JP2019169349A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which both suppression of heat generation and suppression of reduction in battery capacity when a short circuit occurs due to an impact from the outside of the battery are achieved. A positive electrode, a negative electrode, and an intermediate layer disposed between the positive electrode and the negative electrode, the intermediate layer including a skeleton and a ceramic filler. The skeleton has a porous three-dimensional network structure formed of a porous polyimide resin, and is filled with a ceramic filler. The polyimide resin has a porosity of 60% or more and 80% or less when the ceramic filler is not filled, and has a porosity of 40% or more and 52% or less when the ceramic filler is filled. The ceramic filler is either titanium oxide or alumina, and has an average particle size of 0.3 μm or more and 0.5 μm or less. The intermediate layer contains 5% by mass or more and 40% by mass or less of the ceramic filler. The thickness of the intermediate layer is from 12 μm to 25 μm. [Selection diagram] Fig. 1

Description

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

  Japanese Patent Application Laid-Open No. 2008-123988 (Patent Document 1) discloses a separator layer (I) composed of a microporous film mainly composed of a resin (A) having a melting point of 80 to 130 ° C., and a heat resistant temperature of 150 ° C. or higher. Disclosed is a separator having a porous separator layer (II) mainly containing a filler and containing plate-like particles in at least one of the separator layer (I) and the separator layer (II).

JP 2008-123988 A

  Conventionally, a separator made of a polyolefin resin in which a heat-resistant layer (HRL) is disposed has been used for a non-aqueous electrolyte secondary battery. However, the HRL is likely to be peeled off, dropped off, cracked, etc. due to, for example, an impact from the outside of the battery (hereinafter also referred to as “external input”). Since HRL is generally a ceramic-based layer, it is considered that one of the causes is brittleness. The external input can be simulated by, for example, a nail penetration test.

  When nail penetration occurs as an example of the external input, the positive electrode and the negative electrode are short-circuited with low resistance through the nail which is a low resistance body, and large Joule heat is generated. Due to the Joule heat, the separator around the nail melts, the positive electrode mixture layer and the negative electrode mixture layer come into contact with each other, and a larger short-circuit current continuously flows and generates heat, leading to thermal runaway. Moreover, when the positive electrode (negative electrode) current collector is in direct contact with the negative electrode (positive electrode) composite material layer as well as the short circuit via the nail, a short circuit occurs, resulting in further thermal runaway.

  In the non-aqueous electrolyte secondary battery including the separator disclosed in Patent Document 1, the porous separator layer (II) may be peeled off or dropped off due to external input. For example, when the porous separator layer (II) is peeled off by external input, it is considered that a low-resistance short circuit occurs, leading to thermal runaway, and the temperature of the nonaqueous electrolyte secondary battery increases. That is, the nonaqueous electrolyte secondary battery including the separator disclosed in Patent Document 1 has room for improvement in suppressing heat generation during a short circuit due to external input. Hereinafter, “when short-circuited by an external input” may be abbreviated as “when short-circuited”.

  In addition, as a characteristic generally required for a nonaqueous electrolyte secondary battery, a large battery capacity can be mentioned. However, if an attempt is made to suppress heat generation during a short circuit, the battery resistance may increase and the battery capacity may decrease.

  An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery in which suppression of heat generation when a short circuit occurs due to an impact from the outside of the battery or the like and suppression of reduction in battery capacity are compatible.

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. Hereinafter, the nonaqueous electrolyte secondary battery is also simply referred to as “battery”.
[1] The nonaqueous electrolyte secondary battery includes at least a positive electrode, a negative electrode, and an intermediate layer. The intermediate layer is disposed between the positive electrode and the negative electrode. The intermediate layer includes a skeleton and a ceramic filler. The skeleton is a porous three-dimensional network structure formed of a porous polyimide resin. The polyimide resin has voids, and the voids are filled with a ceramic filler. The polyimide resin has a porosity of 60% or more and 80% or less when not filled with a ceramic filler, and has a porosity of 40% or more and 52% or less when filled with a ceramic filler. The ceramic filler is either titanium oxide or alumina. The ceramic filler has an average particle size of 0.3 μm or more and 0.5 μm or less. An intermediate | middle layer contains 5 to 40 mass% of ceramic fillers. The thickness of the intermediate layer is 12 μm or more and 25 μm or less.

