Non-aqueous electrolyte secondary battery

Abstract

The present invention provides a non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode (11) and a negative electrode are wound along the lengthwise direction of the electrodes with a separator therebetween, said non-aqueous electrolyte secondary battery being characterized in that: the positive electrode (11) has a band-shaped positive electrode collector (32), positive electrode mixture layers (34) which are disposed on both surfaces of the positive electrode collector (32), and a pair of exposed portions (36a, 36b) in which both surfaces of the positive electrode collector (32) are exposed; a positive electrode tab (20) is bonded to the exposed portion (36a); a first protective film (38) which contains a resin is disposed on the positive electrode (11) so as to cover the exposed portion (36a); a second protective film (40) which contains a resin is disposed on the positive electrode (11) so as to cover the exposed portion (36b); and end-portion side surfaces (38a, 38b, 40a, 40b) of the first protective film (38) and the second protective film (40) which extend in the short direction of the positive electrode (11) are formed in a slope shape.

Description

Nonaqueous electrolyte secondary battery

[0001] The present invention relates to a non-aqueous electrolyte secondary battery.

[0002] In a conventional non-aqueous electrolyte secondary battery having a wound electrode assembly, an exposed portion where the surface of a current collector is exposed is formed in the longitudinal middle of a strip-shaped electrode constituting the electrode assembly, and a current collecting tab is connected to the exposed portion. In addition, to prevent the occurrence of an internal short circuit at the exposed portion, an insulating tape is attached to the electrode (e.g., Patent Documents 1 to 3), or a protective film containing a resin is disposed on the electrode (e.g., Patent Documents 4 to 5).

[0003] Japanese Patent Application Laid-Open No. 2001-135298 International Publication No. 2019 / 069890 Japanese Patent Application Laid-Open No. 2008-234855 International Publication No. 2018-154913 Japanese Patent Application Laid-Open No. 10-241696

[0004] Incidentally, nonaqueous electrolyte secondary batteries are required to avoid ignition, smoke emission, and the like due to an internal short circuit even when subjected to a strong impact. One of the causes of a short circuit when a battery is subjected to an impact is a protective layer (insulating tape or protective film) covering an exposed portion. Specifically, a short circuit may occur when the separator in contact with the protective layer breaks at the edge of the protective layer.

[0005] Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte secondary battery that is less likely to cause an internal short circuit even when a strong impact is applied to the battery.

[0006] One aspect of the present disclosure is a nonaqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound along the longitudinal direction of the electrodes with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode has a strip-shaped current collector, composite layers disposed on both sides of the current collector, and a pair of exposed portions where both sides of the current collector are exposed, an electrode tab is joined to one of the pair of exposed portions, a first protective film containing a resin is disposed on the electrode so as to cover one of the pair of exposed portions, and a second protective film containing a resin is disposed on the electrode so as to cover the other of the pair of exposed portions, and at least one of the first protective film and the second protective film has an end side surface extending in the short direction of the electrode and an end side surface extending in the longitudinal direction of the electrode formed in a sloped shape.

[0007] According to the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery that is less likely to cause an internal short circuit even when a strong impact is applied to the battery.

[0008] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, a partial top view of a positive electrode according to an embodiment of the present invention, and a cross-sectional view taken along line L1-L1 in FIG.

[0009] An example of a nonaqueous electrolyte secondary battery according to one aspect of the present disclosure will be described below. The drawings referred to in the following description of the embodiment are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual battery.

[0010] Fig. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in Fig. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween along the longitudinal direction of the electrodes, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical case body 16 with a bottom and a sealing body 17 that closes the opening of the case body 16. Examples of the battery case 15 include a cylindrical or rectangular metal case, a resin case (so-called pouch-type) formed by laminating a resin sheet, and the like.

[0011] The non-aqueous electrolyte has, for example, lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0012] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0013] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0014] The case body 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and supports the sealing body 17 on its upper surface.

[0015] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and all components except for the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the nonaqueous electrolyte secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0016] 1 , a positive electrode tab 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode tab 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the case body 16. The positive electrode tab 20 is connected by welding or the like to the underside of a filter 23, which is the bottom plate of the sealing body 17, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode tab 21 is connected by welding or the like to the inner bottom surface of the case body 16, and the case body 16 serves as the negative electrode terminal.

[0017] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the nonaqueous electrolyte secondary battery 10 will be further described below.

