Cylindrical secondary battery

Abstract

In a cylindrical secondary battery according to one embodiment of the present application, a plurality of positive electrode exposed portions from which a positive electrode current collector is exposed are disposed on the surface of a positive electrode, and the positive electrode exposed portions are in contact with only one of both end portions of the positive electrode in the width direction. The separator has a base layer and a filler layer disposed on a surface of the base layer facing the positive electrode, and the filler layer contains resin particles and has protrusions formed from the resin particles. The surface of the positive electrode is divided into a positive electrode exposed part arrangement region in which the positive electrode exposed part is arranged, and a positive electrode exposed part non-arrangement region adjacent to the positive electrode exposed part arrangement region in the width direction. When the surface of the spacer is defined as a first region facing the positive electrode exposed portion arrangement region and a second region facing the positive electrode exposed portion non-arrangement region, the area ratio S1 of the area of the convex portion in the first region is larger than the area ratio S2 of the area of the convex portion in the second region.

Description

Technical Field

[0001] The present application relates to a cylindrical secondary battery. Background Art

[0002] A cylindrical secondary battery is a battery in which an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is housed in a cylindrical outer packaging 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 that can reversibly absorb and release Li ions. An exposed portion from which the current collector is exposed is formed on the surface of the electrode, and a connector for connecting the electrode to the terminal of the battery is connected to the exposed portion. Patent Document 1 discloses a technology of forming multiple exposed portions on an electrode and connecting connectors to each exposed portion for the purpose of suppressing heat generation at the connector connection portion and improving current collection. In the electrode disclosed in Patent Document 1, an exposed portion is formed over the entire length in the width direction.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 10-261439 Summary of the Invention

[0006] However, in recent years, there has been an increasing demand for higher capacity batteries. From the perspective of higher capacity, it is preferred that the area of ​​the exposed portion where the composite layer is not formed is small. The present inventors did not form the exposed portion over the entire width of the positive electrode, but only formed the exposed portion near the portion where the connector is connected. The present inventors further conducted repeated studies and found that due to repeated charge and discharge, the composite layer is easily peeled off at the end of the positive electrode on the side where the exposed portion is formed. The technology disclosed in Patent Document 1 does not envision the situation where the exposed portion is formed only at one end, so the peeling of the composite layer after the charge and discharge cycle has not been studied, and there is still room for improvement.

[0007] An object of the present application is to provide a cylindrical secondary battery in which separation of a mixture layer after charge and discharge cycles is suppressed.

[0008] The cylindrical secondary battery as one embodiment of the present application is characterized in that it comprises an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer packaging can for storing the electrode body and the non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode collector and a positive electrode mixture layer arranged on the surface of the positive electrode collector, a plurality of positive electrode exposure portions are arranged on the surface of the positive electrode to expose the positive electrode collector, and the positive electrode exposure portion is in contact with only one of the two end portions in the width direction of the positive electrode, and the separator comprises a base material layer and a surface layer arranged on the base material layer facing the positive electrode. The filler layer comprises resin particles and has convex portions formed by the resin particles. When the surface of the positive electrode is divided into a positive electrode exposed portion configuration area in which a positive electrode exposed portion is configured and a positive electrode exposed portion non-configuration area adjacent to the positive electrode exposed portion configuration area in a width direction, and the surface of the separator is set as a first area facing the positive electrode exposed portion configuration area and a second area facing the positive electrode exposed portion non-configuration area, an area ratio S1 of the area of ​​the convex portion in the first area is greater than an area ratio S2 of the area of ​​the convex portion in the second area.

[0009] According to the cylindrical secondary battery of the present application, peeling of the mixture layer after charge and discharge cycles can be suppressed, thereby improving the safety of the cylindrical secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a longitudinal sectional view of a cylindrical secondary battery as an example of an embodiment.

[0011] Figure 2 It will constitute Figure 1 A front view showing the positive electrode and the negative electrode of an electrode assembly of a cylindrical secondary battery in a developed state.

