Non-aqueous electrolyte secondary batteries

Abstract

A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is provided with a positive electrode, a negative electrode and a nonaqueous electrolyte, while being characterized in that: the negative electrode comprises a negative electrode active material that contains an Si-containing material; the Si-containing material contains a first Si-containing material which comprises a silicate phase and silicon particles that are dispersed in the silicate phase, and a second Si-containing material which comprises a carbon phase and silicon particles that are dispersed in the carbon phase; and the difference between the initial charge / discharge efficiency (Efc) of the positive electrode and the initial charge / discharge efficiency (Efa) of the negative electrode, namely (Efc – Efa) satisfies 1% < (Efc – Efa) < 8%.

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Currently, Si-containing materials are attracting attention as materials that can provide high capacity. Si-containing materials are capable of electrochemically absorbing and releasing lithium ions, and are capable of charging and discharging at much higher capacities than graphite materials.

[0003] For example, Patent Document 1 discloses a nonaqueous electrolyte secondary battery that includes a negative electrode containing a Si-containing material and a nonaqueous electrolyte solution containing lithium hexafluorophosphate and having an acid content of 50 ppm or more and 200 ppm or less, and in which the potential of the negative electrode is 0.6 V or more and 1.5 V or less relative to the Li electrode at the end-of-discharge voltage of the battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-27084 Summary of the Invention [Problem to be solved by the invention]

[0005] Although Si-containing materials can increase the capacity of non-aqueous electrolyte secondary batteries, they have a problem of deteriorating charge-discharge cycle characteristics. Although the technology of Patent Document 1 can suppress the deterioration of charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries using Si-containing materials, further improvement is desired.

[0006] Therefore, an object of the present disclosure is to suppress deterioration in charge-discharge cycle characteristics in a non-aqueous electrolyte secondary battery having a negative electrode active material that includes a Si-containing material. [Means for solving the problem]

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode active material containing a Si-containing material. The Si-containing material includes a first Si-containing material having a silicate phase and silicon particles dispersed in the silicate phase, and a second Si-containing material having a carbon phase and silicon particles dispersed in the carbon phase. A difference (Efc - Efa) between an initial charge-discharge efficiency (Efc) of the positive electrode and an initial charge-discharge efficiency (Efa) of the negative electrode satisfies 1% < Efc - Efa < 8%.

Advantages of the Invention

[0008] According to one aspect of the present disclosure, in a non-aqueous electrolyte secondary battery having a negative electrode active material containing a Si-containing material, it is possible to suppress a decrease in charge-discharge cycle characteristics.

Brief Description of the Drawings

[0009] [Figure 1] It is a cross-sectional view of a non-aqueous electrolyte secondary battery which is an example of an embodiment.

Modes for Carrying Out the Invention

[0010] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode active material containing a Si-containing material. The Si-containing material includes a first Si-containing material having a silicate phase and silicon particles dispersed in the silicate phase, and a second Si-containing material having a carbon phase and silicon particles dispersed in the carbon phase. A difference (Efc - Efa) between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode satisfies 1% < Efc - Efa < 8%. According to the non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, a decrease in charge-discharge cycle characteristics can be suppressed. Although the mechanism for achieving the above effect is not clear, the following is speculated. In a non-aqueous electrolyte secondary battery in which Efc - Efa satisfies the range of 1% < Efc - Efa < 8% and includes a first Si-containing material having a silicate phase and silicon particles dispersed in the silicate phase and a second Si-containing material having a carbon phase and silicon particles dispersed in the carbon phase in the negative electrode, in a region where the potential rise at the end of discharge of the negative electrode is large, the second Si-containing material is selectively used for discharge, and the use of the first Si-containing material that is easily deteriorated is restricted. Therefore, it is considered that the progress of deterioration of the first Si-containing material is suppressed and the decrease in charge-discharge cycle characteristics is suppressed. Here, the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode mean the ratio of the initial discharge capacity to the initial charge capacity when a single electrode cell using the positive electrode or the negative electrode as the working electrode and metallic lithium as the counter electrode is charged and discharged under predetermined conditions. The method for manufacturing the single electrode cell and the conditions for charge and discharge are described in the column of the examples.

[0011] Hereinafter, an example of an embodiment will be described in detail with reference to the drawings. Note that the non-aqueous electrolyte secondary battery of the present disclosure is not limited to the embodiments described below. Also, the drawings referred to in the description of the embodiments are schematically illustrated.