  FIG. 1 is a first cross-sectional conceptual diagram for explaining an operation mechanism of the present disclosure, and FIG. 2 is a second cross-sectional conceptual diagram for explaining an operation mechanism of the present disclosure. In FIG. 1, an electrode group 40 including a positive electrode 10, a negative electrode 20, and the intermediate layer 1 is shown. The nonaqueous electrolyte secondary battery includes at least a positive electrode, a negative electrode, and an intermediate layer. The intermediate layer 1 includes a skeleton that is a porous three-dimensional network structure formed of a polyimide resin. FIG. 2 shows a part of the battery when nail penetration occurs as an external input.

Since the skeleton contained in the intermediate layer 1 is a porous three-dimensional network structure formed of a polyimide resin, it is considered to have high flexibility. The polyimide resin has a void, and the void is filled with a ceramic filler having high heat resistance. Therefore, even if nail penetration occurs as an example of external input as shown in FIG. 2, the intermediate layer 1 is prevented from peeling off or cracking in the intermediate layer 1, and a low-resistance short circuit occurs. Is considered to be suppressed. In addition, the intermediate layer 1 is considered to have a larger porosity than a generally used microporous membrane separator. For this reason, it is considered that a reduction in battery capacity is suppressed. That is, it is expected that suppression of heat generation in the case where a short circuit occurs due to impact or the like from the outside of the battery and suppression of reduction in battery capacity are compatible.
[2] The intermediate layer may be disposed so as to be in direct contact with the positive electrode and the negative electrode. That is, the nonaqueous electrolyte secondary battery according to the present disclosure may be configured not to include a separator.

  The intermediate layer 1 has flexibility derived from a polyimide resin and a porous three-dimensional network structure. Therefore, even if the intermediate layer is thicker than 5 μm, for example, the insulation is maintained, and it is considered that the intermediate layer 1 can electrically isolate the positive electrode 10 and the negative electrode 20 independently. Since the nonaqueous electrolyte secondary battery does not include a separator, when a short circuit occurs due to an external input, it is possible to prevent the short circuit from expanding due to the contraction of the separator.

FIG. 1 is a first cross-sectional conceptual diagram for describing an operation mechanism of the present disclosure. FIG. 2 is a second cross-sectional conceptual diagram for describing an operation mechanism of the present disclosure. FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the intermediate layer. FIG. 4 is a conceptual cross-sectional view showing a configuration at the time of nail penetration in the reference embodiment. FIG. 5 is a schematic diagram showing an example of the configuration of the nonaqueous electrolyte secondary battery of the present embodiment.

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

Hereinafter, a lithium ion secondary battery will be described as an example. However, the nonaqueous electrolyte secondary battery of this embodiment should not be limited to a lithium ion secondary battery. The nonaqueous electrolyte secondary battery of the present embodiment may be, for example, a sodium ion secondary battery.
<Nonaqueous electrolyte secondary battery>
FIG. 5 is a schematic diagram showing an example of the configuration of the nonaqueous electrolyte secondary battery of the present embodiment.

