Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode (11) and a negative electrode are wound in the length direction with a separator therebetween, said non-aqueous electrolyte secondary battery being characterized in that: the positive electrode (11) has a positive electrode core body (30) and a positive electrode mixture layer (31) that is disposed on the positive electrode core body (30); a mixture layer non-formation section (32) in which the positive electrode mixture layer (31) is not disposed on the positive electrode core body (30) is provided at one end part of the positive electrode (11) in the width direction of the positive electrode (11); provided on both surfaces of the mixture layer non-formation section (32) are a first protective layer (51) that is disposed so as to contact the positive electrode mixture layer (31) and a second protective layer (52) that is disposed so as to contact one end part (51X) of the first protective layer (51) in the width direction; and the thickness (T1) of the first protective layer (51) is greater than the thickness (T2) of the second protective layer (52).

Description

Non-aqueous electrolyte secondary battery

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

[0002] Non-aqueous electrolyte secondary batteries have been known for some time, comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator in between, a non-aqueous electrolyte, and an outer casing that houses the electrode body and the non-aqueous electrolyte. Generally, the positive electrode includes a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core.

[0003] From the viewpoint of improving the output characteristics of non-aqueous electrolyte secondary batteries, a technique is known in which a portion without a composite layer is provided at one axial end of the electrode body, exposing the positive electrode core, and this portion is bent radially and joined to a current collector plate or the like (see, for example, Patent Document 1). In addition, as shown in Patent Document 2, an insulating protective layer may be formed on a part of the portion without a composite layer for the purpose of suppressing internal short circuits, etc.

[0004] Japanese Patent Publication No. 2000-077054 Japanese Patent Publication No. 2023-082463

[0005] Incidentally, it has been found that repeated charging and discharging causes the positive electrode compound layer to stretch in the width direction, applying stress to areas where the compound layer is not formed, and potentially causing these areas to bend. If these areas bend unintentionally, they may come into contact with the negative electrode, potentially causing an internal short circuit.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound longitudinally with a separator between them, a non-aqueous electrolyte, and an outer casing for housing the electrode body and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and one end of the positive electrode in the width direction is provided with a non-composite mixture layer portion in which the positive electrode mixture layer is not disposed on the positive electrode core, and both sides of the non-composite mixture layer portion are provided with a first protective layer disposed in contact with the positive electrode mixture layer and a second protective layer disposed in contact with one end of the first protective layer in the width direction, wherein the thickness of the first protective layer (T1) is greater than the thickness of the second protective layer (T2).

[0007] According to a non-aqueous electrolyte secondary battery in one aspect of this disclosure, when charging and discharging are repeated, the bending of the non-compound layer portion can prevent contact between the non-compound layer portion and the negative electrode, thereby suppressing the occurrence of an internal short circuit.

[0008] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. This is a perspective view of the electrode body of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. This is a plan view showing the positive electrode of a non-aqueous electrolyte secondary battery, which is an example of an embodiment, in an unfolded state. This is a cross-sectional view taken along line A-A in Figure 3.

[0009] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and this disclosure is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in this disclosure.

[0010] The configuration of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment, will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing a cross-section of the non-aqueous electrolyte secondary battery 10, and Figure 2 is a perspective view of the electrode body 14 that constitutes the non-aqueous electrolyte secondary battery 10. Note that the first protective layer 51 and the second protective layer 52, which will be described later, are not shown in Figure 2.

[0011] As shown in Figures 1 and 2, the non-aqueous electrolyte secondary battery 10 comprises an electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, a non-aqueous electrolyte (not shown), an outer casing 15 that houses the electrode body 14 and the non-aqueous electrolyte, and a sealing body 16 that closes the opening of the outer casing 15. In this specification, the side of the non-aqueous electrolyte secondary battery 10 with the sealing body 16 is referred to as "upper," and the bottom side of the outer casing 15 is referred to as "lower."

[0012] The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 that make up the electrode body 14 are all elongated strips, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The positive electrode 11 protrudes above the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes below the positive electrode 11 and the separator 13. For example, two separators 13 are arranged so as to sandwich the positive electrode 11.

