JP2018106833A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a minute short circuit between an electrode burr and a sharp foreign material even if the electrode burr is generated by the sharp foreign material having stuck to a secondary battery.SOLUTION: A secondary battery includes at least a housing 90, a wound electrode group 40 and an adhesive layer 41. The housing 90 accommodates the wound electrode group 40 and the adhesive layer 41. The adhesive layer 41 is disposed on a surface of the wound electrode group 40. The adhesive layer 41 contains resin 41a of 10 mass% or more and 90 mass% or less and the balance consisting of insulating filler 41b. The adhesive layer 41 has a thickness of 0.1 mm or more. The adhesive layer 41 has peel strength of 0.5 N/m or more. The adhesive layer 41 has a degree of porosity of 0% or more and 25% or less. The insulating filler 41b is flake-like. As to the insulating filler 41b, a ratio of a maximum diameter to a thickness of the insulating filler 41b is 3 or more.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to a secondary battery.

  Japanese Patent Laying-Open No. 2006-091859 (Patent Document 1) discloses a secondary battery in which an insulating sheet having elasticity is disposed between a wound electrode group and an inner wall surface of a housing.

Japanese Patent Laid-Open No. 2006-091859

  As one of failure modes due to external factors of the secondary battery (hereinafter sometimes abbreviated as “battery”), for example, a foreign object having a sharp tip (hereinafter referred to as “sharp foreign object”) pierces the battery. A failure mode is possible. Conventionally, this failure mode has been simulated by a nail penetration test.

  When a sharp foreign material having conductivity, such as a nail, pierces the battery, the positive electrode and the negative electrode are short-circuited through the sharp foreign material. At this time, a large current instantaneously flows through the sharp foreign object. As a result, Joule heat is generated and the battery temperature rises. In patent document 1, the insulating sheet which has a stretching property is arrange | positioned between the winding electrode group and the inner wall face of a housing | casing. It is considered that when the sharp foreign object penetrates the housing, the insulating sheet extends following the sharp foreign object, thereby suppressing a short circuit through the sharp foreign object.

  However, the following inconveniences may occur depending on the shape of the sharp foreign material, the manner of sticking, and the like. That is, there is a possibility that burrs (hereinafter referred to as “electrode burrs”) may be generated from the electrode current collector (typically metal foil) when the electrodes are pierced by sharp foreign substances. When the electrode burr penetrates the insulating sheet, there is a possibility that a minute short circuit occurs between the electrode burr and the sharp foreign material.

  An object of the present disclosure is to suppress a minute short circuit between the electrode burr and the sharp foreign object even when the electrode burr is generated by the sharp foreign object sticking into the secondary battery.

  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 present disclosure should not be limited by the correctness of the mechanism of action.

  The secondary battery of the present disclosure includes at least a housing, a wound electrode group, and an adhesive layer. The housing accommodates the wound electrode group and the adhesive layer. The adhesive layer is disposed on the surface of the wound electrode group. The adhesive layer contains 10% by mass or more and 90% by mass or less of resin and the remaining insulating filler. The adhesive layer has a thickness of 0.1 mm or more. The adhesive layer has a peel strength of 0.5 N / m or more. The adhesive layer has a porosity of 25% or less. The insulating filler is flaky. The ratio of the maximum diameter of the insulating filler to the thickness of the insulating filler is 3 or more.

  In the secondary battery of the present disclosure, the sharp foreign matter penetrating the housing reaches the wound electrode group after passing through the adhesive layer. The adhesive layer has a predetermined adhesive strength. That is, the adhesive layer has a peel strength of 0.5 N / m or more. It is considered that when the sharp foreign matter passes through the adhesive layer, the adhesive layer adheres to the surface of the sharp foreign matter, so that the surface of the sharp foreign matter is covered with the component of the adhesive layer.

  The pressure-sensitive adhesive layer of the present disclosure contains a specific component. That is, the adhesive layer contains 10% by mass or more and 90% by mass or less of resin and the remaining insulating filler. The insulating filler has a flake shape, and the ratio of the maximum diameter to the thickness (hereinafter referred to as “aspect ratio”) is 3 or more. Since the insulating filler having such a shape is highly oriented, it is considered that the insulating filler is oriented along the moving direction of the sharp foreign matter. Therefore, the surface of the sharp foreign matter is covered with the resin and the oriented insulating filler. As a result, even when an electrode burr is generated, an oriented insulating filler is interposed between the electrode burr and the sharp foreign material, so that a micro short circuit occurs between the electrode burr and the sharp foreign material. This is considered to be suppressed.

