Nonaqueous-electrolyte secondary battery

Abstract

This nonaqueous-electrolyte secondary battery comprises an electrode body in which a positive electrode (11) and a negative electrode are arranged with a separator interposed therebetween. The positive electrode (11) and / or the negative electrode comprises mixture layers (32) disposed on both surfaces of an electrode core (31) and protective layers (40a, 40b) disposed on both surfaces of the electrode core (31). At least some part of each of mixture-layer non- formation portions (33a, 33b) disposed on both surfaces of the electrode core is covered with the protective layer. On each thickness-direction side of the electrode core, some part of the protective layer is disposed between the electrode core (31) and the mixture layer (32). On both surfaces of the electrode core, the positions (E1, E2) of the boundaries between the mixture-layer formation portions (34a, 34b), in which the mixture layers are directly formed on the electrode core (31), and protective-layer formation portions (35a, 35b), in which the protective layers are formed, are arranged so as not to coincide with each other along the thickness direction.

Description

Nonaqueous electrolyte secondary battery

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

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been known that include an electrode assembly in which a positive electrode and a negative electrode are disposed with a separator interposed therebetween. The positive electrode includes a positive electrode core and a positive electrode mixture layer formed on the positive electrode core.

[0003] Patent Document 1 discloses a positive electrode for a non-aqueous electrolyte secondary battery, in which a region where a positive electrode core is exposed without a positive electrode mixture layer is provided at a widthwise end of the positive electrode, and a protective layer containing insulating particles such as inorganic particles as a main component is provided in this region. Patent Document 1 also discloses that a part of the protective layer is located between the positive electrode core and the mixture layer.

[0004] Japanese Patent Application Laid-Open No. 2020-167067

[0005] In the manufacturing process of electrodes such as positive electrodes, it is considered that the protective layer contains inorganic particles and a binder, and the mixture layer is compressed by pressing to increase the density of the active material in the mixture layer. In the configuration described in Patent Document 1, if the positive electrode mixture layer and the protective layer are simply applied to both sides of the positive electrode core in a symmetrical positional relationship on both sides in the thickness direction of the positive electrode core, cracks may occur in the positive electrode mixture layer near the boundary between the positive electrode mixture layer and the protective layer during the pressing process. Furthermore, even if cracks do not occur during the pressing process, there is a problem in that cracks are likely to occur in the positive electrode mixture layer near the boundary between the positive electrode mixture layer and the protective layer when a load of a certain level or more is applied to the positive electrode, such as during winding or charge / discharge.

[0006] Therefore, an object of the nonaqueous electrolyte secondary battery of the present disclosure is to suppress the occurrence of cracks in the mixture layer when a protective layer is provided on both sides of the electrode to cover the portion where the mixture layer is not formed.

[0007] The non-aqueous electrolyte secondary battery according to the present disclosure is a non-aqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are arranged with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode includes an electrode core, a mixture layer provided on both sides of the electrode core, and a protective layer provided on both sides of the electrode core and having inorganic particles and a binder, wherein mixture layer-free portions where no mixture layer is formed are provided on both sides of the electrode core, and at least a portion of each of the mixture layer-free portions provided on both sides of the electrode core is covered with a protective layer, and a portion of the protective layer is provided between the electrode core and the mixture layer on both sides of the electrode core in the thickness direction, and the boundary positions on both sides of the electrode core between the mixture layer-formed portion where the mixture layer is formed directly on the electrode core and the protective layer-formed portion where a protective layer is formed do not overlap each other in the thickness direction.

[0008] In the nonaqueous electrolyte secondary battery according to the present disclosure, in a configuration in which protective layers are provided on both sides of an electrode to cover portions where a mixture layer is not formed, a portion of the protective layer is provided between the electrode core and the mixture layer on both sides in the thickness direction of the electrode core. Furthermore, on both sides of the electrode core, the boundary positions between the mixture layer-forming portion where the mixture layer is formed directly on the electrode core and the protective layer-forming portion where a protective layer is formed are arranged so as not to overlap each other in the thickness direction of the electrode core. This makes it possible to suppress the occurrence of cracks in the mixture layer near the boundary positions between the mixture layer-forming portion and the protective layer-forming portion.

