized) to generate ions of an alkali metal or an alkaline earth metal (lithium ions in the case of the all-solid-state lithium ion secondary battery), and the generated ions are replenished (applied) by moving to the negative electrode side through the solid electrolyte layer. Since the ion replenishment is performed before the all-solid secondary battery is used, the ion replenishment is also referred to as pre-doping differently from the ion replenishment at the time of use.

On the other hand, during discharge, the metal ions accumulated in the negative electrode are returned (moved) to the positive electrode side, and electrons generated in the negative electrode are supplied to the working site 6 and reach the positive electrode. In the illustrated example of the all-solid-state secondary battery, a bulb is used in the operating site 6, and the bulb is turned on by discharge.

In the all-solid-state secondary battery of the present invention, the negative electrode active material layer can take various forms.

Examples of the form that can be used for the negative electrode active material layer include a negative electrode active material layer containing a negative electrode active material described later, a negative electrode active material layer containing a silicon material or a silicon-containing alloy that exhibits a high battery capacity (also referred to as Si negative electrode), a lithium metal layer, and a form in which a solid electrolyte layer and a negative electrode current collector are laminated without having a negative electrode active material layer (a form in which a negative electrode active material layer is not formed in advance). The all-solid-state secondary battery of the present invention can appropriately select the form of the negative electrode active material layer in accordance with the required characteristics, production conditions, and the like.

In an all-solid-state secondary battery of an embodiment in which a negative electrode active material layer is not formed in advance, a part of ions (alkali metal ions) of a metal belonging to group 1 of the periodic table or ions (alkaline earth metal ions) of a metal belonging to group 2 of the periodic table, which are accumulated in a negative electrode current collector during charging, is bonded to electrons, and the negative electrode active material layer is formed by utilizing a phenomenon that the ions are deposited as a negative electrode active material (for example, a metal) on the negative electrode current collector (including an interface with a solid electrolyte layer or voids in the solid electrolyte layer). That is, the all-solid-state secondary battery of this embodiment causes the metal deposited on the negative electrode current collector to function as the negative electrode active material layer. For example, lithium metal has a theoretical capacity 10 times or more higher than that of graphite commonly used as a negative electrode active material. Therefore, the lithium metal layer can be formed by depositing lithium metal on the negative electrode current collector, and the thickness can be made thinner in an amount that the negative electrode active material layer is not formed (laminated) in advance, and an all-solid-state secondary battery with further improved energy density can be realized.

As described above, the all-solid-state secondary battery of the embodiment in which the negative electrode active material layer is not formed in advance includes both the uncharged embodiment (the embodiment in which the negative electrode active material is not precipitated) and the charged embodiment (the embodiment in which the negative electrode active material is precipitated). In the present invention, the term "all-solid-state secondary battery of an embodiment in which the negative electrode active material layer is not formed in advance" simply means that the negative electrode active material layer is not formed in the layer forming step in the battery production, and the negative electrode active material layer is formed on the negative electrode current collector by charging as described above.

< solid electrolyte layer >

The solid electrolyte layer 3 contains an inorganic solid electrolyte (in the form of particles, also referred to as inorganic solid electrolyte particles) having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table and a component described later in a range not impairing the effect of the present invention, and usually does not contain a positive electrode active material and/or a negative electrode active material.

The solid electrolyte layer is a layer that exhibits the above-described ion conductivity and functions as a separator that exhibits electronic insulation, and the solid electrolyte layer provided in a conventional all-solid-state secondary battery can be applied without particular limitation. The solid electrolyte layer may be formed of particles of the inorganic solid electrolyte described above.

The content of the inorganic solid electrolyte and the like in the solid electrolyte layer is the same as the content in 100 mass% of the solid component of the solid electrolyte composition described later.

< Positive electrode active material layer >

The positive electrode active material layer contains an inorganic solid electrolyte having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table, a positive electrode active material layer, and components described later in a range not impairing the effects of the present invention. In addition, in the first uncharged state of the all-solid secondary battery, it is one of preferable embodiments to contain a negative electrode active material precursor described later. The inorganic solid electrolyte, the positive electrode active material, the negative electrode active material precursor, and the like will be described later.

The content of the positive electrode active material, the inorganic solid electrolyte, the negative electrode active material precursor, and the like in the positive electrode active material layer is the same as the content of the solid content 100 mass% in the composition for a positive electrode described later.

When the cathode active material layer contains the anode active material precursor, ions of the metal element can be replenished (doped) without using a highly active material (for example, lithium metal) in the production of the all-solid secondary battery, and the battery capacity can be improved. Further, by compressing the positive electrode active material layer after the decomposition reaction (by flattening the voids generated by the decomposition), the positive electrode active material layer can be made thin, and the (volume) energy density of the all-solid-state secondary battery can be improved.

The positive electrode active material layer containing the negative electrode active material precursor is preferably applied to the above-described embodiment in which the Si negative electrode or the negative electrode active material layer is not formed in advance. When a Si negative electrode is used as the negative electrode active material layer, the irreversible capacity of the silicon material or the silicon-containing alloy is large, and the decrease in capacity (movable lithium ion amount) due to the first charge becomes large. In the embodiment in which the negative electrode active material layer is not formed in advance, the capacity reduction by the first charge is also large as in the Si negative electrode. However, in an all-solid-state secondary battery having an Si negative electrode and an all-solid-state secondary battery of a system in which a negative electrode active material layer is not formed in advance, the reduced metal ions can be replenished (the metal ions are included in the Si negative electrode) by allowing a negative electrode active material precursor to be contained in a positive electrode active material layer and performing a decomposition reaction at the time of first charging. Further, when the negative electrode active material precursor is contained in the positive electrode active material layer, since the expansion due to the occlusion of metal ions during charging or the expansion due to the deposition of metal (volume expansion of the negative electrode active material layer) can be eliminated by the voids generated by the decomposition reaction of the negative electrode active material precursor in the positive electrode active material layer, the destruction of the solid electrolyte layer can be prevented, and the arrival of dendrites at the positive electrode (the occurrence of short circuits) can be suppressed. Furthermore, by collapsing the voids, the energy density can be increased.

< negative electrode active material layer >

As described above, the negative electrode active material layer is an inorganic solid electrolyte containing a negative electrode active material and, if necessary, having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table, and further contains a layer containing the following components, a lithium metal layer, and the like. The inorganic solid electrolyte, the negative electrode active material, and the like will be described later.

The lithium metal layer that can constitute the negative electrode active material layer is a layer of lithium metal, and specifically includes a layer formed by stacking or molding lithium powder, a lithium foil, a lithium vapor deposition film, and the like.

In the present invention, the negative electrode active material layer is preferably a negative electrode active material layer containing a carbonaceous material in view of reducing volume expansion and volume contraction caused by charge and discharge. On the other hand, from the viewpoint of battery capacity, a system in which the negative electrode active material layer is not formed in advance is preferable, and from the viewpoint of enabling a high battery capacity and effectively preventing the occurrence of short circuits, a Si negative electrode is preferable. If the negative electrode active material layer is formed without forming a Si negative electrode or a negative electrode active material layer in advance, the metal ions can be replenished by first charging, and the battery capacity and energy density can be improved while taking advantage of the Si negative electrode and the above-described embodiments.

The content of the negative electrode active material, the inorganic solid electrolyte, and the like in the negative electrode active material layer is the same as the content of the solid content 100 mass% in the composition for a negative electrode described later.

< thickness of negative electrode active material layer, solid electrolyte layer and positive electrode active material layer >

The thickness of each of the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer is not particularly limited. The thickness of each layer is preferably 10 to 1,000 μm, more preferably 20 μm or more and less than 500 μm. The thickness of the negative electrode active material layer in the embodiment in which the negative electrode active material layer is not formed in advance varies depending on the amount of metal deposited by charging, and therefore cannot be uniquely determined. In the all-solid-state secondary battery, it is further preferable that at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer has a thickness of 50 μm or more and less than 500 μm. When a lithium metal layer is used as the negative electrode active material layer, the thickness of the lithium metal layer is not dependent on the thickness of the negative electrode active material layer, and may be, for example, 0.01 to 100 μm.

< Current collector >

The positive electrode current collector 5 and the negative electrode current collector 1 are preferably electron conductors.

In the present invention, either one of the positive electrode current collector and the negative electrode current collector or both of them may be simply referred to as a current collector.

As a material for forming the positive electrode current collector, in addition to aluminum, an aluminum alloy, stainless steel, nickel, titanium, and the like, a material (a material forming a thin film) in which carbon, nickel, titanium, or silver is treated on the surface of aluminum or stainless steel is preferable, and among these, aluminum and an aluminum alloy are more preferable.

As a material forming the negative electrode current collector, in addition to aluminum, copper, a copper alloy, stainless steel, nickel, titanium, and the like, a material obtained by treating the surface of aluminum, copper, a copper alloy, or stainless steel with carbon, nickel, titanium, or silver is preferable, and aluminum, copper, a copper alloy, and stainless steel are more preferable.

The shape of the current collector is generally a diaphragm shape, but a mesh, a perforated body, a lath body, a porous body, a foam, a molded body of a fiber group, or the like can be used.

The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

The surface of the current collector is preferably formed with irregularities by surface treatment.

In the present invention, functional layers or members and the like may be appropriately inserted or disposed between or outside the respective layers of the negative electrode current collector, the negative electrode active material layer, the solid electrolyte layer, the positive electrode active material layer and the positive electrode current collector. Each layer may be a single layer or a plurality of layers.

< housing >

The all-solid-state secondary battery produced by the method for producing an all-solid-state secondary battery according to the present invention can be used as an all-solid-state secondary battery in the state of the above-described structure according to the application, but is preferably used by being further enclosed in an appropriate case in order to be a dry battery or the like. The case may be a metallic case or a resin (plastic) case. When a metallic case is used, for example, cases made of aluminum alloy and stainless steel can be used. Preferably, the metallic case is divided into a positive-electrode-side case and a negative-electrode-side case, and is electrically connected to the positive-electrode current collector and the negative-electrode current collector, respectively. Preferably, the case on the positive electrode side and the case on the negative electrode side are joined and integrated via a short-circuit prevention gasket.

