阅读说明：本技术 非水电解质二次电池 (Nonaqueous electrolyte secondary battery ) 是由 部田浩司 岛村治成 福本友祐 于 2019-09-09 设计创作，主要内容包括：非水电解质二次电池至少包含正极、负极和电解质。正极包含正极集电体、中间层和正极活性物质层。中间层配置在正极集电体与正极活性物质层之间。中间层至少包含羧甲基纤维素、导电材料和无机填料。(The nonaqueous electrolyte secondary battery includes at least a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector, an intermediate layer, and a positive electrode active material layer. The intermediate layer is disposed between the positive electrode current collector and the positive electrode active material layer. The intermediate layer contains at least carboxymethyl cellulose, a conductive material, and an inorganic filler.)

1. A nonaqueous electrolyte secondary battery comprising at least a positive electrode, a negative electrode and an electrolyte,

the positive electrode comprises a positive electrode current collector, an intermediate layer and a positive electrode active material layer,

the intermediate layer is disposed between the positive electrode current collector and the positive electrode active material layer,

the intermediate layer contains at least carboxymethyl cellulose, a conductive material, and an inorganic filler.

2. The nonaqueous electrolyte secondary battery according to claim 1,

the intermediate layer contains the carboxymethyl cellulose in an amount of 0.5 mass% or more and 40 mass% or less.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2,

the weight average molecular weight of the carboxymethyl cellulose is 25 to 50 ten thousand.

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3,

the intermediate layer does not substantially contain a polymer compound other than the carboxymethyl cellulose.

Technical Field

The present disclosure relates to a nonaqueous electrolyte secondary battery.

Background

Jp 2014-075335 a discloses disposing an undercoat layer between a positive electrode current collector and a positive electrode active material layer. The undercoat layer has a resistance greater than that of the positive electrode current collector.

Disclosure of Invention

As one of the abnormal modes of a nonaqueous electrolyte secondary battery (hereinafter, may be simply referred to as "battery"), it is considered that there is a short circuit due to an external output. That is, it is considered that the conductive sharp object penetrates the case (the outer package of the battery) and thus the sharp object intrudes into the battery. Further, it is considered that the positive electrode and the negative electrode are short-circuited by a sharp object entering the battery. The short circuit caused by the external input can be simulated by, for example, a nail penetration test or the like.

In general, a positive electrode includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer covers the surface of the positive electrode current collector. However, the positive electrode active material layer may be detached by an impact from an external input, and the positive electrode current collector may be exposed from the positive electrode active material layer. It is considered that when the exposed positive electrode current collector is in contact with the negative electrode, the short-circuit current increases. This is considered to be due to the low resistance of the positive electrode current collector. It is considered that the short-circuit current increases, and the heat generation of the battery increases.

In order to suppress exposure of the positive electrode current collector, it is conceivable to provide an intermediate layer. The intermediate layer is disposed between the positive electrode current collector and the positive electrode active material layer. By the presence of the intermediate layer, even if the positive electrode active material layer falls off, it is expected that the contact between the positive electrode current collector and the negative electrode is suppressed.

The resistance of the intermediate layer is required to be larger than that of the positive electrode current collector. However, if the resistance of the intermediate layer becomes too high, the current exchange between the positive electrode current collector and the positive electrode active material layer may be inhibited in normal use. That is, the battery performance may be degraded.

The resistance of the intermediate layer can be adjusted by the composition of the intermediate layer. For example, the intermediate layer comprises an inorganic filler, a conductive material, and a binder. The inorganic filler is an insulating component. It is believed that the more the inorganic filler, the greater the electrical resistance of the intermediate layer. The conductive material is a conductive component. It is believed that the more conductive material, the less resistive the intermediate layer.

The binder is a sticky polymer compound. An adhesive is necessary to fix the intermediate layer. The binder may be, for example, polyvinylidene fluoride (PVdF) or the like. In general, adhesives are also considered to be insulating components.

According to the novel insight of the present disclosure, the binder may be carbonized due to heat generated upon external input. The carbonized binder may have electrical conductivity. By carbonization of the binder, new conductive paths are formed. As a result, the resistance of the intermediate layer becomes small at the time of external input, and the short-circuit current may become large. That is, carbonization of the binder may promote heat generation at the time of external input.

