Secondary battery

Abstract

A secondary battery (10), which is an example of an embodiment, is provided with an electrode body in which a positive electrode (11) and a negative electrode are wound with a separator interposed therebetween, the positive electrode (11) has a wide section (30) and a narrow section (40), the widths of which differ from each other, and the narrow section (40) is provided closer to the winding start side than the center of the positive electrode (11) in the longitudinal direction.

Description

Technical Field

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

[0002] In secondary batteries such as lithium-ion batteries, the positive and negative electrodes are arranged so that the negative electrode's composite layer faces the positive electrode's composite layer, with a separator interposed between them, to prevent metallic lithium from precipitating on the negative electrode. However, repeated charging and discharging of the battery increases internal pressure due to, for example, the expansion of the negative electrode composite layer. This increases the pressure load on the positive electrode, causing it to stretch. Conventional secondary batteries have designed the negative electrode to be one size larger than the positive electrode to maintain its facing position even when the positive electrode stretches during charging and discharging (see Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2019 / 230297 Summary of the Invention

[0006] With the high capacity of secondary batteries in recent years, the expansion of the negative electrode mixture layer during charge and discharge has become further increased, and the elongation of the positive electrode during repeated charge and discharge has become more significant. When the positive electrode is greatly elongated, not only will metallic lithium be deposited at the negative electrode, but it may also cause a local short circuit caused by the contact between the positive electrode and the negative electrode lead. By designing the size of the positive electrode to be smaller, the effect of the elongation of the positive electrode caused by charge and discharge can be reduced. However, if the size of the positive electrode is reduced, the amount of the positive electrode mixture layer involved in charge and discharge is reduced, and the capacity of the secondary battery will be reduced.

[0007] An object of the present application is to provide a secondary battery that can more reliably suppress the occurrence of short circuits and the formation of a negative electrode non-opposing region of the positive electrode even when the positive electrode is stretched due to charge and discharge while maintaining the capacity of the secondary battery.

[0008] A secondary battery according to one embodiment of the present application is characterized in that it comprises an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, wherein the positive electrode has a wide portion and a narrow portion having different widths, and the narrow portion is provided closer to the winding start side than the longitudinal center of the positive electrode.

[0009] According to the secondary battery of the present application, even when the positive electrode is extended by charge and discharge, the occurrence of a short circuit and the formation of a negative electrode non-opposing region of the positive electrode can be suppressed while maintaining the capacity of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1It is a cross-sectional view in the axial direction of a secondary battery as an example of an embodiment.

[0011] Figure 2 This is a diagram showing a positive electrode as an example of an embodiment in a developed state.

[0012] Figure 3 It is a plan view showing a winding structure on the winding start side of a positive electrode as an example of an embodiment.

[0013] Figure 4 This is a diagram showing a positive electrode as another example of the embodiment in a developed state. DETAILED DESCRIPTION

[0014] Repeated charging and discharging of secondary batteries increases the expansion rate of the negative electrode mixture layer that constitutes the negative electrode. Consequently, the pressure load on the positive electrode, which is arranged opposite the negative electrode, gradually increases, and the strain of the positive electrode eventually exceeds the elastic region and reaches the plastic region, causing the positive electrode to stretch. The results of research by the present inventors have shown that in secondary batteries, the elongation of the positive electrode accompanying charging and discharging is more significant at the winding start side (core side) than at the winding end side (peripheral side). This is presumably because when the negative electrode mixture layer expands during charging and discharging, pressure is applied from the outer packaging can containing the electrode body to the interior of the battery.

[0015] According to the secondary battery of the present application, a narrow portion of the positive electrode, designed to be smaller in width than the rest of the positive electrode, is provided closer to the winding start side than the longitudinal center of the positive electrode. This prevents the formation of a non-negative electrode-opposing area on the winding start side of the positive electrode, even during repeated charge and discharge. Furthermore, rather than reducing the overall width of the positive electrode, the width of the positive electrode is reduced only on the winding start side, where the positive electrode's elongation during charge and discharge is more pronounced. This prevents reduction in the positive electrode's area and maintains the secondary battery's capacity.

[0016] Below, with reference to the accompanying drawings, an example of an embodiment of the secondary battery of the present application is described in detail. The embodiment described below is merely an example, and the present application is not limited to the following embodiment. In addition, the present application includes a method of selectively combining the various components of the embodiment described below.

