Nonaqueous electrolyte secondary battery

Abstract

The present invention is characterized in that: a positive electrode mixture layer has a first positive electrode mixture layer that is aligned with a positive electrode current collector exposure part in the longitudinal direction of a positive electrode (11), and a second positive electrode mixture layer that is adjacent to the positive electrode current collector exposure part and the first positive electrode mixture layer in the width direction of the positive electrode; a protective member (36) covers the positive electrode current collector exposure part and a portion of the positive electrode mixture layer, the portion being adjacent to the positive electrode current collector exposure part; a separator (13) has a base material layer (50) and a filler layer (52); the filler layer (52) includes resin particles (54) and has projected parts (56) that are formed by the resin particles (54); and in a surface view of the filler layer (52), the ratio of the area of the projected parts (56) to the area of the surface of the filler layer (52) is 12% or more and 20% or less.

Description

Nonaqueous electrolyte secondary battery

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

[0002] A nonaqueous electrolyte secondary battery is a battery in which an electrode assembly, consisting of a positive electrode and a negative electrode wound with a separator interposed therebetween, is housed in a cylindrical outer can. The positive electrode and the negative electrode each have a current collector and a mixture layer disposed on the surface of the current collector, and the mixture layer contains an active material capable of reversibly absorbing and releasing Li ions. An exposed portion of the current collector is formed on the surface of the electrode, and a tab is attached to the exposed portion to connect the electrode to the battery terminal.

[0003] Patent Document 1 discloses a technique for forming multiple exposed portions in an electrode and connecting tabs to each of the exposed portions, with the aim of suppressing heat generation at the tab connection portion and improving current collection. In the electrode disclosed in Patent Document 1, exposed portions are formed over the entire width of the electrode. Furthermore, a technique is generally known in which the exposed portions and their surrounding areas are covered with a protective member such as insulating tape to ensure the safety of the battery even if the separator is damaged.

[0004] Japanese Patent Application Publication No. 10-261439

[0005] In recent years, batteries have been required to have an ever-increasing capacity. From the viewpoint of increasing capacity, it is preferable that the area of ​​the exposed portion where the mixture layer is not formed is small. The inventors of the present invention have formed the positive electrode current collector exposed portion only in the vicinity of the portion where the tab is connected, rather than forming the positive electrode current collector exposed portion over the entire width direction of the positive electrode.

[0006] However, it has been found that when the above-described structure is adopted for the positive electrode to increase the capacity, lithium deposition may occur in a region of the negative electrode facing the vicinity of the outer edge of the protective member during repeated charge and discharge. From the viewpoint of ensuring the reliability of the nonaqueous electrolyte secondary battery, the deposition of lithium in the negative electrode is undesirable.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector, a positive electrode current collector exposed portion where the positive electrode current collector is exposed is disposed on the surface of the positive electrode, the positive electrode current collector exposed portion is in contact with only one of both ends in the width direction of the positive electrode, a positive electrode tab is connected to the positive electrode current collector exposed portion and is led out from the one end, and the positive electrode mixture layer has a first electrode layer aligned with the positive electrode current collector exposed portion in the longitudinal direction of the positive electrode, the separator has a base material layer and a second positive electrode mixture layer adjacent to the positive electrode current collector exposed portion and the first positive electrode mixture layer in the width direction of the positive electrode, a protective member covers the positive electrode current collector exposed portion and a portion of the positive electrode mixture layer adjacent to the positive electrode current collector exposed portion, the separator has a base material layer and a filler layer arranged on a surface of the base material layer facing the positive electrode, the filler layer contains resin particles and has convex portions formed by the resin particles, and when viewed from the surface of the filler layer, the ratio of the area of ​​the convex portions to the area of ​​the surface of the filler layer is 12% or more and 20% or less.

[0008] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, it is possible to suppress lithium deposition while realizing a high capacity battery.

[0009] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, showing a positive electrode and a negative electrode in an expanded state, which constitute an electrode assembly of the non-aqueous electrolyte secondary battery according to an embodiment of the present invention, and a cross-sectional view for explaining the arrangement of a positive electrode, a negative electrode, and a separator which constitute an electrode assembly of the non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[0010] In nonaqueous electrolyte secondary batteries, multiple positive electrode tabs may be provided to improve current collection at the positive electrode. In this case, from the viewpoint of increasing capacity, it is preferable that the area of ​​the positive electrode current collector exposed portion for connecting the positive electrode tabs is as small as possible. Therefore, a possible embodiment is one in which the positive electrode current collector exposed portion is not formed over the entire width of the positive electrode, but is formed only in the vicinity of the portion where the positive electrode tab is connected.

