Secondary battery

Abstract

A secondary battery (10) according to one embodiment of the present disclosure is provided with a wound electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) interposed therebetween, and is characterized in that: the separator (13) includes a first separator (31) facing a first surface (11A) on the inside of the winding of the positive electrode (11), and a second separator (32) facing a second surface (11B) on the outside of the winding of the positive electrode (11); the ratio of the static friction coefficient of the surface of the winding outside of the first separator (31) in contact with the first surface (11A) of the positive electrode (11) to the static friction coefficient of the surface of the winding inside of the second separator (32) in contact with the second surface (11B) of the positive electrode (11) is 1.3 or more.

Description

Technical Field

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

[0002] Secondary batteries, which consist of a wound electrode assembly consisting of a strip of positive and negative electrodes wound with a separator between them and housed in a metal outer can, have long been widely used. The separator prevents the positive and negative electrodes from contacting and causing a short circuit. Patent Document 1 discloses a technique for suppressing winding deviation when the wound positive and negative electrodes are removed from a winding shaft by making the static friction coefficient of the separator surface facing the positive electrode higher than that of the surface facing the negative electrode.

[0003] Prior art literature

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-195296 Summary of the Invention

[0005] With the recent increase in the capacity of secondary batteries, the negative electrode mixture layer expands significantly during charge and discharge. This significant expansion increases stress within the battery, placing a greater stress load on the electrode plates. This can cause deformation of the electrode plates, potentially leading to reduced battery performance and internal short circuits.

[0006] An object of the present disclosure is to provide a secondary battery capable of suppressing deformation of an electrode plate associated with charge and discharge.

[0007] A secondary battery according to a technical solution disclosed herein comprises a wound electrode body in which a positive electrode and a negative electrode are wound with a separator therebetween, and is characterized in that the separator comprises a first separator opposite to a first surface on the inner side of the winding of the positive electrode and a second separator opposite to a second surface on the outer side of the winding of the positive electrode, and the ratio of the static friction coefficient of the surface on the outer side of the winding of the first separator in contact with the first surface of the positive electrode to the static friction coefficient of the surface on the inner side of the winding of the second separator in contact with the second surface of the positive electrode is greater than 1.3.

[0008] According to the secondary battery according to the present disclosure, deformation of the electrode plate associated with charge and discharge can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a cross-sectional view in the axial direction of a cylindrical battery as an example of an embodiment.

[0010] Figure 2 This is a diagram showing a portion of a transverse cross section of a wound electrode assembly included in a cylindrical battery as an example of an embodiment.

[0011] Figure 3 This is a diagram showing a portion of a transverse cross section of a wound electrode assembly included in a cylindrical battery as another example of the embodiment.

[0012] Figure 4A This is an X-ray CT image of the cross-sectional shape of a cylindrical battery used in the simulation of the embodiment.

[0013] Figure 4B is an image of a computational model used in the simulation of the embodiment.

[0014] Figure 5 This is a diagram showing material property values ​​used in the simulation of the examples.

[0015] Figure 6 It is a graph showing the simulation results of Comparative Example 1. DETAILED DESCRIPTION

[0016] In a secondary battery with a wound electrode body, when the negative electrode mixture layer expands with charge and discharge, there is a tendency for the vertical resistance applied to the surface outside the positive electrode to be greater than the vertical resistance applied to the surface inside the positive electrode. In previous secondary batteries, two identical separators are usually used in a manner that clamps the positive electrode, so the static friction coefficient of the surface of the separator that contacts the surface inside the positive electrode is the same as the static friction coefficient of the surface of the separator that contacts the surface outside the positive electrode. Since friction is represented by the product of the static friction coefficient and the vertical resistance, in existing secondary batteries, the friction force applied to the surface outside the positive electrode is greater than the friction force applied to the surface inside the positive electrode. As a result, the deformation of the plate associated with charge and discharge is promoted, which may cause a reduction in battery performance, internal short circuit, etc.

[0017] The inventors found that by making the ratio of the static friction coefficient of the surface of the diaphragm in contact with the surface of the positive electrode winding inside to the static friction coefficient of the surface of the diaphragm in contact with the surface of the positive electrode winding outside be 1.3 or more, the deformation of the plate associated with charging and discharging can be suppressed. The secondary battery disclosed herein has a static friction coefficient of the surface of the diaphragm in contact with the surface of the positive electrode winding inside being greater than the static friction coefficient of the surface of the diaphragm in contact with the surface of the positive electrode winding outside, so that the friction force applied to the surface of the positive electrode winding outside and the friction force applied to the surface of the positive electrode winding inside are close to each other. As a result, the deformation of the plate caused by the difference in friction between the surface of the positive electrode winding inside and the surface of the positive electrode winding outside, which is associated with charging and discharging, can be suppressed.

