Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery comprises: an electrode body obtained by winding a strip-shaped positive electrode and a strip-shaped negative electrode in the longitudinal direction with a separator therebetween; and an exterior body which accommodates the electrode body, wherein a fixing tape for fixing a winding end of the electrode body is stuck onto the outermost peripheral surface of the electrode body, and the Young's modulus of the negative electrode is 12-20 GPa.

Description

Nonaqueous electrolyte secondary battery

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery comprising a wound electrode body.

[0002] For some time, non-aqueous electrolyte secondary batteries have been widely used, in which a wound electrode body, consisting of a strip-shaped positive electrode and a strip-shaped negative electrode wound around a separator, is housed in an outer casing. In such batteries, the outermost circumference of the electrode body is fixed to prevent the winding from loosening after winding, and in particular, the end of the winding of the electrode body is sometimes fixed with tape to prevent the outermost part from peeling off when inserting the electrode body into the outer casing (see Patent Documents 1 and 2).

[0003] Japanese Patent Publication No. 2009-199974 Japanese Patent Publication No. 2005-216754

[0004] Incidentally, the electrodes of a non-aqueous electrolyte secondary battery expand during charging, and the outermost layer may experience pressure from the outer casing. Furthermore, repeated charging and discharging causes the electrodes to expand significantly compared to their initial state, thus increasing this pressure. Since fixing tape is attached to the outermost surface of the electrodes, repeated charging and discharging can cause deformation of the electrode plates near the outermost layer of the electrodes, starting from the ends of the fixing tape where stress tends to concentrate. If the deformation of the electrode plates becomes large, there is a risk of internal short circuits, so suppressing the deformation of the electrode plates is an important issue.

[0005] Therefore, the objective of this disclosure is to provide a non-aqueous electrolyte secondary battery that suppresses deformation of the electrode plate near the outermost periphery of the electrode body caused by charge-discharge cycles.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound along the longitudinal direction with a separator in between, and an outer casing that houses the electrode body, wherein a fixing tape for fixing the end of the winding of the electrode body is attached to the outermost outer surface of the electrode body, and the Young's modulus of the negative electrode is 12 GPa or more and 20 GPa or less.

[0007] According to the non-aqueous electrolyte secondary battery described herein, deformation of the electrode plate near the outermost periphery of the electrode body due to charge-discharge cycles can be suppressed.

[0008] This is an axial cross-sectional view of a cylindrical secondary battery, which is an example of an embodiment. This is a perspective view of the electrode body of the secondary battery shown in Figure 1. This is a radial cross-sectional view of the vicinity of the outermost periphery of the electrode body shown in Figure 2.

[0009] An example of an embodiment of this disclosure is described in detail below. In the following description, specific shapes, materials, directions, and numerical values ​​are illustrative examples to facilitate understanding of this disclosure and can be modified as appropriate to suit the application, purpose, and specifications. Furthermore, if the following description includes multiple embodiments and modifications, it is intended from the outset that their characteristic features may be combined as appropriate.

[0010] Figure 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. In the secondary battery 10 shown in Figure 1, the electrode body 14 and the non-aqueous electrolyte (not shown) are housed in an outer casing 15. For the sake of explanation, the side with the sealing body 16 will be referred to as "upper" and the bottom side of the outer casing 15 will be referred to as "lower".

[0011] The electrode body 14 has a wound-type structure in which a strip-shaped positive electrode 11 and a negative electrode 12 are wound longitudinally via a separator 13. 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 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 surface coated with a material such as an aramid resin or ceramic may be used.

[0012] Non-aqueous electrolytes include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent (organic solvent), carbonates, lactones, ethers, ketones, and esters can be used, and two or more of these solvents can be used in mixture form. When using a mixture of two or more solvents, it is preferable to use a mixed solvent containing a cyclic carbonate and a linear carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) can be used as cyclic carbonates, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as linear carbonates. As the electrolyte salt, LiPF ６ LiBF ４ , and LiCF ３ SO ３ These and mixtures thereof can be used. The solubility of the electrolyte salt in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less. The non-aqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel polymer or the like.

[0013] The opening of the outer casing 15 is sealed by the sealing body 16, thereby creating a sealed interior for the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through a through-hole in the insulating plate 17 and is welded to the lower surface of the filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, becomes the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through-hole in the insulating plate 18 towards the bottom of the outer casing 15 and is welded to the inner surface of the bottom of the outer casing 15. In the secondary battery 10, the outer casing 15 becomes the negative electrode terminal.

