Secondary battery

Abstract

This secondary battery is characterized by having an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) interposed therebetween, wherein the negative electrode (12) has, on a winding direction inner end side of the electrode body (14), a non-opposing portion (12a) that is not opposite of the positive electrode (11) with the separator (13) therebetween, and when X is the average value of gaps between a circulating portion (12c) from a winding direction outer end (point E2) of the non-opposing portion (12a) to a position (point E3) that is one full turn toward the winding direction inner side, and a negative electrode (12d) (the negative electrode from a point E4 to the point E2) positioned one full turn outside of the circulating portion (12c), Xmax is the maximum value of the gaps, and Xmin is the minimum value of the gaps, the relationships Xmax ≤ X × 1.3 and X × 0.7 ≤ Xmin are satisfied.

Description

secondary battery

[0001] This disclosure relates to secondary batteries.

[0002] As a secondary battery with high power output and high energy density, secondary batteries equipped with an electrode body in which the positive and negative electrodes are wound with a separator in between are widely used.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, wherein the negative electrode includes a non-facing portion wound for 1.25 turns or more from the inner end in the winding direction of the electrode body via the separator in a state that does not face the positive electrode, and the non-facing portion has a negative electrode composite layer forming portion on at least one surface, which is continuous from the outer end in the winding direction to the inner side in the winding direction, and the negative electrode composite layer forming portion is wound for 0.75 turns or more.

[0004] As shown in Patent Document 1, by providing a non-opposing portion on the inner end side in the winding direction of the electrode body that does not face the positive electrode, the safety of the battery can be ensured, for example, by ensuring that gas escape from the center of the electrode body is possible.

[0005] International Publication No. 2018 / 116876

[0006] Incidentally, in secondary batteries equipped with wound electrodes, localized stress may be applied near the center of the electrode when it expands during charging and discharging. This can cause, for example, deformation (e.g., buckling, bending) of the negative electrode near the beginning of the positive electrode winding, leading to non-uniformity of the charge-discharge reaction within the electrode surface, or a decrease in the roundness of the center of the electrode, resulting in reduced electrolyte flow within the electrode. Furthermore, reduced electrolyte flow can increase battery resistance, potentially leading to a decrease in battery performance.

[0007] Therefore, the purpose of this disclosure is to provide a secondary battery that can alleviate localized stress generated near the center of a wound electrode body during charging and discharging of the secondary battery.

[0008] The secondary battery according to this disclosure has an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, the negative electrode has a non-facing portion on the inner end side in the winding direction of the electrode body that does not face the positive electrode via the separator, and the average value of the gap between the circumferential portion from the outer end in the winding direction of the non-facing portion to a position one full turn inward in the winding direction and the negative electrode located one full turn outside the circumferential portion is X, and the maximum value of the gap is X ｍａｘ The minimum value of the gap is X ｍｉｎ In that case, X ｍａｘ ≤X × 1.3 and X × 0.7 ≤X ｍｉｎ It is characterized by satisfying the following conditions.

[0009] According to this disclosure, it is possible to provide a secondary battery that can alleviate localized stress generated near the center of a wound electrode body during charging and discharging of the secondary battery.

[0010] This is a schematic cross-sectional view of a secondary battery, which is an example of an embodiment. This figure schematically shows the portion of the electrode body on the inner end side in the winding direction in the A-A cross-section of Figure 1. This is a schematic cross-sectional view showing the configuration of the negative electrode on the inner end side in the winding direction of the electrode body.

[0011] The following describes in detail an example of an embodiment of the secondary battery related to this disclosure.

[0012] Figure 1 is a schematic cross-sectional view of a secondary battery, which is an example of an embodiment. The secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, an electrolyte, insulating plates 18a and 18b arranged above and below the electrode body 14, respectively, and a battery case 15 which is an outer casing. The battery case 15 is composed of a case body 16 that houses the electrode body 14 and a non-aqueous electrolyte, and a sealing body 17 that closes the opening of the case body 16. The battery case 15 is not limited to a cylindrical or rectangular metal case, but may also be a resin case (so-called pouch type) formed by laminating a resin sheet, for example.

