Nonaqueous electrolyte secondary battery

Abstract

The present invention provides a nonaqueous electrolyte secondary battery in which electrode plate deformation near a winding start end part of a positive electrode caused by charge / discharge cycles can be suppressed.　Disclosed is a nonaqueous electrolyte secondary battery in which a negative electrode (12) that constitutes a wound electrode body has a negative electrode mixture layer (32). The negative electrode mixture layer (32) has: a non-facing part (12a) that is disposed on the inner end side in the winding direction of the electrode body and does not face a positive electrode (11) with a separator interposed therebetween; and a facing part (12b) that is disposed on the outer side, in the winding direction, from the outer end in the winding direction of the non-facing part (12a) and that faces the positive electrode (11) with the separator interposed therebetween. The length of the non-facing part (12a) in the winding direction is not less than 0.3 turns. The inner circumferential surface of the negative electrode mixture layer (32) is provided with a recess (33) that straddles the boundary between the non-facing part (12a) and the facing part (12b), and the length of the recess (33) in the winding direction from the boundary to the outer end in the winding direction of the recess 33 is less than one turn.

Description

Nonaqueous electrolyte secondary battery

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

[0002] BACKGROUND ART In recent years, non-aqueous electrolyte secondary batteries having an electrode assembly in which a positive electrode and a negative electrode are arranged opposite each other with a separator interposed therebetween have been widely used as high-power, high-energy density secondary batteries.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery including a wound electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, in which the negative electrode includes a non-facing portion wound 1.25 or more times from the inner end of the wound electrode body in the winding direction in a state in which the negative electrode does not face the positive electrode via the separator, and the non-facing portion has, on at least one surface, a negative electrode composite layer forming portion in which the negative electrode composite layer is formed, continuing from the outer end in the winding direction toward the inner side in the winding direction, and the negative electrode composite layer forming portion is wound 0.75 or more times.

[0004] As in Patent Document 1, by providing a non-facing portion of the negative electrode that does not face the positive electrode on the inner end side of the winding direction of the electrode body, the circularity of the winding core portion (center portion) of the electrode body can be improved. This makes it possible to maintain, for example, the gas escape properties of the winding core portion, thereby improving the safety of the battery.

[0005] International Publication No. 2018 / 116876 Japanese Patent Application Publication No. 11-111327 Publication No. 11-265706 International Publication No. 2018 / 180748

[0006] In a non-aqueous electrolyte secondary battery having a wound electrode body, when the electrode body expands with charge / discharge cycles, stress is applied locally to the center of the electrode body, which may cause deformation of the electrode plate near the winding start end of the positive electrode.

[0007] Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte secondary battery that can suppress plate deformation near the winding start end of the positive electrode that occurs during charge / discharge cycles.

[0008] The non-aqueous electrolyte secondary battery according to the present disclosure comprises an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, the negative electrode having a negative electrode composite layer disposed on at least one surface of a negative electrode core, the negative electrode composite layer having a non-facing portion disposed on an inner end side of the electrode assembly in the winding direction and not facing the positive electrode with the separator interposed therebetween, and a facing portion disposed outward in the winding direction from the outer end of the non-facing portion in the winding direction and facing the positive electrode with the separator interposed therebetween, the length of the non-facing portion in the winding direction being 0.3 or more revolutions, and a recessed portion formed on the inner peripheral surface of the negative electrode composite layer that straddles the boundary between the non-facing portion and the facing portion, the length of the recessed portion in the winding direction from the boundary to the outer end of the recessed portion in the winding direction being less than one revolution.

[0009] According to the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery capable of suppressing plate deformation near the winding start end of the positive electrode that occurs due to charge / discharge cycles.

[0010] Fig. 2 is a schematic cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment. Fig. 3 is a diagram showing a schematic view of a portion of an inner end side in the winding direction of an electrode body along the AA cross section in Fig. 1. Fig. 4 is a schematic cross-sectional view showing the configuration of a negative electrode and a positive electrode on the inner end side in the winding direction of an electrode body. Fig. 5 is a schematic cross-sectional view showing the state of the winding start end side of the negative electrode and the positive electrode before winding.

[0011] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail.