[0009] Fig. 2 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. Fig. 3 is a schematic development view of a positive electrode, which is one of the electrodes shown in Fig. 1. Fig. 4 is a cross-sectional view of Fig. 2 taken along the line AA in Fig. 2. Fig. 5 is a view corresponding to Fig. 3 showing a case in which the positive electrode is bent during winding. Fig. 6 is a view corresponding to Fig. 3 of a positive electrode constituting a nonaqueous electrolyte secondary battery of a comparative example.

[0010] Hereinafter, a nonaqueous electrolyte secondary battery according to the present disclosure will be described with reference to the drawings. Figures 1 to 4 illustrate a nonaqueous electrolyte secondary battery including a wound electrode assembly, in which a mixture layer-free portion and a protective layer are provided at the end of the positive electrode on the winding start side. It should be noted that the nonaqueous electrolyte secondary battery according to the present disclosure is not limited to the embodiments described below.

[0011] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment of the present invention. Fig. 2 is a schematic development view of a positive electrode 11, which is one of the electrodes shown in Fig. 1.

[0012] 1 , the nonaqueous electrolyte secondary battery 10 includes a strip-shaped positive electrode 11 and negative electrode 12 having opposite polarities, a separator 13, and a wound electrode assembly 14 in which the positive electrode 11 and negative electrode 12 are wound with the separator 13 interposed therebetween. The nonaqueous electrolyte secondary battery 10 also includes a cylindrical outer can 15 with a bottom that houses the electrode assembly 14, and a sealing body 16 that closes the opening of the outer can 15. The outer can 15 houses a nonaqueous electrolyte together with the electrode assembly 14. The positive electrode 11 corresponds to one electrode, and the negative electrode 12 corresponds to the other electrode.

[0013] The exterior can 15 is a cylindrical metal container with a bottom, and has a tubular portion 15a and a bottom provided at one end of the tubular portion 15a in the axial direction α. ​​The exterior can 15 has a grooved portion 21 (described below) formed on the other end in the axial direction α, which is the open end of the tubular portion 15a, and the sealing body 16 is supported by the grooved portion 21 to close the opening of the exterior can 15. Hereinafter, for convenience of explanation, the sealing body 16 side of the nonaqueous electrolyte secondary battery 10 will be referred to as the top, and the bottom side of the exterior can 15 will be referred to as the bottom.

[0014] The nonaqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolytic solution), and may be a solid electrolyte using a gel polymer or the like. The nonaqueous electrolyte secondary battery 10 is preferably a lithium ion battery. The electrolyte salt may be, for example, LiBF ４ , LiPF ６ Examples of the non-aqueous solvent include esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine.

[0015] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP). From the viewpoint of suppressing a decrease in the charge-discharge cycle characteristics of a nonaqueous electrolyte secondary battery or improving the output characteristics, the nonaqueous electrolyte preferably contains 5% by mass or more of FEC, and more preferably 5% by mass to 15% by mass of FEC, relative to the mass of the nonaqueous electrolyte.

[0016] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0017] As described above, the electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction β of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and lateral directions of the electrode plate. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0018] A positive electrode tab 19 and a negative electrode tab 20 are connected to the electrode body 14. The positive electrode tab 19 electrically connects the positive electrode 11 and the sealing body 16. The positive electrode tab 19 is provided, for example, at the center of the positive electrode 11 in the longitudinal direction of the electrode plate, at a position away from the winding start end and winding end end of the electrode body 14, approximately at the center of the radial direction β of the electrode body 14. The positive electrode tab 19 corresponds to an electrode tab. The positive electrode tab 19 is a strip-shaped conductive member. There are no particular limitations on the material of which the positive electrode tab 19 is made, but it is preferable that the positive electrode tab 19 be made of a metal containing aluminum as its main component.

[0019] The negative electrode tab 20 is joined to an exposed portion of the core provided at the winding start end, which is one end in the longitudinal direction of the negative electrode 12. In the example shown in FIG. 1 , the positive electrode tab 19 passes through the opening of the upper insulating plate 17 and extends toward the sealing body 16, and is joined to the underside of the sealing body 16, with the sealing body 16 serving as the positive electrode terminal. The negative electrode tab 20 passes through a through-hole in the annular lower insulating plate 18, is bent to fit along the inner surface of the bottom of the outer can 15, and is connected to the inner surface of the bottom of the outer can 15 by welding or the like, with the outer can 15 serving as the negative electrode terminal. The negative electrode tab 20 is a strip-shaped conductive member. The material of the negative electrode tab 20 is not particularly limited. The negative electrode tab 20 is preferably made of a metal primarily composed of nickel or copper, or a metal containing both nickel and copper.