The all-solid-state secondary battery manufactured by the manufacturing method of the present invention exhibits a high battery capacity and a high (volumetric) energy density. That is, the all-solid-state secondary battery of the present invention is configured to be capable of exhibiting sufficient battery characteristics even when the all-solid-state secondary battery includes the negative electrode active material layer formed by pre-doping the metal ions into the negative electrode active material layer by the first charge, and the negative electrode active material layer is formed using a silicon material or a silicon-containing alloy having a large irreversible capacity as the negative electrode active material, and the all-solid-state secondary battery does not have to be formed in advance as the negative electrode active material layer. Further, the positive electrode active material layer in which voids formed by the first charge are compressed is provided, and the volume is smaller than that before the first charge, and therefore, the positive electrode active material layer exhibits a high energy density.

Furthermore, even if the structural layer of the all-solid-state secondary battery is formed from solid particles and (rapid) charge and discharge of the all-solid-state secondary battery are repeated, occurrence of short circuits can be suppressed. Such occurrence of short circuits can be suppressed even when a layer made of graphite and a lithium metal layer are used as the negative electrode active material layer.

The all-solid-state secondary battery of the present invention exhibiting the above excellent characteristics is preferably used in a state of being pressed and restrained in the stacking direction of the structural layers (the overlapping direction of the structural layers, generally, the thickness direction of the structural layers). Accordingly, even when the amount of the negative electrode active material is reduced during discharge, the contact between the solid electrolyte layer and the negative electrode active material is maintained, and particularly, in a mode in which the metal deposited on the negative electrode current collector as the negative electrode active material layer functions, the amount of inactivation (isolated metal amount) of the metal due to charge and discharge can be reduced, so that the reduction in the battery capacity due to charge and discharge is suppressed, and excellent cycle characteristics are exhibited.

Use of all-solid-state secondary battery

The all-solid-state secondary battery of the present invention can be applied to various uses. The application method is not particularly limited, and examples of the electronic device include a notebook computer, a pen-input computer, a mobile computer, an electronic book reader, a mobile phone, a wireless telephone handset, a pager, a handheld terminal, a portable facsimile machine, a portable copier, a portable printer, a stereo headphone, a camcorder, a liquid crystal television, a portable vacuum cleaner, a portable CD, a compact disc, an electric shaver, a transceiver, an electronic organizer, a calculator, a portable recorder, a radio, a backup power source, and a memory card. Other consumer goods include automobiles (e.g., electric cars), electric cars, motors, lighting fixtures, toys, game machines, load regulators, clocks, flashlights, cameras, and medical devices (e.g., cardiac pacemakers, hearing aids, and shoulder massagers). Moreover, it can be used as various military supplies and aviation supplies. And, it can also be combined with a solar cell.

[ method for manufacturing all-solid-state secondary battery of the present invention ]

Next, a method for manufacturing the all-solid-state secondary battery according to the present invention (also referred to as a manufacturing method of the present invention) will be described.

The production method of the present invention sequentially performs the following steps.

(positive electrode active material layer) formation step: a step of forming a positive electrode active material layer on one surface (laminated layer) of the solid electrolyte layer using a positive electrode composition containing a positive electrode active material and a negative electrode active material precursor

(step of charging laminate): charging a laminate including a positive electrode active material layer and a solid electrolyte layer

(for positive electrode active material layer) compression step: a step of compressing at least the positive electrode active material layer by applying pressure after the step of charging

The production method of the present invention preferably further comprises the following formation step.

(solid electrolyte layer) formation step: process for forming solid electrolyte layer using solid electrolyte composition containing solid electrolyte

The formation step can be performed before or after the step of forming the positive electrode active material layer and the step of forming the negative electrode active material layer described below, and the order of execution in each formation step can be appropriately determined according to the form and the formation method of each layer to be formed.

The manufacturing method of the present invention may include the following discharge step.

(step of discharging the laminate): step of discharging the laminate

In the production method of the present invention, the step of discharging may or may not be provided after the step of compressing, and preferably the step of discharging is not provided before the step of compressing.

In the case where the all-solid-state secondary battery is a system in which the negative electrode active material layer is formed in advance, the production method of the present invention preferably further includes the following formation step.

(negative electrode active material layer) formation step: forming a negative electrode active material layer using a negative electrode active material, preferably a carbonaceous material as the negative electrode active material, or a negative electrode composition containing silicon or an alloy containing silicon

The forming step is preferably performed before the charging step.

In the present invention, "sequentially performing the steps" means performing a certain step and another step in chronological order, and includes a mode in which another step (including a stop step) is performed between the certain step and the another step. The mode of sequentially performing a certain step and another step includes a mode of performing the steps at appropriately changed time, place, or performer.

In the manufacturing method of the present invention, the solid electrolyte layer, the positive electrode active material layer, and the negative electrode active material layer are formed separately. Each layer may be formed alone or as a laminate, or 2 or more kinds of layers may be formed together or sequentially. Each layer is usually formed in a sheet or plate shape, and may include a base material, other layers, and the like.

The substrate is not particularly limited as long as it can support the solid electrolyte layer, and examples thereof include the materials described above for the current collector, and sheet-like bodies (plate-like bodies) of organic materials, inorganic materials, and the like. Examples of the organic material include various polymers, and specific examples thereof include polyethylene terephthalate, polypropylene, polyethylene, and cellulose. Examples of the inorganic material include glass and ceramic.

Examples of the other layer include a protective layer (release sheet), a current collector, and a coating layer. The solid electrolyte layer used in the embodiment in which the negative electrode active material layer is not formed in advance preferably has a negative electrode current collector on the surface thereof.

In the present invention, a sheet containing a solid electrolyte layer and not containing a positive electrode active material layer and a negative electrode active material layer is referred to as a solid electrolyte sheet, a sheet containing a negative electrode active material layer is referred to as a negative electrode sheet, and a sheet containing a positive electrode active material layer is referred to as a positive electrode sheet.

The layer thickness of each layer is the same as that described in the all-solid secondary battery of the present invention.

In the case of manufacturing an all-solid secondary battery, a solid electrolyte layer, a positive electrode active material layer, and a negative electrode active material layer in the case of an all-solid secondary battery having a negative electrode active material layer in advance are formed (prepared).

< Process for Forming solid electrolyte layer >

In carrying out this step, a solid electrolyte composition is prepared.

The solid electrolyte composition contains an inorganic solid electrolyte, and further contains a binder, a dispersion medium, a conductive assistant described later, and other components as appropriate.

The solid electrolyte composition is preferably a nonaqueous composition. In the present invention, the nonaqueous composition includes a form in which the water content (also referred to as a water content) is 200ppm or less, in addition to a form in which water is not contained. The water content of the solid electrolyte layer is preferably 150ppm or less, more preferably 100ppm or less, and still more preferably 50ppm or less. The water content indicates the amount of water contained in the solid electrolyte composition (mass ratio with respect to the solid electrolyte composition). The water content can be determined by filtering the solid electrolyte composition with a 0.45 μm membrane filter and by karl fischer titration.

Hereinafter, components contained in the solid electrolyte composition and components that can be contained in the solid electrolyte composition will be described.

Inorganic solid electrolytes

In the present invention, the inorganic solid electrolyte refers to an inorganic solid electrolyte, and the solid electrolyte refers to a solid electrolyte capable of moving ions inside thereof. Since organic materials, which are main ion conductive materials, are not included, they are clearly distinguished from organic solid electrolytes (polymer electrolytes typified by polyethylene oxide (PEO) and the like, and organic electrolyte salts typified by lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and the like). Further, since the inorganic solid electrolyte is a solid in a stable state, it is not usually dissociated or dissociated into cations and anions. At this point, an inorganic electrolyte salt (LiPF) that is also dissociated from cations and anions or is dissociated in the electrolyte or the polymer₆、LiBF₄LiFSI, LiCl, etc.). The inorganic solid electrolyte is not particularly limited as long as it has ion conductivity of a metal belonging to group 1 or group 2 of the periodic table, and generally does not have electron conductivity.

The inorganic solid electrolyte has ion conductivity of a metal belonging to group 1 or group 2 of the periodic table. The inorganic solid electrolyte can be used by appropriately selecting a solid electrolyte material suitable for use in such a product. The inorganic solid electrolyte includes (i) a sulfide-based inorganic solid electrolyte, (ii) an oxide-based inorganic solid electrolyte, (iii) a halide-based inorganic solid electrolyte, and (iv) a hydride-based inorganic solid electrolyte, and is preferably a sulfide-based inorganic solid electrolyte from the viewpoint of high ion conductivity and easy bonding of interfaces between particles. In the present invention, the inorganic solid electrolyte material suitable for use in such a product can be appropriately selected and used.

When the all-solid-state secondary battery of the present invention is an all-solid-state lithium ion secondary battery, the inorganic solid electrolyte preferably has ion conductivity of lithium ions.

(i) Sulfide-based inorganic solid electrolyte

The sulfide-based inorganic solid electrolyte contains a sulfur atom, and is preferably a compound having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table and also having electronic insulating properties. The sulfide-based inorganic solid electrolyte preferably contains at least Li, S, and P as elements and has lithium ion conductivity, but may contain other elements than Li, S, and P according to the purpose or circumstances.

As the sulfide-based inorganic solid electrolyte, for example, a lithium ion-conductive sulfide-based inorganic solid electrolyte satisfying a composition represented by the following formula (I) can be cited.

L_a1M_b1P_c1S_d1A_e1Formula (I)

In the formula, L represents an element selected from Li, Na and K, and Li is preferable. M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al and Ge. A represents an element selected from I, Br, Cl and F. a 1-e 1 represent the composition ratio of each element, and a1: b1: c1: d1: e1 satisfies 1-12: 0-5: 1: 2-12: 0-10. a1 is preferably 1 to 9, more preferably 1.5 to 7.5. b1 is preferably 0 to 3, more preferably 0 to 1. d1 is preferably 2.5 to 10, more preferably 3.0 to 8.5. e1 is preferably 0 to 5, more preferably 0 to 3.

As described below, the composition ratio of each element can be controlled by adjusting the compounding ratio of the raw material compound in producing the sulfide-based inorganic solid electrolyte.

The sulfide-based inorganic solid electrolyte may be amorphous (glass), may be crystallized (glass-ceramic), or may be partially crystallized. For example, a Li-P-S glass containing Li, P, and S, or a Li-P-S glass ceramic containing Li, P, and S can be used.

The sulfide-based inorganic solid electrolyte can be prepared by reacting lithium sulfide (Li)₂S), phosphorus sulfides (e.g., phosphorus pentasulfide (P)₂S₅) Phosphorus monomer, sulfur monomer, sodium sulfide, hydrogen sulfide, lithium halide (e.g., LiI, LiBr, LiCl), and sulfide of the element represented by M (e.g., SiS)₂、SnS、GeS₂) At least 2 or more raw materials.