The battery 100 includes an exterior material 50. The exterior material 50 is made of, for example, an aluminum laminate film. That is, the battery 100 is a laminate type battery. However, in the present embodiment, the type and form of the battery 100 should not be particularly limited. Battery 100 may be, for example, a rectangular battery or a cylindrical battery. The positive electrode tab 51 and the negative electrode tab 52 communicate with the inside and outside of the exterior material 50, respectively. The positive electrode tab 51 is, for example, an aluminum (Al) thin plate. The negative electrode tab 52 is, for example, a copper (Cu) thin plate. The exterior material 50 may include a CID, a gas discharge valve, a liquid injection hole, and the like (all not shown).
<Positive electrode>
The positive electrode 10 can be a strip-shaped sheet. The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode mixture layer 12. The positive electrode mixture layer 12 is formed on the surface of the positive electrode current collector 11. The positive electrode mixture layer 12 may be formed on both the front and back surfaces of the positive electrode current collector 11. The positive electrode current collector 11 may be, for example, an aluminum (Al) foil. The positive electrode current collector 11 may have a thickness of 10 to 30 μm, for example.
<< Positive electrode mixture layer >>
The positive electrode mixture layer 12 includes a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer 12 may include, for example, 80 to 98% by weight of a positive electrode active material, 1 to 15% by weight or less of a conductive material, and 1 to 5% by weight or less of a binder. The positive electrode mixture layer 12 may have a thickness of 100 to 200 μm, for example.
(Positive electrode active material, conductive material and binder)
The positive electrode active material, the conductive material, and the binder should not be particularly limited. Examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM), LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA), LiMnO _2. LiMn ₂ O ₄ , LiFePO ₄ or the like may be used. The conductive material may be, for example, acetylene black (AB), furnace black, vapor grown carbon fiber (VGCF), graphite or the like. The binder may be, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), or the like.
<Negative electrode>
The negative electrode 20 can be a strip-shaped sheet. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode mixture layer 22. The negative electrode mixture layer 22 is formed on the surface of the negative electrode current collector 21. The negative electrode mixture layer 22 may be formed on both the front and back surfaces of the negative electrode current collector 21. The negative electrode current collector 21 may be, for example, a copper (Cu) foil. The negative electrode current collector 21 may have a thickness of 5 to 30 μm, for example.
<Negative electrode mixture layer>
The negative electrode mixture layer 22 includes a negative electrode active material, a conductive material, and a binder. The negative electrode mixture layer 22 may include, for example, 95 to 99% by mass of a negative electrode active material and 1 to 5% by mass of a binder. The negative electrode mixture layer 22 may further contain a conductive additive.
(Negative electrode active material and binder)
The negative electrode active material should not be particularly limited. The negative electrode active material may be, for example, graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, or the like. One kind of negative electrode active material may be used alone. Two or more negative electrode active materials may be used in combination. The binder should not be particularly limited. The binder may be, for example, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).
<Intermediate layer>
As shown in FIG. 1, the intermediate layer 1 is disposed between the positive electrode 10 and the negative electrode 20. As shown in FIG. 3, the intermediate layer 1 includes a skeleton composed of a porous polyimide resin 61 and a ceramic filler 60.

  The mid layer 1 includes 5% by mass or more and 40% by mass or less of the ceramic filler 60. When the content of the ceramic filler 60 in the intermediate layer 1 is less than 5% by mass, the amount of the ceramic filler 60 filled in the voids 62 of the polyimide resin 61 may not be sufficient. Therefore, it is considered that the suppression of heat generation at the time of short circuit becomes insufficient. When the content of the ceramic filler 60 in the intermediate layer 1 exceeds 40% by mass, the porosity of the polyimide resin 61 in a state where the ceramic filler 60 is excessively filled in the voids 62 of the polyimide resin 61 and the ceramic filler 60 is filled. Is expected to decrease. Therefore, it is considered that the battery resistance increases and the battery capacity decreases.

The thickness of the intermediate layer 1 is 12 μm or more and 25 μm or less. When the thickness of the intermediate layer 1 is less than 12 μm, the suppression of heat generation may be insufficient during a short circuit. When the thickness of the interlayer 1 is larger than 25 μm, the battery resistance may increase and the battery capacity may decrease.
《Skeleton》
The skeleton is a porous three-dimensional network structure formed by a porous polyimide resin 61. As a method for forming the skeleton, for example, a polyamic acid is applied to the surface of the positive electrode 10 or the negative electrode 20 and heat-treated. As an example of the skeleton formation method, as shown in the following reaction formula, a polyamic acid obtained by polymerizing pyrometic acid dihydrate and 4,4′-diaminodiphenyl ether is subjected to heat treatment to be imidized. The method of doing can be mentioned. Thereby, a skeleton made of the polyimide resin 61 can be formed. The intermediate layer 1 can be manufactured by filling the skeleton with the ceramic filler 60.

<Polyimide resin>
The polyimide resin 61 has a gap 62. The void 62 is filled with a ceramic filler 60. The polyimide resin 61 has a porosity of 60% or more and 80% or less in a state where the ceramic filler 60 is not filled, and 40% or more and 52% or less when the void 62 is filled with the ceramic filler 60. Has porosity.