[0017] In the embodiments described below, a cylindrical secondary battery is exemplified as a secondary battery in which a wound electrode assembly 14 is housed in a bottomed cylindrical outer can 16. However, the outer can of the secondary battery is not limited to a cylindrical outer can. Other embodiments of the secondary battery of the present application include a prismatic battery having a prismatic outer can, a button-shaped battery having a button-shaped outer can, and a soft-pack battery having an outer can composed of a laminate sheet including a metal layer and a resin layer.

[0018] Figure 1 1 is a diagram schematically showing a cross section of a secondary battery 10 as an example of an embodiment. Figure 1 As shown, the secondary battery 10 includes an electrode body 14, a non-aqueous electrolyte (not shown), and an outer can 16 for storing 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. The outer can 16 is a metal container with a bottom and a cylindrical shape, which is open on one side in the axial direction. The opening of the outer can 16 is sealed by a sealing body 17. It should be noted that Figure 1 In order to facilitate understanding of the arrangement relationship of the positive electrode 11, the negative electrode 12, and the separator 13 in the electrode assembly 14, the number of windings is reduced compared to the actual situation. Hereinafter, the side of the sealing body 17 in the axial direction (height direction) of the secondary battery 10 is referred to as "upper," and the side of the bottom of the outer can 16 in the axial direction is referred to as "lower."

[0019] The non-aqueous electrolyte has lithium ion conductivity and can be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0020] 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 the non-aqueous solvent 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.

[0021] As a solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. A 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 after absorbing a non-aqueous solvent can be used. Examples of polymer materials include fluororesins, acrylic resins, and polyether resins.

[0022] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode body 14 are all long, strip-like objects that are spirally wound and alternately stacked along 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 longer in both the length and width (short side) directions than the positive electrode 11. 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 secondary battery 10 includes insulating plates 18 and 19 arranged above and below the electrode body 14, respectively.

[0023] The positive electrode 11 includes a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. The positive electrode core 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 film having the metal disposed on the surface. The positive electrode mixture layer includes a positive electrode active material, a conductive agent, and a binder. For example, a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder is applied to the positive electrode core, and after the coating is dried, it is compressed to form positive electrode mixture layers on both sides of the positive electrode core, thereby producing the positive electrode 11.

[0024] The positive electrode mixture layer 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 to contain at least one selected from Co, Ni, Al, and Mn. As an example of a suitable 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.

[0025] Examples of conductive agents included in the positive electrode mixture layer include carbon blacks such as acetylene black and Ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), and the like.

[0026] The negative electrode 12 includes a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core 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 film having the metal disposed on the surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and a conductive agent as needed. A negative electrode mixture slurry containing a negative electrode active material and a binder is applied to the surface of the negative electrode core. After the coating is dried, it is compressed to form negative electrode mixture layers on both sides of the negative electrode core, thereby producing the negative electrode 12.

[0027] The negative electrode mixture layer preferably contains a carbon material and a silicon-containing material as the negative electrode active material. The combined use of a carbon material and a silicon-containing material facilitates achieving both high capacity and excellent cycle characteristics. For example, the negative electrode mixture layer can contain at least one of an element that alloys with lithium, such as Sn, and a material containing the element.

[0028] Regarding the content of silicon-containing material, from the viewpoint of high capacity, it is preferably 3% by mass or more of the total mass of the negative electrode active material, more preferably 5% by mass or more, and even more preferably 8% by mass or more. Generally speaking, since the silicon-containing material has a larger expansion rate during charge and discharge than the carbon material, the elongation of the positive electrode in the width direction becomes more significant if charge and discharge are repeated. Although the details will be described later, in this embodiment, a narrow portion 40 is formed on the winding start side of the positive electrode 11, in which the width of the positive electrode 11 is smaller than that of other parts. Therefore, even in the case of repeated charge and discharge, the generation of short circuits caused by the elongation of the positive electrode 11 and the generation of non-opposite areas of the positive electrode can be suppressed. In other words, when a silicon-containing material is included as the negative electrode active material, the effect of the present application becomes more significant.

[0029] The carbon material serving 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, it is preferred to use 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.

