Non-aqueous electrolyte and non-aqueous electrolyte secondary battery

Abstract

To provide a nonaqueous electrolyte and a nonaqueous electrolyte secondary battery which hardly cause expansion of a battery cell.SOLUTION: The nonaqueous electrolyte is used for a nonaqueous electrolyte secondary battery in which a negative electrode contains at least one of compounds of silicon, germanium, and tin as negative electrode active material particles. The nonaqueous electrolyte contains one or more silane compounds of formulae (1) and (2). (R1 is a C2-20 alkenyl or alkynyl group; R2 is a C1-20 alkyl group; X is a C1-20 alkylene group or a C2-20 alkenylene or alkynylene group; l is an integer of 1-3; and m is an integer of 1-2.)SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery.

Background Art

[0002] In recent years, small electronic devices typified by mobile terminals have become widely popular, and further miniaturization, weight reduction, and long life are strongly demanded. In response to such market demands, development of secondary batteries that are particularly small and lightweight and can obtain a high energy density has been promoted. This secondary battery is being considered for application not only to small electronic devices but also to large electronic devices typified by automobiles and power storage systems typified by houses.

[0003] Among them, lithium-ion secondary batteries are easy to miniaturize and increase in capacity, and can obtain a higher energy density than lead batteries and nickel-cadmium batteries, and thus are highly expected.

[0004] The above lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution together with a separator, and the negative electrode contains a negative electrode active material involved in charge and discharge reactions.

[0005] As this negative electrode active material, carbon-based active materials are widely used. On the other hand, further improvement in battery capacity is required from recent market demands. In order to improve the battery capacity, use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times larger than the theoretical capacity of graphite (372 mAh / g), so a significant improvement in battery capacity can be expected. Development of silicon-based materials as negative electrode active materials has been studied not only for elemental silicon but also for compounds typified by alloys and oxides. In addition, the shape of the negative electrode active material has been studied from a standard coating type for carbon-based active materials to an integrated type that is directly deposited on a current collector.

[0006] However, when silicon is used as the main raw material for the negative electrode active material, the negative electrode active material expands and contracts during charge and discharge, so it is prone to cracking mainly in the vicinity of the surface layer of the negative electrode active material. In addition, ionic substances are generated inside the negative electrode active material, making the negative electrode active material prone to cracking. When the surface layer of the negative electrode active material cracks, a new surface is generated, increasing the reaction area of the negative electrode active material. At this time, the decomposition reaction of the electrolyte occurs on the new surface, and a film, which is a decomposition product of the electrolyte, is formed on the new surface, consuming the electrolyte and making the cycle characteristics prone to deterioration.

[0007] So far, various studies have been conducted on negative electrode materials and electrode configurations for lithium-ion secondary batteries using silicon materials as the main component in order to improve the initial battery efficiency and cycle characteristics.

[0008] Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using the vapor phase method (see, for example, Patent Document 1). In addition, in order to obtain a high battery capacity and safety, a carbon material (electronic conductive material) is provided on the surface layer of silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve the cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer with a high oxygen ratio near the current collector is formed (see, for example, Patent Document 3). Also, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, and it is formed so that the average oxygen content is 40 at% or less and the oxygen content increases in the vicinity of the current collector (see, for example, Patent Document 4).

[0009] There is also a report of using fluoroethylene carbonate (FEC) as an electrolyte additive to suppress the decomposition reaction of the electrolyte accompanying the charge and discharge of the silicon active material (see, for example, Patent Document 5). Since the fluorine-based electrolyte forms a stable Solid Electrolyte Interphase (SEI) film on the silicon surface, it becomes possible to suppress the deterioration of the silicon material.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0011] As described above, in recent years, small electronic devices typified by mobile terminals have been promoted to have higher performance and more functions, and the lithium-ion secondary battery, which is the main power source thereof, is required to have an increased battery capacity. As one method for solving this problem, the development of a lithium-ion secondary battery having a negative electrode made mainly of a silicon material is desired. In addition, a lithium-ion secondary battery using a silicon material is desired to have cycle characteristics that are as close as possible to those of a lithium-ion secondary battery using a carbon-based active material. Therefore, a fluorine-based additive has been developed, and the battery characteristics tended to be improved. However, by repeating charge and discharge, the fluorine-based solvent is consumed, the amount of electrolyte decomposition products deposited on the surface of the silicon material increases, and the reversibly moving lithium is deactivated in a form incorporated into the decomposition products. As a result, not only the battery cycle characteristics but also the expansion of the battery cell due to the swelling phenomenon were insufficient compared to the battery characteristics using a carbon-based active material.

[0012] The present invention has been made in view of the above problems, and an object thereof is to provide a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery in which a battery cell is less likely to expand even when a negative electrode material such as a silicon material is used.

