Non-aqueous electrolyte secondary battery

Abstract

The present invention provides a non-aqueous electrolyte secondary battery that makes it possible to obtain improved productivity while reducing electrode plate deformation. A non-aqueous electrolyte secondary battery according to the present disclosure comprises: an electrode body in which a positive electrode and a negative electrode are wound via a separator therebetween; a non-aqueous electrolyte; and an outer case in which the electrode body and the non-aqueous electrolyte are contained. The positive electrode includes a positive electrode current collector, and a positive electrode mixture layer formed on a surface of the positive electrode current collector. The surface of the separator opposite the positive electrode mixture layer includes a high friction region formed in an area of less than six turns in a winding direction from a position opposite the winding inner end of the positive electrode mixture layer, and a low friction region adjacent to the high friction region.

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries, which have electrodes in which the positive and negative electrodes are arranged opposite each other with a separator in between, have been widely used as secondary batteries with high power output and high energy density.

[0003] For example, Patent Document 1 discloses a technique for improving the ease with which the core can be removed when manufacturing a wound electrode body by setting the static friction coefficient of the separator surface to 0.45 or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-126275 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, in non-aqueous electrolyte secondary batteries in which wound electrode bodies are housed in an outer casing, when the electrode bodies expand during charge-discharge cycles, pressure is applied to the electrode bodies from the outer casing, which can cause electrode plate deformation, resulting in bending of the electrode plates. Since electrode plate deformation can be a cause of internal short circuits, suppressing electrode plate deformation is an important issue.

[0006] As a result of the intensive studies by the inventors, it has been found that the electrode plate deformation is likely to occur in the range of several turns in the winding direction from the inner end of the winding of the positive electrode mixture layer. At this time, it has been found that the positive electrode and the separator are bent while being deformed in the winding direction respectively. Therefore, when the friction coefficient of the surface of the separator is small, the amount of deformation of the positive electrode tends to increase. Further, when the friction coefficient of the surface of the separator is large, when winding the electrode body, the separator may adhere to the feeding roller, resulting in the displacement of the separator and the reduction of the productivity of the battery.

[0007] An object of the present disclosure is to improve the productivity while suppressing the electrode plate deformation in a non-aqueous electrolyte secondary battery.

Means for Solving the Problems

[0008] The non-aqueous electrolyte secondary battery according to the present disclosure includes an electrode body in which a positive electrode and a negative electrode are wound via a separator, and an exterior body that houses the electrode body. The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The surface of the separator facing the positive electrode mixture layer includes a high friction region formed in the range of two or more turns and less than six turns in the winding direction from the position facing the inner end of the winding of the positive electrode mixture layer, and a low friction region adjacent to the high friction region in the winding direction.

Effects of the Invention

[0009] According to the non-aqueous electrolyte secondary battery according to the present disclosure, it is possible to achieve both suppression of electrode plate deformation and improvement of productivity.

Brief Description of the Drawings

[0010] [Figure 1] It is a longitudinal sectional view of a cylindrical secondary battery which is an example of an embodiment. [Figure 2] It is a lateral sectional view of a cylindrical secondary battery which is an example of an embodiment. [Figure 3] It is a diagram for explaining a method for evaluating the deformation of the negative electrode.

Modes for Carrying Out the Invention

[0011] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical exterior body will be exemplified. However, the electrode body is not limited to the wound type, and may be a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one via a separator. The exterior body is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a coin shape, or the like. Further, the exterior body may be a pouch type composed of a laminate sheet including a metal layer and a resin layer.

[0012] FIG. 1 is a longitudinal sectional view of a cylindrical secondary battery 10 which is an example of an embodiment. Further, FIG. 2 is a lateral sectional view of the cylindrical secondary battery 10 which is an example of an embodiment. The secondary battery 10 has an electrode body 14 and a non-aqueous electrolyte (not shown) housed in an exterior body 15, and the upper end portion of the exterior body 15 is sealed with a sealing body 16, whereby the inside of the secondary battery 10 is sealed. Hereinafter, for convenience of explanation, the side of the sealing body 16 will be referred to as "upper" and the bottom side of the exterior body 15 will be referred to as "lower" for explanation.