[0030] Any silicon-containing material may be a 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 the D50 of graphite. The volume-based D50 of a composite material is, for example, 1 μm to 15 μm. It should be noted that a single silicon-containing material may be used alone, or two or more may be used in combination.

[0031] 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 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.

[0032] An example of a suitable composite material containing Si is a composite material having a sea-island structure in which fine Si is substantially uniformly dispersed in an amorphous silicon oxide phase and having a general formula of SiO as a whole. x Composite particles represented by (0<x≤2). The main component of silicon oxide may be silicon dioxide. The content ratio (x) of oxygen relative to Si is, for example, 0.5≤x<2.0, and preferably 0.8≤x≤1.5.

[0033] As with the positive electrode mixture layer, the binder contained in the negative electrode mixture layer can also include fluororesins, PAN, polyimide, acrylic resins, polyolefins, etc., but styrene butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer preferably includes CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. Combinations of SBR with CMC or its salts, PAA or its salts, etc. are suitable. The negative electrode mixture layer may also include a conductive agent such as CNTs.

[0034] The separator 13 uses a porous sheet with ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. In addition, a resin layer with high heat resistance, such as an aromatic polyamide resin, may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0035] A positive electrode lead 20 is connected to the positive electrode 11, and a negative electrode lead 21 is connected to the winding end side of the negative electrode 12. The positive electrode lead 20 extends toward the sealing body 17 after passing through the through hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like. The cover 27 constituting the top plate of the sealing body 17 is electrically connected to the internal terminal plate 23, and the cover 27 serves as the positive terminal. In addition, the negative electrode lead 21 is connected to the inner surface of the bottom of the metal outer can 16 by welding or the like, and the outer can 16 serves as the negative terminal.

[0036] As described above, the outer can 16 is a metal container with a bottom and a cylindrical shape that is open on one side in the axial direction. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior and the insulation between the outer can 16 and the sealing body 17. The outer can 16 has a groove 22 formed on the side surface, which supports the sealing body 17 and has a portion of the side surface protruding inward. The groove 22 is preferably formed in an annular shape along the circumference of the outer can 16, and the sealing body 17 is supported by its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove 22 and the open end of the outer can 16 that is clamped against the sealing body 17.

[0037] The outer diameter of the outer can 16 is, for example, not less than 20 mm and not more than 50 mm. By increasing the outer diameter of the outer can 16, the volume of the electrode body 14 that can be accommodated inside the outer can 16 increases, and the capacity of the secondary battery 10 can be increased. However, when the outer diameter of the outer can 16 is increased and the volume of the electrode body 14 accommodated inside the outer can 16 is increased, the pressure load on the positive electrode 11 becomes greater. In this embodiment, a narrow portion 40 is formed on the side where the winding of the positive electrode 11 starts, in which the width of the positive electrode 11 is smaller than that of other parts. Therefore, even when the volume of the electrode body 14 is large, the generation of a short circuit caused by the elongation of the positive electrode 11 accompanying charging and discharging and the generation of a non-negative electrode-opposing area of ​​the positive electrode can be suppressed. In other words, when the outer diameter of the outer can 16 is increased and the volume of the electrode body 14 accommodated inside the outer can 16 is increased, the effect of the present application becomes more significant. Therefore, an example of a suitable range of the outer diameter of the outer can 16 is 25 mm or more and 50 mm or less, more preferably 30 mm or more and 50 mm or less, and even more preferably 35 mm or more and 50 mm or less.

[0038] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26 and a cover 27 are stacked in sequence from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and an insulating member 25 is sandwiched between their respective peripheral portions. When an abnormality occurs in the secondary battery 10 and the internal pressure rises, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 toward the cover 27 side, thereby blocking the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 breaks and gas is discharged from the opening of the cover 27.

[0039] Below, in reference Figure 2 and Figure 3 At the same time, the positive electrode 11 will be described in detail.

[0040] Figure 2 It will constitute Figure 1 FIG. 1 is an example of a front view showing a positive electrode 11 of an electrode assembly 14 included in a secondary battery 10 in a developed state. Figure 3 1 is a top view schematically showing the winding structure of the positive electrode 11 at the winding start side. Figure 2 In the figure, the width of the narrow width portion 40 described later is exaggerated for clarity of the drawings. Figure 3 In FIG. 1 , the region where the narrow width portion 40 is formed is indicated by hatching.