  However, the adhesive layer needs to have a thickness of 0.1 mm or more. When the thickness of the adhesive layer is less than 0.1 mm, it is difficult to densely coat the surface of the sharp foreign matter. As a result, there is a possibility that the suppression of minute short-circuiting between the electrode burr and the sharp foreign substance is insufficient.

  The adhesive layer needs to have a porosity of 0% to 25%. When the porosity of the adhesive layer exceeds 25%, the adhesive layer does not become dense, and a micro short circuit may occur between the electrode burr and the sharp foreign matter.

FIG. 1 is a schematic diagram illustrating an example of a configuration of a secondary battery according to an embodiment of the present disclosure. FIG. 2 is an example of a schematic cross-sectional view parallel to the XZ plane of FIG. FIG. 3 is an example of a schematic cross-sectional view parallel to the YZ plane of FIG. FIG. 4 is a conceptual diagram for explaining the action of the adhesive layer. FIG. 5 is a conceptual diagram for explaining the aspect ratio. FIG. 6 is a schematic cross-sectional view illustrating an example of a configuration of a secondary battery according to a modified example of the present disclosure. FIG. 7 is a graph showing the relationship between the voltage drop amount in the nail penetration test and the thickness of the adhesive layer. FIG. 8 is a graph showing the relationship between the voltage drop amount in the nail penetration test and the resin composition ratio. FIG. 9 is a graph showing the relationship between the voltage drop amount in the nail penetration test and the aspect ratio of the insulating filler.

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

<Secondary battery>
Below, a lithium ion secondary battery is demonstrated as an example of a secondary battery. However, the secondary battery of the present disclosure should not be limited to a lithium ion secondary battery.

  FIG. 1 is a schematic diagram illustrating an example of the configuration of the secondary battery according to the present embodiment. The battery 100 includes a housing 90. The housing 90 has a rectangular shape (flat rectangular parallelepiped). However, the casing of the present embodiment may be cylindrical. The housing 90 may be made of a metal material such as pure aluminum (Al), an Al alloy, or stainless steel. However, the casing 90 may be made of, for example, an aluminum laminate film or the like as long as a predetermined sealing property can be realized.

  The housing 90 includes a case 91 and a lid 92. Case 91 is a container having an opening. The lid 92 is configured to close the opening of the case 91. The lid 92 may be joined to the case 91 by laser welding, for example. The lid 92 includes a positive electrode terminal 81 and a negative electrode terminal 82. The lid 92 may include a safety valve, a liquid injection hole (both not shown), and the like.

  FIG. 2 is an example of a schematic cross-sectional view parallel to the XZ plane of FIG. The housing 90 stores the wound electrode group 40 and an electrolytic solution (not shown). An adhesive layer 41 is disposed on the surface of the wound electrode group 40. That is, the battery 100 includes at least the housing 90, the wound electrode group 40, and the adhesive layer 41.

<Adhesive layer>
FIG. 3 is an example of a schematic cross-sectional view parallel to the YZ plane of FIG. The adhesive layer 41 is disposed on the surface of the wound electrode group 40 (that is, the outermost periphery of the wound electrode group 40). The adhesive layer 41 contains 10 mass% or more and 90 mass% or less of resin 41a and the remaining insulating filler 41b. The adhesive layer 41 is formed, for example, by applying a resin composition containing a resin 41 a and an insulating filler 41 b to the surface of the wound electrode group 40. The coating method should not be specifically limited. For example, the adhesive layer 41 can be formed by spray coating or the like.

  FIG. 4 is a conceptual diagram for explaining the action of the adhesive layer. The sharp foreign matter 200 (for example, a nail-like foreign matter) that penetrates the housing 90 reaches the wound electrode group 40 after passing through the adhesive layer 41. The adhesive layer 41 has a peel strength of 0.5 N / m or more. Therefore, when the sharp foreign material 200 passes through the adhesive layer 41, the adhesive layer 41 is considered to adhere to the surface of the sharp foreign material 200 and cover the surface of the sharp foreign material 200. That is, it is considered that the adhesive layer 41 is transferred to the surface of the sharp foreign object 200. For this reason, the sharp foreign material 200 reaches the wound electrode group 40 with its surface covered with the adhesive layer 41. Thereby, it is considered that the short circuit between the positive electrode 10 and the negative electrode 20 through the sharp foreign material 200 is suppressed.