Means for Solving the Problems

[0013] In order to solve the above problems, the present invention provides a non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery in which the negative electrode contains at least one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles, and the non-aqueous electrolyte contains at least one silane compound selected from silane compounds represented by the following general formulas (1) to (5).

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0014] Such a silane compound has high electron acceptability and excellent reductive decomposability on the negative electrode surface, and thus has the characteristic of forming a film (SEI film) on the negative electrode surface. Therefore, when the non-aqueous electrolyte of the present invention is used in a non-aqueous electrolyte secondary battery including a negative electrode containing at least one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles, battery swelling can be suppressed.

[0015] At this time, it is preferable that the energy level of the lowest unoccupied molecular orbital (LUMO) of the silane compound is -0.40 eV or less.

[0016] With such energy levels, the silane compound is likely to undergo reductive decomposition.

[0017] Moreover, the energy level of the highest occupied molecular orbital (HOMO) of the silane compound is preferably -8.8 eV or higher.

[0018] With such energy levels, the reactivity after reductive decomposition, particularly the radical reactivity, is improved, and a high-quality film (SEI film) is easily obtained.

[0019] Moreover, the content of the silane compound contained in the non-aqueous electrolyte is preferably 0.1 mass% to 5.0 mass%.

[0020] With such a content, a sufficient film (SEI film) is easily formed, and the swelling of the battery cell is easily suppressed. Also, it is easy to prevent the increase in resistance due to excessive film (SEI film) formation.

[0021] Moreover, in the non-aqueous electrolyte of the present invention, the negative electrode active material particles in the negative electrode contain silicon oxide particles coated with a carbon layer, and the silicon oxide particles contain Li 2 SiO 3 and the Li 2 SiO 3 can be crystalline.

[0022] The non-aqueous electrolyte of the present invention can be particularly preferably used when the negative electrode active material in the negative electrode is such.

[0023] At this time, the negative electrode active material particles have a peak caused by the Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα rays before charging and discharging the negative electrode active material particles, the crystallite size corresponding to the crystal plane is 5.0 nm or less, and the ratio A / B of the intensity A of the peak caused by the Si(111) crystal plane to the intensity B of the peak caused by the Li 2 SiO 3 (111) crystal plane is represented by the following formula (6) 0.4 ≦ A / B ≦ 1.0 ···(6) It is preferable to satisfy

[0024] Such negative electrode active material particles can exhibit high slurry stability without impairing the ease of conversion from Li 2 SiO 3 to Li 4 SiO 4 Therefore, the non-aqueous electrolyte of the present invention can be suitably used for a non-aqueous electrolyte secondary battery using a negative electrode containing such negative electrode active material particles.

[0025] Further, in the non-aqueous electrolyte of the present invention, when the potential of Li / Li + is taken as a reference of 0 V, it is preferable that the silane compound decomposes in the range of 0.23 V or more to form a film on the negative electrode.

[0026] Since such a silane compound decomposes at a high potential of 0.23 V or more and has a feature of forming a film (SEI film) on the surface of the negative electrode, it can be suitably used for a non-aqueous electrolyte secondary battery containing at least any one of a silicon compound, a germanium compound, and a tin compound as a negative electrode active material particle having a capacity on the high potential side.

[0027] Further, it is preferable that the film formed by the decomposition of the silane compound is in a stable state in the range of 0.70 V or more when the potential of Li / Li + is taken as a reference of 0 V.

[0028] In this way, if the film, which is a decomposition product of the silane compound, is stable without decomposing in the range of 0.70 V or more, an effect of suppressing the swelling of the battery cell can be easily obtained even when a negative electrode having a capacity on the high potential side is used.

[0029] Further, the present invention provides a non-aqueous electrolyte secondary battery characterized by comprising the above non-aqueous electrolyte together with a positive electrode and a negative electrode.

[0030] Since such a non-aqueous electrolyte secondary battery includes the non-aqueous electrolyte of the present invention, it is possible to suppress battery swelling.

Advantages of the Invention

[0031] The silane compounds represented by general formulas (1) to (5) contained in the non-aqueous electrolyte of the present invention have high electron-accepting properties and excellent reductive decomposability on the surface of the negative electrode, and thus have the characteristic of forming a film (SEI film) on the surface of the negative electrode. Therefore, when the non-aqueous electrolyte of the present invention is used in a non-aqueous electrolyte secondary battery including a negative electrode containing at least one of a silicon compound, a germanium compound, and a tin compound as a negative electrode active material particle, battery swelling can be suppressed.

Embodiments for Carrying Out the Invention

[0032] As described above, there has been a demand for a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery in which the battery cell is less likely to expand even when a negative electrode material such as a silicon material is used.

[0033] As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by introducing at least one alkenyl group or alkynyl group into a silane compound containing at least two or more silicon atoms, and have completed the present invention.

[0034] That is, the present invention is a non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery in which the negative electrode contains at least one of a silicon compound, a germanium compound, and a tin compound as a negative electrode active material particle, and the non-aqueous electrolyte contains at least one silane compound selected from the silane compounds represented by the following general formulas (1) to (5).