[0041] like Figure 2 As shown, the positive electrode 11 has a wide portion 30 and a narrow portion 40 of different widths. Here, the wide portion 30 refers to a region of the positive electrode 11 that is equal to or wider than the width of the positive electrode 11 at the winding end 11B of the positive electrode 11. Furthermore, the narrow portion 40 refers to a region of the positive electrode 11 that is narrower than the width of the positive electrode 11 at the winding end 11B of the positive electrode 11. It should be noted that in this specification, the winding start end 11A of the positive electrode 11 refers to the longitudinal end of the positive electrode 11 located on the winding start side (core side) of the electrode body 14. Furthermore, the winding end 11B of the positive electrode 11 refers to the longitudinal end of the positive electrode 11 located on the winding end side (outer periphery) of the electrode body 14.

[0042] like Figure 2 As shown, the narrow portion 40 is provided on the winding start side closer to the longitudinal center of the positive electrode 11. As described above, the pressure load on the positive electrode 11 during repeated charging and discharging of the secondary battery 10 becomes greater on the winding start side than on the winding end side. That is, the effect of the elongation of the positive electrode 11 during repeated charging and discharging is more significant on the winding start side than on the winding end side. Therefore, by providing the narrow portion 40 on the winding start side of the positive electrode 11, even if the positive electrode 11 elongates on the winding start side of the positive electrode 11, the generation of a short circuit caused by the elongation of the positive electrode 11 and the generation of a non-negative electrode-opposing area of ​​the positive electrode can be suppressed. In addition, by not providing the narrow portion 40 on the winding end side of the positive electrode 11 where the elongation of the positive electrode 11 is less affected, but providing the wide portion 30, the area of ​​the positive electrode 11 can be ensured. As a result, the reduction in the capacity of the secondary battery 10 can be suppressed.

[0043] In this embodiment, the narrow portion 40 may be provided only on the winding start side relative to the longitudinal center of the positive electrode 11, and not on the winding end side relative to the longitudinal center of the positive electrode 11. This ensures the area of ​​the positive electrode 11 and suppresses the reduction in the capacity of the secondary battery 10. Figure 1 ), the positive electrode mixture layer is formed in the entire region of the wide portion 30 and the narrow portion 40 .

[0044] like Figure 2 As shown, the width W of the narrow portion 40 is 40 The width W of the wide portion 30 is preferably 30 99% or less, more preferably 98% or less, and even more preferably 97% or less. In this case, the generation of short circuits accompanying the elongation of the positive electrode 11 and the generation of areas where the positive electrode and the negative electrode do not face each other can be suppressed. In addition, the width W of the narrow portion 40 is 40 The width W of the wide portion 30 is preferably 30 In this case, the area of ​​the positive electrode 11 can be ensured, and the reduction in the capacity of the secondary battery 10 can be suppressed. 40 An example of a suitable range is the width W of the wide portion 30. 30 The content of the organic matter is 92% or more and 99% or less, more preferably 93% or more and 98% or less, and even more preferably 94% or more and 97% or less.

[0045] It should be noted that, in this embodiment, the width W of the wide portion 30 is 30 and the width W of the narrow portion 40 40 The width W of the wide portion 30 is uniform along the longitudinal direction of the positive electrode 11. 30 The width of the positive electrode 11 is the same as the width of the positive electrode 11 at the winding end 11B of the positive electrode 11. The narrow portion 40 has a shape in which the width decreases to a substantially uniform length from both ends of the wide portion 30 in the width direction.

[0046] like Figure 2 As shown, the length L of the narrow width portion 40 is 40 The length L of the narrow portion 40 is preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less of the length of the positive electrode 11. In this case, since the proportion of the wide portion 30 in the positive electrode 11 increases, the area of ​​the positive electrode 11 can be ensured, and the reduction in the capacity of the secondary battery 10 can be suppressed. 40 The lower limit of θ is, for example, 1% of the length of the positive electrode 11 .