Li-P-S glass and Li-P-S glass ceramic₂S and P₂S₅In the ratio of Li₂S:P₂S₅The molar ratio of (a) to (b) is preferably 60:40 to 90:10, and more preferably 68:32 to 78: 22. By mixing Li₂S and P₂S₅When the ratio (b) is in this range, the lithium ion conductivity can be improved. Specifically, the lithium ion conductivity can be preferably set to 1 × 10^-4S/cm or more, more preferably 1X 10^-3And more than S/cm. There is no particular upper limit, but actually 1X 10^-1S/cm or less.

Specific examples of the sulfide-based inorganic solid electrolyte include the following combinations of raw materials. For example, Li can be cited₂S-P₂S₅、Li₂S-P₂S₅-LiCl、Li₂S-P₂S₅-H₂S、Li₂S-P₂S₅-H₂S-LiCl、Li₂S-LiI-P₂S₅、Li₂S-LiI-Li₂O-P₂S₅、Li₂S-LiBr-P₂S₅、Li₂S-Li₂O-P₂S₅、Li₂S-Li₃PO₄-P₂S₅、Li₂S-P₂S₅-P₂O₅、Li₂S-P₂S₅-SiS₂、Li₂S-P₂S₅-SiS₂-LiCl、Li₂S-P₂S₅-SnS、Li₂S-P₂S₅-Al₂S₃、Li₂S-GeS₂、Li₂S-GeS₂-ZnS、Li₂S-Ga₂S₃、Li₂S-GeS₂-Ga₂S₃、Li₂S-GeS₂-P₂S₅、Li₂S-GeS₂-Sb₂S₅、Li₂S-GeS₂-Al₂S₃、Li₂S-SiS₂、Li₂S-Al₂S₃、Li₂S-SiS₂-Al₂S₃、Li₂S-SiS₂-P₂S₅、Li₂S-SiS₂-P₂S₅-LiI、Li₂S-SiS₂-LiI、Li₂S-SiS₂-Li₄SiO₄、Li₂S-SiS₂-Li₃PO₄、Li₁₀GeP₂S₁₂And the like. The mixing ratio of the raw materials is not limited. As a method for synthesizing a sulfide-based inorganic solid electrolyte material using such a raw material composition, for example, an amorphization method can be cited. Examples of the amorphization method include a mechanical milling method, a solution method, and a melt quenching method. This is because the treatment at normal temperature can be performed, and the manufacturing process can be simplified.

(ii) Oxide-based inorganic solid electrolyte

The oxide-based inorganic solid electrolyte is preferably a compound containing an oxygen atom, having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table, and having electronic insulation properties.

As for the oxide-based inorganic solid electrolyte, 1 × 10 is preferable as the ion conductivity^-6S/cm or more, more preferably 5X 10^-6S/cm or more, particularly preferably 1X 10^-5And more than S/cm. The upper limit is not particularly limited, but is actually 1X 10^{- 1}S/cm or less.

Specific examples of the compound include Li_xaLa_yaTiO₃〔xa＝0.3～0.7、ya＝0.3～0.7〕(LLT)、Li_xbLa_ybZr_zbM^bb _mbO_nb(M^bbIs at least one element of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In and Sn, xb is more than or equal to 5 and less than or equal to 10, yb is more than or equal to 1 and less than or equal to 4, zb is more than or equal to 1 and less than or equal to 4, mb is more than or equal to 0 and less than or equal to 2, Nb is more than or equal to 5 and less than or equal to 20. ) Li_xcB_ycM^cc _zcO_nc(M^ccIs at least one element of C, S, Al, Si, Ga, Ge, In and Sn, xc satisfies 0 < xc < 5, yc satisfies 0 < yc < 1, zc satisfies 0 < zc < 1, and nc satisfies 0 < nc < 6. ) Li_xd(Al，Ga)_yd(Ti，Ge)_zdSi_adP_mdO_nd(wherein, 1 is more than or equal to xd is less than or equal to 3, 0 is more than or equal to yd is less than or equal to 1,0 is more than or equal to zd is less than or equal to 2, 0 is more than or equal to ad is less than or equal to 1, 1 is more than or equal to md is less than or equal to 7, and 3 is more than or equal to nd is less than or equal to 13), Li_(3-2xe)M^ee _xeD^eeO (xe represents a number of 0 to 0.1, M)^eeRepresents a 2-valent metal atom. D^eeRepresents a halogen atom or a combination of 2 or more halogen atoms. ) Li_xfSi_yfO_zf(1≤xf≤5、0＜yf≤3、1≤zf≤10)、Li_xgS_ygO_zg(1≤xg≤3、0＜yg≤2、1≤zg≤10)、Li₃BO₃-Li₂SO₄、Li₂O-B₂O₃-P₂O₅、Li₂O-SiO₂、Li₆BaLa₂Ta₂O₁₂、Li₃PO_(4-3/2w)N_w(w satisfies w < 1) and Li having a Lithium super ionic conductor (LISICON) type crystal structure_3.5Zn_0.25GeO₄La having perovskite crystal structure_0.55Li_0.35TiO₃And LiTi having a NASICON (sodium super ionic conductor) type crystal structure₂P₃O₁₂、Li_1+xh+yh(Al，Ga)_xh(Ti，Ge)_2-xhSi_yhP_3-yhO₁₂(wherein 0. ltoreq. xh. ltoreq.1, 0. ltoreq. yh. ltoreq.1) and Li having a garnet crystal structure₇La₃Zr₂O₁₂(LLZ) and the like. Also, a phosphorus compound containing Li, P, and O is preferable. For example, lithium phosphate (Li) may be mentioned₃PO₄) LiPON in which a part of oxygen in lithium phosphate is substituted with nitrogen, and LiPOD¹(D¹Is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.), etc. And, LiA can also be preferably used¹ON(A¹At least one selected from Si, B, Ge, Al, C, Ga, etc.), etc.

(iii) Halide-based inorganic solid electrolyte

The halide-based inorganic solid electrolyte is preferably a compound containing a halogen atom, having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table, and having electronic insulation properties.

The halide-based inorganic solid electrolyte is not particularly limited, and examples thereof include Li described in LiCl, LiBr, LiI, ADVANCED MATERIALS, 2018, 30, 1803075₃YBr₆、Li₃YCl₆And (c) a compound such as a quaternary ammonium compound. Among them, Li is preferable₃YBr₆、Li₃YCl₆。

(iv) Hydride inorganic solid electrolyte

The hydride-based inorganic solid electrolyte is preferably a compound containing a hydrogen atom, having ion conductivity of a metal belonging to group 1 or group 2 of the periodic table, and having electronic insulation properties.

The hydride-based inorganic solid electrolyte is not particularly limited, and examples thereof include LiBH₄、Li₄(BH₄)₃I、3LiBH₄-LiCl, etc.

The inorganic solid electrolyte is preferably a particle. In this case, the particle diameter (volume average particle diameter) of the inorganic solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, and more preferably 0.1 μm or more. The upper limit is preferably 100 μm or less, and more preferably 50 μm or less. The particle size of the inorganic solid electrolyte was measured by the following procedure. In a 20mL sample bottle, the inorganic solid electrolyte particles were diluted with water (heptane in the case of a water-unstable substance) to prepare a1 mass% dispersion. The diluted dispersion sample was irradiated with ultrasonic waves at 1kHz for 10 minutes and then immediately used in the test. Using this dispersion sample, data collection was performed 50 times using a laser diffraction/scattering particle size distribution measuring apparatus LA-920 (trade name, manufactured by HORIBA, ltd.) and a quartz cell for measurement at a temperature of 25 ℃, thereby obtaining a volume average particle diameter. Other detailed conditions and the like are as required in reference to JIS Z8828: 2013 "particle size analysis-dynamic light scattering method". 5 samples were made for each grade and the average was used.

The inorganic solid electrolyte may be used alone in 1 kind, or may be used in 2 or more kinds.

The content of the inorganic solid electrolyte in the solid electrolyte composition is not particularly limited, and is preferably 50 mass% or more, more preferably 70 mass% or more, and particularly preferably 90 mass% or more of 100 mass% of the solid component from the viewpoints of dispersibility, reduction in interface resistance, and adhesiveness. The upper limit is not particularly limited and can be set to 100 mass%, but from the same viewpoint, it is preferably 99.99 mass% or less, more preferably 99.95 mass% or less, and particularly preferably 99.9 mass% or less.

In the present invention, the solid component (solid component) is a component that does not disappear by volatilization or evaporation when the solid electrolyte composition is subjected to a drying treatment at 130 ℃ for 6 hours under a pressure of 1mmHg and a nitrogen atmosphere. Typically, the components are components other than the dispersion medium described later.

-binders-

The solid electrolyte composition may contain a binder for binding solid particles such as an inorganic solid electrolyte.

As the binder, an organic polymer is exemplified, and a known organic polymer suitable for the production of an all-solid secondary battery can be used without particular limitation. Examples of such organic polymers include fluorine-containing resins, hydrocarbon-based thermoplastic resins, acrylic resins, polyurethane resins, polyurea resins, polyamide resins, polyimide resins, polyester resins, polyether resins, polycarbonate resins, and cellulose derivative resins. The binder is preferably a particle. The binder may be used alone in 1 kind, or may be used in 2 or more kinds. When the solid electrolyte composition contains a binder, the content of the binder in the solid component of the solid electrolyte composition is not particularly limited, and is, for example, preferably 0.1 to 10 mass%, more preferably 1 to 10 mass%, and still more preferably 2 to 5 mass%.

-a dispersing medium

The solid electrolyte composition of the present invention also preferably contains a dispersion medium.

The dispersion medium may be any dispersion medium that disperses the components contained in the solid electrolyte composition. In the present invention, the dispersion medium is preferably a nonaqueous dispersion medium containing no water, and is usually selected from organic solvents. In the present invention, the dispersion medium does not contain water means that the dispersion medium contains 0.1 mass% or less of water in addition to the embodiment in which the content of water is 0 mass%. Among them, the water content in the solid electrolyte composition is preferably set within the above range (nonaqueous composition).

The organic solvent is not particularly limited, and examples thereof include various organic solvents such as alcohol compounds, ether compounds, amide compounds, amine compounds, ketone compounds, aromatic compounds, aliphatic compounds, nitrile compounds, and ester compounds.