[0013] The positive electrode 11 comprises a positive electrode core 30 and a positive electrode mixture layer 31 formed on the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is formed on both sides of the positive electrode core 30, excluding the non-mixture layer portion 32, which will be described later. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0014] The positive electrode composite layer 31 contains particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal elements constituting the lithium metal composite oxide are, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, or lithium metal composite oxides containing Ni, Co, and Al.

[0015] Examples of conductive agents included in the positive electrode mixture layer 31 include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0016] As shown in Figures 1 and 2, the positive electrode 11 has a non-compound layer portion 32 at the upper axial end of the electrode body 14, where the positive electrode compound layer 31 is not provided on the positive electrode core body 30. The non-compound layer portion 32 is provided over the range from the beginning end to the end end of the winding in the longitudinal direction of the elongated positive electrode 11. The non-compound layer portion 32 is bent radially inward starting from the upper end of the second protective layer 52, which will be described later, and is welded to the lower surface of the positive electrode current collector plate 17 on its upper side. By joining the non-compound layer portion 32 to the positive electrode current collector plate 17, the contact area between the non-compound layer portion 32 and the positive electrode current collector plate 17 is increased, so the internal resistance of the positive electrode 11 can be reduced compared to when the positive electrode 11 and the positive electrode current collector plate 17 are connected by a positive electrode tab or the like.

[0017] The negative electrode 12 comprises a negative electrode core 40 and a negative electrode mixture layer 41 formed on the negative electrode core 40. The negative electrode core 40 can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 41 contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both sides of the negative electrode core 40, excluding the non-mixture layer portion 42 described later. The negative electrode 12 can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0018] The negative electrode mixture layer 41 preferably contains a carbon material and a silicon-containing material as negative electrode active materials. Including a silicon-containing material as a negative electrode active material makes it easier to achieve high capacity. In addition, as a negative electrode active material, a material containing at least one of an element that alloys with Li, such as Sn, and a material containing said element may be used in combination.

[0019] From the viewpoint of increasing capacity, the silicon-containing material content is preferably 5% by mass or more, and more preferably 10% by mass or more, of the total mass of the negative electrode active material. Generally, silicon-containing materials exhibit greater volume changes during charging and discharging compared to carbon materials. Therefore, when a silicon-containing material is included as the negative electrode active material, the negative electrode mixture layer 41 tends to expand when charging and discharging is repeated. This compresses the positive electrode mixture layer 31, making it more prone to elongation in the vertical direction, and the non-mixture layer portion 32 of the positive electrode 11 becomes more prone to bending. Thus, when a silicon-containing material is included as the negative electrode active material, the effects of this disclosure, described later, are more pronounced.

[0020] The carbon material that functions as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. In particular, it is preferable to use artificial graphite such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, or earthy graphite, or a mixture thereof as the carbon material. The volume-based D50 of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0021] Silicon-containing materials can be any material containing Si, and examples include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The D50 of composite materials is generally smaller than that of graphite. The volume-based D50 of composite materials is, for example, 1 μm or more and 15 μm or less. One type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0022] A suitable silicon-containing material (composite material) is a composite particle comprising an ionic conductive phase, a Si phase dispersed in the ionic conductive phase, and a conductive layer covering the surface of the ionic conductive phase. The ionic conductive phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ionic conductive phase is a continuous phase composed of an aggregate of particles finer than those of the Si phase. The conductive layer is composed of a material with higher conductivity than the ionic conductive phase and forms a good conductive path in the negative electrode composite layer 41.

[0023] A suitable example of a Si-containing composite material has a sea-island structure in which fine Si particles are dispersed substantially uniformly in an amorphous silicon oxide phase, and the overall general formula is SiO ｘ These are composite particles represented by (0 < x ≤ 2). The main component of silicon oxide may be silicon dioxide. The oxygen content ratio (x) to Si is, for example, 0.5 ≤ x < 2.0, and preferably 0.8 ≤ x ≤ 1.5.