An object of the present disclosure is to suppress heat generation at the time of external input.

The technical means and effects of the present disclosure will be described below. However, the mechanism of action of the present disclosure encompasses presumption. The scope of protection sought should not be limited, whether the mechanism of action is correct or not.

The nonaqueous electrolyte secondary battery includes at least a positive electrode, a negative electrode and an electrolyte. The positive electrode includes a positive electrode current collector, an intermediate layer, and a positive electrode active material layer. The intermediate layer is disposed between the positive electrode current collector and the positive electrode active material layer. The intermediate layer contains at least carboxymethyl cellulose, a conductive material, and an inorganic filler.

The inorganic filler is an insulating component. The conductive material is a conductive component. The inorganic filler and the conductive material are necessary for the intermediate layer to have a predetermined resistance.

Carboxymethyl cellulose (CMC) can function as a binder. When the CMC monomer is heated, the CMC is carbonized like PVdF. The carbonized CMC may form a conductive path.

According to the novel insight of the present disclosure, in case the mixture of CMC and inorganic filler is heated, CMC may be burned without carbonization. In the case where the mixture of PVdF or the like and the inorganic filler is heated, PVdF or the like may be carbonized. Burnout of CMC is considered to be a characteristic phenomenon embodied in a mixture of CMC and inorganic filler.

The interlayers of the present disclosure comprise a mixture of CMC and inorganic filler. In the intermediate layer of the present disclosure, since CMC may be burned when an external input is made, it is expected that a conductive path by the carbonized CMC does not substantially occur. Further, it is considered that the composition ratio of the inorganic filler in the intermediate layer becomes high due to the burnout of the CMC. This can increase the resistance of the intermediate layer and suppress the short-circuit current.

In addition, it is considered that CMC is burnt by reaction with oxygen. That is, it is considered that oxygen is consumed due to the burnout of CMC. It is considered that oxygen is released from the positive electrode when external input is made. It is considered that oxygen participates in a combustion reaction of an electrolyte or the like. The oxygen is consumed by the burnout of the CMC, and thus, the combustion reaction of the electrolyte and the like can be expected to be suppressed. By suppressing the combustion reaction, heat generation at the time of external input can be expected to be small.

By the synergistic effect of the above actions, it is expected that heat generation at the time of external input is suppressed in the battery of the present disclosure.

The intermediate layer may contain 0.5 to 40 mass% of carboxymethyl cellulose.

It is believed that the more CMC, the more oxygen consumption is associated with CMC burnout. When the CMC content of the intermediate layer is 0.5 mass% or more, heat generation at the time of external input can be expected to be small.

CMC is believed to hinder ion conduction in the intermediate layer. Thus, it is considered that the less the CMC, the more active the ion conduction in the intermediate layer. When the CMC content of the intermediate layer is 40 mass% or less, it is expected that ion conduction becomes active. As a result, the resistance increase rate in normal use is expected to decrease.

The weight average molecular weight of the carboxymethyl cellulose may be 25 to 50 ten thousand.

When the weight average molecular weight (Mw) of CMC is 25 ten thousand or more, heat generation at the time of external input can be expected to be small. This is because it is considered that the larger the Mw of CMC is, the more the amount of oxygen consumed accompanying the burning of CMC becomes. When the Mw of CMC is 50 ten thousand or less, the resistance increase rate in normal use can be expected to decrease. This is because it is considered that the smaller the Mw of CMC, the more difficult it is for CMC to become an obstacle to the movement of ions.

The intermediate layer may not substantially contain a polymer compound other than carboxymethyl cellulose.

In the above-mentioned embodiment [ 1 ], it is considered that the intermediate layer may further contain a polymer compound (binder or the like) other than CMC. This is because it is considered that, by virtue of CMC being at least a part of the polymer compound, the conductive path due to carbide at the time of external input can be reduced.

It is considered that when the intermediate layer does not substantially contain a polymer compound other than CMC, the conductive path due to carbide is further reduced at the time of external input. This can reduce heat generation at the time of external input.