  The peel strength of the pressure-sensitive adhesive layer 41 can be adjusted, for example, by the composition of the pressure-sensitive adhesive layer 41 (type of resin, resin composition ratio, shape of insulating filler, etc.). The “peel strength” of the adhesive layer 41 is measured by a 90 ° peel test in accordance with “JIS Z 0237: Adhesive tape / adhesive sheet test method”. The measurement is performed three times or more. An arithmetic average of three or more times is adopted as a measurement result.

  If the peel strength is less than 0.5 N / m, the adhesive layer 41 is difficult to be transferred to the surface of the sharp foreign object 200, and the surface of the sharp foreign object 200 may not be sufficiently covered. The adhesive layer 41 may have a peel strength of 30 N / m or less, for example. When the peel strength of the adhesive layer 41 exceeds 30 N / m, it may be difficult to handle the wound electrode group 40 after the adhesive layer 41 is formed. For example, there is a possibility that the operation of inserting the wound electrode group 40 into the housing 90 may be hindered.

  The adhesive layer 41 has a thickness of 0.1 mm or more. When the thickness of the pressure-sensitive adhesive layer 41 is less than 0.1 mm, the pressure-sensitive adhesive layer 41 transferred to the surface of the sharp foreign material 200 also becomes thin, and it is difficult to cover the surface of the sharp foreign material 200 densely. The adhesive layer 41 may have a thickness of 10 mm or less, for example. If the thickness of the adhesive layer 41 exceeds 10 mm, it may be difficult to construct a battery having a high volumetric energy density because the occupied volume of the adhesive layer 41 is large.

  The thickness of the adhesive layer 41 is measured in the cross section in the thickness direction of the adhesive layer 41. For the measurement, an optical microscope (for example, a digital microscope manufactured by Keyence Corporation) or the like can be used. The thickness is measured at three or more locations. An arithmetic average of three or more places is adopted as a measurement result.

  The adhesive layer 41 has a porosity of 0% or more and 25% or less. When the porosity of the adhesive layer 41 exceeds 25%, it is difficult to coat the surface of the sharp foreign material 200 densely. The porosity may be, for example, 0% or more and 5% or less, or 5% or more and 25% or less.

The porosity can be adjusted by, for example, the resin composition ratio, the coating method, and the like. The porosity is calculated by the following formula.
Porosity = (V1−V2) ÷ V1
In the formula, V1 indicates the apparent volume of the adhesive layer 41, and V2 indicates the true volume of the adhesive layer 41. The apparent volume is a product of the thickness of the adhesive layer 41 and the area of the adhesive layer 41. The true volume is calculated by dividing the mass of the adhesive layer 41 by the true density of the adhesive layer 41. The true density of the adhesive layer 41 is calculated from the true density of each material constituting the adhesive layer 41 and the composition of the adhesive layer 41 (mass ratio of each material).

  In the adhesive layer 41, the constituent ratio of the resin 41a is 10% by mass or more and 90% by mass or less. When the composition ratio of the resin 41a is less than 10% by mass, it is difficult to realize a peel strength of 0.5 N / m or more. If the composition ratio of the resin 41a exceeds 90% by mass, the composition ratio of the insulating filler 41b is low, so that a minute short circuit may occur between the electrode burr 201 and the sharp foreign material 200. The composition ratio of the resin 41a may be, for example, 10% by mass or more and 50% by mass or less, or 50% by mass or more and 90% by mass or less.

(resin)
As long as the adhesive layer 41 has a peel strength of 0.5 N / m or more, the type of the resin 41a should not be particularly limited. The resin 41a preferably includes a functional group capable of forming a hydrogen bond in the polymer structure. Examples of the functional group capable of forming a hydrogen bond include a hydroxyl group, a carboxy group, and a fluorine functional group. Resins containing these functional groups tend to exhibit tackiness suitable for this embodiment. From the viewpoint of peel strength, the functional group is preferably a fluorine functional group. The resin 41a may be, for example, polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVdF), vinylidene fluoride / hexafluoropropylene copolymer, and the like. One type of resin may be used alone, or two or more types of resins may be used in combination.

