Secondary battery

Abstract

Provided is a secondary battery capable of suppressing deformation of an electrode plate associated with charging and discharging. A secondary battery having an electrode body in which a positive electrode (11) and a negative electrode (12) in which a negative electrode mixture layer (50) is disposed on a negative electrode core (48) are wound with a separator interposed therebetween, the secondary battery being characterized in that: the negative electrode (12) has an outer peripheral non-facing portion (44) and an inner peripheral non-facing portion (46), which do not face the positive electrode (11) with the separator interposed therebetween, at a winding start-side end portion; at least one of the surface of the outer peripheral non-facing portion (44) and the surface of the inner peripheral non-facing portion (46) has a low-friction region in which the coefficient of static friction with the facing spacer is 0.4 or less.

Description

Technical Field

[0001] This disclosure relates to secondary batteries. Background Technology

[0002] Lithium-ion batteries and other rechargeable batteries are used as power sources in a wide range of devices, including electric vehicles, requiring further increases in capacity. However, in rechargeable batteries with wound electrode bodies consisting of positive and negative electrodes wound with spacers between them, localized stress is applied within the electrode body as it expands during charging and discharging, potentially causing deformation of at least one of the positive and negative electrodes. In particular, localized stress is easily applied to the center of the electrode body (the core portion), making electrode deformation prone to occur at the beginning of the winding process.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery having a wound electrode body. This wound electrode body is formed by spirally winding a positive electrode and a negative electrode with a negative electrode active material layer formed on the surface of a strip-shaped negative electrode current collector, separated by a spacer. The negative electrode includes a negative electrode lead that is joined to the starting end of the winding of the negative electrode current collector. The negative electrode is wound more than one turn from its inner end in the winding direction, separated by the spacer, without being opposite to the positive electrode. The negative electrode includes an insulating tape adhered to the surface of the negative electrode current collector in the winding direction, spanning the surface of the negative electrode lead. According to Patent Document 1, by adhering the insulating tape to the negative electrode current collector in a manner spanning the surface of the negative electrode lead, plate deformation accompanying charging and discharging can be suppressed.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2018 / 180748 Summary of the Invention

[0007] However, in the existing technology, plate deformation sometimes occurs depending on the charging and discharging conditions, leaving room for improvement. Furthermore, plate deformation can sometimes lead to self-discharge caused by internal short circuits in the battery, making it important to suppress plate deformation.

[0008] Therefore, the purpose of this disclosure is to provide a secondary battery capable of suppressing plate deformation associated with charging and discharging.

[0009] This disclosure discloses a secondary battery having an electrode body formed by winding a positive electrode and a negative electrode having a negative electrode composite material layer disposed on a negative electrode core, separated by a spacer. The negative electrode has a non-opposite portion at the winding start end that is not opposite to the positive electrode separated by the spacer, and the surface of the non-opposite portion has a low friction region with a friction coefficient of 0.4 or less between it and the opposing spacer.

[0010] According to this disclosure, a secondary battery is provided that can suppress plate deformation associated with charging and discharging. Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view of a secondary battery as an example of an implementation method.

[0012] Figure 2 It is a schematic representation Figure 1 A partial view of the inner end side of the electrode body with section AA in the winding direction.

[0013] Figure 3 It is a schematic cross-sectional view showing the state of the negative and positive electrodes at the beginning of winding before winding.

[0014] Figure 4 This is a schematic cross-sectional view illustrating an example of the structure of an insulating tape.

[0015] Figure 5 This is a schematic cross-sectional view showing the state of the negative and positive electrodes at the winding start end side before winding in Embodiment 1.

[0016] Figure 6 This is a schematic cross-sectional view showing the state of the negative and positive electrodes at the beginning of winding before winding in Comparative Example 1.

[0017] Figure 7 This is a schematic diagram of a device used to determine the coefficient of static friction. Detailed Implementation

[0018] The following is a detailed description of one embodiment of the secondary battery involved in this disclosure.

[0019] Figure 1 This is a schematic cross-sectional view of a secondary battery as an example of an implementation method. Figure 1 The secondary battery 10 shown includes a wound electrode body 14 formed by winding a positive electrode 11 and a negative electrode 12 with a spacer 13, a non-aqueous electrolyte, insulating plates 18a and 18b respectively disposed above and below the electrode body 14, and a battery casing 15 as an outer body. The battery casing 15 is composed of a casing body 16 that houses the electrode body 14, the non-aqueous electrolyte, etc., and a sealing body 17 that seals the opening of the casing body 16. The battery casing 15 is not limited to a cylindrical or square metal casing; for example, it can also be a resin casing formed by laminating resin sheets (so-called laminated type).

[0020] Non-aqueous electrolytes, such as those with lithium-ion conductivity, can be liquid electrolytes (electrolytes) or solid electrolytes.

[0021] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents may include, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. Non-aqueous solvents may contain halogen substitutes (e.g., fluoroethylene carbonate) formed by replacing at least a portion of the hydrogen atoms in these solvents with halogen atoms such as fluorine. For the electrolyte salt, lithium salts such as LiPF6 are used, for example.

[0022] In addition, solid electrolytes can be, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc. As inorganic solid electrolytes, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes, for example, contain lithium salts and matrix polymers, or non-aqueous solvents, lithium salts and matrix polymers. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel. Examples of polymer materials include fluoropolymers, acrylic resins, polyether resins, etc. Furthermore, non-aqueous electrolytes are one example; aqueous electrolytes can also be used, provided they are applicable.

[0023] The casing body 16 is, for example, a bottomed cylindrical metal container. A gasket 27 is provided between the casing body 16 and the sealing body 17 to ensure the airtightness of the battery interior. The casing body 16 has, for example, a portion of the side extending inward to support the sealing body 17. The extension 21 is preferably formed in a ring shape along the circumference of the casing body 16, and supports the sealing body 17 on its upper surface.