[0012] Fig. 1 is a schematic 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, a nonaqueous electrolyte, insulating plates 18a and 18b disposed above and below the electrode assembly 14, and a battery case 15 serving as an exterior body. The battery case 15 is composed of a case body 16 that houses the electrode assembly 14, the nonaqueous electrolyte, and the like, and a sealing body 17 that closes the opening of the case body 16. The battery case 15 is not limited to a cylindrical or rectangular metal case, and may be, for example, a resin case (so-called pouch-type) formed by laminating a resin sheet.

[0013] The non-aqueous electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0014] The liquid electrolyte (electrolytic solution) contains, for example, 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

[0015] Furthermore, examples of the solid electrolyte that can be used include solid or gel polymer electrolytes, inorganic solid electrolytes, and the like. 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. The matrix polymer is, for example, 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, halogen-based solid electrolytes, and the like).

[0016] The case body 16 is, for example, a cylindrical metal container with a bottom. A gasket 27 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 21, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 21 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.

[0017] The sealing body 17 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 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 24 are electrically connected to each other. 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. 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 23 deforms and ruptures, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure further increases, the upper valve body 25 ruptures, and gas is discharged from the opening of the cap 26.

[0018] In the nonaqueous electrolyte secondary battery 10 shown in FIG. 1 , a positive electrode lead 19 attached to the positive electrode 11 extends through a through-hole in an insulating plate 18a toward the sealing body 17 and is connected by welding or the like to the underside of a filter 22, which is the bottom plate of the sealing body 17. As a result, a cap 26, which is the top plate of the sealing body 17 and is electrically connected to the filter 22, serves as a positive electrode terminal. Furthermore, a negative electrode lead 20a connected to the negative electrode 12 at the winding start side of the electrode body 14 and a negative electrode lead 20b connected to the negative electrode 12 at the winding end side of the electrode body 14 extend through an insulating plate 18b toward the bottom side of the case body 16 and are connected to the inner bottom surface of the case body 16 by welding or the like. As a result, the case body 16 serves as a negative electrode terminal.

[0019] FIG. 2 is a schematic diagram showing the inner end of the electrode assembly in the winding direction in the A-A cross section of FIG. 1 . In FIG. 2 , to facilitate understanding of the relative positions, the negative electrode 12 is shown with a solid line, the positive electrode 11 with a dashed line, and the separator 13 with a dashed line. Also, in FIG. 2 , the gaps between the positive electrode 11, the negative electrode 12, and the separator 13 are exaggerated. The electrode assembly 14 is formed by winding the positive electrode 11 and the negative electrode 12 with the separator 13 interposed therebetween. Specifically, a strip-shaped positive electrode 11, a strip-shaped negative electrode 12, and a pair of strip-shaped separators 13 are stacked in the order of one separator 13, the positive electrode 11, the other separator 13, and the negative electrode 12, and then this stack is spirally wound to produce the electrode assembly 14. In the electrode assembly 14, the longitudinal direction of each electrode is the winding direction, and the width direction of each electrode is the winding axis direction.

[0020] FIG. 3 is a schematic cross-sectional view showing the configuration of the negative electrode and positive electrode at the inner end side in the winding direction of the electrode assembly. FIG. 4 is a schematic cross-sectional view showing the state of the negative electrode and positive electrode at the winding start end side before winding. In FIGS. 3 and 4 , the separator 13 disposed between the positive electrode 11 and the negative electrode 12 is not shown. As shown in FIGS. 3 and 4 , the negative electrode 12 includes, for example, a negative electrode core 30 and a negative electrode composite layer 32 disposed on the negative electrode core 30. The negative electrode composite layer 32 is formed, for example, on both sides of the negative electrode core 30, and includes a negative electrode composite layer 32a formed on an inner peripheral surface 30a of the negative electrode core 30 facing radially inward of the electrode assembly 14, and a negative electrode composite layer 32b formed on an outer peripheral surface 30b of the negative electrode core 30 facing radially outward of the electrode assembly 14.