[0018] Fig. 2 is a partial top view of a positive electrode according to an embodiment, observed from one main surface side, and Fig. 3 is a cross-sectional view taken along line L1-L1 in Fig. 2. In Fig. 2, a first protective film 38, which will be described later, is shown in a see-through view to clarify the configuration of the positive electrode 11. In Figs. 2 and 3, arrow X indicates the longitudinal direction of the positive electrode 11, arrow Y indicates the lateral direction of the positive electrode 11, and arrow Z indicates the thickness direction of the positive electrode 11.

[0019] The positive electrode 11 includes a strip-shaped positive electrode current collector 32 and a positive electrode composite layer 34 disposed on both sides of the positive electrode current collector 32. The positive electrode 11 has a pair of exposed portions (36a, 36b) in which both sides of the positive electrode current collector 32 are exposed, formed in a longitudinal middle portion of the positive electrode 11. For example, the pair of exposed portions (36a, 36b) are formed in a region that is 1 / 5 to 4 / 5 of the longitudinal length of the positive electrode 11 when the longitudinal length of the positive electrode 11 is divided into five equal parts. The pair of exposed portions (36a, 36b) may be formed at the longitudinal end portions of the positive electrode 11. Specifically, the pair of exposed portions (36a, 36b) may be formed at the longitudinal end portions of the positive electrode 11 at the end portion closest to the start end of the winding direction of the positive electrode 11, at the end portion closest to the end portion of the winding direction of the positive electrode 11, or at both of these ends.

[0020] The positive electrode tab 20 is joined to one exposed portion 36a of the pair of exposed portions (36a, 36b). The exposed portions (36a, 36b) are exposed portions of the surface of the positive electrode current collector 32 that are not covered by the positive electrode composite layer 34, and are provided on both sides of the positive electrode 11, overlapping in the thickness direction of the positive electrode 11. The exposed portions (36a, 36b) shown in FIG. 2 are formed with a predetermined width over the entire width of the positive electrode 11 in the lateral direction. Although not shown in the drawings, the exposed portions (36a, 36b) may be formed on one end side of the positive electrode 11 in the lateral direction. In this case, it is desirable that the exposed portions (36a, 36b) be formed, for example, with a length of 50% or less of the entire width of the positive electrode 11 from one end in the lateral direction.

[0021] The positive electrode current collector 32 may be, for example, a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, or a film having such a metal disposed on its surface. The thickness of the positive electrode current collector 32 is, for example, 10 μm or more and 30 μm or less.

[0022] The positive electrode mixture layer 34 is preferably formed on the entire surface of each of the positive electrode current collectors 32, excluding the exposed portions (36a, 36b). The positive electrode mixture layer 34 preferably contains, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode 11 is fabricated, for example, by compressing the positive electrode mixture layer 34 formed by applying and drying a positive electrode mixture slurry containing the positive electrode active material and the like to both surfaces of the positive electrode current collector 32. The exposed portions (36a, 36b) can be fabricated, for example, by removing a portion of the fabricated positive electrode mixture layer 34. Alternatively, the exposed portions (36a, 36b) may be fabricated, for example, by masking a portion of the positive electrode current collector 32 to form an uncoated portion of the positive electrode mixture slurry.

[0023] Examples of the positive electrode active material include lithium (Li) and Li composite oxides containing transition metal elements such as cobalt (Co), manganese (Mn), and nickel (Ni). The Li composite oxides may contain additional elements other than Co, Mn, and Ni, such as aluminum (Al), zirconium (Zr), boron (B), magnesium (Mg), scandium (Sc), yttrium (Y), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), lead (Pb), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), and silicon (Si).

[0024] Examples of the conductive material include carbon black such as acetylene black and ketjen black, carbon powder such as graphite, etc. These may be used alone or in combination of two or more.

[0025] Examples of binders include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, polyolefin resins, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyethylene oxide (PEO), etc. These may be used alone or in combination of two or more.

[0026] The nonaqueous electrolyte secondary battery 10 includes a first protective film 38 disposed on the positive electrode composite layer 34 and the exposed portion 36a of the positive electrode 11 so as to cover one exposed portion 36a of the pair of exposed portions (36a, 36b), and a second protective film 40 disposed on the positive electrode composite layer 34 and the exposed portion 36b of the positive electrode 11 so as to cover the other exposed portion 36b of the pair of exposed portions (36a, 36b). The first protective film 38 preferably covers the entire exposed portion 36a, and the second protective film 40 preferably covers the entire exposed portion 36b. Note that, because the positive electrode tab 20 is joined to the exposed portion 36a, the first protective film 38 also covers the positive electrode tab 20 located on the exposed portion 36a. The first protective film 38 and the second protective film 40 are protective films containing resin. As will be described later, the first protective film 38 and the second protective film 40 are produced by applying a resin solution onto the positive electrode 11, and are different from a protective tape that includes a resin substrate and an adhesive layer.