[0024] The sealing body 17 has a structure in which a filter 22, a lower valve core 23, an insulator 24, an upper valve core 25, and a cover 26 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulator 24 are electrically connected to each other. The lower valve core 23 and the upper valve core 25 are connected to each other at their respective central portions, and the insulator 24 is sandwiched between their respective peripheral portions. When the internal pressure of the secondary battery 10 rises due to heat generated by internal short circuits, for example, the lower valve core 23 deforms and breaks by pushing the upper valve core 25 upwards towards the cover 26 side, cutting off the current path between the lower valve core 23 and the upper valve core 25. When the internal pressure rises further, the upper valve core 25 breaks, and gas is discharged from the opening of the cover 26.

[0025] exist Figure 1In the secondary battery 10 shown, the positive electrode lead 19, mounted on the positive electrode 11, extends through the through hole in the insulating plate 18a toward the sealing body 17 and is connected to the lower surface of the filter 22, which serves as the base plate of the sealing body 17, by welding or the like. Thus, the top plate, i.e., the cover 26, of the sealing body 17, which is electrically connected to the filter 22, becomes the positive terminal. Furthermore, in Figure 1 In the secondary battery 10 shown, the negative electrode lead 20a, which is connected to the winding start end of the negative electrode 12, and the negative electrode lead 20b, which is connected to the winding end end of the negative electrode 12, extend through the insulating plate 18b toward the bottom side of the housing body 16, and are connected to the bottom inner surface of the housing body 16 by welding or the like. Thus, the housing body 16 becomes the negative terminal.

[0026] Figure 2 It means Figure 1 A schematic diagram of the inner end side of the winding direction of the electrode body with section AA. Figure 2 In the diagram, to easily understand the configuration relationship, solid lines represent negative electrode 12, dashed lines represent positive electrode 11, and dotted lines represent spacer 13. Additionally, in... Figure 2 The gap between the positive electrode 11, the negative electrode 12, and the spacer 13 is exaggerated in the image. The electrode body 14 is constructed by winding the positive electrode 11 and the negative electrode 12 with the spacer 13 in between. The electrode body 14 is manufactured, for example, by stacking a strip-shaped positive electrode 11, a strip-shaped negative electrode 12, and a pair of strip-shaped spacers 13 in the order of one spacer 13, positive electrode 11, another spacer 13, and negative electrode 12, and then winding the stacked body into a spiral shape. In the electrode body 14, the length direction of each electrode is the winding direction, and the width direction of each electrode is the winding axis direction.

[0027] like Figure 2 As shown, the negative electrode 12 has a non-opposing portion 40 on the winding start end side. This non-opposing portion 40 is composed of an outer peripheral non-opposing portion 44 and an inner peripheral non-opposing portion 46 that are not opposed to the positive electrode 11 across the spacer 13. Additionally, the negative electrode 12 has an insulating member, which will be described later. Figure 2 The insulating member is not shown, but it is disposed on the non-opposite portion 40. Additionally, the negative electrode 12 has an opposing portion 42 that faces the positive electrode 11 across a spacer 13. The opposing portion 42 and the non-opposite portion 40 are continuously wound together.

[0028] The non-opposing portion 40 has an outer peripheral non-opposing portion 44 and an inner peripheral non-opposing portion 46. Furthermore, the outer peripheral non-opposing portion 44 refers to the non-opposing portion located on the outer side in the radial direction of the wound negative electrode 12, and the inner peripheral non-opposing portion 46 refers to the non-opposing portion located on the inner side in the radial direction of the wound negative electrode 12. Figure 2 The non-opposite portion 40 shown (outer peripheral non-opposite portion 44 and inner peripheral non-opposite portion 46) starts from the winding end of the negative electrode 12. Figure 2Starting from point E1, it is wound 1.5 turns. That is, the non-opposite portion 40 (the outer peripheral non-opposite portion 44 and the inner peripheral non-opposite portion 46) starts from... Figure 2 Point E1 extends along the winding direction to point E2. The number of turns of the non-opposite portion 40 (outer peripheral non-opposite portion 44 and inner peripheral non-opposite portion 46) is not particularly limited, but is preferably 1.5 turns or more, more preferably 1.5 turns or more and 3 turns or less.

[0029] In this embodiment, the surface of the non-opposing portion has a low-friction region with a static friction coefficient of 0.4 or less between it and the opposing spacer 13. By having the surface of the non-opposing portion 40 have the aforementioned low-friction region, for example, even if local stress is applied to the center of the electrode body due to charging and discharging, the negative electrode 12 on the winding start end side will slide, the stress applied to the electrode is alleviated, and thus the electrode plate deformation associated with charging and discharging is suppressed. From the perspective of suppressing electrode plate deformation associated with charging and discharging, the static friction coefficient in the low-friction region is preferably, for example, 0.3 or less. In addition, from a manufacturing point of view, the lower limit of the aforementioned static friction coefficient is preferably 0.05 or more. Here, the surface of the non-opposing portion 40 in this disclosure can be either the surface of the non-opposing portion 40 itself or the surface of a component disposed on the non-opposing portion (e.g., an insulating component described later). Moreover, it is possible to configure the entire surface of the non-opposing portion to have the aforementioned low-friction region, or it is possible to configure a portion of the surface of the non-opposing portion to have the aforementioned low-friction region. In addition, as Figure 2 As shown, the non-opposing portion 40 has an outer peripheral non-opposing portion 44 and an inner peripheral non-opposing portion 46, but it is sufficient that at least either the surface on the outer peripheral non-opposing portion 44 or the surface on the inner peripheral non-opposing portion 46 has the aforementioned low-friction region. The method for measuring the static friction coefficient is described in the Examples section.