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0035] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

[0036] <Silane compound> As described above, the non-aqueous electrolyte of the present invention contains a silane compound selected from silane compounds represented by the following general formulas (1) to (5). [Chemical formula] [Chemical formula] [Chemical formula] [Chemical formula] [Chemical formula]

[0037] The non-aqueous electrolyte of the present invention contains a silane compound having 2 to 4 silicon atoms in the compound, as shown in general formulas (1) to (5). When the number of silicon atoms contained in the compound is 2 to 4, the molecular weight of the film (SEI film) after reductive decomposition tends to be high, and a film (SEI film) excellent in strength and decomposition resistance is easily obtained. On the other hand, when the number of silicon atoms contained in the compound is 5 or more, the solubility in the non-aqueous electrolyte decreases.

[0038] In general formulas (1) to (5), R 1 is an alkenyl group or an alkynyl group having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 2 to 5 carbon atoms.

[0039] R 1 Specific examples of the alkenyl group of R include linear alkenyl groups such as vinyl group, n-propenyl group, n-butenyl group, n-pentenyl group, n-hexenyl group, n-heptenyl group, n-octenyl group, n-nonenyl group, n-decenyl group, n-undecenyl group, n-dodecenyl group; branched alkenyl groups such as isopropenyl group, isobutenyl group, isopentenyl group, isohexenyl group, isoheptenyl group, isooctenyl group, isononyl group, isodecenyl group, isoundecyl group.

[0040] Among these, from the viewpoint of improving the reductive decomposability of the silane compound, promoting the polymerization reaction between silane compounds or between a silane compound and another additive, and improving the strength and decomposition resistance of the film (SEI film), a vinyl group and an n-propenyl group are preferred.

[0041] R 1 Specific examples of the alkynyl group of R include linear alkynyl groups such as ethynyl group, 1-propynyl group, 1-butynyl group, 1-pentynyl group, 1-hexynyl group, 1-heptynyl group, 1-octynyl group, 1-nonynyl group, 1-decynyl group, 1-undecynyl group, 1-dodecynyl group; branched alkynyl groups such as 3-methyl-1-butynyl group, 3,3-dimethyl-1-butynyl group, 3-methyl-1-pentynyl group, 4-methyl-1-pentynyl group, 3,3-dimethyl-1-pentynyl group, 3,4-methyl-1-pentynyl group, 4,4-dimethyl-1-pentynyl group.

[0042] Among these, from the viewpoint of improving the reductive decomposability of the silane compound, promoting the polymerization reaction between silane compounds or between a silane compound and another additive, and improving the strength and decomposition resistance of the film (SEI film), an ethynyl group, a 1-propynyl group, and a 1-butynyl group are preferred.

[0043] In general formulas (1) to (5), R 2 is an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 4 carbon atoms.

[0044] R 2 Specific examples of the alkyl group of R include linear alkyl groups such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group; branched alkyl groups such as isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group, isohexyl group, isoheptyl group, isooctyl group, tert-octyl group, isononyl group, isodecyl group, isoundecyl group.

[0045] Among these, from the viewpoint that there is less steric hindrance and the reaction between silane compounds proceeds more easily, a methyl group is preferred.

[0046] In general formulas (1) to (5), X is an alkylene group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 4 carbon atoms, or an alkenylene group or alkynylene group having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 2 to 4 carbon atoms.

[0047] Specific examples of the alkylene group of X include linear alkylene groups such as methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group; branched-chain alkylene groups such as propylene group, isobutylene group, isopentylene group.

[0048] Among these, from the viewpoint that the proportion of silicon in the film (SEI) increases and a high-quality film (SEI film) is easily obtained, a methylene group, an ethylene group, and a trimethylene group are preferred.

[0049] Specific examples of the alkenylene group of X include vinylene group, 1-propenylene group, 2-propenylene group, 1-butenylene group, 2-butenylene group, 1-pentenylene group, 2-pentenylene group, 1-hexenylene group, 2-hexenylene group, 1-octenylene group and the like.

[0050] Among these, from the viewpoint that the proportion of silicon in the film (SEI) increases and a high-quality film (SEI film) is easily obtained, the vinylene group, 1-propenylene group, and 2-propenylene group are preferred.

[0051] Specific examples of the alkynylene group of X include ethynylene group, propynylene group, butynylene group, pentynylene group, hexynylene group, heptynylene group, octynylene group, nonynylene group, decynylene group, undecynylene group, dodecynylene group and the like.

[0052] Among these, from the viewpoint that the proportion of silicon in the film (SEI) increases and a high-quality film (SEI film) is easily obtained, the ethynylene group and propynylene group are preferred.

[0053] In general formulas (1) to (5), l is independently an integer of 1 to 3, and m is independently an integer of 1 to 2.