[0014] The outer casing 15 is, for example, a metal outer casing in the shape of a bottomed cylindrical can. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the secondary battery 10. The outer casing 15 has grooves 21 that support the sealing body 16, which are formed, for example, by pressing the side surface from the outside. The grooves 21 are preferably formed in an annular shape along the circumferential direction of the outer casing 15, and their upper surface supports the sealing body 16.

[0015] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in order from the electrode body 14 side. Each component constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. If the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge towards the cap 26 and separate from the lower valve body 23, thereby interrupting the electrical connection between the two. If the internal pressure rises further, the upper valve body 25 may rupture, and gas may be discharged from the opening 26a of the cap 26.

[0016] Next, an overview of the electrode body 14 will be described with reference to Figure 2. Figure 2 is a perspective view of the electrode body 14 provided in the secondary battery 10 shown in Figure 1.

[0017] As described above, the electrode body 14 has a wound structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound in a spiral shape via a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all formed in a strip shape and are wound in a spiral shape around a winding core arranged along the winding axis, so that they are alternately stacked in the radial direction of the electrode body 14. The negative electrode 12 is formed to be slightly larger in size than the positive electrode 11. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the short direction of the positive electrode 11 and the negative electrode 12 is the axial direction. In the winding direction, the side facing the winding axis is called the winding start side, and the opposite side is called the winding end side. In addition, in the positive electrode 11, the negative electrode 12, the electrode body 14, and the positive electrode mixture layer and negative electrode mixture layer described later, the end on the winding start side is called the winding start end, and the end on the winding end side is called the winding end end. Furthermore, in the radial direction of the electrode body 14, the side with the winding axis is referred to as the inner circumference, and the opposite side as the outer circumference.

[0018] One end of a positive electrode lead 19 is connected to the positive electrode 11 by ultrasonic welding or the like, and the other end of the positive electrode lead 19 extends axially from the upper end of the electrode body 14 in the example shown in Figure 2. One end of a negative electrode lead 20 is connected to the negative electrode 12 by ultrasonic welding or the like, and the other end of the negative electrode lead 20 extends axially from the lower end of the electrode body 14 in the example shown in Figure 2.

[0019] A fixing tape 30 is attached to the outermost surface of the electrode body 14 to secure the end of the winding of the electrode body 14. That is, the fixing tape 30 overlaps with the end of the winding of the electrode body 14 in the radial direction of the electrode body 14. In the example shown in Figure 2, the negative electrode 12 is exposed on the outermost surface of the electrode body 14, and the end of the winding of the negative electrode 12 and the end of the winding of the electrode body 14 are the same. The outermost surface of the electrode body 14 may be made of a separator 13. The position and number of fixing tapes 30 are not particularly limited as long as they can secure the end of the winding of the electrode body 14, but for example, as shown in Figure 2, one may be provided at each end in the axial direction of the electrode body 14, or one may be provided at either end in the axial direction of the electrode body 14.

[0020] The length of the fixing tape 30 is not particularly limited, but it is preferable that it is at least half the circumference (length of one turn) of the outermost surface of the electrode body 14. The length of the fixing tape 30 may be longer than the circumference (length of one turn) of the outermost surface of the electrode body 14, but it is preferable that it be shorter than the circumference of the outermost surface of the electrode body 14. This allows the fixing tape 30 to not overlap with the end of the composite layer of the positive electrode 11 or the negative electrode 12 in the radial direction of the electrode body 14, as shown in Figure 2, and enables the fixing tape 30 to not overlap with the end of the composite layer of the positive electrode 11 or the negative electrode 12 in the radial direction of the electrode body 14, as will be described later.

[0021] The width of the fixing tape 30 is, for example, 10% to 40% of the height of the electrode body 14. Furthermore, the sum of the widths of the fixing tape 30 on the outermost surface of the electrode body 14 is, for example, 20% to 50% of the height of the electrode body 14. Specific examples of the width of the fixing tape 30 are 3 mm to 30 mm.

