Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery having high capacity and excellent safety. This non-aqueous electrolyte secondary battery includes a wound electrode body in which strip-shaped positive and negative electrodes are wound via a separator, and an exterior body housing the electrode body, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector, the thickness of the negative electrode mixture layer is 40-60 µm, the negative electrode mixture layer contains graphite and a silicon-containing material as negative electrode active materials, the silicon-containing material includes an ion-conductive phase and an Si phase dispersed within the ion-conductive phase, the content of the silicon-containing material in the negative electrode active material is 30-50 mass%, and the content of the Si phase in the silicon-containing material is 40-70 mass%.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery including a wound electrode assembly.

[0002] In recent years, there has been a demand for increasingly higher capacity non-aqueous electrolyte secondary batteries such as lithium ion batteries. For example, Patent Document 1 discloses a technology for increasing the capacity of a battery by using, as a negative electrode active material for a negative electrode, a silicon-containing material that can occlude more lithium ions per unit mass than carbon-based materials such as graphite.

[0003] JP 2010-212228 A

[0004] Conventionally, non-aqueous electrolyte secondary batteries have been widely used, in which a wound electrode assembly, in which strip-shaped positive and negative electrodes are wound, is housed in an outer casing. When a wound electrode assembly is subjected to a strong external impact, high pressure is applied near the end of the winding of the negative electrode mixture layer, which may cause a portion of the separator to break and lead to an internal short circuit. High-capacity non-aqueous electrolyte secondary batteries require more advanced safety measures because they release a large amount of energy in the event of a short circuit.

[0005] An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery that has high capacity and excellent safety.

[0006] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes a wound electrode assembly in which strip-shaped positive and negative electrodes are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly. The negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The thickness of the negative electrode mixture layer is 40 μm or more and 60 μm or less. The negative electrode mixture layer contains graphite and a silicon-containing material as negative electrode active materials. The silicon-containing material contains an ion-conducting phase and a Si phase dispersed in the ion-conducting phase. The content of the silicon-containing material in the negative electrode active material is 30% by mass or more and 50% by mass or less, and the content of the Si phase in the silicon-containing material is 40% by mass or more and 70% by mass or less.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure can suppress the occurrence of internal short circuits and improve safety.

[0008] Fig. 2 is an axial cross-sectional view of a cylindrical secondary battery according to an example embodiment. Fig. 3 is a perspective view of a wound electrode body provided in the secondary battery shown in Fig. 1. Fig. 4 is a cross-sectional view showing, in a developed state, the positional relationship of a positive electrode, a negative electrode, and a separator constituting an electrode body according to an example embodiment near the winding end.

[0009] Hereinafter, an example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the cylindrical secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is assumed from the beginning that the characteristic portions of those embodiments and modified examples can be appropriately combined and used.

[0010] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. The secondary battery 10 shown in FIG. 1 includes an electrode assembly 14 and a nonaqueous electrolyte (not shown) housed in an outer casing 15. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Examples of nonaqueous solvents (organic solvents) for the nonaqueous electrolyte include carbonates, lactones, ethers, ketones, esters, and the like. Two or more of these solvents can be mixed together. When two or more solvents are mixed together, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as the chain carbonate. The electrolyte salt of the non-aqueous electrolyte is LiPF ６ , LiBF ４ , LiCF ３ SO ３ etc., and mixtures thereof can be used. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less. For convenience of explanation, the following description will be given with the sealing body 16 side as the "upper" and the bottom side of the exterior body 15 as the "lower".

[0011] The opening of the exterior body 15 is closed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the underside 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 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 to the bottom side of the exterior body 15 and is welded to the inner bottom surface of the exterior body 15. In addition, the negative electrode 12 is located on the outermost peripheral surface of the electrode body 14 and is in contact with the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal.

[0012] The exterior body 15 is, for example, a cylindrical metal exterior can with a bottom. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the airtightness of the interior of the secondary battery 10. The exterior body 15 has a grooved portion 21 that supports the sealing body 16, formed, for example, by pressing the side surface from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and supports the sealing body 16 on its upper surface.

[0013] The sealing body 16 includes 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 this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. 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 peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge toward the cap 26 and separate from the lower valve body 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may rupture, allowing gas to be released from the opening 26a of the cap 26.

[0014] Next, the electrode assembly 14 will be described with reference to FIG. 2 . FIG. 2 is a perspective view of the electrode assembly 14. As described above, the electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all formed in strip shapes and are spirally wound around a winding axis, resulting in an alternating stacked state in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the length direction and width direction than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0015] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator include olefin-based resins such as polyethylene and 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-based resin. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, and the surface of the separator 13 may be coated with a material such as an aramid-based resin or ceramic.