The dispersion medium contained in the solid electrolyte composition may be 1 type or 2 or more types.

The content of the dispersion medium in the solid electrolyte composition is not particularly limited, but is preferably 20 to 80 mass%, more preferably 30 to 70 mass%, and particularly preferably 40 to 60 mass%.

Other ingredients-

The solid electrolyte composition may contain other components.

The other components are not particularly limited, and various additives and the like can be mentioned.

Examples of the additives include a thickener, a crosslinking agent (a substance which undergoes a crosslinking reaction by radical polymerization, polycondensation, or ring-opening polymerization), a polymerization initiator (a substance which generates an acid or a radical by heat or light), an antifoaming agent, a leveling agent, a dehydrating agent, and an antioxidant.

The content of the other components in the solid electrolyte composition is not particularly limited and may be appropriately set.

Preparation of solid electrolyte compositions

The solid electrolyte composition can be prepared, for example, as a solid mixture or slurry by mixing the inorganic solid electrolyte, more appropriate, binder, dispersion medium, other components, and the like in various mixers that are generally used.

The mixing method is not particularly limited, and can be performed using a known mixer such as a ball mill, a bead mill, or a disk mill. Also, the mixing conditions are not particularly limited. The mixed atmosphere may be any atmosphere such as atmospheric pressure, dry air (dew point-20 ℃ C. or lower), or inert gas (e.g., argon, helium, nitrogen). Since the inorganic solid electrolyte reacts with moisture, it is preferable to perform mixing under dry air or in an inert gas.

Formation of a solid electrolyte layer

The solid electrolyte layer is not particularly limited, and can be produced by a molding method in which a solid electrolyte composition is molded under pressure, or a coating and drying method in which a solid electrolyte composition (slurry) containing a dispersion medium is coated and dried, and then, pressure is preferably applied.

The method for forming the solid electrolyte composition may be any method as long as the solid electrolyte composition can be formed into a layer or a film, and various known forming methods can be applied, and press forming (for example, press forming using a hydraulic cylinder press) is preferable. The pressure during molding is not particularly limited, but is usually preferably in the range of 50 to 1500MPa, more preferably 150 to 600MPa, and still more preferably 100 to 300 MPa. The molding (pressing) time may be short (for example, within several hours) or long (1 day or more).

Heating may be performed simultaneously with pressurization of the solid electrolyte composition, and in the present invention, it is preferable to perform the pre-molding without heating, for example, it is preferable to mold at an ambient temperature of 10 to 50 ℃. The atmosphere in the molding is preferably under dry air or in an inert gas.

Examples of the method for applying the solid electrolyte composition (slurry) include wet coating methods such as spin coating, dip coating, slit coating, stripe coating, and bar coating. The drying temperature is not particularly limited, and is, for example, preferably 30 to 300 ℃ and more preferably 60 to 250 ℃.

The application dry layer of the solid electrolyte composition is preferably pressurized. The method and pressure for pressurization are not particularly limited, and, for example, the same method and pressure as those for the formation of the above-described solid electrolyte composition can be suitably employed. For example, the pressurization may be performed after the active material layer is laminated.

< step of Forming Anode active Material layer >

In the case of the all-solid-state secondary battery of the embodiment in which the negative electrode active material layer is formed in advance, the manufacturing method of the present invention performs the step of forming the negative electrode active material layer.

In the present step, a composition for a negative electrode was prepared.

The composition for a negative electrode contains a negative electrode active material, preferably an inorganic solid electrolyte, a conductive auxiliary agent, and further, a binder, a dispersion medium, a lithium salt, and other components as appropriate. The composition for a negative electrode may be the negative electrode active material itself, and is preferably a nonaqueous composition.

The inorganic solid electrolyte, binder, dispersion medium and other components that can be used in the composition for a negative electrode are as described above. The lithium salt can use a lithium salt used in an all-solid secondary battery without particular limitation.

Negative electrode active material-

The negative electrode active material used in the present invention is a material capable of intercalating and deintercalating ions of a metal element belonging to group 1 or group 2 of the periodic table. The negative electrode active material is preferably a negative electrode active material capable of reversibly intercalating and deintercalating lithium ions. The material is not particularly limited as long as it has the above-described characteristics, and examples thereof include a carbonaceous material, an oxide (including a complex oxide) of a metal or semimetal element, a lithium simple substance, a lithium alloy, and a negative electrode active material capable of being alloyed with lithium (forming an alloy with lithium). Among them, from the viewpoint of reliability, a carbonaceous material, an oxide of a semimetal element, a metal composite oxide, or a lithium monomer is preferable. From the viewpoint of being able to increase the capacity of the all-solid-state secondary battery, a negative electrode active material that is able to be alloyed with lithium is preferable.

The carbonaceous material used as the negative electrode active material means a material substantially composed of carbon. Examples of the carbonaceous material include carbon materials obtained by firing various synthetic resins such as petroleum pitch, carbon black such as Acetylene Black (AB), graphite (e.g., artificial graphite such as natural graphite and vapor-phase-grown graphite), PAN (polyacrylonitrile) resin, and furfuryl alcohol resin. Examples of the carbon fibers include various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor grown carbon fibers, dehydrated PVA (polyvinyl alcohol) -based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, mesophase microspheres, graphite whiskers, and plate-like graphite.

These carbonaceous materials can also be classified into non-graphitizable carbonaceous materials (also referred to as hard carbon) and graphite-based carbonaceous materials according to the degree of graphitization. The carbonaceous material preferably has the surface spacing, density, and crystallite size described in Japanese patent application laid-open Nos. 62-22066, 2-6856, and 3-45473. The carbonaceous material may not be a single material, but a mixture of natural graphite and artificial graphite as described in Japanese patent application laid-open No. 5-90844, graphite having a coating layer as described in Japanese patent application laid-open No. 6-4516, and the like may be used.

As the carbonaceous material, hard carbon or graphite can be preferably used, and graphite is more preferably used.

The oxide of a metal or semimetal element suitable as the negative electrode active material is not particularly limited as long as it is an oxide capable of occluding and releasing lithium, and an oxide of a metal element (metal oxide), a composite oxide of a metal element or a composite oxide of a metal element and a semimetal element (collectively referred to as a metal composite oxide), and an oxide of a semimetal element (semimetal oxide) may be mentioned. As these oxides, amorphous oxides are preferable, and chalcogenides which are reaction products of metal elements and elements of group 16 of the periodic table are further preferable. In the present invention, a semimetal element means an element showing properties between a metal element and a non-semimetal element, and typically includes 6 elements of boron, silicon, germanium, arsenic, antimony, and tellurium, and further includes 3 elements of selenium, polonium, and astatine. The amorphous substance refers to a material having a broad scattering band having an apex in a region having a 2 θ value of 20 ° to 40 ° by X-ray diffraction using CuK α rays, and may have a crystalline diffraction line. The most intense diffraction line among the crystalline diffraction lines observed at 2 θ values in the range of 40 ° to 70 ° is preferably 100 times or less, more preferably 5 times or less, of the diffraction line intensity at the apex of the broad scattering band observed at 2 θ values in the range of 20 ° to 40 °, and particularly preferably a diffraction line having no crystallinity.

Among the group of compounds composed of the amorphous oxide and the chalcogenide, the amorphous oxide or the chalcogenide of a semimetal element is more preferable, and particularly, the (composite) oxide or the chalcogenide is preferable which is composed of 1 kind of element (for example, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) alone or 2 or more kinds of elements selected from groups 13(IIIB) to 15(VB) of the periodic table. Specific examples of preferred amorphous oxides and chalcogenides include, for example, Ga₂O₃、GeO、PbO、PbO₂、Pb₂O₃、Pb₂O₄、Pb₃O₄、Sb₂O₃、Sb₂O₄、Sb₂O₈Bi₂O₃、Sb₂O₈Si₂O₃、Sb₂O₅、Bi₂O₃、Bi₂O₄、GeS、PbS、PbS₂、Sb₂S₃Or Sb₂S₅。

Examples of the negative electrode active material that can be used together with an amorphous oxide mainly containing Sn, Si, and Ge include carbonaceous materials, lithium monomers, lithium alloys, and negative electrode active materials that can be alloyed with lithium, which can occlude and/or release lithium ions or lithium metals.

From the viewpoint of high current density charge/discharge characteristics, it is preferable that the oxide of a metal or semimetal element, particularly a metal (composite) oxide and the chalcogenide described above contain at least one of titanium and lithium as a constituent component. Examples of the lithium-containing metal composite oxide (lithium composite metal oxide) include a composite oxide of lithium oxide and the above-mentioned metal (composite) oxide or the above-mentioned chalcogenide, and more specifically, Li₂SnO₂。

Negative electrode active materialFurther, as the metal oxide, a metal oxide containing titanium (titanium oxide) is preferably used. In particular, due to Li₄Ti₅O₁₂(lithium titanate [ LTO ]]) It is preferable from the viewpoint that the volume change during occlusion and release of lithium ions is small, and therefore, the lithium ion secondary battery has excellent rapid charge/discharge characteristics, and can improve the life of the lithium ion secondary battery while suppressing deterioration of the electrode.

The lithium alloy to be used as the negative electrode active material is not particularly limited as long as it is an alloy generally used as a negative electrode active material for a secondary battery, and examples thereof include a lithium aluminum alloy.

The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is a material that is generally used as a negative electrode active material for a secondary battery. Such an active material expands and contracts greatly due to charge and discharge of the all-solid-state secondary battery. Examples of the active material include a negative electrode active material (alloy) containing silicon or tin, and metals such as Al and In, preferably a negative electrode active material (active material containing silicon) containing silicon capable of achieving a higher battery capacity, and more preferably an active material containing silicon In which the content of silicon is 50 mol% or more of all the constituent elements.

In general, negative electrodes containing these negative electrode active materials (Si negative electrodes containing active materials containing silicon elements, Sn negative electrodes containing active materials containing tin elements, and the like) can store more Li ions than carbon negative electrodes (graphite, acetylene black, and the like). That is, the occlusion amount of Li ions per unit mass increases. Therefore, the battery capacity can be increased. As a result, the battery driving time can be prolonged.

Examples of the active material containing a silicon element include silicon materials such as Si and SiOx (0 < x.ltoreq.1), and silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, lanthanum and the like (for example, LaSi₂、VSi₂La-Si, Gd-Si, Ni-Si) or organized active substances (e.g. LaSi₂/Si) additionally contains SnSiO₃、SnSiS₃And active materials of silicon element and tin element. In addition, SiOx can be used as a negative electrode active material (semi-active material) by itselfMetal oxide), and can be used as a negative electrode active material (precursor material thereof) alloyed with lithium because Si is generated by the operation of the all-solid secondary battery.

