阅读说明：本技术 制备锂二次电池的方法 (Method for preparing lithium secondary battery ) 是由 金贵龙 禹昇希 金孝植 于 2019-11-26 设计创作，主要内容包括：本发明涉及一种可以有效地进行预锂化的制备锂二次电池的方法,其中,根据本发明,在锂二次电池的制备期间,制备在其中央形成有开口的闭合方形带状锂箔,并且将负极设置在该锂箔的开口中,但是通过将负极和锂箔设置为彼此不重叠并且将负极接片设置为与锂箔接触,可以在无需单独的预锂化工艺的情况下进行负极的预锂化。(The present invention relates to a method of manufacturing a lithium secondary battery in which prelithiation can be efficiently performed, wherein, according to the present invention, during the manufacture of the lithium secondary battery, a closed square strip-shaped lithium foil having an opening formed in the center thereof is manufactured, and a negative electrode is disposed in the opening of the lithium foil, but prelithiation of the negative electrode can be performed without a separate prelithiation process by disposing the negative electrode and the lithium foil so as not to overlap each other and disposing a negative electrode tab in contact with the lithium foil.)

1. A method of preparing an all-solid-state lithium secondary battery, the method comprising:

preparing an anode by forming an anode active material layer including a first solid electrolyte on both surfaces of a current collector;

preparing a lithium foil having an opening formed in the center thereof and having a closed band shape, wherein lithium is coated on one surface or both surfaces of the copper foil;

disposing the negative electrode in the opening of the lithium foil, but disposing the negative electrode not to overlap the lithium foil except for a negative electrode tab, disposing the negative electrode tab to be in contact with the lithium foil, and preventing a portion where the negative electrode tab and the lithium foil are in contact with each other from being coated with lithium;

applying a second solid electrolyte onto at least one surface of the structure formed thereby;

disposing a positive electrode including a third solid electrolyte on the second solid electrolyte; and

the stack thus prepared is enclosed in a casing.

2. The method of claim 1, wherein the negative active material comprises at least one selected from the group consisting of: at least one selected from the group consisting of silicon (Si), tin (Sn), aluminum (Al), antimony (Sb), and zinc (Zn) or an oxide thereof; and is selected from the group consisting of Co_x1O_y1(1≤x1≤3,1≤y1≤4)、Ni_x2O_y2(1≤x2≤3,1≤y2≤4)、Fe_x3O_y3(1≤x3≤3,1≤y3≤4)、TiO₂、MoO₂、V₂O₅And Li₄Ti₅O₁₂Is composed ofMetal oxides of the group.

3. The method of claim 1, wherein the opening has the same size and shape as the negative electrode except for the negative electrode tab.

4. The method of claim 1, wherein the first solid electrolyte, the second solid electrolyte, and the third solid electrolyte are the same or different from one another.

5. The method of claim 1 or claim 4, wherein the first solid electrolyte, the second solid electrolyte, and the third solid electrolyte each independently comprise at least one selected from inorganic solid electrolytes and organic solid electrolytes.

6. The method of claim 1, wherein the lithium foil has a size no greater than a second solid electrolyte coating portion and has a thickness no greater than a thickness of the negative electrode.

7. The method of claim 1, further comprising aging after the encapsulating.

8. The method of claim 7, wherein the aging is performed at a temperature of 10 ℃ to 200 ℃ and a pressure of 1bar to 5,000bar for 2 hours to 48 hours.

9. A method of preparing a lithium secondary battery, the method comprising:

preparing an anode by forming anode active material layers on both surfaces of a current collector;

preparing a lithium foil having an opening formed in the center thereof and having a closed band shape, wherein lithium is coated on one surface or both surfaces of the copper foil;

disposing the negative electrode in the opening of the lithium foil, but disposing the negative electrode not to overlap the lithium foil except for a negative electrode tab, disposing the negative electrode tab to be in contact with the lithium foil, and preventing a portion where the negative electrode tab and the lithium foil are in contact with each other from being coated with lithium;

providing a spacer on at least one surface of the structure thus formed;

arranging a positive electrode on the separator; and

the thus prepared stack was contained in a battery case, and a liquid electrolyte was injected into the battery case.

10. The method according to claim 9, wherein the separator is a polyolefin-based porous polymer film or a porous non-woven fabric.

11. The method of claim 9, wherein the lithium foil has a thickness no greater than a dimension of the separator and no greater than a thickness of the negative electrode.