[0011] However, when a positive electrode having such a configuration is used, it has been found that, during repeated charge and discharge, lithium deposition occurs in the negative electrode in a region facing the vicinity of the outer edge of the protective member covering the exposed portion of the positive electrode current collector. Although the detailed mechanism is unclear, it is presumed that this is due to a gap formed between the positive electrode and the separator due to a step at the outer edge of the protective member. It is presumed that non-aqueous electrolyte tends to accumulate in this gap, causing an imbalance in the charge and discharge reaction within the electrode body and making lithium deposition more likely.

[0012] As will be described in detail later, the separator of the nonaqueous electrolyte secondary battery of the present disclosure has a filler layer containing a predetermined amount of resin particles disposed on the surface facing the positive electrode. By providing a filler layer containing resin particles on the surface of the separator, it is possible to reduce the gap between the positive electrode and the separator that occurs at the outer edge of the protective member. As a result, it is possible to suppress bias in the charge / discharge reaction within the electrode body and suppress lithium precipitation.

[0013] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below with reference to Figures 1 to 3. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is initially assumed that the characteristic portions of these embodiments and modified examples will be used in appropriate combinations.

[0014] First, the overall configuration of a nonaqueous electrolyte secondary battery 10 will be described with reference to Fig. 1. Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 that is an example of an embodiment. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14 and a nonaqueous electrolyte (not shown) housed in an outer can 15. For ease of explanation, the following description will refer to the sealing body 16 side of the nonaqueous electrolyte secondary battery 10 as the "top" and the bottom side of the outer can 15 as the "bottom."

[0015] The electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long strips that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The separator 13 is formed to be slightly larger than the positive electrode 11 and the negative electrode 12, and two separators 13 are arranged to sandwich the positive electrode 11.

[0016] As the non-aqueous solvent (organic solvent) of the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc. can be used, and two or more of these solvents can be mixed and used. When two or more solvents are mixed and used, 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, LiPF ６ , LiBF ４ , LiCF ３ SO ３ The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less.

[0017] The sealing body 16 seals the opening at the top end of the outer can 15, thereby sealing the interior of the nonaqueous electrolyte secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode assembly 14. The positive electrode tab 19 extends vertically through a through-hole in the insulating plate 17 and connects the filter 22, which is the bottom plate of the sealing body 16, to the positive electrode 11 included in the electrode assembly 14. This connects the positive electrode 11 to the sealing body 16, and in the nonaqueous electrolyte secondary battery 10, the cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. The positive electrode tab 19 is, for example, an aluminum tab. On the other hand, the negative electrode tab 20 extends through a through-hole in the insulating plate 18 to the bottom side of the outer can 15 and is welded to the inner bottom surface of the outer can 15. This connects the negative electrode 12 to the outer can 15, and in the nonaqueous electrolyte secondary battery 10, the outer can 15 serves as the negative electrode terminal. The negative electrode tab 20 is, for example, a nickel tab.

[0018] The number of positive electrode tabs 19 extending from the electrode assembly 14 is not particularly limited. Using multiple positive electrode tabs 19 improves the current collection ability of the positive electrode 11, thereby improving the output characteristics of the nonaqueous electrolyte secondary battery 10. The greater the number of positive electrode tabs 19, the better the current collection ability of the positive electrode 11, but the cost of the nonaqueous electrolyte secondary battery 10 increases. Therefore, from the viewpoint of achieving both the above-mentioned effect and cost, the number of positive electrode tabs 19 is preferably 1 to 20, and more preferably 3 to 15. The positive electrode tabs 19 extending from the electrode assembly 14 may be connected directly to the sealing member 16 or may be connected to the sealing member 16 via a known current collecting member.

[0019] 1 , the negative electrode tab 20 is led out from near the inner end of the negative electrode 12 and connected to the outer can 15. The position of the negative electrode tab 20 is not limited to the example shown in FIG. 1 , and the negative electrode tab 20 may be provided only near the outer end of the negative electrode 12, or may be provided near both the inner end and the outer end of the negative electrode 12. Alternatively, an exposed negative electrode current collector portion may be formed at the outer end of the negative electrode 12 and brought into contact with the inner circumferential surface of the outer can 15, thereby electrically connecting the outer end of the negative electrode 12 to the outer can 15 without using the negative electrode tab 20.

[0020] The outer can 15 is a cylindrical metal container with a bottom and an opening on one axial side. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure the airtightness of the interior of the nonaqueous electrolyte secondary battery 10. The outer can 15 has a grooved portion 21 that supports the sealing body 16, formed, for example, by pressing the side surface from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and supports the sealing body 16 on its upper surface.

[0021] The sealing body 16 includes 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 this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may break, causing the upper valve body 25 to swell toward the cap 26 and separate from the lower valve body 23, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may break, allowing gas to be released through a vent in the cap 26.