[0012] Figure 3 Is used to illustrate the composition Figure 2 A cross-sectional view showing the arrangement of the positive electrode, negative electrode, and separator of the electrode assembly shown. DETAILED DESCRIPTION

[0013] In cylindrical secondary batteries, multiple positive electrode connectors are sometimes provided for the purpose of improving the current collection in the positive electrode. In this case, from the perspective of high capacity, the area of ​​the positive electrode exposed portion for connecting the positive electrode connector is preferably as small as possible. Therefore, it is possible to consider a method in which the positive electrode exposed portion is not formed over the entire length of the width direction of the positive electrode, but is formed only near the portion where the positive electrode connector is connected. However, it has been found that when a positive electrode having such a method is used, it is easy for the mixture layer to peel off at the end of the side of the positive electrode where the exposed portion is formed due to charge and discharge cycles. This can be considered to be because when the electrode body expands and contracts due to charge and discharge, the end of the side of the positive electrode where the exposed portion is formed is easier to move along the length direction than the end on the opposite side. The present inventors have conducted extensive research and discovered that by making the contact area with the positive electrode in the first region larger than the contact area with the positive electrode in the second region, with the first region facing the positive electrode exposed portion arrangement region where the positive electrode exposed portion exists, and the second region facing the positive electrode exposed portion non-arrangement region where the positive electrode exposed portion does not exist, peeling of the material mixture layer can be suppressed. This is believed to be due to a smaller difference in elongation during charge and discharge between the two ends of the positive electrode in the width direction.

[0014] Below, in reference Figures 1 to 3 At the same time, an example of an embodiment of the cylindrical secondary battery of the present application is described in detail. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating the understanding of the present invention and may be appropriately changed according to the specifications of the cylindrical secondary battery. In addition, in the following description, when multiple embodiments and variations are included, it is initially envisaged that their characteristic parts will be appropriately combined and used. In addition, in this specification, when a phrase such as "approximately" is used, it is used in the same meaning as a phrase such as "approximately", and requirements such as "approximately to" are satisfied as long as they are substantially the same.

[0015] Figure 1 1 is a longitudinal sectional view of a cylindrical secondary battery 10 (hereinafter referred to as secondary battery 10 ) as an example of an embodiment. Figure 1 The secondary battery 10 shown contains an electrode assembly 14 and a nonaqueous electrolyte (not shown) in an outer can 15. For convenience, the following description will refer to the sealing member 16 as "upper" and the bottom of the outer can 15 as "lower."

[0016] The electrode body 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with a separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long strips, which are wound in a spiral and alternately stacked along the radial direction of the electrode body 14. The separator 13 is formed to be slightly larger than the positive electrode 11 and the negative electrode 12, and two separators are arranged so as to sandwich the positive electrode 11.

[0017] Carbonates, lactones, ethers, ketones, esters, etc. can be used as non-aqueous solvents (organic solvents) for non-aqueous electrolytes, and two or more of these solvents can be mixed. When two or more solvents are mixed, a mixed solvent containing cyclic carbonates and chain carbonates is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as cyclic carbonates, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as chain carbonates. LiPF6, LiBF4, LiCF3SO3, etc. and mixtures thereof can be used as electrolyte salts for non-aqueous electrolytes. The amount of electrolyte salt dissolved in the non-aqueous solvent can be set to, for example, 0.5 mol / L or more and 2.0 mol / L or less.

[0018] The sealing body 16 seals the opening at the upper end of the outer can 15, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode tab 19 passes through the through hole of the insulating plate 17 and extends up and down, connecting the filter 22, which serves as the bottom plate of the sealing body 16, to the positive electrode 11 contained in the electrode body 14. In this way, the positive electrode 11 and the sealing body 16 are connected, and in the secondary battery 10, the cover 26, which serves as the top plate of the sealing body 16 and is electrically connected to the filter 22, becomes the positive terminal. The positive electrode tab 19 is, for example, an aluminum tab. On the other hand, the negative electrode tab 20 passes through the through hole of the insulating plate 18 and extends to the bottom side of the outer can 15 and is welded to the bottom inner surface of the outer can 15. In this way, the negative electrode 12 and the outer can 15 are connected, and in the secondary battery 10, the outer can 15 becomes the negative terminal. The negative electrode tab 20 is, for example, a nickel tab.