[0016] In the radial direction β, the side of the winding axis is referred to as the inner winding side, and the opposite side is referred to as the outer winding 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 lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction α. ​​In the winding direction γ, the side of the winding axis is referred to as the winding start side, and the opposite side is referred to as the winding end side. Furthermore, in the positive electrode 11 and the negative electrode 12, and the negative electrode mixture layer described below, the end on the winding end side is referred to as the winding end. The positive electrode lead 19 extends in the axial direction α from approximately the center in the radial direction from the center to the outermost periphery at the upper end of the electrode body 14. Furthermore, the negative electrode lead 20 extends in the axial direction α from near the winding axis at the lower end of the electrode body 14.

[0017] Next, the positive electrode 11 and negative electrode 12 constituting the electrode assembly 14 will be described in detail with reference to Fig. 3. Fig. 3 is a cross-sectional view showing the positional relationship of the positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 according to one example of the embodiment in a developed state near the winding end, and shows a cross section along the longitudinal direction of the positive electrode 11, negative electrode 12, and separator 13.

[0018] The positive electrode 11 has a strip-shaped positive electrode current collector 30 and a positive electrode mixture layer 32 formed on the surface of the positive electrode current collector 30. In this embodiment, the positive electrode mixture layer 32 is formed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 may be, for example, a foil of a metal such as aluminum, or a film having such a metal disposed on its surface. A suitable positive electrode current collector 30 is a foil of a metal whose main component is aluminum or an aluminum alloy. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0019] The positive electrode mixture layer 32 is formed on the entire surface of the positive electrode current collector 30 except for the positive electrode current collector exposed portion. The positive electrode current collector exposed portion is a portion of the surface of the positive electrode current collector 30 that is not covered with the positive electrode mixture layer 32. In this embodiment, a positive electrode current collector exposed portion is also provided at approximately the center of the positive electrode 11 in the longitudinal direction γ, and a positive electrode lead 19 is joined to the positive electrode current collector 30 at this positive electrode current collector exposed portion. The positive electrode current collector exposed portion to which the positive electrode lead is joined is preferably provided on both surfaces of the positive electrode 11 so as to overlap in the thickness direction of the positive electrode 11.

[0020] The positive electrode mixture layer 32 preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both surfaces of the positive electrode current collector 30, followed by drying and rolling. The positive electrode current collector exposed portion is provided, for example, by intermittent application in which the positive electrode mixture slurry is not applied to a part of the positive electrode current collector 30.

[0021] As the positive electrode active material, a lithium-containing transition metal oxide containing a transition metal element such as Co, Mn, or Ni can be used. The lithium-containing transition metal oxide is not particularly limited, but may be any of the following oxides represented by the general formula: Li １＋ｘ MO ２(wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0022] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black (CB) such as acetylene black (AB) and Ketjen black, and carbon materials such as graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These materials may be used alone or in combination of two or more.

[0023] The negative electrode 12 has a strip-shaped negative electrode current collector 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode current collector 40. The negative electrode current collector 40 may be, for example, a foil of a metal such as copper, or a film having such a metal disposed on its surface. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0024] In the present embodiment, the negative electrode mixture layer 42 is formed on both surfaces of the negative electrode current collector 40, with a first negative electrode mixture layer 421 formed on the inner side of the wound negative electrode current collector 40 and a second negative electrode mixture layer 422 formed on the outer side of the wound negative electrode current collector 40. The negative electrode mixture layer 42 is formed on the entire area of ​​both surfaces of the negative electrode current collector 40 except for a negative electrode current collector exposed portion 44, which will be described later.

[0025] The winding end 421e of the first negative electrode mixture layer 421 coincides with the winding end of the negative electrode current collector 40 and forms the winding end of the negative electrode 12. Note that the winding end 421e of the first negative electrode mixture layer 421 may be located closer to the winding start side than the winding end of the negative electrode current collector 40. Because the first negative electrode mixture layer 421 faces the positive electrode mixture layer 32 via the separator 13, when a strong external impact is applied near the winding end 421e of the first negative electrode mixture layer 421, the separator 13 may break, potentially causing an internal short circuit. As will be described later, by reducing the thickness of the first negative electrode mixture layer 421 and optimizing the composition of the negative electrode active material, it is possible to increase capacity and improve safety.