[0054] Specific examples of general formulas (1) to (5) include 1,2-bis(trivinylsilyl)ethene, 1,2-bis(triethynylsilyl)ethene, 1,2-bis(diethynylmethylsilyl)ethene, 1,2-bis(ethynyldimethylsilyl)ethene, 1,2-bis(divinylmethylsilyl)ethene, 1,2-bis(dimethylvinylsilyl)ethene, bis[2-(trivinylsilyl)ethenyl]divinylsilane, bis[2-(divinylmethylsilyl)ethenyl]divinylsilane, bis[2-(dimethylvinylsilyl)ethenyl]divinylsilane, bis[2-(trivinylsilyl)ethenyl]methylvinylsilane, bis[2-(divinylmethylsilyl)ethenyl]methylvinylsilane, bis[2-(dimethylvinylsilyl)ethenyl]methylvinylsilane, 1,2-bis[2-(trivinylsilyl)ethenyldivinylsilyl]ethene, 1,2-bis[2-(divinylmethylsilyl)ethenyldivinylsilyl]ethene, 1,2-bis[2-(dimethylvinylsilyl)ethenyldivinylsilyl]ethene, 1,2-bis(trivinylsilyl)methane, 1,2-bis(divinylmethylsilyl)methane, 1,2-bis(dimethylvinylsilyl)methane, 1,2-bis(trivinylsilyl)ethane, 1,2-bis(methyldivinylsilyl)ethane, 1,2-bis(dimethylvinylsilyl)ethane, bis[2-(trivinylsilyl)methyl]methylvinylsilane, bis[2-(divinylmethylsilyl)methyl]methylvinylsilane, bis[2-(dimethylvinylsilyl)methyl]methylvinylsilane, bis[2-(trivinylsilyl)ethyl]methylvinylsilane, bis[2-(divinylmethylsilyl)ethyl]methylvinylsilane, bis[2-(dimethylvinylsilyl)ethyl]methylvinylsilane, tris[2-(trivinylsilyl)methyl]vinylsilane, tris[2-(divinylmethylsilyl)methyl]vinylsilane, tris[2-(dimethylvinylsilyl)methyl]vinylsilane, tris[2-(trivinylsilyl)ethyl]vinylsilane, tris[2-(divinylmethylsilyl)ethyl]vinylsilane, tris[2-(dimethylvinylsilyl)ethyl]vinylsilane, and the like.

[0055] The silane compounds represented by the above general formulas (1) to (3) can be obtained, for example, by reacting vinylsilane in the presence of a metathesis catalyst. Further, the silane compounds represented by the above general formulas (4) and (5) can be obtained, for example, by reacting a haloalkylvinylsilane with an organometallic reagent prepared from magnesium and a vinylhalosilane.

[0056] [Content in non-aqueous electrolyte] The content of the general formulas (1) to (5) in the non-aqueous electrolyte is preferably 0.1% by mass to 5.0% by mass, more preferably 0.1% by mass to 4.0% by mass, and still more preferably 0.1% by mass to 2.0% by mass. With such a content, a sufficient film (SEI film) is likely to be formed, and it is easy to suppress the swelling of the battery cell. Also, it is easy to prevent the increase in resistance due to the formation of an excessive film (SEI film).

[0057] [Lowest unoccupied molecular orbital (LUMO) energy level] The lowest unoccupied molecular orbital (LUMO) energy level of the silane compound is preferably -0.40 eV or less, more preferably -0.50 eV or less, still more preferably -0.60 eV or less, and particularly preferably -0.65 eV or less. With such an energy level, the silane compound is likely to undergo reductive decomposition.

[0058] [Highest occupied molecular orbital (HOMO) energy level] The highest occupied molecular orbital (HOMO) energy level of the silane compound is preferably -8.8 eV or more, more preferably -8.0 eV or more, still more preferably -7.5 eV or more, and particularly preferably -7.3 eV or more. With such an energy level, the reactivity after reductive decomposition, particularly the radical reactivity, is improved, and it is easy to obtain a high-quality film (SEI film).

[0059] [Calculation method of energy level] The energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) can be determined from quantum chemical calculations. Software for quantum chemical calculations such as Gaussian and GAMESS can be used. From the viewpoints of calculation accuracy and calculation cost, the density functional method is preferably used as the calculation method. B3LYP is preferably used as the exchange-correlation functional, and 6-311+G(d,p) is preferably used as the basis function.

[0060] [Decomposition potential of silane compound] The silane compound contained in the non-aqueous electrolyte of the present invention is characterized by decomposing at a relatively high potential. Therefore, in order to obtain a sufficient battery cell expansion suppression effect, it is necessary to use a negative electrode containing any one of a silicon compound, a germanium compound, and a tin compound having a capacity on the high potential side. Using Li / Li + as a reference (0 V), in a graphite negative electrode having no capacity at 0.24 V or higher, the silane compound is not sufficiently decomposed, and the battery cell expansion suppression effect cannot be obtained. Therefore, the present invention is premised on a non-aqueous electrolyte secondary battery in which the negative electrode is a non-aqueous electrolyte containing at least any one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles. Hereinafter, the potential is based on the potential of Li / Li + at 0 V.