[0030] As a method for forming the aforementioned low-friction region, there are also methods that modify the surface of the non-opposing portion 40 itself, but it is preferable to use a method of arranging an insulating member on the non-opposing portion 40 as described later. Hereinafter, an example of an embodiment in which an insulating member is arranged on the non-opposing portion 40 (the outer peripheral non-opposing portion 44 and the inner peripheral non-opposing portion 46) will be described.

[0031] Figure 3 This is a schematic cross-sectional view showing the state of the negative and positive electrodes at the beginning of winding before winding. For example... Figure 3 As shown, the negative electrode 12 has a negative electrode core 48 and a negative electrode composite material layer 50 disposed on the negative electrode core 48. The negative electrode composite material layer 50 may be formed on only one side of the negative electrode core 48, or it may be formed on both sides of the negative electrode core 48. Figure 3In the negative electrode 12 shown, the outer peripheral non-opposing portion 44 is composed of a negative electrode composite material layer 50 disposed on the negative electrode core 48 and an outer peripheral exposed portion 48a on the negative electrode core 48 where the negative electrode composite material layer 50 is not disposed. However, this structure is not limited to this. For example, the outer peripheral non-opposing portion 44 can be composed of the negative electrode composite material layer 50 disposed on the negative electrode core 48, or it can be composed of the outer peripheral exposed portion 48a on the negative electrode core 48 where the negative electrode composite material layer 50 is not disposed. Similarly, the inner peripheral non-opposing portion 46 is not limited to being composed of the negative electrode composite material layer 50 disposed on the negative electrode core 48 and an inner peripheral exposed portion 48b on the negative electrode core 48 where the negative electrode composite material layer 50 is not disposed. It can be composed of the inner peripheral exposed portion 48b on the negative electrode core 48 where the negative electrode composite material layer 50 is not disposed, or it can be composed of the negative electrode composite material layer 50 disposed on the negative electrode core 48.

[0032] The negative electrode 12 has a first insulating member 52a disposed on the outer peripheral non-opposite portion 44 and a second insulating member 52b disposed on the inner peripheral non-opposite portion 46. Figure 3 The first insulating member 52a shown is disposed on the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 and on the outer peripheral exposed portion 48a. Furthermore, the first insulating member 52a may be disposed entirely or partially on the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44, or entirely or partially on the outer peripheral exposed portion 48a. Figure 3 The second insulating member 52b shown is disposed on the negative electrode composite material layer 50 within the inner peripheral non-opposing portion 46 and on the inner peripheral exposed portion 48b. Alternatively, the second insulating member 52b may be disposed entirely or partially on the negative electrode composite material layer 50 within the inner peripheral non-opposing portion 46, or entirely or partially on the inner peripheral exposed portion 48b.

[0033] As described above, from the perspective of suppressing electrode deformation associated with charging and discharging, it is sufficient that at least one of the surfaces on the outer peripheral non-opposing portion 44 and the inner peripheral non-opposing portion 46 has the aforementioned low-friction region. Therefore, it is sufficient that at least one of the surfaces of the first insulating member 52a disposed on the outer peripheral non-opposing portion 44 and the second insulating member 52b disposed on the inner peripheral non-opposing portion 46 has the aforementioned low-friction region. That is, it is sufficient that at least one of the static friction coefficient between the surface of the insulating member 52a disposed on the outer peripheral non-opposing portion 44 and the opposing spacer (not shown), and the static friction coefficient between the surface of the second insulating member 52b disposed on the inner peripheral non-opposing portion 46 and the opposing spacer (not shown) satisfies the aforementioned range.

[0034] From the perspective of suppressing the deformation of the electrode plates that accompanies charging and discharging, when winding the negative electrode 12, the first insulating member 52a is preferably disposed on the outer peripheral non-opposite portion 44 in the circumferential direction (i.e., the winding direction of the negative electrode 12) for more than 1.5 turns, and more preferably disposed on the outer peripheral non-opposite portion 44 in more than 1.5 turns and less than 3 turns.

[0035] The first insulating member 52a can be disposed on the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44, or it can be disposed on the outer peripheral exposed portion 48a within the outer peripheral non-opposing portion 44, such as... Figure 3 As shown, it can also be disposed on both the outer peripheral exposed portion 48a within the outer peripheral non-opposing portion 44 and on the negative electrode composite material layer 50. In this embodiment, for example, from the viewpoint of suppressing electrode plate deformation associated with charging and discharging, it is preferable that at least one of the surfaces on the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 and the surfaces on the negative electrode composite material layer 50 of the inner peripheral non-opposing portion 46 has the aforementioned low-friction region. Considering this, when the first insulating member 52a is provided on the outer peripheral non-opposing portion 44, it is also possible that the first insulating member 52a is provided on the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44, and the surface of the first insulating member 52a on the negative electrode composite material layer 50 has the aforementioned low-friction region. That is, if the first insulating member 52a is provided on the non-opposing portion 44 on the outer periphery, the first insulating member 52a may also be provided on the negative electrode composite material layer 50 inside the non-opposing portion 44 on the outer periphery, and the static friction coefficient between the surface of the first insulating member 52a on the negative electrode composite material layer 50 and the opposing spacer may be set to the range described above.

[0036] Furthermore, in this embodiment, for example, from the perspective of suppressing electrode plate deformation associated with charging and discharging, the aforementioned low-friction area on the surface of the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 preferably occupies 80% or more and 100% or less of the total area of ​​the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44. Considering this, when the first insulating member 52a is provided on the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44, the aforementioned low-friction area on the surface of the first insulating member 52a may also occupy 80% or more and 100% or less of the total area of ​​the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44. That is, the ratio of the overlapping area of ​​the aforementioned low-friction area on the surface of the first insulating member 52a with the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 may also be set to 80% or more and 100% or less.