[0027] In this embodiment, in at least one of the first protective film 38 and the second protective film 40, at least one of the end side surface extending in the short direction of the positive electrode 11 and the end side surface extending in the longitudinal direction of the positive electrode 11 is formed in a sloped shape. The sloped end side surface means that the end side surface of the protective film is inclined rather than perpendicular to the surface of the current collector, and the end side surface of the protective film may be rounded. Furthermore, the end side surface of the protective film extending in the short direction of the positive electrode 11 is the side surface of the end of the protective film in the longitudinal direction of the positive electrode 11 in a plan view seen from the thickness direction of the positive electrode 11. Furthermore, the end side surface of the protective film extending in the longitudinal direction of the positive electrode 11 is the side surface of the end of the protective film in the short direction of the positive electrode 11 in a plan view seen from the thickness direction of the positive electrode 11.

[0028] In FIG. 3 , the end side surfaces (38 a, 38 b) of the first protective film 38 extending in the lateral direction of the positive electrode 11 are formed in a sloped shape. That is, the end side surfaces (38 a, 38 b) on the positive electrode composite material layer 34 constituting the positive electrode 11 are inclined with respect to the surface of the positive electrode composite material layer 34. Note that, in the first protective film 38, only the end side surface 38 a may be formed in a sloped shape, or only the end side surface 38 b may be formed in a sloped shape. Also, in FIG. 3 , the end side surfaces (40 a, 40 b) of the second protective film 40 extending in the lateral direction of the positive electrode 11 are formed in a sloped shape. That is, the end side surfaces (40 a, 40 b) on the positive electrode composite material layer 34 constituting the positive electrode 11 are inclined with respect to the surface of the positive electrode composite material layer 34. Note that, in the second protective film 40, only the end side surface 40 a may be formed in a sloped shape, or only the step side surface 40 b may be formed in a sloped shape. Although not illustrated in the drawings, as described above, the end side surface (38c and / or 38d) of the first protective film 38 extending in the longitudinal direction of the positive electrode 11 may be formed in a sloped shape, and the end side surface of the second protective film 40 extending in the longitudinal direction of the positive electrode 11 may be formed in a sloped shape.

[0029] In this embodiment, at least one of the first protective film 38 and the second protective film 40 has a sloped end side extending in the short direction of the positive electrode 11 and at least one of the end side sides extending in the longitudinal direction of the positive electrode 11. This reduces the step at the boundary between the protective film and the positive electrode 11 (e.g., in FIG. 3 , the boundary between the first protective film 38 and the positive electrode composite layer 34 and the boundary between the second protective film 40 and the positive electrode composite layer 34). This reduces the linear pressure at the boundary and its surroundings, suppressing separator breakage and making internal short circuits less likely to occur, even when a strong impact is applied to the battery. Forming the end side of the protective film into a sloped shape is preferably applied to both the first protective film 38 and the second protective film 40, in order to further suppress the occurrence of internal short circuits when a strong impact is applied to the battery.

[0030] Furthermore, in the first protective film 38 and the second protective film 40, the end side surfaces extending in the short direction of the positive electrode 11 are more likely to be subjected to a higher linear pressure when an impact is applied to the battery than the end side surfaces extending in the long direction of the positive electrode 11, so it is preferable that at least the end side surfaces extending in the short direction of the positive electrode 11 are formed in a sloped shape.

[0031] The inclination angle of the sloped end side surface is preferably 30° or more and 60° or less with respect to the surface of the positive electrode current collector 32, in order to further suppress the occurrence of an internal short circuit when a strong impact is applied to the battery.

[0032] The first protective film 38 and the second protective film 40 are formed, for example, by applying a resin solution to the positive electrode composite layer 34 and the exposed portions (36a, 36b). For example, by adjusting the viscosity of the resin solution, the end side surfaces of the first protective film 38 and the second protective film 40 can be formed to have a sloped shape. The viscosity of the resin solution can be adjusted, for example, by adding a solvent such as N-methyl-2-pyrrolidone. Furthermore, after the first protective film 38 and the second protective film 40 are formed, the end side surfaces of the protective films may be processed to have a sloped shape.