[0061] The decomposition potential (with the potential of Li / Li + as a reference (0 V)) of the silane compound contained in the non-aqueous electrolyte of the present invention is preferably 0.23 to 0.70 V, more preferably 0.25 to 0.60 V, still more preferably 0.27 to 0.55 V, and particularly preferably 0.30 to 0.50 V. With such a decomposition potential, a film (SEI film) for suppressing the expansion of the battery cell is easily obtained. The decomposition potential of the silane compound can be measured by, for example, cyclic voltammetry (CV).

[0062] [Decomposition potential of silane compound decomposition product (film)] The silane compound contained in the non-aqueous electrolyte of the present invention decomposes to form a film (SEI film). Such a decomposition product (film) is preferably in a stable state (does not decompose) at 0.70 V or higher. If it does not decompose at the above potential, even when a negative electrode having a capacitance on the high potential side is used, an effect of suppressing the swelling of the battery cell is easily obtained. In particular, a negative electrode containing silicon oxide has a large capacitance at 0.7 V or higher, and thus is compatible with the silane compound contained in the non-aqueous electrolyte of the present invention.

[0063] The silane compound contained in the non-aqueous electrolyte of the present invention has a high electron accepting property and excellent reductive decomposability on the surface of the negative electrode. In particular, it decomposes at a high potential of 0.23 V or higher and forms a film (SEI film) on the surface of the negative electrode. Therefore, it is used for protecting a negative electrode having a capacitance on the high potential side of 0.23 V or higher, and is particularly compatible with a negative electrode mainly made of a silicon material.

[0064] In addition, since the silane compound contained in the non-aqueous electrolyte of the present invention has a structure rich in reactivity with a plurality of silicon atoms, it easily forms a high-quality film (SEI film) after reductive decomposition, particularly a film (SEI film) excellent in strength and decomposition resistance.

[0065] Such a film (SEI film) is not easily broken even when charge and discharge are repeated, and can suppress further decomposition of the electrolytic solution (for example, solvent, additive, etc.). As a result, it becomes possible to suppress the swelling of the battery cell due to the swelling phenomenon.

[0066] The silane compound contained in the non-aqueous electrolyte of the present invention effectively protects the Li silicate part constituting the silicon-based negative electrode active material, and can also stably form a film (SEI film) with Li 2 SiO 3 and Li 2 SiO 3 formed by conversion of Li 4 SiO 4 to Li

[0067] The Li silicate part is known to decompose at a high potential of 0.7 V or higher. However, the film (SEI film) formed by the silane compound contained in the non-aqueous electrolyte of the present invention is also excellent in decomposition resistance at a high potential, so that the decomposition of Li silicate can be suppressed.

[0068] <Non-aqueous electrolyte secondary battery> [Non-aqueous electrolyte] The non-aqueous electrolyte of the present invention is one in which an electrolyte salt is dissolved in a non-aqueous solvent and contains the compounds (1) to (5), and may contain other materials as additives. At least a part of the active material layer or the separator is impregnated with the non-aqueous electrolyte.

[0069] Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, or tetrahydrofuran. Among these, from the viewpoint of obtaining better characteristics, it is desirable to use at least one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. In this case, by combining a high-viscosity solvent such as ethylene carbonate and propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, the dissociation property of the electrolyte salt and the ion mobility can be improved, and more excellent characteristics can be obtained.

[0070] When using an alloy-based negative electrode containing a silicon-based negative electrode material, it is particularly desirable that the solvent contains at least one of a halogenated chain carbonate or a halogenated cyclic carbonate. Thereby, during charge and discharge, particularly during charging, a stable film is formed on the surface of the negative electrode active material. Here, the halogenated chain carbonate is a chain carbonate having a halogen as a constituent element (at least one hydrogen is substituted by a halogen). Further, the halogenated cyclic carbonate is a cyclic carbonate having a halogen as a constituent element (that is, at least one hydrogen is substituted by a halogen).

[0071] The type of halogen is not particularly limited, but fluorine is preferable from the viewpoint of forming a better-quality film than other halogens. Also, the number of halogens is preferably as large as possible from the viewpoint that the resulting film is more stable and the reduction of the decomposition reaction of the electrolyte.

[0072] Examples of the halogenated chain carbonate include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, and the like. Examples of the halogenated cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one, 4,5-difluoro-1,3-dioxolan-2-one, and the like.

[0073] The electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), and the like.

[0074] From the viewpoint of obtaining high ionic conductivity, the content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less, more preferably 0.8 mol / kg or more and 2.0 mol / kg or less, still more preferably 0.8 mol / kg or more and 1.5 mol / kg or less with respect to the non-aqueous solvent.