12. The method according to claim 9, further comprising impregnating with an electrolyte solution at a temperature of 10 ℃ to 200 ℃ for 2 hours to 48 hours after accommodating the stack thus prepared in the battery case and injecting the liquid electrolyte into the battery case.

Technical Field

Cross Reference to Related Applications

This application claims the benefit of korean patent application No. 10-2018-0147161, filed by the korean intellectual property office at 26.11.2018, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a method of manufacturing a lithium secondary battery in which pre-lithiation can be efficiently performed, and more particularly, to a method of manufacturing a lithium secondary battery in which a closed square tape-shaped lithium foil formed with an opening at the center thereof is manufactured during the manufacture of the lithium secondary battery and a negative electrode is disposed in the opening of the lithium foil, but by disposing the negative electrode and the lithium foil so as not to overlap each other and disposing a negative electrode tab so as to be in contact with the lithium foil, pre-lithiation of the negative electrode can be performed without a separate pre-lithiation process.

Background

As the technical development and demand for mobile devices increase, the demand for secondary batteries as an energy source has significantly increased, and among these secondary batteries, lithium secondary batteries having high energy density, high operating potential, long cycle life, and low self-discharge rate have been commercialized and widely used.

Such as LiCoO₂、LiMnO₂、LiMn₂O₄Or LiCrO₂And the like are used as a positive electrode active material constituting a positive electrode of a lithium secondary battery, metal lithium (metal lithium), a carbon based material such as graphite (graphite) or activated carbon (activated carbon), or a carbon based material such as silicon oxide (SiO)_x) Such a material is used as an anode active material constituting an anode. Among these anode active materials, metallic lithium is mainly used initially, but recently, a carbon-based material is mainly used because the following phenomenon occurs: as the charge and discharge cycles progress, the battery is destroyed due to damage of the separator caused by the growth of lithium atoms on the surface of the metallic lithium. However, for carbon-based materials, there are disadvantages in that: its capacity is small because its theoretical capacity is only about 372mAh/g, and therefore, various studies have been made to replace the carbon-based material as the anode active material by using a silicon (Si) based material having a high theoretical capacity (4,200 mAh/g).

Charging and discharging of a lithium secondary battery are performed while repeating a process of inserting (intercalation) lithium ions from a positive electrode active material of a positive electrode into a negative electrode active material of a negative electrode and extracting (deintercalation) lithium ions from the negative electrode active material of the negative electrode.

Theoretically, lithium intercalation and deintercalation reactions in the anode active material are completely reversible, but in practice, more lithium than the theoretical capacity of the anode active material is consumed and only a portion of the lithium is recovered during discharge. Therefore, after the second cycle, a smaller amount of lithium ions are intercalated during charging, but most of the intercalated lithium ions are deintercalated during discharging. Therefore, the capacity difference between the first charge reaction and the discharge reaction is called irreversible capacity loss, and since commercially available lithium secondary batteries are manufactured in a state where lithium ions are supplied from the cathode and lithium is not present in the anode, it is important to minimize the irreversible capacity loss during initial charge and discharge.

It is known that such initial irreversible capacity loss is mainly caused by an Electrolyte decomposition (Electrolyte decomposition) reaction on the surface of the anode active material, and a Solid Electrolyte Interface (SEI) is formed on the surface of the anode active material by the electrochemical reaction caused by the Electrolyte decomposition. There is a limitation in that a large amount of lithium ions are consumed when the SEI is formed, thereby causing irreversible capacity loss, but the SEI formed at the initial stage of charging may prevent lithium ions from reacting with a negative electrode or other materials during charging and discharging and may act as an Ion Tunnel (Ion Tunnel) through which only lithium ions pass, and thus, the SEI helps to improve the cycle characteristics of the lithium secondary battery by inhibiting further electrolyte decomposition reactions. Therefore, a method of improving initial irreversibility caused by the formation of SEI is required, and one of the methods includes: a method of pre-lithiating a lithium secondary battery by performing pre-lithiation before the preparation of the lithium secondary battery so that side reactions generated during first charge occur in advance. As described above, in the case where the prelithiation is performed, when the actually prepared secondary battery is charged and discharged, since the first cycle is performed in a state where the irreversibility is reduced accordingly, there is an advantage in that: initial irreversibility may be reduced.