[0018] Hereinafter, an example of an embodiment of the secondary battery involved in the present disclosure will be described in detail with reference to the accompanying drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. In addition, a solution formed by selectively combining the various components of the embodiment described below is also included in the present disclosure. In addition, in this specification, when a word such as "approximately" is used, it is used with the same meaning as a word such as "approximately", and a condition such as "approximately to" is satisfied as long as it is substantially the same.

[0019] The following examples illustrate cylindrical batteries in which a wound electrode assembly is housed in a bottomed cylindrical outer can. However, the outer can of the battery is not limited to a cylindrical outer can. For example, a rectangular outer can (a rectangular battery) or an outer can composed of a laminate sheet including a metal layer and a resin layer (a laminated battery) may also be used.

[0020] Figure 1 1 is a diagram schematically showing a cross section of a cylindrical battery (hereinafter referred to as a battery) 10 as an example of an embodiment. Figure 1 As shown, the battery 10 includes an electrode body 14, a non-aqueous electrolyte (not shown), and an outer can 20 for accommodating the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. More specifically, the electrode body 14 has a structure in which the positive electrode 11 and the negative electrode 12 are wound with a first separator 31 disposed on the inner side of the winding of the positive electrode 11 and a second separator 32 disposed on the outer side of the winding of the positive electrode 11 interposed therebetween. The outer can 20 is a metal container in the shape of a bottom cylinder with an opening on one axial side, and the opening of the outer can 20 is blocked by a sealing body 19. In addition, in Figure 1 In the figure, the number of windings is shown to be smaller than the actual number in order to facilitate understanding of the arrangement relationship of the positive electrode 11, negative electrode 12, and separator 13 in the electrode assembly 14. Hereinafter, the side of the sealing body 19 in the axial direction (height direction) of the battery 10 is referred to as "upper," and the side of the bottom of the outer can 20 in the axial direction is referred to as "lower."

[0021] Non-aqueous electrolytes have ion conductivity (for example, lithium ion conductivity) and can be either liquid electrolytes (electrolyte solutions) or solid electrolytes.

[0022] The liquid electrolyte (electrolyte) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents thereof. The non-aqueous solvent may contain a halogen-substituted product (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF6.

[0023] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, or the like is used. The polymer electrolyte, for example, comprises a lithium salt and a matrix polymer, or comprises a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent is used. As the polymer material, for example, fluororesins, acrylic resins, polyether resins, etc. are used. As the inorganic solid electrolyte, for example, materials known in all-solid-state lithium-ion secondary batteries (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0024] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode body 14 are all long, strip-shaped bodies, wound into a spiral shape and alternately stacked in the radial direction of the electrode body 14. To prevent lithium precipitation, the negative electrode 12 is formed to be one size larger than the positive electrode 11. In other words, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length and width (short side) directions. The separator 13 is formed to be at least one size larger than the positive electrode 11, and two separators are arranged to sandwich the positive electrode 11. The battery 10 includes insulating plates 15 and 16 arranged above and below the electrode body 14, respectively.

[0025] A positive electrode lead 17 is connected to the positive electrode 11, and a negative electrode lead 18 is connected to the winding start side of the negative electrode 12. The positive electrode lead 17 extends through a through-hole in the insulating plate 15 to the sealing body 19 side, while the negative electrode lead 18 extends through a through-hole in the insulating plate 16 to the bottom 21 side of the outer can 20. The positive electrode lead 17 is connected to the lower surface of the internal terminal plate 24 of the sealing body 19 by welding or the like, and the sealing body 19 serves as the positive electrode terminal. The negative electrode lead 18 is connected to the inner surface of the bottom 21 of the metal outer can 20 by welding or the like, and the outer can 20 serves as the negative electrode terminal.

[0026] The outer can 20 is a metal container with a bottomed cylindrical shape and an open vertical side. The outer can 20 has a bottom 21 and a side wall 22. The side wall 22 is the portion of the outer can 20 excluding the bottom 21 and is formed with a groove 23, which will be described later.

[0027] A gasket 27 is provided between the outer can 20 and the sealing body 19 to ensure the airtightness of the battery interior and the insulation between the outer can 20 and the sealing body 19. The outer can 20 is provided with a groove 23, which supports the sealing body 19 and extends inward from a portion of the side wall 22. The groove 23 is preferably formed in an annular shape along the circumference of the outer can 20 and supports the sealing body 19 on its upper surface. The sealing body 19 is fixed to the upper portion of the outer can 20 by means of the groove 23 and the open end of the outer can 20 riveted to the sealing body 19.

