JP2018174064A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which enables the reduction in heat generation at the time of nail pricking and the reduction in heat generation in the state of being overcharged.SOLUTION: A nonaqueous electrolyte secondary battery comprises at least a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte. The positive electrode 10 includes a positive electrode current collector 11, an intermediate layer 5 and a positive electrode mixture layer 12. The intermediate layer 5 is interposed between the positive electrode current collector 11 and the positive electrode mixture layer 12. The intermediate layer 5 includes a first layer 1 and a second layer 2. The first layer 1 is disposed on a surface of the positive electrode current collector 11. The second layer 2 is interposed between the first layer 1 and the positive electrode mixture layer 12. The first layer 1 and the second layer 2 each have a thickness of 0.5 μm or larger. The first layer 1 includes an electrically insulative filler of 87 mass% or more and less than 100 mass%, a first conductive filler as its the balance, and a binder. The second layer 2 includes polyamic acid of 60 mass% or more and less than 100 mass%, and as its balance a second conductive filler.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a non-aqueous electrolyte secondary battery.

  JP-A-2006-072221 (Patent Document 1) discloses a non-aqueous electrolyte secondary battery (hereinafter referred to as “battery”) in which an intermediate layer is disposed between a positive electrode current collector and a positive electrode mixture layer. A).

JP 2006-072221 A

  In an abnormal mode such as nail penetration or overcharge, it is required to suppress battery heat generation. “Nailing” refers to an abnormal mode in which a conductive foreign object having a sharp tip penetrates the battery. In nail penetration, the positive electrode and the negative electrode are short-circuited through the conductive foreign matter. As a result, Joule heat is generated and the battery generates heat. Furthermore, the positive electrode mixture layer may be peeled off from the positive electrode current collector due to an impact when the conductive foreign material penetrates the positive electrode, and the positive electrode current collector may be exposed. When the exposed positive electrode current collector and the negative electrode are short-circuited, a large current flows and the amount of heat generation increases.

  On the other hand, “overcharge” indicates an abnormal mode in which the battery is charged beyond the full charge capacity of the battery. It is considered that the heat generation in overcharging is caused by the phase transition (structural change) of the positive electrode active material, the decomposition reaction of the positive electrode active material, and the like.

  In Patent Document 1, an intermediate layer is disposed between the positive electrode current collector and the positive electrode mixture layer. The intermediate layer is said to contain particles having high thermal conductivity, high hardness, and high resistivity. At the time of nail penetration, the intermediate layer releases Joule heat due to a short circuit and further suppresses exposure of the positive electrode current collector. Therefore, the intermediate layer is expected to suppress heat generation during nail penetration. However, it is considered that there is room for improvement in consideration of heat generation during overcharging, which is an abnormal mode that does not involve a short circuit.

  An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery in which heat generation during nail penetration is suppressed and heat generation during overcharge can be suppressed.

  Hereinafter, the technical configuration and effects of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The scope of the claims should not be limited by the correctness of the action mechanism.

  The nonaqueous electrolyte secondary battery includes at least a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The positive electrode includes a positive electrode current collector, an intermediate layer, and a positive electrode mixture layer. The intermediate layer is interposed between the positive electrode current collector and the positive electrode mixture layer. The intermediate layer includes a first layer and a second layer. The first layer is disposed on the surface of the positive electrode current collector. The second layer is interposed between the first layer and the positive electrode mixture layer. Each of the first layer and the second layer has a thickness of 0.5 μm or more. The first layer includes 87% by mass or more and less than 100% by mass of an electrically insulating filler, and the remaining first conductive filler and binder. A 2nd layer contains 60 mass% or more and less than 100 mass% polyamic acid, and the 2nd electroconductive filler of the remainder.

  The intermediate layer of the present disclosure is expected to exhibit a heat generation suppressing effect against both nail penetration and overcharge. The intermediate layer includes a first layer and a second layer. The main component of the first layer is an electrically insulating filler. By disposing the first layer on the surface of the positive electrode current collector, exposure of the positive electrode current collector can be suppressed during nail penetration. That is, a short circuit between the positive electrode current collector and the negative electrode can be suppressed.