[0024] The binder in the negative electrode mixture layer 41 may be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., similar to the positive electrode mixture layer, but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, a combination of SBR and CMC or a salt thereof, PAA or a salt thereof is preferred. The negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0025] As shown in Figures 1 and 2, the negative electrode 12 has a non-compound layer portion 42 at the lower axial end of the electrode body 14 where the negative electrode compound layer 41 is not provided on the negative electrode core body 40. The non-compound layer portion 42 is provided over the range from the beginning end to the end end of the winding in the longitudinal direction of the elongated negative electrode 12, similar to the case of the positive electrode 11. The non-compound layer portion 42 is bent radially inward at its lower end and welded to the negative electrode current collector plate 18. In addition, the non-aqueous electrolyte secondary battery 10 may not have a negative electrode current collector plate 18, and the non-compound layer portion 42 may be directly joined to the inner surface of the bottom plate of the outer casing 15.

[0026] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0027] Non-aqueous electrolytes are lithium ion conductive. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0028] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0029] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0030] The outer container 15 is a bottomed cylindrical metal container with one end open in the axial direction, and the opening of the outer container 15 is sealed by a sealing body 16.

[0031] A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the battery. The outer casing 15 has a grooved portion 21 formed on its side surface, which protrudes inward to support the sealing body 16. 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. The sealing body 16 is fixed to the upper part of the outer casing 15 by the grooved portion 21 and the open end of the outer casing 15 which is crimped to the sealing body 16.

[0032] The sealing body 16 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 order from the electrode body 14 side. Each component constituting 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 filter 22 has at least one through hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges.

[0033] When the non-aqueous electrolyte secondary battery 10 abnormally generates heat and the internal pressure of the non-aqueous electrolyte secondary battery 10 rises, the lower valve body 23 is deformed and broken so as to push up the upper valve body 25 toward the cap 26 side, and the current path between the lower valve body 23 and the upper valve body 25 is interrupted. When the internal pressure further rises, the upper valve body 25 is broken, and gas is discharged from the through hole 26a of the cap 26. Since the discharge of this gas can prevent the internal pressure of the non-aqueous electrolyte secondary battery 10 from rising excessively and the non-aqueous electrolyte secondary battery 10 from bursting, the safety of the non-aqueous electrolyte secondary battery 10 is improved. The configuration of the sealing body 16 is not limited to this as long as it can close the opening of the outer can 15.

[0034] The non-aqueous electrolyte secondary battery 10 has a metal positive electrode current collector plate 17 on the upper side of the electrode body 14. The positive electrode current collector plate 17 is made of, for example, aluminum, an aluminum alloy, or the like. A non-composite layer forming portion 32 of the positive electrode 11 is connected to the lower surface of the positive electrode current collector plate 17 by welding or the like. The shape of the positive electrode current collector plate 17 is not particularly limited, and for example, it may have a disc or annular shape, or may have a substantially cross shape. Also, a positive electrode lead 20 is connected to the upper surface of the positive electrode current collector plate 17. The positive electrode lead 20 extends toward the sealing body 16 through the through hole of the insulating plate 19, and the upper end portion of the positive electrode lead 20 is connected to the lower surface of the filter 22 of the sealing body 16 by welding or the like. Therefore, the cap 26 constituting the top plate of the sealing body 16 is electrically connected to the filter 22, and the cap 26 serves as a positive electrode terminal.

[0035] The non-aqueous electrolyte secondary battery 10 also has a metal negative electrode current collector plate 18 on the lower side of the electrode body 14. A non-composite layer forming portion 42 of the negative electrode 12 is connected to the upper surface of the negative electrode current collector plate 18. Also, the negative electrode current collector plate 18 is joined to the inner surface of the bottom plate of the outer can 15. Therefore, the outer can 15 electrically connected to the negative electrode 12 through the negative electrode current collector plate 18 serves as a negative electrode terminal.

[0036] Next, the positive electrode 11 will be described in detail while further referring to FIGS. 3 and 4. FIG. 3 is a plan view schematically showing the developed state of the positive electrode 11, and FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3.

[0037] As shown in Figures 3 and 4, the positive electrode 11 has a positive electrode core 30 and positive electrode mixture layers 31 arranged on both sides of the positive electrode core 30. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The thickness of the positive electrode mixture layers 31 is, for example, 50 μm or more and 100 μm or less on one side of the positive electrode core 30.