[0028] The sealing member 19 is a disc-shaped component equipped with a safety valve. The sealing member 19 has a structure in which an internal terminal plate 24, an insulating member 25, and a rupture disc 26 are stacked in this order from the electrode body 14 side. The internal terminal plate 24 is a metal plate consisting of a thick outer peripheral portion 24A for connecting to the positive lead 17 and a thinner central portion 24B that separates from the outer peripheral portion 24A when the internal pressure of the battery exceeds a predetermined threshold. Multiple vent holes 24C are formed in the outer peripheral portion 24A.

[0029] The explosion-proof plate 26 is arranged opposite to the internal terminal plate 24 via the insulating component 25. An opening portion 25A is formed in the radial center portion of the insulating component 25, and a vent hole 25B is formed in the portion overlapping with the vent hole 24C of the internal terminal plate 24. The explosion-proof plate 26 has a valve portion 26A that breaks when the internal pressure of the battery 10 exceeds a specified threshold value, and the valve portion 26A is connected to the central portion 24B of the internal terminal plate 24 by welding or the like. The insulating component 25 insulates the portion other than the connection portion between the central portion 24B and the valve portion 26A. In addition, the outer peripheral portion of the explosion-proof plate 26 surrounding the valve portion 26A is retained between the rivet portion formed by bending the opening of the outer can 20 inward and the groove portion 23 via a gasket 27.

[0030] The valve portion 26A is formed in the radial center of the explosion-proof plate 26, and includes a joint portion arranged in the radial center and protruding toward the inner side of the battery, and a thin-walled portion formed around the joint portion. The joint portion of the valve portion 26A passes through the opening portion 25A of the insulating member 25 and is engaged with the central portion 24B. When an abnormality occurs in the battery 10 and the internal pressure rises, the explosion-proof plate 26 is pressed upward by the high-temperature gas generated, the internal terminal plate 24 breaks, the central portion 24B separates from the outer peripheral portion 24A, and the valve portion 26A deforms to protrude toward the outside of the battery. As a result, the current path in the sealing body 19 is cut off. Moreover, after the current path is cut off, when the internal pressure of the battery 10 further rises, the thin-walled portion of the valve portion 26A breaks, forming a gas exhaust port on the explosion-proof plate 26.

[0031] In addition, the structure of the sealing body 19 is not limited to Figure 1 The sealing member 19 may have a laminated structure including two valve members, or may have a convex sealing member cover covering the valve member.

[0032] Below, refer to Figure 2 The electrode body 14 will be described in detail.

[0033] Figure 2 1 is a diagram showing a portion of a transverse cross section of a wound electrode body 14, and is a diagram for explaining the arrangement of the positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14. Figure 2 In order to facilitate understanding of the arrangement relationship among the positive electrode 11 , the negative electrode 12 , and the separator 13 , the spacing between the layers is separated compared to the actual situation.

[0034] [positive electrode]

[0035] like Figure 1 and Figure 2 As shown, the positive electrode 11 includes a positive electrode core 40 and a positive electrode mixture layer 41 disposed on the positive electrode core 40. The positive electrode core 40 can be made of a foil of a metal such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a thin film having the metal disposed on the surface. The positive electrode mixture layer 41 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be manufactured, for example, by coating the positive electrode core 40 with a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder, and then drying the coating and compressing it to form the positive electrode mixture layer 41 on both sides of the positive electrode core 40.

[0036] The positive electrode mixture layer 41 contains a particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium metal composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among them, it is preferred that it contains at least one selected from Co, Ni, Al, and Mn. As an example of a preferred composite oxide, a lithium metal composite oxide containing Ni, Co, and Mn and a lithium metal composite oxide containing Ni, Co, and Al can be cited.

[0037] The lithium-containing composite oxide is, for example, a secondary particle formed by the aggregation of multiple primary particles. The volume-based median particle size (D50) of the composite oxide is not particularly limited, but as an example, it is 3 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less. When the composite oxide is a secondary particle formed by the aggregation of primary particles, the D50 of the composite oxide refers to the D50 of the secondary particle. D50 refers to the particle size at which the cumulative frequency of the smaller particle size in the volume-based particle size distribution reaches 50%, and is also called the median diameter. The particle size distribution of the composite oxide (the same applies to the case of the negative electrode active material) can be measured using a laser diffraction particle size distribution analyzer (for example, MT3000II manufactured by Microtrack Bell Co., Ltd.) with water as the dispersion medium.

[0038] The average particle size of the primary particles constituting the lithium-containing composite oxide is, for example, 0.05 μm to 1 μm. The average particle size of the primary particles is calculated by averaging the diameters of the circumscribed circles of the primary particles extracted by analyzing a scanning electron microscope (SEM) image of a secondary particle cross section.