[0019] Figure 1 In the example shown, three positive electrode terminals 19 are derived from the electrode body 14, but the number of positive electrode terminals 19 derived from the electrode body 14 is not particularly limited. Since the current collection of the positive electrode 11 is improved by using multiple positive electrode terminals 19, the output characteristics of the secondary battery 10 can be improved. The more positive electrode terminals 19 there are, the higher the current collection of the positive electrode 11, but the cost of the secondary battery 10 increases. Therefore, from the perspective of taking into account the above-mentioned effects and costs, the number of positive electrode terminals 19 is preferably more than 3 and less than 10, and more preferably more than 3 and less than 8. It should be noted that the more than 3 positive electrode terminals 19 derived from the electrode body 14 can be directly connected to the sealing body 16, or can be connected to the sealing body 16 via a known current collecting member. The negative electrode terminal 20 is, for example, Figure 1 As shown, the negative electrode tab 20 is led out from the vicinity of the inner end of the winding of the negative electrode 12 and connected to the outer can 15. The arrangement position of the negative electrode tab 20 is not limited to Figure 1In the example shown, the negative electrode tab 20 may be provided only near the outer end of the winding of the negative electrode 12, or may be provided both near the inner end and near the outer end of the winding of the negative electrode 12. Alternatively, a negative electrode exposed portion 44 may be formed at the outer end of the winding of the negative electrode 12, and the exposed negative electrode portion 44 may be brought into contact with the inner circumferential surface of the outer can 15, thereby electrically connecting the outer end of the winding 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 open side axially. A gasket 27 is provided between the outer can 15 and the sealing member 16 to ensure the airtightness of the secondary battery 10. The outer can 15 has a groove 21 formed, for example, by pressing the side surface from the outside, to support the sealing member 16. The groove 21 is preferably formed in an annular shape along the circumference of the outer can 15, and its upper surface supports the sealing member 16.

[0021] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25 and a cover 26 stacked in sequence from the electrode body 14 side. The components constituting the sealing body 16 have, for example, a disc shape or a ring shape, and the components except 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 central portions, and an insulating member 24 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat, for example, the lower valve body 23 breaks, and the upper valve body 25 bulges toward the cover 26 side and detaches from the lower valve body 23, thereby blocking the electrical connection between the two. When the internal pressure rises further, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cover 26.

[0022] Below, in reference Figure 2 At the same time, the positive electrode 11 and the negative electrode 12 are described. Figure 2 It will constitute Figure 1 The positive electrode 11 and the negative electrode 12 of the electrode body 14 of the secondary battery 10 are shown in a front view in an unfolded state. Figure 2 As shown, in order to prevent lithium precipitation, the negative electrode 12 is generally formed slightly larger than the positive electrode 11. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction.

[0023] The positive electrode 11 includes a positive electrode current collector 30 and a positive electrode mixture layer 32 disposed on the surface of the positive electrode current collector 30. Furthermore, a plurality of positive electrode exposure portions 34 are disposed on the surface of the positive electrode 11, where the positive electrode current collector 30 is exposed. The positive electrode exposure portion 34 is in contact with only one end portion 11a of the two end portions in the width direction of the positive electrode 11. That is, the positive electrode exposure portion 34 does not extend to the other end portion 11b in the width direction of the positive electrode 11. Thus, since the positive electrode mixture layer 32 exists between the positive electrode exposure portions 34, the area of ​​the positive electrode mixture layer 32 increases, thereby improving the battery capacity of the secondary battery 10. Furthermore, since one of the positive electrode tabs 19 is connected to each of the positive electrode exposure portions 34, the current collection performance of the positive electrode 11 is improved, thereby improving the output characteristics of the secondary battery 10.

[0024] The positive electrode current collector 30 can be made of a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, or a film having the metal disposed on the surface. The thickness of the positive electrode current collector 30 is, for example, 10 μm to 30 μm.

[0025] 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 to 150 μm 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. For example, a positive electrode mixture slurry containing the positive electrode active material, a conductive agent, and a binder is applied to both sides of the positive electrode current collector 30, and after drying, the coated film is rolled using a roller or the like to produce a positive electrode.

[0026] Examples of the positive electrode active material contained in the positive electrode mixture layer include lithium transition metal composite oxides containing transition metal elements such as Co, Mn, and Ni. For example, lithium transition metal composite oxides are Li x CoO2、Li x NiO2、Li x MnO2、Li x Co y Ni 1-y O2、Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4、Li x Mn 2-y M yO4, LiMPO4, Li2MPO4F (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). These may be used alone or in combination.