[0026] Near the winding end of the negative electrode 12, a negative electrode current collector exposed portion 44 is formed on the outside of the winding of the negative electrode current collector 40. The negative electrode current collector exposed portion 44 is a portion of the surface of the negative electrode current collector 40 that is not covered with the negative electrode mixture layer 42. This negative electrode current collector exposed portion 44 formed near the winding end of the negative electrode 12 comes into contact with the inner circumferential surface of the exterior body 15 (see FIG. 1 ), thereby electrically connecting the negative electrode 12 and the exterior body 15. Note that in this embodiment, the negative electrode 12 also has a negative electrode current collector exposed portion near the winding start end, and the negative electrode lead 20 is joined to the negative electrode current collector 40 at this negative electrode current collector exposed portion.

[0027] The thickness of the negative electrode mixture layer 42 is 40 μm or more and 60 μm or less. That is, the first negative electrode mixture layer 421 and the second negative electrode mixture layer 422 each have a thickness of 40 μm or more and 60 μm or less. The thicknesses of the first negative electrode mixture layer 421 and the second negative electrode mixture layer 422 may be different or the same. If the thickness of the first negative electrode mixture layer 421 exceeds 60 μm, breakage of the separator 13 cannot be sufficiently suppressed.

[0028] The anode mixture layer 42 preferably contains anode active material and a binder. The anode mixture layer 42 is produced, for example, by applying anode mixture slurry containing anode active material, a binder, water, and the like to both surfaces of the anode current collector 40, followed by drying and rolling. The anode current collector exposed portion 44 is provided, for example, by intermittent application in which the anode mixture slurry is not applied to a part of the anode current collector 40.

[0029] The negative electrode mixture layer 42 contains graphite and a silicon-containing material as negative electrode active materials. The content of the silicon-containing material in the negative electrode active material is 30% by mass or more and 50% by mass or less. Within this range, high capacity can be achieved while improving safety. Examples of graphite include natural graphite such as flake graphite, massive artificial graphite, and artificial graphite such as graphitized mesophase carbon microbeads.

[0030] The silicon-containing material is a composite particle including an ion-conducting phase and a Si phase dispersed in the ion-conducting phase. The Si phase is formed by dispersing Si in the form of fine particles. The silicon-containing material has, for example, a sea-island structure in which fine Si particles are dispersed substantially uniformly in the ion-conducting phase. The ion-conducting phase is, for example, an amorphous carbon phase, a lithium silicate phase, a silicon oxide phase, a titanium oxide phase, a zirconium oxide phase, or the like. The ion-conducting phase is preferably an amorphous carbon phase. In this case, the silicon-containing material becomes a composite particle composed of silicon and carbon (hereinafter referred to as SiC). Because the amorphous carbon phase is soft, fracture of the separator 13 can be more significantly suppressed even when SiC containing a large amount of hard Si phase is used.

[0031] The content of the Si phase in the silicon-containing material is 40% by mass or more and 70% by mass or less. As described above, by setting the thickness of the negative electrode mixture layer to 40 μm or more and 60 μm or less, setting the content of the silicon-containing material in the negative electrode active material to 30% by mass or more and 50% by mass or less, and setting the content of the Si phase in the silicon-containing material to 40% by mass or more and 70% by mass or less, it is possible to achieve high capacity and improve safety.

[0032] The binder contained in the negative electrode mixture layer 42 may be, for example, the same resin as that used in the positive electrode 11, but when preparing the negative electrode mixture slurry in an aqueous solvent, it is preferable to use styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, etc. These may be used alone or in combination of two or more.

[0033] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0034] Example 1 [Preparation of Positive Electrode] Aluminum-containing lithium nickel cobalt oxide was used as the positive electrode active material. This positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 100:2:1, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. The coating was rolled using a rolling roller and cut to a predetermined electrode size to prepare a positive electrode. An exposed portion where the surface of the positive electrode current collector was exposed was provided approximately in the center of the longitudinal direction of the positive electrode, and an aluminum positive electrode tab was welded to it.

[0035] [Preparation of Negative Electrode] A mixture of artificial graphite and SiC in a mass ratio of 50:50 was used as the negative electrode active material. The Si phase content in the SiC was 70 mass%, and the discharge capacity per 1 g of negative electrode active material was 1.3 Ah / g. This negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 100:1:1, and a negative electrode mixture slurry was prepared using water as a dispersion medium. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil with a thickness of 8 μm, and the coating was dried. The coating was rolled using a rolling roller and cut to a predetermined electrode size to prepare a negative electrode. The first negative electrode mixture layer and the second negative electrode mixture layer both had a thickness of 60 μm. In addition, exposed portions where the surface of the negative electrode current collector was exposed were provided near the winding start and end of the negative electrode. A negative electrode tab made of nickel was welded to the exposed portion near the winding start end.