[0013] The electrolyte may, for example, be ionic conductive (e.g., lithium ion conductive). The electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0014] The liquid electrolyte (electrolytic solution) includes, for example, 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 of these. As an example of the non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents thereof can be mentioned. The non-aqueous solvent may contain a halogen-substituted product (for example, fluoroethylene carbonate, etc.) in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF ６ and the like are used.

[0015] Further, as the solid electrolyte, for example, a solid or gel polymer electrolyte, an inorganic solid electrolyte, etc. can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of the polymer material include fluororesins, acrylic resins, polyether resins, etc. As the inorganic solid electrolyte, for example, materials known in all-solid lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Note that although the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may be an aqueous electrolyte.

[0016] The case body 16 is, for example, a bottomed cylindrical metal container. A gasket 27 is provided between the case body 16 and the sealing body 17 to ensure the airtightness inside the battery. The case body 16 has, for example, a projecting portion 21 that supports the sealing body 17, where a part of the side surface portion projects inward. The projecting portion 21 is preferably formed in an annular shape along the circumferential direction of the case body 16, and supports the sealing body 17 on its upper surface.

[0017] The sealing body 17 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are laminated in this order from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 24 is electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at the central portions thereof, and the insulating member 24 is interposed between the peripheral edges thereof. When the internal pressure of the secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 23 is deformed and broken so as to push up the upper valve body 25 toward the cap 26 side, and the current path between the lower valve body 23 and the upper valve body 25 is interrupted. When the internal pressure further rises, the upper valve body 25 is broken, and gas is discharged from the opening of the cap 26.

[0018] In the secondary battery 10 shown in FIG. 1, the positive electrode lead 19 attached to the positive electrode 11 extends toward the sealing body 17 through the through hole of the insulating plate 18a, and is connected to the lower surface of the filter 22 which is the bottom plate of the sealing body 17 by welding or the like. Thereby, the cap 26 which is the top plate of the sealing body 17 electrically connected to the filter 22 becomes the positive electrode terminal. Further, the negative electrode lead 20a connected to the negative electrode 12 on the winding start side of the electrode body 14 and the negative electrode lead 20b connected to the negative electrode 12 on the winding end side of the electrode body 14 extend through the insulating plate 18b to the bottom side of the case body 16, and are connected to the inner surface of the bottom of the case body 16 by welding or the like. Thereby, the case body 16 becomes the negative electrode terminal.

[0019] FIG. 2 is a diagram schematically showing a portion on the inner end side in the winding direction of the electrode body in the A - A cross section of FIG. 1. In FIG. 2, in order to make the arrangement relationship easy to understand, the negative electrode 12 is shown by a solid line, the positive electrode 11 is shown by a broken line, and the separator 13 is shown by a one - dot chain line. Further, in FIG. 2, the gaps between the positive electrode 11, the negative electrode 12, and the separator 13 are exaggerated. The electrode body 14 is formed by winding the positive electrode 11 and the negative electrode 12 with the separator 13 interposed therebetween. Specifically, a strip - shaped positive electrode 11, a strip - shaped negative electrode 12, and a pair of strip - shaped separators 13 are laminated in the order of one separator 13, the positive electrode 11, the other separator 13, and the negative electrode 12, and then this laminate is wound in a spiral shape to produce the electrode body 14. In the electrode body 14, the longitudinal direction of each electrode becomes the winding direction, and the width direction of each electrode becomes the winding axis direction.

[0020] As shown in FIG. 2, the negative electrode 12 has a non-facing portion 12a that does not face the positive electrode 11 via the separator 13 on the inner end side in the winding direction, which is the start side of the electrode body 14. Further, the negative electrode 12 is wound following the non-facing portion 12a and has a facing portion 12b that faces the positive electrode 11 via the separator 13. The non-facing portion 12a shown in FIG. 2 is a region from a point E1, which is the inner end in the winding direction of the non-facing portion 12a, to a point E2, which is the outer end in the winding direction of the non-facing portion 12a. The non-facing portion 12a shown in FIG. 2 is wound 1.5 turns from the inner end in the winding direction (point E1). The number of winding turns of the non-facing portion 12a may be, for example, 1 turn or more, or 1.5 turns or more and 3 turns or less.