Examples of the negative electrode active material containing tin include Sn, SnO, and SnO₂、SnS、SnS₂And an active material further containing the silicon element and the tin element. Further, a composite oxide with lithium oxide, for example, Li can be cited₂SnO₂。

In the present invention, the negative electrode active material can be used without particular limitation, and from the viewpoint of battery capacity, a negative electrode active material that can be alloyed with lithium is a preferred embodiment, and among these, the silicon material or the silicon-containing alloy (alloy containing a silicon element) is more preferred, and silicon (Si) or the silicon-containing alloy is further preferred.

The shape of the negative electrode active material is not particularly limited, and is preferably a particle shape. The particle diameter (volume average particle diameter) of the negative electrode active material is preferably 0.1 to 60 μm. A common pulverizer or classifier is used to obtain a predetermined particle size. For example, a mortar, a ball mill, a sand mill, a vibration ball mill, a satellite ball mill, a planetary ball mill, a rotary air-flow type jet mill, a sieve, or the like can be preferably used. In the pulverization, wet pulverization in which an organic solvent such as water or methanol coexists may be performed. In order to obtain a desired particle diameter, classification is preferably performed. The classification method is not particularly limited, and a sieve, an air classifier, or the like can be used. The classification can be performed by using both dry and wet methods. The average particle diameter of the negative electrode active material particles can be measured by the same method as the method for measuring the volume average particle diameter of the inorganic solid electrolyte.

In the present invention, the chemical formula of the compound obtained by the firing method can be calculated from the mass difference of the powder before and after firing by Inductively Coupled Plasma (ICP) emission spectroscopy as a measurement method and as a simple method.

The surface of the negative electrode active material may be coated with a different metal oxide. As the surface-coating agent, there may be mentionedAnd metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples thereof include titanic acid spinel, tantalum oxide, niobium oxide, and lithium niobate compound, and specific examples thereof include Li₄Ti₅O₁₂、Li₂Ti₂O₅、LiTaO₃、LiNbO₃、LiAlO₂、Li₂ZrO₃、Li₂WO₄、Li₂TiO₃、Li₂B₄O₇、Li₃PO₄、Li₂MoO₄、Li₃BO₃、LiBO₂、Li₂CO₃、Li₂SiO₃、SiO₂、TiO₂、ZrO₂、Al₂O₃、B₂O₃And the like.

Also, the surface of the electrode containing the negative electrode active material may be surface-treated with sulfur or phosphorus.

The surface of the particles of the negative electrode active material may be subjected to surface treatment with actinic rays or an active gas (plasma or the like) before and after the surface coating.

The negative electrode active material may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

When the negative electrode active material layer is formed, the negative electrode active material layer has a unit area (cm)²) The mass (mg) (weight per unit area) of the negative electrode active material (b) is not particularly limited. The battery capacity can be determined as appropriate according to the designed battery capacity.

Conductive aid

The composition for a negative electrode preferably further contains a conductive auxiliary, and particularly, an active material containing a silicon element as a negative electrode active material is preferably used in combination with the conductive auxiliary.

The conductive aid is not particularly limited, and a conductive aid generally known as a conductive aid can be used. For example, natural graphite, artificial graphite and other graphites, acetylene black, Ketjen black (Ketjen black), furnace black and other carbon blacks, needle coke and other amorphous carbons, vapor grown carbon fibers, carbon nanotubes and other carbon fibers, graphene, fullerene and other carbonaceous materials, metal powders, metal fibers, such as copper and nickel, or conductive polymers, such as polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene derivatives, may be used as the electron conductive material.

In the present invention, when the active material and the conductive auxiliary agent are used in combination, the conductive auxiliary agent, which does not cause Li insertion and release and does not function as the active material when the battery is charged and discharged, is used as the conductive auxiliary agent. Therefore, among the conductive aids, those capable of exerting the function of the active material in the active material layer during charge and discharge of the battery are classified as active materials rather than conductive aids. Whether or not the active material functions during charging and discharging of the battery is determined by the combination with the active material, not by the sole determination.

The shape of the conductive aid is not particularly limited, and is preferably a particle shape.

The conductive assistant may be used in 1 kind, or 2 or more kinds.

The content of the negative electrode active material in the negative electrode composition is not particularly limited, and is preferably 100% by mass or less, more preferably 10 to 80% by mass, and still more preferably 20 to 80% by mass, based on 100% by mass of the solid content.

When the composition for a negative electrode contains an inorganic solid electrolyte, the total content of the inorganic solid electrolyte and the negative electrode active material in the composition for a negative electrode is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, further preferably 50% by mass or more, particularly preferably 70% by mass or more, and most preferably 90% by mass or more, of the solid content of 100% by mass. The upper limit is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and particularly preferably 99% by mass or less.

The content of the conductive auxiliary in the negative electrode composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass, based on 100% by mass of the solid content.

The content of each of the binder and the dispersion medium in the negative electrode composition is not particularly limited, and can be, for example, the content described above in the solid electrolyte composition.

The content of the lithium salt and other components in the negative electrode composition is not particularly limited, and may be appropriately set, for example, the above content in the solid electrolyte composition.

Preparation of composition for negative electrode

The composition for a negative electrode can be prepared under the same method and conditions as those for the preparation of the above-described solid electrolyte composition.

Formation of the negative electrode active material layer

The negative electrode active material layer is not particularly limited and can be prepared under the same method and conditions as the formation of the solid electrolyte layer described above. In the formation of the negative electrode active material layer, the composition for a negative electrode applied and dried may be heated while being pressurized. The heating temperature is not particularly limited, and is generally in the range of 30 to 300 ℃.

The method for forming the negative electrode active material layer on the surface of the solid electrolyte layer opposite to (on the other side of) the positive electrode active material layer is not particularly limited, and a general method can be applied. For example, a method of forming a solid electrolyte layer and a negative electrode active material layer separately and laminating the two layers, and a method of forming a negative electrode active material layer or a solid electrolyte layer on the surface of a solid electrolyte layer or a negative electrode active material layer are given.

The method of laminating the two layers is not particularly limited, and a method of laminating by pressure bonding, a method of placing a negative electrode active material on the surface of the solid electrolyte layer and pressurizing, a bonding method, and the like can be cited.

The method of pressure bonding lamination is not particularly limited, and for example, a method of placing (disposing) a negative electrode active material layer on the surface of a solid electrolyte layer and then pressing the same may be mentioned. In the method of pressure-bonding lamination and the method of pressurizing the surface of the solid electrolyte layer with the negative electrode active material, the method and conditions of pressure-bonding lamination or pressurization are not particularly limited as long as both layers can be pressure-bonded. The pressure is not limited as long as it can be pressure-bonded to the negative electrode active material layer, and may be, for example, 1MPa or more, preferably 1 to 150MPa, and more preferably 5 to 60 MPa. The pressure bonding lamination or pressing may be performed under heating, and in the present invention, it is preferably performed under non-heating, and for example, it is more preferably performed at an ambient temperature of 0 to 50 ℃. The environment in which the press lamination or pressurization is performed is the same as that in the preparation of the solid electrolyte composition.

The bonding method is not particularly limited, and for example, a method in which an electrolyte solution is applied to the surface of the solid electrolyte layer and then the negative electrode active material layer is placed (arranged) may be mentioned. The electrolyte used is not particularly limited.

The method of forming the negative electrode active material layer or the solid electrolyte layer directly on the surface of the solid electrolyte layer or the negative electrode active material layer is not particularly limited, and for example, a method of coating the surface of the solid electrolyte layer or the negative electrode active material layer with a composition for a negative electrode or a solid electrolyte composition and drying the same can be cited. The method and conditions for coating and drying are not particularly limited, and for example, the method and conditions for coating and drying the solid electrolyte composition can be applied.

In the case of the all-solid-state secondary battery, the negative electrode active material layer is formed by a charging step described later. In this case, a compound (for example, a positive electrode active material or the like) that generates ions of a metal belonging to group 1 or group 2 of the periodic table is used instead of the negative electrode active material. The negative electrode active material layer can be formed by bonding an ion generated from the compound to an electron at or near the negative electrode current collector and depositing the ion as a metal.

< Process for Forming Positive electrode active Material layer >

The composition for a positive electrode is prepared when the step of forming a positive electrode active material layer is performed.

The composition for a positive electrode contains a positive electrode active material and a negative electrode active material precursor, preferably contains an inorganic solid electrolyte and a conductive auxiliary agent, and further contains a binder, a dispersion medium, a lithium salt and other components as appropriate. The composition for a positive electrode is preferably a nonaqueous composition.

The inorganic solid electrolyte, the conductive aid, the binder, the dispersion medium, the lithium salt and other components that can be used in the composition for a positive electrode are as described above.

Positive electrode active material-

The positive electrode active material layer used in the present invention is a substance capable of intercalating and deintercalating ions of a metal element belonging to group 1 or group 2 of the periodic table. The positive electrode active material layer is preferably a metal oxide (preferably a transition metal oxide).

The positive electrode active material is preferably a material capable of reversibly intercalating and deintercalating lithium ions. The material is not particularly limited as long as it has the above-described characteristics, and may be a transition metal oxide, an organic substance, an element capable of forming a complex with Li such as sulfur, a complex of sulfur and a metal, or the like.

Among these, as the positive electrode active material, a transition metal oxide is preferably used, and a transition metal element M is more preferably contained^a(1 or more elements selected from Co, Ni, Fe, Mn, Cu and V). Further, the transition metal oxide may be mixed with the element M^b(an element of group 1(Ia), an element of group 2(IIa), Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like of the periodic Table of metals other than lithium). The amount to be mixed is preferably in relation to the transition metal element M^aThe amount (100 mol%) of the (C) component is 0 to 30 mol%. More preferably as Li/M^aIs mixed so that the molar ratio of (A) to (B) is 0.3 to 2.2.

Specific examples of the transition metal oxide include (MA) a transition metal oxide having a layered rock-salt structure, (MB) a transition metal oxide having a spinel structure, (MC) a lithium-containing transition metal phosphate compound, (MD) a lithium-containing transition metal halophosphoric acid compound, and (ME) a lithium-containing transition metal silicate compound.