The term "substantially not included" means that the content of the polymer compound is an amount such that the influence thereof can be ignored even if the polymer compound is carbonized. The content of the polymer compound other than CMC may be, for example, 0 mass% or more and 0.1 mass% or less.

The above and other objects, features, aspects and advantages of the present disclosure will become apparent from the following detailed description of the present disclosure, which is to be read in connection with the accompanying drawings.

Drawings

Fig. 1 is a schematic diagram showing an example of the structure of the nonaqueous electrolyte secondary battery of the present embodiment.

Fig. 2 is a schematic diagram showing an example of the structure of the electrode group according to the present embodiment.

Fig. 3 is a schematic sectional view showing an example of the positive electrode structure of the present embodiment.

Fig. 4 is a schematic flowchart showing a method for manufacturing a positive electrode according to the present embodiment.

Detailed Description

Hereinafter, embodiments of the present disclosure (referred to as "the present embodiments" in the present specification) will be described. However, the following description does not limit the scope of the claims.

< nonaqueous electrolyte Secondary Battery >

Fig. 1 is a schematic diagram showing an example of the structure of the nonaqueous electrolyte secondary battery of the present embodiment.

The battery 100 is a nonaqueous electrolyte secondary battery. Battery 100 includes a housing 80. The case 80 may be made of, for example, an aluminum (Al) alloy. The housing 80 is a square (flat rectangular parallelepiped) container. However, the shape of the housing 80 should not be particularly limited. The housing 80 may be, for example, a cylindrical container. The case 80 may be, for example, a pouch made of an Al laminated film or the like.

The housing 80 has terminals 81. The case 80 may further have, for example, a cid (current interrupt device), a gas discharge valve, a liquid injection hole, and the like. The case 80 houses the electrode group 50 and an electrolyte (not shown). The electrode group 50 is electrically connected to the terminal 81.

Fig. 2 is a schematic diagram showing an example of the structure of the electrode group according to the present embodiment.

The electrode group 50 is of a wound type. The electrode group 50 is formed by sequentially stacking the positive electrode 10, the separator 30, the negative electrode 20, and the separator 30, and further winding them in a spiral shape. That is, battery 100 includes at least positive electrode 10, negative electrode 20, and an electrolyte (not shown). The electrode group 50 may be shaped flat.

The electrode group 50 may be of a stack type. That is, the electrode group 50 may be formed by alternately stacking 1 or more positive electrodes 10 and negative electrodes 20. Separators 30 are disposed between the positive electrode 10 and the negative electrode 20, respectively.

Further, the battery 100 may not include the separator 30. When, for example, the battery 100 is an all-solid battery, the battery 100 may not include the separator 30.

< Positive electrode >

Fig. 3 is a schematic sectional view showing an example of the positive electrode structure of the present embodiment.

The positive electrode 10 is a sheet. The positive electrode 10 includes a positive electrode current collector 11, an intermediate layer 13, and a positive electrode active material layer 12. The intermediate layer 13 is disposed between the positive electrode current collector 11 and the positive electrode active material layer 12. The intermediate layer 13 and the positive electrode active material layer 12 may be disposed only on one side of the positive electrode current collector 11. The intermediate layer 13 and the positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode current collector 11.

Positive electrode collector

The positive electrode current collector 11 is a conductive sheet. The thickness of the positive electrode current collector 11 may be, for example, 1 μm or more and 17 μm or less. The positive electrode collector 11 may be, for example, an Al foil. The thickness of the Al foil may be, for example, 5 μm or more and 17 μm or less. The positive electrode collector 11 may be, for example, a titanium (Ti) foil. The thickness of the Ti foil may be, for example, 1 μm or more and 15 μm or less.

In the present embodiment, the thickness of each structure can be measured using, for example, a micrometer. The thickness of each structure can be measured, for example, in a cross-sectional microscope image (e.g., a scanning electron microscope image) or the like. The thickness is measured at least 3 points. An arithmetic mean of at least 3 is used.