[0013] As the non-aqueous solvent (organic solvent) of the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc. can be used, and these solvents can be used by mixing two or more kinds thereof. When mixing and using two or more kinds of solvents, it is preferable to use a mixed solvent containing a cyclic carbonate and a chain carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. can be used as the chain carbonate. As the electrolyte salt of the non-aqueous electrolyte, LiPF6, LiBF4, LiCF3SO3, etc. and mixtures thereof can be used. The dissolution amount of the electrolyte salt with respect to the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L.

[0014] As shown in Figure 2, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13. The number of turns of the electrode body is, for example, 10 to 30 turns based on the positive electrode 11. The positive electrode 11, the negative electrode 12, and the separator 13 all have a strip-like shape and are wound in the longitudinal direction. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11, for example, in order to suppress lithium deposition, and is formed to be longer than the positive electrode 11 in both the longitudinal and transverse (up and down) directions. The separator 13 is preferably formed to be larger in both width and length than the positive electrode 11 and the negative electrode 12, as illustrated in Figure 2, in order to prevent electrical contact between the positive electrode 11 and the negative electrode 12.

[0015] In this embodiment, the inner end 11e of the positive electrode mixture layer 11b coincides with the inner end of the positive electrode 11. On the other hand, the inner end of the negative electrode mixture layer 12b does not coincide with the inner end of the negative electrode 12, and an exposed portion is provided at the inner end of the negative electrode 12 where the negative electrode mixture layer 12b is not formed, and the negative electrode current collector 12a is exposed. The negative electrode lead 20 is welded to this exposed portion. The positive electrode 11 has an exposed portion at the longitudinal center where the positive electrode current collector 11a is exposed, and the positive electrode lead 19 is welded to this exposed portion. Alternatively, an exposed portion may be provided at the outer end of the negative electrode 12, and the negative electrode lead 20 may be connected to this exposed portion, or the negative electrode 12 and the outer casing 15 may be electrically connected by the exposed portion abutting against the inner surface of the outer casing 15.

[0016] As shown in Figure 1, insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the lower surface of the filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, becomes the positive electrode terminal. On the other hand, the negative electrode lead 20 extends to the bottom side of the casing 15 through a through hole in the insulating plate 18 and is welded to the bottom of the casing 15. In the secondary battery 10, the casing 15 becomes the negative electrode terminal. If the negative electrode lead 20 is installed at the outer end of the winding, the negative electrode lead 20 extends to the bottom side of the casing 15, passing outside the insulating plate 18 and is welded to the inner surface of the bottom of the casing 15.

[0017] The outer casing 15 is, for example, a metal outer casing in the shape of a bottomed cylindrical can. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the secondary battery 10. The outer casing 15 has, for example, a grooved portion 21 that supports the sealing body 16, formed by pressing the side portion from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer casing 15, and its upper surface supports the sealing body 16 via the gasket 27.

[0018] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. If the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge towards the cap 26 and separate from the lower valve body 23, thereby interrupting the electrical connection between them. If the internal pressure rises further, the upper valve body 25 may rupture, and gas may be discharged from the opening 26a of the cap 26.

[0019] The following will provide a detailed explanation of the positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode body 14, with particular emphasis on the separator 13.

[0020] [Positive electrode] The positive electrode 11 comprises a positive electrode current collector 11a and a positive electrode mixture layer 11b formed on the surface of the positive electrode current collector 11a. The positive electrode mixture layer 11b is preferably formed on both sides of the positive electrode current collector 11a, as shown in Figure 2. The positive electrode current collector 11a can be made of a metal foil stable within the potential range of the positive electrode 11, such as aluminum, or a film with the metal arranged on its surface. The positive electrode mixture layer 11b includes, for example, a positive electrode active material, a binder, a conductive agent, etc. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc., onto the positive electrode current collector 11a, drying the coating, and then rolling to form the positive electrode mixture layer 11b on both sides of the positive electrode current collector 11a.

[0021] Examples of the positive electrode active material contained in the positive electrode mixture layer 11b include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal oxide is, for example, Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4, Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of two or more. In terms of achieving high capacity of the non-aqueous electrolyte secondary battery, the positive electrode active material preferably contains lithium nickel composite oxides such as Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3), etc. Inorganic particles such as tungsten oxide, aluminum oxide, and lanthanoid-containing compounds may be adhered to the particle surface of the lithium transition metal oxide.

[0022] Examples of conductive agents included in the positive electrode mixture layer 11b include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), graphene, and graphite. These may be used individually or in combination of two or more types.