  In the first layer, it is considered that the gaps between the electrically insulating fillers are not completely filled and holes are formed. The main component of the second layer is polyamic acid. Polyamic acid is a precursor of polyimide. The polyamic acid is first melted by the Joule heat at the time of nail penetration. The melt of polyamic acid is thought to fill the vacancies in the first layer. When the ambient temperature further increases, a dehydration cyclization reaction (imidization reaction) proceeds in the polyamic acid molecule. Thereby, it is thought that polyamic acid becomes a polyimide.

  Polyimide is excellent in heat resistance and electrical insulation. Polyimide has a low thermal conductivity. Therefore, when the polyamic acid becomes polyimide, the periphery of the short-circuited portion can be electrically and thermally insulated. Thereby, it is considered that expansion of the short-circuit area is suppressed and heat generation is suppressed.

  Polyamic acids can also respond to heat generation during overcharging. That is, it is considered that the polyamic acid melt fills the pores of the first layer and becomes polyimide even during overcharge. As a result, the positive electrode current collector and the positive electrode mixture layer can be electrically and thermally insulated. As a result, the progress of the charging reaction of the positive electrode active material and the heating of the positive electrode active material can be suppressed, and the phase transition and decomposition reaction of the positive electrode active material can be suppressed. That is, heat generation during overcharging can be suppressed.

FIG. 1 is a schematic diagram illustrating an example of a configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. FIG. 2 is a conceptual cross-sectional view illustrating a configuration of a positive electrode according to an embodiment of the present disclosure.

  Hereinafter, an embodiment of the present disclosure (hereinafter also referred to as “the present embodiment”) will be described. However, the following description does not limit the scope of the claims. For example, in this specification, a lithium ion secondary battery is described as an example of a nonaqueous electrolyte secondary battery. However, as long as the secondary battery includes a nonaqueous electrolyte, the nonaqueous electrolyte secondary battery is a lithium ion secondary battery. Should not be limited to. The nonaqueous electrolyte secondary battery of the present embodiment can be, for example, a sodium ion secondary battery.

<Nonaqueous electrolyte secondary battery>
FIG. 1 is a schematic diagram illustrating an example of a configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. Battery 100 includes a housing 50. The housing 50 is cylindrical. However, the housing of the present embodiment should not be limited to a cylindrical shape. The casing may be, for example, rectangular (flat rectangular parallelepiped). The housing 50 can be made of a metal material such as iron (Fe), stainless steel (SUS), or aluminum (Al) alloy. The housing 50 may be made of, for example, a composite material (for example, an aluminum laminate film) of a metal material and a resin material. The housing 50 may include, for example, a current interrupt mechanism (CID), a liquid injection hole, a gas discharge valve, and the like.

  The housing 50 accommodates the electrode group 40 and a non-aqueous electrolyte (not shown). The electrode group 40 includes a positive electrode 10, a negative electrode 20, and a separator 30. That is, the battery 100 includes at least the positive electrode 10, the negative electrode 20, the separator 30, and the nonaqueous electrolyte. The electrode group 40 is a wound electrode group. That is, the electrode group 40 is configured by stacking the positive electrode 10, the separator 30, the negative electrode 20, and the separator 30 in this order, and further winding them in a spiral shape. The electrode group of this embodiment may be a stacked electrode group. A stacked electrode group can be configured by alternately stacking positive and negative electrodes with a separator interposed therebetween.

《Positive electrode》
The positive electrode 10 is a strip-shaped sheet. FIG. 2 is a conceptual cross-sectional view illustrating a configuration of a positive electrode according to an embodiment of the present disclosure. FIG. 2 conceptually shows a cross section in the thickness direction of the positive electrode 10. The positive electrode 10 includes a positive electrode current collector 11, an intermediate layer 5, and a positive electrode mixture layer 12. In FIG. 2, the intermediate layer 5 and the positive electrode mixture layer 12 are disposed only on one side (one side) of the positive electrode current collector 11. You may arrange | position on (front and back both surfaces).