[0038] As described above, the positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. Here, the tensile elongation at break of the positive electrode core 30 is preferably 3% or more, and more preferably 5% or more. By setting the tensile elongation at break of the positive electrode core 30 to 3% or more, breakage of the positive electrode core 30 during winding of the electrode body 14 can be suppressed. In addition, by setting the tensile elongation at break of the positive electrode core 30 to 3% or more, the winding core diameter of the electrode body 14 can be reduced. As a result, the area of ​​the positive electrode 11 and the negative electrode 12 can be increased, making it easier to achieve higher capacity. Furthermore, by setting the tensile elongation at break of the positive electrode core 30 to 3% or more, bending of the non-composite layer portion 32 during repeated charging and discharging becomes more likely, and the effects of the present disclosure described later are more pronounced. The tensile elongation at break of the positive electrode core 30 is determined by performing a tensile test in accordance with the tensile testing method for metallic materials specified in JIS Z 2241.

[0039] As shown in Figures 3 and 4, the positive electrode 11 has a non-compound layer portion 32 at its upper end where the positive electrode compound layer 31 is not disposed on the positive electrode core 30. The non-compound layer portion 32 has a substantially uniform width over the range from the winding start end 11X to the winding end 11Y in the longitudinal direction of the positive electrode 11. The width of the non-compound layer portion 32 may be, for example, 2 mm or more and 25 mm or less, or 3 mm or more and 20 mm or less.

[0040] In the lower region of the non-composite layer forming portion 32, a first protective layer 51 disposed so as to contact the positive electrode composite layer 31 and a second protective layer 52 disposed so as to contact the upper end 51X of the first protective layer 51 are provided on both surfaces of the non-composite layer forming portion 32, respectively. Although details will be described later, the thickness of the first protective layer 51 is configured to be larger than the thickness of the second protective layer 52. At the time of manufacturing the electrode body 14, the non-composite layer forming portion 32 is bent radially inward starting from the upper end 52X of the second protective layer 52, and the region where the positive electrode core 30 above the second protective layer 52 is exposed is joined to the lower surface of the positive electrode current collector plate 17.

[0041] The first protective layer 51 and the second protective layer 52 are, for example, insulating layers containing an inorganic material and a resin material (binder). By providing the first protective layer 51 and the second protective layer 52 on both surfaces of the non-composite layer forming portion 32, direct contact between the positive electrode core 30 (non-composite layer forming portion 32) and the negative electrode 12 is suppressed. As a result, the occurrence of an internal short circuit is suppressed, and the reliability of the non-aqueous electrolyte secondary battery 10 is improved.

[0042] The materials of the first protective layer 51 and the second protective layer 52 may be different from each other, but in the present embodiment, they are made of the same material. Examples of the inorganic material contained in the first protective layer 51 and the second protective layer 52 include metal oxides, metal nitrides, metal fluorides, carbides, etc. Examples of the metal oxide include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, manganese oxide, etc. Examples of the metal nitride include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, silicon nitride, etc. Examples of the metal fluoride include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, etc. Examples of the carbide include silicon carbide, boron carbide, titanium carbide, tungsten carbide, etc. Further, the inorganic material is 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), etc. of porous aluminosilicate, talc (Mg ３Si ４ O １０ (OH) ２ ) and other layered silicates, barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ ) and other minerals may also be used. These may be used alone or in combination of two or more.

[0043] The inorganic material is composed of, for example, particulate inorganic particles. 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 in the volume-based particle size distribution becomes 50% from the smaller particle size side, and is also called the median diameter. The particle size distribution of the inorganic particles can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac Bell Co., Ltd.) with water as the dispersion medium.

[0044] The content of the inorganic material in the first protective layer 51 and the second protective layer 52 is, for example, 60% by mass or more and 99% by mass or less, preferably 70% by mass or more and 95% by mass or less, based on the total mass of the first protective layer 51 and the second protective layer 52, respectively. When the content of the inorganic material is within the above range, for example, it becomes easier to form the first protective layer 51 and the second protective layer 52 on the surface of the positive electrode core 30.