[0027] In order to achieve a high capacity of the secondary battery 10, the positive electrode active material preferably contains a lithium nickel composite oxide. Examples of the lithium nickel composite oxide include Li x NiO2、Li x Co y Ni 1-y O2、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), etc. The higher the Ni content of the lithium nickel composite oxide, the higher the capacity.

[0028] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, graphite and other carbon-based particles, etc. These may be used alone or in combination of two or more.

[0029] Examples of the binder contained in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, and polyolefin-based resins. These may be used alone or in combination of two or more.

[0030] The surface of the positive electrode 11 can be divided into a positive electrode exposed portion arrangement region 38, where the positive electrode exposed portion 34 is arranged, and a positive electrode exposed portion non-arrangement region 39 adjacent to the positive electrode exposed portion arrangement region 38 in the width direction. Both the positive electrode exposed portion arrangement region 38 and the positive electrode exposed portion non-arrangement region 39 extend in the longitudinal direction. The ratio of the width length of the positive electrode exposed portion arrangement region 38 to the width length of the positive electrode exposed portion non-arrangement region 39 is preferably 1:1 to 1:10, and more preferably 1:2 to 1:8. Due to the presence of the thin positive electrode exposed portion 34, the positive electrode exposed portion arrangement region 38 is subjected to less pressure in the radial direction of the electrode body than the positive electrode exposed portion non-arrangement region 39, resulting in greater movement during charge and discharge, which can easily cause delamination of the positive electrode mixture layer 32. By adjusting the arrangement of the resin particles 54 on the surface of the separator 13 facing the positive electrode 11 as described later, the difference in movement between the positive electrode exposed portion arrangement region 38 and the positive electrode exposed portion non-arrangement region 39 during charge and discharge can be reduced, thereby suppressing peeling of the positive electrode mixture layer 32 .

[0031] The negative electrode 12 includes 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 exposure portion 44 where the negative electrode current collector 40 is exposed, for example, at the inner end of the winding in the longitudinal direction. The negative electrode tab 20 is connected to the negative electrode exposure portion 44.

[0032] The negative electrode current collector can be made of a metal foil such as copper that is stable in the potential range of the negative electrode, or a film having the metal disposed on the surface. The thickness of the negative electrode current collector is, for example, 5 μm to 30 μm.

[0033] The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector. The negative electrode mixture layer comprises, for example, a negative electrode active material and a binder. For example, a negative electrode mixture slurry comprising a negative electrode active material, a binder, etc. is applied to both sides of the negative electrode current collector, the coating is dried, and then rolled using a roller or the like to produce a negative electrode.

[0034] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly store and release lithium ions. Carbon materials such as graphite are generally used. The graphite may be natural graphite such as flake graphite, block graphite, or earthy graphite, or block artificial graphite or artificial graphite such as graphitized mesocarbon microbeads.

[0035] As the negative electrode active material, metals such as Si and Sn alloyed with Li, metal compounds containing Si and Sn, lithium titanium composite oxides, etc. can be used. x (0.5≤x≤1.6) Si-containing compounds, or Li 2y SiO（2＋y） A Si-containing compound represented by (0<y<2) in which Si fine particles are dispersed in a lithium silicate phase is used in combination with graphite.

[0036] Examples of the binder contained in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and partially neutralized salts are also possible), and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0037] Below, in reference Figure 3 The separator 13 is described below. The separator 13 separates the positive electrode 11 and the negative electrode 12 from each other, and prevents the positive electrode 11 and the negative electrode 12 from coming into contact with each other and causing a short circuit. Figure 3 Is used to illustrate the composition Figure 2 1 is a cross-sectional view showing the arrangement of the positive electrode 11 , the negative electrode 12 , and the separator 13 of the electrode assembly 14 .

[0038] like Figure 3 As shown, the separator 13 includes 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 only on one side of the substrate layer 50, and the filler layer 52 faces the positive electrode 11, while the substrate layer 50 faces the negative electrode 12. It should be noted that the form of the separator 13 is not limited to Figure 3 In the example shown, the filler layer 52 may be disposed on both surfaces of the base material layer 50 .

