Nonaqueous electrolyte secondary battery

Abstract

Provided is a nonaqueous electrolyte secondary battery which is provided with an electrode body that is obtained by winding a positive electrode (11) and a negative electrode along the long-side direction of the electrodes with a separator being interposed therebetween, the nonaqueous electrolyte secondary battery being characterized in that: the positive electrode (11) has a belt-shaped positive electrode current collector (32), a positive electrode mixture layer (34) disposed on both surfaces of the positive electrode current collector (32), and a pair of exposure parts (36a, 36b) in which both surfaces of the positive electrode current collector (32) are exposed; a positive electrode tab (20) is joined to the exposure part (36a); a first protective layer (38) is disposed on the positive electrode (11) so as to cover the exposure part (36a); a second protective layer (40) is disposed on the positive electrode (11) so as to cover the exposure part (36b); and, with respect to the first protective layer (38), end parts (38a, 38b) that extend in the short-side direction of the positive electrode (11) are each formed in a non-linear shape in a plan view seen from the thickness direction of the positive electrode (11).

Description

Non-aqueous 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 layer is disposed on the electrode so as to cover one of the pair of exposed portions, and a second protective layer 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 layer and the second protective layer, at least one of an end extending in the short-side direction of the electrode and an end extending in the longitudinal direction of the electrode is formed in a non-linear shape in a plan view seen in the thickness direction of the electrode.

[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 nonaqueous electrolyte secondary battery according to an embodiment; FIG. 2 is a partial top view observed from one main surface side of a positive electrode according to an embodiment; FIG. 3 is a cross-sectional view taken along line L1-L1 in FIG. 2; FIG. 4 is a partial top view observed from one main surface side of a positive electrode according to another embodiment; FIG. 5 is a partial top view observed from one main surface side of a positive electrode according to another embodiment; FIG. 6 is a partial top view observed from one main surface side of a positive electrode according to another embodiment;

[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 layer 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 layer 38 disposed on the positive electrode composite layer 34 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 layer 40 disposed on the positive electrode composite layer 34 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 layer 38 preferably covers the entire exposed portion 36a, and the second protective layer 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 layer 38 also covers the positive electrode tab 20 located on the exposed portion 36a.

[0027] In this embodiment, in at least one of the first protective layer 38 and the second protective layer 40, at least one of the end portion extending in the short-side direction of the positive electrode 11 and the end portion extending in the longitudinal direction of the positive electrode 11 is formed in a non-linear shape in a plan view seen from the thickness direction of the positive electrode 11 (hereinafter, referred to as a plan view). Here, non-linear means including a non-linear portion such as an arc, curve, or bend. Furthermore, the end portion of the protective layer extending in the short-side direction of the positive electrode 11 is the end portion of the protective layer in the longitudinal direction of the positive electrode 11 in a plan view. Furthermore, the end portion of the protective layer extending in the longitudinal direction of the positive electrode 11 is the end portion of the protective layer in the short-side direction of the positive electrode 11 in a plan view.

[0028] An example of a nonlinear shape will be described below with reference to FIGS. 2 to 7 , using the first protective layer 38 as an example. In FIG. 2 , the ends (38a, 38b) of the first protective layer 38 extending in the short direction of the positive electrode 11 are entirely arc-shaped, bulging outward in a planar view. The nonlinear region may be the entire ends (38a, 38b) of the first protective layer 38, or a portion of the ends. For example, as shown in FIG. 4 , a portion of the ends (38a, 38b) of the first protective layer 38 may be arc-shaped, bulging outward in a planar view. Furthermore, for example, as shown in FIG. 5 , a portion of the end 38a of the first protective layer 38 may be arc-shaped, recessed inward in a planar view, and a portion of the end 38b of the first protective layer 38 may be arc-shaped, bulging outward in a planar view. The nonlinear shape is not particularly limited, and may be, for example, a wave shape as shown in FIG. 6 or a sawtooth shape as shown in FIG. 7 in addition to the aforementioned arc shape. Such a nonlinear shape may be applied only to the end 38a of the first protective layer 38, or only to the end 38b of the first protective layer 38. Furthermore, such a nonlinear shape may be applied to at least one of the end portions 38c and 38d of the first protective layer 38 extending in the longitudinal direction of the positive electrode 11. Furthermore, such a nonlinear shape may be applied to at least one of the end portions of the second protective layer 40 extending in the lateral direction of the positive electrode 11 and the end portions of the second protective layer 40 extending in the longitudinal direction of the positive electrode 11.

[0029] In this embodiment, in at least one of the first protective layer 38 and the second protective layer 40, at least one of the ends extending in the short direction of the positive electrode 11 and the ends extending in the longitudinal direction of the positive electrode 11 is formed nonlinearly in a plan view. This is thought to alleviate the linear pressure applied to the end, even when a strong impact is applied to the battery. This suppresses breakage of the separator in contact with the protective layer at the end portion of the protective layer, making internal short circuits less likely to occur. The aspect in which the end portion of the protective layer is formed nonlinearly is preferably applied to both the first protective layer 38 and the second protective layer 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 layer 38 and the second protective layer 40, the ends extending in the short direction of the positive electrode 11 are more likely to be subjected to high linear pressure when an impact is applied to the battery than the ends extending in the long direction of the positive electrode 11, so it is preferable that at least the ends extending in the short direction of the positive electrode 11 are formed in a non-linear shape in a plan view. The ends of the first protective layer 38 and the second protective layer 40 extending in the long direction of the positive electrode 11 may be located outside the positive electrode 11 and not supported by the positive electrode 11, but the ends extending in the short direction of the positive electrode 11 are supported by the positive electrode 11 and are therefore more likely to be subjected to high linear pressure when an impact is applied to the battery.