[0020] An exposed portion of the surface of the negative electrode core that constitutes the negative electrode 12 is disposed on the outermost peripheral surface of the electrode body 14, and the negative electrode core abuts against the inner peripheral surface of the tubular portion 15a of the outer can 15. This electrically connects the winding start end and winding end of the negative electrode 12 to the outer can 15, ensuring good current collection.

[0021] Referring to Figures 2 and 3, the positive electrode 11 includes a strip-shaped positive electrode core 31 corresponding to the electrode core, a positive electrode mixture layer 32 formed on both sides of the positive electrode core 31, and positive electrode protective layers 40a, 40b formed on both sides of the positive electrode core 31. In Figure 2, the positive electrode mixture layer 32 is indicated by a dark sandy area, and the positive electrode protective layers 40a, 40b are indicated by a light sandy area. The positive electrode core 31 can be a foil of a metal such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. A suitable positive electrode core 31 is a foil of a metal primarily composed of aluminum or an aluminum alloy. The thickness of the positive electrode core 31 is, for example, 10 μm to 30 μm.

[0022] The positive electrode mixture layer 32 preferably contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is formed on both sides of the positive electrode core. The thickness of the positive electrode mixture layer 32 is, for example, 40 μm to 100 μm. The positive electrode active material may be, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like. The positive electrode tab 19 is joined to the positive electrode core 31 by ultrasonic welding or the like.

[0023] The positive electrode 11 is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode core 31, followed by drying and compressing.

[0024] Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium-containing transition metal oxides are not particularly limited, but include those represented by the general formula Li １＋ｘ MO ２ (wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0025] Examples of the conductive agent include carbon black (CB) such as acetylene black (AB) and Ketjen black, and carbon materials such as graphite. Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These may be used alone or in combination of two or more.

[0026] At the winding start end, which is the end in the length direction (the direction of arrow γ in FIG. 2 ) of the positive electrode core 31, there are provided on both sides a mixture layer-free portion 33a on the outer surface of the winding and a mixture layer-free portion 33b on the inner surface of the winding, where the positive electrode mixture layer is not formed, over the entire width direction (the direction of arrow δ in FIG. 2 ) of the positive electrode 11. The mixture layer-free portions 33a, 33b are portions of the surface of the positive electrode core 31 that are not covered with the positive electrode mixture layer 32. Almost the entire area of ​​each mixture layer-free portion 33a, 33b is covered with protective layers 40a, 40b, which will be described later.

[0027] The positive electrode tab 19 is joined, for example, by ultrasonic welding, to a core exposed portion formed over the entire width direction at the longitudinal middle portion of one surface of the positive electrode 11. In this state, the positive electrode tab 19 extends from one end (upper end) of the positive electrode core 31 in the width direction δ.

[0028] The negative electrode 12 has a strip-shaped negative electrode core corresponding to the electrode core, and negative electrode mixture layers formed on both sides of the negative electrode core. The negative electrode core can be made of a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core is, for example, 5 μm to 30 μm. The negative electrode mixture layer contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR). The thickness of the negative electrode mixture layer is, for example, 40 μm to 100 μm. Examples of the negative electrode active material include graphite and Si-containing materials. The negative electrode tab 20 is preferably joined to the negative electrode core by ultrasonic welding or the like.

[0029] The negative electrode 12 is produced by applying a negative electrode mixture slurry containing, for example, a negative electrode active material, a binder, water, and the like, to both sides of a negative electrode core, followed by drying and compressing.

[0030] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys or composite oxides containing these, can be used. The binder contained in the negative electrode mixture layer is, for example, the same resin as that used in the positive electrode 11. When preparing the negative electrode mixture slurry using an aqueous solvent, styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, etc. can be used. These may be used alone or in combination of two or more.

[0031] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The separator 13 is preferably made of an olefin resin such as polyethylene or polypropylene. The thickness of the separator 13 is, for example, 10 μm to 50 μm. Separators 13 tend to be thinner as batteries become higher in capacity and power output. The separator 13 has a melting point of, for example, about 130°C to 180°C.

[0032] An annular gasket 27 is interposed between the exterior can 15 and the sealing body 16. The sealing body 16 is fixed by crimping to the upper end portion, which is the open end portion of the exterior can 15, via the gasket 27. Specifically, the upper end portion of the exterior can 15 is crimped to the peripheral edge of the sealing body 16 via the gasket 27. This seals the inside of the battery.