For example, conventional prelithiation methods may include a method of depositing lithium on the negative electrode or a method of directly contacting the negative electrode with lithium. However, the method of depositing lithium has disadvantages in that: in order to deposit lithium on the anode, it is expensive to provide equipment for deposition, and in mass production, workability is poor due to the time required.

Therefore, there is a need to develop a new anode for a lithium secondary battery that can perform more efficient prelithiation.

In order to develop a lithium secondary battery having improved safety, it is also required to develop a battery using a solid electrolyte instead of a conventional liquid electrolyte.

[ Prior art documents ]

[ patent document ]

(patent document 1) KR 2014-0104152A

Disclosure of Invention

Technical problem

An aspect of the present invention provides a method of manufacturing a lithium secondary battery, in which pre-lithiation may be performed without performing a separate pre-lithiation process.

Technical scheme

According to an aspect of the present invention, there is provided a method of manufacturing an all-solid lithium secondary battery, the method including:

preparing an anode by forming an anode active material layer including a first solid electrolyte on both surfaces of a current collector;

preparing a lithium foil having an opening formed in the center thereof and having a closed band shape, wherein lithium is coated on one surface or both surfaces of the copper foil;

disposing a negative electrode in the opening of the lithium foil, but disposing the negative electrode not to overlap the lithium foil except for a negative electrode tab, disposing the negative electrode tab to be in contact with the lithium foil, and preventing a portion where the negative electrode tab and the lithium foil are in contact with each other from being coated with lithium;

applying a second solid electrolyte onto at least one surface of the structure formed thereby;

disposing a positive electrode including a third solid electrolyte on the second solid electrolyte; and

the stack thus prepared is enclosed in a casing.

According to another aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery, the method including:

preparing an anode by forming anode active material layers on both surfaces of a current collector;

preparing a lithium foil having an opening formed in the center thereof and having a closed band shape, wherein lithium is coated on one surface or both surfaces of the copper foil;

disposing a negative electrode in the opening of the lithium foil, but disposing the negative electrode not to overlap the lithium foil except for a negative electrode tab, disposing the negative electrode tab to be in contact with the lithium foil, and preventing a portion where the negative electrode tab and the lithium foil are in contact with each other from being coated with lithium;

providing a spacer on at least one surface of the structure thus formed;

arranging a positive electrode on the separator; and

the thus prepared stack was contained in a battery case, and a liquid electrolyte was injected into the battery case.

Advantageous effects

In the present invention, since lithium of the lithium foil layer moves to the active material layer of the negative electrode without a complicated prelithiation process, thus prelithiation is easily induced, the negative electrode prepared according to the preparation method of the present invention can secure initial reversibility, and thus electrochemical performance of the lithium secondary battery can be improved.

Drawings

Fig. 1 is a schematic view illustrating that a negative electrode is disposed in a central opening of a square band-shaped lithium foil in a method of manufacturing a lithium secondary battery according to the present invention;

fig. 2 is a schematic view illustrating that a negative electrode is disposed in a central opening of a square strip-shaped lithium foil; and

fig. 3 is a schematic plan view illustrating a structure in which a closed square tape-shaped lithium foil with an opening formed in the center, a negative electrode, and a solid electrolyte or a separator are stacked in a method of manufacturing a lithium secondary battery according to the present invention.

Detailed Description

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

It will be understood that the words or terms used in the specification and claims should not be construed as limited to the meanings defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having a meaning that is consistent with the technical idea of the invention and the context of the related art, based on the principle that the inventor can appropriately define the meaning of the words or terms in order to best explain the present invention.

The method of preparing a lithium secondary battery according to the present invention includes the steps of: preparing a negative electrode; preparing a lithium foil having an opening formed in the center thereof and having a closed band shape, wherein lithium is coated on one surface or both surfaces of the copper foil; disposing a negative electrode in the opening of the lithium foil, but disposing the negative electrode not to overlap the lithium foil except for a negative electrode tab, disposing the negative electrode tab to be in contact with the lithium foil, and preventing a portion where the negative electrode tab and the lithium foil are in contact with each other from being coated with lithium; applying a solid electrolyte or providing a separator on at least one surface of the structure thus formed; disposing a positive electrode on the solid electrolyte or the separator; and accommodating the thus prepared stack in a battery case.

The lithium secondary battery according to the present invention may be an all solid-state lithium secondary battery or a lithium secondary battery using a liquid electrolyte.