[0037] Considering the suppression of electrode deformation associated with charging and discharging, such as Figure 3As shown, the first insulating member 52a is preferably disposed on the outer peripheral non-opposing portion 44 starting from the circumferential inner end edge 44a of the outer peripheral non-opposing portion 44. Alternatively, the first insulating member 52a may protrude from the outer peripheral non-opposing portion 44 and be disposed on the outer peripheral opposing portion, but considering factors such as battery capacity, it is preferable not to dispose of it on the outer peripheral opposing portion.

[0038] From the perspective of suppressing the deformation of the electrode plate that accompanies charging and discharging, the second insulating member 52b is preferably disposed on the inner peripheral non-opposite portion 46 in a circumferential direction of more than 0.9 turns, and the area ratio of the overlap with the inner peripheral non-opposite portion 46 is preferably more than 50% and less than 100%.

[0039] The second insulating member 52b can be disposed on the negative electrode composite material layer 50 within the inner peripheral non-opposing portion 46, or it can be disposed on the inner peripheral exposed portion 48b within the inner peripheral non-opposing portion 46, such as... Figure 3 As shown, it can also be disposed on both the inner peripheral exposed portion 48b within the inner peripheral non-opposing portion 46 and on the negative electrode composite material layer 50. In this embodiment, as described above, it is preferable that at least one of the surfaces of the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 and the surfaces of the negative electrode composite material layer 50 within the inner peripheral non-opposing portion 46 has the aforementioned low-friction region. Considering this, when the second insulating member 52b is provided on the inner peripheral non-opposing portion 46, it is also possible that the second insulating member 52b is provided on the negative electrode composite material layer 50 within the inner peripheral non-opposing portion 46, and the surface of the second insulating member 52b on the negative electrode composite material layer 50 has the aforementioned low-friction region. That is, when the second insulating member 52b is provided on the inner peripheral non-opposing portion 46, it is also possible that the second insulating member 52b is provided on the negative electrode composite material layer 50 within the inner peripheral non-opposing portion 46, and the static friction coefficient between the surface of the second insulating member 52b on the negative electrode composite material layer 50 and the opposing spacer is set to the aforementioned range. Furthermore, in this embodiment, for example, from the perspective of suppressing electrode plate deformation associated with charging and discharging, the surface of the inner peripheral exposed portion 48b preferably has the aforementioned low-friction area. Considering this, when the second insulating member 52b is provided on the inner peripheral non-opposing portion 46, it is also possible that the second insulating member 52b is provided on the inner peripheral exposed portion 48b within the inner peripheral non-opposing portion 46, and the surface of the second insulating member 52b on the inner peripheral exposed portion 48b has the aforementioned low-friction area. That is, if the second insulating member 52b is provided on the inner peripheral side non-opposing portion 46, the second insulating member 52b may also be provided on the inner peripheral side exposed portion 48b within the inner peripheral side non-opposing portion 46, and the coefficient of friction between the surface of the second insulating member 52b on the inner peripheral side exposed portion 48b and the opposing spacer may be set to the range described above.

[0040] Considering the suppression of electrode deformation associated with charging and discharging, such as Figure 3 As shown, the second insulating member 52b is preferably disposed on the inner peripheral non-opposing portion 46, for example, starting from the inner circumferential inner edge 46a of the inner peripheral non-opposing portion 46. Alternatively, the second insulating member 52b may protrude from the inner peripheral non-opposing portion 46 and be disposed on the inner peripheral opposing portion, but considering factors such as battery capacity, it is preferable not to dispose of it on the inner peripheral opposing portion.

[0041] For insulating members applicable to the first insulating member 52a and the second insulating member 52b, examples include insulating sheets and insulating tapes. Considering factors such as reducing the static friction coefficient with the spacer and facilitating the formation of the aforementioned low-friction areas on the surface, the insulating member preferably contains a fluoropolymer as its main component, and more preferably contains at least one of polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene (FEP) as its main component. In this invention, a main component refers to a component containing 50% by mass or more relative to the total amount of constituent components. That is, having at least one of PTFE and FEP as a main component means containing at least 50% by mass of either PTFE or FEP. Alternatively, the insulating member may also be a sheet formed by forming a coating on the surface of a resin sheet. Considering factors such as reducing the static friction coefficient with the spacer and facilitating the formation of the aforementioned low-friction areas on the surface, the coating preferably contains a fluoropolymer as its main component, and more preferably contains at least one of PTFE and FEP as its main component.

[0042] Figure 4 This is a schematic cross-sectional view illustrating an example of the structure of the insulating tape. The insulating tape 52 described below applies to the first insulating member 52a and the second insulating member 52b. The insulating tape 52 includes, for example, a substrate layer 54 and an adhesive layer 56. The insulating tape 52 has a laminated structure in which the adhesive layer 56 and the substrate layer 54 are sequentially stacked from the non-opposing side. Therefore, the surface of the substrate layer 54 becomes the surface of the insulating tape 52 opposite to the spacer. The thickness of the insulating tape 52 is preferably 0.02 mm or more and 0.1 mm or less, considering factors such as flexibility and strength.

[0043] For example, considering factors such as reducing the static friction coefficient with the spacer and facilitating the formation of the aforementioned low-friction areas on the surface, the substrate layer 54 preferably contains a fluoropolymer as the main component, and more preferably contains at least one of polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene (FEP) as the main component. The substrate layer 54 may, for example, contain other resins such as polyolefins (e.g., polyethylene, polypropylene, etc.), polystyrene, polyesters (e.g., polyethylene terephthalate, etc.), polyimide, polyamide, polyamide-imide, polycarbonate, and polyphenylene sulfide.