(Insulating filler)
The insulating filler 41b has a flake shape. The insulating filler 41b may have a shape such as a substantially disk shape, a rectangular plate shape, or a polygonal plate shape, for example. The aspect ratio (maximum diameter / thickness) of the insulating filler is 3 or more. FIG. 5 is a conceptual diagram for explaining the aspect ratio. FIG. 5 shows a substantially disc-shaped insulating filler as an example. The maximum diameter (L) indicates the maximum diameter of the surface (P1) having the maximum area among the plurality of surfaces constituting the surface of the insulating filler. The thickness (h) indicates the maximum distance between the surface (P2) paired with the surface (P1) and the surface (P1). The insulating filler 41b may have a maximum diameter (L) of 2 μm or more and 20 μm or less, for example.

  The aspect ratio is measured by an optical microscope or an electron microscope. The aspect ratio is measured for 10 or more insulating fillers 41b. An arithmetic average of 10 or more is adopted as a measurement result.

  The insulating filler 41 b having an aspect ratio of 3 or more is easily oriented along the movement of the sharp foreign material 200. Thereby, it is considered that the surface of the sharp foreign material 200 is densely covered with the insulating filler 41b. Even if the electrode burr 201 is generated, the oriented insulating filler 41b is considered to suppress a minute short circuit between the electrode burr 201 and the sharp foreign material.

  When the aspect ratio of the insulating filler 41b is less than 3, the insulating filler 41b is not sufficiently oriented, and there is a possibility that the suppression of the micro short-circuit becomes insufficient. It is currently difficult to produce a filler having an aspect ratio exceeding 30. Therefore, the insulating filler 41b may have an aspect ratio of 30 or less. However, the insulating filler 41b may have an aspect ratio exceeding 30 if it can be manufactured. The insulating filler 41b may have an aspect ratio of 3 or more and 30 or less, may have an aspect ratio of 5 or more and 15 or less, and may have an aspect ratio of 7 or more and 10 or less.

As long as it has an aspect ratio of 3 or more, the material of the insulating filler 41b should not be particularly limited. The insulating filler may be made of, for example, alumina (Al ₂ O ₃ ), boehmite (Al ₂ O ₃ .H ₂ O), silica (SiO ₂ ), titania (TiO ₂ ), or the like. The insulating filler 41b can be prepared, for example, by a sol-gel method.

《Wound electrode group》
The wound electrode group 40 includes a positive electrode 10, a negative electrode 20, and a separator 30. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 are all strip-shaped sheets. The wound electrode group 40 is configured by stacking the positive electrode 10, the separator 30, and the negative electrode 20 in this order and further winding them.

(Positive electrode)
The positive electrode 10 includes a positive electrode mixture layer and a positive electrode current collector. The positive electrode current collector may be, for example, an Al foil. The positive electrode current collector may have a thickness of about 10 to 30 μm, for example. The positive electrode mixture layer is formed on the surface of the positive electrode current collector. The positive electrode mixture layer may have a thickness of about 10 to 150 μm, for example. The positive electrode mixture layer contains a positive electrode active material, a conductive material, a binder, and the like. The positive electrode mixture layer contains, for example, 80 to 98% by mass of a positive electrode active material, 1 to 15% by mass of a conductive material, and 1 to 5% by mass of a binder.

The positive electrode active material, the conductive material, and the binder should not be particularly limited. The positive electrode active material may be, for example, LiCoO ₂ , LiNiO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ or the like. 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), polytetrafluoroethylene (PTFE), or the like.

(Negative electrode)
The negative electrode 20 includes a negative electrode mixture layer and a negative electrode current collector. The negative electrode current collector may be, for example, a copper (Cu) foil. The negative electrode current collector may have a thickness of about 5 to 20 μm, for example. The negative electrode mixture layer is formed on the surface of the negative electrode current collector. The negative electrode mixture layer may have a thickness of about 10 to 150 μm, for example. The negative electrode mixture layer contains a negative electrode active material, a binder material, and the like. The negative electrode mixture layer contains, 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 active material and the binder should not be particularly limited. The negative electrode active material may be, for example, graphite, graphitizable carbon, non-graphitizable carbon, silicon, silicon oxide, tin, tin oxide, or the like. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like.