[0022] The fixing tape 30 comprises, for example, a base layer and an adhesive layer formed on the surface of the base layer. The base layer can be appropriately selected from viewpoints such as strength, resistance to electrolytes, processability, and cost, and can be made of, for example, PP (polypropylene), PI (polyimide), PET (polyethylene terephthalate), and PPS (polyphenylene sulfide). The adhesive layer is preferably made of a resin that is adhesive at room temperature, and can be made of, for example, an acrylic resin or a rubber resin.

[0023] Next, the positive electrode 11 and negative electrode 12 constituting the electrode body 14 will be described with reference to Figure 3. Figure 3 is a radial cross-sectional view of the vicinity of the outermost periphery of the electrode body 14 shown in Figure 2.

[0024] The positive electrode 11 has, for example, a strip-shaped positive electrode current collector and a positive electrode mixture layer formed on both sides of the positive electrode current collector. The positive electrode current collector can be, for example, a metal foil such as aluminum, or a film with the metal arranged on its surface. The positive electrode mixture layer may contain, for example, a positive electrode active material, a binder, and a conductive agent. The positive electrode active material is the main component of the positive electrode mixture layer and accounts for, for example, 90% or more of the total mass of the positive electrode mixture layer. In this specification, "main component" means the component with the highest mass ratio. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, and a conductive agent to the surface of the positive electrode current collector, drying it to form a positive electrode mixture layer, and then rolling this positive electrode mixture layer.

[0025] A positive electrode current collector exposed portion is formed on the surface of the positive electrode 11, and a positive electrode lead 19 is connected to the positive electrode current collector exposed portion. The positive electrode current collector exposed portion is the part of the positive electrode current collector's surface that is not covered by the positive electrode mixture layer, and is provided, for example, by intermittent coating, in which the positive electrode mixture slurry is not applied to a part of the positive electrode current collector.

[0026] In the example shown in Figure 3, the positive electrode mixture layer is formed on both sides of the positive electrode current collector up to the end of the winding of the positive electrode 11, and the end of the winding of the positive electrode 11 is the same as the end of the winding 40 of the positive electrode mixture layer. Note that the configuration of the positive electrode 11 near the outermost circumference of the electrode body 14 is not limited to the example shown in Figure 3, for example, the positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or an exposed portion of the positive electrode current collector may be formed near the end of the winding of the positive electrode 11.

[0027] The positive electrode active material is composed mainly of, for example, a lithium transition metal composite oxide. Elements other than Li contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, Si, and P. A suitable example of a lithium transition metal composite oxide is a composite oxide containing at least one of Ni, Co, and Mn. Specific examples include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al.

[0028] Examples of conductive agents included in the positive electrode mixture layer include acetylene black (AB) and carbon black (CB) such as Ketjenblack, as well as carbon-based particles such as carbon nanotubes (CNT), graphene, and graphite. These may be used individually or in combination of two or more. Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more.

[0029] The negative electrode 12 includes, for example, a strip-shaped negative electrode current collector and a negative electrode mixture layer formed on both sides of the negative electrode current collector. The negative electrode current collector can be, for example, a metal foil such as copper, or a film with the metal arranged on its surface. The negative electrode mixture layer may include, for example, a negative electrode active material and a binder. The negative electrode active material is the main component of the negative electrode mixture layer and accounts for, for example, 90% or more of the total mass of the negative electrode mixture layer. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, a thickener, etc., to the surface of the negative electrode current collector and drying it to form a negative electrode mixture layer, and then rolling this negative electrode mixture layer.

[0030] An exposed portion of the negative electrode current collector is formed on the surface of the negative electrode 12. The exposed portion of the negative electrode current collector is the part of the surface of the negative electrode current collector that is not covered by the negative electrode mixture layer, and is provided, for example, by intermittent coating in which the negative electrode mixture slurry is not applied to a part of the negative electrode current collector. Near the winding start end of the negative electrode 12, an exposed portion of the negative electrode current collector is formed where the surface of the negative electrode current collector is not covered by the negative electrode mixture layer, and the negative electrode lead 20 is connected to this exposed portion of the negative electrode current collector.