[0044] The adhesive layer 56 is primarily used to impart adhesion to the insulating tape 52 relative to the negative electrode 12. The adhesive layer 56 is formed by applying an adhesive to one surface of the substrate layer 54. The adhesive constituting the adhesive layer 56 can be a hot-melt type that exhibits adhesion upon heating or a thermosetting type that cures upon heating; from a productivity point of view, an adhesive that exhibits adhesion at room temperature is preferred. Examples of adhesives include acrylic adhesives and synthetic rubber adhesives.

[0045] Insulating tape 52 is not limited to Figure 4 The configuration shown could also include, for example, a layer containing inorganic particles between the substrate layer 54 and the adhesive layer 56. This inorganic particle layer, for example, has a structure in which inorganic particles are dispersed in a resin matrix constituting the layer. The inorganic particle layer is formed, for example, by coating a resin solution containing inorganic particles onto one surface of the substrate layer 54. Examples of inorganic particles include metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles. Examples of resin matrices include acrylic resins, urethane resins, and their elastomers.

[0046] For the negative electrode core 48 constituting the negative electrode 12, a foil of a metal that is stable within the potential range of the negative electrode, such as copper or a copper alloy, or a thin film of the metal disposed on the surface can be used. The thickness of the negative electrode core 48 is, for example, in the range of 7 μm to 50 μm.

[0047] Furthermore, the negative electrode composite material layer 50 constituting the negative electrode 12 includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode composite material layer 50 is, for example, in the range of 10 μm to 100 μm. The negative electrode composite material layer 50 can be manufactured, for example, by coating a negative electrode composite material slurry containing a negative electrode active material and a binder onto the negative electrode core 48, drying the coating, and then calendering it.

[0048] The negative electrode active material contained in the negative electrode composite layer 50 is not particularly limited to any material that can reversibly absorb, store, and release lithium ions, such as carbon materials and Si-based materials. From the perspective of increasing battery capacity, the negative electrode active material preferably contains Si-based materials.

[0049] Carbon materials can be, for example, previously known carbon materials used as negative electrode active materials, such as natural graphite such as flake graphite, block graphite, and ochre graphite, blocky artificial graphite (MAG), graphitized mesophase carbon microspheres (MCMB), etc.

[0050] As a Si-based material, there are no particular limitations as long as it can reversibly absorb, store, and release lithium ions, such as Si particles, Si-containing alloy particles, and Si compound particles. Among these, Si compound particles are preferred.

[0051] Examples of Si compound particles include Si compound particles having a silicate phase and Si particles dispersed in the silicate phase, Si compound particles having a silicon oxide phase and Si particles dispersed in the silicon oxide phase, and Si compound particles having a carbon phase and Si particles dispersed in the carbon phase.

[0052] For example, considering factors such as high lithium-ion conductivity, the silicate phase preferably contains at least one element selected from lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium. Among these, considering factors such as high lithium-ion conductivity, the silicate phase is preferably a silicate phase containing lithium (hereinafter, sometimes referred to as lithium silicate phase).

[0053] Lithium silicate phase, for example, is given by formula: Li 2z SiO 2+z (0 < z < 2) indicates that, from the perspectives of stability, ease of manufacture, and lithium-ion conductivity, z preferably satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2.

[0054] Si compound particles, such as those of the general formula SiO, are dispersed within a silicon oxide phase. x (Preferably in the range of 0 < x < 2, more preferably in the range of 0.5 ≤ x ≤ 1.6). Si compound particles in which Si particles are dispersed in the carbon phase are represented, for example, by the general formula SixC1y (preferably in the range of 0 < x ≤ 1 and 0 < y ≤ 1, more preferably in the range of 0.3 ≤ x ≤ 0.45 and 0.7 ≤ y ≤ 0.55).

[0055] Preferably, a conductive coating made of a highly conductive material is formed on the surface of Si-based material particles. Examples of conductive coatings include carbon coatings, metal coatings, and metal compound coatings; however, carbon coatings are preferred from the perspective of electrochemical stability. Carbon coatings can be formed, for example, by using a CVD method with acetylene or methane, or by mixing coal tar pitch, petroleum pitch, phenolic resin, etc., with a silicon-based active material and then heat-treating the mixture. Alternatively, a conductive coating can be formed by using a binder to fix conductive fillers such as carbon black onto the surface of Si-based material particles.

[0056] From the perspective of increasing battery capacity, the content of Si-based materials is preferably 5% by mass or more relative to the total mass of the negative electrode composite material layer 50.

[0057] In addition to carbon materials and Si-based materials, negative electrode active materials can also include other materials capable of reversibly absorbing and releasing lithium ions. Examples of such other materials include Sn, Sn-containing alloys, Sn-based materials such as tin oxide, and Ti-based materials such as lithium titanate.

[0058] Examples of adhesives include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), and polyethylene oxide (PEO).

[0059] The positive electrode 11 has a positive electrode core and a positive electrode composite material layer formed on the surface of the positive electrode core. The positive electrode composite material layer is preferably formed on both sides of the positive electrode core. For the positive electrode core, a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum, or a thin film of the metal disposed on the surface, can be used. The positive electrode composite material layer includes, for example, a positive electrode active material, a binder, and a conductive agent. The positive electrode composite material layer can be manufactured, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a binder, and a conductive agent onto the positive electrode core, drying the coating, and then calendering it.

[0060] Examples of positive electrode active materials included in the positive electrode composite layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides are, for example, Li. x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1－y O2, Li x Co y M 1－y O z Li x Ni 1－y M y O z Li x Mn2O4, Li x Mn 2－y M y O4, LiMPO4, Li2MPO4F (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). They can be used individually or in combination. From the perspective of achieving high battery capacity, the positive electrode active material preferably contains Li. xNiO2, Li x Co y Ni 1－y O2, Li x Ni 1－y M y O z (At least one of M, Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3) and other lithium-nickel composite oxides. Inorganic particles such as tungsten oxide, aluminum oxide, and lanthanide-containing compounds can be fixed on the surface of the lithium transition metal oxide particles.