Intermediate layer

The intermediate layer 13 is disposed between the positive electrode current collector 11 and the positive electrode active material layer 12. The thickness of the intermediate layer 13 may be, for example, 0.5 μm or more and 10 μm or less. The thickness of the intermediate layer 13 may be, for example, 0.5 μm or more and 5 μm or less. The intermediate layer 13 contains at least CMC, a conductive material, and an inorganic filler.

(CMC)

CMC functions as a binder. The details of the mechanism are not clear, but CMC can be burned by heating by the coexistence of CMC and inorganic filler. By burning the CMC without carbonization, heat generation at the time of external input can be expected to be reduced.

The CMC may be, for example, an acid type CMC (CMC-H). CMC may be, for example, sodium salt (CMC-Na), lithium salt (CMC-Li), ammonium salt (CMC-NH)₄) And the like. The etherification degree of CMC should not be particularly limited. The etherification degree may be, for example, 0.5 or more and 1 or less.

(CMC content)

The CMC in the intermediate layer 13 may be contained, for example, in an amount of 0.2 mass% or more and 45 mass% or less. The CMC in the intermediate layer 13 may be contained, for example, in an amount of 0.5 mass% or more and 40 mass% or less. When the CMC content of the intermediate layer 13 is 0.5 mass% or more, heat generation at the time of external input can be expected to be small. When the CMC content is 40 mass% or less, the resistance increase rate in normal use can be expected to decrease.

The CMC content of the intermediate layer 13 may be, for example, 2 mass% or more. The CMC content of the intermediate layer 13 may be, for example, 10 mass% or more. The CMC content of the intermediate layer 13 may be, for example, 30 mass% or less. The CMC content of the intermediate layer 13 may be, for example, 20 mass% or less.

(weight average molecular weight of CMC)

The weight average molecular weight (Mw) of CMC may be, for example, 20 to 52 ten thousand. The Mw of the CMC may be, for example, 25 to 50 ten thousand. When the Mw of the CMC is 25 ten thousand or more, heat generation at the time of external input can be expected to be small. When the Mw of CMC is 50 ten thousand or less, the resistance increase rate in normal use can be expected to decrease. The Mw of the CMC may be, for example, 33 ten thousand or more. The Mw of the CMC may be 40 ten thousand or less.

The Mw of CMC is determined by GPC (gel permeation chromatography).

The Mw of the CMC was determined from the calibration curve of the standard sample and the dissolution time of the CMC. The standard sample was pullulan. The Mw was measured at least 3 times. An arithmetic mean of at least 3 times was used.

(conductive Material)

The conductive material is a conductive component. The conductive material is typically a population of particles. The conductive material in the intermediate layer 13 may be contained, for example, in an amount of 0.5 mass% or more and 5 mass% or less. The conductive material should not be particularly limited. The conductive material may be, for example, a carbon material. The conductive material may be at least 1 selected from, for example, carbon black, graphite, Vapor Grown Carbon Fiber (VGCF), Carbon Nanotube (CNT), and graphene. The carbon black may be at least 1 selected from, for example, Acetylene Black (AB), ketjen black (registered trademark, KB), Furnace Black (FB), Channel Black (CB), and Thermal Black (TB).

(inorganic Filler)

The inorganic filler is an insulating component. The inorganic filler may constitute the balance other than CMC and conductive material in the intermediate layer 13. The inorganic filler in the intermediate layer 13 may be contained, for example, in an amount of 45 mass% or more and 99.3 mass% or less. The inorganic filler in the intermediate layer 13 may be contained, for example, in an amount of 52 mass% or more and 96.8 mass% or less. The inorganic filler in the intermediate layer 13 may be contained, for example, in an amount of 57 mass% or more and 96.5 mass% or less.

The inorganic filler is a particle group. The inorganic filler D50 may be, for example, 0.1 to 3 μm. "D50" represents a particle size at which the cumulative particle volume from the fine particle side becomes 50% of the total particle volume in a volume-based particle size distribution measured by a laser diffraction method. The shape of the inorganic filler should not be particularly limited. The inorganic filler may be, for example, spherical, massive, needle-like, flake-like, etc.

The inorganic filler may be at least 1 selected from, for example, boehmite, α alumina, titanium oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, and zinc hydroxide.