[0033] The resin contained in the first protective film 38 and the second protective film 40 (i.e., the resin contained in the resin solution) may be, for example, a curable resin or a thermoplastic resin. Examples of the curable resin include a thermosetting resin and a photocurable resin. Examples of the thermosetting resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin; novolac-type epoxy resins such as naphthalene-containing novolac-type epoxy resin, trisphenolmethane-type epoxy resin, tetrakisphenolethane-type epoxy resin, dicyclopentadiene-type epoxy resin, and phenolbiphenyl-type epoxy resin; biphenyl-type epoxy resins such as tetramethylbiphenyl-type epoxy resin; polycyclic aromatic epoxy resins such as epoxy resins having a naphthalene structure, epoxy resins having an anthracene structure, and epoxy resins having a pyrene structure; hydrogenated alicyclic epoxy resins such as hydrogenated bisphenol A-type epoxy resin; and mesogen-skeleton epoxy resins such as terephthalylidene-type epoxy resins having a mesogen group as a skeleton. Examples of photocurable resins include those obtained by mixing a lauryl acrylate / acrylic acid copolymer with an acrylic polyfunctional monomer (or oligomer) such as polyoxazoline, polyisocyanate, melamine resin, polycarbodiimide, polyol, or polyamine, and polymerizing the mixture by ultraviolet irradiation or electron beam irradiation (and heating as needed). The resin solution may contain a curing agent or a photopolymerization initiator as needed.Examples of thermoplastic resins include polyethylene resin, polypropylene resin, polybutadiene resin, cyclic olefin resin, polymethylpentene resin, polystyrene resin, ethylene vinyl acetate copolymer, ethylene vinyl alcohol copolymer resin, styrene butadiene copolymer, ethylene acrylic acid ester copolymer, acrylonitrile-styrene resin, acrylonitrile-chlorinated polystyrene-styrene copolymer resin, acrylonitrile-acrylic rubber-styrene copolymer resin, acrylonitrile-butadiene-styrene copolymer resin, silicone resin, acetate resin, cellulose acetate resin, methacrylic resin, acrylic resin, vinyl chloride resin, chlorinated polyethylene resin, fluorine Examples of the resin include modified polyethylene resin, polyvinylidene fluoride resin, nylon resin, polyacetal resin, polyester resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene terephthalate resin, polycarbonate resin, modified polyphenylene ether resin, thermoplastic polyurethane elastomer, polyphenylene sulfide resin, polyether ether ketone resin, liquid crystal polymer, polytetrafluoroethylene resin, polyfluoroalkoxy resin, polyetherimide resin, polysulfone resin, polyketone resin, thermoplastic polyimide resin, polyamideimide resin, polyarylate resin, polysulfone resin, and polyethersulfone resin.

[0034] The resin is preferably a thermoplastic resin, as this improves the flexibility of the first protective film 38 and the second protective film 40. Among the above-mentioned thermoplastic resins, it is more preferable to use at least one of a styrene-butadiene copolymer and polyvinylidene fluoride. By improving the flexibility of the first protective film 38 and the second protective film 40, even when a strong impact is applied to the battery, the linear pressure at the boundary and its periphery is further alleviated, and separator breakage is further suppressed, making it less likely that an internal short circuit will occur. The first protective film 38 and the second protective film 40 may contain an inorganic filler, such as titania, alumina, silica, or zirconia.

[0035] The negative electrode 12 includes a strip-shaped negative electrode current collector and negative electrode composite layers disposed on both sides of the negative electrode current collector. The negative electrode current collector may be a foil of a metal, such as copper, that is stable within the potential range of the negative electrode, or a film having such a metal disposed on its surface. The negative electrode 12 has a pair of exposed portions (not shown) formed on both sides of the negative electrode current collector. The pair of exposed portions are provided on both sides of the negative electrode 12, overlapping in the thickness direction of the negative electrode 12. The pair of exposed portions are formed at the longitudinal ends of the negative electrode 12, at the ends on the winding end side of the negative electrode 12. However, the pair of exposed portions may be formed at the longitudinal ends of the negative electrode 12, at the ends on the winding start side of the negative electrode 12, or at both longitudinal ends of the negative electrode 12 (the ends on the winding start side and the winding end side of the negative electrode 12). The pair of exposed portions may also be formed in the longitudinal middle of the negative electrode 12. The exposed portion is preferably formed with a predetermined width over the entire length of the negative electrode 12 in the lateral direction, but may be formed on one end side of the negative electrode 12 in the lateral direction.