[0039] Examples of the conductive agent contained in the positive electrode mixture layer 41 include carbon black such as acetylene black and Ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, and carbon materials such as graphene. Examples of the binder contained in the positive electrode mixture layer 41 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), and the like.

[0040] [negative electrode]

[0041] like Figure 1 and Figure 2 As shown, the negative electrode 12 includes a negative electrode core 50 and a negative electrode mixture layer 51 disposed on the negative electrode core 50. The negative electrode core 50 can be made of a foil of a metal such as copper or a copper alloy that is stable within the potential range of the negative electrode 12, or a thin film having the metal disposed on the surface. The negative electrode mixture layer 51 contains a negative electrode active material, a binder, and, if necessary, a conductive agent. The negative electrode 12 can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 50, drying the coating, and then compressing the coating to form the negative electrode mixture layers 51 on both sides of the negative electrode core 50.

[0042] The negative electrode mixture layer 51 preferably contains a carbon material and a silicon-containing material as the negative electrode active material. The inclusion of a silicon-containing material facilitates achieving both high capacity and excellent cycle characteristics. For example, the negative electrode mixture layer 51 may contain at least one of an element that alloys with Li, such as Sn, and a material containing the element.

[0043] From the perspective of high capacity, the content of silicon-containing material is preferably 15% by mass or more of the total mass of the negative electrode active material, more preferably 20% by mass or more, and further preferably 25% by mass or more. Generally, silicon-containing materials have a larger volume change during charge and discharge than carbon materials. Therefore, when silicon-containing material is used as the negative electrode active material, if charge and discharge are repeated, the stress inside the battery increases further and the deformation of the plate becomes more significant. In this embodiment, the surface (first surface) 11A (refer to the inner surface of the winding of the separator 13 and the positive electrode 11) is Figure 2 ) has a larger static friction coefficient than the surface (second surface) 11B of the separator 13 that is wound around the outer side of the positive electrode 11 (see Figure 2 ) The static friction coefficient of the surfaces facing each other can be adjusted, so that the friction force applied to the first surface 11A of the positive electrode 11 and the friction force applied to the second surface 11B of the positive electrode 11 can be made close, and the details will be described later. As a result, the deformation of the electrode plate caused by the difference in friction between the first surface 11A and the second surface 11B of the positive electrode 11 accompanying charging and discharging can be suppressed. Therefore, when a silicon-containing material is included as the negative electrode active material, the effect of the present disclosure becomes more significant. The upper limit of the content of the silicon-containing material is, for example, 70% by mass of the total mass of the negative electrode active material.

[0044] The carbon material that functions as the negative electrode active material is, for example, at least one selected from natural graphite, artificial graphite, soft carbon, and hard carbon. Among these, the carbon material preferably uses at least artificial graphite such as bulk artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB), natural graphite such as flake graphite, bulk graphite, and earthy graphite, or a mixture thereof. The volume-based D50 of the carbon material is, for example, 1 μm to 30 μm, preferably 5 μm to 25 μm.

[0045] The silicon-containing material may be any material containing Si. Examples thereof include silicon alloys, silicon compounds, and composite materials containing Si. Composite materials containing Si are preferred. The D50 of a composite material is generally smaller than that of graphite. The volume-based D50 of a composite material is, for example, 1 μm to 15 μm. The silicon-containing material may be used alone or in combination of two or more.

[0046] Suitable silicon-containing materials (composite materials) are composite particles comprising an ion-conducting phase, a Si phase dispersed within the ion-conducting phase, and a conductive layer covering the surface of the ion-conducting phase. The ion-conducting phase is, for example, at least one selected from a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ion-conducting phase is a continuous phase composed of a collection of particles finer than the Si phase. The conductive layer is composed of a material with higher conductivity than the ion-conducting phase and forms a good conductive path in the negative electrode mixture layer 51.

[0047] An example of a preferred composite material containing Si is a composite material having a sea-island structure in which fine Si is dispersed substantially uniformly in an amorphous silicon oxide phase, and is represented as a whole by the general formula SiO x Composite particles represented by (0<x≤2). The main component of silicon oxide may be silicon dioxide. The content ratio (x) of oxygen to Si is, for example, 0.5≤x<2.0, and preferably 0.8≤x≤1.5.

[0048] The binder contained in the negative electrode mixture layer 51 is the same as that in the positive electrode mixture layer 41. Fluorine-containing resins, PAN, polyimide, acrylic resins, polyolefins, etc. can be used, with styrene-butadiene rubber (SBR) being preferred. Furthermore, the negative electrode mixture layer 51 preferably contains CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. Among them, SBR is preferably used in combination with CMC or its salts, PAA or its salts, etc. The negative electrode mixture layer 51 may contain a conductive agent such as CNTs.