[0023] Examples of binders included in the positive electrode mixture layer 11b include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used individually or in combination of two or more types. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0024] [Negative electrode] The negative electrode 12 comprises a negative electrode current collector 12a and a negative electrode mixture layer 12b formed on the surface of the negative electrode current collector 12a. The negative electrode mixture layer 12b is preferably formed on both sides of the negative electrode current collector 12a, as shown in Figure 2. The negative electrode current collector 12a can be made of a metal foil stable in the negative electrode potential range, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 12b includes, for example, a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode current collector 12a, drying the coating, and then rolling it to form the negative electrode mixture layer 12b on both sides of the negative electrode current collector 12a.

[0025] The negative electrode active material contained in the negative electrode mixture layer 12b is not particularly limited as long as it can reversibly occlude and release lithium ions, and generally carbon-based active materials such as graphite are used. The graphite may be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Further, as the negative electrode active material, metals alloying with Li such as Si and Sn, metal compounds containing Si, Sn, etc., lithium titanium composite oxides, etc. may be used. As the negative electrode active material other than the carbon-based active material, a silicon-based active material is preferable. Examples of the silicon-based active material include Si-containing compounds represented by SiO x (0.5 ≦ x ≦ 1.6), or Li 2y SiO (2+y) Si-containing compounds in which fine particles of Si are dispersed in a lithium silicate phase represented by (0 < y < 2). The content of the silicon-based active material in the negative electrode mixture layer 12b is, for example, 1% by mass to 15% by mass, preferably 5% by mass to 10% by mass, based on the total mass of the negative electrode active material.

[0026] It is preferable that a conductive film is formed on the particle surface of the silicon-based active material. Examples of the constituent material of the conductive film include at least one selected from carbon materials, metals, and metal compounds. Among them, carbon materials such as amorphous carbon are preferable. The carbon film can be formed by, for example, a CVD method using acetylene, methane, etc., a method of mixing coal pitch, petroleum pitch, phenol resin, etc. with silicon-based active material particles and performing heat treatment. Alternatively, a conductive film may be formed by fixing a conductive filler such as carbon black to the particle surface of the silicon-based active material using a binder.

[0027] For the binder contained in the negative electrode mixture layer 12b, fluorine-containing resins such as PTFE and PVDF, PAN, polyimide, acrylic resin, polyolefin, etc. may be used as in the case of the positive electrode, but preferably styrene-butadiene rubber (SBR) is used. Further, the negative electrode mixture layer may contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. The negative electrode mixture layer contains, for example, SBR and CMC or its salt.

[0028] [Separator] The surface of the separator 13 facing the positive electrode mixture layer 11b includes a high-friction region formed in the range of 2 to 6 turns in the winding direction R from a position facing the inner end 11e of the positive electrode mixture layer 11b, and a low-friction region adjacent to the high-friction region in the winding direction R. This allows for suppression of positive electrode bending by the high-friction region, while suppression of separator winding misalignment by the low-friction region.

[0029] The coefficient of friction in the high-friction region is preferably 0.6 or higher. The upper limit of the coefficient of friction in the high-friction region is, for example, 1.1, from the viewpoint of the running stability of the separator during winding. Furthermore, the coefficient of friction in the low-friction region is preferably 0.4 or lower. The lower limit of the coefficient of friction in the low-friction region is, for example, 0.1, from the viewpoint of preventing the separator from shifting on the supply reel.

[0030] The separator 13 includes, for example, a porous substrate 13a and an inorganic particle layer containing inorganic particles formed on the surface of the substrate 13a. In this embodiment shown in Figure 2, the separator 13 has a first inorganic particle layer 13b formed on the surface of the substrate 13a and a second inorganic particle layer 13c formed on the surface of the first inorganic particle layer 13b on the surface facing the positive electrode mixture layer 11b (hereinafter, the first inorganic particle layer 13b and the second inorganic particle layer 13c may be collectively referred to as the inorganic particle layer). In Figure 2, the first inorganic particle layer 13b is formed over the entire surface of the separator 13 facing the positive electrode mixture layer 11b. The second inorganic particle layer 13c is formed on the surface of the first inorganic particle layer 13b in a range of 2 to 6 turns in the winding direction R from a position facing the winding end 11e of the positive electrode mixture layer 11b. That is, the surface of the first inorganic particle layer 13b is a low-friction region, and the surface of the second inorganic particle layer 13c is a high-friction region. The first inorganic particle layer 13b and the second inorganic particle layer 13c can be manufactured, for example, by a microgravure coating method. After applying a dispersion containing inorganic particles for forming the first inorganic particle layer 13b to the surface of the substrate 13a, the separator 13 can be manufactured by intermittently applying the dispersion containing inorganic particles for forming the first inorganic particle layer 13b again using the microgravure coating method.