  The polyimide resin 61 having a porosity of 60% or more and 80% or less in the porosity of the polyimide resin 61 in the state where the ceramic filler 60 is not filled (hereinafter also referred to as “original porosity of the skeleton part”) is formed in the void 62. When the ceramic filler 60 is filled, the porosity of the polyimide resin 61 in the state where the ceramic filler 60 is filled (hereinafter also referred to as “the porosity of the skeleton after filling the filler”) is 40% or more and 52% or less. It is thought to become. The porosity can be calculated from the thickness of the intermediate layer 1, the weight of the intermediate layer 1, and the specific gravity of the intermediate layer 1.

When the porosity of the skeleton after filling with the filler is less than 40%, it is considered that the battery resistance increases and the battery capacity decreases. When the porosity of the skeleton after filling the filler is greater than 52%, the adhesion between the skeleton and the ceramic filler 60 may be reduced. Therefore, it is considered that the suppression of heat generation at the time of short circuit becomes insufficient.
《Ceramic filler》
The ceramic filler 60 is either titanium oxide or alumina. Since titanium oxide and alumina have electrical insulation and high heat resistance, it is expected to suppress heat generation during a short circuit. In general, boehmite or aluminum hydroxide containing a hydroxyl group is also used as a flame retardant. However, in order to suppress heat generation at the time of a short circuit by the flame retardant containing these hydroxyl groups, a flame retardant containing a large amount of hydroxyl groups is used. May be necessary.

  The ceramic filler 60 has an average particle size of 0.3 μm or more and 0.5 μm or less. In the present specification, the “average particle size” is a particle size distribution (which may be described as “d50”) at an integrated value of 50% in a volume-based particle size distribution measured by a laser diffraction / scattering method. Show.

When the average particle diameter of the ceramic filler 60 is less than 0.3 μm, the skeleton part porosity after filling the filler may be larger than 52%. In such a case, it is considered that the adhesion between the skeleton and the ceramic filler 60 is not sufficient, and the ceramic filler 60 may be peeled off from the skeleton at the time of a short circuit. Therefore, there is a possibility that suppression of heat generation at the time of a short circuit becomes insufficient. When the average particle diameter of the ceramic filler 60 exceeds 0.5 μm, the skeleton porosity after filling the filler may be less than 40%. In such a case, the battery resistance may increase and the battery capacity may decrease.
<Separator>
The separator is generally used to electrically isolate the positive electrode 10 and the negative electrode 20. In the present disclosure, the intermediate layer 1 alone can electrically isolate the positive electrode 10 and the negative electrode 20. Therefore, a separator is not essential, but may be configured to include a separator in addition to the intermediate layer 1.

  The separator is preferably a microporous film such as polyethylene (PE) or polypropylene (PP). The separator may have a single-layer structure of PE, or may have a three-layer structure in which a PP film, a PE film, and a PP film are stacked in this order. The thickness of the separator may be about 9 to 30 μm, for example. When the separator has the above-described three-layer structure, the thickness of the PE layer may be, for example, about 3 to 10 μm, and the thickness of the PP layer may be, for example, about 3 to 10 μm. The separator may include a heat resistant layer (HRL) on its surface. The HRL includes a heat resistant material. Examples of the heat resistant material include metal oxide particles such as alumina, and a high melting point resin such as polyimide.

Here, the average pore diameter of the separator is considered to be 0.1 μm. Therefore, when it is assumed that the separator is included, it is considered difficult to fill the pores of the separator with the ceramic filler 60 used in the present disclosure. The separator has a porosity of about 60%. For this reason, even if the pores of the separator can be filled, the porosity of the separator after filling the filler may be reduced, and the battery capacity may be reduced.
<Nonaqueous electrolyte>
The battery includes a non-aqueous electrolyte. The nonaqueous electrolyte includes a nonaqueous solvent and a supporting salt. The non-aqueous solvent may be a cyclic or chain carbonate such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). The supporting salt may be a Li salt such as lithium hexafluorophosphate (LiPF6) or lithium tetrafluoroborate (LiBF4). The concentration of the Li salt may be, for example, about 0.5 to 2.0 mol / L. The non-aqueous electrolyte may contain additives such as vinylene carbonate (VC) and cyclohexylbenzene (CHB).
<Method for producing non-aqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery of this embodiment can be manufactured by a manufacturing method including at least the following (1) to (3), for example.