[0045] The resin material contained in the first protective layer 51 and the second protective layer 52 is preferably a polymer material. 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 its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0046] Here, as shown in Figure 4, the thickness (T1) of the first protective layer 51 is greater than the thickness (T2) of the second protective layer 52. That is, a step is formed at the boundary between the first protective layer 51 and the second protective layer 52, which is the upper end 51X of the first protective layer 51. As a result of the inventors' investigations, it was found that when charging and discharging are repeated, the positive electrode composite layer 31 stretches in the width direction, stress is applied to the non-composite portion of the composite layer 32, and the non-composite portion 32 may bend. If an unintended part of the non-composite portion 32 bends, it may come into contact with the negative electrode 12 facing the non-composite portion 32, potentially causing an internal short circuit.

[0047] As in this embodiment, by making the thickness (T1) of the first protective layer 51 greater than the thickness (T2) of the second protective layer 52, when repeated charging and discharging occurs and stress is applied to the non-compound layer area 32, the boundary portion between the first protective layer 51 and the second protective layer 52 deforms preferentially, relieving the stress applied to the non-compound layer area 32 and suppressing unintended bending of the non-compound layer area 32. In other words, the boundary portion between the first protective layer 51 and the second protective layer 52 functions as an easily deformable portion. As a result, contact between the non-compound layer area 32 and the opposing negative electrode 12 is suppressed, and the occurrence of internal short circuits can be suppressed. When the first protective layer 51 and the second protective layer 52 are made of the same material, the first protective layer 51 refers to the region of the protective layer (insulating layer) formed on the surface of the non-compound layer portion 32 that is below the stepped portion (on the positive electrode compound layer 31 side), and the second protective layer 52 refers to the region of the protective layer formed on the surface of the non-compound layer portion 32 that is above the stepped portion. Furthermore, the thickness of the first protective layer 51 (T1) and the thickness of the second protective layer 52 (T2) refer to the thickness on one side of the positive electrode core body 30 and represent the maximum thickness in each region.

[0048] The ratio (T1 / T2) of the thickness of the first protective layer 51 to the thickness (T2) of the second protective layer 52 is preferably 1.5 or greater, and more preferably 1.7 or greater. By setting this ratio (T1 / T2) to 1.5 or greater, the boundary portion between the first protective layer 51 and the second protective layer 52 becomes more readily deformable, and unintended bending of the non-composite portion 32 of the composite layer is further suppressed. The upper limit of this ratio (T1 / T2) is not particularly limited and is, for example, 20.

[0049] Furthermore, the height of the step formed at the boundary between the first protective layer 51 and the second protective layer 52 is, for example, 5 μm or more, preferably 10 μm or more, and more preferably 20 μm or more. The greater the height of the step formed at the boundary between the first protective layer 51 and the second protective layer 52, the more readily the boundary between the first protective layer 51 and the second protective layer 52 deforms.

[0050] The thickness (T1) of the first protective layer 51 is less than or equal to the thickness of the positive electrode mixture layer 31 on one side of the positive electrode core 30, and may be, for example, 10 μm or more and 100 μm or less, or 20 μm or more and 80 μm or less. In this embodiment, the thickness (T1) of the first protective layer 51 is uniform in the longitudinal and width directions of the positive electrode 11. Furthermore, the thickness (T1) of the first protective layer 51 is uniform on both sides of the positive electrode core 30.

[0051] The thickness (T2) of the second protective layer 52 is smaller than the thickness (T1) of the first protective layer 51, and is, for example, 5 μm or more and 70 μm or less, and may be 20 μm or more and 50 μm or less. By making the thickness (T2) of the second protective layer 52 5 μm or more, the occurrence of internal short circuits when the non-composite layer 32 and the negative electrode 12 come into contact can be suppressed. Furthermore, by making the thickness (T2) of the second protective layer 52 20 μm or more, the occurrence of internal short circuits when the non-composite layer 32 and the negative electrode 12 come into contact can be further suppressed. In this embodiment, the thickness (T2) of the second protective layer 52 is uniform in the longitudinal and width directions of the positive electrode 11. Also, the thickness (T2) of the second protective layer 52 is uniform on both sides of the positive electrode core 30.