Hereinafter, a method of manufacturing a lithium secondary battery according to the present invention will be described in detail.

Negative electrode and method for preparing the same

The negative electrode 100 of the present invention includes:

a negative electrode current collector, a negative electrode active material layer 102 formed on both surfaces of the negative electrode current collector, and a negative electrode tab 106 protruding from the current collector.

Each of the anode active material layers 102 formed on both surfaces of the anode current collector may be formed at a ratio of 1:3 to 300 with respect to the thickness of the anode current collector, and may be generally formed to a thickness of 50 μm to 2,000 μm. In the case where the thickness of the anode active material layer 102 is formed to have a ratio less than 1:3 with respect to the thickness of the anode current collector, the capacity may be excessively small, and in the case where the thickness of the anode active material layer 102 is formed to have a ratio greater than 1:300 with respect to the thickness of the anode current collector, smooth charge and discharge may not be performed due to an increase in the resistance of the battery.

The anode current collector is not particularly limited as long as it has high conductivity and does not cause undesirable chemical changes in the battery, and, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver or the like, and aluminum-cadmium alloy may be used. In addition, the anode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to improve adhesion of the anode active material. For example, the anode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, and the like.

The negative electrode can be prepared by the following method: an anode slurry is prepared by dissolving or dispersing an anode active material, a conductive agent and/or a binder in a solvent, and both surfaces of an anode current collector are coated with the anode slurry and then pressed.

The negative active material may include at least one selected from the group consisting of: at least one selected from the group consisting of silicon (Si), tin (Sn), aluminum (Al), antimony (Sb), and zinc (Zn) or an oxide thereof; and is selected from the group consisting of Co_x1O_y1(1≤x1≤3,1≤y1≤4)、Ni_x2O_y2(1≤x2≤3,1≤y2≤4)、Fe_x3O_y3(1≤x3≤3,1≤y3≤4)、TiO₂、MoO₂、V₂O₅And Li₄Ti₅O₁₂Metal oxides in the group consisting of.

For example, the anode active material is a mixed anode active material of a silicon-based anode active material and a carbon-based anode active material, wherein the anode active material may include the silicon-based anode active material and the carbon-based anode active material in a weight ratio of 1:99 to 50:50, such as 5:95 to 20: 80.

If the silicon-based anode active material is included in an amount less than the above range, it may be difficult to achieve a high capacity battery because it is difficult to increase the energy density, and if the silicon-based anode active material is included in an amount greater than the above range, the volume expansion degree of the anode may increase.

The negative electrode active material may be included in an amount of 80 to 99 wt%, for example, 85 to 98 wt%, with respect to the total weight of the negative electrode active material layer. When the anode active material is included within the above amount range, excellent capacity characteristics may be exhibited.

The conductive agent is used to provide conductivity to the electrode, wherein any conductive agent may be used without particular limitation so long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive agent may be: graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any one of them or a mixture of two or more of them may be used. The conductive agent may be included in an amount of 0 to 30 wt% based on the total weight of the anode active material layer.

In addition, the binder improves the adhesion between the anode active material particles and the adhesion between the anode active material and the current collector. Specific examples of binders may be: polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more of them may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the anode active material layer.

The solvent used in the preparation of the negative electrode slurry may be a solvent commonly used in the art, and, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone), or water may be used alone, or a mixture thereof may be used. The amount of the solvent used may be appropriately adjusted in consideration of the coating thickness, production yield and viscosity of the slurry.

In the case where the anode is used as an anode of an all solid-state lithium secondary battery, a solid electrolyte (first solid electrolyte) is included in the anode. The reason for this is that, in an all-solid battery, lithium ions can be transported to an active material only when a solid electrolyte is included in an electrode. The solid electrolyte may be included in an amount of 1 to 50 wt% based on the total weight of the anode active material layer.

The solid electrolyte may be an inorganic solid electrolyte or an organic solid electrolyte.

The inorganic solid electrolyte may include an oxide-based inorganic solid electrolyte, a phosphate-based inorganic solid electrolyte, a nitride-based inorganic solid electrolyte, a sulfide-based inorganic solid electrolyte, or a mixture thereof.