[0047] like Figure 2 and Figure 3As shown, when the number of turns of the positive electrode is n, the narrow portion 40 is preferably provided within the range from the second turn to the (n×1 / 3)th turn on the winding start side of the positive electrode 11. That is, the wide portion 30 is continuously wound from the winding start end 11A of the positive electrode 11 toward the winding end side for more than one turn and less than two turns. Furthermore, the narrow portion 40 is provided within the range from the terminal end 30A of the wide portion 30 provided at the winding start side to the (n×1 / 3)th turn. Furthermore, the wide portion 30 is provided continuously from the terminal end 40A of the narrow portion 40 toward the winding end side. The number of turns n of the positive electrode 11 is not particularly limited, but as an example, it is 20 to 40. When the number of turns n is 30, the 30th turn becomes the outermost circumference of the positive electrode 11.

[0048] As described above, the pressure load on the positive electrode 11 during repeated charging and discharging of the secondary battery 10 increases at the winding start side compared to the winding end side. However, the results of the present inventors' research have shown that the widthwise elongation of the positive electrode 11 due to charging and discharging is small within the first week from the winding start end 11A of the positive electrode 11. This is speculated to be because when pressure is applied to the positive electrode 11 due to charging and discharging, the positive electrode 11 tends to elongate in the longitudinal direction, while the widthwise elongation decreases within the first week from the winding start end 11A. On the other hand, it is speculated that after the second week from the winding start end 11A, when pressure is applied to the positive electrode 11 due to charging and discharging, the positive electrode 11 has no room to elongate in the longitudinal direction, but instead elongates in the width direction. Therefore, by providing the wide portion 30 in the first week of the positive electrode 11, where the widthwise elongation of the positive electrode 11 is small, the area of ​​the positive electrode 11 can be ensured, thereby suppressing the reduction in the capacity of the secondary battery 10.

[0049] Furthermore, the present inventors' research has revealed that the pressure load on the positive electrode 11 during repeated charge and discharge of the secondary battery 10 reaches its maximum in the range from the second to the fifth turn of the winding start side of the positive electrode 11. Therefore, the narrow width portion 40 is more preferably provided in the range from the second to the fifth turn of the winding start side of the positive electrode 11.

[0050] In this embodiment, the width W of the narrow portion 40 is 40 The length direction of the positive electrode 11 is uniform, but it is not limited to this. For example, it can also be as follows Figure 4 As shown, the width W of the narrow portion 40 is 40 The positive electrode 11 is different in the longitudinal direction. As described above, the pressure load on the positive electrode 11 during repeated charge and discharge of the secondary battery 10 becomes larger at the winding start side than at the winding end side. Figure 4 As shown, the width W of the narrow portion 40 decreases toward the winding start side of the positive electrode 11. 40 , it is possible to reduce the influence of the elongation of the positive electrode 11 in the width direction while ensuring the area of ​​the positive electrode 11 .

[0051] In this embodiment, the weight per unit area of ​​the positive electrode mixture layer applied to the wide portion 30 is the same as the weight per unit area of ​​the positive electrode mixture layer applied to the narrow portion 40. However, this is not limiting. For example, the weight per unit area of ​​the positive electrode mixture layer applied to the narrow portion 40 may be smaller than the weight per unit area of ​​the positive electrode mixture layer applied to the wide portion 30.

[0052] The narrow width portion 40 can be produced, for example, by producing the positive electrode 11 having a uniform width in the longitudinal direction and then cutting the positive electrode 11 into a desired shape using a cutting mechanism such as a laser cutter or a cutter.

[0053] Example

[0054] Hereinafter, the present application will be further described using examples, but the present application is not limited to these examples.

[0055] <Example 1>

[0056] [Production of positive electrode]

[0057] Using lithium nickel cobalt oxide (LiNi 0.88 Co 0.09 Al 0.03 O2) as the positive electrode active material. 100 parts by mass of LiNi 0.88 Co 0.09 Al 0.03 O2, 1.0 parts by mass of acetylene black, and 0.9 parts by mass of polyvinylidene fluoride (PVDF) were mixed in a dispersion medium of N-methylpyrrolidone (NMP) to prepare a positive electrode mixture slurry. The prepared positive electrode mixture slurry was evenly coated on both sides of a positive electrode core made of 15μm thick aluminum foil. Then, after removing the NMP from the coating in a dryer at a temperature of 100-150°C, the coating was compressed using a roller press to produce a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode core. It should be noted that the width of the positive electrode is 63.4mm and is uniform across the entire length of the positive electrode.