[0012] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical case body 16 with a bottom and a sealing member 17 that closes the opening of the case body 16. Note that, instead of the wound electrode assembly 14, other types of electrode bodies may be used, such as a laminated electrode body formed by alternately stacking positive and negative electrodes with separators interposed therebetween. Examples of the battery case 15 include cylindrical, prismatic, coin-shaped, or button-shaped metal outer cans, and pouch outer cans formed by laminating a resin sheet and a metal sheet.

[0013] Case body 16 is, for example, a cylindrical metal outer can with a bottom. A gasket 28 is provided between case body 16 and sealing body 17 to ensure airtightness inside the battery. Case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports sealing body 17. Protruding portion 22 is preferably formed in an annular shape along the circumferential direction of case body 16, and supports sealing body 17 on its upper surface.

[0014] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to one another at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the nonaqueous electrolyte secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0015] 1 , a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in an insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside an insulating plate 19 and extends toward the bottom of the case body 16. The positive electrode lead 20 is connected to the underside of a filter 23, which is the bottom plate of the sealing body 17, by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the case body 16 by welding or the like, and the case body 16 serves as the negative electrode terminal.

[0016] Each component of the nonaqueous electrolyte secondary battery 10 will be described in detail below.

[0017] [Negative electrode] The negative electrode 12 has a negative electrode current collector made of, for example, a metal foil and a negative electrode composite layer formed on the current collector. The negative electrode current collector may be, for example, a foil of a metal such as copper that is stable within the potential range of the negative electrode, or a film with such a metal disposed on the surface layer. The negative electrode composite layer contains a negative electrode active material including a Si-containing material. The negative electrode composite layer preferably contains a binder, a conductive material, etc.

[0018] The negative electrode 12 can be produced, for example, by preparing a negative electrode composite slurry containing a negative electrode active material, a binder, a conductive material, and the like, applying this negative electrode composite slurry onto a negative electrode current collector, drying it to form a negative electrode composite layer, and then performing a compression step in which the negative electrode composite layer is compressed using a rolling roller or the like.

[0019] The Si-containing material contained in the negative electrode mixture layer includes a first Si-containing material including a silicate phase and silicon particles dispersed in the silicate phase, and a second Si-containing material having a carbon phase and silicon particles dispersed in the carbon phase.

[0020] A suitable first Si-containing material has a sea-island structure in which fine silicon particles are uniformly dispersed in an amorphous silicate phase, and is represented by the general formula SiO x(0.5 ≦ x ≦ 1.6) includes Si-containing materials and the like. The content of silicon particles is preferably 30% by mass or more and 80% by mass or less, more preferably 35% by mass or more and 75% by mass or less, and even more preferably 55% by mass or more and 70% by mass or less, based on the total mass of the first Si-containing material, for example, in terms of achieving high capacity of the battery. Also, the average particle size of the silicon particles is generally 500 nm or less before charge and discharge, preferably 200 nm or less, and more preferably 50 nm or less. After charge and discharge, it is preferably 400 nm or less, and more preferably 50 nm or less. The average particle size of the silicon particles is measured by observing the particle cross-section of the first Si-containing material using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and specifically, it is obtained as the average value of the longest diameters of 100 silicon particles.

[0021] The silicate phase of the first Si-containing material preferably contains at least one of an alkali metal element and an alkaline earth metal element, particularly preferably contains a lithium element, for example, in terms of improving lithium ion conductivity. Also, the silicate phase of the first Si-containing material preferably contains lithium silicate represented by the general formula Li 2z SiO (2+z) (0 < z < 2).

[0022] A suitable second Si-containing material preferably does not contain crystalline carbon in its carbon phase, for example, in terms of suppressing the degradation of charge-discharge cycle characteristics of the battery or achieving high capacity of the battery. The content of silicon particles in the second Si-containing material is preferably 30% by mass or more and 80% by mass or less, more preferably 35% by mass or more and 75% by mass or less, and even more preferably 55% by mass or more and 70% by mass or less, based on the total mass of the second Si-containing material, for example, in terms of achieving high capacity of the battery. Also, the average particle size of the silicon particles is generally 500 nm or less before charge and discharge, preferably 200 nm or less, and more preferably 100 nm or less. After charge and discharge, it is preferably 400 nm or less, and more preferably 100 nm or less.