[0049] [Diaphragm]

[0050] like Figure 1 and Figure 2 As shown, the separator 13 is arranged between the positive electrode 11 and the negative electrode 12 to prevent the positive electrode 11 and the negative electrode 12 from contacting and causing a short circuit. The separator 13 uses, for example, a porous sheet with ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, non-woven fabrics, etc. There are no particular restrictions on the material of the porous sheet, and examples include polyethylene, polypropylene, copolymers of polyethylene and α-olefins such as polyolefins (PAO), acrylic resins, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide (PPS), polyetheretherketone (PEEK), fluororesins, etc. In addition, in this embodiment, as Figure 2 As shown, the diaphragm 13 has a single-layer structure.

[0051] The separator 13 includes a first separator 31 that faces the first surface 11A of the positive electrode 11 and a second separator 32 that faces the second surface 11B of the positive electrode 11. That is, the surface 31B of the first separator 31 on the outer side of the winding (the winding outer surface) is in contact with the first surface 11A of the positive electrode 11, and the surface 32A of the second separator 32 on the inner side of the winding (the winding inner surface) is in contact with the second surface 11B of the positive electrode 11. The thicknesses of the first separator 31 and the second separator 32 may be substantially the same or different. In this embodiment, the first separator 31 and the second separator 32 have substantially the same thickness. The thicknesses of the first separator 31 and the second separator 32 are preferably greater than or equal to 3 μm and less than or equal to 20 μm, and more preferably greater than or equal to 5 μm and less than or equal to 15 μm.

[0052] Here, the static friction coefficient of the wound outer surface 31B of the first separator 31 is μ 31B , the static friction coefficient of the winding inner surface 32A of the second diaphragm 32 is set to μ 32A When the static friction coefficient μ 31B Relative to the static friction coefficient μ 32A The ratio (μ 31B / μ 32A ) is 1.3 or more. 31B / μ 32A By setting the ratio to 1.3 or greater, the frictional force applied to the first surface 11A of the positive electrode 11 during charge and discharge can be made close to the frictional force applied to the second surface 11B of the positive electrode 11. As a result, deformation of the electrode plate caused by the difference in frictional force between the first surface 11A and the second surface 11B of the positive electrode 11 during charge and discharge can be suppressed.

[0053] In addition, μ 31B / μ 32A It is preferably 1.32 or more, and more preferably 1.35 or more. In this case, the friction force applied to the first surface 11A of the positive electrode 11 and the friction force applied to the second surface 11B of the positive electrode 11 during charge and discharge can be closer to each other. 31B / μ 32A It is preferably 5.0 or less, more preferably 3.0 or less. 31B / μ 32A If the value is greater than 5.0, the friction force applied to the first surface 11A of the positive electrode 11 during charge and discharge may be greater than the friction force applied to the second surface 11B of the positive electrode 11 .

[0054] The static friction coefficient μ between the wound outer surface 31B of the first separator 31 and the wound inner surface 32A of the second separator 32 is 31B 、μ 32A For example, it is 0.3 or more and 1.0 or less. The above-mentioned static friction coefficient is a value measured according to the method described in JIS K7125:1999 "Plastics - Films and sheets - Friction coefficient test method".

[0055] By changing the static friction coefficient μ between the wound outer surface 31B of the first separator 31 and the wound inner surface 32A of the second separator 32, 31B 、μ 32A Methods for improving the stability of the first diaphragm 31 and the second diaphragm 32 include changing the material of the first diaphragm 31 and the second diaphragm 32, changing the surface processing, etc. In this embodiment, by using porous sheets made of different materials for the first diaphragm 31 and the second diaphragm 32, the static friction coefficient of the first diaphragm 31 is made larger than the static friction coefficient of the second diaphragm 32.

[0056] In addition, when the static friction coefficient of the wound inner surface 31A of the first separator 31 is μ 31A , the static friction coefficient of the wound outer surface 32B of the second diaphragm 32 is set to μ 32B When μ 31A and μ 32B As described above, in this embodiment, the first diaphragm 31 and the second diaphragm 32 have a single-layer structure and are composed of porous sheets of different materials. Therefore, the static friction coefficient μ of the winding inner surface 31A of the first diaphragm 31 is 31A and the static friction coefficient μ of the wrap outer surface 31B 31B When the opposing electrode plates are the same, the static friction coefficient μ of the wound inner surface 32A of the second separator 32 is substantially the same. 32A and the static friction coefficient μ of the wrap outer surface 32B 32B In the case where the opposing electrode plates are identical, the static friction coefficients are substantially the same. In addition, in this specification, the static friction coefficients being substantially the same means that the difference between the static friction coefficients is the difference in the degree of deviation when the static friction coefficients are measured, for example, the difference between the static friction coefficients is within 10%.