Specific examples of (MA) the transition metal oxide having a layered rock-salt structure include LiCoO₂(lithium cobaltate [ LCO ]])、LiNi₂O₂(lithium nickelate) and LiNi_0.85Co_0.10Al_0.05O₂(Nickel cobalt lithium aluminate [ NCA)])、LiNi_1/3Co_1/3Mn_{1/ 3}O₂(lithium nickel manganese cobaltate [ NMC ]]) And LiNi_0.5Mn_0.5O₂(lithium manganese nickelate).

Specific examples of (MB) transition metal oxides having a spinel structure include LiMn₂O₄(LMO)、LiCoMnO₄、Li₂FeMn₃O₈、Li₂CuMn₃O₈、Li₂CrMn₃O₈And Li₂NiMn₃O₈。

Examples of the (MC) lithium-containing transition metal phosphate compound include LiFePO₄And Li₃Fe₂(PO₄)₃Isoolivine-type iron phosphate salt, LiFeP₂O₇Iso-pyrophosphoric acid iron species, LiCoPO₄Isophosphoric acid cobalt compounds and Li₃V₂(PO₄)₃Monoclinic NASICON-type vanadium phosphate salts such as (lithium vanadium phosphate).

Examples of the (MD) lithium-containing transition metal halophosphor compound include Li₂FePO₄F, etc. iron fluorophosphate, Li₂MnPO₄F, etc. manganese fluorophosphate and Li₂CoPO₄And cobalt fluorophosphates such as F.

As the (ME) lithium-containing transition metal silicate compound, for example, Li is cited₂FeSiO₄、Li₂MnSiO₄And Li₂CoSiO₄And the like.

In the present invention, (MA) a transition metal oxide having a layered rock-salt type structure is preferable, and LCO or NMC is more preferable.

The shape of the positive electrode active material is not particularly limited, and is preferably a particle shape. The volume average particle diameter (sphere-equivalent average particle diameter) of the positive electrode active material is not particularly limited. For example, the thickness can be set to 0.1 to 50 μm. In order to make the positive electrode active material have a predetermined particle size, a general pulverizer or classifier may be used. The positive electrode active material obtained by the firing method may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, and an organic solvent. The average particle diameter of the positive electrode active material particles can be measured by the same method as the method for measuring the volume average particle diameter of the inorganic solid electrolyte.

The surface of the positive electrode active material may be coated with another metal oxide, as in the case of the negative electrode active material.

The positive electrode active material may be used alone in 1 kind, or may be used in 2 or more kinds.

When the positive electrode active material layer is formed, the positive electrode active material layer has a unit area (cm)²) The mass (mg) (weight per unit area) of the positive electrode active material (b) is not particularly limited. The battery capacity can be determined as appropriate according to the designed battery capacity.

Negative electrode active material precursor

The negative electrode active material precursor is a compound in which ions (metal ions) of a metal element belonging to group 1 or group 2 of the periodic table are generated (released) in the positive electrode active material layer by a charging step described later. The generated metal ions reach the negative electrode active material layer or the like by charging of the all-solid-state secondary battery to thereby pre-dope the negative electrode active material layer. In the all-solid-state secondary battery of the embodiment in which the negative electrode active material layer is not formed in advance, the metal ions reach the negative electrode current collector, bond with electrons, and precipitate as a metal, thereby predoping the negative electrode active material layer.

The negative electrode active material precursor is not particularly limited as long as it has such characteristics or functions, and includes a compound containing the above metal element, but is different from a lithium salt as a supporting electrolyte used as a material of an all-solid secondary battery in that it releases and decomposes lithium ions at the first charge and does not contribute to the release of lithium ions at the next charge. In this way, the negative electrode active material precursor is a compound different from the positive electrode active material in that lithium ions caused by charge and discharge cannot be reversibly inserted and released.

The negative electrode active material precursor is preferably an inorganic compound containing the metal element, more preferably an inorganic salt that generates the metal ion and an anion, still more preferably a carbonate, an oxide, or a hydroxide of the metal element (alkali metal or alkaline earth metal), and particularly preferably a compound selected from carbonates. The inorganic salt is not particularly limited, and is preferably an inorganic salt that generates a gas at normal temperature and pressure by decomposition, preferably in a charged environment. For example, carbonate generates carbonate ions with ions of a metal element by oxidative decomposition. The generated ions of the metal element become a constituent material of the negative electrode active material layer, and the carbonate ions are converted into carbon dioxide gas, thereby being released (disappeared) from the positive electrode active material layer to the outside. Therefore, the carbonate does not remain in the positive electrode active material layer containing the decomposed product, and deterioration of the battery characteristics (energy density) due to the carbonate can be avoided.

When the all-solid-state secondary battery is an all-solid-state lithium ion secondary battery, the metal element forming the negative electrode active material precursor is preferably lithium.

Examples of the negative electrode active material precursor include inorganic salts of the metal elements, such as carbonates, oxides, hydroxides, and halides, and organic salts of the metal elements, such as carboxylates (e.g., oxalates). As the compound (lithium salt) containing a lithium element as a precursor of the negative electrode active material, specific examples thereof include lithium carbonate, lithium oxide, lithium hydroxide, lithium fluoride, lithium chloride, lithium oxalate, lithium iodide, lithium nitride, lithium sulfide, lithium phosphide, lithium nitrate, lithium sulfate, lithium phosphate, lithium oxalate, lithium formate, lithium acetate, and the like, and lithium carbonate, lithium oxide, or lithium hydroxide is preferable, and lithium carbonate is more preferable from the viewpoint of being capable of being handled safely (low in hygroscopicity) in the air.

The positive electrode composition may contain 1 kind of negative electrode active material precursor, or may contain 2 or more kinds.

The average particle diameter of the negative electrode active material precursor is not particularly limited, but is preferably 0.01 to 10 μm, and more preferably 0.1 to 1 μm. The average particle diameter is a value measured in the same manner as the average particle diameter of the inorganic solid electrolyte particles described above.

The content of the positive electrode active material in the positive electrode composition is not particularly limited, and is preferably 10 to 95 mass%, more preferably 30 to 90 mass%, even more preferably 50 to 85 mass%, and particularly preferably 55 to 80 mass% in 100 mass% of the solid content.

When the composition for a positive electrode contains an inorganic solid electrolyte, the total content of the inorganic solid electrolyte and the positive electrode active material layer in the composition for a positive electrode is preferably 5 mass% or more, more preferably 10 mass% or more, further preferably 15 mass% or more, further preferably 50 mass% or more, particularly preferably 70 mass% or more, and most preferably 90 mass% or more, per 100 mass% of the solid content. The upper limit is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and particularly preferably 99% by mass or less.

The content of the negative electrode active material precursor in the positive electrode composition varies depending on the ion amount of the metal element to be supplemented, and therefore cannot be uniquely determined, and is preferably 50 mass% or less, more preferably 5 to 30 mass%, and further preferably 7 to 20 mass% in 100 mass% of the solid content, for example. The total content of the positive electrode active material and the negative electrode active material precursor in the composition for a positive electrode is not particularly limited, and is preferably 70 to 90 mass%.

The content of the conductive auxiliary in the positive electrode composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass, based on 100% by mass of the solid content.

The content of each of the binder and the dispersion medium in the composition for a positive electrode is not particularly limited, and can be, for example, the content described above in the solid electrolyte composition.

The content of the other components in the composition for a positive electrode is not particularly limited, and may be appropriately set, for example, the content described above in the solid electrolyte composition can be set.

Preparation of a composition for a positive electrode

The composition for a positive electrode can be prepared under the same method and conditions as those for the preparation of the above-described solid electrolyte composition.

Formation of the positive electrode active material layer

The positive electrode active material layer is not particularly limited and can be prepared under the same method and conditions as the formation of the solid electrolyte layer described above. In the process of forming the positive electrode active material layer, the composition for a positive electrode applied and dried is preferably heated while being pressurized. The heating temperature is not particularly limited, and is generally in the range of 30 to 300 ℃.

The method for forming the positive electrode active material layer on the surface of the solid electrolyte layer opposite to (one of) the negative electrode active material layer is not particularly limited, and a general method can be applied. For example, a method of forming a solid electrolyte layer and a positive electrode active material layer separately and laminating the two layers, and a method of forming a positive electrode active material layer or a solid electrolyte layer on the surface of a solid electrolyte layer or a positive electrode active material layer are given.

As a method for forming the positive electrode active material layer on one surface of the solid electrolyte layer, the same method as that for forming the negative electrode active material layer on the other surface of the solid electrolyte layer can be cited, except that a positive electrode active material, a positive electrode active material layer, or a composition for a positive electrode is used instead of a negative electrode active material, a negative electrode active material layer, or a composition for a negative electrode.

The step of forming the solid electrolyte layer and the positive electrode active material layer is performed as described above, and a laminate including the positive electrode active material layer and the solid electrolyte layer is produced. When the all-solid-state secondary battery is a system in which the negative electrode active material layer is formed in advance, the step of forming the negative electrode active material layer is further performed to produce a laminate including the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer.

The laminate obtained in this manner is an all-solid-state secondary battery before initial charging and compression, also referred to as an all-solid-state secondary battery precursor.

< Process for charging laminate >

In the production method of the present invention, a step of charging the obtained laminate is performed next.

The charging conditions may be conditions that can oxidatively decompose the negative electrode active material precursor in the positive electrode active material layer, and examples thereof include the following conditions.

Current: 0.05 to 1mA/cm²

Voltage: 4.2-4.5V

Charging time: 1 to 20 hours

Temperature: 25-60 DEG C

Since the negative electrode active material precursor is released with anions (generated compounds) to the outside of the laminate, the charging step is preferably performed in an open state, not in a closed state. The environment at this time was the same as that at the time of preparing the solid electrolyte composition.

The step of charging is preferably performed by pressing and constraining the laminate in the lamination direction. This can suppress problems (e.g., damage to the solid electrolyte layer) caused by volume fluctuations of the negative electrode active material layer. The pressure at this time is not particularly limited, but is preferably 0.05MPa or more, and more preferably 1 MPa. The upper limit is not limited as long as the pressure does not compress the positive electrode active material layer, and is, for example, preferably less than 10MPa, and more preferably 8MPa or less.

In this step, charging may be performed 1 time or a plurality of times.

