Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises: an electrode body in which a band-shaped positive electrode and a band-shaped negative electrode are wound along the longitudinal direction with a separator interposed therebetween; and an exterior body that accommodates the electrode body. A negative electrode mixture layer contains graphite and a silicon-containing material, the amount of the silicon-containing material being 35–80 mass% with respect to the total mass of the graphite and the silicon-containing material. The Young's modulus of the negative electrode is 12–20 GPa. In the negative electrode, the distance between a position that is 0.25 turns toward the winding end side from a position facing the outer peripheral side of the winding start end of the positive electrode with the separator interposed therebetween, and a position that is 0.75 turns toward the winding end side from a position facing the outer peripheral side of the winding start end of the positive electrode with the separator interposed therebetween, is 4.5 mm or less.

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] In recent years, there has been an increasing demand for higher capacity in non-aqueous electrolyte secondary batteries such as lithium-ion batteries. For example, Patent Document 1 discloses a technology for increasing the capacity of batteries by using a silicon-containing material as the negative electrode active material, which can absorb more lithium ions per unit mass compared to carbon-based materials such as graphite.

[0003] Japanese Patent Publication No. 2010-212228

[0004] Conventionally, 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. When the electrode body expands during charge-discharge cycles, pressure acts on the electrode body from the outer casing. In high-capacity batteries, silicon-containing materials undergo larger volume changes during charge-discharge compared to carbon materials, so the negative electrode facing the starting end of the positive electrode mixture layer may deform, such as bending, within the electrode body, potentially causing an internal short circuit. The technology disclosed in Patent Document 1 does not take into consideration the deformation of the negative electrode, and there is still room for improvement in terms of enhancing battery safety.

[0005] The purpose of this disclosure is to provide a non-aqueous electrolyte secondary battery that has high capacity and excellent safety.

[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 longitudinally with a separator between them, and an outer casing for housing the electrode body, wherein the negative electrode mixture layer contains graphite and a silicon-containing material, and the content of the silicon-containing material is 35% by mass or more and 80% by mass or less with respect to the total mass of the graphite and silicon-containing material, the Young's modulus of the negative electrode is 12 GPa or more and 20 GPa or less, and the distance between a position 0.25 turns toward the end of the winding from a position facing the outer circumference of the starting end of the winding of the positive electrode via a separator and a position 0.75 turns toward the end of the winding from a position facing the outer circumference of the starting end of the winding of the positive electrode via a separator is 4.5 mm or less.

[0007] The non-aqueous electrolyte secondary battery described herein makes it possible to achieve both high capacity and safety.

[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 wound electrode body of the secondary battery shown in Figure 1. This is a radial cross-sectional view of the electrode body near the winding center axis shown in Figure 2.

[0009] In the following, an example of an embodiment of a cylindrical secondary battery according to this disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc., are examples to facilitate understanding of the present invention and can be appropriately modified to suit the specifications of the cylindrical secondary battery. Furthermore, if the following description includes multiple embodiments and modifications, it is intended from the outset that their characteristic parts may be used in appropriate combinations.

[0010] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10, which is an example of an embodiment. In the secondary battery 10 shown in Figure 1, an electrode body 14 and a non-aqueous electrolyte (not shown) are housed in an outer casing 15. The electrode body 14 has a wound structure in which a strip-shaped positive electrode 11 and a negative electrode 12 are wound around a separator 13. As the non-aqueous solvent (organic solvent) for the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, and esters can be used, and two or more of these solvents can be mixed and used. When two or more solvents are mixed and used, 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 an electrolyte salt for non-aqueous electrolytes, LiPF ６ LiBF ４ , and LiCF ３ SO ３These and mixtures thereof can be used. The amount of electrolyte salt soluble in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less. For the sake of explanation, the side of the sealing body 16 will be referred to as "upper" and the bottom side of the outer casing 15 as "lower".

[0011] 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 tab 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 tab 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. Furthermore, the negative electrode 12 is located on the outermost outer surface of the electrode body 14, and the negative electrode 12 is in contact with the outer casing 15. In the secondary battery 10, the outer casing 15 becomes the negative electrode terminal.