[0023] A conductive layer made of a highly conductive material may be formed on the particle surfaces of the first Si-containing material and the second Si-containing material. An example of a suitable conductive layer is a carbon coating made of a carbon material. The carbon coating may be made of, for example, carbon black, acetylene black, ketjen black, graphite, or a mixture of two or more of these. Examples of methods for carbon-coating the particle surfaces of the Si-containing material include a CVD method using acetylene, methane, or the like, and a method of mixing particles of the Si-containing material with coal pitch, petroleum pitch, phenolic resin, or the like and then heat-treating the mixture. Alternatively, the carbon coating may be formed by adhering carbon powder such as carbon black to the particle surfaces using a binder.

[0024] The mass ratio of the second Si-containing material to the first Si-containing material (mass of the second Si-containing material / mass of the first Si-containing material) is preferably 0.2 or more and 20 or less, and more preferably 2 or more and 10 or less, for example, in order to suppress deterioration of charge-discharge cycle characteristics.

[0025] The total content of the Si-containing material is preferably 5% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less, relative to the total mass of the negative electrode active material, for example, from the viewpoint of suppressing a decrease in charge-discharge cycle characteristics and increasing the capacity of the battery.

[0026] The negative electrode active material may contain, in addition to the aforementioned Si-containing material, a known material capable of absorbing and releasing lithium ions. As a material to be contained in addition to the aforementioned Si-containing material, for example, a carbon material is preferred, and graphite particles are particularly preferred, in terms of suppressing deterioration of charge-discharge cycle characteristics. Graphite particles may be natural graphite, artificial graphite, or the like, but are not particularly limited. The interplanar spacing (d 002) is, for example, preferably 0.3354 nm or more, more preferably 0.3357 nm or more, and preferably less than 0.340 nm, more preferably 0.338 nm or less. The crystallite size (Lc(002)) of the graphite particles determined by X-ray diffraction is, for example, preferably 5 nm or more, more preferably 10 nm or more, and preferably 300 nm or less, more preferably 200 nm or less. The interplanar spacing (d 002 When the surface roughness (Tc) and the crystallite size (Lc(002)) satisfy the above ranges, the battery capacity of the secondary battery tends to be larger than when the surface roughness (Tc) and the crystallite size (Lc(002)) do not satisfy the above ranges.

[0027] The content of the graphite particles is preferably 80% by mass or more and 90% by mass or less relative to the total mass of the negative electrode active material, for example, from the viewpoint of increasing the capacity of the secondary battery and improving the charge / discharge cycle characteristics.

[0028] Examples of binders include fluorine-based resins, PAN, polyimide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or salts thereof, polyacrylic acid (PAA) or salts thereof (PAA-Na, PAA-K, etc., or partially neutralized salts), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0029] Examples of conductive materials include carbon particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphite, etc. These may be used alone or in combination of two or more.

[0030] [Positive electrode] The positive electrode 11 is composed of a positive electrode current collector, such as a metal foil, and a positive electrode composite layer formed on the positive electrode current collector. The positive electrode current collector can be a foil of a metal, such as aluminum, that is stable within the potential range of the positive electrode, or a film with such a metal disposed on its surface. The positive electrode composite layer contains, for example, a positive electrode active material, a binder, a conductive material, etc.

[0031] The positive electrode 11 can be produced, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a binder, a conductive material, etc. onto a positive electrode current collector, drying the slurry to form a positive electrode composite layer, and then performing a compression step in which the positive electrode composite layer is compressed using a rolling roller or the like.

[0032] Examples of the positive electrode active material include lithium transition metal composite oxides. Metal elements contained in the lithium transition metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, it is preferable to contain at least one of Ni, Co, and Mn. An example of a suitable lithium transition metal composite oxide is a composite oxide represented by the general formula LiMO2 (wherein M is Ni and X, X is a metal element other than Ni, and the proportion of Ni is 50 mol% to 95 mol% based on the total number of moles of the metal elements excluding Li). Examples of X in the formula include Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W.

[0033] Examples of conductive materials include carbon particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphite, etc. These may be used alone or in combination of two or more.

[0034] The binding material includes, for example, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. These may be used alone or in combination of two or more kinds.