[0022] Next, the positive electrode 11 and the negative electrode 12 will be described with further reference to Fig. 2. Fig. 2 is a front view showing the positive electrode 11 and the negative electrode 12 constituting the electrode body 14 provided in the nonaqueous electrolyte secondary battery 10 of Fig. 1 in a developed state. As shown in Fig. 2, the negative electrode 12 is generally formed to have dimensions slightly larger than the positive electrode 11 in order to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer in both the longitudinal and width directions than the positive electrode 11.

[0023] As shown in FIGS. 1 and 2 , the positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 32 disposed on the surface of the positive electrode current collector 30. A positive electrode current collector exposed portion 34, where the positive electrode current collector 30 is exposed, is disposed on the surface of the positive electrode 11. The positive electrode current collector exposed portion 34 is in contact with only one end 11a of both widthwise ends of the positive electrode 11. In other words, the positive electrode current collector exposed portion 34 does not extend to the other widthwise end 11b of the positive electrode 11. The positive electrode mixture layer 32 can be divided into a first positive electrode mixture layer 32a aligned with the positive electrode current collector exposed portion 34 in the longitudinal direction of the positive electrode 11, and a second positive electrode mixture layer 32b adjacent to the positive electrode current collector exposed portion 34 and the first positive electrode mixture layer 32a in the widthwise direction of the positive electrode 11. As a result, the positive electrode mixture layer 32 (first positive electrode mixture layer 32a) is present between the positive electrode current collector exposed portions 34, increasing the area of ​​the positive electrode mixture layer 32 and improving the battery capacity of the nonaqueous electrolyte secondary battery 10.

[0024] The first positive electrode mixture layer 32a and the second positive electrode mixture layer 32b may have the same thickness or may have different thicknesses. For example, the thickness of the first positive electrode mixture layer 32a may be smaller than the thickness of the second positive electrode mixture layer 32b. If the first positive electrode mixture layer 32a and the second positive electrode mixture layer 32b have different thicknesses, a step is likely to occur at the outer edge of the protective member 36. Therefore, if the first positive electrode mixture layer 32a and the second positive electrode mixture layer 32b have different thicknesses, the effects of the present disclosure are more pronounced.

[0025] A plurality of positive electrode current collector exposed portions 34 are preferably arranged on the surface of the positive electrode 11. Since one of the positive electrode tabs 19 is connected to each of the positive electrode current collector exposed portions 34, the current collecting ability of the positive electrode 11 is improved, and the output characteristics of the nonaqueous electrolyte secondary battery 10 are improved. Furthermore, the effect of the technology disclosed herein becomes more pronounced as the number of positive electrode current collector exposed portions 34 increases. The number of positive electrode current collector exposed portions 34 is preferably 1 to 20, more preferably 3 to 15, and particularly preferably 3 to 10.

[0026] 2 , the positive electrode current collector exposed portion 34, the positive electrode tab 19, and a portion of the positive electrode mixture layer 32 adjacent to the positive electrode current collector exposed portion 34 are covered with a protective member 36. In other words, the protective member 36 covers the positive electrode tab 19, the positive electrode current collector exposed portion 34, and a portion of the positive electrode mixture layer 32. The protective member 36 is an insulating member that prevents an internal short circuit between the positive electrode tab 19 and the positive electrode current collector exposed portion 34 and the opposing negative electrode mixture layer 42 if the separator 13 is torn.

[0027] The protective member 36 is, for example, an adhesive tape having a substrate and an adhesive portion formed on one surface of the substrate. A heat-resistant layer containing inorganic particles such as metal oxide can be provided between the substrate and the adhesive portion. The substrate can be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate). The thickness of the substrate is, for example, 5 μm or more and 50 μm or less.

[0028] The adhesive portion is a portion for adhering the protective member 36 to the surface of the positive electrode 11. The thickness of the adhesive portion is, for example, 1 μm or more and 30 μm or less. The adhesive portion may contain at least one of a rubber-based polymer and an acrylic-based polymer. The rubber-based polymer and the acrylic-based polymer have adhesive properties, and therefore can adhere the protective member 36 to the surface of the positive electrode 11. The adhesive portion may further contain, for example, a silicone-based polymer.

[0029] A foil of a metal such as aluminum that is stable in the potential range of the positive electrode, a film having such a metal disposed on the surface, or the like can be used for the positive electrode current collector 30. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0030] The positive electrode mixture layer 32 is preferably formed on both sides of the positive electrode current collector 30. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode current collector 30. The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode can be produced, for example, by applying a positive electrode mixture slurry including a positive electrode active material, a conductive agent, a binder, etc. to both sides of the positive electrode current collector 30, drying the coating, and then rolling the coating using a roller or the like.