[0075] In addition to the silane compounds represented by general formulas (1) to (5), the non-aqueous electrolyte of the present invention can contain an unsaturated carbon-bonded cyclic carbonate, sultone (cyclic sulfonic acid ester), and acid anhydride as further separate additives. The unsaturated carbon-bonded cyclic carbonate can be included from the viewpoints of a stable film form on the negative electrode surface during charge and discharge and suppression of the decomposition reaction of the non-aqueous electrolyte, and examples thereof include vinylene carbonate or vinyl ethylene carbonate. Further, sultone can be included from the viewpoint of improving the chemical stability of the battery, and examples thereof include propane sultone and propene sultone. Furthermore, acid anhydride can be included from the viewpoint of improving the chemical stability of the electrolyte, and examples thereof include propane disulfonic anhydride.

[0076] The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode and a negative electrode in addition to the above non-aqueous electrolyte.

[0077] [Positive Electrode] The positive electrode has, for example, a configuration in which a positive electrode active material layer is provided on both sides or one side of a positive electrode current collector.

[0078] Here, the positive electrode current collector is formed of a conductive material such as aluminum, for example.

[0079] On the other hand, the positive electrode active material layer contains any one or two or more of positive electrode materials capable of intercalating and deintercalating lithium ions, and may contain other materials such as a binder, a conductive aid, and a dispersant according to the design. In this case, the binder and the conductive aid can be the same as those of the negative electrode binder and the negative electrode conductive aid described later, for example.

[0080] Examples of the positive electrode material include lithium-containing compounds such as composite oxides having lithium and transition metal elements or phosphate compounds having lithium and transition metal elements from the viewpoints of obtaining a high battery capacity and excellent cycle characteristics. As the transition metal element, nickel, iron, manganese, and cobalt are preferable, and the lithium-containing compound is a compound having at least one or more of these transition metal elements. Examples of the chemical formula of the thium-containing compound include, for example, LixM1O2 or LiyM 2 PO 4 It is represented by. In the formula, M1 and M2 represent at least one or more transition metal elements. The values of x and y represent different values depending on the charge and discharge state of the battery, but generally satisfy 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

[0081] Specific examples of the composite oxide having lithium and a transition metal element include, for example, lithium cobalt composite oxide (Li x CoO 2 ), lithium nickel composite oxide (Li x NiO 2 ), lithium nickel cobalt composite oxide, lithium nickel cobalt composite oxide (lithium nickel cobalt aluminum composite oxide; NCA, lithium nickel cobalt manganese composite oxide + NCM), and the like.

[0082] Specific examples of the phosphate compound having lithium and a transition metal element include, for example, lithium iron phosphate compound (LiFePO 4 ), lithium iron manganese phosphate compound (LiFe 1-u Mn u PO 4 , provided that 0 < u < 1), and the like. By using these positive electrode materials, a high battery capacity can be obtained and excellent cycle characteristics can also be obtained.

[0083] [Negative electrode] The negative electrode has, for example, a configuration having a negative electrode active material layer on a negative electrode current collector. This negative electrode active material layer may be provided on both sides or only one side of the negative electrode current collector.

[0084] [Negative electrode current collector] The negative electrode current collector is an excellent conductive material and is composed of a material having excellent mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

[0085] From the perspective of improving the physical strength of the negative electrode current collector, it is preferable that, in addition to copper (Cu) and nickel (Ni), the negative electrode current collector contains carbon (C) and sulfur (S). In particular, when there is an active material layer that expands during charging, the current collector containing the above elements has the effect of suppressing electrode deformation including the current collector. The content of the above-mentioned contained elements is not particularly limited, but from the perspective of obtaining a higher deformation suppression effect, it is preferably 100 mass ppm or less respectively. Such a deformation suppression effect can further improve the cycle characteristics.

[0086] Also, the surface of the negative electrode current collector may or may not be roughened. Examples of the roughened negative electrode current collector include metal foils that have been electrolytically treated, embossed, or chemically etched. Examples of the non-roughened negative electrode current collector include rolled metal foils.

[0087] [Negative electrode active material layer] The negative electrode active material layer contains a negative electrode active material capable of occluding (inserting) and releasing lithium ions, and from the perspective of battery design, it may further contain other materials such as a negative electrode binder (binder) and a conductive aid. The negative electrode active material contains negative electrode active material particles, and the negative electrode active material particles contain at least any one of silicon compound particles (silicon-based negative electrode active material), germanium compound particles (germanium-based negative electrode active material), and tin compound particles (tin-based negative electrode active material). Among them, it is preferable to contain silicon compound particles, and particularly preferably to contain silicon compound particles containing a silicon compound containing oxygen.