[0021] FIG. 3 is a schematic cross-sectional view showing the configuration of the negative electrode on the inner end side in the winding direction of the electrode body. In FIG. 3, the positive electrode 11 and the separator 13 are not shown. Also, in FIG. 3, the gap between the negative electrodes in the radial direction of the electrode body 14 is exaggeratedly shown. As shown in FIG. 3, the negative electrode 12 has, for example, a negative electrode core 30 and a negative electrode composite layer 32 formed on the negative electrode core 30. The negative electrode composite layer 32 shown in FIG. 3 is formed on both sides of the negative electrode core 30, but is not limited thereto and may be formed on only one side of the negative electrode core 30. Further, in the non-facing portion 12a, the negative electrode composite layer 32 is not disposed on the negative electrode core 30, and a core exposed portion 30a where the negative electrode core 30 is exposed is formed.

[0022] In the present embodiment, the average value of the gap between the circumferential portion 12c from the outer end in the winding direction (point E2) of the non-facing portion 12a to the position (point E3) one turn inward in the winding direction and the negative electrode 12d located one turn outside the circumferential portion 12c is X, the maximum value of the gap is X ｍａｘ and the minimum value of the gap is M ｍｉｎ When this is done, X ｍａｘ ≦ X × 1.3, and X × 0.7 ≦ X ｍｉｎThe following conditions are met. The negative electrode 12d located one full turn outside the circumferential portion 12c from point E2 to point E3 in the non-opposing portion 12a is the portion from point E4 in Figure 3 along the winding direction to point E2. Point E4 is the point one full turn along the winding direction from the outer end (point E2) of the non-opposing portion 12a in the winding direction. Here, the gap between the circumferential portion 12c and the negative electrode 12d is the value obtained by subtracting the thickness of the negative electrode composite layer 32 and separator 13 between the cores from the straight-line distance in the radial direction between the negative electrode core 30 in the circumferential portion 12c of the non-opposing portion 12a and the negative electrode core 30 in the negative electrode 12d one full turn outside (between cores). For example, at point E2 shown in Figure 3, the gap between the peripheral portion 12c and the negative electrode 12d at point E2 is obtained by subtracting the thickness of the negative electrode composite layer 32 and separator 13 between the negative electrode cores of points E2 and E4 from the straight-line distance between the negative electrode core 30 of the peripheral portion 12c at point E2 and the negative electrode core 30 of the negative electrode 12d at point E4, which is located one circumference outside the peripheral portion. Similarly, at point E3 shown in Figure 3, the gap between the peripheral portion 12c and the negative electrode 12d at point E3 is obtained by subtracting the thickness of the negative electrode composite layer 32 and separator 13 between the negative electrode cores of points E3 and E2 from the straight-line distance between the negative electrode core 30 of the peripheral portion 12c at point E3 and the negative electrode core 30 of the negative electrode 12d at point E2, which is located one circumference outside the peripheral portion.

[0023] The gap between the circumferential portion 12c and the negative electrode 12d can be measured by the following method. By observing the cross-section of the electrode body 14 using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR), the linear distance in the radial direction of the electrode body between the negative electrode core 30 of the circumferential portion 12c of the non-opposing portion 12a and the negative electrode core 30 of the negative electrode 12d one circumference outward is measured. By subtracting the thickness of the negative electrode composite layer and separator between the negative electrode cores from this value, the gap between the circumferential portion 12c and the negative electrode 12d can be determined. Of the gaps determined in this way, the largest gap is the maximum value of the gap between the circumferential portion 12c and the negative electrode 12d, and the smallest gap is the minimum value of the gap between the circumferential portion 12c and the negative electrode 12d. Furthermore, the gap is determined at 25 equally spaced points along the winding direction in the same manner as described above, and the average value of these values ​​is the average value of the gap between the circumferential portion 12c and the negative electrode 12d.