The inorganic filler may be at least 1 selected from, for example, rutile type titanium oxide, anatase type titanium oxide, alumina, boehmite, and magnesium hydroxide.

(other Components)

The intermediate layer 13 may further contain other components as long as it contains CMC, a conductive material, and an inorganic filler. The content of the other components may be, for example, 0.1 mass% or more and 10 mass% or less. As other components, for example, a solid electrolyte and the like can be considered.

Other components may be, for example, a polymer compound other than CMC. The polymer compound other than CMC may be, for example, an organic filler. The polymer compound other than CMC may be, for example, a binder. The binder may be at least 1 selected from, for example, acrylic resin and PVdF. The acrylic resin means a high molecular compound formed by polymerizing at least 1 monomer selected from the group consisting of acrylic acid esters, methacrylic acid esters, and acrylonitrile.

However, a polymer compound other than CMC may be carbonized at the time of external input. Since the intermediate layer 13 does not substantially contain a polymer compound other than CMC, heat generation at the time of external input can be expected to be small. The intermediate layer 13 may be substantially composed of only CMC, conductive material, and inorganic filler.

Positive electrode active material layer

The positive electrode active material layer 12 is formed on the surface of the intermediate layer 13. The thickness of the positive electrode active material layer 12 may be 50 μm or more and 100 μm or less. The positive electrode active material layer 12 contains at least a positive electrode active material. For example, the positive electrode active material layer 12 may contain 0.1 mass% to 10 mass% of a conductive material, 0.1 mass% to 10 mass% of a binder, and the balance of a positive electrode active material.

The positive electrode active material is typically a particle group. The positive electrode active material D50 may be, for example, 1 μm or more and 30 μm or less. The positive electrode active material should not be particularly limited. The positive electrode active material may be at least 1 selected from, for example, lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganate, and lithium iron phosphate.

The nickel cobalt lithium aluminate represents a compound represented by, for example, the following formula (1). x1 may be, for example, 0.88.

LiNi_x1Co_y1Al_z1O₂…(1)

[ wherein x1, y1 and z1 satisfy 0.82. ltoreq. x 1. ltoreq.0.95, 0.01. ltoreq. y 1. ltoreq.0.15, 0.01. ltoreq. z 1. ltoreq.0.15, and x1+ y1+ z 1. ltoreq.1 ]

Lithium nickel cobalt manganese oxide is a compound represented by, for example, the following formula (2).

LiNi_x2Co_y2Mn_z2O₂…(2)

[ wherein x2, y2 and z2 satisfy 0.35. ltoreq. x 2. ltoreq.0.95, 0.01. ltoreq. y 2. ltoreq.0.60, 0.01. ltoreq. z 2. ltoreq.0.60, and x2+ y2+ z 2. ltoreq.1 ]

The positive electrode active material may contain an additive. The additives may be, for example, alkaline earth metals, transition metals, base metals, semi-metals, and the like. The additive may be a compound (e.g., a metal oxide, etc.). The additive may replace, for example, a base material element (e.g., LiCoO)₂Co in (b), etc.). The additive may be attached to the surface of the base material particle. The positive electrode active material may contain 1 additive alone. The positive electrode active material may contain 2 or more additives. The content of the additive may be, for example, 5m o l% or less in total.

The conductive material contained in the positive electrode active material layer 12 should not be particularly limited. The conductive material may be at least 1 selected from, for example, carbon black, graphite, soft carbon, hard carbon, VGCF, CNT, and graphene.

The binder contained in the positive electrode active material layer 12 should not be particularly limited. The binder may be at least 1 selected from, for example, PVdF, vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), acrylic resin, and Polytetrafluoroethylene (PTFE).

Method for producing Positive electrode

Fig. 4 is a flowchart showing an outline of the method for manufacturing the positive electrode according to the present embodiment.

According to the present embodiment, there is also provided a method for manufacturing a positive electrode for a nonaqueous electrolyte secondary battery. The positive electrode of the present embodiment is produced by a method including at least "a" preparation of the 1 st dispersion liquid "," b "preparation of the 2 nd dispersion liquid", "c" formation of the intermediate layer ", and" d "formation of the positive electrode active material layer".