[0057] In addition, if Figure 3 As shown in FIG, the first separator 31 and the second separator 32 may have a laminated structure composed of a plurality of porous layers having different static friction coefficients on the surfaces. Figure 3In the example shown, the first diaphragm 31 and the second diaphragm 32 have a stacked structure consisting of two porous layers with different surface static friction coefficients. In more detail, the first diaphragm 31 includes a first porous layer 33 and a second porous layer 34 provided on the outer surface of the winding of the first porous layer 33 and having a surface static friction coefficient greater than that of the first porous layer 33. In addition, the second diaphragm 32 includes a first porous layer 35 and a second porous layer 36 provided on the outer surface of the winding of the first porous layer 35 and having a static friction coefficient greater than that of the first porous layer 35. There is no particular limitation on the ratio of the thickness of the first porous layers 33, 35 and the second porous layers 34, 36, and it is, for example, 5:95 to 95:5. In addition, the ratio of the thickness of the first porous layers 33, 35 and the second porous layers 34, 36 may be the same in the first diaphragm 31 and the second diaphragm 32, or may be different from each other. Figure 3 In the illustrated example, the thickness ratio of the first porous layers 33 and 35 to the second porous layers 34 and 36 of the first separator 31 and the second separator 32 is 50:50.

[0058] In addition, Figure 3 In the example shown, the first separator 31 and the second separator 32 are made of the same material. That is, the first porous layer 33 and the first porous layer 35 are made of the same material, and the second porous layer 34 and the second porous layer 36 are made of the same material. As a result, if the opposing electrode plates are the same, the static friction coefficient μ of the winding inner surface 31A of the first separator 31 is 31A The static friction coefficient μ of the inner surface 32A of the second separator 32 is 32A The static friction coefficient μ of the wound outer surface 31B of the first separator 31 is substantially the same as 31B The static friction coefficient μ with the wound outer surface 32B of the second diaphragm 32 32B Since the opposing electrode plates are actually different, by forming the first separator 31 and the second separator 32 from the same material, the structure of the secondary battery of the present disclosure can be realized with a single separator 13 , thereby improving productivity.

[0059] The materials constituting the first porous layers 33, 35 and the second porous layers 34, 36 are not particularly limited as long as they are different from each other. As mentioned above, examples thereof include polyolefins such as polyethylene, polypropylene, copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyesters, cellulose, polyimide, polyphenylene sulfide, polyetheretherketone, fluororesins, etc.

[0060] In addition, any one of the first porous layers 33, 35 and the second porous layers 34, 36 may be a heat-resistant layer containing a filler and a binder. Examples of fillers include metal oxide particles such as aluminum oxide, metal nitride particles, metal fluoride particles, metal carbide particles, and sulfide particles. These may be used alone or in combination of two or more. Examples of binders 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 its salts, polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0061] Alternatively, the first porous layer 33 and the first porous layer 35 may be made of different materials, and the second porous layer 34 and the second porous layer 36 may be made of different materials. In this case, the static friction coefficient μ of the winding inner surface 31A of the first separator 31 is 31A The static friction coefficient μ of the inner surface 32A of the second separator 32 is 32A In addition, the static friction coefficient μ of the wound outer surface 31B of the first separator 31 is different from each other. 31B The static friction coefficient μ of the wound outer surface 32B of the second separator 32 is 32B Also different from each other.

[0062] In the above embodiment, the first separator 31 and the second separator 32 have a single-layer structure or a two-layer stacked structure, but this is not limiting. For example, the first separator 31 and the second separator 32 may have a stacked structure consisting of three or more porous layers. Furthermore, the number of layers in the first separator 31 and the number of layers in the second separator 32 may differ. For example, the first separator 31 may have a single-layer structure, while the second separator 32 may have a stacked structure consisting of two porous layers.

[0063] Example

[0064] Hereinafter, the present disclosure will be further described with reference to examples, but the present disclosure is not limited to these examples.

[0065] <Example 1>

[0066] For cylindrical batteries with wound electrode bodies, a calculation model was created based on the X-ray CT image of the cross-sectional shape, and the deformation of the electrode plate during negative electrode expansion was evaluated through computer simulation using this calculation model. Figure 4AAs shown in the figure, the cross-sectional shape of the cylindrical battery was imaged using an inspeXio SMX-255CT FPD HR manufactured by Shimadzu Corporation. Then, image data corresponding to the X-ray CT image was created on a computer using SpaceCaiM. Figure 4B As shown in the figure, HyperWorks was used to mesh the generated image data and create a computational model of a wound electrode assembly with a single-layer separator. By creating the computational model based on X-ray CT images of the cross-sectional shape of an actual cylindrical battery, the roundness of the electrode assembly and the gap between the electrode plates can be faithfully reproduced, thereby improving the accuracy of the simulation.