[0061] Examples of conductive agents included in the positive electrode composite layer include carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon materials. Examples of binders included in the positive electrode composite layer are the same binders used in the negative electrode 12.

[0062] For the spacer 13, a porous sheet with ion-permeable and insulating properties can be used, for example. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The preferred material for the spacer is an olefin-based resin such as polyethylene or polypropylene, or cellulose. The spacer 13 can also be a laminate containing a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, a multilayer spacer containing a polyethylene layer and a polypropylene layer can be used, or a spacer with an aromatic polyamide resin, ceramic, or other material coated on its surface can be used.

[0063] Example

[0064] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited to these examples.

[0065] <Example 1>

[0066] [The production of the positive electrode]

[0067] 100 parts by weight of LiNi 0.88 Co 0.09 Al 0.03O2, 1 part by mass of acetylene black (AB), and 0.9 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode composite slurry. Next, the positive electrode composite slurry was coated onto both sides of a 15 μm thick aluminum foil and allowed to dry. Then, the coating was calendered using rollers and cut into specified electrode sizes to fabricate a positive electrode with positive electrode composite layers formed on both sides of the positive electrode core. An exposed portion without the positive electrode composite layer was provided at the center of the positive electrode along its length, and aluminum positive electrode leads were welded to this exposed portion.

[0068] [Making the negative electrode]

[0069] A dispersion of 92 parts by weight of graphite powder, 6 parts by weight of Si-based material, 1 part by weight of sodium carboxymethyl cellulose (CMC-Na), and 1 part by weight of styrene-butadiene rubber (SBR) was mixed, and water was added as appropriate to prepare a negative electrode composite slurry. Next, the negative electrode composite slurry was coated onto both sides of an 8 μm thick copper foil, and the coating was allowed to dry. Then, the coating was calendered using a roller and cut into specified electrode sizes to create a negative electrode with a negative electrode composite layer formed on both sides of the negative electrode core. Exposed portions without a negative electrode composite layer were provided at both ends of the negative electrode along its length, and nickel negative electrode leads were welded to these exposed portions. Additionally, an insulating member was provided at the end of the negative electrode along its length that became the winding start side. For the insulating member, a fluoropolymer tape coated with an acrylic adhesive on a fluoropolymer substrate was used. The placement of the insulating member in Example 1 will be described below.

[0070] Figure 5This is a schematic cross-sectional view showing the state of the negative and positive electrodes at the winding start end side before winding in Embodiment 1. In Embodiment 1, a first insulating member 52a (fluoropolymer tape) is disposed on the outer peripheral exposed portion 48a within the outer peripheral non-opposing portion 44 of the negative electrode 12 and on the negative electrode composite material layer 50, such that the substrate layer becomes a tape surface. Additionally, a second insulating member 52b (fluoropolymer tape) is disposed on the inner peripheral exposed portion 48b within the inner peripheral non-opposing portion 46 of the negative electrode 12 and on the negative electrode composite material layer 50, such that the substrate layer becomes a tape surface. The area ratio of the first insulating member 52a disposed on the outer peripheral non-opposing portion 44 to the outer peripheral exposed portion 48a within the outer peripheral non-opposing portion 44 is 100%, and the area ratio of the first insulating member 52a to the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 is 94%. Furthermore, when winding the negative electrode 12, the first insulating member 52a is arranged circumferentially in the outer peripheral non-opposing portion 44 for 2.1 turns (number of turns: 2.1 turns). On the other hand, the second insulating member 52b arranged on the inner peripheral non-opposing portion 46 overlaps with the inner peripheral non-opposing portion 46 by 97% of the area. Also, when winding the negative electrode 12, the second insulating member 52b is arranged circumferentially in the inner peripheral non-opposing portion 46 for 2.1 turns (number of turns: 2.1 turns).

[0071] <Coefficient of static friction>

[0072] The static friction coefficient between the surface of the fluoropolymer tape used as the first insulating member 52a disposed on the outer peripheral non-opposing portion 44 and the second insulating member 52b disposed on the inner peripheral non-opposing portion 46 and the opposing spacer used in the fabrication of the wound electrode body is 0.20. That is, both the surface of the first insulating member 52a and the surface of the second insulating member 52b have a low-friction region with a static friction coefficient of 0.20 with respect to the opposing spacer. Furthermore, as described above, the area ratio of the overlap between the first insulating member 52a and the negative electrode composite material layer 50 in the outer peripheral non-opposing portion 44 is 94%. Therefore, the aforementioned low-friction region on the surface of the first insulating member 52a accounts for 94% of the total surface area of ​​the negative electrode composite material layer 50 in the outer peripheral non-opposing portion 44.

[0073] The method for determining the static friction coefficient is as follows. Figure 7 This is a schematic diagram of a device used to determine the coefficient of static friction. Figure 7The apparatus 60 shown includes a test bench 62, pulleys 64, a line 66 mounted on the pulleys, and a counterweight 68 mounted on one end of the line 66 and positioned on the test bench 62. A first test piece 70 is fixed to the bottom surface of the counterweight 68. A second test piece 72 is fixed to the test bench 62 so as to face the first test piece 70 fixed to the bottom surface of the counterweight 68. The other end of the line 66 is connected to a tensile testing machine (not shown). The tensile testing machine is, for example, Autograph (Shimadzu Corporation, model AG-X). The counterweight 68 has a weight of 630g. The first test piece 70 is a spacer (size: 4cm × 3cm) with 0.1mL of non-aqueous electrolyte added. The non-aqueous electrolyte is a non-aqueous electrolyte used in non-aqueous electrolyte secondary batteries. The second test piece 72 is a fluoropolymer tape (size: 10cm × 6cm), with the substrate layer facing the spacer. Furthermore, in Example 2 described later, an FEP sheet was prepared as the second test piece 72. Additionally, in Comparative Example 1 described later, two test pieces were prepared as the second test piece 72: a negative electrode composite material layer formed on a copper foil and a polypropylene strip. Furthermore, in Comparative Example 2 described later, a polypropylene strip was prepared as the second test piece 72. When using a polypropylene strip as the test piece, the substrate layer is positioned opposite the spacer.