The oxide-based inorganic solid electrolyte may include Lithium Lanthanum Titanium Oxide (LLTO), Lithium Lanthanum Zirconium Oxide (LLZO), LISICON or a mixture thereof,

the phosphate-based inorganic solid electrolyte may include any one selected from the group consisting of Lithium Aluminum Titanium Phosphate (LATP), Lithium Aluminum Germanium Phosphate (LAGP), and a mixture thereof,

the nitride-based inorganic solid electrolyte may include LiPON (lithium phosphorus oxynitride), and

the sulfide-based inorganic solid electrolyte may include Li₁₀GeP₂S₁₂、Li₂S-P₂S₅、Li₂S-P₂S₅-LiI、Li₂S-P₂S₅-Li₂O、Li₂S-P₂S₅-Li₂O-LiI、Li₂S-SiS₂、Li₂S-SiS₂-LiI、Li₂S-SiS₂-LiBr、Li₂S-SiS₂-LiCl、Li₂S-SiS₂-B₂S₃-LiI、Li₂S-SiS₂-P₂S₅-LiI、Li₂S-B₂S₃、Li₂S-P₂S₅-Z_mS_n(wherein m and n are positive numbers, and Z is any one of germanium (Ge), Zn and gallium (Ga)), L_i2S-GeS₂、Li₂S-SiS₂-Li₃PO₄、Li₂S-SiS₂-Li_xMO_y(wherein x and y are positive numbers, and M is any one of phosphorus (P), Si, Ge, boron (B), Al, Ga, and indium (In)), and a mixture thereof.

The organic solid electrolyte may be a polymer electrolyte formed by adding a polymer resin to a solvated lithium salt, and the polymer resin may include one selected from the group consisting of: polyether-based polymers, polycarbonate-based polymers, acrylate-based polymers, polysiloxane-based polymers, phosphazene-based polymers, polyethylene derivatives, polyethylene oxide (PEO), polyethylene glycol, alkylene oxide derivatives, phosphate ester polymers, polylysine (aggregation lysine), polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups, or a mixture of two or more thereof.

Preparation of lithium foil

In order to prepare the lithium secondary battery of the present invention, a closed band-shaped lithium foil 200 having an opening 202 formed at the center thereof is prepared.

The opening 202 may be prepared to have the same size and shape as the negative electrode 100 except for the negative electrode tab 106, and the lithium foil 200 may be prepared by coating lithium on a copper foil having a desired shape. In fig. 1, the lithium foil 200 includes a lithium coated portion 204 and a lithium uncoated portion 206, in which portions in contact with the negative electrode 100 and the negative electrode tab 106 are not coated with lithium.

Negative electrode 100 does not overlap lithium foil 200 except for negative electrode tab 106, but the outer boundary of negative electrode 100 does not overlap the inner boundary of lithium foil 200.

The lithium foil 200 is prepared so that its size is not larger than a solid electrolyte-coated portion to be described later, and its thickness is not larger than that of the negative electrode.

Preparation of all-solid-state lithium Secondary Battery (Using solid electrolyte)

The negative electrode 100 is disposed in the opening 202 of the lithium foil 200 described above, but the negative electrode 100 and the lithium foil 200 except for the negative electrode tab 106 are disposed so as not to overlap each other, and the negative electrode tab 106 is disposed so as to be in contact with the lithium foil 200.

Fig. 2 shows the product obtained as described above, wherein the negative electrode 100 is arranged in the opening 202 of the lithium foil 200.

Next, a solid electrolyte 300 (see fig. 3) is provided by applying the solid electrolyte (second solid electrolyte) 300 onto at least one surface of the formed structure (the structure of fig. 2).

The solid electrolyte 300 serves as both an electrolyte and a separator in the all-solid-state lithium secondary battery, wherein one selected from the solid electrolyte (first solid electrolyte) compounds that may be included in the above-described anode may be used, and they may be the same as or different from each other.

Next, a positive electrode is disposed on the applied solid electrolyte.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

The positive electrode may be prepared according to a conventional positive electrode preparation method well known in the art. For example, the positive electrode can be prepared by the following method: dissolving or dispersing components constituting a positive electrode active material layer (i.e., a positive electrode active material, a conductive agent, and/or a binder) in a solvent to prepare a positive electrode slurry, and coating at least one surface of a positive electrode current collector with the positive electrode slurry, drying, and then pressing; alternatively, the positive electrode may be prepared by: the positive electrode slurry was cast on a separate support, and then the film separated from the support was laminated on a positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, or the like may be used. In addition, the cathode current collector may generally have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to improve adhesion of the cathode active material. For example, the cathode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, and the like.