[0088] The negative electrode active material contains at least any one of silicon compound particles (silicon-based negative electrode active material), germanium compound particles (germanium-based negative electrode active material), and tin compound particles (tin-based negative electrode active material). Among them, it is preferable to contain silicon compound particles, and particularly preferably to contain silicon oxide material (silicon compound containing oxygen). This silicon compound SiO x The x, which is the composition ratio of silicon to oxygen constituting it, is preferably a number satisfying 0.8 ≦ x ≦ 1.2 from the perspectives of cycle characteristics and the resistance of silicon oxide. Among them, SiOx It is preferable that the composition of the silicon compound has x closer to 1 in order to obtain high cycle characteristics. Note that the composition of the silicon compound in the present invention does not necessarily mean a purity of 100%, and it may contain trace amounts of impurity elements.

[0089] The silicon compound preferably contains as little crystalline Si as possible. By containing as little crystalline Si as possible, it is possible to prevent the reactivity with the electrolyte from becoming too high, and as a result, it is possible to prevent the battery characteristics from deteriorating.

[0090] The silicon compound contains Li, and a part of it is Li 2 SiO 3 It is desirable that it has become. This Li 2 SiO 3 is crystalline, but is active with respect to charge and discharge, and is Li in a slurry state 2 SiO 3 remains as it is, but by repeating charge and discharge, Li 4 SiO 4 changes to.

[0091] Li 2 SiO 3 The higher the crystallinity of, the more difficult it is to convert to Li 4 SiO 4 On the other hand, in the case of low crystallinity, it is likely to elute into the slurry, so there is an optimal range.

[0092] Specifically, the negative electrode active material particles have a peak caused by the Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα rays before charging and discharging the negative electrode active material particles, and the crystallite size corresponding to the crystal plane is 5.0 nm or less, and Li 2 SiO 3 The ratio A / B of the intensity A of the peak caused by the Si(111) crystal plane to the intensity B of the peak caused by the Li 0.4 ≦ A / B ≦ 1.0 ···(6) It is preferable to satisfy.

[0093] The degree of thickening of lithium silicate and the degree of crystallization of Si (for example, the crystallite size corresponding to the Si(111) crystal plane) can be confirmed by X-ray diffraction (hereinafter also referred to as "XRD").

[0094] As the X-ray diffractometer, D8 ADVANCE manufactured by Bruker can be used. The X-ray source uses Cu Kα rays and a Ni filter, and measures from 10 to 40 ° at an output of 40 kV / 40 mA, a slit width of 0.3 °, a step width of 0.008 °, and a counting time of 0.15 seconds per step.

[0095] The peak caused by the Si(111) crystal plane appears around 2θ = 28.4° in the X-ray diffraction chart.

[0096] The crystallite size corresponding to the Si(111) crystal plane is preferably 5.0 nm or less, more preferably 4.0 nm or less, still more preferably 2.5 nm or less, and substantially amorphous is desirable.

[0097] Li 2 SiO 3 The ratio A / B of the intensity A of the peak caused by the Si(111) crystal plane to the intensity B of the peak caused by the Li 2 SiO 3 (111) crystal plane is preferably 0.40 ≦ A / B ≦ 1.00, more preferably 0.45 ≦ A / B ≦ 0.75, still more preferably 0.50 ≦ A / B ≦ 0.70. Here, Li

[0098] The median diameter of the negative electrode active material by the laser diffraction method is preferably 5.0 μm or more and 15.0 μm or less, more preferably 5.5 μm or more and 10.0 μm or less, still more preferably 6.0 μm or more and 8.0 μm or less, from the viewpoint of controlling the reaction with the electrolyte or suppressing the expansion of the negative electrode active material accompanying charge and discharge.

[0099] The negative electrode active material layer may contain a mixed negative electrode active material material including the silicon-based negative electrode active material and the carbon-based active material. Thereby, the electric resistance of the negative electrode active material layer is reduced, and it becomes possible to relieve the expansion stress accompanying charging. Examples of the carbon-based active material include natural graphite, artificial graphite, hard carbon, soft carbon, and the like.

[0100] The negative electrode active material layer of the present invention contains the negative electrode active material of the present invention capable of occluding and releasing lithium ions, and may further contain other materials such as a negative electrode binder (binder) and a conductive aid from the viewpoint of battery design.

[0101] As the negative electrode binder, for example, any one or more of a polymer material, a synthetic rubber, etc. can be used. Examples of the polymer material include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxymethyl cellulose, and the like. Examples of the synthetic rubber include styrene-butadiene rubber, fluorine rubber, ethylene propylene diene, and the like.

[0102] Examples of the negative electrode conductive aid include carbon fine particles, carbon black, acetylene black, graphite, ketjen black, carbon nanotubes, carbon nanofibers, etc., and any one or more of these can be used.

[0103] The negative electrode active material layer is formed, for example, by a coating method. The coating method is a method in which a silicon-based negative electrode active material, a binder, etc. are mixed with a negative electrode conductive aid and a carbon-based active material as necessary, and then dispersed in an organic solvent, water, etc. and coated.