[0031] In the example shown in FIG. 3, the negative electrode 12 has, in the vicinity of the winding end, in the order toward the winding end side, a double-sided mixture layer region 12a in which negative electrode mixture layers are formed on both surfaces of the negative electrode current collector, a single-sided mixture layer region 12b in which a negative electrode mixture layer is formed only on the inner peripheral side surface of the negative electrode current collector, and a plain region 12c in which no negative electrode mixture layer is formed on both surfaces of the negative electrode current collector. That is, in the single-sided mixture layer region 12b, a negative electrode current collector exposed portion is provided on the outer peripheral side surface of the negative electrode current collector, and in the plain region 12c, negative electrode current collector exposed portions are provided on both surfaces of the negative electrode current collector. In this specification, the "winding end of the mixture layer" means the end on the winding end side of a portion where a mixture layer is formed on at least one surface of the current collector in the positive electrode 11 or the negative electrode 12. In the example shown in FIG. 3, the winding end 42 of the negative electrode mixture layer is the end on the winding end side of the single-sided mixture layer region 12b.

[0032] The fixing tape 30 preferably does not overlap with at least one of the winding end 40 of the positive electrode mixture layer and the winding end 42 of the negative electrode mixture layer in the radial direction of the electrode body 14, and more preferably does not overlap with either of the winding end 40 of the positive electrode mixture layer and the winding end 42 of the negative electrode mixture layer in the radial direction of the electrode body 14. By not overlapping the winding ends 40 and 42 with the fixing tape 30, the pressure applied to the vicinity of the winding ends 40 and 42 during charging and discharging of the battery is reduced, and the effect of suppressing deformation of the electrode plate becomes more remarkable.

[0033] The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions, but preferably contains graphite and a silicon-containing material. The silicon-containing material has a higher capacity than graphite, but has a larger volume change during charge and discharge than graphite.

[0034] The graphite as the negative electrode active material may be any of natural graphite such as flaky graphite, massive graphite, and earthy graphite, and artificial graphite such as massive artificial graphite and graphitized mesophase carbon microbeads.

[0035] The silicon-containing material may be any material containing Si, and examples thereof include Si particles, silicon alloys, silicon compounds, and composite materials containing Si. Note that the silicon-containing material may be used alone or in combination of two or more.

[0036] A suitable silicon-containing material (the above composite material) is a composite material including an ion conductive phase and Si particles dispersed in the ion conductive phase. The ion conductive phase is, for example, at least one selected from the group consisting of a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase. The silicide phase is a phase of a compound composed of Si and an element more electropositive than Si. As an example, NiSi, Mg ２ Si, TiSi ２ and the like can be mentioned. The ion conductive phase is a continuous phase composed of an aggregate of particles finer than the Si particles.

[0037] The average value of the size of the Si particles is preferably 1 nm or more and 200 nm or less, and more preferably 1 nm or more and 100 nm or less. The average size of the Si particles is calculated by imaging a SEM image of the particle cross-section of the silicon-containing material and averaging the diameters of the circumscribed circles of the Si particles extracted by image analysis. The average size of the Si particles may be, for example, 1 nm or more and 10 nm or less. By reducing the size of the Si particles, it is possible to suppress the particle expansion rate accompanying charge and discharge while maintaining a high capacity.

[0038] The above composite material may have a conductive layer covering the surface of the ion conductive phase. The conductive layer is composed of a material having higher conductivity than the ion conductive layer and forms a good conductive path in the negative electrode active material layer. The conductive layer is, for example, a carbon film composed of a conductive carbon material. For the conductive carbon material, carbon black such as acetylene black and ketjen black, graphite, and amorphous carbon with low crystallinity (non-crystalline carbon) can be used. Considering the ensuring of conductivity and the diffusibility of Li ions into the particles, the thickness of the conductive layer is preferably 1 nm or more and 200 nm or less, and more preferably 5 nm or more and 100 nm or less. The thickness of the conductive layer can be measured by observing the cross-section of the composite material using SEM or a transmission electron microscope (TEM).

[0039] An example of a suitable composite material containing Si is a composite material (SiC) having a sea-island structure in which Si particles are dispersed in a carbon phase. In at least a part of the silicon-containing material, it is preferable that the ion conductive phase is the carbon phase. The carbon phase is preferably an amorphous carbon phase. The carbon phase may contain a crystalline phase component, but it is preferable that the amorphous phase component is more. The amorphous carbon phase is composed of, for example, a carbon material in which the average interplane spacing of the (002) plane measured by X-ray diffraction method exceeds 0.34 nm. Note that the composite material containing a carbon phase may or may not have a conductive layer different from the carbon phase.