As the positive electrode active material, for example, there can be used: such as lithium cobalt oxide (LiCoO)₂) And lithium nickel oxide (LiNiO)₂) Like layered compounds, or from at least one transition metalA substituted compound; lithium manganese oxides, e.g. Li_{1+ y}Mn_2-yO₄(wherein y is 0 to 0.33), LiMnO₃、LiMn₂O₃And LiMnO₂(ii) a Lithium copper oxide (Li)₂CuO₂) (ii) a Vanadium oxides, such as LiV₃O₈、LiFe₃O₄、V₂O₅And Cu₂V₂O₇(ii) a From the formula LiNi_1-yM_yO₂(wherein M ═ cobalt (Co), manganese (Mn), Al, copper (Cu), iron (Fe), magnesium (Mg), B, or Ga, and y is 0.01 to 0.3); represented by the chemical formula LiMn_2-yM_yO₂(wherein M ═ Co, nickel (Ni), Fe, chromium (Cr), Zn, or tantalum (Ta), and y is 0.01 to 0.1) or Li₂Mn₃MO₈(wherein M ═ Fe, Co, Ni, Cu, or Zn); LiMn₂O₄Wherein a portion of Li is substituted with alkaline earth metal ions; a disulfide compound; or Fe₂(MoO₄)₃However, the positive electrode active material is not limited thereto.

In addition, the binder and the conductive agent may be the same as those previously described in the negative electrode.

In the case where the positive electrode is used as a positive electrode of an all solid-state lithium secondary battery, a solid electrolyte (third solid electrolyte) is included in the positive electrode. The reason for this is that, in an all-solid battery, lithium ions can be transported to an active material only when a solid electrolyte is included in an electrode.

One selected from the solid electrolyte (first solid electrolyte) compounds that can be included in the above-described anode may be used as the solid electrolyte, and they may be the same as or different from each other.

The all solid-state lithium secondary battery of the present invention can be prepared by accommodating (packaging) the prepared stack in a battery case.

Since the prelithiation of the all solid-state lithium secondary battery of the present invention occurs through aging after encapsulation, the all solid-state lithium secondary battery of the present invention has advantages in that: prelithiation may be performed without performing a separate prelithiation process.

The aging can be carried out at a temperature of 10 ℃ to 200 ℃ and a pressure of 1bar to 5,000bar for 2 hours to 48 hours.

If the aging temperature and time are less than 10 ℃ and less than 2 hours, respectively, pre-lithiation may not be sufficiently performed, and it may be difficult to maintain its shape since lithium metal is melted at a temperature greater than 200 ℃. Since 48 hours is sufficient to complete prelithiation, the anode need not be aged for more than 48 hours. The reason why the pressure is applied is to facilitate ion transport by lowering the interface resistance in the all-solid battery, and a pressure within the above-described pressure range is suitable for this purpose.

As described above, the all solid-state lithium secondary battery denotes a battery in which a liquid or polymer electrolyte used in a conventional lithium secondary battery is replaced with a solid electrolyte material, wherein the all solid-state lithium secondary battery is chemically stable since a flammable solvent is not used in the battery, and at the same time, ignition or explosion caused by leakage or decomposition reaction of a conventional electrolyte solution does not occur at all, and thus, safety can be greatly improved. Further, since Li metal or Li alloy can be used as the anode material, there are advantages in that: the energy density of the battery with respect to mass and volume can be significantly improved. In addition, the all-solid lithium secondary battery is suitable for achieving high energy density by stacking electrodes and a solid electrolyte.

That is, according to the above-described preparation method of the present invention, an all solid-state lithium secondary battery having the advantages of the all solid-state lithium secondary battery and, at the same time, capable of performing pre-lithiation without a separate process can be prepared.

Preparation of lithium Secondary Battery (Using liquid electrolyte)

The negative electrode was disposed in the opening of the lithium foil described above, but the negative electrode and the lithium foil were disposed so as not to overlap each other, and the negative electrode tab was disposed so as to be in contact with the lithium foil (this process is the same as the process in which the negative electrode was disposed in the opening of the lithium foil during the preparation of the all solid-state lithium secondary battery described above). In this case, the lithium foil is prepared so that its size is not larger than a separator 300 to be described later, and its thickness is not larger than that of the negative electrode.

Then, the spacer 300 is disposed on at least one surface of the formed structure.

The separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions, wherein any separator may be used as the separator without particular limitation as long as it is generally used for a secondary battery, and specifically, a separator having a high moisture retention capacity for an electrolyte and a low resistance to the transport of electrolyte ions may be used. Specifically, a porous polymer film, for example, a porous polymer film prepared from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a laminated structure having two or more layers thereof may be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of high-melting glass fibers or polyethylene terephthalate fibers, may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure may be selectively used.

Next, the positive electrode is disposed on the separator.

The same positive electrode used in the above-described all-solid battery may be used as the positive electrode, but does not necessarily include a solid electrolyte.

After the positive electrode is provided, the lithium secondary battery of the present invention can be prepared by accommodating the stack prepared as described above in a battery case and injecting a liquid electrolyte into the battery case.

The liquid electrolyte is mainly an organic liquid electrolyte, which may include an organic solvent and a lithium salt.

Any organic solvent may be used as the organic solvent without particular limitation so long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, the following may be used: ester-based solvents such as methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), gamma-butyrolactone (gamma-butyrolactone), and epsilon-caprolactone (epsilon-caprolactone); ether-based solvents such as dibutyl ether (dibutyl ether) or tetrahydrofuran (tetrahydrofuran); ketone based solvents such as cyclohexanone (cyclohexoxanone); aromatic hydrocarbon-based solvents such as benzene (benzzene) and fluorobenzene (fluorobenzene); or carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), Ethylene Carbonate (EC), and Propylene Carbonate (PC); alcohol-based solvents such as ethanol and isopropanol; nitriles such as Ra-CN (where Ra is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double-bonded aromatic rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1, 3-dioxolane; or sulfolane (sulfolane). Among these solvents, a carbonate-based solvent may be used, and, for example, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) having high ionic conductivity and high dielectric constant, which can improve charge/discharge performance of a battery, may be used. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution may be excellent.

The lithium salt may be used without particular limitation so long as it is a compound capable of providing lithium ions used in the lithium secondary battery. In particular, LiPF₆、LiClO₄、LiAsF₆、LiBF₄、LiSbF₆、LiAlO₄、LiAlCl₄、LiCF₃SO₃、LiC₄F₉SO₃、LiN(C₂F₅SO₃)₂、LiN(C₂F₅SO₂)₂、LiN(CF₃SO₂)₂LiCl, LiI, or LiB (C)₂O₄)₂May be used as the lithium salt. The lithium salt may be used in a concentration range of 0.1M to 2.0M. In the case where the concentration of the lithium salt is included within the above range, since the electrolyte may have appropriate conductivity and viscosity, it may be obtainedExcellent electrolyte performance is obtained and lithium ions can be efficiently moved.

In order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery, at least one additive, such as: halogenated alkylene carbonate-based compounds such as difluoroethylene carbonate; pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ethylene glycol dimethyl ether (glyme), hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

After the liquid electrolyte is injected, since the pre-lithiation is performed by impregnating with the electrolyte solution at a temperature of 10 to 200 ℃ for 2 to 48 hours, lithium in the lithium foil may diffuse into the anode.

The impregnation may be carried out at a temperature of 20 ℃ to 70 ℃ for 2 hours to 36 hours.

If the impregnation temperature and time are less than 10 ℃ and less than 2 hours, respectively, the prelithiation may not be sufficiently performed, and it may be difficult to maintain its shape since the lithium metal is melted at a temperature greater than 200 ℃. Since 48 hours is sufficient to complete prelithiation, the anode need not be aged for more than 48 hours.

Although the lithium secondary battery according to the present invention has been described mainly in the form of a single cell, it is applicable to various types of lithium secondary batteries.

Specifically, the lithium secondary battery of the present invention may be manufactured through a winding process, or may be manufactured through a lamination, stacking, and/or folding process of a separator and an electrode. Further, the lithium secondary battery of the present invention may be applied to all types such as a cylinder type, a prism type, a coin type, and a pouch type according to the shape of the case, and may be, for example, a roll type, a stack-folding type (including a stack-Z-folding type), or a laminate-stack type according to the form accommodated in the case.

Examples

Hereinafter, the present invention will be described in detail according to examples. However, the following examples are given only to illustrate the present invention and are not intended to limit the scope of the present invention.