[0021] 2 to 4 , negative electrode composite material layer 32 has a non-facing portion 12a that does not face positive electrode 11 via separator 13, on the inner end side in the winding direction, which is the winding start side of electrode body 14. Negative electrode composite material layer 32 also has a facing portion 12b that follows non-facing portion 12a and is disposed outward in the winding direction from the outer end in the winding direction of non-facing portion 12a, facing positive electrode 11 via separator 13.

[0022] The non-facing portion 12a is a region of the negative electrode composite material layer 32, extending from point E3, which faces the winding start end (point D1) of the positive electrode 11 on the inner circumferential side with the separator 13 interposed therebetween, to point E2, which is the winding start end of the negative electrode composite material layer. That is, point E2 corresponds to the inner end of the non-facing portion 12a in the winding direction, and point E3 corresponds to the outer end of the non-facing portion 12a in the winding direction. The non-facing portion 12a has an inner circumferential composite non-facing portion 12d made of the negative electrode composite material layer 32a formed on the inner circumferential surface 30a of the negative electrode core 30, and an outer circumferential composite non-facing portion 12e made of the negative electrode composite material layer 32b formed on the outer circumferential surface 30b of the negative electrode core 30. In FIG. 3 , the inner ends of the inner circumferential composite non-facing portion 12d and the outer circumferential composite non-facing portion 12e in the winding direction are both located at point E2, but they may be located at different points. In this case, of the inner ends of the inner peripheral composite non-facing portion 12d and the outer peripheral composite non-facing portion 12e in the winding direction, the one that is closer to the inner winding direction end of the negative electrode 12 is the inner winding direction end of the non-facing portion 12a. As shown in Figures 3 and 4 , the negative electrode 12 may have a core non-facing portion 12c in which the negative electrode composite layer 32 is not formed on the surface of the negative electrode core 30, in a region from the inner winding direction end (point E2) of the non-facing portion 12a to the inner winding direction end (point E1) of the negative electrode 12.

[0023] In this embodiment, the length of the non-facing portion 12a in the winding direction is 0.3 or more circumferences, preferably 0.7 or more circumferences, and more preferably 0.7 or more circumferences and 1.0 or less circumferences. When the length of the non-facing portion 12a in the winding direction satisfies the above range, for example, the circularity of the winding core of the electrode body 14 is maintained, and the winding core can function as a gas exhaust passage.

[0024] As described above, the non-facing portion 12a has the inner circumferential composite non-facing portion 12d and the outer circumferential composite non-facing portion 12e, but the lengths of these portions in the winding direction may be different. That is, the non-facing portion 12a in the winding direction may include a region having only one of the inner circumferential composite non-facing portion 12d and the outer circumferential composite non-facing portion 12e. This configuration also allows, for example, the circularity of the winding core of the electrode body 14 to be maintained, and allows the winding core to function as a gas exhaust passage.

[0025] As shown in Figures 3 and 4, a recess 33 is formed on the inner peripheral surface of the negative electrode composite layer 32, spanning the boundary (point E3) between the non-facing portion 12a and the facing portion 12b. That is, the recess 33 is located opposite the inner peripheral side of the winding start end (point D1) of the positive electrode 11, with the separator 13 interposed therebetween. As a result, when the electrode assembly 14 expands with charge / discharge cycles, the stress applied from the center of the electrode assembly 14 to the winding start end of the positive electrode 11 is alleviated by the recess 33 facing the winding start end of the positive electrode 11, thereby suppressing electrode plate deformation near the winding start end of the positive electrode 11. Although not shown in the figures, the recess 33 extends along the width direction of the negative electrode 12, which is parallel to the winding axis direction of the electrode assembly 14, and preferably extends from one end to the other end in the width direction of the negative electrode 12.

[0026] The recess 33 can be made, for example, by forming the negative electrode composite layer 32a on the inner circumferential surface 30a of the negative electrode core 30, and then scraping off the negative electrode composite layer 32a corresponding to the position of the recess 33. When scraping off the negative electrode composite layer 32a, the negative electrode composite layer 32a may be scraped off so that the inner circumferential surface 30a of the negative electrode core 30 is exposed, or a portion of the negative electrode composite layer 32a may be scraped off so that the negative electrode composite layer 32a remains on the inner circumferential surface 30a of the negative electrode core 30.