[0074] During the test, the tensile testing machine is driven, and an external force is applied to the counterweight 68 via line 66 at a speed of 20 mm / min. The external force is gradually increased, and the force at which the spacer begins to move is measured as the static friction force. Then, the static friction coefficient is calculated using the following formula.

[0075] μ s =F s / F p

[0076] μ s static friction coefficient

[0077] F s Static friction (N)

[0078] F p The normal force generated by the mass of counterweight 68 (=1.96N)

[0079] [Preparation of non-aqueous electrolytes]

[0080] A non-aqueous electrolyte was prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent consisting of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, and dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.5 mol / L.

[0081] [Construction of a non-aqueous electrolyte secondary battery]

[0082] A wound electrode body is formed by winding the aforementioned positive and negative electrodes with a spacer between them. Insulating plates are placed above and below the electrode body, and the electrode body is housed within the main body of the casing. The negative electrode lead is soldered to the bottom of the main body of the casing, and the positive electrode lead is soldered to the sealing body. After injecting a non-aqueous electrolyte into the main body of the casing, the opening of the main body of the casing is sealed with the sealing body through a gasket, thus forming a non-aqueous electrolyte secondary battery.

[0083] <Example 2>

[0084] Instead of the fluoropolymer tape used as an insulating member in Example 1, an FEP sheet was used, and the non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1. The static friction coefficient between the surface of the FEP sheet used as an insulating member disposed on the outer peripheral non-opposing portion 44 and the inner peripheral non-opposing portion 46 and the opposing spacer used in the fabrication of the wound electrode body is 0.40. That is, the surfaces of the first insulating member 52a and the second insulating member 52b both have low-friction areas with a static friction coefficient of 0.40 with respect to the opposing spacer.

[0085] <Comparative Example 1>

[0086] Figure 6 This is a schematic cross-sectional view showing the state of the negative and positive electrodes at the winding start end side before winding in Comparative Example 1. In Comparative Example 1, a first insulating member 52a is disposed on the outer peripheral exposed portion 48a within the outer peripheral non-opposing portion 44 of the negative electrode 12 and on the negative electrode composite material layer 50, such that the substrate layer becomes the tape surface. The area ratio of the first insulating member 52a disposed on the outer peripheral non-opposing portion 44 to the outer peripheral exposed portion 48a within the outer peripheral non-opposing portion 44 is 100%, and the area ratio of the first insulating member 52a to the negative electrode composite material layer 50 within the outer peripheral non-opposing portion 44 is 13%. Furthermore, when winding the negative electrode 12, the first insulating member 52a is disposed circumferentially throughout the outer peripheral non-opposing portion 44 for 1.0 turns (number of turns: 1.0 turns). For the first insulating member 52a, a polypropylene tape coated with an acrylic adhesive on a polypropylene substrate is used.

[0087] The static friction coefficient between the surface of the polypropylene tape used as the first insulating member 52a disposed on the outer peripheral non-opposing portion 44 and the opposing spacer used in the manufacture of the wound electrode body is 0.42. Furthermore, the static friction coefficient between the surface of the negative electrode composite material layer 50 of the outer peripheral non-opposing portion 44 not covered by the polypropylene tape and the opposing spacer used in the manufacture of the wound electrode body is 0.59. Additionally, in the inner peripheral non-opposing portion 46 where the polypropylene tape is not disposed, the static friction coefficient between the surface of the negative electrode composite material layer 50 of the inner peripheral non-opposing portion 46 and the opposing spacer used in the manufacture of the wound electrode body is 0.59, and the static friction coefficient between the inner peripheral exposed portion 48b of the inner peripheral non-opposing portion 46 and the opposing spacer used in the manufacture of the wound electrode body is 0.41.

[0088] <Comparative Example 2>

[0089] Instead of the fluoropolymer tape used as an insulating component in Example 1, the polypropylene tape used in Comparative Example 1 was used, and the non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0090] [Evaluation of plate deformation]

[0091] The non-aqueous electrolyte secondary batteries of each embodiment and comparative example were charged with a constant current of 0.3 It until the battery voltage reached 4.2V, and then charged with a constant voltage of 4.2V until the current reached 0.02 It. They were then discharged with a constant current of 1.0 It until the battery voltage reached 2.7V. This charge-discharge cycle was performed for 10 cycles. After 10 cycles, the cross-section of the center of the electrode body of the non-aqueous electrolyte secondary battery was observed using an X-ray CT apparatus (Shimadzu SMX-225CT FPD HR) to confirm whether electrode deformation had occurred. The results are summarized in Table 1.

[0092] [Table 1]

[0093]

[0094] In Comparative Examples 1 and 2, electrode deformation was confirmed, but in Examples 1 and 2, electrode deformation was not confirmed. From this result, it can be said that, as in the examples, by making the surface of the non-opposing portion have a low-friction region with a static friction coefficient of 0.4 or less between it and the opposing spacer (i.e., by making the static friction coefficient between the surface of the non-opposing portion and the opposing spacer 0.4 or less), the occurrence of electrode deformation associated with charging and discharging can be suppressed.