[0033] The exterior can 15 has a grooved portion 21 formed, for example, by pressing the side surface from the outside, that supports the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior can 15, and supports the sealing body 16 on its upper surface.

[0034] The sealing body 16 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are layered. Each component constituting the sealing body 16 has, for example, a disk or ring shape, and each component except for the insulating member 24 is electrically connected to each other. The cap 26 has an annular flange on its outer periphery and a hat-like shape with a cylindrical portion in the center with a closed upper end. The internal terminal plate 22 has a central hole that penetrates vertically. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. The components constituting the sealing body 16 are stacked axially on the flange portion of the sealing body 16.

[0035] When the internal pressure of the battery increases and reaches a predetermined value, the lower valve body 23 deforms and pushes the upper valve body 25 toward the cap 26, causing it to break, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure further increases and reaches a predetermined value, the upper valve body 25 breaks, causing gas to be discharged from the opening 26a of the cap 26.

[0036] The configuration of the winding start end of the positive electrode will be described in detail below with reference to Figures 2 and 3. The regions 33a, 33b without a mixture layer formed thereon are provided from the winding start end 11a of the positive electrode 11 toward the winding end, and the regions 33a, 33b have the same predetermined length on both sides of the positive electrode 11. The regions 33a, 33b without a mixture layer formed thereon are provided across almost the entire width of the positive electrode 11.

[0037] These mixture layer non-forming portions 33 a, 33 b reduce the thickness of winding start end 11 a of the positive electrode, thereby suppressing stress concentration on negative electrode 12 facing winding start end 11 a of positive electrode 11. This makes it possible to suppress deformation of negative electrode 12 in the vicinity of winding start end 11 a of positive electrode 11.

[0038] The length of the portions 33a, 33b where no mixture layer is formed is preferably 1.0 mm or more in the longitudinal direction of the positive electrode 11. By making the lengths of the portions 33a, 33b where no mixture layer is formed 1.0 mm or more, deformation of the negative electrode 12 near the winding start end 11a of the positive electrode 11 can be further suppressed. The upper limit of the length of the portions 33a, 33b where no mixture layer is formed is not particularly limited, but is, for example, 5.0 mm.

[0039] Furthermore, the mixture layer-free portions 33a, 33b are covered with protective layers 40a, 40b that are thinner than the positive electrode mixture layer 32. The protective layers 40a, 40b contain inorganic particles and a binder, which are insulating materials, and the positive electrode core 31 has lower resistance than the positive electrode mixture layer 32. Therefore, contact between the mixture layer-free portions 33a, 33b and the negative electrode 12 would cause an internal short circuit. Therefore, by covering the mixture layer-free portions 33a, 33b with the protective layers 40a, 40b containing inorganic particles and a binder, contact between the mixture layer-free portions 33a, 33b and the negative electrode 12 is prevented, thereby preventing an internal short circuit. The protective layers 40a, 40b are formed from the winding start end 11a of the positive electrode 11 toward the winding end, covering almost the entire area of ​​the mixture layer-free portions 33a, 33b. This further prevents an internal short circuit.

[0040] Furthermore, parts of the protective layers 40a, 40b are provided between the positive electrode core 31 and the positive electrode mixture layer 32. This improves the adhesion between the positive electrode core 31 and the positive electrode mixture layer 32, suppresses peeling of the positive electrode mixture layer 32 near the winding start end 32a of the positive electrode mixture layer 32, and more reliably prevents the mixture layer non-forming portions 33a, 33b from being exposed from the protective layers 40a, 40b.

[0041] In the longitudinal direction of the positive electrode 11, the lengths (B1+B2 and B2) of the intervening regions 41a and 41b, which are regions of the protective layers 40a and 40b provided between the positive electrode core 31 and the positive electrode mixture layer 32, are preferably 0.5 mm or more, and more preferably 1.0 mm or more. By making the lengths of the intervening regions 41a and 41b 0.5 mm or more, peeling of the positive electrode mixture layer 32 near the winding start end 32a of the positive electrode mixture layer 32 can be further suppressed.

[0042] As described above, the protective layers 40a and 40b contain inorganic particles and a binder. The mass ratio of the inorganic particles to the binder is preferably in the range of 100:0.5 to 100:50.