[0024] As shown in electrode body 14 of this embodiment, X ｍａｘ≤X × 1.3 and X × 0.7 ≤X ｍｉｎ By satisfying this condition, a relatively uniform gap is secured between the circumferential portion 12c of the non-opposing portion 12a and the negative electrode 12d one circumference outside, thereby easing local stress generated near the center of the electrode body 14 during battery charging and discharging. As a result, for example, deformation of the negative electrode 12 near the winding start end of the positive electrode 11 (e.g., bending, buckling, etc.) is suppressed, non-uniformity of the charge-discharge reaction within the electrode surface is suppressed, the decrease in roundness at the center of the electrode body 14 is suppressed, and the decrease in electrolyte circulation in the electrode body 14 is suppressed. Although there are several patent documents concerning an electrode body 14 having a negative electrode 12 with a non-opposing portion 12a formed on the inner end side in the winding direction of the electrode body 14, none of these documents suggest limiting the maximum and minimum values ​​of the gap between the circumferential portion 12c of the non-opposing portion 12a and the negative electrode 12d one circumference outside to the above-mentioned predetermined range relative to the average value of the gap, or the effects resulting from this.

[0025] Furthermore, when the positive electrode 11, negative electrode 12, and separator 13 are actually wound, the non-opposing portion 12a, which is not supported by the positive electrode 11 via the separator 13, is prone to distortion due to the load applied during winding. Therefore, to suppress the distortion of the non-opposing portion 12a during winding, X ｍａｘ ≤X × 1.3 and X × 0.7 ≤X ｍｉｎ To obtain an electrode body 14 that satisfies the requirements, it is preferable to use different winding speeds for the non-opposing portion 12a and the opposing portion 12b when winding the positive electrode 11, the negative electrode 12, and the separator 13.

[0026] The average value (X) of the gap between the circumferential portion 12c of the non-opposing portion 12a and the negative electrode 12d located one circumference outside the circumferential portion 12c is preferably 30 μm or more and 300 μm or less, and more preferably 50 μm or more and 150 μm or less. By setting the average value (X) of the gap within the above range, for example, the roundness of the central part of the electrode body 14 can be increased.

[0027] In order to efficiently advance the charge-discharge reaction, it is preferable to design the negative electrode 12 to be slightly larger than the positive electrode 11. In this case, the non-opposing portion 12a has a negative electrode composite layer 32 arranged on the negative electrode core 30. The length of the negative electrode composite layer 32 in the winding direction of the non-opposing portion 12a is preferably in the range of 0.1 turns or more and 1 turn or less, and more preferably in the range of 0.1 turns or more and 0.5 turns or less, from the outer end (point E2) in the winding direction of the non-opposing portion 12a toward the inside in the winding direction, in addition to efficiently advancing the charge-discharge reaction as described above, for example, in order to suppress distortion of the non-opposing portion 12a during winding. Furthermore, if the negative electrode composite layer 32 of the non-opposing portion 12a is formed on both the inner circumferential surface of the negative electrode core 30 facing radially inward of the electrode body 14 and the outer circumferential surface of the negative electrode core 30 facing radially outward of the electrode body 14, the lengths of the negative electrode composite layer 32 formed on the inner circumferential surface and the negative electrode composite layer 32 formed on the outer circumferential surface in the winding direction may be the same, or they may be different, as shown in Figure 3.

[0028] Preferably, a core exposure portion 30a is formed in the non-opposing portion 12a, in which the negative electrode core body 30 is exposed. The length of the core exposure portion 30a in the winding direction is preferably in the range of 0.1 turns or more and 1.0 turns or less, and more preferably 0.1 turns or more and 0.5 turns or less, from the inner end in the winding direction of the negative electrode composite layer 32 toward the inside in the winding direction, for example, in order to secure space for installing the negative electrode lead 20a. The core exposure portion 30a of the non-opposing portion 12a may be formed on both the inner and outer circumferential surfaces of the negative electrode core body 30, or on only one side.

[0029] The aforementioned negative electrode lead 20a is preferably positioned with one end on the non-opposing portion 12a. In particular, considering the welding of the negative electrode lead 20a and the negative electrode 12, it is preferable that one end of the negative electrode lead 20a is positioned on the core body exposed portion 30a of the non-opposing portion 12a, as shown in Figure 3. The negative electrode lead 20a on the non-opposing portion 12a has a curved shape with a predetermined mean radius of curvature in a cross-sectional view from the winding axis direction of the electrode body 14 (i.e., in Figure 3). The mean radius of curvature of the curved negative electrode lead 20a is preferably in the range of 70% to 120% and more preferably in the range of 80% to 110% of the mean radius of curvature of the region from the winding start end of the positive electrode 11 (point D1 shown in Figure 2) to a position one full turn outward in the winding direction (point D2 shown in Figure 2) (hereinafter referred to as the first turn portion of the positive electrode). The average radius of curvature of the negative electrode lead 20a refers to the average value of the radius of curvature at the center of each region when the negative electrode lead 20a on the non-opposing portion 12a is divided into three equal parts in the winding direction of the electrode body 14, as viewed in a cross-sectional view from the winding axis direction of the electrode body 14. The average radius of curvature of the first circumference of the positive electrode refers to the average value of the radius of curvature at the center of each region when the first circumference of the positive electrode is divided into ten equal parts in the winding direction of the electrode body 14, as viewed in a cross-sectional view from the winding axis direction of the electrode body 14.