[0027] 3 and 4 has a sidewall of the negative electrode composite material layer 32a on the opposing non-facing portion 12a side and a sidewall of the negative electrode composite material layer 32a on the opposing portion 12b side, and an inner bottom surface, the inner bottom surface being an exposed portion where the inner circumferential surface 30a of the negative electrode core 30 is exposed. In this embodiment, the depth of the recess 33 is preferably 50% or more of the thickness of the negative electrode composite material layer 32a, for example, from the viewpoint of further alleviating stress applied to the winding start end of the positive electrode 11 with charge / discharge cycles, and more preferably 100% of the thickness of the negative electrode composite material layer 32a, i.e., the inner bottom surface of the recess 33 is an exposed portion where the inner circumferential surface 30a of the negative electrode core 30 is exposed. The thickness of the negative electrode composite material layer 32a is determined by measuring the thickness of the negative electrode composite material layer 32a at five points around the recess 33 and averaging the measured values. The depth of the recess 33 is determined by measuring the depth of the recess 33 at five arbitrary positions and averaging these values.

[0028] In this embodiment, the length of the recess 33 in the winding direction from the boundary (point E3) to the outer end (point E5) of the recess 33 in the winding direction is set to a length of less than one revolution. If the length of the recess 33 in the winding direction from the boundary to the outer end of the recess 33 in the winding direction is set to one revolution or more, the recess 33 will be disposed up to the region of the negative electrode 12 that undergoes a battery reaction with the positive electrode 11. This may result in the generation of lithium dendrites in the negative electrode 12 as the battery is charged and discharged over a number of cycles, resulting in a decrease in battery performance.

[0029] Furthermore, with regard to the length of the recess 33 in the winding direction, the length from the inner end (point E4) of the recess 33 in the winding direction to the boundary (point E3) is preferably 0.1 or more turns, and more preferably 0.1 or more turns and 0.2 or less turns. With regard to the length of the recess 33 in the winding direction, the length from the boundary to the outer end of the recess 33 in the winding direction is preferably 0.1 or more turns and less than 1 turn, and more preferably 0.2 or more turns and less than 1 turn. When the winding direction length of the recess 33 satisfies the above range, the stress applied to the winding start end of the positive electrode 11 with the charge / discharge cycle is further alleviated, and electrode plate deformation near the winding start end of the positive electrode 11 may be further suppressed.

[0030] As in this embodiment, the negative electrode 12 preferably has a core non-facing portion 12c. For example, in order to ensure installation space for the negative electrode lead 20a shown in FIG. 1 , the core non-facing portion 12c is preferably wound 0.5 or more times from the inner end (point E2) of the non-facing portion 12a in the winding direction toward the inside in the winding direction. The negative electrode lead 20a shown in FIG. 1 is preferably connected to the negative electrode core 30 of the core non-facing portion 12c provided in the non-facing portion 12a by welding or the like. That is, the negative electrode lead 20a is preferably connected to the negative electrode core 30 on the inner end side of the winding direction of the electrode assembly 14. For example, current collection at two locations, by the negative electrode lead 20b provided on the outer end side of the winding direction of the electrode assembly 14 and the negative electrode lead 20a provided on the inner end side of the winding direction, can reduce the resistance component of the battery. Alternatively, the negative electrode core 30 on the outer end side of the winding direction of the electrode assembly 14 may be in contact with the case body 16. This makes it possible to further reduce the resistance component of the battery.

[0031] The negative electrode core 30 constituting the negative electrode 12 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, or a film having such a metal disposed on the surface layer. The thickness of the negative electrode core 30 is, for example, in the range of 10 μm to 50 μm.

[0032] Furthermore, the negative electrode composite layer 32 constituting the negative electrode 12 contains, for example, a negative electrode active material, a binder, etc. The thickness of the negative electrode composite layer 32 is, for example, in the range of 10 μm to 100 μm. The negative electrode 12 can be produced, for example, by applying a negative electrode composite slurry containing the negative electrode active material, the binder, etc. to the negative electrode core 30, drying the coating, and then rolling the coating to form the negative electrode composite layer 32 on the negative electrode core 30.