[0040] Another example of a suitable composite material containing Si has a sea-island structure in which Si particles are dispersed in an amorphous silicon oxide phase and is generally represented by the general formula SiO ｘ (0.5 ≤ x ≤ 1.5). The main component of silicon oxide may be silicon dioxide. Also, the silicon oxide phase may be doped with Li.

[0041] Another example of a suitable composite material containing Si is a composite material having a sea-island structure in which Si particles are dispersed in an amorphous silicate phase. The silicate phase contains, for example, at least one element selected from the group consisting of elements of Group 1 and Group 2 of the periodic table. Further, the silicate phase may further contain at least one element selected from the group consisting of B, Al, Zr, Nb, Ta, V, La, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W.

[0042] A suitable silicate phase is a lithium silicate phase containing Li. The lithium silicate phase is, for example, a phase of a composite oxide represented by the general formula Li ２ｚ SiO （２＋ｚ） (0 < z < 2). It is preferable that the lithium silicate phase does not contain Li ４ SiO ４ (Z = 2). Li ４ SiO ４It is an unstable compound and reacts with water to become alkaline, which can alter Si and lead to a decrease in charge / discharge capacity. From the viewpoint of stability, productivity, and Li ion conductivity, the lithium silicate phase ２ SiO ３ (Z=1) or Li ２ Si ２ O ５ It is preferable that (Z = 1 / 2) be the main component.

[0043] Any of the materials exemplified above can be used as the silicon-containing material, but SiC is particularly preferred from the viewpoint of achieving both high capacity and suppression of electrode plate deformation. The SiC content in the negative electrode mixture layer is, for example, 35% by mass or more and 80% by mass or less, relative to the total mass of graphite and SiC contained in the negative electrode mixture layer. By keeping the proportion of SiC within this range, it becomes easier to set the Young's modulus of the negative electrode 12, which will be described later, within a predetermined range.

[0044] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0045] The Young's modulus of the negative electrode 12 is between 12 GPa and 20 GPa. This suppresses deformation of the electrode plate near the outermost periphery of the electrode body 14. The Young's modulus of the negative electrode 12 can be adjusted by the material of the negative electrode current collector, the types of negative electrode active material, binder, and thickener contained in the negative electrode mixture layer, and their mixing ratios. Furthermore, the Young's modulus of the negative electrode 12 can also be adjusted by the ratio of graphite to silicon-containing material in the negative electrode active material. For example, increasing the ratio of silicon-containing material in the negative electrode active material can increase the Young's modulus.

[0046] The Young's modulus of the negative electrode 12 is measured for the portion of the negative electrode current collector where the negative electrode mixture layer is formed on both sides. Specifically, under a temperature of 25°C, the portion of the negative electrode current collector where the negative electrode mixture layer is formed on both sides is compressed using a universal testing machine (for example, Shimadzu Corporation's Autograph AG-IS10KN), and the Young's modulus can be calculated from the data of the linear region showing elastic deformation obtained by measuring the relationship between stress and strain of the negative electrode 12. A sample for measuring the Young's modulus may be made by cutting the negative electrode 12 to a predetermined size, or it may be made separately using the same material as the negative electrode 12.

[0047] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0048] <Experimental Example 1> [Fabrication of the positive electrode] As the positive electrode active material, aluminum-containing lithium nickel cobalt oxide (LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ A positive electrode slurry was prepared by mixing the positive electrode active material, graphite, and polyvinylidene fluoride in a solid content mass ratio of 100:1:0.9, and using N-methyl-2-pyrrolidone (NMP) as the dispersion medium. Next, the positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum foil using the doctor blade method, the coating was dried, and the material was rolled using a roller. After that, the positive electrode current collector was cut to a predetermined electrode size to obtain a positive electrode in which positive electrode active material layers were formed on both sides of the positive electrode current collector. Furthermore, an exposed portion of the positive electrode current collector without active material was formed in the middle of the length of the positive electrode, and an aluminum positive electrode lead was connected to this exposed portion of the positive electrode current collector by ultrasonic welding.