[0039] For example, a porous sheet having ion permeability and insulation properties is used as the substrate layer 50. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. The material of the substrate layer 50 is not particularly limited, and examples thereof include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyesters, cellulose, polyimides, polyphenylene sulfide, polyetheretherketone, and fluororesins. The substrate layer 50 may be a single-layer structure or a multi-layer structure. The thickness of the substrate layer 50 is preferably not less than 3 μm and not more than 20 μm, and more preferably not less than 5 μm and not more than 15 μm.

[0040] The filler layer 52 includes resin particles 54 , inorganic particles, and a binder. The filler layer 52 also has projections 56 formed of the resin particles 54 , and the projections 56 protrude from an inorganic particle layer 57 formed of inorganic particles and a binder in the filler layer 52 .

[0041] 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. In addition, the inorganic particles may also be zeolite (M 2 / n O·Al2O3·xSiO2·yH2O, M is a metal element, n is the valence of M, x≥2, y≥0) and other porous aluminosilicates, talc (Mg3Si4O 10 (OH)2) and other layered silicates, barium titanate (BaTiO3), strontium titanate (SrTiO3) and other minerals. These may be used alone or in combination of two or more. The binder is preferably a polymer material, for example, fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide resins, polyamide resins, acrylic resins, polyolefin 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.

[0042] As the material of the resin particles 54, for example, there can be cited acrylic resins containing ethylenically unsaturated carboxylic acid alkyl esters such as methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate, resins containing ethylenically unsaturated monomers containing cyano groups such as acrylonitrile, resins containing ethylenically unsaturated carboxylic acids and their salts such as acrylic acid, methacrylic acid, and maleic acid, etc.

[0043] The resin particles 54 have adhesion to the positive electrode 11. In the secondary battery 10, the resin particles 54 preferably adhere to the positive electrode. By adhering the resin particles 54 to the positive electrode 11, the movement of the positive electrode 11 caused by charging and discharging is suppressed, and the effect of suppressing the separation of the positive electrode mixture layer 32 becomes more significant. The resin particles 54 exhibit adhesion to the positive electrode 11, for example, when retaining a non-aqueous electrolyte.

[0044] When the surface of the separator 13 is formed into a first region 58 facing the positive electrode exposed portion arrangement region 38 and a second region 59 facing the positive electrode exposed portion non-arrangement region 39, the area ratio S1 of the area occupied by the protrusions 56 in the first region 58 is greater than the area ratio S2 of the area occupied by the protrusions 56 in the second region 59. Since S1>S2 makes the frictional force generated between the first region 58 and the positive electrode exposed portion arrangement region 38 greater than the frictional force generated between the second region 59 and the positive electrode exposed portion non-arrangement region 39, the difference in the amount of movement between the positive electrode exposed portion arrangement region 38 and the positive electrode exposed portion non-arrangement region 39 during charge and discharge is reduced, thereby suppressing delamination of the positive electrode mixture layer 32.

[0045] S1 is preferably 2% to 20%, more preferably 4% to 16%, and S2 is preferably 0% to 10%, more preferably 0% to 8%.

[0046] S2 / S1 obtained by dividing S2 by S1 satisfies 0≤S2 / S1<1, preferably satisfies 0≤S2 / S1≤0.5, and more preferably satisfies 0≤S2 / S1≤0.25.

[0047] When fabricating the spacer 13, for example, S1 > S2 can be achieved by making the average particle size (D50) of the resin particles 54 contained in the first region 58 larger than the D50 of the resin particles 54 contained in the first region 58. Alternatively, when fabricating the spacer 13, S1 > S2 can be achieved by making the average particle size (D50) of the resin particles 54 contained in the first region 58 and the second region 59 approximately the same, while also making the number of resin particles 54 contained in the first region 58 larger than the number of resin particles 54 contained in the second region 59. The D50 of the resin particles used in fabricating the spacer 13 is, for example, 1 μm to 10 μm. In this specification, the average particle size (D50) refers to the particle size at which the cumulative frequency of particles from the smaller particle size reaches 50% in a volume-based particle size distribution, also referred to as the median diameter. The particle size distribution of the resin particles is measured by dispersing the particles in a dispersion medium using a laser diffraction particle size distribution measuring apparatus (for example, MT3000II manufactured by Microtrac Bell).