  The positive electrode current collector 11 may be, for example, an Al foil. The positive electrode current collector 11 may have a thickness of 10 to 30 μm, for example. The positive electrode mixture layer 12 may include, for example, 80 to 98% by mass of a positive electrode active material, 1 to 15% by mass of a conductive filler, and the remaining binder. The positive electrode mixture layer 12 may have a thickness of 10 to 200 μm, for example.

The positive electrode active material should not be particularly limited. The positive electrode active material is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.82 Co _0.15 Al _0.03 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ or the like. May be. One type of positive electrode active material may be used alone, or two or more types of positive electrode active materials may be used in combination. The positive electrode active material may have an average particle diameter of 1 to 30 μm, for example. The average particle size in this specification indicates a particle size of 50% cumulative from the fine particle side in the volume-based particle size distribution measured by the laser diffraction scattering method.

  The conductive filler should not be particularly limited. The conductive filler may be, for example, acetylene black (AB), thermal black, furnace black, vapor grown carbon fiber (VGCF), graphite, or the like. One type of conductive filler may be used alone, or two or more types of conductive fillers may be used in combination. The binder should not be particularly limited. The binder may be, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), or the like. One kind of binder may be used alone, or two or more kinds of binders may be used in combination.

《Middle layer》
The intermediate layer 5 is interposed between the positive electrode current collector 11 and the positive electrode mixture layer 12. The intermediate layer 5 includes a first layer 1 and a second layer 2. The first layer 1 is disposed on the surface of the positive electrode current collector 11. The second layer 2 is interposed between the first layer 1 and the positive electrode mixture layer 12. The first layer 1 and the second layer 2 each have a thickness of 0.5 μm or more. The thicknesses of the first layer 1 and the second layer 2 can be measured in a microscopic image of a cross section in the thickness direction of the intermediate layer 5. The microscope may be an optical microscope or an electron microscope. The thickness is measured at at least three locations in the microscope image. An arithmetic average of at least three places is adopted as a measurement result.

  Since the first layer 1 and the second layer 2 each have a thickness of 0.5 μm or more, heat generation can be suppressed both during nail penetration and overcharge. The thicker the first layer 1 and the second layer 2 are expected to increase the heat generation suppressing effect. However, if the first layer 1 and the second layer 2 are excessively thick, the DC resistance may increase. The first layer 1 and the second layer 2 may each have a thickness of, for example, 1 μm or more, or may have a thickness of 1.5 μm or more. Each of the first layer 1 and the second layer 2 may have a thickness of 2.2 μm or less, for example, or may have a thickness of 2 μm or less.

  For example, the first layer 1 and the second layer 2 may have a total thickness of 1 μm or more, a total thickness of 1.5 μm or more, or a total of 2 μm or more. It may have a thickness. The first layer 1 and the second layer 2 may have a total thickness of 3 μm or less, a thickness of 2.5 μm or less, or a thickness of 2.0 μm or less, for example. You may have.

(First layer)
The first layer 1 suppresses the short circuit between the positive electrode current collector 11 and the negative electrode 20 by suppressing the exposure of the positive electrode current collector 11 during nail penetration. The first layer 1 includes an electric insulating filler of 87% by mass or more and less than 100% by mass, and the remaining first conductive filler and binder. When the constituent ratio of the electrically insulating filler is 87% by mass or more and less than 100% by mass, heat generation can be suppressed both during nail penetration and overcharge. It is expected that the higher the composition ratio of the electrically insulating filler, the greater the effect of suppressing heat generation during nail penetration. However, when the constituent ratio of the electrically insulating filler is excessively high, the direct current resistance may increase. The constituent ratio of the electrically insulating filler may be, for example, 93.5% by mass or more. The constituent ratio of the electrically insulating filler may be, for example, 98% by mass or less, or 97% by mass or less.

The electrically insulating filler should not be particularly limited. The electrically insulating filler may be at least one of alumina (α-Al ₂ O ₃ ) and boehmite (AlOOH), for example. The shape of the electrically insulating filler should not be particularly limited. The electrically insulating filler can be, for example, spherical, lump, plate, needle or the like. The electrically insulating filler may have an average particle diameter of 0.1 to 5 μm, for example.