[0035] [Regarding the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode] In this embodiment, the difference (Efc - Efa) between the initial charge-discharge efficiency (Efc) of the positive electrode 11 and the initial charge-discharge efficiency (Efa) of the negative electrode 12 is 1% < Efc - Efa < 8%, preferably 2% ≤ Efc - Efa ≤ 6%. Since Efc - Efa satisfies the range of 1% < Efc - Efa < 8% and the negative electrode 12 contains the first Si-containing material and the second Si-containing material, in the region where the potential rise at the end of discharge of the negative electrode 12 is large, the second Si-containing material is selectively used for discharge, and the use of the first Si-containing material that is easily deteriorated is restricted. Therefore, the progress of deterioration of the first Si-containing material is suppressed, and it is considered that the decrease in charge-discharge cycle characteristics is suppressed. Note that when Efc - Efa is 1 or less, the effect of suppressing the decrease in charge-discharge cycle characteristics cannot be obtained. This is considered to be because elution of Ni, Co, Al, Mn, etc. in the positive electrode occurs in the region where the potential drop at the end of discharge of the positive electrode 11 is large, and they are deposited on the negative electrode plate, thereby promoting negative electrode deterioration. Also, when Efc - Efa is 8 or more, the effect of suppressing the decrease in charge-discharge cycle characteristics cannot be obtained. This is considered to be because both the first Si-containing material and the second Si-containing material are used for discharge in the region where the potential rise at the end of discharge of the negative electrode 12 is large, and the deterioration of the first Si-containing material progresses.

[0036] In this embodiment, in order to satisfy the range of 1% < Efc - Efa < 8%, for example, it is better to adjust the initial charge - discharge efficiency of the negative electrode 12 rather than adjusting the initial charge - discharge efficiency of the positive electrode 11. The adjustment of the initial charge - discharge efficiency of the negative electrode 12 is performed, for example, by adjusting the content ratio, composition, etc. of the first Si - containing material and the second Si - containing material. The initial charge - discharge efficiency of the positive electrode 11 and the initial charge - discharge efficiency of the negative electrode 12 are preferably 85% or more, respectively, in terms of suppressing the decrease in charge - discharge cycle characteristics.

[0037] [Separator] For the separator 13, for example, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non - woven fabrics, etc. As the material of the separator, olefin - based resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin - based resin. Also, a multilayer separator including a polyethylene layer and a polypropylene layer may be used, or a separator with a material such as an aramid - based resin or ceramic coated on the surface of the separator may be used.

[0038] [Non - aqueous electrolyte] The non - aqueous electrolyte includes a non - aqueous solvent and an electrolyte salt dissolved in the non - aqueous solvent. The non - aqueous electrolyte is not limited to a liquid electrolyte (electrolyte solution), and may be a solid electrolyte using a gel - like polymer or the like. For the non - aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non - aqueous solvent may contain a halogen - substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine.

[0039] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, and γ-butyrolactone.

[0040] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methylphenyl ether, and the like. and chain ethers such as ethyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl.

[0041] As the halogen-substituted compound, it is preferable to use fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylates such as methyl fluoropropionate (FMP), and the like.

[0042] The electrolyte salt is preferably a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 、LiCl、LiBr、LiI、lithium chloroborane, lithium lower aliphatic carboxylic acid, borate salts such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 1 or more}, etc. The lithium salt may be used alone or in combination of multiple kinds. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the solvent.

Examples

[0043] Hereinafter, the present disclosure will be further described by examples, but the present disclosure is not limited to these examples.

[0044] <Example 1> [Fabrication of negative electrode] Graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 94.2:2.8:3. This mixture was used as the negative electrode active material. These materials were then mixed in a mass ratio of 100:1:1 (negative electrode active material: carboxymethyl cellulose-sodium (CMC-Na): styrene-butadiene copolymer rubber (SBR)) and optionally mixed with water to prepare a negative electrode composite slurry. This slurry was applied to both sides of a copper foil current collector, the coating film was dried, and then compressed with a rolling roller and dried to produce a negative electrode with a negative electrode composite layer formed on both sides of the negative electrode current collector.

[0045] [Preparation of positive electrode] The composition is LiNi 0.88 Co 0.09 Al 0.03 The positive electrode active material was a lithium transition metal composite oxide (O2), which was mixed with acetylene black as the conductive material and polyvinylidene fluoride as the binder in a mass ratio of 100:1:1, followed by the addition of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite slurry. This slurry was applied to both sides of an aluminum foil, the coating was dried, and then rolled with a rolling roller to produce a positive electrode with a positive electrode composite layer formed on both sides of the positive electrode current collector.