[0036] Although not illustrated in the drawings, the nonaqueous electrolyte secondary battery 10 includes a first protective film disposed on the negative electrode 12 so as to cover one of the pair of exposed portions and the negative electrode tab 21, and a second protective film disposed on the negative electrode 12 so as to cover the other exposed portion of the pair of exposed portions.

[0037] At least one of the first protective film and the second protective film preferably has the same shape as the positive electrode 11 side in order to suppress the occurrence of an internal short circuit when a strong impact is applied to the battery. That is, it is preferable to use a protective film in which at least one of the end side surfaces extending in the short direction of the negative electrode 12 and the end side surfaces extending in the longitudinal direction of the protective film are formed in a sloped shape. In this embodiment, the protective film in which at least one of the end side surfaces extending in the short direction of the electrode and the end side surfaces extending in the longitudinal direction of the protective film are formed in a sloped shape may be applied to at least one of the positive electrode 11 and the negative electrode 12, but is preferably applied to at least the positive electrode 11 side, and more preferably applied to both the positive electrode 11 side and the negative electrode 12 side.

[0038] The negative electrode composite layer preferably contains, for example, a negative electrode active material and a binder. The negative electrode 12 is produced, for example, by compressing a negative electrode composite layer formed by applying and drying a negative electrode composite slurry containing the negative electrode active material and the like to both sides of a negative electrode current collector. The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, and examples thereof include carbon materials such as natural graphite and artificial graphite, lithium-titanium composite oxides, metals that alloy with lithium such as Si and Sn, or alloys and composite oxides containing these. Examples of the binder include the same materials as those used in the positive electrode. Furthermore, a conductive material or the like may be included as necessary.

[0039] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include olefin-based resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, and a separator whose surface is coated with a material such as an aramid-based resin or ceramic may be used.

[0040] The present disclosure is further described by the following embodiments. Aspect 1: A nonaqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound in the longitudinal direction of the electrodes with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode has a strip-shaped current collector, composite layers disposed on both sides of the current collector, and a pair of exposed portions exposing both sides of the current collector, an electrode tab is joined to one of the pair of exposed portions, a first protective film containing a resin is disposed on the electrode so as to cover one of the pair of exposed portions, and a second protective film containing a resin is disposed on the electrode so as to cover the other of the pair of exposed portions, and at least one of the first protective film and the second protective film has an end side surface extending in the short direction of the electrode and an end side surface extending in the longitudinal direction of the electrode formed in a sloped shape. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein the resin contained in the first protective film and the resin contained in the second protective film are thermoplastic resins. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 2, wherein the thermoplastic resin includes at least one of a styrene-butadiene copolymer and a polyvinylidene fluoride resin.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein at least an end side surface of the protective film extending in the short direction of the electrode is formed in a sloped shape.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the protective film is both the first protective film and the second protective film.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the electrode is a positive electrode.

[0041] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Protruding portion, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 32 Positive electrode current collector, 34 Positive electrode composite layer, 36a, 36b Exposed portion, 38 First protective film, 38a, 38b, 38c, 38d, 40a, 40b End side surface, 40 Second protective film.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound along the longitudinal direction of the electrode with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode has a strip-shaped current collector, a composite layer disposed on both surfaces of the current collector, and a pair of exposed portions where both surfaces of the current collector are exposed, an electrode tab is joined to one of the pair of exposed portions, a first protective film containing a resin is disposed on the electrode so as to cover one of the pair of exposed portions, a second protective film containing a resin is disposed on the electrode so as to cover the other of the pair of exposed portions, and in at least one of the first protective film and the second protective film, at least one of an end side surface extending in the short-side direction of the electrode and an end side surface extending in the longitudinal direction of the electrode is formed in a slope shape.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin contained in the first protective film and the resin contained in the second protective film are thermoplastic resins.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the thermoplastic resin contains at least one of a styrene-butadiene copolymer and a polyvinylidene fluoride resin.

4. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein in the protective film, at least the end side surface extending in the short-side direction of the electrode is formed in a slope shape.

5. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the protective film is both the first protective film and the second protective film.

6. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the electrode is a positive electrode.

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