[0033] The negative electrode active material contained in negative electrode composite layer 32 is not particularly limited as long as it can reversibly absorb and release lithium ions, and examples thereof include carbon materials, Si-based materials, etc. From the viewpoint of increasing the capacity of the battery, it is preferable that the negative electrode active material contains a Si-based material.

[0034] The carbon material may be, for example, a conventionally known carbon material used as a negative electrode active material, and examples thereof include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).

[0035] The Si-based material includes, for example, a lithium ion conductive phase and Si particles dispersed in the lithium ion conductive phase. The lithium ion conductive phase includes, for example, at least one of a silicon oxide phase, a silicate phase, and a carbon phase.

[0036] The silicate phase preferably contains at least one element selected from the group 2 elements of the periodic table, including alkali metal elements such as lithium, sodium, potassium, rubidium, cesium, and francium, and elements of Group 2 of the periodic table, including beryllium, magnesium, calcium, strontium, barium, and radium, in terms of high lithium ion conductivity, etc. Among these, a silicate phase containing lithium (hereinafter sometimes referred to as a lithium silicate phase) is preferred in terms of high lithium ion conductivity, etc.

[0037] The lithium silicate phase can be, for example, a compound of the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). From the viewpoints of stability, ease of preparation, lithium ion conductivity, and the like, z preferably satisfies the relationship 0<z<1, and more preferably z=1 / 2.

[0038] The Si-based material in which Si particles are dispersed in a silicon oxide phase is, for example, a material represented by the general formula SiO ｘ (The range of 0<x<2 is preferred, and the range of 0.5≦x≦1.6 is more preferred.) The Si-based material in which Si particles are dispersed in the carbon phase can be represented by, for example, the general formula Si ｘ C ｙ (The ranges of 0<x≦1 and 0<y≦1 are preferred).

[0039] A conductive layer coated with conductive carbon may be formed on the surface of the Si-based material. The conductive layer can be formed, for example, by a CVD method using acetylene, methane, or the like, or by a method in which coal pitch, petroleum pitch, phenolic resin, or the like is mixed with a silicon-based active material and heat-treated. Heat-treatment equipment for the heat treatment can include, for example, a hot air furnace, a hot press, a lamp, a sheath heater, a ceramic heater, a rotary kiln, or the like. Alternatively, the conductive layer can be formed by adhering a conductive filler such as carbon black to the particle surface of the Si-based material using a binder.

[0040] The content of the Si-based material is preferably, for example, 5 mass % or more relative to the total mass of negative electrode mixture layer 32 in terms of increasing the capacity of the battery.

[0041] In addition to carbon materials and Si-based materials, other materials that can reversibly absorb and release lithium ions can be used as negative electrode active materials, such as Sn, alloys containing Sn, Sn-based materials such as tin oxide, and Ti-based materials such as lithium titanate.

[0042] Examples of binders include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), and polyethylene oxide (PEO).

[0043] The positive electrode 11 has a positive electrode core and a positive electrode composite layer formed on the surface of the positive electrode core. The positive electrode composite layer is preferably formed on both sides of the positive electrode core. The positive electrode core can be made of a foil of a metal, such as aluminum, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The positive electrode composite layer contains, for example, a positive electrode active material, a binder, a conductive agent, etc. The positive electrode 11 can be produced, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a binder, a conductive agent, etc., onto the positive electrode core, drying the coating, and then rolling it to form a positive electrode composite layer on both sides of the positive electrode core.

[0044] The positive electrode active material contained in the positive electrode mixture layer can be, for example, a lithium transition metal oxide containing a transition metal element such as Co, Mn, or Ni. ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Li ｘ Ni １－ｙ M ｙ O ｚ , Li ｘ Mn ２ O ４ , Li ｘ Mn ２－ｙ M ｙ O ４ , LiMPO ４ , Li ２ MPO４ F (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3). These may be used alone or in combination. In terms of increasing the capacity of the non-aqueous electrolyte secondary battery, the positive electrode active material is preferably Li ｘ NiO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Ni １－ｙ M ｙ O ｚ It is preferable that the lithium transition metal oxide contains a lithium nickel composite oxide such as (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B; 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3). Inorganic particles such as tungsten oxide, aluminum oxide, and lanthanoid-containing compounds may be adhered to the surface of the lithium transition metal oxide particles.