[0048] The average particle area of ​​the convex portions 56 in the first region 58 is preferably larger than the average particle area of ​​the convex portions 56 in the second region 59. The average particle area of ​​the convex portions 56 in the first region 58 is, for example, 500 μm. 2 Above and 2000μm 2 Hereinafter, the average particle area of ​​the convex portion 56 in the second region 59 is, for example, 0 μm 2 Above and 1500μm 2Here, the average particle area refers to the area per resin particle measured using separator 13 removed from secondary battery 10 after charge and discharge cycles. Specifically, the surface of filler layer 52 is observed using a scanning electron microscope (e.g., SU8220 manufactured by Hitachi High-Technologies Corporation), and the areas of 30 protrusions 56 in each of first region 58 and second region 59 are averaged to obtain the average particle area.

[0049] Example

[0050] Hereinafter, the present application will be further described using examples, but the present application is not limited to these examples.

[0051] <Example>

[0052] [Production of positive electrode]

[0053] Use LiNi 0.88 Co 0.09 Al 0.03 Lithium nickel cobalt oxide containing aluminum represented by O2 is used as the positive electrode active material. 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black (AB) and 0.9 parts by mass of polyvinylidene fluoride (PVDF) are mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added to prepare a positive electrode mixture slurry. Then, the positive electrode mixture slurry is applied to both sides of a strip-shaped positive electrode collector made of aluminum foil with a thickness of 15μm in such a way as to form 8 positive electrode exposed parts. Figure 2 As shown in the example, the exposed positive electrode portion is placed in contact with only one end of the positive electrode in the width direction. After drying, the coating is rolled and cut into the specified electrode plate dimensions, producing a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode current collector. The ratio of the width length of the area where the exposed positive electrode portion is located to the width length of the area where the exposed positive electrode portion is not located is 1:5. Subsequently, aluminum positive electrode tabs are welded to each of the three exposed positive electrode portions.

[0054] [Production of negative electrode]

[0055] A negative electrode mixture slurry was prepared by mixing 95 parts by mass of graphite, 5 parts by mass of Si oxide (SiO), 1 part by mass of sodium carboxymethylcellulose (CMC-Na), and 1 part by mass of styrene butadiene rubber (SBR). An appropriate amount of water was added to prepare the negative electrode mixture slurry. This slurry was then applied to both sides of a strip-shaped negative electrode current collector made of 8μm-thick copper foil. After drying, the slurry was rolled and cut to the specified electrode plate dimensions, producing a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode current collector. At the inner end of the coiled negative electrode, a negative electrode exposed portion was formed where the negative electrode mixture layer was absent and the current collector surface was exposed. A nickel negative electrode tab was welded to the exposed portion.

[0056] [Making spacers]

[0057] Alumina (α-Al₂O₃) particles with an average particle size (D50) of 0.7 μm as inorganic particles, acrylic resin particles with a D50 of 4 μm as resin particles, and an acrylic adhesive emulsion were mixed at a solids mass ratio of 100:2:3. Water was then added to a suitable amount to achieve a solids concentration of 10% by mass to prepare a first dispersion. A second dispersion was prepared in the same manner as the first dispersion, except that the amount of acrylic resin particles added was changed from 2 parts by mass to 1 part by mass.

[0058] A 12μm-thick polyethylene porous substrate was used as the substrate layer. The first dispersion was applied to the first region of the porous substrate facing the positive electrode exposed portion, and the second dispersion was applied to the second region facing the non-positive electrode exposed portion. The coating was then dried by heating in a 50°C oven for 4 hours, forming a filler layer in which acrylic resin particles protruded from the surface of a 3μm-thick inorganic particle layer formed with a binder.

[0059] [Preparation of non-aqueous electrolyte]

[0060] To 100 parts by mass of a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 3:7, 5 parts by mass of vinylene carbonate (VC) was added, and lithium hexafluorophosphate (LiPF6) was dissolved at a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte.

[0061] [Production of Secondary Batteries]

[0062] The positive and negative electrodes are spirally wound with a separator interposed between them to produce a wound electrode body. At this point, the filler layer of the separator faces the positive electrode. Insulating plates are placed above and below the electrode body, and the electrode body is housed in an outer can. The negative electrode connector is welded to the bottom of a cylindrical outer can with a bottom, and the positive electrode connector is welded to the sealing member. After injecting a non-aqueous electrolyte into the outer can, the opening of the outer can is sealed with a sealing member interposed between a gasket to produce a cylindrical secondary battery.