[0067] Here, as parameters of the calculation model, the static friction coefficient (μ1) of the outer surface of the first separator in contact with the inner surface of the positive electrode is set to 0.65, and the static friction coefficient (μ2) of the inner surface of the second separator in contact with the outer surface of the positive electrode is set to 0.50. In other words, the ratio (μ1 / μ2) of the static friction coefficient (μ1) of the outer surface of the first separator to the static friction coefficient (μ2) of the inner surface of the second separator is set to 1.3. In addition, the material properties of the positive electrode, negative electrode, and outer can used in the calculation model are as follows: Figure 5 shown.

[0068] Then, using AdventureCluster, the thickness of the negative electrode mixture layer in the created calculation model was increased while evaluating whether the electrode plate deformed. By performing calculations while increasing the thickness of the negative electrode mixture layer, the stress and displacement at various locations on the electrode body when the negative electrode mixture layer expands during charge and discharge were calculated, and the effects on electrode body deformation were reproduced. In other words, in this simulation, batteries with a structure that does not cause electrode plate deformation even when the thickness of the negative electrode mixture layer is significantly increased can be said to be batteries that are less likely to experience electrode plate deformation associated with the expansion of the negative electrode mixture layer during charge and discharge.

[0069] <Examples 2 to 4, Comparative Examples 1 to 4>

[0070] As parameters of the calculation model, a calculation model was prepared using μ1 and μ2 as the values ​​shown in Table 1. Calculations were performed using the same conditions as in Example 1 for each calculation model to evaluate the presence or absence of plate deformation.

[0071] Here, Figure 6 An example of the results obtained by this simulation is shown. Figure 6 This figure shows the deformation state of the electrode plate when the thickness of the negative electrode mixture layer is increased to 115% to 130% when the initial thickness of the negative electrode mixture is set to 100% in the calculation model of Comparative Example 1. Figure 6As shown, in the structure of Comparative Example 1, when the thickness of the negative electrode mixture layer was set to 115% and 120%, no deformation of the electrode plate occurred. On the other hand, when the thickness of the negative electrode mixture layer was set to 121%, the upper left portion of the winding core of the electrode body ( Figure 6 The electrode plate is deformed (the dotted line portion in the figure). That is, in the structure of Comparative Example 1, the allowable range of the thickness of the negative electrode mixture layer is 120%. Furthermore, when the thickness of the negative electrode mixture layer is 122%, the lower right portion of the winding core ( Figure 6 The dotted line part in the figure also causes deformation of the plate.

[0072] In the calculation models of Examples 1-4 and Comparative Examples 1-4, with the initial negative electrode mixture thickness set to 100%, Table 1 shows whether plate deformation occurred when the thickness of the negative electrode mixture layer was increased to 115%-124%. In Table 1, cases where plate deformation occurred are marked with an "×" and cases where no plate deformation occurred are marked with an "O."

[0073] Table 1

[0074]

[0075] As shown in Table 1, in the structures of Examples 1-4, where the ratio of the static friction coefficient of the outer surface of the first separator to the static friction coefficient of the inner surface of the second separator (μ1 / μ2) was 1.3 or greater, no electrode plate deformation occurred even when the thickness of the negative electrode mixture layer was increased to 121%. On the other hand, in the structures of the comparative examples, electrode plate deformation occurred even when the thickness of the negative electrode mixture layer was 121%. This suggests that by setting the μ1 / μ2 ratio to 1.3 or greater, a secondary battery can be provided that suppresses electrode plate deformation associated with the expansion of the negative electrode mixture layer during charge and discharge.

[0076] The present disclosure will be further described through the following embodiments.

[0077] Technical composition 1: A secondary battery, comprising a wound electrode body formed by winding a positive electrode and a negative electrode with a separator therebetween, the separator comprising a first separator opposite to a first surface on the inner side of the winding of the positive electrode and a second separator opposite to a second surface on the outer side of the winding of the positive electrode, the ratio of the static friction coefficient of the surface on the outer side of the winding of the first separator in contact with the first surface of the positive electrode to the static friction coefficient of the surface on the inner side of the winding of the second separator in contact with the second surface of the positive electrode is greater than 1.3.

[0078] Technical composition 2: According to the secondary battery described in Technical composition 1, the first separator and the second separator respectively have a first porous layer and a second porous layer composed of the same material and having different static friction coefficients on the surface. The first separator is arranged in a manner such that the first porous layer is opposite to the first surface of the positive electrode, and the second separator is arranged in a manner such that the second porous layer is opposite to the second surface of the positive electrode.