[0046] [Preparation of non-aqueous electrolyte] LiPF6 was dissolved at a concentration of 1.4 mol / L in a non-aqueous solvent made by mixing ethylene carbonate (EC), methyl ethylene carbonate (MEC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75, and then 3 mass% of vinylene carbonate (VC) and 0.5 mass% of 1,6-diisocyanate hexane were added to prepare a non-aqueous electrolyte.

[0047] [Preparation of a unipolar cell] The negative electrode was punched to a predetermined size, and the negative electrode composite layer on one side was peeled off. A Ni lead was crimped onto this negative electrode, forming a working electrode. A Ni lead was crimped onto metallic lithium that was sufficiently larger than the negative electrode, forming a counter electrode. The working electrode and counter electrode were opposed to each other via a polyethylene separator to form an electrode assembly. This electrode assembly was covered with an aluminum laminate bag, and the nonaqueous electrolyte was poured into the aluminum laminate bag. The opening of the aluminum laminate bag was then sealed by heat welding while reducing the pressure, forming a single-electrode cell using the negative electrode as the working electrode. Similarly, a single-electrode cell using the positive electrode as the working electrode was also formed.

[0048] A single-electrode cell using the negative electrode as the working electrode was charged at a constant current of 0.1 C at a temperature of 25°C until the battery voltage reached 0.005 V, then at a constant current of 0.05 C until the battery voltage reached 0.005 V, and then at a constant current of 0.01 C until the battery voltage reached 0.005 V. The cell was then discharged at a constant current of 0.1 C until the battery voltage reached 1 V, then at a constant current of 0.05 C until the battery voltage reached 1 V, and finally at a constant current of 0.01 C until the battery voltage reached 1 V. The initial charge and discharge capacities were measured, and the initial charge / discharge efficiency was calculated using the following formula: This was the initial charge / discharge efficiency (Efa) of the negative electrode. Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) x 100

[0049] A single-electrode cell using the positive electrode as the working electrode was charged at a constant current of 0.1 C at a temperature of 25°C until the battery voltage reached 4.2 V, and then charged at a constant voltage until the current value at 4.2 V reached 0.01 C. The cell was then discharged at a constant current of 0.1 C until the battery voltage reached 2.5 V. The initial charge and discharge capacities were measured, and the initial charge and discharge efficiency was calculated using the above formula. This was defined as the initial charge and discharge efficiency (Efc) of the positive electrode.

[0050] In Example 1, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated to be 2.7%.

[0051] [Fabrication of non-aqueous electrolyte secondary battery] (1) An aluminum lead was welded to the positive electrode, and a nickel-copper-nickel lead was welded to the negative electrode. Then, a polyethylene separator was placed between the positive electrode and the negative electrode, and the resulting structure was wound to prepare a wound electrode body. (2) Insulating plates were placed above and below the electrode body, the negative electrode lead was welded to the case body, and the positive electrode lead was welded to the sealing member, and the electrode body was housed within the case body. (3) After the non-aqueous electrolyte was injected into the case body under reduced pressure, the open end of the case body was crimped to a sealing member via a gasket, completing a non-aqueous electrolyte secondary battery.

[0052] [Charge / discharge test] The nonaqueous electrolyte secondary battery was charged at a constant current of 0.3 C in a temperature environment of 25° C. until the battery voltage reached 4.2 V, and then charged at a constant voltage at 4.2 V until the current value reached 0.02 C. Thereafter, the battery was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This cycle was repeated 100 times, and the capacity retention rate after 100 cycles was calculated using the following formula. Capacity retention rate (%) = (discharge capacity at 100th cycle / discharge capacity at 1st cycle) x 100

[0053] <Comparative Example 1> In preparing the negative electrode, graphite particles and a first Si-containing material having silicon particles dispersed in a silicate phase were mixed at a mass ratio of 94:6. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 1, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 2%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 1 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0054] Table 1 summarizes the results of the capacity retention rates in Example 1 and Comparative Example 1. The capacity retention rate values ​​are shown as relative values ​​to the capacity retention rate in Example 1, which is set to 100% (reference), and the capacity retention rate in Comparative Example 1. Note that a larger capacity retention rate value indicates that the deterioration of the charge-discharge cycle characteristics is more suppressed than a smaller capacity retention rate value.