[0012] 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.

[0013] 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.

[0014] Next, the electrode body 14 will be described with reference to Figure 2. Figure 2 is a perspective view of the electrode body 14. As described above, the electrode body 14 has a wound structure in which a positive electrode 11 and a 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 which serves as the winding axis, so that they are alternately stacked in the radial direction of the electrode body 14. The separator 13 is formed to be at least one size larger than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0015] In the radial direction β of the electrode body 14, the side with the winding axis is called the inner circumference side, and the opposite side is called the outer circumference side. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction γ, and the short direction of the positive electrode 11 and the negative electrode 12 is the axial direction α. ​​In the winding direction γ, the side with the winding axis is called the winding start side, and the opposite side is called the winding end side. The ends of the positive electrode 11 and the negative electrode 12 on the winding start side are called the winding start end, and the ends on the winding end side are called the winding end end. The positive electrode tab 19 extends from approximately the center in the radial direction from the center to the outermost circumference at the upper end of the electrode body 14 in the axial direction α. ​​The negative electrode tab 20 extends from near the winding axis at the lower end of the electrode body 14 in the axial direction α.

[0016] The positive electrode 11 has a strip-shaped positive electrode current collector, a positive electrode mixture layer formed on both sides of the positive electrode current collector, and a positive electrode current collector exposed portion where the positive electrode current collector is exposed. For the positive electrode current collector, for example, a metal foil such as aluminum, or a film with the metal arranged on its surface layer can be used.

[0017] The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer is manufactured by applying a positive electrode mixture slurry containing, for example, a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode current collector 30, followed by drying and rolling. The exposed portion of the positive electrode current collector is provided, for example, by intermittent coating, where the positive electrode mixture slurry is not applied to a part of the positive electrode current collector.

[0018] In this embodiment, the positive electrode tab 19 is joined, for example, by ultrasonic welding, to the exposed portion of the positive electrode current collector formed approximately in the center of the longitudinal direction of the positive electrode 11. The position of the positive electrode tab 19 is not limited to the example shown in Figure 2, and may be at any position along the longitudinal direction γ of the positive electrode 11.

[0019] 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.

[0020] 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.

[0021] The negative electrode 12 comprises a strip-shaped negative electrode current collector, a negative electrode mixture layer formed on both sides of the negative electrode current collector, and a negative electrode current collector exposed portion. The negative electrode mixture layer is formed to be larger in the short and long directions than the positive electrode mixture layer from the viewpoint of preventing lithium deposition. For the negative electrode current collector, for example, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper, or a film with the metal arranged on its surface can be used.

[0022] The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The negative electrode mixture layer is manufactured by, for example, applying a negative electrode mixture slurry containing the negative electrode active material, a binder, and a solvent such as water to both sides of the negative electrode current collector, followed by drying and rolling. The exposed portion of the negative electrode current collector is provided, for example, by intermittent coating, where the negative electrode mixture slurry is not applied to a part of the negative electrode current collector.

[0023] In this embodiment, the negative electrode tab 20 is joined, for example, by ultrasonic welding, to the exposed portion of the negative electrode current collector formed near the winding start end of the negative electrode 12. The position of the negative electrode tab 20 is not limited to the example shown in Figure 2, and may be at any position along the longitudinal direction γ of the negative electrode 12.

[0024] The negative electrode active material contains graphite and a silicon-containing material. The silicon-containing material content in the negative electrode mixture layer is 35% by mass or more and 80% by mass or less, relative to the total mass of graphite and silicon-containing material contained in the negative electrode mixture layer. Since the silicon-containing material has a higher capacity than graphite, increasing the proportion of the silicon-containing material to 35% by mass or more allows for higher capacity applications. On the other hand, by setting the proportion of the silicon-containing material to 80% by mass or less, it becomes easier to set the Young's modulus of the negative electrode 12, described later, within a predetermined range.