[0043] The binder preferably contains a resin material. The binder not only functions to bind the inorganic particles together, but also functions as a binder that bonds the positive electrode core 31 and the positive electrode mixture layer 32. This can also prevent the positive electrode mixture layer 32 from peeling off near the winding start end 32 a of the positive electrode mixture layer 32.

[0044] The resin material contained in the binder is preferably a polymer material, and examples thereof include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide-based resins, polyamide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0045] Examples of inorganic materials constituting the inorganic particles include metal oxides, metal nitrides, metal fluorides, and metal carbides. Examples of metal oxides include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide. Examples of metal nitrides include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluorides include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of metal carbides include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. Furthermore, examples of inorganic materials include zeolite (M ２／ｎ O.Al ２ O ３ xSiO ２ ・yH ２ O, M is a metal element, n is the valence of M, x≧2, y≧0), porous aluminosilicates such as talc (Mg ３ Si ４ O １０ (OH) ２ ), layered silicates such as barium titanate (BaTiO ３), strontium titanate (SrTiO ３ These may be used alone or in combination of two or more.

[0046] The average particle size of the inorganic particles is, for example, 0.05 μm or more and 2 μm or less. The average particle size of the inorganic particles means the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of the inorganic particles can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac-Bell) using water as a dispersion medium.

[0047] When the protective layers 40a and 40b contain inorganic particles and a binder as the main components, they may further contain a conductive agent in addition to the inorganic particles and the binder. Here, the term "main component" refers to the component with the highest mass ratio among the components constituting the protective layers 40a and 40b. Examples of the conductive agent contained in the protective layers 40a and 40b include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, graphene, and other carbon materials. These may be used alone or in combination of two or more.

[0048] The thickness of the protective layers 40a, 40b may be, for example, 3 μm or more and 40 μm or less, or 5 μm or more and 30 μm or less, from the viewpoint of suppressing internal short circuits and suppressing peeling of the positive electrode mixture layer 32. The thickness of the protective layers 40a, 40b is preferably 50% or less of the maximum thickness of the positive electrode mixture layer 32, and more preferably 30% or less.

[0049] Furthermore, in the embodiment, on both sides of the positive electrode core 31 in the thickness direction, boundary positions E1 and E2 between the mixture layer forming portions 34a and 34b where the positive electrode mixture layer 32 is formed directly on the positive electrode core 31 and the protective layer forming portions 35a and 35b where the protective layers 40a and 40b are formed are arranged so as not to overlap with each other in the thickness direction of the positive electrode core 31. Because of this configuration, in FIG. 3 , which shows the developed state of the positive electrode 11, the boundary positions E1 and E2 are different from each other in the length direction γ of the positive electrode 11. This can suppress the occurrence of cracks in the positive electrode mixture layer 32. This is thought to be because the boundary positions E1 and E2 are different in the length direction γ of the positive electrode 11, which allows the stress concentration positions in the positive electrode mixture layer 32 on both sides of the positive electrode 11 to be different on both sides in the thickness direction of the positive electrode 11.

[0050] In the length direction γ of the developed state of the positive electrode 11, which corresponds to the winding direction γ2, the distance B1 ( FIG. 3 ) between boundary positions E1 and E2 on both sides in the thickness direction of the positive electrode core 31 is preferably 0.5 mm or more. This allows the positions of stress concentration in the positive electrode mixture layer 32 on both sides of the positive electrode 11 to be significantly different on both sides in the thickness direction of the positive electrode 11, thereby further suppressing the occurrence of cracks in the positive electrode mixture layer 32.

[0051] 4, when the positive electrode 11 is wound, it is preferable that the side having the longer intervening region 41a of both thickness directions of the positive electrode 11 is disposed on the outer side of the winding facing the outer periphery. When the positive electrode 11 is wound, as shown by arrows C1 and C2, stress acts in a compressive direction along the winding direction between the winding start end of the positive electrode mixture layer 32 on the inner side of the winding and the inner circumferential surface of the positive electrode core 31. This prevents the positive electrode mixture layer 32 on the inner side of the winding from moving in a direction that would cause it to peel off from the protective layer 40b.

[0052] On the other hand, when the positive electrode 11 is wound, as indicated by arrows D1 and D2, a tensile stress acts in the winding direction between the winding start end of the positive electrode mixture layer 32 on the outer side of the winding and the outer peripheral surface of the positive electrode core 31. This causes the positive electrode mixture layer 32 on the outer side of the winding to move in a direction that causes it to peel away from the protective layer 40a. However, because the intervening region 41a on the outer side of the winding is longer than the intervening region 41b on the inner side of the winding, the peel resistance acting between the inner peripheral surface of the positive electrode mixture layer 32 on the outer side of the winding and the outer peripheral surface of the protective layer 40a can be made higher than when the outer and inner sides of the winding are reversed. This prevents the positive electrode mixture layer 32 from peeling away from the protective layer 40a.