[0031] The positive electrode active material contained in the positive electrode mixture layer 32 can be, for example, a lithium transition metal composite oxide containing a transition metal element such as Co, Mn, or Ni. ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Li ｘ Ni １－ｙ M ｙ O ｚ , Li ｘ Mn ２ O ４ , Li ｘ Mn ２－ｙ M ｙ O ４ , LiMPO ４ , Li ２ MPO ４ F (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, and 0<x≦1.2, 0<y≦0.9, and 2.0≦z≦2.3). These may be used alone or in combination.

[0032] The positive electrode active material preferably contains a lithium nickel composite oxide, since this can increase the capacity of the nonaqueous electrolyte secondary battery 10. The lithium nickel composite oxide is preferably Li ｘ NiO ２ , Liｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Ni １－ｙ M ｙ O ｚ (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B; 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3) The higher the Ni content of the lithium nickel composite oxide, the higher the capacity.

[0033] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphene, and graphite. These may be used alone or in combination of two or more.

[0034] Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, etc. These may be used alone or in combination of two or more.

[0035] 1 and 2 , the negative electrode 12 has a negative electrode current collector 40 and a negative electrode mixture layer 42 disposed on the surface of the negative electrode current collector 40. The negative electrode 12 has a negative electrode current collector exposed portion 44 where the negative electrode current collector 40 is exposed, for example, at an end on the inner side of the winding in the longitudinal direction. A negative electrode tab 20 is connected to the negative electrode current collector exposed portion 44.

[0036] A foil of a metal such as copper that is stable in the potential range of the negative electrode, or a film having such a metal disposed on the surface layer, can be used for the negative electrode current collector 40. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0037] The negative electrode mixture layer 42 is preferably formed on both sides of the negative electrode current collector 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector 40. The negative electrode mixture layer 42 includes, for example, a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry including a negative electrode active material, a binder, and the like to both sides of the negative electrode current collector 40, drying the coating, and then rolling the coating using a roller or the like.

[0038] The negative electrode active material contained in the negative electrode mixture layer 42 is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads.

[0039] Furthermore, as the negative electrode active material, metals that can be alloyed with Li, such as Si and Sn, metal compounds containing Si, Sn, etc., and lithium-titanium composite oxides may be used. For example, SiO ｘ Si-containing compounds represented by (0.5≦x≦1.6), Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2), or a Si-containing compound in which Si is dispersed in a carbon material, may be used in combination with a carbon material such as graphite.

[0040] Examples of the binder contained in the negative electrode mixture layer 42 include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0041] Next, the separator 13 will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view for explaining the arrangement of the positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode assembly 14, and is an enlarged view of a stepped portion on the outer edge of the protective member 36.

[0042] 3 , the separator 13 has a substrate layer 50 and a filler layer 52 disposed on the surface of the substrate layer 50 facing the positive electrode 11. In this embodiment, the filler layer 52 is disposed on only one surface of the substrate layer 50, with the filler layer 52 facing the positive electrode 11 and the substrate layer 50 facing the negative electrode 12. Note that the form of the separator 13 is not limited to the example shown in FIG. 3 , and the filler layer 52 may be disposed on both surfaces of the substrate layer 50.

[0043] The substrate layer 50 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. The material of the substrate layer 50 is not particularly limited, but examples include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyesters, cellulose, polyimides, polyphenylene sulfide, polyether ether ketones, and fluororesins. The substrate layer 50 may have a single-layer structure or a multi-layer structure.

[0044] The thickness of the base layer 50 is preferably 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.

[0045] The porosity of the substrate layer 50 is preferably, for example, 30% or more and 70% or less in order to ensure ionic conductivity during charging and discharging of the battery. The porosity of the substrate layer 50 is measured by the following method. (1) Ten circular pieces with a diameter of 2 cm are punched out of the substrate layer 50, and the thickness h and mass w of the center of each of the punched pieces of the substrate layer 50 are measured. (2) The volume V and mass W of the 10 pieces are determined from the thickness h and mass w, and the porosity ε is calculated using the following formula: Porosity ε (%) = ((ρV - W) / (ρV)) × 100, where ρ is the density of the material constituting the substrate.

[0046] The filler layer 52 includes inorganic particles, non-conductive resin particles 54, and a binder. The filler layer 52 also has protrusions 56 formed by the resin particles 54, and the protrusions 56 protrude from an inorganic particle layer 58 of the filler layer 52 that is formed by the inorganic particles and the binder.

[0047] The thickness of the inorganic particle layer 58 is preferably smaller than the thickness of the base layer 50, for example, 0.5 μm or more and 10.0 μm or less, and preferably 1.0 μm or more and 5.0 μm or less.