  The first layer 1 needs to have conductivity in normal times other than the abnormal mode. Therefore, the first layer 1 also includes the first conductive filler as the remainder of the electrically insulating filler. The composition ratio of the first conductive filler may be, for example, 1.5% by mass or more, or 2.5% by mass or more. The composition ratio of the first conductive filler may be, for example, 10% by mass or less, or 5% by mass or less. The first conductive filler should not be particularly limited. As the first conductive filler, for example, a material exemplified as the conductive filler of the positive electrode mixture layer 12 may be used. One type of conductive filler may be used alone, or two or more types of conductive fillers may be used in combination.

  The first layer 1 also includes a binder as the remainder of the electrically insulating filler. The binder should not be particularly limited. As the binder, for example, the materials exemplified as the binder of the positive electrode mixture layer 12 can be used. One kind of binder may be used alone, or two or more kinds of binders may be used in combination.

(Second layer)
The intermediate layer 5 includes the second layer 2 in addition to the first layer 1. Thereby, at the time of overcharge, the positive electrode mixture layer 12 and the positive electrode current collector 11 are electrically and thermally insulated, and heat generation can be suppressed. The second layer 2 includes 60% by mass or more and less than 100% by mass of polyamic acid and the remaining second conductive filler. The polyamic acid can be synthesized, for example, by polycondensation of an aromatic tetracarboxylic dianhydride and an aromatic diamine. It is considered that polyamic acid becomes a melt when heated, and when further heated, a dehydration ring-closing reaction occurs in the molecule to become polyimide.

  The aromatic tetracarboxylic dianhydride can be, for example, biphenyltetracarboxylic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and the like. The aromatic diamine can be, for example, metaphenylenediamine (MPD), 4,4'-methylenedianiline (MDA), and the like. The temperature at which the polyamic acid becomes a melt and the temperature at which the imidization reaction starts can be adjusted by, for example, the copolymer composition. For example, the polyamic acid can form a melt at about 90 to 120 ° C. For example, the polyamic acid can undergo an imidization reaction at about 120 to 300 ° C.

  When the composition ratio of the polyamic acid is 60% by mass or more and less than 100% by mass, heat generation can be suppressed both during nail penetration and overcharge. It is expected that the higher the composition ratio of the polyamic acid, the greater the effect of suppressing heat generation during nail penetration and overcharge. However, if the composition ratio of the polyamic acid becomes excessively high, the direct current resistance may increase. The composition ratio of the polyamic acid may be, for example, 80% by mass or more. The composition ratio of the polyamic acid may be 90% by mass or less, or 80% by mass or less.

  The second layer 2 also needs to have conductivity during normal times other than the abnormal mode. Therefore, the second layer 2 contains a second conductive filler as the remainder of the polyamic acid. As the second conductive filler, for example, a material exemplified as the conductive filler of the positive electrode mixture layer 12 may be used. The second conductive filler may be the same material as the first conductive filler, or may be a different material.

<Negative electrode>
The negative electrode 20 is a strip-shaped sheet. The negative electrode 20 includes a negative electrode current collector and a negative electrode mixture layer. The negative electrode current collector may be, for example, a copper (Cu) foil. The negative electrode current collector may have a thickness of 5 to 30 μm, for example. The negative electrode mixture layer is disposed on the surface of the negative electrode current collector. The negative electrode mixture layer may be disposed on both the front and back surfaces of the negative electrode current collector. The negative electrode mixture layer may have a thickness of 10 to 200 μm, for example.

  The negative electrode mixture layer may include, for example, 95 to 99.5% by mass of the negative electrode active material and the remaining binder. The negative electrode active material should not be particularly limited. The negative electrode active material may be graphite, graphitizable carbon, non-graphitizable carbon, silicon, silicon oxide, tin, tin oxide, or the like. One type of negative electrode active material may be used alone, or two or more types of negative electrode active materials may be used in combination. The negative electrode active material may have an average particle diameter of 1 to 30 μm, for example.

  The binder should not be particularly limited. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like. One kind of binder may be used alone, or two or more kinds of binders may be used in combination.