[0079] Technical Configuration 3: The secondary battery according to Technical Configuration 1, wherein the first separator and the second separator are made of different materials.

[0080] Technical composition 4: According to the secondary battery described in Technical composition 3, at least one of the first separator and the second separator has a stacked structure composed of multiple porous layers with different surface static friction coefficients, and the static friction coefficient of the surface of the wound outer side of the first separator is different from the static friction coefficient of the surface of the wound outer side of the second separator.

[0081] Technical configuration 5: According to the secondary battery described in technical configuration 1, the ratio of the static friction coefficient of the surface of the outer side of the winding of the first separator in contact with the first surface of the positive electrode to the static friction coefficient of the surface of the inner side of the winding of the second separator in contact with the second surface of the positive electrode is greater than 1.3 and less than 5.0.

[0082] Technical Configuration 6: The secondary battery according to any one of Technical Configurations 1 to 5, wherein the static friction coefficient of the surface of the wound outer side of the first separator is 0.3 or greater.

[0083] Technical Configuration 7: The secondary battery according to any one of Technical Configurations 1 to 6, wherein the static friction coefficient of the surface of the wound outer side of the first separator is 0.3 or more and 1.0 or less.

[0084] Technical Configuration 8: The secondary battery according to any one of Technical Configurations 1 to 7, wherein the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and the negative electrode mixture layer comprises a silicon-containing material as the negative electrode active material.

[0085] Technical Configuration 9: The secondary battery according to Technical Configuration 8, wherein the content of the silicon-containing material is 15% by mass or more of the total mass of the negative electrode active material.

[0086] Technical Configuration 10: The secondary battery according to Technical Configuration 8, wherein the content of the silicon-containing material is 15% by mass or more and 70% by mass or less of the total mass of the negative electrode active material.

[0087] Description of Reference Numerals

[0088] 10 Secondary battery (cylindrical battery), 11 Positive electrode, 11A Inner surface of the winding, 11B Outer surface of the winding, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Insulating plate, 16 Insulating plate, 17 Positive electrode lead, 18 Negative electrode lead, 19 Sealing member, 20 Outer can, 21 Bottom, 22 Sidewall, 23 Groove, 24 Internal terminal plate, 24A Outer periphery, 24B Center, 24C Vent, 25 Insulating member, 25A Opening, 25B Vent, 26 Explosion-proof plate, 26A Valve, 27 Gasket, 31 First separator, 31A, 32A Inner surface of the winding, 31B, 32B Outer surface of the winding, 32 Second separator, 33, 35 First porous layer, 34, 36 Second porous layer, 40 positive electrode core, 41 positive electrode mixture layer, 50 negative electrode core, 51 negative electrode mixture layer.

Claims

1. A secondary battery comprising a wound electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. The separator includes a first separator facing a first surface on the inner side of the positive electrode and a second separator facing a second surface on the outer side of the positive electrode. A ratio of a static friction coefficient of an outer surface of the first separator in contact with the first surface of the positive electrode to a static friction coefficient of an inner surface of the second separator in contact with the second surface of the positive electrode is 1.3 or greater.

2. The secondary battery according to claim 1, The first separator and the second separator respectively include a first porous layer and a second porous layer made of the same material and having different static friction coefficients on their surfaces. The first separator is arranged so that the first porous layer faces the first surface of the positive electrode. The second separator is arranged so that the second porous layer faces the second surface of the positive electrode.

3. The secondary battery according to claim 1, The first diaphragm and the second diaphragm are made of different materials.

4. The secondary battery according to claim 3, At least one of the first separator and the second separator has a laminated structure composed of a plurality of porous layers having different static friction coefficients on their surfaces. The static friction coefficient of the surface of the outer side of the first separator where the separator is wound is different from the static friction coefficient of the surface of the outer side of the second separator where the separator is wound.

5. The secondary battery according to claim 1, A ratio of a static friction coefficient of the outer surface of the first separator in contact with the first surface of the positive electrode to a static friction coefficient of the inner surface of the second separator in contact with the second surface of the positive electrode is 1.3 or more and 5.0 or less.

6. The secondary battery according to claim 1, The static friction coefficient of the surface of the wound outer side of the first separator is 0.3 or more.

7. The secondary battery according to claim 1, The static friction coefficient of the surface of the wound outer side of the first separator is 0.3 or more and 1.0 or less.

8. The secondary battery according to claim 1, The negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode mixture layer contains a silicon-containing material as a negative electrode active material.

9. The secondary battery according to claim 8, The content of the silicon-containing material is 15% by mass or more of the total mass of the negative electrode active material.

10. The secondary battery according to claim 8, The content of the silicon-containing material is 15 mass % or more and 70 mass % or less of the total mass of the negative electrode active material.

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