[0030] By setting the radius of curvature of the negative electrode lead 20a to the above range, for example, when winding the positive electrode 11, negative electrode 12 and separator 13, the negative electrode 12 located one rotation outside the negative electrode lead 20a is less likely to get caught on the negative electrode lead 20a, and the roundness of the center of the electrode body 14 is increased. As a result, X ｍａｘ ≤X × 1.3 and X × 0.7 ≤X ｍｉｎ This makes it easier to fabricate an electrode body 14 that satisfies the requirements.

[0031] The negative electrode lead 20a is connected, for example, to the core body exposed portion 30a of the non-opposing portion 12a by welding or the like, and then formed into a curved shape having a predetermined radius of curvature by press molding.

[0032] The negative electrode core 30 constituting the negative electrode 12 can be made of a metal foil that is stable in the negative electrode potential range, such as copper or a copper alloy, or a film with the metal arranged on its surface. The thickness of the negative electrode core 30 is, for example, in the range of 10 μm to 50 μm.

[0033] Furthermore, the negative electrode composite layer 32 constituting the negative electrode 12 includes, for example, a negative electrode active material, a binder, etc. The thickness of the negative electrode composite layer 32 is, for example, in the range of 10 μm to 100 μm. The negative electrode 12 can be manufactured, for example, by applying a negative electrode composite slurry containing a negative electrode active material, a binder, etc., onto a negative electrode core body, drying the coating film, and then rolling to form the negative electrode composite layer 32 on the negative electrode core body 30.

[0034] The negative electrode active material contained in the negative electrode composite layer 32 is not particularly limited as long as it can reversibly intercept and release lithium ions, for example, carbon materials, Si-based materials, etc. In terms of increasing the capacity of the battery, it is preferable that the negative electrode active material contains a Si-based material.

[0035] The carbon material may be any conventionally known carbon material used as a negative electrode active material, such as natural graphite including flake graphite, lump graphite, and earthy graphite, or artificial graphite including lump graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).

[0036] Si-based materials include, for example, a lithium ion conducting phase and Si particles dispersed within the lithium ion conducting phase. The lithium ion conducting phase includes, for example, at least one of a silicon oxide phase, a silicate phase, and a carbon phase.

[0037] The silicate phase preferably contains at least one element from Group 2 of the periodic table, which includes the alkali metal elements lithium, sodium, potassium, rubidium, cesium, and francium, and the elements beryllium, magnesium, calcium, strontium, barium, and radium, due to its high lithium ion conductivity, for example. Among these, the silicate phase containing lithium (hereinafter sometimes referred to as the lithium silicate phase) is preferred due to its high lithium ion conductivity.

[0038] The lithium silicate phase is, for example, given by formula: Li ２ｚ SiO ２＋ｚ This is expressed as (0 < z < 2). From the viewpoint of stability, ease of fabrication, lithium-ion conductivity, etc., it is preferable that z satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2.

[0039] Si-based materials in which Si particles are dispersed in a silicon oxide phase include, for example, materials with the general formula SiO ｘ (The range 0 < x < 2 is preferred, and the range 0.5 ≤ x ≤ 1.6 is more preferred). A Si-based material in which Si particles are dispersed in a carbon phase is, for example, represented by the general formula Si ｘ C ｙ (Preferably in the ranges 0 < x ≤ 1 and 0 < y ≤ 1).