[0053] In order to prevent this peeling, the length (B1+B2) of the intervening region 41a on the outer side of the wound cathode 11 shown in Fig. 3 is preferably (B1+B2) ≥ 3.0 mm and more preferably (B1+B2) ≤ 10.0 mm.

[0054] The protective layers 40a and 40b can be formed by applying a protective layer slurry containing inorganic particles and a binder to the surface of the positive electrode core 31 and drying the coating. The protective layer slurry is prepared by mixing the inorganic particles and the binder and adding an appropriate amount of water, N-methyl-2-pyrrolidone (NMP), or the like. Examples of methods for applying the protective layer slurry include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing. The method for drying the prepared coating is not particularly limited, and may be, for example, natural drying, ventilation drying using warm air or the like, heat drying, reduced pressure / vacuum drying, or a combination thereof. After forming the protective layers 40a, 40b, positive electrode mixture slurry is applied so as to overlap parts of the protective layers 40a, 40b while forming the mixture layer non-forming parts 33a, 33b, and the coating is dried and compressed, thereby forming the protective layers 40a, 40b between the positive electrode core 31 and the positive electrode mixture layer 32. The mixture layer non-forming parts 33a, 33b and the protective layers 40a, 40b may be formed at the winding end side of the positive electrode 11 in addition to the winding start side.

[0055] As described above, the positive electrode 11 of this embodiment is configured such that the protective layers 40a, 40b covering the mixture layer non-forming portions 33a, 33b are provided on both sides of the positive electrode 11, and portions of the protective layers 40a, 40b are provided between the positive electrode core 31 and the positive electrode mixture layer 32 on both sides in the thickness direction of the positive electrode core 31. Furthermore, on both sides of the positive electrode core 31, boundary positions E1, E2 between the mixture layer forming portions 34a, 34b where the positive electrode mixture layer 32 is formed directly on the positive electrode core 31 and the protective layer forming portions 35a, 35b where the protective layers 40a, 40b are formed are different from each other in the length direction γ of the positive electrode 11. This allows the stress concentration positions in the positive electrode mixture layer 32 on both sides of the positive electrode 11 to be arranged so as not to overlap each other in the thickness direction of the positive electrode 11, thereby suppressing the occurrence of cracks in the positive electrode mixture layer 32.

[0056] 5 is a diagram corresponding to FIG. 3 of a positive electrode 50 constituting a nonaqueous electrolyte secondary battery of a comparative example. In this comparative example, protective layers 60a, 60b are provided on both sides of the positive electrode 50 to cover the mixture layer-free portions 53a, 53b. Portions of the protective layers 60a, 60b are provided between the positive electrode core 51 and the positive electrode mixture layer 52 on both sides of the positive electrode core 51 in the thickness direction. Furthermore, on both sides of the positive electrode core 51, boundary positions F1, F2 between mixture layer-formed portions 54a, 54b where the positive electrode mixture layer 52 is formed directly on the positive electrode core 51 and protective layer-formed portions 55a, 55b where the protective layers 60a, 60b are formed overlap each other in the thickness direction of the positive electrode core 51. In this case, in the length direction γ of the positive electrode 50, the lengths B2 of the intervening regions 54, which are regions of the protective layers 60a, 60b provided between the positive electrode core 51 and the positive electrode mixture layer 52, are the same.

[0057] In such a comparative example, the positions of stress concentration in the positive electrode mixture layer 52 on both sides of the positive electrode 50 tend to coincide with the longitudinal direction of the positive electrode 50. Therefore, in the comparative example, cracks may occur in the positive electrode mixture layer 52 at the boundaries between the mixture layer forming portions 54a, 54b and the protective layers 60a, 60b during the pressing process. That is, cracks may occur in the positions indicated by arrows G1 and G2 in the positive electrode mixture layer 52 in FIG. 5. Even if cracks do not occur during the pressing process, cracks are likely to occur in the positions indicated by arrows G1 and G2 in the positive electrode mixture layer 52 when a load of a certain level or greater is applied to the positive electrode 50 during winding, charge / discharge, or the like.