[0048] Examples of inorganic particles include metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles. 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. Furthermore, inorganic particles include zeolite (M ２／ｎ O.Al ２ O ３ xSiO ２ ・yH ２ O, M is a metal element, n is the valence of M, x≧2, y≧0), porous aluminosilicates such as talc (Mg ３ Si ４ O １０ (OH) ２ ), layered silicates such as barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ These may be used alone or in combination of two or more.

[0049] The volume-based average particle size (D50) of inorganic particles is, for example, 0.05 μm or more and 2 μm or less. The volume-based average particle size (D50) of inorganic particles means the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of inorganic particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell) using water as a dispersion medium.

[0050] The content of inorganic particles in the filler layer 52 is, for example, 70% by mass or more and 99% by mass or less, preferably 80% by mass or more and 99% by mass or less, and more preferably 85% by mass or more and 99% by mass or less, relative to the total mass of the filler layer 52.

[0051] Examples of the material of the resin particles 54 contained in the filler layer 52 include acrylic resins made of ethylenically unsaturated carboxylic acid alkyl esters such as methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate; resins made of cyano group-containing ethylenically unsaturated monomers such as acrylonitrile; and resins made of ethylenically unsaturated carboxylic acids and salts thereof such as acrylic acid, methacrylic acid, and maleic acid.

[0052] The volume-based average particle size (D50) of the resin particles 54 is not particularly limited as long as it can protrude from the inorganic particle layer 58 and form the convex portions 56, but is preferably 0.5 μm or more and 20.0 μm or less, and more preferably 2.0 μm or more and 10.0 μm or less. The volume-based average particle size (D50) of the resin particles 54, like the volume-based average particle size (D50) of inorganic particles, refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also referred to as the median diameter. The particle size distribution of the resin particles 54 can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell) using water as a dispersion medium.

[0053] Here, when viewed from the surface of the filler layer 52, the ratio of the area of ​​the protrusions 56 (resin particles 54) to the surface area of ​​the filler layer 52 is 12% or more, preferably 13% or more, and more preferably 14% or more. By setting the ratio of the area of ​​the protrusions 56 to the surface area of ​​the filler layer 52 to 12% or more, the separator 13 covers the steps at the outer edge of the protective member 36 while being moderately adhered to the positive electrode 11. This reduces gaps between the positive electrode 11 and the separator 13 that occur at the outer edge of the protective member 36. As a result, bias in the charge / discharge reaction within the electrode assembly 14 is suppressed, and lithium precipitation can be suppressed. In other words, if the ratio of the area of ​​the protrusions 56 to the surface area of ​​the filler layer 52 is less than 12%, gaps are more likely to occur between the positive electrode 11 and the separator 13 at the outer edge of the protective member 36. Since the non-aqueous electrolyte is likely to accumulate in the gaps, the charge / discharge reaction within the electrode body 14 becomes unbalanced, and lithium deposition becomes more likely to occur.

[0054] Furthermore, when viewed from the surface of the filler layer 52, the ratio of the area of ​​the protrusions 56 (resin particles 54) to the surface area of ​​the filler layer 52 is 20% or less, preferably 19% or less, and more preferably 18% or less. When viewed from the surface of the filler layer 52, if the ratio of the area of ​​the protrusions 56 to the surface area of ​​the filler layer 52 exceeds 20%, gaps are more likely to occur between the positive electrode 11 and the separator 13 at the outer edge of the protective member 36, which may result in lithium precipitation. When viewed from the surface of the filler layer 52, if the ratio of the area of ​​the protrusions 56 to the surface area of ​​the filler layer 52 exceeds 20%, the ionic conductivity of the separator 13 tends to decrease. Therefore, when viewed from the surface of the filler layer 52, the ratio of the area of ​​the convex portions 56 (resin particles 54) to the area of ​​the surface of the filler layer 52 is 12% or more and 20% or less, preferably 13% or more and 19% or less, and more preferably 14% or more and 18% or less.

[0055] Furthermore, when the surface of the filler layer 52 is observed with a scanning electron microscope (SEM, for example, SU8220 manufactured by Hitachi High-Technologies Corporation), it is preferable that 40 to 300 resin particles are detected in an area of ​​100 μm × 100 μm. This forms an appropriate uneven structure on the surface of the separator 13, which can alleviate internal stress caused by expansion and contraction of the positive electrode 11 and the negative electrode 12 when the nonaqueous electrolyte secondary battery 10 is charged and discharged. As a result, deformation of the positive electrode 11 can be suppressed.