[0040] A conductive layer coated with conductive carbon may be formed on the surface of the Si-based material. The conductive layer can be formed by, for example, a CVD method using acetylene, methane, etc., or by mixing coal pitch, petroleum pitch, phenolic resin, etc. with a silicon-based active material and performing heat treatment. Examples of heat treatment equipment that can be used include a hot air furnace, hot press, lamp, sheath heater, ceramic heater, rotary kiln, etc. Alternatively, a conductive layer may be formed by fixing a conductive filler such as carbon black to the particle surface of the Si-based material using a binder.

[0041] In terms of increasing the battery capacity, the Si-based material content is preferably 5% by mass or more relative to the total mass of the negative electrode composite layer 32.

[0042] In addition to carbon materials and Si-based materials, other materials that can reversibly intercept and release lithium ions can be used as negative electrode active materials, such as Sn, Sn-containing alloys, Sn-based materials such as tin oxide, and Ti-based materials such as lithium titanate.

[0043] Examples of binders include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), polyethylene oxide (PEO), and the like.

[0044] The positive electrode 11 comprises a positive electrode core and a positive electrode composite layer formed on the surface of the positive electrode core. Preferably, the positive electrode composite layer is formed on both sides of the positive electrode core. The positive electrode core can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, or a film with the metal arranged on its surface. The positive electrode composite layer includes, for example, a positive electrode active material, a binder, a conductive agent, etc. The positive electrode 11 can be manufactured, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a binder, a conductive agent, etc., onto the positive electrode core, drying the coating, and then rolling it to form the positive electrode composite layer on both sides of the positive electrode core.

[0045] 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 include, for example, Li ｘ CoO ２ Li ｘ NiO ２ Li ｘ MnO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Co ｙ M １－ｙ O ｚ Li ｘ Ni １－ｙ M ｙ O ｚ Li ｘ Mn ２ O ４ Li ｘ Mn ２－ｙ M ｙ O ４ LiMPO ４ Li ２ MPO４ F (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). These may be used individually or in combination of multiple types. In terms of enabling high capacity of non-aqueous electrolyte secondary batteries, the positive electrode active material is Li ｘ NiO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Ni １－ｙ M ｙ O ｚ It is preferable to include a lithium nickel composite oxide such as (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). Inorganic particles such as tungsten oxide, aluminum oxide, and lanthanide-containing compounds may be fixed to the surface of the lithium transition metal oxide particles.

[0046] Examples of conductive agents included in the positive electrode composite layer include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), graphene, and graphite. The binder included in the positive electrode composite layer is the same as that used for the negative electrode 12.

[0047] For the separator 13, for example, a porous sheet having ion permeability and insulating properties can be used. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, olefin resins such as polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it may be a multilayer separator containing a polyethylene layer and a polypropylene layer, or a separator 13 with a material such as aramid resin or ceramic coated on its surface may be used.

[0048] 10 Secondary battery, 11 Positive electrode, 12, 12d Negative electrode, 12a Non-opposing part, 12b Opposing part, 12c Circular part, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18a, 18b Insulating plate, 19 Positive electrode lead, 20a, 20b Negative electrode lead, 21 Protruding part, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 30 Negative electrode core body, 30a Core body exposed part, 32 Negative electrode composite layer.

Claims

1. A secondary battery having an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, wherein the negative electrode has a non-facing portion on the inner end side in the winding direction of the electrode body that does not face the positive electrode via the separator, and the average value of the gap between the circumferential portion from the outer end in the winding direction of the non-facing portion to a position one full turn inward in the winding direction and the negative electrode located one full turn outside the circumferential portion is X, and the maximum value of the gap is X ｍａｘ The minimum value of the gap is X ｍｉｎ In that case, X ｍａｘ ≤X × 1.3 and X × 0.7 ≤X ｍｉｎ A secondary battery that satisfies the following conditions.

2. The secondary battery according to claim 1, wherein the average value X of the gap is in the range of 30 μm or more and 300 μm or less.

3. A secondary battery according to claim 1 or 2, having a negative electrode lead, one end of the negative electrode lead positioned on the non-opposing portion, and in a cross-sectional view of the electrode body as seen from the winding axis direction, the mean radius of curvature of the negative electrode lead on the non-opposing portion is in the range of 70% to 120% of the mean radius of curvature in the region from the starting end of the positive electrode winding to a position one full turn outward in the winding direction.

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