(a preparation of the first Dispersion 1)

The method for manufacturing a positive electrode of the present embodiment includes: the first dispersion was prepared by mixing at least CMC, inorganic filler and water.

The details of the CMC and the inorganic filler are as described above. A general mixing device may be used in the mixing operation. For example, a homomixer, a planetary mixer, or the like can be used. The solid content ratio in the mixing may be, for example, 30 mass% or more and 60 mass% or less. The "solid content ratio" represents the ratio of components other than the solvent (water).

The CMC aqueous solution can be prepared by mixing CMC and water in advance. The inorganic filler may then be mixed into the CMC aqueous solution.

After the CMC and the inorganic filler were sufficiently mixed, water was added to the 1 st dispersion. After water was added, the 1 st dispersion was stirred. The final solid content ratio of the 1 st dispersion may be, for example, 25 mass% or more and 45 mass% or less.

(b. preparation of Dispersion 2)

The method for manufacturing a positive electrode of the present embodiment includes: the 2 nd dispersion is prepared by mixing at least the 1 st dispersion with a conductive material.

The details of the conductive material are as previously described. The mixing operation may use a general mixing device. The final solid content ratio of the 2 nd dispersion may be, for example, 30 mass% or more and 45 mass% or less. Water may be added as appropriate to adjust the solid content ratio.

By mixing the conductive material, the dispersant, and water in advance, a conductive material dispersion liquid (conductive paste) can be prepared. The solid content ratio of the conductive material dispersion liquid may be, for example, 30 mass% or more and 45 mass% or less. The second dispersion can be prepared by mixing the conductive material dispersion with the first dispersion 1.

(c. formation of intermediate layer)

The method for manufacturing a positive electrode of the present embodiment includes: the intermediate layer 13 is formed by applying the 2 nd dispersion to the surface of the positive electrode current collector 11 and drying.

The details of the positive electrode collector are as described above. The coating operation may use a general coating apparatus. For example, a gravure coater, a blade coater, a multifunction coater, a die coater, a blade coater, an inkjet coater, and the like can be used. The drying operation may use a general drying apparatus. For example, a hot air drying furnace or the like can be used. The drying temperature may be, for example, 60 ℃ or higher and 110 ℃ or lower. The drying time can be adjusted according to, for example, the drying temperature. For example, when the drying temperature is about 100 ℃, the drying time may be about 10 minutes.

(d. formation of Positive electrode active Material layer)

The method for manufacturing a positive electrode of the present embodiment includes: the positive electrode 10 is manufactured by forming the positive electrode active material layer 12 on the surface of the intermediate layer 13.

For example, a positive electrode active material, a conductive material, a binder, and a solvent are mixed to prepare an active material paste. Details of the positive electrode active material, the conductive material, and the binder are as described above. The solvent is selected according to the kind of the binder. The solvent may be, for example, N-methyl-2-pyrrolidone (NMP) or the like.

The active material paste is applied to the surface of the intermediate layer 13 and dried, whereby the positive electrode active material layer 12 can be formed. The coating operation may use a general coating apparatus. After the positive electrode active material layer 12 is dried, the positive electrode active material layer 12 may be compressed. The positive electrode 10 is manufactured by forming the positive electrode active material layer 12. The positive electrode 10 may be cut into a predetermined shape in conformity with the design of the battery 100.

The positive electrode 10 is manufactured through the above operation.

As described above, the method for manufacturing a positive electrode according to the present embodiment includes at least the following steps (a) to (d).

(a) The first dispersion was prepared by mixing at least CMC, an inorganic filler and water.

(b) The 2 nd dispersion is prepared by mixing at least the 1 st dispersion and a conductive material.

(c) The intermediate layer 13 is formed by applying the 2 nd dispersion to the surface of the positive electrode current collector 11 and drying.

(d) The positive electrode 10 is manufactured by forming the positive electrode active material layer 12 on the surface of the intermediate layer 13.

It is considered that, according to the method for manufacturing a positive electrode of the present embodiment, the CMC and the inorganic filler are easily brought into contact in the intermediate layer 13. As a result, it is expected that CMC will be easily burned.