[0056] The resin particles 54 have adhesive properties with the positive electrode 11, and in the nonaqueous electrolyte secondary battery 10, the resin particles 54 are preferably adhered to the positive electrode 11. By adhering the resin particles 54 to the positive electrode 11, it is possible to reduce gaps between the positive electrode 11 and the separator 13 that occur at the outer edge of the protective member 36. Furthermore, by adhering the resin particles 54 to the positive electrode 11, movement of the positive electrode 11 due to charge and discharge is suppressed, and the effect of suppressing peeling of the positive electrode mixture layer 32 becomes more pronounced. The resin particles 54 may exhibit adhesive properties with respect to the positive electrode 11, for example, when a nonaqueous electrolyte is held. Note that having adhesive properties means that when the separator 13 is pressure-bonded to the positive electrode 11 in an overlapping state, the surface of the positive electrode 11 and the surface of the separator 13 can be in contact with each other and not separate.

[0057] The adhesive strength of the filler layer 52 is preferably 7 N / m or more, and more preferably 10 N / m or more. By making the adhesive strength of the filler layer 52 7 N / m or more, it is possible to further reduce the gap between the positive electrode 11 and the separator 13 that occurs at the outer edge of the protective member 36. As a result, bias in the charge / discharge reaction within the electrode body 14 is suppressed, and lithium precipitation can be further suppressed. Furthermore, the adhesive strength of the filler layer 52 is preferably 20 N / m or less, and more preferably 19 N / m or less. If the adhesive strength of the filler layer 52 exceeds 20 N / m, the area in contact with the positive electrode 11 may become too large, which may reduce the ionic conductivity of the separator 13. Therefore, the adhesive strength of the filler layer 52 is preferably 7 N / m or more and 20 N / m or less, and more preferably 10 N / m or more and 19 N / m or less. The adhesive strength of the filler layer 52 can be measured by compressing the non-aqueous electrolyte, the filler layer 52, and the positive electrode mixture layer 32 with a heat press, and dividing the load applied when the positive electrode mixture layer 32 is peeled off from the filler layer 52 by the width of the adhesive surface between the positive electrode mixture layer 32 and the filler layer 52 using a precision load measuring device (for example, MODEL-1605VCL manufactured by Aiko Engineering Co., Ltd.).

[0058] The binder contained in the filler layer 52 functions to bond the inorganic particles serving as fillers together and to bond the fillers to the base material layer 50. The binder is preferably a polymer material, and examples thereof include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide-based resins, polyamide-based resins, acrylic resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0059] A method for forming the filler layer 52 containing the inorganic particles and the resin particles 54 on the surface of the separator 13 includes preparing a dispersion liquid in which the inorganic particles and the resin particles 54 are dispersed, applying the dispersion liquid to the surface of the base material layer 50, and drying the dispersion liquid. Examples of methods for applying the dispersion liquid to the surface of the base material layer 50 include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing, and among these, gravure coating is preferred.

[0060] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0061] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ An aluminum-containing lithium nickel cobalt oxide represented by the formula (I) was used. The above positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a solids mass ratio of 100:1:0.9, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a strip-shaped positive electrode current collector made of aluminum foil with a thickness of 15 μm, dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector. Then, eight positive electrode current collector exposed portions in which the positive electrode mixture layer was not present and the positive electrode current collector surface was exposed were provided at one end of the positive electrode in the longitudinal direction. 2 , the ratio t1 / t2 calculated from the widthwise length t1 of the first positive electrode mixture layer and the widthwise length t2 of the second positive electrode mixture layer was 1 / 5. An aluminum positive electrode tab was welded to the exposed portion of the positive electrode current collector. Then, insulating tape was attached as a protective member so as to cover the exposed portion of the positive electrode current collector, the positive electrode tab, and a portion of the positive electrode mixture layer adjacent to the exposed portion of the positive electrode current collector.

[0062] [Fabrication of Negative Electrode] Graphite, silicon oxide (SiO), sodium carboxymethyl cellulose (CMC-Na), and styrene butadiene rubber (SBR) were mixed in a solids mass ratio of 88:12:1:1, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a strip-shaped negative electrode current collector made of copper foil with a thickness of 8 μm, dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode current collector. A negative electrode current collector exposed portion in which the negative electrode mixture layer was not present and the current collector surface was exposed was provided at the inner end of the winding of the negative electrode, and a nickel negative electrode tab was welded to the negative electrode current collector exposed portion.

[0063] [Preparation of separator] Alumina (α-Al) was used as inorganic particles having an average particle size (D50) of 0.7 μm. ２ O ３ ) particles, acrylic resin particles as resin particles having a D50 of 3.5 μm, and an acrylic acid ester-based binder emulsion were mixed in a solid content mass ratio of 100:8:3, and then an appropriate amount of water was added to give a solid content concentration of 10 mass % to prepare a first dispersion.