[0095] [Postscript] (1)

[0097] A secondary battery has an electrode body, which is formed by winding a positive electrode and a negative electrode having a negative electrode composite material layer disposed on a negative electrode core, separated by a spacer.

[0098] The negative electrode has a non-opposite portion at the winding start end that is not opposite to the positive electrode separated by the spacer.

[0099] The surface of the non-opposing portion has a low-friction region with a static friction coefficient of 0.4 or less between it and the opposing spacer. (2)

[0101] According to the secondary battery described in (1) above, wherein,

[0102] The static friction coefficient is below 0.3. (3)

[0104] According to the secondary battery described in (1) or (2) above, the static friction coefficient is 0.05 or higher. (4)

[0106] According to any one of (1) to (3) above, the secondary battery, wherein,

[0107] The negative electrode includes an insulating member disposed on the non-opposite portion.

[0108] The surface of the insulating component has the low-friction area. (5)

[0110] According to the secondary battery described in (4) above, wherein,

[0111] The insulating component is an insulating tape. (6)

[0113] According to the secondary battery described in (5) above, wherein,

[0114] The insulating tape has a stacked structure in which an adhesive layer and a substrate layer are stacked sequentially from the non-opposite side. (7)

[0116] According to the secondary battery described in (6) above, wherein,

[0117] The substrate layer contains fluoropolymer as the main component. (8)

[0119] According to the secondary battery described in (4) above, wherein,

[0120] The insulating component comprises at least one of polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) as the main component. (9)

[0122] According to any one of (4) to (8) above, the secondary battery, wherein,

[0123] The thickness of the insulating component is 0.02 mm or more and 0.1 mm or less. (10)

[0125] According to any one of (1) to (9) above, the secondary battery, wherein,

[0126] The non-opposing portion includes an outer peripheral non-opposing portion and an inner peripheral non-opposing portion.

[0127] At least one of the surfaces on the negative electrode composite material layer in the outer peripheral non-opposing portion and the surfaces on the negative electrode composite material layer in the inner peripheral non-opposing portion has the low-friction region. (11)

[0129] According to the secondary battery described in (10) above, wherein,

[0130] The low-friction region occupies more than 80% and less than 100% of the total surface area of ​​the negative electrode composite material layer within the non-opposing portion on the outer periphery. (12)

[0132] According to any one of (1) to (11) above, the secondary battery, wherein,

[0133] The non-opposing portion includes an inner peripheral non-opposing portion, which has an inner peripheral exposed portion on the negative electrode core where no negative electrode composite material layer is formed.

[0134] The surface on the exposed inner circumferential side has the low-friction area.

[0135] Explanation of reference numerals in the attached figures

[0136] 10. Secondary battery; 11. Positive electrode; 12. Negative electrode; 13. Spacer; 14. Electrode body; 15. Battery casing; 16. Casing body; 17. Sealing body; 18a, 18b. Insulating plate; 19. Positive lead; 20a, 20b. Negative lead; 21. Protrusion; 22. Filter; 23. Lower valve core; 24. Insulator; 25. Upper valve core; 26. Cover; 27. Gasket; 40. Non-opposite part; 42. Opposite part; 44. Outer peripheral non-opposite part Part; 44a, 46a, circumferential inner edge; 46, inner circumferential non-opposite part; 48, negative electrode core; 48a, outer circumferential exposed part; 48b, inner circumferential exposed part; 50, negative electrode composite material layer; 52, insulating tape; 52a, first insulating member; 52b, second insulating member; 54, substrate layer; 56, adhesive layer; 60, device; 62, test bench; 64, pulley; 66, wire; 68, counterweight; 70, first test piece; 72, second test piece.

Claims

1. A secondary battery having an electrode body, the electrode body being formed by winding a positive electrode and a negative electrode having a negative electrode composite material layer disposed on a negative electrode core, separated by a spacer, wherein, The negative electrode has a non-opposite portion at the winding start end that is not opposite to the positive electrode separated by the spacer. The surface of the non-opposing portion has a low-friction region with a friction coefficient of less than 0.4 with respect to the opposing spacer.

2. The secondary battery according to claim 1, wherein, The static friction coefficient is below 0.

3.

3. The secondary battery according to claim 1 or 2, wherein, The static friction coefficient is 0.05 or higher.

4. The secondary battery according to claim 1 or 2, wherein, The negative electrode includes an insulating member disposed on the non-opposite portion. The surface of the insulating component has the low-friction area.

5. The secondary battery according to claim 4, wherein, The insulating component is an insulating tape.

6. The secondary battery according to claim 5, wherein, The insulating tape has a stacked structure in which an adhesive layer and a substrate layer are stacked sequentially from the non-opposite side.

7. The secondary battery according to claim 6, wherein, The substrate layer contains fluoropolymer as the main component.

8. The secondary battery according to claim 4, wherein, The insulating component comprises at least one of polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) as the main component.

9. The secondary battery according to claim 4, wherein, The thickness of the insulating component is 0.02 mm or more and 0.1 mm or less.

10. The secondary battery according to claim 1 or 2, wherein, The non-opposing portion includes an outer peripheral non-opposing portion and an inner peripheral non-opposing portion. At least one of the surfaces on the negative electrode composite material layer in the outer peripheral non-opposing portion and the surfaces on the negative electrode composite material layer in the inner peripheral non-opposing portion has the low-friction region.

11. The secondary battery according to claim 10, wherein, The low-friction region occupies more than 80% and less than 100% of the total surface area of ​​the negative electrode composite material layer within the non-opposing portion on the outer periphery.

12. The secondary battery according to claim 1 or 2, wherein, The non-opposing portion includes an inner peripheral non-opposing portion, which has an inner peripheral exposed portion on the negative electrode core where no negative electrode composite material layer is formed. The surface on the exposed inner circumferential side has the low-friction area.

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