<< Separator >>
The separator 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator 30 is a strip-shaped sheet. For example, the separator 30 may have a thickness of 10 to 30 μm. The separator 30 is an electrically insulating porous film. The separator 30 can be made of, for example, polyethylene (PE), polypropylene (PP), or the like. Separator 30 may have a multilayer structure, for example. The separator 30 may be configured, for example, by stacking a PP porous film, a PE porous film, and a PP porous film in this order.

《Nonaqueous electrolyte》
The nonaqueous electrolyte of this embodiment is a liquid electrolyte, that is, an electrolytic solution. The electrolyte group is impregnated in the electrode group 40. However, the non-aqueous electrolyte of this embodiment may be a gel electrolyte or a solid electrolyte.

  The electrolytic solution includes a solvent and a supporting electrolyte. The solvent is aprotic. The solvent may be, for example, a mixed solvent of a cyclic carbonate and a chain carbonate. The mixing ratio may be, for example, about “cyclic carbonate: chain carbonate = 1: 9 to 5: 5” in volume ratio. The cyclic carbonate may be, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. The chain carbonate may be, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) or the like. The cyclic carbonate and the chain carbonate may be used alone or in combination of two or more.

The electrolytic solution can include, for example, a supporting electrolyte of 0.5 to 2 mol / l. The supporting electrolyte may be, for example, LiPF ₆ , LiBF ₄ , Li [N (FSO ₂ ) ₂ ] or the like. One type of supporting electrolyte may be used alone, or two or more types of supporting electrolytes may be used in combination. The electrolytic solution may contain various functional additives in addition to the solvent and the supporting electrolyte. Examples of the functional additive include vinylene carbonate (VC), Li [B (C ₂ O ₄ ) ₂ ] (LiBOB), cyclohexylbenzene (CHB), and the like.

  Examples will be described below. However, the following examples do not limit the scope of the claims.

<Manufacture of non-aqueous electrolyte secondary batteries>
Sample No. shown in Table 1 below. 1-22 were produced. In Table 1 below, for example, a sample with “*” such as “Sample No. 4 *” is a comparative example. The other samples are examples.

<< Sample No. 1 >>
1. 1. Production of positive electrode 1-1. Formation of first layer The following materials were prepared.
Electrical insulating filler: Alumina (Sumitomo Chemical Co., Ltd., product name “AKP3000”)
First conductive filler: AB (manufactured by DENKA, product name “DENKA BLACK”)
Binder: PVdF (manufactured by Kureha, grade “# 7200”)
Solvent: N-methyl-2-pyrrolidone (NMP)
Positive electrode current collector: strip-shaped Al foil

  The electrically insulating filler, the first conductive filler, the binder, and the solvent were mixed by a stirrer “CLEAMIX” manufactured by M Technique. Thereby, a slurry for the first layer was prepared. The solid content composition of the slurry for the first layer was “electric insulating filler: first conductive filler: binder = 87: 10: 3” by mass ratio. The slurry for the first layer was applied to the surface of the positive electrode current collector by a gravure coater and dried. Thereby, the first layer was formed. The first layer was formed to have a thickness of 1 μm.

1-2. Formation of second layer The following materials were prepared.
Polyamic acid: Ube Industries, product name "UPIA-AT"
Second conductive filler: AB (manufactured by Denka, product name “Denka Black”)
Solvent: NMP

  The polyamic acid, the second conductive filler, and the solvent were mixed by a stirrer “CLEAMIX” manufactured by M Technique. As a result, a slurry for the second layer was prepared. The solid content composition of the slurry for the second layer was “polyamic acid: second conductive filler = 70: 30” by mass ratio. The slurry for the second layer was applied to the surface of the first layer by a gravure coater and dried. Thereby, the second layer was formed. The second layer was formed to have a thickness of 1 μm. From the above, an intermediate layer was formed. The intermediate layer includes a first layer and a second layer.