[0025] The graphite used as the negative electrode active material may be any of the following: natural graphite such as flake graphite, lump graphite, and earthy graphite, or artificial graphite such as lump graphite and graphitized mesophase carbon microbeads.

[0026] Silicon-containing materials can be any material containing Si, and examples include Si particles, silicon alloys, silicon compounds, and Si-containing composite materials. Note that one type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0027] A suitable silicon-containing material (the composite material described above) is a composite material comprising an ionic conductive phase and Si particles dispersed in the ionic conductive phase. The ionic 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 compound phase consisting of Si and an element more electrically positive than Si, such as NiSi and Mg.２ Si, TiSi ２ These are some examples. The ionic conducting phase is a continuous phase composed of an aggregate of particles smaller than Si particles.

[0028] The average size of the Si particles is preferably between 1 nm and 200 nm, and more preferably between 1 nm and 100 nm. The average size of the Si particles is calculated by capturing SEM images 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, between 1 nm and 10 nm. By reducing the size of the Si particles, it is possible to suppress the particle expansion rate associated with charging and discharging while maintaining high capacity.

[0029] The above composite material may have a conductive layer covering the surface of the ion-conducting phase. The conductive layer is composed of a material with higher conductivity than the ion-conducting layer and forms good conductive paths in the negative electrode mixture layer. The conductive layer is, for example, a carbon film composed of a conductive carbon material. The conductive carbon material can be carbon black such as acetylene black and Ketjen black, graphite, or amorphous carbon with low crystallinity. The thickness of the conductive layer is preferably 1 nm to 200 nm, and more preferably 5 nm to 100 nm, taking into consideration the securing of conductivity and the diffusion of Li ions into the particle interior. The thickness of the conductive layer can be measured by cross-sectional observation of the composite material using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0030] An example of a suitable composite material containing Si is a composite material having a sea-island structure in which Si particles are dispersed in a carbon phase (SiC). It is preferable that the ion-conducting phase in at least a portion of the silicon-containing material is a carbon phase. It is preferable that the carbon phase is an amorphous carbon phase. The carbon phase may contain crystalline phase components, but it is preferable that the amorphous phase components are more abundant. The amorphous carbon phase is composed of a carbon material in which the average interplanar spacing of (002) planes, as measured by X-ray diffraction, exceeds 0.34 nm. The composite material containing the carbon phase may have a conductive layer separate from the carbon phase, or it may not have such a conductive layer.

[0031] 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 as a whole, has a general formula SiO ｘ (0.5 ≤ x ≤ 1.5). The main component of the silicon oxide may be silicon dioxide. Also, the silicon oxide phase may be doped with Li.

[0032] 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. Also, 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.

[0033] 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 ４ is an unstable compound and reacts with water to show alkalinity, which may cause deterioration of Si and lead to a decrease in charge-discharge capacity. From the viewpoints of stability, productivity, and Li ion conductivity, etc., it is preferable that the lithium silicate phase has Li ２ SiO ３ (Z = 1) or Li ２ Si ２ O ５ (Z = 1 / 2) as the main component.

[0034] As the silicon-containing material, any of the materials exemplified above can be used, but from the viewpoint of achieving both high capacity and suppression of electrode deformation, SiC is particularly preferable.

[0035] Examples of the binder included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (such as PAA-Na and PAA-K, and partially neutralized salts may also be used), and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0036] The Young's modulus of the negative electrode 12 is 12 GPa or more and 20 GPa or less. By setting L in the vicinity of the winding center of the electrode body 14 to a predetermined value as described later while the Young's modulus of the negative electrode 12 is within this range, the deformation of the negative electrode 12 facing the start end of winding of the positive electrode mixture layer can be suppressed. The value of the Young's modulus of the negative electrode 12 can be adjusted by the material of the negative electrode current collector, the types of the negative electrode active material, binder, and thickener contained in the negative electrode mixture layer, and their mixing ratios. Further, the value of the Young's modulus of the negative electrode 12 can also be adjusted by the ratio of graphite and the silicon-containing material in the negative electrode active material. For example, by increasing the ratio of the silicon-containing material in the negative electrode active material, the Young's modulus can be increased.