The method for producing a positive electrode according to the present embodiment may include at least the following steps (a) to (d).

(a) The 1 st dispersion was prepared by mixing at least a binder, an inorganic filler and water.

(b) The 2 nd dispersion is prepared by mixing at least the 1 st dispersion and a conductive material.

(c) The intermediate layer 13 is formed by applying the 2 nd dispersion to the surface of the positive electrode current collector 11 and drying.

(d) The positive electrode 10 is manufactured by forming the positive electrode active material layer 12 on the surface of the intermediate layer 13.

The binder is a polymer compound which burns out when heated to 450 ℃ in the coexistence of an inorganic filler.

Here, "burnout" means that "the mass remaining rate after heating" is 0 mass% or more and 1 mass% or less. The mass remaining ratio after heating was determined by the following formula (3):

mass residual rate after heating is M₁÷M₀×100…(3)

[ in the formula, M₀Represents the mass of the polymer compound before the heat test, M₁Represents the mass of the polymer compound after the heat test ]

The sequence of the heating test is shown in the examples described later.

< negative electrode >

The negative electrode 20 is a sheet. The anode 20 includes an anode current collector 21 and an anode active material layer 22. The aforementioned intermediate layer 13 may be disposed between the anode current collector 21 and the anode active material layer 22. By including the intermediate layer 13 in the negative electrode 20, heat generation at the time of external input can be expected to be reduced.

The negative electrode current collector 21 is a conductive sheet. The thickness of the negative electrode current collector 21 may be, for example, 1 μm or more and 15 μm or less. The negative electrode collector 21 may be, for example, a copper (Cu) foil. The thickness of the Cu foil may be 5 μm or more and 12 μm or less. The thickness of the Cu foil may be 5 μm or more and 8 μm or less. The negative electrode collector 21 may be, for example, a Ti foil. The thickness of the Ti foil may be, for example, 1 μm or more and 15 μm or less.

The anode active material layer 22 is formed on the surface of the anode current collector 21. The anode active material layer 22 may be formed on only one surface of the anode current collector 21. The negative electrode active material layer 22 may be formed on both the front and back surfaces of the negative electrode current collector 21. The thickness of the anode active material layer 22 may be 40 μm or more and 125 μm or less. The anode active material layer 22 contains at least an anode active material. For example, the anode active material layer 22 may be composed of 0.1 mass% to 10 mass% of a conductive material, 0.1 mass% to 10 mass% of a binder, and the balance of an anode active material.

The negative electrode active material is typically a particle group. The D50 of the negative electrode active material may be, for example, 1 μm or more and 30 μm or less. The anode active material should not be particularly limited. The anode active material may be at least 1 selected from, for example, graphite, soft carbon, hard carbon, amorphous carbon, and silicon oxide. The negative electrode active material may be, for example, a material in which the surface of graphite is coated with amorphous carbon.

When the negative electrode active material contains silicon oxide, the content of silicon oxide may be 4 mass% or more and 70 mass% or less with respect to the entire negative electrode active material. The silicon oxide may be previously doped with lithium (Li). The silicon (Si) in the Li-doped silicon oxide (LiSiO) may comprise more than 10 and less than 80 m.

In the present embodiment, the capacity ratio (the ratio of the negative electrode capacity to the positive electrode capacity) may be, for example, 1.05 or more and 2.2 or less. The capacity ratio is obtained by dividing the negative electrode capacity by the positive electrode capacity. The negative electrode capacity is obtained by multiplying the total mass of the negative electrode active materials contained in the negative electrode 20 by the specific capacity of the negative electrode active material. The positive electrode capacity is determined by multiplying the total mass of the positive electrode active materials contained in the positive electrode 10 by the specific capacity of the positive electrode active material.

The conductive material contained in the anode active material layer 22 should not be particularly limited. The conductive material may be at least 1 selected from, for example, carbon black, CNT, and graphene.

The binder contained in the anode active material layer 22 should not be particularly limited. The binder may be at least 1 selected from, for example, CMC and Styrene Butadiene Rubber (SBR).