[0031] The configuration of the inorganic particle layer on the surface of the substrate 13a is not limited to the example in Figure 2. For example, the second inorganic particle layer 13c may be formed on the surface of the substrate 13a, rather than on the surface of the first inorganic particle layer 13b. The separator 13 may have inorganic particle layers on both the surface facing the positive electrode mixture layer 11b and the surface facing the negative electrode mixture layer 12b. However, from the viewpoint of productivity, it is preferable to have the inorganic particle layer only on the surface facing the positive electrode mixture layer 11b.

[0032] The base material 13a is a porous sheet having ion permeability and insulating properties, and is composed of, for example, a microporous thin film, woven fabric, nonwoven fabric, etc. The material of the base material 13a is not particularly limited, but examples include polyethylene, polypropylene, polyolefins such as copolymers of polyethylene and α-olefin, acrylic resin, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide, polyether ether ketone, and fluororesin. Although a polyolefin base material 13a may oxidize and degrade when exposed to the potential of the positive electrode 11, the inorganic particle layer formed on the surface of the base material 13a facing the positive electrode mixture layer 11b effectively suppresses the oxidative degradation of the base material 13a. Furthermore, the inorganic particle layer improves the heat resistance of the separator 13.

[0033] The inorganic particle layer is a porous layer mainly composed of inorganic particles. Examples of inorganic particles included in the inorganic particle layer include metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles.

[0034] Examples of metal oxide particles include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide. Examples of metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of metal carbide particles include silicon carbide, boron carbide, titanium carbide, and tungsten carbide.

[0035] Inorganic particles are zeolites (M 2 / n Porous aluminosilicates such as O·Al2O3·xSiO2·yH2O (where M is a metal element, n is the valence of M, x≧2, y≧0), talc (Mg3Si4O 10Layered silicates such as (OH)2), minerals such as barium titanate (BaTiO3) and strontium titanate (SrTiO3) may also be used. These may be used individually or in combination of two or more. The inorganic particle content in the inorganic particle layer is preferably 85 to 99% by mass, and more preferably 90 to 98% by mass, relative to the total mass of the inorganic particle layer.

[0036] The average particle size (D50) of the inorganic particles contained in the second inorganic particle layer 13c (high friction region) is preferably 0.3 μm or less from the viewpoint of improving adhesion with the opposing positive electrode mixture layer 11b. In this specification, D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of inorganic particles can be measured using a laser diffraction particle size distribution analyzer (e.g., Microtrac-Bell Co., Ltd., MT3000II) with water as the dispersion medium. The lower limit of D50 for the inorganic particles contained in the second inorganic particle layer 13c is, for example, 0.1 μm from the viewpoint of suppressing aggregation of inorganic particles in the dispersion.

[0037] The average particle diameter (D50) of the inorganic particles contained in the first inorganic particle layer 13b (low friction region) is preferably 0.6 μm or more from the viewpoint of improving slipperiness with the feed roller. The upper limit of D50 of the inorganic particles contained in the first inorganic particle layer 13b is, for example, 1.5 μm from the viewpoint of suppressing peeling of the first inorganic particle layer 13b.

[0038] The thickness of the first inorganic particle layer 13b is preferably smaller than the thickness of the substrate 13a, for example, 0.5 μm to 5 μm. The thickness of the second inorganic particle layer 13c is, for example, 0.5 μm to 5 μm.

[0039] The inorganic particle layer preferably further contains a binder. The binder has the function of bonding individual inorganic particles to each other and to the substrate 13a. Examples of binders include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more. The binder content in the inorganic particle layer is preferably 0.5 to 10% by mass, and more preferably 1 to 5% by mass, relative to the total mass of the inorganic particle layer.

[0040] The coefficient of friction of the first inorganic particle layer 13b and the second inorganic particle layer 13c is preferably adjusted by the average particle diameter of the inorganic particles, as in the example above, but it may also be adjusted by the shape and material of the inorganic particles, as well as the type and amount of binder. [Examples]

[0041] The present disclosure will be further illustrated below with reference to examples, but the present disclosure is not limited to these examples.