[0052] Preferably, the first protective layer 51 is provided on the surface of the non-compound layer portion 32 in a region that is radially opposite to the negative electrode 12. In this case, when the non-compound layer portion 32 bends starting from the boundary between the first protective layer 51 and the second protective layer 52 during repeated charging and discharging, the occurrence of an internal short circuit can be suppressed.

[0053] In this embodiment, the first protective layer 51 and the second protective layer 52 have a substantially constant width along the longitudinal direction of the positive electrode 11. The width of the first protective layer 51 can be appropriately set according to the width of the negative electrode 12, for example, 1 mm or more and 5 mm or less. The width of the second protective layer 52 may be smaller than the width of the first protective layer 51, for example, 1 mm or more and 3 mm or less. The widths of the first protective layer 51 and the second protective layer 52 may be the same.

[0054] As described above, the first protective layer 51 and the second protective layer 52 are provided on both sides of the positive electrode core 30, respectively. However, if the first protective layer 51 and the second protective layer 52 are provided on only one side of the positive electrode core 30, and the protective layer on the other side of the positive electrode core 30 has a uniform thickness in the width direction, the boundary portion between the first protective layer 51 and the second protective layer 52 will not deform preferentially when charging and discharging is repeated, and the effects of this disclosure cannot be achieved. In other words, in order to preferentially deform the boundary portion between the first protective layer 51 and the second protective layer 52 and suppress the occurrence of internal short circuits, it is necessary to provide the first protective layer 51 and the second protective layer 52 on both sides of the positive electrode core 30.

[0055] The first protective layer 51 and the second protective layer 52 are formed, for example, by applying an insulating slurry containing an inorganic material and a resin material to the surface of the non-composite layer 32 (positive electrode core 30) and drying the coating film. In this case, by making the amount of material applied to the area where the first protective layer 51 is formed greater than the amount of material applied to the area where the second protective layer 52 is formed, the thickness (T1) of the first protective layer 51 can be made greater than the thickness (T2) of the second protective layer 52. However, the method of forming the first protective layer 51 and the second protective layer 52 is not limited to this. For example, the insulating slurry forming the first protective layer 51 and the insulating slurry forming the second protective layer 52 may be made of different materials. Also, the first protective layer 51 and the second protective layer 52 may be formed by bonding an insulating film material to both sides of the non-composite layer 32 with an adhesive or the like.

[0056] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0057] <Example 1> [Preparation of the positive electrode] A lithium transition metal oxide containing Ni, Co, and Mn was used as the positive electrode active material. The above positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solid content mass ratio of 98:1:1, and a positive electrode mixture slurry was prepared using N-methylpyrrolidone (NMP) as the dispersion medium. The slurry was applied to both sides of a long aluminum foil positive electrode core with a thickness of 15 μm, and the coating film was dried and compressed to obtain a positive electrode in which a positive electrode mixture layer (thickness on one side: 75 μm) was formed on both sides of the positive electrode core. At this time, a 6 mm wide non-composite portion was provided at one end in the width direction of the positive electrode, where the positive electrode mixture layer was not formed.

[0058] Alumina (Al) as an inorganic material with an average uniform particle size of 0.7 μm ２ O ３ A mixture of particles and polyvinylidene fluoride (PVDF) as a resin material (binder) was mixed in a solid content mass ratio of 90:10. Then, an appropriate amount of NMP was added to make the solid content concentration 30% by mass to prepare an insulating slurry. The insulating slurry was then applied to predetermined areas on both sides of the non-composite-formed portion of the positive electrode composite layer so as to be in contact with the positive electrode composite layer, and the coating film was dried. At this time, the amount applied to the area where the first protective layer is formed was greater than the amount applied to the area where the second protective layer is formed. As a result, the thickness of the first protective layer (T1) was 10 μm, and the thickness of the second protective layer (T2) was 5 μm. The widths of the first and second protective layers were kept constant along the longitudinal direction of the positive electrode. The width of the first protective layer was set to 2 mm, and the width of the second protective layer was set to 1 mm.