[0064] A 12 μm-thick porous polyethylene substrate was used as the substrate layer. The first dispersion was applied to the surface of the porous substrate facing the positive electrode. The coating was then dried in an oven at 50° C. for 4 hours to produce a filler layer in which acrylic resin particles protruded from the surface of a 3 μm-thick inorganic particle layer formed from the binder.

[0065] When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), the ratio of the area of ​​the convex portions (acrylic resin particles) to the area of ​​the surface of the filler layer (hereinafter referred to as the "area ratio of the convex portions") was 16%. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 160 acrylic resin particles were detected in an area of ​​100 μm × 100 μm. Furthermore, when the adhesive strength of the filler layer was measured using the method described above, it was 18 N / m.

[0066] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / L of ammonium hydroxide in water.

[0067] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A wound electrode assembly was fabricated by spirally winding the positive and negative electrodes with a separator interposed therebetween. At this time, the filler layer of the separator faced the positive electrode. Insulating plates were placed on the top and bottom of the electrode assembly, respectively, and the electrode assembly was housed in an outer can. The negative electrode tab was welded to the bottom of the cylindrical outer can with a bottom, and the positive electrode tab was welded to a sealing member. After injecting a non-aqueous electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket, thereby fabricating a non-aqueous electrolyte secondary battery.

[0068] [Evaluation of Lithium Deposition] The fabricated nonaqueous electrolyte secondary battery was charged to 4.2 V at a constant current of 0.7 C in a temperature environment of 25° C., and then charged at a constant voltage of 4.2 V until the current value reached 0.01 C. After a 1-hour rest, the battery was discharged to 2.5 V at a constant current of 0.3 C. This constituted one cycle, and 100 cycles were performed. Thereafter, the nonaqueous electrolyte secondary battery was disassembled, and the area of ​​lithium deposited on the surface of the negative electrode was measured. The lithium deposition area ratio was calculated using the following formula: Li deposition area ratio [%] = (area of ​​lithium deposited on the surface of the negative electrode) / (area of ​​the protective member) × 100

[0069] Example 2 In the production of a separator, alumina (α-Al ２ O ３A second dispersion was prepared by mixing acrylic resin particles having a D50 of 3.5 μm, acrylic resin particles as resin particles, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:5:3, and then adding an appropriate amount of water to adjust the solid content concentration to 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the second dispersion was applied to the surface of the porous substrate serving as the substrate layer that faced the positive electrode.

[0070] When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), the area ratio of the convex portions was 12%. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 100 acrylic resin particles were detected in an area of ​​100 μm × 100 μm. Furthermore, when the adhesive strength of the filler layer was measured using the method described above, it was 10 N / m.

[0071] Comparative Example 1 In the production of a separator, alumina (α-Al ２ O ３ A third dispersion was prepared by mixing resin particles and an acrylic acid ester-based binder emulsion at a solids mass ratio of 100:3, and then adding an appropriate amount of water to adjust the solids concentration to 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the third dispersion was applied to the surface of the porous substrate serving as the substrate layer, facing the positive electrode. In other words, the filler layer of Comparative Example 1 did not contain resin particles.

[0072] Comparative Example 2 In the production of a separator, alumina (α-Al ２ O ３ A fourth dispersion was prepared by mixing acrylic resin particles having a D50 of 3.5 μm, acrylic resin particles as resin particles, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:3.5:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass %. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the fourth dispersion was applied to the surface of the porous substrate serving as the substrate layer that faced the positive electrode.

[0073] When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), the area ratio of the convex portions was 10%. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 70 acrylic resin particles were detected in an area of ​​100 μm × 100 μm. Furthermore, when the adhesive strength of the filler layer was measured using the method described above, it was 7 N / m.

[0074] Comparative Example 3 In the production of a separator, alumina (α-Al ２ O ３ A fifth dispersion was prepared by mixing acrylic resin particles having a D50 of 3.5 μm, acrylic resin particles as resin particles, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:2:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass %. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the fifth dispersion was applied to the surface of the porous substrate serving as the substrate layer that faced the positive electrode.

[0075] When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), the area ratio of the convex portions was 7%. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 40 acrylic resin particles were detected in an area of ​​100 μm × 100 μm. Furthermore, when the adhesive strength of the filler layer was measured using the method described above, it was 5 N / m.

[0076] Comparative Example 4 In the production of a separator, alumina (α-Al ２ O ３ A sixth dispersion was prepared by mixing acrylic resin particles having a D50 of 3.5 μm, acrylic resin particles as resin particles, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:11:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the sixth dispersion was applied to the surface of the porous substrate serving as the substrate layer that faced the positive electrode.

[0077] When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), the area ratio of the convex portions was 22%. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 220 acrylic resin particles were detected in an area of ​​100 μm × 100 μm. Furthermore, when the adhesive strength of the filler layer was measured using the method described above, it was 34 N / m.