[0058] As a modified example of the embodiment, each of the positive electrode mixture layers on both sides in the thickness direction of the positive electrode may have an inclined portion in which the surface of the positive electrode mixture layer is inclined so that the thickness of the positive electrode mixture layer decreases toward the winding start end of the positive electrode mixture layer. By providing the inclined portion, it is possible to reduce the thickness of the winding start end of the positive electrode while eliminating a step formed near the winding start end of the positive electrode mixture layer. This further alleviates stress concentration on the negative electrode 12, and further suppresses deformation of the negative electrode, even when charging and discharging are repeated.

[0059] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0060] Example 1 Preparation of Positive Electrode Mixture Slurry Lithium nickel oxide (LiNi) containing cobalt and aluminum was used as the positive electrode active material. ０．８８ Co ０．０９ Al ０．０３ O ２ 100 parts by mass of this positive electrode active material, 1 part by mass of acetylene black (AB) as a conductive agent, and 1 part by mass of polyvinylidene fluoride (PVDF) as a binder were mixed together, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a positive electrode mixture slurry.

[0061] [Preparation of Slurry for Protective Layer] Titanium oxide (TiO ２ 100 parts by mass of the cellulose acylate sintered body and 20 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed together, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a positive electrode mixture slurry.

[0062] [Preparation of Positive Electrode] The above-mentioned protective layer slurry was applied to the winding start and end positions of both sides of a positive electrode substrate substrate having a shape in which at least 50 positive electrode substrates made of aluminum foil having a thickness of 15 μm and a width of 62.6 mm were connected, while changing the length on both sides in the thickness direction as shown in FIG. 3. The coating was dried to form a protective layer. Then, the above-mentioned positive electrode mixture slurry was applied to both sides of the positive electrode substrate substrate so as to overlap a portion of the protective layer, while forming a mixture layer non-forming portion at the winding start and end positions. After drying the coating, the positive electrode was cut to a predetermined electrode size and compressed with a roller at a linear pressure stronger than usual to prepare a positive electrode. At this time, the overlap length B2 of the intervening regions 41a, 41b on both sides of the thickness direction of the positive electrode in the length direction γ was 3.0 mm, and the length difference B1 of the intervening regions 41a, 41b on both sides of the thickness direction of the positive electrode in the length direction γ was 0.5 mm.

[0063] [Confirmation of the Presence or Absence of Cracks in Positive Electrode During Pressing Process] The presence or absence of cracks in the positive electrode mixture layer due to compression during the press process was confirmed at a total of 100 locations, from the winding start end and winding end, of 50 positive electrodes obtained from the positive electrode core substrate. At this time, the presence or absence of cracks was evaluated as "present" when cracks were present at one or more locations, and the absence or absence of cracks was evaluated as "absent" when no cracks were present. <Example 2> A positive electrode was produced in the same manner as in Example 1, except that the difference B1 in the length direction γ of the intervening regions 41 a, 41 b on both sides of the thickness direction of the positive electrode was set to 1.0 mm, and the presence or absence of cracks was confirmed.

[0064] Example 3 A positive electrode was produced in the same manner as in Example 1, except that the difference B1 in the length in the longitudinal direction γ of the intervening regions 41 a, 41 b on both sides in the thickness direction of the positive electrode was set to 2.0 mm, and the presence or absence of cracks was confirmed.

[0065] Example 4 A positive electrode was produced in the same manner as in Example 1, except that the difference B1 in the length direction γ of the intervening regions 41 a, 41 b on both sides of the thickness direction of the positive electrode was set to 3.0 mm, and the occurrence of cracks was confirmed.

[0066] Comparative Example 1 A positive electrode was produced in the same manner as in Example 1, except that, in the same manner as in the configuration shown in FIG. 5 , the difference B1 in the length in the longitudinal direction γ of the intervening region 54 on both sides in the thickness direction of the positive electrode was set to 0.0 mm, that is, the length B2 of the intervening region 54 on both sides in the thickness direction of the positive electrode was set to the same. The presence or absence of cracks was then confirmed.

[0067] Table 1 shows the results of Examples 1 to 4 and Comparative Example 1.

[0068]

[0069] As shown in Table 1, no cracks occurred in the positive electrode mixture layer in the positive electrodes of Examples 1 to 4, but cracks occurred in the positive electrode mixture layer in the positive electrode of Comparative Example 1. Therefore, it was confirmed that the occurrence of cracks in the positive electrode mixture layer can be suppressed by covering the portion where the mixture layer is not formed with a protective layer, providing a part of the protective layer between the positive electrode core and the positive electrode mixture layer, and differentiating the length of the intervening region on both sides in the thickness direction of the positive electrode.