[0063] [Charge and discharge cycle test]

[0064] The secondary battery was charged at a constant current of 0.3 It until the battery voltage reached 4.2 V, then charged at a constant voltage of 4.2 V until the current reached 0.02 It. Thereafter, it was discharged at a constant current of 0.5 It until the battery voltage reached 2.5 V. This charge-discharge cycle was repeated 200 times, with a 20-minute rest period between each cycle.

[0065] [Measurement of gap amount]

[0066] After the charge-discharge cycle test, the secondary battery was cross-sectionally observed in the radial direction of the electrode assembly using an X-ray CT scanner (SMX-225CTFPD HR, manufactured by Shimadzu Corporation). The length of the gap between the positive and negative electrodes was measured in the radial direction of the electrode assembly at one end of the positive electrode in the width direction (the side where the positive electrode exposed portion was located). The maximum value measured was defined as the gap length.

[0067] [Evaluation of peeling of the mixture layer]

[0068] The secondary battery after the charge-discharge cycle test was observed cross-sectionally in the radial direction of the electrode assembly using an X-ray CT apparatus to confirm whether or not the mixture layer was peeled off near the winding center of the electrode assembly.

[0069] <Example 2>

[0070] In the preparation of the separator, a secondary battery was prepared and evaluated in the same manner as in Example 1, except that the amount of acrylic resin particles added in the first dispersion was changed from 2 parts by mass to 1 part by mass, and the amount of acrylic resin particles added in the second dispersion was changed from 1 part by mass to 0.5 parts by mass.

[0071] <Example 3>

[0072] In the preparation of the separator, a secondary battery was prepared and evaluated in the same manner as in Example 1, except that the amount of acrylic resin particles added in the first dispersion was changed from 2 parts by mass to 1 part by mass, and the amount of acrylic resin particles added in the second dispersion was changed from 1 part by mass to 0.25 parts by mass.

[0073] <Example 4>

[0074] A secondary battery was produced and evaluated in the same manner as in Example 1 except that the amount of acrylic resin particles added in the second dispersion was changed from 1 part by mass to 0.5 parts by mass in the production of the separator.

[0075] <Example 5>

[0076] A secondary battery was produced and evaluated in the same manner as in Example 1 except that no acrylic resin particles were added to the second dispersion in the production of the separator.

[0077] <Comparative Example 1>

[0078] A secondary battery was produced and evaluated in the same manner as in Example 1 except that no acrylic resin particles were added to the first dispersion and the second dispersion in the production of the separator.

[0079] Comparative Example 2

[0080] In the preparation of the separator, a secondary battery was prepared and evaluated in the same manner as in Example 1, except that the amount of acrylic resin particles added in the first dispersion was changed from 2 parts by mass to 0.5 parts by mass, and the amount of acrylic resin particles added in the second dispersion was changed from 1 part by mass to 0.5 parts by mass.

[0081] Comparative Example 3

[0082] A secondary battery was produced and evaluated in the same manner as in Example 1 except that the amount of acrylic resin particles added in the first dispersion was changed from 2 parts by mass to 1 part by mass in the production of the separator.

[0083] The evaluation results of the secondary batteries of the Examples and Comparative Examples are shown in Table 1. The gap size was evaluated using four levels: less than 10 μm, 10 μm to 20 μm, 20 μm to 30 μm, and greater than 30 μm. Table 1 also shows the average particle area of ​​the resin particles contained in the first region and the average particle area of ​​the resin particles contained in the second region, measured using separators removed from cylindrical secondary batteries after charge and discharge cycle testing.

[0084] [Table 1]

[0085]

[0086] No delamination of the positive electrode mixture layer was observed in the secondary batteries of Examples 1 to 5. On the other hand, in the secondary batteries of Comparative Examples 1 to 3, areas where the positive electrode mixture layer had delaminated from the positive electrode current collector were observed. This indicates that delamination of the mixture layer after charge and discharge cycles can be suppressed by making the area ratio S1 of the area occupied by the protrusions in the first region of the separator greater than the area ratio S2 of the area occupied by the protrusions in the second region of the separator.