[0036] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.3 mol / L of ammonium hydroxide in water.

[0037] [Secondary Battery Fabrication] A wound electrode assembly was fabricated by spirally winding a positive electrode and a negative electrode with a 14 μm-thick polyethylene separator between them. Insulating plates were placed on the top and bottom of the electrode assembly, and the electrode assembly was housed in a cylindrical metal outer can with a bottom. The negative electrode tab was welded to the bottom of the outer can, and the positive electrode tab was welded to a sealing member. The exposed portion near the end of the winding contacted the outer can, and the negative electrode was connected to the outer can at both longitudinal ends. After injecting a nonaqueous electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket to fabricate an 18650-type secondary battery. The capacity of this secondary battery was 4.2 Ah.

[0038] [Impact Test] An impact test was performed using the fabricated secondary battery. The secondary battery was charged at a constant current of 0.3 C to 50% SOC under a 25°C environment. Next, a test conforming to the T6 impact test under UN transport test conditions was performed. Specifically, a metal round bar with a diameter of 15.8 mm was placed in the center of the secondary battery, and a 9.1 kg weight was dropped from a height of 70 cm. The test was performed with the end of the first negative electrode mixture layer formed on the inner side of the negative electrode current collector facing the upper side of the secondary battery. The secondary battery was then disassembled, and the separator was checked for damage. Those without damage were judged to be OK. Ten batteries were tested, and the number of batteries judged to be OK was used for evaluation. The weight drop height specified in the T6 impact test was 61 cm.

[0039] Example 2 A secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in the fabrication of the negative electrode, the coating amount of the negative electrode mixture slurry was adjusted so that the thicknesses of the first negative electrode mixture layer and the second negative electrode mixture layer were both changed to 50 μm.

[0040] Example 3 A secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in the fabrication of the negative electrode, the coating amount of the negative electrode mixture slurry was adjusted so that the thicknesses of the first negative electrode mixture layer and the second negative electrode mixture layer were both changed to 40 μm.

[0041] Example 4 A secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the negative electrode was fabricated using SiC with a Si phase content of 40 mass% and the mass ratio of artificial graphite to SiC in the negative electrode active material was changed to 70:30. The discharge capacity per 1 g of this negative electrode active material was 0.9 Ah / g. The capacity of this secondary battery was 3.9 Ah.

[0042] <Comparative Example> A secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in the fabrication of the negative electrode, the mass ratio of artificial graphite to SiC in the negative electrode active material was changed to 90:10, and the coating amount of the negative electrode mixture slurry was adjusted to change the thickness of both the first negative electrode mixture layer and the second negative electrode mixture layer to 80 μm. The discharge capacity per 1 g of this negative electrode active material was 0.6 Ah / g. The capacity of this secondary battery was 3.6 Ah.

[0043]

[0044] As shown in Table 1, none of the secondary batteries of the examples showed any separator damage after the impact test, but 3 out of 10 secondary batteries of the comparative examples showed separator damage. These results show that by setting the thickness of the negative electrode mixture layer to 40 μm or more and 60 μm or less, setting the content of the silicon-containing material in the negative electrode active material to 30 mass% or more and 50 mass% or less, and setting the content of the Si phase in the silicon-containing material to 40 mass% or more and 70 mass% or less, it is possible to achieve high capacity and improve safety.

[0045] REFERENCE SIGNS LIST 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Exterior body, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved portion, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 30 Positive electrode current collector, 32 Positive electrode mixture layer, 40 Negative electrode current collector, 42 Negative electrode mixture layer, 421 First negative electrode mixture layer, 421e Winding end, 422 Second negative electrode mixture layer, 44 Negative electrode current collector exposed portion

Claims

1. A non-aqueous electrolyte secondary battery comprising a wound electrode assembly in which strip-shaped positive and negative electrodes are wound with a separator interposed therebetween, and an exterior body that houses the electrode assembly, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on a surface of the negative electrode current collector, the negative electrode mixture layer has a thickness of 40 μm or more and 60 μm or less, the negative electrode mixture layer contains graphite and a silicon-containing material as negative electrode active materials, the silicon-containing material contains an ion-conducting phase and a Si phase dispersed in the ion-conducting phase, the content of the silicon-containing material in the negative electrode active material is 30% by mass or more and 50% by mass or less, and the content of the Si phase in the silicon-containing material is 40% by mass or more and 70% by mass or less.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ion-conducting phase is an amorphous carbon phase.

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