[0070] In the above embodiment, a configuration including a wound electrode body was described in which a mixture layer non-forming portion and a protective layer were provided at the winding start end of the positive electrode. However, the configuration of the present disclosure is not limited to this. For example, the configuration of the present disclosure can also be applied to a configuration including a wound electrode body in which a mixture layer non-forming portion and a protective layer are provided at the widthwise end of the positive electrode that coincides with the axial direction of the electrode body. The configuration of the present disclosure can also be applied to a configuration including a stacked electrode body in which multiple positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween, in which a mixture layer non-forming portion and a protective layer are provided at the widthwise or lengthwise end of the positive electrode. In the above embodiment, a case was described in which one electrode including a mixture layer non-forming portion and a protective layer was a positive electrode. However, the configuration of the present disclosure can also be applied when the other electrode is a negative electrode. In the above embodiment, a configuration was described in which almost the entire area of ​​each of the mixture layer non-forming portions provided on both sides of the electrode core was covered with a protective layer. However, a configuration in which only a portion of the mixture layer non-forming portion was covered with a protective layer may also be applied.

[0071] The present disclosure is 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 arranged with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode includes an electrode core, a mixture layer provided on both sides of the electrode core, and a protective layer provided on both sides of the electrode core and having inorganic particles and a binder, wherein both sides of the electrode core are provided with mixture layer-free sections where the mixture layer is not formed, at least a portion of each of the mixture layer-free sections provided on both sides of the electrode core is covered with the protective layer, and a portion of the protective layer is provided between the electrode core and the mixture layer on both sides of the electrode core in the thickness direction, and wherein on both sides of the electrode core, the boundary positions between the mixture layer-formed section where the mixture layer is formed directly on the electrode core and the protective layer-formed section where the protective layer is formed do not overlap each other in the thickness direction. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the electrode body has the positive electrode and the negative electrode wound with the separator interposed therebetween, and the boundary positions on both sides of the electrode core are different from each other in the winding direction.Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 2, wherein the distance between the boundary positions on both sides in the thickness direction of the electrode core in the winding direction is 0.5 mm or more.Configuration 4: The nonaqueous electrolyte secondary battery according to Configuration 2 or 3, wherein the mixture layer-free portion is provided at a winding start end of one of the electrodes.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the one of the electrodes is the positive electrode.

[0072] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11, 11a, 11b, 11c, 11d positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 15a cylindrical portion, 16 sealing body, 17 upper insulating plate, 18 lower insulating plate, 19 positive electrode tab, 20 negative electrode tab, 21 grooved portion, 22 internal terminal plate, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 27 gasket, 31 positive electrode core, 32 positive electrode mixture layer, 33a, 33b mixture layer non-forming portion, 40a, 40b, 70, 80 laminated protective tape, 41, 71, 81 base tape, 42, 72, 82 covering tape body, 43 covering tape, 50a, 50b, 52a, 52b protective tape, 60 Crack, 62 foreign matter, 73, 83 first covering tape, 74, 84 second covering tape.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are arranged with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode comprises an electrode core, a mixture layer provided on both sides of the electrode core, and a protective layer provided on both sides of the electrode core and having inorganic particles and a binder, wherein both sides of the electrode core are provided with mixture layer-free sections where the mixture layer is not formed, at least a portion of each of the mixture layer-free sections provided on both sides of the electrode core is covered with the protective layer, and a portion of the protective layer is provided between the electrode core and the mixture layer on both sides of the electrode core in the thickness direction, and wherein on both sides of the electrode core, boundary positions between the mixture layer-formed section where the mixture layer is formed directly on the electrode core and the protective layer-formed section where the protective layer is formed do not overlap each other in the thickness direction.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode body is formed by winding the positive electrode and the negative electrode with the separator interposed therebetween, and the boundary positions on both sides of the electrode core are different from each other in the winding direction.

3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the distance between the boundary positions on both sides of the electrode core in the thickness direction in the winding direction is 0.5 mm or more.

4. The nonaqueous electrolyte secondary battery according to claim 2, wherein the portion without a mixture layer is provided at a winding start end of the one electrode.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the one electrode is the positive electrode.

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