[0031] The first protective layer 38 and the second protective layer 40 are made of, for example, a protective tape or a protective film containing resin.

[0032] The protective tape has, for example, a base layer and an adhesive layer provided on the base layer. The edges of the protective tape are cut to have the non-linear shape described above. Then, the protective tape is attached to the positive electrode 11 with the adhesive layer side facing the positive electrode 11 so as to cover the exposed portions (36 a, 36 b) with the protective tape.

[0033] The base layer is not particularly limited as long as it is a layer mainly made of an organic material. Here, "mainly made of an organic material" means that the proportion of organic material is the highest among the materials constituting the base layer. In terms of the strength of the protective tape, the content of the organic material is, for example, preferably 80% by mass or more, more preferably 90% by mass or more, relative to the total mass of the base layer. Examples of organic materials include polyolefins (e.g., polyethylene, polypropylene, etc.), polystyrene, polyesters (e.g., polyethylene terephthalate, etc.), polyimides, polyamides, polyamideimides, polycarbonates, and polyphenylene sulfides.

[0034] The thickness of the substrate layer is not limited, but is preferably, for example, 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 30 μm or less.

[0035] The adhesive layer is formed, for example, by applying an adhesive to one surface of the substrate. Examples of adhesives include acrylic resins, natural rubber, synthetic rubber, silicone, epoxy resins, melamine resins, and phenolic resins. These may be used alone or in combination of two or more. Furthermore, the adhesive layer may contain additives such as tackifiers, crosslinkers, antioxidants, colorants, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, and antistatic agents, as needed.

[0036] The protective tape may include a heat-resistant layer. The heat-resistant layer may be provided between the base layer and the adhesive layer, or on the base layer on the side opposite the adhesive layer. The heat-resistant layer may contain an inorganic filler such as titania, alumina, silica, or zirconia.

[0037] The thickness of the protective tape is not particularly limited, but may be, for example, in the range of 10 μm or more and 60 μm or less.

[0038] The protective film containing resin is formed, for example, by applying a resin solution onto the positive electrode mixture layer 34 and the exposed portions (36 a, 36 b). When applying the resin solution, it is preferable to mask the positive electrode mixture layer 34 etc. so that the edges of the protective film have the non-linear shape described above.

[0039] Examples of the resin contained in the protective film (i.e., the resin contained in the resin solution) include curable resins and thermoplastic resins. Examples of the curable resin include thermosetting resins and photocurable resins. Examples of the thermosetting resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as naphthalene-containing novolac-type epoxy resins, trisphenolmethane-type epoxy resins, tetrakisphenolethane-type epoxy resins, dicyclopentadiene-type epoxy resins, and phenolbiphenyl-type epoxy resins, biphenyl-type epoxy resins such as tetramethylbiphenyl-type epoxy resins, 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 resins, 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, polyethersulfone resin, etc. The protective film may contain an inorganic filler such as titania, alumina, silica, or zirconia.

[0040] 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) that expose 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 that are closer to the winding direction terminal 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 that are closer to the winding start side of the negative electrode 12, or at both longitudinal ends of the negative electrode 12 (the ends that are closer to the winding start side and the winding end side of the negative electrode). 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.

[0041] Although not shown in the drawings, the nonaqueous electrolyte secondary battery 10 includes a first protective layer 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 layer disposed on the negative electrode 12 so as to cover the other of the pair of exposed portions.

[0042] At least one of the first protective layer and the second protective layer preferably has the same shape as the positive electrode 11 side in terms of suppressing 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 layer in which at least one of the ends extending in the short direction and the long direction of the negative electrode 12 in the protective layer is formed non-linearly in a planar view. Furthermore, like the positive electrode 11 side, the first protective layer and the second protective layer may be composed of a protective tape, a protective film containing a resin, or the like. In this embodiment, a protective layer in which at least one of the ends extending in the short direction and the long direction of the electrode is formed non-linearly in a planar view 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.

[0043] The negative electrode mixture 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 mixture layer formed by applying and drying a negative electrode mixture 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 binders include the same materials as those used in the positive electrode. The negative electrode mixture layer may contain a conductive material, etc., as necessary.

[0044] 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.

[0045] The present disclosure will be further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween along the longitudinal direction of the electrodes, 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 layer is disposed on the electrode so as to cover one of the pair of exposed portions, and a second protective layer 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 layer and the second protective layer, at least one of an end extending in the short-side direction of the electrode and an end extending in the longitudinal direction of the electrode is formed in a non-linear shape in a plan view seen in the thickness direction of the electrode. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein at least an end of the protective layer extending in the short-side direction of the electrode is formed in a non-linear shape in a plan view seen from the thickness direction of the electrode.Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the protective layer is both the first protective layer and the second protective layer.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the electrode is a positive electrode.

[0046] 10 Lithium ion 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 Insulator, 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 layer, 38a, 38b, 38c, 38d End portion, 40 Second protective layer.

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 layer is disposed on the electrode so as to cover one of the pair of exposed portions, a second protective layer 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 layer and the second protective layer, at least one of an end portion extending in the short-side direction of the electrode and an end portion extending in the longitudinal direction of the electrode is formed in a non-linear shape in a plan view as viewed from the thickness direction of the electrode.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein in the protective layer, at least the end portion extending in the short-side direction of the electrode is formed in a non-linear shape in a plan view as viewed from the thickness direction of the electrode.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the protective layer is both the first protective layer and the second protective layer.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the electrode is a positive electrode.

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