[0049] [Fabrication of the negative electrode] As the negative electrode active material, a mixture of 65 parts by mass of graphite powder and 35 parts by mass of SiC was used. 100 parts by mass of this negative electrode active material was mixed with 3 parts by mass of styrene-butadiene rubber (SBR) as a binder and 1 part by mass of carboxymethylcellulose (CMC) as a thickener, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil using the doctor blade method, the coating was dried, and the material was rolled using a roller. After that, the negative electrode current collector was cut to a predetermined electrode size to obtain a negative electrode with negative electrode active material layers formed on both sides of the negative electrode current collector. Furthermore, an exposed portion of the negative electrode current collector without active material was formed near the winding start end of the negative electrode, and a nickel negative electrode lead was connected to this exposed portion of the negative electrode current collector by ultrasonic welding. Furthermore, as shown in Figure 3, a single-sided composite layer region and a plain region were formed near the end of the negative electrode winding. The Young's modulus of the portion of the negative electrode current collector where the negative electrode composite layer was formed on both sides was 14 GPa.

[0050] [Electrode Fabrication] A wound electrode body was fabricated by winding the fabricated positive and negative electrodes in a spiral pattern via a separator, with the negative electrode positioned at the outermost circumference. The separator used was a polyethylene microporous membrane with a heat-resistant layer formed on one side, in which polyamide and alumina fillers were dispersed. Fixing tape was attached to both axial ends of the electrode body, including the winding end of the negative electrode, as shown in Figure 2, to secure the electrode body. Furthermore, as shown in Figure 3, the fixing tape was made so as not to overlap with either the winding end of the positive electrode mixture layer or the winding end of the negative electrode mixture layer.

[0051] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate and dimethyl carbonate are mixed in a volume ratio of 1:3 (25°C), and then 5% by mass of vinylene carbonate and LiPF are added to the mixed solvent. ６ A non-aqueous electrolyte was obtained by adding the solution to a concentration of 1 mol / L.

[0052] [Fabrication of a secondary battery] Insulating plates were placed above and below the electrode body, respectively. The negative electrode lead was welded to the bottom of the outer casing, and the positive electrode lead was welded to the sealing body. The electrode body was then housed in a bottomed cylindrical metal outer casing. After that, a non-aqueous electrolyte was injected into the inside of the outer casing. Furthermore, the open end of the outer casing was sealed with a sealing body via a gasket to fabricate a cylindrical non-aqueous electrolyte secondary battery.

[0053] [Evaluation of Negative Electrode Deformation] The above secondary battery was charged with a constant current of 0.3C at a temperature of 25°C until the battery voltage reached 4.2V, and then charged with a constant voltage until the current value reached 0.02C at 4.2V. After a 20-minute pause, it was discharged with a constant current of 1C until the battery voltage reached 3.0V, and then paused for another 20 minutes. This charge-discharge cycle was considered one cycle, and repeated 200 times. After 200 cycles, the secondary battery was disassembled, and the deformation of the negative electrode near the outermost edge of the electrode body was visually observed. The above evaluation was performed on 10 secondary batteries, and the deformation of the negative electrode was evaluated by the number of batteries in which deformation of the negative electrode was observed.

[0054] <Example 2> In the preparation of the electrode body, the fixing tape was attached to the outermost circumference of the electrode body so that it did not overlap with the end of the winding of the positive electrode mixture layer, but overlapped with the end of the winding of the winding of the negative electrode mixture layer. A secondary battery was then prepared and evaluated in the same manner as in Example 1.

[0055] <Example 3> In the preparation of the electrode body, the fixing tape was attached to the outermost circumference of the electrode body so that it did not overlap with the winding end of the negative electrode mixture layer, but overlapped with the winding end of the positive electrode mixture layer. A secondary battery was then prepared and evaluated in the same manner as in Example 1.

[0056] <Example 4> In the preparation of the negative electrode, a secondary battery was prepared and evaluated in the same manner as in Example 1, except that the mixing ratio of graphite powder and SiC was changed from 65:35 to 50:50 by mass ratio. The Young's modulus of the negative electrode where the negative electrode mixture layer was formed on both sides of the current collector was 15 GPa.

[0057] <Example 5> In the preparation of the electrode body, the fixing tape was attached to the outermost circumference of the electrode body so that it did not overlap with the winding end of the positive electrode mixture layer, but overlapped with the winding end of the negative electrode mixture layer. A secondary battery was then prepared and evaluated in the same manner as in Example 4.