1-3. Formation of Positive Electrode Mixture Layer The following materials were prepared.
Cathode active material: LiNi _0.82 Co _0.15 Al _0.03 O ₂
Conductive filler: AB (manufactured by DENKA, product name “DENKA BLACK”)
Binder: PVdF

The positive electrode active material, the conductive filler, and the binder were mixed by the planetary mixer. Thus, a slurry for the positive electrode mixture layer was prepared. The solid content composition of the slurry for the positive electrode mixture layer was “positive electrode active material: conductive filler: binder = 88: 10: 2” by mass ratio. The slurry for the positive electrode mixture layer was applied to the surface of the intermediate layer by a comma coater (registered trademark) and dried. As a result, a positive electrode mixture layer was formed. The positive electrode mixture layer was rolled so as to have a density of 3.0 g / cm ³ . The positive electrode was manufactured from the above.

2. Production of negative electrode The following materials were prepared.
Negative electrode active material: Graphite Binder: SBR and CMC
Solvent: Water Negative electrode current collector: Banded Cu foil

  The negative electrode active material, the binder, and the solvent were mixed by a planetary mixer. As a result, a slurry for the negative electrode mixture layer was prepared. The solid content composition of the slurry for the negative electrode mixture layer was “negative electrode active material: SBR: CMC = 98: 1: 1” by mass ratio. The slurry for the negative electrode mixture layer was applied to the surface of the negative electrode current collector by a comma coater (registered trademark) and dried. As a result, a negative electrode mixture layer was formed. The negative electrode mixture layer was rolled so as to have a predetermined density. From the above, a negative electrode was produced.

3. Assembly A strip-shaped separator was prepared. The separator had a thickness of 25 μm. The separator was assumed to have a three-layer structure. That is, the separator is formed by laminating a porous film made of PP, a porous film made of PE, and a porous film made of PP in this order.

  The positive electrode, the separator, the negative electrode, and the separator were laminated in this order, and these were wound in a spiral shape to produce an electrode group. A cylindrical housing was prepared. The housing has a size of 18650 (diameter = 18 mm, height = 65 mm). The electrode group was stored in the housing.

An electrolytic solution having the following composition was prepared.
Solvent: [EC: DMC: EMC = 3: 4: 3 (volume ratio)]
Supporting electrolyte: LiPF ₆ (1 mol / l)

  The electrolyte was injected into the housing. The case was sealed. From the above, a nonaqueous electrolyte secondary battery (lithium ion secondary battery) was manufactured. This non-aqueous electrolyte secondary battery has a rated capacity of 1 Ah.

<< Sample No. 2-5 >>
As shown in Table 1 below, sample no. As in 1, a battery was manufactured.

<< Sample No. 6-9 >>
As shown in Table 1 below, sample No. 4 was changed except that the composition ratio of each component of the second layer was changed. As in 1, a battery was manufactured.

<< Sample No. 10-14 >>
As shown in Table 1 below, the sample No. is changed except that the thickness of the first layer is changed. As in 1, a battery was manufactured.

<< Sample No. 15-19 "
As shown in Table 1 below, the sample No. is changed except that the thickness of the second layer is changed. As in 1, a battery was manufactured.

<< Sample No. 20 >>
Except that boehmite is used as an electrically insulating filler instead of alumina, sample No. As in 1, a battery was manufactured.

<< Sample No. 21 >>
Sample No. 4 was used except that PVdF was used instead of polyamic acid. A battery was produced as in 1.

<< Sample No. 22
Except that the second layer is not formed (the intermediate layer does not include the second layer), the sample No. As in 1, a battery was manufactured.

<Evaluation>
1. Nail penetration test The battery was fully charged by constant current-constant voltage charging (current at constant current charging = 1 A, voltage at constant voltage charging = 4.2 V, end current = 50 mA). A thermocouple was attached to the battery. A nail having a body diameter of 3 mm was prepared. In a 25 ° C. environment, a nail was pierced on the side of the battery at a speed of 120 mm / second. The maximum temperature reached after the nail was pierced was measured. The results are shown in Table 1 below. It shows that the lower the maximum temperature reached, the less heat generated during nail penetration.