[0042] <Example 1> [Fabrication of the positive electrode] 100 parts by mass of LiNi 0.88 Co 0.09 Al 0.03O2, 1 part by mass of acetylene black (AB), and 0.9 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to both sides of a 15 μm thick aluminum foil, and the coating was dried. After rolling the coating using a roller, it was cut to a predetermined electrode size (thickness 0.144 mm, width 62.6 mm, length 861 mm) to produce a positive electrode with positive electrode slurry layers formed on both sides of the positive electrode current collector. An exposed portion was provided in the longitudinal center of the positive electrode where the positive electrode slurry layer was not formed and the positive electrode current collector was exposed, and an aluminum positive electrode lead was welded to this exposed portion.

[0043] [Fabrication of the negative electrode] A negative electrode slurry was prepared by mixing 95 parts by mass of graphite powder, 5 parts by mass of Si oxide, 1 part by mass of carboxymethylcellulose sodium (CMC-Na), and 1 part by mass of styrene-butadiene rubber (SBR) dispersion, and adding an appropriate amount of water. Next, the negative electrode slurry was applied to both sides of an 8 μm thick copper foil, and the coating was dried. After rolling the coating using a roller, it was cut to a predetermined electrode size, and a negative electrode was fabricated in which a negative electrode slurry layer was formed on both sides of the negative electrode current collector. An exposed portion was provided at one end in the longitudinal direction of the negative electrode (the end located on the inside of the electrode body's winding) where the negative electrode slurry layer was not formed and the negative electrode current collector was exposed, and a nickel negative electrode lead was welded to this exposed portion.

[0044] [Separator fabrication] A porous polyethylene substrate with a thickness of 12 μm was prepared. α-Al2O3 powder with an average particle size (D50) of 0.8 μm and an acrylic ester-based binder emulsion were mixed in a solid content mass ratio of 97:3. An appropriate amount of water was then added to prepare a first dispersion solution to achieve a solid content concentration of 10% by mass. The first dispersion solution was applied to the entire surface of one side of the substrate using a microgravure coater. The coating was then heated and dried in a 50°C oven for 4 hours to form a first inorganic particle layer with an average thickness of 4 μm on one side of the substrate.

[0045] Furthermore, a second dispersion was prepared by mixing α-Al2O3 powder with an average particle size (D50) of 0.3 μm with an acrylic acid ester-based binder emulsion in a solid content mass ratio of 97:3, and then adding an appropriate amount of water to achieve a solid content concentration of 10% by mass. The second dispersion was intermittently applied to the surface of the first inorganic particle layer using a microgravure coater, and the coating film was heated and dried in a 50°C oven for 4 hours to form a second inorganic particle layer with an average thickness of 3 μm, thereby fabricating a separator. When the positive electrode, negative electrode, and separator were wound to form an electrode body, the second dispersion was applied so that the second inorganic particle layer was formed in a range of two turns in the winding direction from a position opposite the inner end of the positive electrode mixture layer.

[0046] The friction coefficients of the surfaces of the first inorganic particle layer and the second inorganic particle layer were measured using the method described above. The friction coefficient of the first inorganic particle layer was 0.4, and the friction coefficient of the second inorganic particle layer was 0.6.

[0047] [Fabrication of electrode bodies] A wound electrode body was fabricated by spirally winding the positive and negative electrodes with a separator in between. The separator was positioned so that the first and second inorganic particle layers faced the positive electrode mixture layer, and the second inorganic particle layer was on the inside of the wound electrode body. The number of turns of the electrode body was set to 18, based on the positive electrode.

[0048] [Preparation of non-aqueous electrolytes] A non-aqueous electrolyte was prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, and then dissolving lithium hexafluoride phosphate (LiPF6) at a concentration of 1.5 mol / liter.

[0049] [Fabrication of non-aqueous electrolyte secondary batteries] Insulating plates were placed above and below the electrode assembly, and the electrode assembly was housed in an outer casing. The negative electrode lead was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode lead was welded to the sealing body. After injecting a non-aqueous electrolyte into the outer casing, the opening of the outer casing was sealed with the sealing body via a gasket, and then the device was left to stand in a 60°C constant temperature bath for 15 hours to produce a non-aqueous electrolyte secondary battery. The capacity of the produced secondary battery was 4600mAh.