[0037] The Young's modulus of the negative electrode 12 is measured for the portions where the negative electrode mixture layers are formed on both surfaces of the negative electrode current collector. Specifically, under the temperature condition of 25°C, the portions where the negative electrode mixture layers are formed on both surfaces of the negative electrode current collector are compressed by a universal testing machine (for example, Autograph AG-IS10KN manufactured by Shimadzu Corporation), and it can be calculated from the data of the linear region showing the elastic deformation obtained by measuring the relationship between the stress and strain of the negative electrode 12. The sample for measuring the Young's modulus may be prepared by cutting the negative electrode 12 into a predetermined dimension, or may be separately prepared using the same material as the negative electrode 12.

[0038] Next, while referring to FIG. 3, the configuration in the vicinity of the winding center of the electrode body 14 will be described. FIG. 3 is a radial cross-sectional view in the vicinity of the winding center axis O of the electrode body 14 shown in FIG. 2. In FIG. 3, the separator 13 and the negative electrode tab 20 are not shown.

[0039] In the example shown in Figure 3, a positive electrode mixture layer is formed on both sides of the positive electrode current collector up to the winding start end 11s of the positive electrode 11, and the winding start end 11s of the positive electrode 11 is the same as the winding start end of the positive electrode mixture layer. The negative electrode 12 has, near the winding start end, a double-sided mixture layer region where a negative electrode mixture layer is formed on both sides of the negative electrode current collector, and a plain region where no negative electrode mixture layer is formed on both sides of the negative electrode current collector, in order toward the winding start side. That is, in the plain region, exposed portions of the negative electrode current collector are provided on both sides of the negative electrode current collector. Note that the configuration near the winding center of the electrode body 14 is not limited to the example shown in Figure 3, and for example, a single-sided mixture layer region where a negative electrode mixture layer is formed only on the inner circumferential surface of the negative electrode current collector may exist between the double-sided mixture layer region and the plain region.

[0040] In the negative electrode 12, the distance L between position X, which is 0.25 turns toward the end of the winding from the position facing the outer circumference of the winding start end 11s of the positive electrode 11 via the separator 13, and position Y, which is 0.75 turns toward the end of the winding from the position facing the outer circumference of the winding start end 11s of the positive electrode 11 via the separator 13, is 4.5 mm or less. By keeping L 4.5 mm or less and setting the Young's modulus of the negative electrode 12 to 12 GPa or more and 20 GPa or less, deformation of the negative electrode 12 facing the winding start end of the positive electrode mixture layer can be suppressed. The lower limit of L is, for example, 1 mm.

[0041] In Figure 3, line N1 is the line connecting the winding center axis O and the winding start end 11s of the positive electrode. Line N2 is the line obtained by rotating line N1 0.25 turns toward the winding end side of the electrode body 14, with the winding center axis O as the axis of rotation. Line N3 is the line obtained by rotating line N1 0.75 turns toward the winding end side, with the winding center axis O as the axis of rotation. That is, the angle θ1 between line N1 and line N2 is 90°, and the angle θ2 between line N1 and line N3 is 270°. X is the point where line N2 intersects the negative electrode 12 facing the winding start end 11s of the positive electrode 11 via the separator 13 on the outer circumference side, and Y is the point where line N3 intersects the negative electrode 12 facing the winding start end 11s of the positive electrode 11 via the separator 13 on the outer circumference side. The distance L between X and Y is determined with respect to the center of the thickness direction of the negative electrode 12.

[0042] 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.

[0043] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0044] <Example 1-1> [Preparation of 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.

[0045] [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 in which negative electrode active material layers were formed on both sides of the negative electrode current collector. 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, the Young's modulus of the negative electrode in the area where negative electrode compound layers were formed on both sides of the negative electrode current collector was 14 GPa.

[0046] [Electrode Fabrication] A wound electrode body was fabricated by winding the fabricated positive and negative electrodes around a winding core, which served as the winding axis, via a separator, with the negative electrode positioned on the outermost periphery. 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.