< separator >

The separator 30 is a porous film. The separator 30 is electrically insulating. The separator 30 may have a single-layer structure. The separator 30 may be constituted only by a porous film made of, for example, Polyethylene (PE). The thickness of the separator 30 having a single-layer structure may be, for example, 5 μm or more and 30 μm or less.

The separator 30 may also have a multilayer structure. The separator 30 may be formed by laminating a porous film made of polypropylene (PP), a porous film made of PE, and a porous film made of PP in this order. The thickness of the separator 30 having a multilayer structure may be, for example, 10 μm or more and 30 μm or less. In the separator 30 having a multilayer structure, the thickness of each of the PP porous film and the PE porous film may be, for example, 3 μm or more and 10 μm or less.

The heat-resistant film may be formed on a surface of the separator 30, the thickness of the heat-resistant film may be 2 μm or more and 12 μm or less, the heat-resistant film includes a heat-resistant material, for example, the heat-resistant film may be composed of 2 mass% or more and 30 mass% or less of a binder, and the balance of an inorganic filler, the binder should not be particularly limited, the binder may be at least 1 selected from, for example, acrylic resin, PVdF-HFP, aramid, SBR, and PTFE, the inorganic filler should not be particularly limited, the inorganic filler may be at least 1 selected from, for example, boehmite, α alumina, titanium oxide, zirconium oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, and zinc hydroxide.

Further, a heat-resistant film may be formed on the surface of the positive electrode active material layer 12. The heat-resistant film may be formed on the surface of the anode active material layer 22.

< electrolyte >

The electrolyte is a Li ion conductor. The electrolyte may be any of a liquid electrolyte, a gel electrolyte, and a solid electrolyte. The liquid electrolyte may be, for example, an electrolytic solution, an ionic liquid, or the like. In the present specification, an electrolytic solution is described as an example of the electrolyte.

ElectrolysisThe liquid comprises a solvent and a supporting salt. The supporting salt is dissolved in the solvent. The concentration of the support salt may be, for example, 0.5 to 2M/L (0.5 to 2M). The supporting salt may be selected from, for example, LiPF₆、LiBF₄、LiN(FSO₂)₂And LiN (CF)₃SO₂)₂At least 1 kind of (1).

The solvent is aprotic. The solvent may contain, for example, cyclic carbonates and chain carbonates. The mixing ratio of the cyclic carbonate and the chain carbonate may be, for example, "cyclic carbonate: chain carbonate 1: 9-5: 5 (volume ratio) ". The cyclic carbonate may be at least 1 selected from, for example, Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), and fluoroethylene carbonate (FEC).

The chain carbonate may be at least 1 selected from, for example, dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), and diethyl carbonate (DEC).

The solvent may contain, for example, a lactone, a cyclic ether, a chain ether, a carboxylic acid ester, or the like. The lactone may be, for example, gamma-butyrolactone (GBL), delta-valerolactone (DVL), or the like. The cyclic ether may be, for example, Tetrahydrofuran (THF), 1, 3-Dioxolane (DOL), 1, 4-Dioxane (DX), or the like. The chain ether may be 1, 2-Dimethoxyethane (DME) or the like. The carboxylic acid ester may be, for example, Methyl Formate (MF), Methyl Acetate (MA), Methyl Propionate (MP), or the like.

The electrolyte may further contain various additives in addition to the solvent and the supporting salt. The concentration of the additive may be, for example, above 0.005 ml/L and below 0.5 ml/L. Examples of the additives include gas generating agents (so-called "overcharge additives"), sei (solid electrolyte interface) film forming agents, and flame retardants.

The gas generating agent may be, for example, Cyclohexylbenzene (CHB), Biphenyl (BP), or the like. The SEI film-forming agent may be, for example, Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), LiB (C)₂O₄)₂、LiBF₂(C₂O₄)、LiPF₂(C₂O₄)₂、LiPO₂F₂Propane Sultone (PS), Ethylene Sulfite (ES), and the like. The flame retardant may be, for example, phosphazeneAnd the like. The electrolyte may contain 1 additive alone. The electrolyte may contain 2 or more additives.