(Separator)
The separator 30 is an electrically insulating porous film. The separator 30 electrically isolates the positive electrode 10 and the negative electrode 20. Separator 30 may have a thickness of 5 to 30 μm, for example. The separator 30 can be constituted by, for example, a porous polyethylene (PE) film, a porous polypropylene (PP) film, or the like. The separator 30 may include a multilayer structure. For example, the separator 30 may be configured by laminating a porous PP film, a porous PE film, and a porous PP film in this order. The separator 30 may include a heat resistant layer on the surface thereof. The heat resistant layer 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.

<Electrolyte>
The electrolytic solution includes a lithium salt and a solvent. The solvent is aprotic. The solvent may be, for example, a mixture of a cyclic carbonate and a chain carbonate. The mixing ratio of the cyclic carbonate and the chain carbonate may be a volume ratio, for example, cyclic carbonate: chain carbonate = 1: 9 to 5: 5. Examples of the cyclic carbonate may include 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 electrolytic solution contains, for example, a 0.5 to 2.0 mol / L lithium salt. The lithium salt may be, for example, LiPF ₆ , LiBF ₄ , Li [N (FSO ₂ ) ₂ ], Li [N (CF ₃ SO ₂ ) ₂ ] and the like.

<Modification>
FIG. 6 is a schematic cross-sectional view illustrating an example of a configuration of a secondary battery according to a modified example of the present disclosure. In addition to the surface (outermost circumference) of the wound electrode group 40, the adhesive layer 42 may be disposed at the center (innermost circumference) of the wound electrode group 40. Except for the location, the configuration of the adhesive layer 42 may be the same as or different from that of the adhesive layer 41. However, the adhesive layer 42 also contains 10% by mass or more and 90% by mass or less of resin and the remaining insulating filler, has a thickness of 0.1 mm or more, and has a peel strength of 0.5 N / m or more, It has a porosity of 0% to 25%, contains flaky insulating filler, and the insulating filler has an aspect ratio of 3 or more. By arranging the adhesive layer 42 also on the innermost periphery of the wound electrode group 40, it is considered that the effect of suppressing a micro short circuit is further improved.

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

<Manufacture of secondary batteries>
Example 1
(Manufacture of positive electrode)
The following materials were prepared:
Cathode active material: LiNi _1/3 Co _1/3 Mn _1/3 O ₂
Conductive material: AB
Binder: PVdF
Solvent: N-methyl-2-pyrrolidone (NMP)
Positive electrode current collector: Al foil (thickness: 20 μm)

  A positive electrode slurry was prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent. In the positive electrode slurry, the solid content was “positive electrode active material: conductive material: binder = 90: 8: 2” by mass ratio.

The positive electrode slurry was applied to the surface (both front and back surfaces) of the positive electrode current collector and dried to form a positive electrode mixture layer. The mass per unit area of the positive electrode mixture layer was 15 mg / cm ² per side. The positive electrode mixture layer was rolled to a predetermined thickness. This produced a positive electrode. The positive electrode was cut into a strip shape. The width dimension of the positive electrode mixture layer was 110 mm.

(Manufacture of negative electrode)
The following materials were prepared:
Negative electrode active material: Natural graphite Binder: CMC and SBR
Solvent: Water Negative electrode current collector: Cu foil (thickness: 10 μm)

A negative electrode slurry was prepared by mixing the negative electrode active material, the binder, and the solvent. In the negative electrode slurry, the solid content was “negative electrode active material: CMC: SBR = 98: 1: 1” by mass ratio. The negative electrode slurry was applied to the surface (both front and back surfaces) of the negative electrode current collector and dried to form a negative electrode mixture layer. The mass per unit area of the negative electrode mixture layer was 15 mg / cm ² per side. The negative electrode mixture layer was rolled to a predetermined thickness. This produced a negative electrode. The negative electrode was cut into a strip shape. The width dimension of the negative electrode mixture layer was 115 mm.

(Manufacture of separators)
A surface (both front and back surfaces) of a porous PE membrane (thickness: 20 μm, width dimension: 120 mm) was prepared. A heat-resistant layer having a thickness of 4 μm was formed on the surface of the porous PE film. The heat-resistant layer was composed of alumina and acrylic resin.