[0087] The present application is further described through the following embodiments.

[0088] Composition: 1

[0089] A cylindrical secondary battery comprises an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer can for accommodating the electrode body and the non-aqueous electrolyte.

[0090] The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector.

[0091] A plurality of positive electrode exposure portions where the positive electrode current collector is exposed are arranged on the surface of the positive electrode.

[0092] The positive electrode exposed portion is in contact with only one of the two ends in the width direction of the positive electrode.

[0093] The separator includes a base material layer and a filler layer disposed on a surface of the base material layer facing the positive electrode.

[0094] The filler layer contains resin particles and has protrusions formed by the resin particles.

[0095] In the case where the surface of the positive electrode is divided into a positive electrode exposed portion arrangement region where the positive electrode exposed portion is arranged and a positive electrode exposed portion non-arrangement region adjacent to the positive electrode exposed portion arrangement region in the width direction, and the surface of the separator is provided as a first region facing the positive electrode exposed portion arrangement region and a second region facing the positive electrode exposed portion non-arrangement region,

[0096] An area ratio S1 of the area of ​​the convex portion in the first region is greater than an area ratio S2 of the area of ​​the convex portion in the second region.

[0097] Composition: 2

[0098] According to the cylindrical secondary battery according to Configuration 1, the S1 is 2% to 20%, and the S2 is 0% to 10%.

[0099] Composition: 3

[0100] According to the cylindrical secondary battery according to configuration 1 or 2, an average particle area of ​​the protrusions in the first region is larger than an average particle area of ​​the protrusions in the second region.

[0101] Composition: 4

[0102] The cylindrical secondary battery according to any one of configurations 1 to 3, wherein the average particle area of ​​the protrusions in the first region is 500 μm 2 Above and 2000μm 2 Hereinafter, the average particle area of ​​the protrusions in the second region is 0 μm 2 Above and 1500μm 2 the following.

[0103] Description of Reference Numerals

[0104] 10 (Cylindrical) secondary battery, 11 positive electrode, 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 slot, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 lid, 26a opening, 27 gasket, 30 positive electrode collector, 32 positive electrode mixture layer, 34 positive electrode exposed portion, 38 positive electrode exposed portion arrangement region, 39 positive electrode exposed portion non-arrangement region, 40 negative electrode collector, 42 negative electrode mixture layer, 44 negative electrode exposed portion, 50 base layer, 52 filler layer, 54 resin particles, 56 protrusion, 58 first region, 59 second region.

Claims

1. A cylindrical secondary battery comprising an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, a non-aqueous electrolyte, and a cylindrical outer can for accommodating the electrode body and the non-aqueous electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer disposed on a surface of the positive electrode current collector. A plurality of positive electrode exposure portions where the positive electrode current collector is exposed are arranged on the surface of the positive electrode. The positive electrode exposed portion is in contact with only one of the two ends in the width direction of the positive electrode. The separator includes a base material layer and a filler layer disposed on a surface of the base material layer facing the positive electrode. The filler layer includes resin particles and has protrusions formed by the resin particles. In the case where the surface of the positive electrode is divided into a positive electrode exposed portion arrangement region where the positive electrode exposed portion is arranged and a positive electrode exposed portion non-arrangement region adjacent to the positive electrode exposed portion arrangement region in the width direction, and the surface of the separator is provided as a first region facing the positive electrode exposed portion arrangement region and a second region facing the positive electrode exposed portion non-arrangement region, An area ratio S1 of the area of ​​the convex portion in the first region is greater than an area ratio S2 of the area of ​​the convex portion in the second region.

2. The cylindrical secondary battery according to claim 1, wherein The S1 is greater than or equal to 2% and less than or equal to 20%, and the S2 is greater than or equal to 0% and less than or equal to 10%.

3. The cylindrical secondary battery according to claim 1, wherein An average particle area of ​​the protrusions in the first region is larger than an average particle area of ​​the protrusions in the second region.

4. The cylindrical secondary battery according to claim 1, wherein The average particle area of ​​the protrusions in the first region is 500 μm 2 Above and 2000μm 2 Hereinafter, the average particle area of ​​the protrusions in the second region is 0 μm 2 Above and 1500μm 2 the following.

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