[0058] Then, a cutter was used to create a narrow portion in the area between the second and seventh turns of the positive electrode body. The positive electrode was cut so that the narrow portion was 96.5% of the width of the wide portion at the end of the positive electrode winding.

[0059] [Production of negative electrode]

[0060] Mix in such a way that the graphite powder accounts for 90 parts by mass and the Si oxide accounts for 10 parts by mass. 100 parts by mass of the negative electrode active material, 1 part by mass of CMC as a thickener and 1 part by mass of styrene butadiene rubber as a binder are mixed in water to prepare a negative electrode mixture slurry. The negative electrode mixture slurry is applied to both sides of the negative electrode core of a copper foil with a thickness of 8 μm to form a negative electrode mixture layer. Then, after drying, the negative electrode is compressed using a compression roller in such a way that the thickness of the negative electrode is 0.160 mm to produce a negative electrode. It should be noted that the width of the negative electrode is 64.0 mm and is uniform in the longitudinal direction of the negative electrode.

[0061] [Preparation of non-aqueous electrolyte]

[0062] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1.2 mol / L in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of 3:3:4 (25° C.).

[0063] An aluminum lead is attached to a portion of the positive electrode, and a nickel lead is attached to the winding end of the negative electrode. The positive and negative electrodes are then spirally wound with a polyolefin separator interposed therebetween to produce a wound electrode assembly. Insulating plates are placed above and below the electrode assembly, and the assembly is housed in an outer can. The negative electrode lead is welded to the bottom of a cylindrical outer can with a bottom, and the positive electrode lead is welded to a sealing member. Electrolyte is poured into the outer can, and the can opening is sealed with a sealing member interposed with a gasket to produce a cylindrical battery.

[0064] <Example 2>

[0065] During positive electrode production, a cutter was used to create a narrow portion between 2 and 6 turns of the positive electrode. The positive electrode was cut so that the narrow portion was 96.5% of the width of the wide portion at the final winding end of the positive electrode. The remaining configuration was identical to that of Example 1.

[0066] <Example 3>

[0067] During positive electrode production, a cutter was used to create a narrow portion between 2 and 5 turns of the positive electrode. The positive electrode was cut so that the narrow portion was 96.5% of the width of the wide portion at the final winding end of the positive electrode. The remaining configuration was identical to that of Example 1.

[0068] <Example 4>

[0069] During the production of the positive electrode, a 63.6 mm wide positive electrode was prepared. A narrow portion was created using a cutter between 2 and 6 turns of the positive electrode during winding. The positive electrode was cut so that the narrow portion was 96.5% of the width of the wide portion at the winding end of the positive electrode. The remaining configuration was the same as in Example 1.

[0070] <Example 5>

[0071] During positive electrode production, a 63.6 mm wide positive electrode was prepared. A narrow portion was created using a cutter between 2 and 5 turns of the positive electrode during winding. The positive electrode was cut so that the narrow portion was 96.2% of the width of the wide portion at the winding end of the positive electrode. The remaining configuration was the same as in Example 1.

[0072] <Comparative Example 1>

[0073] The positive electrode was produced in the same manner as in Example 1, except that a positive electrode having a width of 63.0 mm was produced and no narrow width portion was formed in the positive electrode.

[0074] Comparative Example 2

[0075] The positive electrode was produced in the same manner as in Example 1, except that a positive electrode having a width of 62.0 mm was produced and no narrow width portion was formed in the positive electrode.

[0076] Comparative Example 3

[0077] The positive electrode was produced in the same manner as in Example 1, except that a positive electrode having a width of 61.2 mm was produced and no narrow width portion was formed in the positive electrode.

[0078] [Evaluation of initial discharge capacity]

[0079] At an ambient temperature of 25° C., the test battery was charged to 4.2 V at a constant current of 0.2 It, then charged to 0.02 It at a constant voltage of 4.2 V. Thereafter, the battery was discharged to 2.5 V at a constant current of 0.2 It, and the resulting discharge capacity was evaluated.