(1) Preparing the positive electrode and the negative electrode.
(2) Forming a skeleton having a porous three-dimensional network structure by applying a polyamide paint (for example, polyamic acid solution) to the surface of either the positive electrode or the negative electrode and drying it.

(3) Filling the voids of the polyamide resin forming the skeleton with a ceramic filler.
FIG. 4 is a conceptual cross-sectional view showing a configuration at the time of nail penetration in the reference embodiment.

  The battery is disposed between the positive electrode 10 including the positive electrode mixture layer 12 and the positive electrode current collector 11, the negative electrode 20 including the negative electrode mixture layer 22 and the negative electrode current collector 21, and the positive electrode 10 and the negative electrode 20. Separator 30 is included. An HRL 31 containing a ceramic filler is disposed on the surface of the separator 30.

  For example, when nail penetration occurs as an external input in such a battery, a part of the negative electrode mixture layer 22 is peeled off (ie, part of the negative electrode 20 is peeled off) due to the nail 70 as shown in FIG. There is a possibility that part of the peeling occurs. HRL31 contains a ceramic filler and is considered to be brittle when nail piercing. Since peeling occurs in part of the negative electrode 20 and part of the HRL 31, it is considered that there is room for improvement in suppressing heat generation during a short circuit.

Examples of the present disclosure are described below. However, the following description does not limit the scope of the claims.
<Example 1>
1. Preparation of negative electrode The following materials were prepared.

Negative electrode active material: Graphite (average particle size: 25 μm)
Binder: SBR and CMC
Solvent: Water Negative electrode current collector: Cu foil A negative electrode active material, a binder, and a 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 “graphite: SBR: CMC = 98: 1: 1” by mass ratio. The slurry was applied to the surface of the negative electrode current collector 21 by an applicator. The negative electrode mixture layer slurry was dried. Thereby, the negative electrode mixture layer 22 was formed. The negative electrode mixture layer 22 was rolled so as to have a predetermined density. Thus, negative electrode 20 was manufactured. The negative electrode 20 was cut into a predetermined size.
2. Formation of intermediate layer (formation of skeleton)
A polyamic acid solution was prepared. A polyamic acid solution was applied to the surface of the negative electrode 20 by a die coater. The applied polyamic acid solution was dried at 140 ° C. for 2 hours. As a result, the solvent was removed, and a porous three-dimensional network structure formed of the polyimide resin 61 was formed on the surface of the negative electrode 20. That is, a skeleton was formed. The porosity of the polyamide resin (that is, the original porosity of the skeleton part) was 80%. The method for measuring the porosity is as described above.
(Ceramic filler filling)
A titanium oxide filler having an average particle size of 0.3 μm was prepared as the ceramic filler 60. The titanium oxide filler was dispersed in a CMC aqueous solution and an acrylic binder to prepare a ceramic filler slurry. The ceramic filler slurry was applied to the skeleton formed of the polyimide resin 61 with a gravure coater. As a result, the void 62 of the polyimide resin 61 was filled with the titanium oxide filler (that is, the ceramic filler 60). Thus, the intermediate layer 1 was formed on the surface of the negative electrode 20. The content of the titanium oxide filler in the intermediate layer 1 is 40% by mass, the porosity of the polyamide resin filled with the titanium oxide filler (that is, the porosity of the skeleton after filling the filler) is 43%, and the intermediate layer 1 The thickness of was set to 15 μm.
3. Preparation of positive electrode The following materials were prepared.