[0058] <Example 6> In the preparation of the electrode body, the fixing tape was attached to the outermost circumference of the electrode body so that it did not overlap with the winding end of the negative electrode mixture layer, but overlapped with the winding end of the positive electrode mixture layer. A secondary battery was then prepared and evaluated in the same manner as in Example 4.

[0059] <Comparative Example 1> A secondary battery was manufactured and evaluated in the same manner as in Example 1, except that the mixing ratio of graphite powder and SiC in the preparation of the negative electrode was changed from 65:35 to 94:6 by mass ratio. The Young's modulus of the negative electrode where the negative electrode mixture layer was formed on both sides of the current collector was 10 GPa.

[0060] <Comparative Example 2> In the preparation of the electrode body, the fixing tape was attached to the outermost circumference of the electrode body so that it did not overlap with the end of the winding of the positive electrode mixture layer, but overlapped with the end of the winding of the winding of the negative electrode mixture layer. A secondary battery was prepared and evaluated in the same manner as in Comparative Example 1.

[0061] <Comparative Example 3> In the preparation of the electrode body, the fixing tape was attached to the outermost circumference of the electrode body so that it did not overlap with the winding end of the negative electrode mixture layer, but overlapped with the winding end of the positive electrode mixture layer. A secondary battery was then prepared and evaluated in the same manner as in Comparative Example 1.

[0062] Table 1 shows the evaluation results for the examples and comparative examples.

[0063]

[0064] Examples 1 to 6 showed fewer batteries with negative electrode deformation compared to Comparative Examples 1 to 3. In particular, in Examples 1 and 4, where the fixing tape did not overlap with either the winding end of the positive electrode mixture layer or the winding end of the negative electrode mixture layer in the radial direction of the electrode body, no negative electrode deformation occurred.

[0065] The present disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator between them, and an outer casing housing the electrode body, wherein a fixing tape is attached to the outermost outer surface of the electrode body to fix the end of the winding of the electrode body, and the Young's modulus of the negative electrode is 12 GPa or more and 20 GPa or less. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the negative electrode comprises graphite and a silicon-containing material. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the positive electrode and the negative electrode each have a current collector and a composite layer formed on the surface of the current collector, and the fixing tape does not overlap with at least one of the end of the winding of the composite layer of the positive electrode and the end of the winding of the composite layer of the negative electrode in the radial direction of the electrode body. Configuration 4: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the positive electrode and the negative electrode each have a current collector and a composite layer formed on the surface of the current collector, and the fixing tape does not overlap with either the winding end of the composite layer of the positive electrode or the winding end of the composite layer of the negative electrode in the radial direction of the electrode bodies. Configuration 5: The non-aqueous electrolyte secondary battery according to any one of Configurations 2 to 4, wherein the silicon-containing material is a composite material having a sea-island structure in which Si particles are dispersed in a carbon phase, and the content of the composite material is 35% by mass or more and 80% by mass or less with respect to the total mass of the graphite and the composite material.

[0066] 10 (Non-aqueous electrolyte) secondary battery, 11 Positive electrode, 12 Negative electrode, 12a Double-sided compound layer region, 12b Single-sided compound layer region, 12c Plain region, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 30 Fixing tape, 40 End of winding of positive electrode compound layer, 42 End of winding of negative electrode compound layer

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator in between, and an outer casing for housing the electrode body, wherein a fixing tape for fixing the end of the winding of the electrode body is attached to the outermost outer surface of the electrode body, and the Young's modulus of the negative electrode is 12 GPa or more and 20 GPa or less.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode comprises graphite and a silicon-containing material.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode and the negative electrode each have a current collector and a composite layer formed on the surface of the current collector, and the fixing tape does not overlap with at least one of the winding ends of the composite layer of the positive electrode and the winding ends of the composite layer of the negative electrode in the radial direction of the electrode bodies.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode and the negative electrode each have a current collector and a composite layer formed on the surface of the current collector, and the fixing tape does not overlap with either the winding end of the composite layer of the positive electrode or the winding end of the composite layer of the negative electrode in the radial direction of the electrode bodies.

5. The non-aqueous electrolyte secondary battery according to claim 2, wherein the silicon-containing material is a composite material having a sea-island structure in which Si particles are dispersed in a carbon phase, and the content of the composite material is 35% by mass or more and 80% by mass or less with respect to the total mass of the graphite and the composite material.

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