[0047] [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.

[0048] [Fabrication of the 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. A non-aqueous electrolyte was then 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. The fabricated secondary battery was observed in the radial cross-section using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR), and L in Figure 3 was found to be 4.2 mm.

[0049] [Evaluation of Initial Discharge Capacity and 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 was 0.02C at 4.2V. After a 20-minute pause, the battery was discharged with a constant current of 1C until the battery voltage reached 3.0V, and the discharge capacity at this time was taken as the initial discharge capacity. After another 20-minute pause, this charge-discharge cycle was considered one cycle, and repeated 200 times. After the charge-discharge cycle, the secondary battery was examined using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR) to observe the cross-section near the winding center of the electrode body and evaluate whether or not there was deformation of the negative electrode.

[0050] <Comparative Example 1-1> A secondary battery was manufactured and evaluated in the same manner as in Example 1-1, except that the outer diameter of the winding core was increased to 4.7 mm in the preparation of the electrode body.

[0051] <Example 2-1> 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 was changed from 65:35 to 50:50 by mass ratio in the preparation of the negative electrode. The Young's modulus of the negative electrode current collector where the negative electrode mixture layer was formed on both sides was 15 GPa. The length L was 4.2 mm.

[0052] <Comparative Example 2-1> A secondary battery was manufactured and evaluated in the same manner as in Example 2-1, except that the outer diameter of the winding core was increased to make L 4.7 mm in the preparation of the electrode body.

[0053] <Comparative Example 2-2> In the preparation of the negative electrode, a negative electrode current collector with a lower Young's modulus was used compared to the negative electrode current collector used in Example 2-1. A secondary battery was then prepared and evaluated in the same manner as in Example 2-1. The Young's modulus of the negative electrode current collector in the area where the negative electrode mixture layer was formed on both sides was 10 GPa. The length L was 4.2 mm.

[0054] <Comparative Example 3-1> 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. The length L was 4.2 mm.

[0055] <Comparative Example 3-2> In the preparation of the electrode body, a secondary battery was prepared and evaluated in the same manner as in Comparative Example 3-1, except that the outer diameter of the winding core was increased to make L 4.7 mm.

[0056] The evaluation results for the examples and comparative examples are shown in Table 1. In Table 1, the initial discharge capacity of secondary batteries other than Example 1-1 is a relative value when the initial discharge capacity of the secondary battery in Example 1-1 is set to 100.

[0057]

[0058] The secondary batteries in the examples had a large initial discharge capacity and no deformation of the negative electrode. This demonstrates the goal of achieving both. On the other hand, comparative examples 1-1 and 2-1, where L was greater than 4.5 mm, and comparative example 2-2, where Young's modulus was less than 12 GPa, all showed deformation of the negative electrode. Therefore, it can be seen that by including silicon-containing material in a predetermined proportion, setting the Young's modulus to 12 GPa or more and 20 GPa, and L to 4.5 mm or less, both high capacity and safety can be achieved. Comparative examples 3-1 and 3-2 had small initial discharge capacities.

[0059] 10 Secondary battery, 11 Positive electrode, 11s Winding start end, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode tab, 20 Negative electrode tab, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket

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 between them, and an outer casing for housing the electrode body, wherein the negative electrode contains graphite and a silicon-containing material, and the content of the silicon-containing material is 35% by mass or more and 80% by mass or less of the total mass of the graphite and the silicon-containing material, the Young's modulus of the negative electrode is 12 GPa or more and 20 GPa or less, and the distance between a position 0.25 turns toward the end of the winding of the electrode body from a position facing the outer circumference of the starting end of the winding of the positive electrode via the separator, and a position 0.75 turns toward the end of the winding of the positive electrode from a position facing the outer circumference of the starting end of the winding of the positive electrode via the separator, is 4.5 mm or less.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the silicon-containing material is a composite material having a sea-island structure in which Si particles are dispersed in a carbon phase.

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