[0059] [Fabrication of the negative electrode] A mixture of graphite and Si oxide (SiO) in a mass ratio of 95:5 was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber dispersion, and carboxymethylcellulose sodium were mixed in a solid content mass ratio of 98:1:1, and a negative electrode mixture slurry was prepared using water as the dispersion medium. This slurry was applied to a negative electrode core made of a long copper foil with a thickness of 8 μm, and the coating film was dried and compressed to obtain a negative electrode in which a negative electrode mixture layer was formed on the negative electrode core. At this time, a non-composite portion of the negative electrode mixture layer was provided at one end in the width direction of the negative electrode.

[0060] [Preparation of non-aqueous electrolyte] 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, to which 5 parts by mass of vinylene carbonate (VC) is added, and LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / liter of [the substance].

[0061] [Preparation of Test Cell] The positive electrode, the negative electrode, and the polyethylene separator described above were wound in a spiral shape using a cylindrical winding core to obtain an electrode body. At this time, the winding was done so that the upper end of the negative electrode (negative electrode mixture layer) was positioned 1.5 mm above the upper end of the positive electrode mixture layer. A positive electrode current collector plate and a negative electrode current collector plate were then placed on the upper and lower ends of the prepared electrode body, and the portion of the positive electrode without a mixture layer at the upper end of the electrode body and the portion of the negative electrode without a mixture layer at the lower end of the electrode body were bent radially inward and welded to the positive electrode current collector plate and the negative electrode current collector plate, respectively. At this time, the portion of the positive electrode without a mixture layer was bent radially inward starting from the upper end of the second protective layer.

[0062] Subsequently, the electrode assembly was housed in a bottomed cylindrical outer casing, the negative electrode current collector plate was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode current collector plate and the sealing body were connected with a positive electrode lead. After pouring in the non-aqueous electrolyte, the opening of the outer casing was sealed with the sealing body via a gasket to fabricate a test cell (non-aqueous electrolyte secondary battery).

[0063] [Evaluation of the presence or absence of bending in areas where the compound layer is not formed after cycling] The fabricated test cells were charged to 4.2V with a constant current of 0.5C at a temperature of 25°C, and then charged at a constant voltage of 4.2V until the current value was equivalent to 0.02C. After that, they were discharged with a constant current of 0.5C until the voltage was 2.5V. This constituted one cycle, and 100 cycles were performed. After 100 cycles, X-ray CT images were taken of the test cells using a Shimadzu inspXio SMX-255CT FPD HR. Then, the presence or absence of bending in each area where the compound layer is not formed on the positive electrode of the battery was visually confirmed at the position facing the negative electrode. The ratio of the number of areas where the compound layer is not formed at the position facing the negative electrode to the total number of areas where the compound layer is not formed in the CT image (hereinafter sometimes referred to as the "bending ratio") was calculated. The above test was performed on two test cells, and the average value of the bending ratio in the two test cells was calculated.

[0064] <Example 2> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the thickness (T1) of the first protective layer was set to 30 μm.

[0065] <Example 3> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the thickness (T1) of the first protective layer was set to 60 μm.

[0066] <Example 4> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the thickness of the first protective layer (T1) was set to 40 μm and the thickness of the second protective layer (T2) was set to 30 μm.

[0067] <Example 5> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the thickness of the first protective layer (T1) was set to 50 μm and the thickness of the second protective layer (T2) was set to 30 μm.

[0068] <Example 6> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the thickness of the first protective layer (T1) was set to 60 μm and the thickness of the second protective layer (T2) was set to 30 μm.

[0069] <Comparative Example 1> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the insulating slurry was applied to achieve a uniform thickness across the width direction. That is, the positive electrode of Comparative Example 1 had only a first protective layer and no second protective layer. The thickness (T1) of the first protective layer was set to 30 μm, and the width of the first protective layer was set to 3 mm.

[0070] <Comparative Example 2> In the preparation of the positive electrode, the test cell was prepared and evaluated in the same manner as in Comparative Example 1, except that the thickness of the first protective layer (T1) was set to 60 μm.