In this charging step, the negative electrode active material precursor in the positive electrode active material layer is oxidized and decomposed to generate metal ions and anions. The generated metal ions move to or near the negative electrode active material layer to dope the negative electrode active material layer. On the other hand, the negative ions may remain in the positive electrode active material layer, but it is preferable that the gas is changed and released to the outside of the laminate. As described above, in the manufacturing method of the present invention, the pre-doping can be performed safely and simply in a state where lithium metal or the like is not used.

When the charging is finished in this way, voids from the anode active material precursor oxidized and decomposed are generated in the cathode active material layer.

The porosity (porosity including all voids derived from the voids of the negative electrode active material precursor) in the positive electrode active material layer after charging varies depending on the type or particle diameter of the positive electrode active material layer, the formation condition of the positive electrode active material layer, the type, particle diameter, content, and the like of the negative electrode active material precursor, and therefore cannot be uniquely determined, and can be set to 5 to 30%, for example, preferably 15 to 25%.

The following method was used to determine the porosity of the positive electrode active material layerTo be measured. That is, an arbitrary cross section of the positive electrode active material layer was observed with a Scanning Electron Microscope (SEM), and an obtained SEM photograph was taken at a magnification of 3 ten thousand times to determine the area of the void in a field of view of 3 μm × 2.5 μm, and this area was divided by the field of view area (7.5 μm)²) And the resulting value (percentage).

In the all-solid-state secondary battery of the embodiment in which the negative electrode active material layer is not formed in advance, a negative electrode current collector or the like which can form a basis for forming an ion of a metal belonging to group 1 or group 2 of the periodic table can be suitably used. In this charging step, not only the coating due to the decomposition of the negative electrode active material precursor but also the negative electrode active material layer is formed.

< Process of discharging laminated body >

In the manufacturing method of the present invention, the step of discharging the laminate can be performed.

The discharge conditions are not particularly limited, and for example, the following conditions may be mentioned.

Current: 0.05 to 1mA/cm²

Voltage: 2.5-3.0V

Charging time: 1 to 20 hours

Temperature: 25-60 DEG C

From the viewpoint of being able to release anions of the negative electrode active material precursor to the outside of the laminate, the step of discharging in a state where the laminate is open is preferred. The environment at this time was the same as that at the time of preparing the solid electrolyte composition.

Preferably, the step of discharging is performed by pressurizing and constraining the laminate in the lamination direction. As a result, the adhesion between the current collector and the electrode layer can be maintained. The pressure at this time is not particularly limited, and may be set to the above-mentioned pressure range in the charging step, and may be the same as or different from the pressure in the charging step.

In this step, the discharge may be performed 1 time or more.

In this discharge step, metal ions are generated from the negative electrode active material layer or the vicinity thereof and reach the positive electrode active material layer. However, the positive electrode active material into which the metal ions are further introduced does not completely fill the voids from the negative electrode active material precursor, and the positive electrode active material layer may have voids (remains) that are compressed in the compression step described later.

The porosity of the positive electrode active material layer after discharge is not particularly limited, and may be, for example, 10% or more, and preferably 20% or more.

In an all-solid-state secondary battery of an embodiment in which a negative electrode active material layer is not formed in advance, a metal deposited in a discharging step and a charging step is ionized and moved to a positive electrode active material layer (the negative electrode active material layer is reduced in volume or disappears).

In the present invention, the charging in the above-described charging step is referred to as initial charging, and the discharging in the above-described discharging step is referred to as initial discharging. The initial charge and the initial discharge are collectively referred to as the initialization, and the initialization may be performed for 1 cycle or a plurality of cycles with 1 initial charge and 1 initial discharge as 1 cycle.

< step of compressing Positive electrode active Material layer >

In the manufacturing method of the present invention, a step of compressing the positive electrode active material layer by applying pressure is performed next.

In this step, the voids formed in the charged positive electrode active material layer or the voids remaining in the discharged positive electrode active material layer are compressed (flattened), and the positive electrode active material layer becomes thin (densified). Thereby, the total thickness (volume) of the all-solid secondary battery is reduced, and the energy density is improved.

The step of compressing may be performed so long as at least the positive electrode active material layer can be compressed, and when the charged positive electrode active material layer is compressed, it is preferable to compress the positive electrode active material layer by pressurizing the laminate which is the all-solid-state secondary battery precursor.

The method for compressing the positive electrode active material layer under pressure is not particularly limited, and various known compression methods can be applied, and compression (for example, compression using a hydraulic cylinder press) is preferable. The pressure in this step is not particularly limited as long as it is a pressure capable of crushing the voids, and is preferably higher than the pressure restriction in the step of charging. The pressure may be appropriately determined depending on the kind, content, void amount, and the like of the positive electrode active material layer, and is preferably set to a range of 10 to 1000MPa, for example. The lower limit of the pressure is more preferably 40MPa or more, further preferably 50MPa or more, particularly preferably 60MPa or more, and most preferably 80MPa or more, and the upper limit is more preferably 1000MPa or less, and further preferably 750MPa or less. The pressing time is not particularly limited, and may be a short time (for example, within several hours) or a long time (1 day or more).

The heating may be performed simultaneously with the pressure compression of the positive electrode active material layer, but in the present invention, the pressure compression is preferably performed without heating, and for example, the pressure compression is preferably performed at an ambient temperature of 10 to 50 ℃. The environment for the pressurization and compression is not particularly limited, and a mixed environment of the solid electrolyte composition may be mentioned.

The compression step is preferably performed at least in a state where the positive electrode active material layer, generally an all-solid secondary battery precursor, is not applied with voltage (not charged and discharged). In the present invention, the non-applied voltage means a mode in which a voltage of 2.5 to 3.0V corresponding to the end voltage of the initial discharge is applied, in addition to a mode in which no voltage is applied to the positive electrode active material layer or the like.

The positive electrode active material layer is compressed until the porosity of the positive electrode active material layer after compression is smaller than the porosity of the positive electrode active material layer after charging. This compression is desirably performed until the voids from the negative electrode active material precursor are completely compressed (until the void ratio of the positive electrode active material layer before charging is reached), but actually, the compression is performed until the void ratio of the positive electrode active material layer before charging is close to that before charging. For example, the positive electrode active material layer is compressed to a porosity higher by 1.5%, preferably higher by 1%, more preferably higher by 0.5% than the porosity before charging.

The step of compressing is different from the pressurization constraint preferably applied when using an all-solid secondary battery, from the viewpoint of compressing the positive electrode active material layer (compressing the voids).

In general, when an all-solid secondary battery is manufactured, a laminate (all-solid secondary battery precursor) further including a negative electrode active material layer is not pressurized at a pressure at which any layer is compressed, by the form of the positive electrode active material layer, the solid electrolyte layer, and the all-solid secondary battery. This is because, when voids are present in the negative electrode active material layer and the positive electrode active material layer, cracks or fractures are generated in the solid electrolyte layer present between the two layers, and the function of the secondary battery cannot be sufficiently exhibited.

However, in the production method of the present invention, since the step of compressing the positive electrode active material layer is performed after the step of charging, voids from the negative electrode active material precursor are formed in the positive electrode active material layer of the compressed laminate, and voids in the negative electrode active material layer hardly increase after the formation of the negative electrode active material layer. In this way, the production method of the present invention, in which the laminate is pressurized by setting the void amount in the positive electrode active material layer and the negative electrode active material layer, can compress the positive electrode active material layer without causing cracks or fractures in the solid electrolyte layer. In the case of a step in which discharge is not performed before the step of compression (a step in which charge is performed without intervening in the step of discharge and a step of compression), the occurrence of cracks or the like in the solid electrolyte layer can be more effectively suppressed.

The process of compression is carried out in the above-described manner to manufacture an initially charged, preferably initialized, all-solid secondary battery. As described above, the all-solid-state secondary battery exhibits a high battery capacity and a high energy density.

Examples

The present invention will be described in further detail below with reference to examples. The present invention is not limited to this explanation. In the following examples, "parts" and "%" representing the composition are based on mass unless otherwise specified.

< Synthesis example 1: synthesis of sulfide-based inorganic solid electrolyte Li-P-S-based glass

As sulfide-based inorganic solid electrolytes, Li-P-S-based glasses have been synthesized by non-patent documents of t.ohtomo, a.hayashi, m.tatsumisago, y.tsuchida, s.hama, k.kawamoto, Journal of Power Sources, 233, (2013), pp231-235, and a.hayashi, s.hama, h.morimoto, m.tatsumisago, t.minia, chem.lett., (2001), pp 872-873.

Specifically, 2.42g of lithium sulfide (Li) was weighed in a glove box under an argon atmosphere (dew point-70 ℃ C.)₂Inc. of Aldrich > 99.98%) and 3.90g of phosphorus pentasulfide (P)₂S₅Inc., aldrich. having a purity of > 99%), and was put into a mortar made of agate and mixed for 5 minutes using an agate-made pestle. In addition, Li₂S and P₂S₅In a molar ratio of Li₂S:P₂S₅＝75:25。

66 zirconia beads having a diameter of 5mm were put into a 45mL zirconia container (manufactured by Fritsch co., ltd.), and the total amount of the mixture of lithium sulfide and phosphorus pentasulfide was further put into the container, and the container was sealed under an argon atmosphere. This vessel was mounted on a planetary ball mill P-7 (trade name) manufactured by Fritsch co., Ltd, and mechanically ground at a rotation speed of 510rpm at a temperature of 25 ℃ for 20 hours to obtain 6.20g of a yellow powder sulfide-based inorganic solid electrolyte (Li-P-S-based glass). The ionic conductivity was 0.28 mS/cm. The particle diameter of the Li-P-S glass measured by the above-mentioned measurement method was 1 μm.

Example 1

In this example, an all-solid-state secondary battery having a positive electrode active material layer containing a negative electrode active material precursor and a Si negative electrode (negative electrode active material layer) was manufactured.

< production of solid electrolyte sheet >

100mg of the synthesized sulfide-based inorganic solid electrolyte was placed in a cylinder having an inner diameter of 10mm manufactured by Macor (registered trademark), and pressing was performed for 1 minute under an argon atmosphere at 25 ℃ with a pressure of 180 MPa. Thus, a solid electrolyte sheet composed of a sulfide-based inorganic solid electrolyte (thickness 600 μm) was obtained.