Positive electrode active material: LiNi _0.8 Co _0.15 Mn _0.05 O ₂ (NCA)
Conductive material: AB
Binder: PVdF
Solvent: N-methyl-2-pyrrolidone (NMP)
Positive electrode current collector: Al foil NCA, AB, PVdF, and NMP were mixed by a 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 “NCA: AB: PVdF = 98: 1: 1” in terms of mass ratio. The slurry for the positive electrode mixture layer was applied to the surface of the intermediate layer 1 and the surface of the positive electrode current collector 11 by a comma coater (registered trademark) and dried. As a result, the positive electrode mixture layer 12 was formed on the surface of the intermediate layer 1, and the positive electrode current collector 11 was disposed on the surface of the positive electrode mixture layer 12. The positive electrode mixture layer 12 was rolled so as to have a density of 3.5 / cm ³ . Thus, the positive electrode 10 was manufactured. That is, an electrode group 40 including the positive electrode 10, the negative electrode 20, and the intermediate layer 1 disposed between the positive electrode 10 and the negative electrode 20 was manufactured.
4). Assembly The electrode group 40 was housed in an exterior material 50 made of an aluminum laminate film. An electrolyte solution was injected into the exterior material 50. The electrolytic solution includes the following components. The packaging material 50 was sealed. From the above, the battery 100 according to Example 1 was manufactured. The battery 100 has a rated capacity of 1 Ah.

Li salt: LiPF ₆ (1 mol / l)
Solvent: [EC: DMC: EMC = 3: 4: 3 (volume ratio)]
<Example 2 to Example 12, Comparative Example 1 to Comparative Example 7>
As shown in Table 1 below, the original porosity of the skeleton part, the type of ceramic filler 60, the average particle size of the ceramic filler 60, the content of the ceramic filler 60, the skeleton part porosity after filling the filler, the intermediate layer 1 A battery 100 was manufactured in the same manner as in Example 1 except that the thickness of the battery was changed.
<Example 13>
As shown in Table 1 below, a battery was produced in the same manner as in Example 12 except that a separator 30 having a thickness of 12 μm was disposed between the positive electrode 10 and the negative electrode 20. In addition, the separator 30 has HRL31 and the porosity of HRL31 was 58%.
<Comparative Example 8>
As shown in Table 1 below, the skeleton made of polyimide was not formed, the filler slurry containing 96% by mass of alumina was applied on the negative electrode 20, and the intermediate layer 1 made of alumina was formed, A battery was manufactured in the same manner as in Example 1 except that the thickness of the intermediate layer 1 was 4 μm and that the separator 30 having a thickness of 20 μm was disposed between the positive electrode 10 and the negative electrode 20. It was. In addition, the separator 30 has HRL31 and the porosity of HRL31 was 58%.
<Comparative Example 9>
As shown in Table 1 below, a battery was manufactured in the same manner as in Comparative Example 8 except that the thickness of the intermediate layer 1 was 20 μm and the separator 30 was not disposed.
<Evaluation>
1. Nail penetration test The battery is fully charged. The battery was warmed to 65 ° C. A nail 70 having a body diameter of 3 mm was prepared. A nail 70 was passed through the battery at a speed of 10 mm / sec. The battery surface temperature was monitored at a position 1 cm away from the position where the nail 70 was inserted. The maximum temperature reached after nail penetration was measured. The result is shown in the column of “Achieved temperature” in Table 1 below. It means that the lower the maximum temperature, the more the battery temperature rise during the nail penetration test is suppressed, that is, the heat generation during the short circuit is suppressed.
2. OCV defect rate measurement test For each of the above Examples and Comparative Examples, 10 batteries were prepared, and the number of defects that occurred until the battery was completed (including initial charge) was counted. The presence or absence of defects was counted including the presence or absence of defects other than OCV defects, but all the defects that occurred this time were OCV defects). The OCV failure is a failure in which the OCV (open circuit voltage) decreases even when charging (during initial charging). The results are shown in the column of “Table 1 OCV failure rate” below. The lower the value, the lower the OCV defect rate.
3. Measurement of battery capacity The battery was charged and discharged under the following conditions. Thereby, the capacity (initial capacity) of the CC discharge was measured. The measurement results are shown in the “Battery capacity” column of Table 1 below.

CCCV charge: CC current = 1 / 3C, CV voltage = 4.2V, cut current = 0.1C
CC discharge: CC current = 1 / 3C, cut voltage = 2.5V

<Result>
As shown in Table 1 above, in Example 1 to Example 13, suppression of heat generation during short circuit and suppression of reduction in battery capacity were compatible.

  From the results of Example 5 to Example 6, it can be understood that when the original porosity of the skeleton increases, the porosity of the skeleton after filling the filler also increases. It was confirmed that although the battery capacity increased with the increase in the porosity of the skeleton after filling with the filler, the ultimate temperature increased.