(Configuration of wound electrode group)
The positive electrode and the negative electrode were stacked with the separator interposed therebetween, and further wound along the longitudinal direction of each member, thereby forming a wound electrode group. The wound electrode group was formed into a flat shape.

(Adhesive layer placement)
The following materials were prepared:
Resin: PVdF
Insulating filler: boehmite (flakes, aspect ratio: 5, maximum diameter: 20 μm)
Solvent: NMP

  A slurry was prepared by mixing the resin, the insulating filler, and the solvent. The solid content was “resin: insulating filler = 50: 50” by mass ratio. The slurry was apply | coated to the surface (outermost periphery) of the winding electrode group by spray application, and it dried. Thereby, an adhesive layer having a thickness of 0.5 mm was formed.

  A predetermined area of the adhesive layer was cut out together with the separator. The thickness of the adhesive layer and the mass per unit area were measured. The porosity was calculated by the method described above. The cut out adhesive layer was attached to a stainless steel plate. The peel strength when the adhesive layer was peeled from the stainless steel plate was measured by a 90 ° peel test.

(Electrolyte)
An electrolyte solution containing the following components was prepared.
Solvent: [EC: EMC: DEC = 3: 5: 2 (volume ratio)]
Lithium salt: LiPF ₆ (1 mol / l)

(Enclosure in a housing)
A rectangular housing (vertical dimension: 75 mm, width dimension: 120 mm, depth dimension: 15 mm, plate thickness: 1 mm) was prepared. The wound electrode group in which the adhesive layer was disposed was inserted into the casing. Electrolyte was injected into the housing. The case was sealed. From the above, a secondary battery (rectangular lithium ion secondary battery) was manufactured. This secondary battery is designed to have a capacity of 5 Ah in a voltage range of 3.0 to 4.1V.

(Initial charge / discharge)
In a 25 ° C. environment, the battery was charged to 4.1 V with a current of 5 A. The battery was discharged to 3.0 V with a current of 5 A across a 5-minute pause. Thereafter, the initial discharge capacity was measured by the following constant current-constant voltage charge (CC-CV charge) and constant current-constant voltage discharge (CC-CV discharge).
CC-CV charge: current = 5A, CV voltage = 4.1V, end current = 50mA
CC-CV discharge: current = 5A, CV voltage = 3.0V, end current = 50mA

<< Comparative Example 1 >>
A battery was produced by the same production method as in Example 1 except that the adhesive layer was not disposed on the surface of the wound electrode group.

<< Comparative Example 2 >>
A battery was manufactured by the same manufacturing method as in Example 1 except that the resin composition ratio was 100% by mass (that is, an adhesive layer containing no insulating filler was formed).

<< Examples 2 to 5, Comparative Examples 5 and 6 >>
As shown in Table 1 below, a battery was manufactured by the same manufacturing method as in Example 1 except that the aspect ratio of the insulating filler was changed.

<< Comparative Example 7 >>
As shown in Table 1 below, a battery was manufactured by the same manufacturing method as in Comparative Example 6 except that the resin composition ratio was changed.

<< Examples 7 and 8, Comparative Examples 4 and 11 >>
As shown in Table 1 below, a battery was manufactured by the same manufacturing method as in Example 1 except that the resin composition ratio was changed.

<< Examples 9 and 10, Comparative Example 10 >>
As shown in Table 1 below, a battery was manufactured by the same manufacturing method as in Example 1 except that the type of resin was changed. “Modified PE” indicates a polyethylene having a hydroxyl group introduced, and “modified PP” indicates a polypropylene having a hydroxyl group introduced.

<< Examples 11 to 13, Comparative Example 9 >>
As shown in Table 1 below, a battery was manufactured by the same manufacturing method as in Example 1 except that the thickness of the adhesive layer was changed.

<Nail penetration test>
The SOC (State Of Charge) of the battery was adjusted to 100%. A nail having a body diameter of 3 mm and a point R of 1 mm was prepared as a sharp foreign material. A nail was pierced into the battery at a speed of 1 mm / sec. The amount of voltage drop 1 second after the nail was pierced into the battery was measured. The results are shown in Table 1 below. It shows that the smaller the amount of voltage drop, the smaller the short circuit between the electrode burr and the nail.