[0055] [Table 1]

[0056] As shown in the results in Table 1, Example 1 and Comparative Example 1 have the same Efc-Efa of 2%, but when the capacity retention rate of Example 1 having both the first Si-containing material and the second Si-containing material is taken as 100%, the capacity retention rate of Comparative Example 1 having only the first Si-containing material is 98.7%. Therefore, it can be said that Example 1 suppressed the deterioration of the charge-discharge cycle characteristics compared to Comparative Example 1.

[0057] <Example 2> In preparing the negative electrode, graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 92.7:4.3:3. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Example 2, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 4%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Example 2 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0058] <Comparative Example 2> In preparing the negative electrode, graphite particles and a first Si-containing material having silicon particles dispersed in a silicate phase were mixed in a mass ratio of 92.5:7.5. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 2, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 4%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 2 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0059] Table 2 summarizes the results of the capacity retention rates in Example 2 and Comparative Example 2. The capacity retention rate values ​​are shown as relative values, with the capacity retention rate of Example 2 set as 100% (reference) and the capacity retention rate of Comparative Example 2.

[0060] [Table 2]

[0061] As shown in the results in Table 2, Example 2 and Comparative Example 2 had the same Efc-Efa of 4%, but when the capacity retention rate of Example 2, which had both the first Si-containing material and the second Si-containing material, was set to 100%, the capacity retention rate of Comparative Example 2, which had only the first Si-containing material, was 98.5%. Therefore, it can be said that Example 2 suppressed the deterioration of the charge-discharge cycle characteristics compared to Comparative Example 2.

[0062] Example 3 In preparing the negative electrode, graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 90.2:6.8:3. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Example 3, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 6%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Example 3 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0063] <Comparative Example 3> In preparing the negative electrode, graphite particles and a first Si-containing material having silicon particles dispersed in a silicate phase were mixed at a mass ratio of 90:10. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 3, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 6%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 3 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0064] Table 3 summarizes the results of the capacity retention rates in Example 3 and Comparative Example 3. The capacity retention rate values ​​are shown as relative values, with the capacity retention rate of Example 3 set as 100% (reference) and the capacity retention rate of Comparative Example 3.

[0065] [Table 3]

[0066] As shown in the results in Table 3, Example 3 and Comparative Example 3 have the same Efc-Efa of 6%, but when the capacity retention rate of Example 3 having both the first Si-containing material and the second Si-containing material is set to 100%, the capacity retention rate of Comparative Example 3 having only the first Si-containing material is 98.3%. Therefore, it can be said that Example 3 suppressed the deterioration of the charge-discharge cycle characteristics compared to Comparative Example 3.

[0067] Example 4 In preparing the negative electrode, graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 93.2:1.5:5.3. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Example 4, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 3%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Example 4 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0068] <Comparative Example 4> In preparing the negative electrode, graphite particles and a second Si-containing material having silicon particles dispersed within a carbon phase were mixed at a mass ratio of 94:6. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 4, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 3%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 4 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0069] Table 4 summarizes the results of the capacity retention rates in Example 4 and Comparative Example 4. The capacity retention rate values ​​are shown as relative values, with the capacity retention rate of Example 4 set as 100% (reference) and the capacity retention rate of Comparative Example 4.

[0070] [Table 4]

[0071] As shown in the results in Table 4, Example 4 and Comparative Example 4 had the same Efc-Efa of 6%, but when the capacity retention rate of Example 4 having both the first Si-containing material and the second Si-containing material was taken as 100%, the capacity retention rate of Comparative Example 4 having only the second Si-containing material was 98.0%. Therefore, it can be said that Example 4 suppressed the deterioration of the charge-discharge cycle characteristics compared to Comparative Example 4.

[0072] <Example 5> In preparing the negative electrode, graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 90.7:4:5.3. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Example 5, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 6%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Example 4 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0073] <Comparative Example 5> In preparing the negative electrode, graphite particles and a first Si-containing material having silicon particles dispersed in a silicate phase were mixed at a mass ratio of 90:10. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 5, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 6%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 5 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0074] Table 5 summarizes the results of the capacity retention rates in Example 5 and Comparative Example 5. The capacity retention rate values ​​are shown as relative values, with the capacity retention rate of Example 5 set as 100% (reference) and the capacity retention rate of Comparative Example 5.