  From a comparison between Example 12 and Example 13, the intermediate layer 1 may be in direct contact with both the positive electrode 10 and the negative electrode 20, and a separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. Indicated. That is, it was shown that the battery 100 according to the present disclosure can omit the separator 30.

  In Comparative Example 1, the reached temperature was high. In Comparative Example 1, the content of the ceramic filler in the intermediate layer 1 was less than 5% by mass, and the skeleton part porosity after filling the filler was larger than 52%. Therefore, it is considered that the suppression of heat generation at the time of short circuit is insufficient.

  In Comparative Example 2, the battery capacity was low. In Comparative Example 2, the content of the ceramic filler in the intermediate layer 1 was higher than 40% by mass, and the skeleton porosity after filling the filler was less than 40%. Therefore, it is considered that the battery resistance is increased and the battery capacity is decreased.

  In Comparative Example 3, the battery capacity was low. In Comparative Example 3, the original porosity of the skeleton part was less than 60%. Therefore, the skeleton part porosity after filling with the filler was less than 40%. As a result, it is considered that the battery resistance increased and the battery capacity decreased.

  In Comparative Example 4, the ultimate temperature was high. In Comparative Example 4, the average particle size of the ceramic filler was less than 0.3 μm. Therefore, the porosity of the skeleton after filling the filler was greater than 52%. As a result, it is considered that the suppression of heat generation at the time of short circuit is insufficient.

  In Comparative Example 5, the battery capacity was low. In Comparative Example 5, the average particle size of the ceramic filler was larger than 0.5 μm. Therefore, the skeleton part porosity after filling with the filler was less than 40%. As a result, it is considered that the battery resistance increased and the battery capacity decreased.

  In Comparative Example 6, the ultimate temperature was high. In Comparative Example 6, the thickness of the intermediate layer 1 was less than 12 μm. Therefore, it is considered that the suppression of heat generation at the time of short circuit is insufficient.

  In Comparative Example 7, the battery capacity was low. In Comparative Example 7, the thickness of the intermediate layer 1 was greater than 25 μm. Therefore, it is considered that the battery resistance is increased and the battery capacity is decreased.

  In Comparative Example 8, the ultimate temperature was high. When nail penetration has occurred, part of the negative electrode 20 or part of the HRL 31 may have occurred.

  In Comparative Example 9, the OCV defect rate was 100%. The battery 100 according to the comparative example 9 does not include the intermediate layer 1 formed of the polyimide resin 61 and does not include the separator 30. Therefore, it is considered that the OCV defect rate has become a high value.

  The embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The technical scope defined by the description of the scope of claims includes all modifications within the meaning and scope equivalent to the scope of claims.

  DESCRIPTION OF SYMBOLS 1 Intermediate | middle layer, 10 Positive electrode, 11 Positive electrode collector, 12 Positive electrode compound material layer, 20 Negative electrode, 21 Negative electrode collector, 22 Negative electrode compound material layer, 30 Separator, 31 HRL, 40 Electrode group, 50 Exterior material, 51 Positive electrode Tab, 52 Negative electrode tab, 60 Ceramic filler, 61 Polyimide resin, 62 Void, 70 Nail.

Claims (1)

Including at least a positive electrode, a negative electrode, and an intermediate layer;
The intermediate layer is disposed between the positive electrode and the negative electrode;
The intermediate layer includes a skeleton and a ceramic filler,
The skeleton is a porous three-dimensional network structure formed of a porous polyimide resin,
The polyimide resin has voids,
The void is filled with the ceramic filler,
The polyimide resin has a porosity of 60% or more and 80% or less in a state where the ceramic filler is not filled, and a porosity of 40% or more and 52% or less in a state where the ceramic filler is filled. Have
The ceramic filler is either titanium oxide or alumina,
The ceramic filler has an average particle size of 0.3 μm or more and 0.5 μm or less,
The intermediate layer includes 5% by mass or more and 40% by mass or less of the ceramic filler,
The intermediate layer has a thickness of 12 μm or more and 25 μm or less.
Non-aqueous electrolyte secondary battery.

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