< making of negative plate >

Preparation of composition for negative electrode

In a 45mL vessel (manufactured by Fritsch co., Ltd) made of zirconia, 66 zirconia beads having a diameter of 5mm were put in, and 9.0g of the Li-P-S glass synthesized in the above synthesis example 1, 1.3g of particles of a modified polyvinylidene fluoride resin (PVDF) (4500-20 (trade name), manufactured by ARKEMA) as a binder, and 12g of diisobutyl ketone as a dispersion medium were added, and then the vessel was mounted on a planetary ball mill P-7 (trade name, manufactured by Fritsch co., Ltd), and stirring was continued at a rotation speed of 300rpm at a temperature of 25 ℃ for 2 hours.

9.0g of Si Powder (Silicon Powder, 1 to 5 μm in average particle diameter by the above measurement method, manufactured by Alfa Aesar Co., Ltd.) and 0.9g of acetylene black as a conductive aid were further added, 5g of diisobutyl ketone was further added, and then the vessel was mounted on a planetary ball mill P-7 (trade name, Fritsch Co., Ltd.) and stirred at a rotation speed of 150rpm at a temperature of 25 ℃ for 5 minutes. In this way, a composition (slurry) for a negative electrode was prepared.

Film formation of negative electrode active material layer-

The prepared composition for a negative electrode was wet-coated on a copper foil having a thickness of 8 μm at a weight per unit area of 2 mg/diameter of 10mm, dried at 100 ℃, and temporarily pressed at 180MPa to form an Si negative electrode active material layer.

Thus, a negative electrode sheet having a copper foil and a Si negative electrode active material layer (thickness 30 μm) was produced.

< lamination of solid electrolyte sheet and negative electrode sheet >

The negative electrode sheet was laminated on a solid electrolyte sheet so that the Si negative electrode active material layer of the disk-shaped negative electrode sheet punched out of the produced negative electrode sheet into a disk shape with a diameter of 10mm was in contact with the surface of the disk-shaped solid electrolyte sheet punched out of the solid electrolyte sheet into a disk shape with a diameter of 10mm, and was pressure-bonded for 1 minute under an argon atmosphere at 25 ℃ with a pressure of 24 MPa. Thus, a negative electrode sheet in which solid electrolyte layers were laminated was produced.

< manufacture of Positive plate >

Next, a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer was produced.

Preparation of a composition for a positive electrode

Into a 45mL vessel (manufactured by Fritsch Co., Ltd.) made of zirconia were charged 66 zirconia beads having a diameter of 5mm, and 2.0g of the Li-P-S glass synthesized in the above synthesis example 1, 0.1g of styrene butadiene rubber (product code 182907, manufactured by Aldrich Co., Ltd.), and 22g of octane as a dispersion medium were charged. Then, the vessel was mounted in a planetary ball mill P-7 manufactured by Fritsch co., ltd., and stirred at a rotation speed of 300rpm at a temperature of 25 ℃ for 2 hours. Then, a positive electrode active material layer LiNi was formed_0.85Co_0.10Al_0.05O₂(lithium nickel cobalt aluminate) 7.11g and Li as a precursor of a negative electrode active material₂CO₃0.79g of (lithium carbonate, average particle diameter 1 μm) was charged into a container, and the container was again mounted on the planetary ball mill P-7, and mixing was continued at a rotation speed of 100rpm at a temperature of 25 ℃ for 15 minutes. In this way, a composition (slurry) for a positive electrode containing a negative electrode active material precursor was obtained.

Next, the composition for a positive electrode obtained above was coated on an aluminum foil having a thickness of 20 μm as a current collector with a weight per unit area of 15 mg/diameter 10mm using a bake-type applicator, and heated at 80 ℃ for 2 hours to dry the composition for a positive electrode. Then, the positive electrode composition dried to a predetermined density was heated (120 ℃) and pressurized (600MPa, 1 minute) using a hot press. Thus, a positive electrode sheet having an aluminum foil and a positive electrode active material layer (thickness 110 μm) was produced.

< manufacture of all-solid-state secondary battery >

Preparation of the laminate

A liquid obtained by mixing an electrolyte solution for a lithium ion battery with polyethylene oxide (PEO) was applied to the surface of the solid electrolyte layer of the disk-shaped negative electrode sheet on which the solid electrolyte layer was laminated, and a positive electrode active material layer of a disk-shaped positive electrode sheet punched out to have a diameter of 10mm from the produced positive electrode sheet was attached. In this way, a disk-shaped laminate (all-solid-state secondary battery precursor) composed of the Si negative electrode current collector, the Si negative electrode active material layer, the solid electrolyte layer, the positive electrode active material layer, and the positive electrode current collector was obtained.

Procedure of charging (initial charging)

The whole obtained disk-shaped laminate was constrained in the lamination direction at a constraining pressure of 8MPa, and subjected to a current of 0.09mA/cm²Initial charging was performed under the conditions of voltage 4.2V, charging time 20 hours and temperature of 25 ℃. Lithium ions generated from lithium carbonate by this initial charge are applied as a lithium alloy to the Si negative electrode active material layer, and carbon dioxide gas is released to the outside of the battery. The positive electrode active material layer after initial charging was observed, and as a result, the porosity (based on the above measurement method) was increased by 7% to 15% with respect to the positive electrode active material layer before initial charging.

-a process of compression-

After the initial charging, the restraint of the disk-shaped stacked body is released, a pressure of 100MPa is applied between the positive electrode current collector and the Si negative electrode current collector, and the disk-shaped stacked body after the initial charging is pressed in the stacking direction to compress the positive electrode active material layer. This compression was performed at room temperature (25 ℃) using a hot press, without applying a voltage (charge and discharge) to the disk-shaped laminate over 1 hour.

As a result of observation of the positive electrode active material layer, the positive electrode active material layer was compressed (thinned) to a state in which the porosity increased by 1% (a state in which the voids of the positive electrode active material layer before initial charging were compressed by 6% of the porosity).

Thus, an all-solid-state secondary battery of the layer structure shown in fig. 1 was manufactured.

Comparative example 1

An all-solid secondary battery was manufactured in the same manner as in example 1, except that the pressure in the compression step was set to 8 MPa. The positive electrode active material layer in this all-solid secondary battery had a porosity of 7% and was not compressed (thinned) before and after the compression step.

Comparative example 2

In this example, an all-solid-state secondary battery having a positive electrode active material layer and a Si negative electrode (Si negative electrode active material layer) that did not contain a negative electrode active material precursor was manufactured.

In the method for manufacturing the all-solid-state secondary battery of example 1, an all-solid-state secondary battery including a positive electrode active material layer containing no negative electrode active material precursor was manufactured in the same manner as in the manufacturing of the all-solid-state secondary battery of example 1, using the following composition for a positive electrode (the positive electrode sheet was manufactured in the same manner as in example 1), except that the step of compressing was not performed.

Preparation of a composition for a positive electrode

Into a 45mL vessel (manufactured by Fritsch Co., Ltd.) made of zirconia were charged 66 zirconia beads having a diameter of 5mm, and 2.0g of the Li-P-S glass synthesized in the above synthesis example 1, 0.1g of styrene butadiene rubber (product code 182907, manufactured by Aldrich Co., Ltd.), and 22g of octane as a dispersion medium were charged. Then, the vessel was mounted in a planetary ball mill P-7 manufactured by Fritsch co., ltd., and stirred at a rotation speed of 300rpm at a temperature of 25 ℃ for 2 hours. Then, a positive electrode active material layer LiNi was formed_0.85Co_0.10Al_0.05O₂7.9g of (lithium nickel cobalt aluminate) was charged into a vessel, and the vessel was again set in the planetary ball mill P-7, and mixing was continued at a temperature of 25 ℃ and a rotational speed of 100rpm for 15 minutes. Thus, a positive electrode composition was obtained.

< evaluation: charge-discharge cycle characteristic test

Before the charge-discharge cycle characteristic test, each of the all-solid secondary batteries fabricated as described above was constrained in the stacking direction at a constraining pressure of 8MPa and at a value of 0.09mA/cm²And an end voltage of 2.5V, a charging time of 18 hours, and a temperature of 25 ℃ were initialized by performing initial discharge.

Next, using each all-solid-state secondary battery, charge and discharge were (rapidly) performed under the following conditions, and a charge and discharge cycle characteristic test (severe acceleration conditions) was performed.

(Condition)

Will be at 2.2mA/cm²Is charged to 4.25V and is charged at 2.2mA/cm²The current density of (2) was discharged to 2.5V, and the charge and discharge cycles were repeated for 7 cycles as 1 cycle.

The charge capacity and discharge capacity were measured every 1 cycle, and the charge-discharge efficiency was obtained from the following equation, and the charge-discharge cycle characteristics were evaluated.

Formula (II): charge-discharge efficiency (%) [ discharge capacity/charge capacity ] × 100

The results of the charge-discharge cycle characteristic test are shown below.

Example 1

The discharge capacity at 7 cycles of the all-solid secondary battery of example 1 was equal to that of comparative example 2 (the same weight per unit area as that of the positive electrode active material layer) using 7.9g of the positive electrode active material NCA. Thus, it was confirmed that the all-solid-state secondary battery exhibited a discharge capacity equal to that of comparative example 2, and the battery volume was reduced and the volumetric energy density was improved by making the positive electrode active material layer thinner.

And, the charge-discharge efficiency was stabilized at 99% for all 7 cycles. This shows that the occurrence of short circuits can be suppressed. Further, interfacial separation between the negative electrode active material layer and the solid electrolyte layer due to volume expansion and contraction of the negative electrode active material layer can be prevented, and a high discharge capacity can be maintained.

After ion beam milling of the cross-sectional portion of the solid electrolyte layer, the occurrence of cracks and fractures was not observed by SEM observation.

Comparative example 1

Since the positive electrode active material layer of the all-solid secondary battery of comparative example 1 was not compressed, no improvement in the volumetric energy density was observed.

Comparative example 2

Since the positive electrode active material layer of the all-solid-state secondary battery of comparative example 2 does not contain the negative electrode active material precursor, the decrease in the amount of lithium metal in the Si negative electrode active material layer cannot be compensated for, and the discharge capacity is insufficient. Further, since the thickness of the positive electrode active material layer was constant (unchanged), no improvement in the volumetric energy density was observed.

Having described the invention in connection with its embodiments, it is believed that the invention is not limited by any of the details of the description, unless otherwise specified, but is rather broadly construed in any manner without departing from the spirit and scope of the invention as set forth in the appended claims.

This application claims priority based on japanese patent application 2019-.

Description of the symbols

1-negative electrode current collector, 2-negative electrode active material layer, 3-solid electrolyte layer, 4-positive electrode active material layer, 5-positive electrode current collector, 6-working site, 10-all-solid-state secondary battery.