Example 1 preparation of all solid-state lithium Secondary Battery

The anode active material slurry was prepared by adding 80 wt% of AN anode active material (graphite), 3 wt% of a conductive agent (Denka black), 3.5 wt% of a binder (SBR), 1.5 wt% of a thickener (CMC), and a solid polymer electrolyte (PEO6: LiTFSI) to Acrylonitrile (AN). Both surfaces of the copper current collector were coated with the prepared anode active material slurry, dried and pressed to prepare an anode, and then the anode was punched into a circular shape.

Lithium was coated on a copper foil by a roll method to prepare a lithium foil, and a closed circular band-shaped lithium foil having an opening of the same shape and size as the negative electrode was prepared.

The prepared negative electrode was disposed in the opening of the prepared lithium foil.

After PEO6: LiTFSI as a solid electrolyte was coated on the top surface of the anode of the above-prepared structure to a thickness of 0.1mm, pressure was applied to combine the anode with the solid electrolyte. Then, LiCoO was added₂Positive electrode [ similarly to the negative electrode, solid polymer electrolyte is also included in the positive electrode (PEO6: LiTFSI)]Disposed on the top surface of the solid electrolyte and then pressurized to bond the positive electrode. A stack in the form of a positive electrode/a solid polymer electrolyte/a negative electrode (disposed in an opening of a lithium foil) was prepared through the above-described battery preparation process, and was received in a coin battery to prepare a coin-type full cell.

The full cell was aged at a pressure of 250bar at a temperature of 60 ℃ for 12 hours to perform pre-lithiation.

Example 2 preparation of lithium Secondary Battery Using liquid electrolyte

An anode active material slurry was prepared by adding 92 wt% of an anode active material (graphite: SiO ═ 7:3), 3 wt% of a conductive agent (Denka black), 3.5 wt% of a binder (SBR), and 1.5 wt% of a thickener (CMC) to water. Both surfaces of the copper current collector were coated with the prepared anode active material slurry, dried and pressed to prepare an anode, and then the anode was punched into a circular shape.

Lithium was coated on a copper foil by a roll method to prepare a lithium foil, and a closed circular band-shaped lithium foil having an opening of the same shape and size as the negative electrode was prepared.

The prepared negative electrode was disposed in the opening of the prepared lithium foil.

In the case of disposing the polyolefin separator in the above-prepared structure and LiCoO₂After between the positive electrodes, the stack was housed in a coin cell. Then, an electrolyte solution in which 2 wt% of FEC was added to a solvent in which EC and EMC were mixed in a volume ratio of 3:7 and LiPF was dissolved at a concentration of 1M was injected into the coin battery to prepare a coin-type full battery₆。

For prelithiation, the full cell was immersed in the electrolyte solution at room temperature for 12 hours.

Comparative example 1.

A coin-type full cell was prepared in the same manner as in example 1, except that: a strip-shaped lithium foil having an opening is not used.

Comparative example 2.

A coin-type full cell was prepared in the same manner as in example 2, except that: a strip-shaped lithium foil having an opening is not used.

Test example 1 Cyclic Charge/discharge test

The coin-type full cells prepared in examples and comparative examples were subjected to reversibility test using an electrochemical charger/discharger. By applying a current to a voltage of 4.2V (vs. Li/Li) at a current density of 0.1C rate during charging⁺) The coin-type full cells were charged and discharged to a voltage of 2.5V at the same current density during the discharge, and the first cycle charge/discharge efficiency (initial efficiency,%) is listed in table 1 below. In this case, the initial is calculated by the following equationEfficiency.

The charge/discharge test was performed at 60 ℃ for example 1 and comparative example 1 using a solid electrolyte, and at room temperature for example 2 and comparative example 2 using a liquid electrolyte.

Initial efficiency (%) — (discharge capacity in first cycle/charge capacity in first cycle) × 100

[ Table 1]

	First cycle charge/discharge efficiency (%)
		Example 1	85
Example 2	86
		Comparative example 1	64
Comparative example 2	80

As shown in table 1, it can be confirmed that the initial reversible efficiency of examples 1 and 2 is significantly higher than that of comparative examples 1 and 2, wherein it is considered that the reason is that: pre-lithiation of the lithium in the lithium foil layer to the active material layer of the negative electrode occurs without a complicated process.

[ description of symbols ]

100: negative electrode

102: negative electrode active material layer

106: negative electrode tab

200: lithium foil

202: opening of the container

204: lithium coated part

206: uncoated portion of lithium

300: applied solid electrolyte or separator