[0050] [Evaluation of winding misalignment] Ten of the above-described electrode bodies were fabricated, and the flatness of the separator ends on the upper surface of the electrode bodies was observed using a stereomicroscope. If the vertical difference between the separator ends was 0.3 mm or more, it was determined that a winding misalignment had occurred in the electrode body, and the number of electrode bodies with winding misalignment was evaluated.

[0051] [Evaluation of plate deformation] The above non-aqueous electrolyte secondary battery was charged with a constant current of 1380mA (0.3It) until the battery voltage reached 4.2V, and then charged again with a constant voltage of 4.2V until the current reached 92mA (0.02It). Subsequently, it was discharged with a constant current of 4600mA (1.0It) until the battery voltage reached 2.7V. This charge-discharge cycle was repeated 500 times, with a 20-minute rest period between each cycle. After 500 cycles, the non-aqueous electrolyte secondary battery was charged with a constant current of 1380mA (0.3It) until the battery voltage reached 4.2V, and then charged again with a constant voltage of 4.2V until the current reached 92mA (0.02It) to reach a charged state. The non-aqueous electrolyte secondary battery in this charged state was observed in cross-section near the winding center of the electrode body using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR). As shown in Figure 3, if deformation (bending) of the electrode plate (at least one of the positive and negative electrodes) with an angle θ of 150° or less was observed, it was determined that electrode plate deformation was present, and the presence or absence of electrode plate deformation was evaluated.

[0052] <Example 2> In the preparation of the separator, the electrode body and battery were manufactured and evaluated in the same manner as in Example 1, except that a second inorganic particle layer was formed in a range of four turns in the winding direction from a position opposite the inner end of the positive electrode mixture layer.

[0053] <Example 3> In preparing the separator, the electrode body and battery were prepared and evaluated using the same method as in Example 1, except that the α-Al2O3 powder used in the second dispersion was changed to α-Al2O3 powder with a D50 of 0.3 μm.

[0054] <Comparative Example 1> Except for not forming a second inorganic particle layer in the separator fabrication, the electrode body and battery were fabricated and evaluated using the same method as in Example 1.

[0055] <Comparative Example 2> In the preparation of the separator, the electrode body and battery were manufactured and evaluated in the same manner as in Example 1, except that a second inorganic particle layer was formed in a range of six turns in the winding direction from a position opposite the inner end of the positive electrode mixture layer.

[0056] <Comparative Example 3> In preparing the separator, the electrode body and battery were prepared and evaluated in the same manner as in Example 1, except that the α-Al2O3 powder used in the first dispersion was changed to α-Al2O3 powder with a D50 of 0.2 μm, and the second inorganic particle layer was not formed.

[0057] Table 1 shows the evaluation results of winding misalignment and electrode deformation for the experimental and comparative examples. Table 1 also includes the D50 and friction coefficient of the first inorganic particle layer, as well as the D50, friction coefficient, and range of the second inorganic particle layer.

[0058] [Table 1]

[0059] As can be seen from the evaluation results in Table 1, winding misalignment and electrode deformation were suppressed in Examples 1 to 3. On the other hand, electrode deformation occurred in Comparative Example 1, and winding misalignment occurred in Comparative Examples 2 and 3. [Explanation of symbols]

[0060] 10 Secondary battery, 11 Positive electrode, 11a Positive electrode current collector, 11b Positive electrode mixture layer, 11e Inner end of winding, 12 Negative electrode, 12a Negative electrode current collector, 12b Negative electrode mixture layer, 13 Separator, 13a Substrate, 13b First inorganic particle layer, 13c Second inorganic particle layer, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17,18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, and an outer casing that houses the electrode body, The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The surface of the separator facing the positive electrode mixture layer includes a high-friction region formed in a range of 2 to 6 turns in the winding direction from a position facing the inner end of the winding of the positive electrode mixture layer, and a low-friction region adjacent to the high-friction region in the winding direction. The coefficient of friction in the aforementioned high-friction region is 0.6 or more and 1.1 or less. The coefficient of friction in the low-friction region is 0.1 or more and 0.4 or less. Nonaqueous electrolyte secondary battery.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator includes an inorganic particle layer containing inorganic particles on at least the surface facing the positive electrode mixture layer.

3. The average particle diameter (D50) of the inorganic particles included in the high-friction region is 0.3 μm or less. D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution. The non-aqueous electrolyte secondary battery according to claim 2, wherein the particle size distribution of the inorganic particles is measured using a laser diffraction particle size distribution analyzer with water as the dispersion medium.

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