<Result>
As shown in Table 1 above, in the examples in which the adhesive layer satisfies the following conditions (1) to (5), the short-circuit was suppressed as compared with the comparative example not satisfying the same conditions.
(1) The adhesive layer contains 10% by mass or more and 90% by mass or less of resin and the remaining insulating filler.
(2) The adhesive layer has a thickness of 0.1 mm or more.
(3) The adhesive layer has a peel strength of 0.5 N / m or more.
(4) The adhesive layer has a porosity of 0% to 25%.
(5) The insulating filler is flaky, and the aspect ratio of the insulating filler is 3 or more.

《Adhesive layer thickness》
From the results of Examples 1, 11 to 13, and Comparative Examples 1, 3, and 9, the amount of voltage drop is large when the thickness of the adhesive layer is less than 0.1 mm. If the thickness of the adhesive layer is less than 0.1 mm, it is considered that the surface of the nail cannot be covered densely. As the thickness of the adhesive layer increases, the amount of voltage drop decreases. It is considered that the short-circuit resistance is increased by increasing the thickness of the adhesive layer transferred to the surface of the nail. FIG. 7 is a graph showing the relationship between the voltage drop amount in the nail penetration test and the thickness of the adhesive layer. The horizontal axis of FIG. 7 is displayed on a logarithmic scale. As shown in FIG. 7, when the thickness of the adhesive layer is less than 0.1 mm, the voltage drop amount increases rapidly.

<Composition ratio of resin>
From the results of Examples 1, 7, 8, and Comparative Examples 2, 4, 9, 11, the voltage drop amount is small when the resin composition ratio is 10% by mass or more and 90% by mass or less. FIG. 8 is a graph showing the relationship between the voltage drop amount in the nail penetration test and the resin composition ratio. As shown in FIG. 8, when the resin composition ratio is less than 10% by mass, the voltage drop amount increases rapidly. It is thought that due to the lack of resin, the peel strength is lowered and the adhesive layer is difficult to be transferred to the surface of the nail.

  In Comparative Example 2, the amount of voltage drop is large. Since there is no insulating filler, it is considered that a minute short circuit between the electrode burr and the nail cannot be sufficiently suppressed.

<Aspect ratio of insulating filler>
From the results of Examples 1 to 6 and Comparative Examples 5 to 6, the amount of voltage drop is small when the aspect ratio is 3 or more. FIG. 9 is a graph showing the relationship between the voltage drop amount in the nail penetration test and the aspect ratio of the insulating filler. As the aspect ratio increases, the amount of voltage drop decreases. This is probably because the larger the aspect ratio, the easier the orientation of the insulating filler.

<Porosity of adhesive layer>
From the results of Examples 1 and 7, and Comparative Examples 4, 8, and 9, the voltage drop amount is small when the porosity of the adhesive layer is 25% or less. On the other hand, when the porosity of the adhesive layer exceeds 25%, the amount of voltage drop increases. Since the nail is not densely covered, it is considered that a micro short circuit has occurred between the nail and the electrode burr.

<Resin types>
From the results of Examples 1, 9, 10 and Comparative Example 10, as long as the adhesive layer satisfies the above conditions (1) to (5), the effect of suppressing micro short-circuiting is recognized regardless of the type of resin. In Comparative Example 10 in which latex rubber (elastic rubber) was used as the resin, the peel strength could not be measured because the adhesive layer was broken during the peel strength measurement. In Comparative Example 10, the amount of voltage drop is large.

  The above embodiments and examples are to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 positive electrode, 20 negative electrode, 30 separator, 40 wound electrode group, 41, 42 adhesive layer, 41a resin, 41b insulating filler, 81 positive electrode terminal, 82 negative electrode terminal, 90 housing, 91 case, 92 lid, 100 battery, 200 Sharp foreign matter, 201 Electrode burr.

Claims (1)

Including at least a housing, a wound electrode group and an adhesive layer;
The housing houses the wound electrode group and the adhesive layer,
The adhesive layer is disposed on the surface of the wound electrode group,
The adhesive layer contains 10% by mass or more and 90% by mass or less of resin, and the remaining insulating filler,
The adhesive layer has a thickness of 0.1 mm or more,
The adhesive layer has a peel strength of 0.5 N / m or more,
The adhesive layer has a porosity of 0% to 25%,
The insulating filler is flaky,
The ratio of the maximum diameter of the insulating filler to the thickness of the insulating filler is 3 or more.
Secondary battery.