[0080] [Evaluation of positive electrode elongation]

[0081] At the 100th charge-discharge cycle, X-ray CT images of each battery were taken using an inspeXio SMX-255CT FPDHR manufactured by Shimadzu Corporation. The X-ray CT images of each battery were used to confirm the presence of areas where the positive and negative electrodes did not face each other.

[0082] The initial capacities of the batteries of Examples and Comparative Examples and the presence or absence of the formation of the positive electrode non-negative electrode facing region after 100 cycles are shown in Table 1. The initial capacities in Table 1 are relative values ​​with the battery of Comparative Example 1 being 100, and larger values ​​indicate better initial capacities.

[0083] [Table 1]

[0084]

[0085] As shown in Table 1, the batteries of the examples all suppress the generation of the negative electrode non-opposing area of ​​the positive electrode accompanying charge and discharge while maintaining the initial capacity. It is speculated that this is because, in advance, the elongation of the positive electrode caused by charge and discharge is taken into account, and the narrow width portion is set only on the winding start side of the positive electrode. In addition, in the battery of Comparative Example 3, which has reduced the width of the positive electrode as a whole by taking into account the elongation of the positive electrode caused by charge and discharge, although the generation of the negative electrode non-opposing area of ​​the positive electrode accompanying charge and discharge is suppressed, the initial capacity is greatly reduced as the area of ​​the positive electrode is reduced. That is, in a battery with a reduced width of the positive electrode as a whole, it is difficult to take into account both the initial capacity of the battery and the generation of the negative electrode non-opposing area of ​​the positive electrode accompanying charge and discharge.

[0086] Furthermore, the batteries of Examples 3 and 5, which had narrowed portions located between 2 and 5 turns when the positive electrode was wound, showed increased initial capacity compared to the batteries of Example 1, which had narrowed portions located between 2 and 7 turns when the positive electrode was wound, and the batteries of Examples 2 and 4, which had narrowed portions located between 2 and 6 turns when the positive electrode was wound. This is because the area of ​​the positive electrode was increased by reducing the area where the narrowed portions were formed.

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

[0088] Configuration 1: A secondary battery comprising an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, wherein the positive electrode has a wide portion and a narrow portion having different widths, and the narrow portion is provided closer to the winding start side than the longitudinal center of the positive electrode.

[0089] Configuration 2: The secondary battery according to Configuration 1, wherein, when the number of windings of the positive electrode is n, the narrow portion is provided within a range from the second to (n×1 / 3)th turns from the winding start side of the positive electrode.

[0090] Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the narrow width portion is provided within a range from the second to fifth turns from the winding start side of the positive electrode.

[0091] Configuration 4: The secondary battery according to any one of Configurations 1 to 3, wherein the width of the narrow portion is 92% to 99% of the width of the wide portion.

[0092] Configuration 5: The secondary battery according to any one of Configurations 1 to 4, wherein the negative electrode includes a negative electrode core and a negative electrode mixture layer formed on the negative electrode core, and the negative electrode mixture layer includes a silicon-containing material as the negative electrode active material.

[0093] Configuration 6: The secondary battery according to Configuration 5, wherein the content of the silicon-containing material is 3% by mass or more of the total mass of the negative electrode active material.

[0094] Description of Reference Numerals

[0095] 10 Secondary battery (cylindrical battery), 11 Positive electrode, 11A Winding start end, 11B Winding end end, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Slotted portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Lid, 28 Gasket, 30 Wide portion, 30A, 40A terminals, 40 Narrow portion.

Claims

1. A secondary battery comprising an electrode body formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, The positive electrode has a wide portion and a narrow portion with different widths. The narrow width portion is provided on a winding start side relative to the longitudinal center of the positive electrode.

2. The secondary battery according to claim 1, wherein When the number of windings of the positive electrode is n, The narrow width portion is provided in a range from the second turn to the (n×1 / 3)th turn on the winding start side of the positive electrode.

3. The secondary battery according to claim 1, wherein The narrow width portion is provided in a range from the second to the fifth turn on the winding start side of the positive electrode.

4. The secondary battery according to claim 1, wherein The width of the narrow portion is not less than 92% and not more than 99% of the width of the wide portion.

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

6. The secondary battery according to claim 5, wherein The content of the silicon-containing material is 3% by mass or more of the total mass of the negative electrode active material.

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