[0078] The results of the lithium deposition area of ​​the nonaqueous electrolyte secondary batteries of the examples and comparative examples are shown in Table 1. Table 1 also shows the area ratio of the convex portions of each separator, the number of resin particles detected in a 100 μm × 100 μm area, and the adhesive strength of the filler layer.

[0079]

[0080] As shown in Table 1, the nonaqueous electrolyte secondary batteries of the examples did not experience any lithium precipitation, even after repeated charge and discharge. This is presumably because the presence of an appropriate amount of resin particles on the surface of the separator allows the separator to cover the steps at the outer edge of the protective member, thereby reducing the gap between the positive electrode and the separator that occurs at the outer edge of the protective member. On the other hand, the nonaqueous electrolyte secondary batteries of Comparative Examples 2 and 3, in which the area ratio of the protrusions was less than 12%, and the nonaqueous electrolyte secondary battery of Comparative Example 4, in which the area ratio of the protrusions was more than 20%, experienced lithium precipitation after repeated charge and discharge. This is presumably due to the formation of gaps between the positive electrode and the separator at the outer edge of the protective member. Therefore, it can be said that by setting the area ratio of the protrusions to 12% or more and 20% or less, the gap between the positive electrode and the separator at the outer edge of the protective member is reduced, thereby suppressing lithium precipitation.

[0081] The present disclosure will be further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector, a positive electrode current collector exposed portion where the positive electrode current collector is exposed is disposed on the surface of the positive electrode, the positive electrode current collector exposed portion is in contact with only one of both ends in the width direction of the positive electrode, a positive electrode tab is connected to the positive electrode current collector exposed portion and is led out from the one end, and the positive electrode mixture layer includes a first positive electrode mixture layer aligned with the positive electrode current collector exposed portion in the longitudinal direction of the positive electrode, and a second positive electrode mixture layer in the width direction of the positive electrode. a second positive electrode mixture layer adjacent to the positive electrode current collector exposed portion and the first positive electrode mixture layer facing the positive electrode current collector exposed portion, a protective member covering the positive electrode current collector exposed portion and a portion of the positive electrode mixture layer adjacent to the positive electrode current collector exposed portion, the separator having a base material layer and a filler layer disposed on a surface of the base material layer facing the positive electrode, the filler layer containing resin particles and having protrusions formed by the resin particles, and a ratio of an area of ​​the protrusions to an area of ​​the surface of the filler layer in a surface view of the filler layer is 12% or more and 20% or less. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein 40 to 300 of the resin particles are detected in an area of ​​100 μm × 100 μm when the surface of the filler layer is observed with a scanning electron microscope. Aspect 4: The nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 3, wherein the resin particles are non-conductive particles.

[0082] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 11a, 11b end portion, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17, 18 insulating plate, 19 positive electrode tab, 20 negative electrode tab, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 27 gasket, 30 positive electrode current collector, 32 positive electrode mixture layer, 32a first positive electrode mixture layer, 32b second positive electrode mixture layer, 34 positive electrode current collector exposed portion, 36 protective member, 40 negative electrode current collector, 42 negative electrode mixture layer, 44 negative electrode current collector exposed portion, 50 substrate layer, 52 filler layer, 54 resin particles, 56 convex portion, 58 inorganic particle layer

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector, a positive electrode current collector exposed portion where the positive electrode current collector is exposed is disposed on the surface of the positive electrode, the positive electrode current collector exposed portion is in contact with only one of both end portions in the width direction of the positive electrode, a positive electrode tab is connected to the positive electrode current collector exposed portion and is led out from the one end, the positive electrode mixture layer has: a first positive electrode mixture layer aligned with the positive electrode current collector exposed portion in the longitudinal direction of the positive electrode, and a second positive electrode mixture layer adjacent to the positive electrode current collector exposed portion and the first positive electrode mixture layer in the width direction of the positive electrode, and a protective member covers the positive electrode current collector exposed portion and a portion of the positive electrode mixture layer adjacent to the positive electrode current collector exposed portion, the separator has a base material layer and a filler layer disposed on a surface of the base material layer facing the positive electrode, the filler layer contains resin particles and has convex portions formed by the resin particles, and when viewed from the surface of the filler layer, a ratio of an area of ​​the convex portions to an area of ​​the surface of the filler layer is 12% or more and 20% or less.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the resin particles have adhesive properties, and the adhesive strength of the filler layer is 7 N / m or more and 20 N / m or less.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein when the surface of said filler layer is observed with a scanning electron microscope, 40 to 300 of said resin particles are detected in an area of ​​100 μm×100 μm.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin particles are non-conductive particles.

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