[0045] Examples of the conductive agent contained in the positive electrode mixture layer include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphene, and graphite. Examples of the binder contained in the positive electrode mixture layer include the same binders as those used in the negative electrode 12.

[0046] 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 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 the surface of the separator 13 may be coated with a material such as an aramid-based resin or ceramic.

[0047] [Note] (1) A non-aqueous electrolyte secondary battery including an electrode assembly formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode composite layer disposed on a surface of the negative electrode core, the negative electrode composite layer having a non-facing portion disposed on an inner end of the electrode assembly in the winding direction and not facing the positive electrode with the separator interposed therebetween, and a facing portion disposed outward in the winding direction from the outer end of the non-facing portion in the winding direction and facing the positive electrode with the separator interposed therebetween, the length of the non-facing portion in the winding direction being 0.3 or more revolutions, a recess formed in an inner peripheral surface of the negative electrode composite layer spanning a boundary between the non-facing portion and the facing portion, and the length of the recess in the winding direction from the boundary to the outer end of the recess in the winding direction being less than one revolution. (2) The non-aqueous electrolyte secondary battery according to (1), wherein the depth of the recess is 50% or more of the thickness of the negative electrode composite layer. (3) The nonaqueous electrolyte secondary battery according to (1) or (2), wherein the inner bottom surface of the recess is an exposed portion where the inner peripheral surface of the negative electrode core is exposed. (4) The nonaqueous electrolyte secondary battery according to any one of (1) to (3), wherein the length of the non-facing portion in the winding direction is 0.7 or more revolutions. (5) The nonaqueous electrolyte secondary battery according to any one of (1) to (4), wherein the length of the recess in the winding direction from the inner end of the recess in the winding direction to the boundary is 0.1 or more revolutions, and the length of the recess in the winding direction from the boundary to the outer end of the recess in the winding direction is 0.1 or more revolutions but less than 1 revolution. (6) The nonaqueous electrolyte secondary battery according to (5), wherein the length of the recess in the winding direction from the boundary to the outer end of the recess in the winding direction is 0.2 or more revolutions but less than 1 revolution.

[0048] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 12a non-facing portion, 12b facing portion, 12c core non-facing portion, 12d inner peripheral side composite non-facing portion, 12e outer peripheral side composite non-facing portion, 13 separator, 14 electrode body, 15 battery case, 16 case body, 17 sealing body, 18a, 18b insulating plate, 19 positive electrode lead, 20a, 20b negative electrode lead, 21 protruding portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 27 gasket, 30 negative electrode core body, 30a inner peripheral surface, 30b outer peripheral surface, 32, 32a, 32b negative electrode composite layer, 33 recess.

Claims

1. A non-aqueous electrolyte secondary battery having an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode composite layer arranged on a surface of the negative electrode core, the negative electrode composite layer having a non-facing portion arranged on an inner end side of the electrode body in a winding direction and not facing the positive electrode with the separator interposed therebetween, and a facing portion arranged outward in the winding direction from an outer end of the non-facing portion in the winding direction and facing the positive electrode with the separator interposed therebetween, the length of the non-facing portion in the winding direction is 0.3 or more revolutions, a recess is formed on an inner peripheral surface of the negative electrode composite layer so as to straddle the boundary between the non-facing portion and the facing portion, and the length of the recess in the winding direction from the boundary to the outer end of the recess in the winding direction is less than one revolution.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the depth of the recess is 50% or more of the thickness of the negative electrode mixture layer.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the inner bottom surface of the recess is an exposed portion where the inner peripheral surface of the negative electrode core is exposed.

4. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the length of said non-facing portion in the winding direction is 0.7 or more turns.

5. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the length in the winding direction from an inner end of the recess in the winding direction to the boundary is 0.1 revolutions or more, and the length in the winding direction from the boundary to an outer end of the recess in the winding direction is 0.1 revolutions or more but less than 1 revolution.

6. The nonaqueous electrolyte secondary battery according to claim 5, wherein the length in the winding direction from the boundary to the outer end of the recess in the winding direction is equal to or greater than 0.2 revolutions and less than one revolution.

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