2. Overcharge test A thermocouple was attached to the battery. In a 25 ° C. environment, the battery was charged to 4.5 V with a constant current of 1C. The maximum temperature reached of the battery was measured. The results are shown in Table 1 below. It shows that heat generation during overcharge is suppressed as the maximum temperature reached is lower.

3. Input characteristics The SOC (State Of Charge) of the battery was adjusted to 50%. The battery was charged for 10 seconds with a constant current of 10 A in a 25 ° C. environment. The amount of voltage increase 10 seconds after the start of charging was measured. The DC resistance was calculated by dividing the voltage increase by the current. The results are shown in Table 1 below.

<Result>
1. Sample No. 1-5
In the sample in which the constituent ratio of the electrically insulating filler of the first layer was 87% by mass or more, heat generation was suppressed during both nail penetration and overcharge. However, an increase in DC resistance is observed in a sample in which the composition ratio of the first layer of the electrically insulating filler exceeds 97% by mass. Taking DC resistance into consideration, the constituent ratio of the electrically insulating filler of the first layer may be 87 mass% or more and 97 mass% or less.

2. Sample No. 6-9
In the sample in which the composition ratio of the polyamic acid in the second layer was 60% by mass or more, heat generation was suppressed both during nail penetration and overcharge. However, an increase in DC resistance is observed in the sample in which the composition ratio of the polyamic acid in the second layer exceeds 80% by mass. In consideration of direct current resistance, the composition ratio of the polyamic acid of the second layer may be 60% by mass or more and 80% by mass or less.

3. Sample No. 10-14
In the sample having a thickness of the first layer of 0.5 μm or more, heat generation was suppressed both during nail penetration and overcharge. However, in the sample in which the thickness of the first layer exceeds 2 μm (sample in which the total thickness of the first layer and the second layer exceeds 3 μm), an increase in DC resistance is observed. Taking DC resistance into consideration, the thickness of the first layer may be not less than 0.5 μm and not more than 2 μm. The total thickness of the first layer and the second layer may be 3 μm or less.

4). Sample No. 15-19
In the sample in which the thickness of the second layer was 0.5 μm or more, heat generation was suppressed both during nail penetration and overcharge. However, in the sample in which the thickness of the second layer exceeds 2 μm (sample in which the total thickness of the first layer and the second layer exceeds 3 μm), an increase in DC resistance is observed. In consideration of direct current resistance, the thickness of the second layer may be not less than 0.5 μm and not more than 2 μm. The total thickness of the first layer and the second layer may be 3 μm or less.

5. Sample No. 20
Even when the electrically insulating filler of the first layer was changed from alumina to boehmite, heat generation was suppressed both during nail penetration and overcharge. Therefore, the electrically insulating filler may be at least one of alumina and boehmite.

6). Sample No. 21, 22
In the absence of the second layer, heat generation during overcharging was not suppressed. Also, when polyamic acid was replaced with PVdF, heat generation during overcharging was not suppressed.

  The above embodiments and examples are illustrative in all respects and not restrictive. The technical scope defined by the description of the claims includes all modifications within the meaning and scope equivalent to the description of the claims.

  DESCRIPTION OF SYMBOLS 1 1st layer, 2nd layer, 5 intermediate layer, 10 positive electrode, 11 positive electrode current collector, 12 positive electrode compound material layer, 20 negative electrode, 30 separator, 40 electrode group, 50 housing, 100 battery (non-aqueous electrolyte 2 Next battery).

Claims (1)

Including at least a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
The positive electrode includes a positive electrode current collector, an intermediate layer and a positive electrode mixture layer,
The intermediate layer is interposed between the positive electrode current collector and the positive electrode mixture layer,
The intermediate layer includes a first layer and a second layer,
The first layer is disposed on a surface of the positive electrode current collector;
The second layer is interposed between the first layer and the positive electrode mixture layer,
Each of the first layer and the second layer has a thickness of 0.5 μm or more,
The first layer includes 87% by mass or more and less than 100% by mass of an electrically insulating filler, and the remaining first conductive filler and binder,
The second layer includes 60% by mass or more and less than 100% by mass of polyamic acid, and the remaining second conductive filler.
Non-aqueous electrolyte secondary battery.

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