[0075] [Table 5]

[0076] As shown in the results in Table 5, Example 5 and Comparative Example 5 had the same Efc-Efa of 6%, but when the capacity retention rate of Example 5 having both the first Si-containing material and the second Si-containing material was taken as 100%, the capacity retention rate of Comparative Example 5 having only the first Si-containing material was 98.1%. Therefore, it can be said that Example 5 suppressed the deterioration of the charge-discharge cycle characteristics compared to Comparative Example 5.

[0077] <Comparative Example 6> In preparing the negative electrode, graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 97.5:0.5:2. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 6, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 0%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 6 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0078] <Comparative Example 7> In preparing the negative electrode, graphite particles and a first Si-containing material having silicon particles dispersed in a silicate phase were mixed at a mass ratio of 94:6. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 7, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 0%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 7 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0079] Table 6 summarizes the results of the capacity retention rates in Comparative Examples 6 and 7. The capacity retention rate values ​​are shown as relative values, with the capacity retention rate of Comparative Example 7 being set as 100% (reference).

[0080] [Table 6]

[0081] As shown in the results in Table 6, when Efc-Efa was 0%, the capacity retention rate of Comparative Example 6 having both the first Si-containing material and the second Si-containing material was almost the same as that of Comparative Example 7 having only the first Si-containing material, and the effect of suppressing the deterioration of charge-discharge cycle characteristics was not obtained.

[0082] <Comparative Example 8> In preparing the negative electrode, graphite particles, a first Si-containing material having silicon particles dispersed in a silicate phase, and a second Si-containing material having silicon particles dispersed in a carbon phase were mixed in a mass ratio of 91:7:2. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 8, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 8%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 8 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0083] <Comparative Example 9> In preparing the negative electrode, graphite particles and a first Si-containing material having silicon particles dispersed in a silicate phase were mixed at a mass ratio of 92:8. A single-electrode cell was prepared using the negative electrode as the working electrode in the same manner as in Example 1, except that this mixture was used as the negative electrode active material, and the initial charge-discharge efficiency (Efa) of the negative electrode was calculated. In Comparative Example 9, the difference between the initial charge-discharge efficiency (Efc) of the positive electrode and the initial charge-discharge efficiency (Efa) of the negative electrode was 8%. Furthermore, a nonaqueous electrolyte secondary battery was prepared using the negative electrode prepared in Comparative Example 9 in the same manner as in Example 1, and the capacity retention rate after 100 cycles was calculated.

[0084] Table 7 summarizes the results of the capacity retention rates in Comparative Examples 8 and 9. The capacity retention rate values ​​are shown as relative values, with the capacity retention rate of Comparative Example 8 set as 100% (reference), and the capacity retention rate of Comparative Example 9.

[0085] [Table 7]

[0086] As shown in the results in Table 7, when Efc-Efa was 8%, the capacity retention rate of Comparative Example 8 having both the first Si-containing material and the second Si-containing material was almost the same as that of Comparative Example 9 having only the first Si-containing material, and the effect of suppressing the deterioration of charge-discharge cycle characteristics was not obtained. [Explanation of symbols]

[0087] 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 battery case, 16 case body, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 protruding portion, 23 filter, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket.

Claims

1. A positive electrode, a negative electrode, and a non-aqueous electrolyte are provided. the negative electrode has a negative electrode active material including a Si-containing material, the Si-containing material includes a first Si-containing material having a silicate phase and silicon particles dispersed within the silicate phase, and a second Si-containing material having a carbon phase and silicon particles dispersed within the carbon phase; a difference (Efc-Efa) between an initial charge-discharge efficiency (Efc) of the positive electrode and an initial charge-discharge efficiency (Efa) of the negative electrode satisfying 1%<Efc-Efa<8%.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a mass ratio of the second Si-containing material to the first Si-containing material (mass of the second Si-containing material / mass of the first Si-containing material) is 0.2 or more and 20 or less.

3. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the Si-containing material is 5% by mass or more and 20% by mass or less with respect to the total mass of the negative electrode active material.

4. 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the carbon phase of the second Si-containing material does not contain crystalline carbon.

5. 5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the silicate phase of the first Si-containing material contains at least one element of an alkali metal element or an alkaline earth metal element.

6. The silicate phase of the first Si-containing material has the general formula Li ２ｚ SiO （２＋ｚ） 6. The nonaqueous electrolyte secondary battery according to claim 1, comprising a lithium silicate represented by (0<z<2).

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