[0071] Table 1 shows the evaluation results for the bending ratio of each test cell. In Table 1, the bending ratio was evaluated using ◎, ○, and × based on the following evaluation criteria: ◎: Bending ratio is 0% (no bending occurs at the position opposite the negative electrode) ○: Bending ratio is greater than 0% but less than 10% ×: Bending ratio is 10% or more

[0072]

[0073] As shown in Table 1, the test cell of the example shows a significantly reduced degree of bending compared to the test cell of the comparative example. Furthermore, in the test cell of the example, deformation occurred after the cycle, starting from the boundary between the first protective layer and the second protective layer. Therefore, by providing a thickness difference between the first protective layer and the second protective layer, the non-compound layer formation area deforms starting from the boundary between the first and second protective layers, the stress applied to the non-compound layer formation area is relieved, and bending of the non-compound layer formation area at the position facing the negative electrode can be suppressed.

[0074] Furthermore, a comparison between Example 1 and Examples 2 and 3, and between Example 4 and Examples 5 and 6, suggests that increasing the ratio (T1 / T2) of the thickness of the first protective layer to the thickness of the second protective layer (T2) can further suppress the bending of the non-formed compound layer at the position facing the negative electrode.

[0075] This disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound longitudinally via a separator, a non-aqueous electrolyte, and an outer casing for housing the electrode body and the non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and a non-composite mixture layer portion is provided at one end of the positive electrode in the width direction, and a first protective layer disposed in contact with the positive electrode mixture layer and a second protective layer disposed in contact with one end of the first protective layer in the width direction are provided on both sides of the non-composite mixture layer portion, and the thickness of the first protective layer (T1) is greater than the thickness of the second protective layer (T2), the non-aqueous electrolyte secondary battery. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the thickness (T1) of the first protective layer is less than or equal to the thickness of the positive electrode mixture layer, and the ratio (T1 / T2) of the thickness of the first protective layer to the thickness (T2) of the second protective layer is 1.5 or more. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the thickness (T2) of the second protective layer is 5 μm or more. Configuration 4: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the thickness (T2) of the second protective layer is 20 μm or more. Configuration 5: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the first protective layer is provided in a region of the surface of the non-mixture layer portion that faces the negative electrode in the radial direction. Configuration 6: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the first protective layer and the second protective layer include an inorganic material and a resin material. Configuration 7: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the tensile elongation at break of the positive electrode core is 3% or more. Configuration 8: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the negative electrode contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5% by mass or more of the total mass of the negative electrode active material.

[0076] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 11X Winding start end, 11Y Winding end, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer can, 16 Sealing body, 17 Positive electrode current collector plate, 18 Negative electrode current collector plate, 19 Insulating plate, 20 Positive electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Through hole, 27 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 32 Mixture layer non-formed section, 40 Negative electrode core body, 41 Negative electrode mixture layer, 42 Mixture layer non-formed section, 51 First protective layer, 52 Second protective layer

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are wound longitudinally with a separator between them; a non-aqueous electrolyte; and an outer casing for housing the electrode body and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and a non-composite mixture layer portion is provided at one end of the positive electrode in the width direction, and a first protective layer disposed in contact with the positive electrode mixture layer and a second protective layer disposed in contact with one end of the first protective layer in the width direction are provided on both sides of the non-composite mixture layer portion, and the thickness of the first protective layer (T1) is greater than the thickness of the second protective layer (T2).

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness (T1) of the first protective layer is less than or equal to the thickness of the positive electrode mixture layer, and the ratio (T1 / T2) of the thickness of the first protective layer to the thickness (T2) of the second protective layer is 1.5 or more.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness (T2) of the second protective layer is 5 μm or more.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness (T2) of the second protective layer is 20 μm or more.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first protective layer is provided on the surface of the portion where the mixture layer is not formed, in a region facing radially from the negative electrode.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first protective layer and the second protective layer comprise an inorganic material and a resin material.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the tensile elongation at break of the positive electrode core is 3% or more.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5% by mass or more of the total mass of the negative electrode active material.

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