[0104] [Separator] The separator isolates the lithium metal or the positive electrode and the negative electrode, prevents current short - circuit due to contact between the two electrodes, and allows lithium ions to pass through. This separator is formed, for example, by a porous membrane made of synthetic resin or ceramic, and may have a laminated structure in which two or more porous membranes are laminated. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, polyethylene, etc.

Example

[0105] Hereinafter, the examples and comparative examples of the present invention will be shown to explain the present invention more specifically, but the present invention is not limited to these examples.

[0106] <Common items of Examples and Comparative Examples> [Energy levels of HOMO and LUMO] After performing structural optimization on the silane compound, the energy levels of HOMO and LUMO were calculated. Gaussian 16 was used as the quantum chemical calculation software. The B3LYP exchange - correlation functional and the 6 - 311+G(d,p) basis function were used, and the calculation was performed using the density functional method.

[0107] [Cyclic voltammetry] After mixing ethylene carbonate (EC) and dimethyl carbonate (DMC), a silane compound was dissolved to prepare an electrolyte. The composition of EC and DMC was EC:DMC = 30:70 by volume ratio, and the composition of the EC / DMC mixed solvent and the silane compound was mixed solvent:silane compound = 95:5 by mass ratio. Cyclic voltammetry (CV) measurement was performed on the obtained electrolyte. A SUS304 plate (immersion area 3 cm 2 ) was used as the working electrode, a platinum wire as the counter electrode, and Ag / Ag + (internal solution: acetonitrile, 0.1 mol / L silver nitrate, 0.1 mol / L tetrabutylammonium perchlorate) was used as the reference electrode. Also, the scanning rate was 50 mV / second.

[0108] [Example 1] [Fabrication of negative electrode] As the negative electrode current collector, an electrolytic copper foil with a thickness of 15 μm was used. This electrolytic copper foil contained carbon and sulfur at concentrations of 70 ppm by mass, respectively.

[0109] As the silicon-based negative electrode active material, KSC-7130 (silicon oxide particles containing "Li-SiO-C", Li 2 SiO 3 and coated with a carbon layer, median diameter 6.5 μm, manufactured by Shin-Etsu Chemical Co., Ltd., see Journal of Power Sources 450 (2020) 227699), artificial graphite (median diameter 15 μm), as the negative electrode conductive assistant, carbon nanotubes and carbon fine particles with a median diameter of about 50 nm, and as the negative electrode binder, sodium polyacrylate and carboxymethyl cellulose were mixed at a dry mass ratio of 9.3:83.7:1:1:4:1, and then diluted with pure water to form a negative electrode mixture slurry.

[0110] The negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 °C for 1 hour. The deposition amount (areal density) of the negative electrode active material layer per unit area on one side of the dried negative electrode was 7.0 mg / cm 2 .

[0111] [Preparation of Non-aqueous Electrolyte] After mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) as non-aqueous solvents, lithium hexafluorophosphate: LiPF 6 was dissolved in this mixed solvent to prepare an electrolytic solution. In this case, the composition of the solvent was EC:DMC = 30:70 by volume ratio, and the content of the electrolyte salt was 1 mol / kg with respect to the solvent.

[0112] To the prepared electrolyte, 1.0 wt%, 2.0 wt%, and 0.1 wt% of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and Si-1 in Table 1 were added as film-forming additives, respectively, to prepare a non-aqueous electrolyte. Note that Si-1 in Table 1 is 1,2-bis(trivinylsilyl)ethene, and in the general formula (1), R 1This is the case where the vinyl group is present, X is a vinylene group, and l = 3.

[0113] [Fabrication of a non-aqueous electrolyte secondary battery] Next, a coin cell was assembled as follows. First, a Li foil with a thickness of 1 mm was punched out to a diameter of 16 mm and attached to an aluminum clad. The negative electrode obtained by the above method was punched out to a diameter of 15 mm, faced the Li foil through a separator, and after injecting the non-aqueous electrolyte obtained by the above method, a 2032 coin cell, which is a non-aqueous electrolyte secondary battery, was fabricated.

[0114] [Evaluation of the battery] For the fabricated coin cell, the charging rate was set to be equivalent to 0.03C, and charging (first charge) was performed in the CCCV mode. The CV was 0V and the termination current was 0.04 mA. Next, the discharging rate was similarly set to 0.03C, and the discharging termination voltage was set to 1.2V, and CC discharging (first discharge) was performed.

[0115] To examine the initial charge-discharge characteristics, the initial efficiency (hereinafter also referred to as the "initial efficiency") was calculated as follows. Initial efficiency (%) = (first discharge capacity / first charge capacity) × 100

[0116] Based on the obtained initial efficiency data, the positive electrode was designed and the following battery evaluations were performed.

[0117] [Expansion rate of the battery cell (evaluation of swelling)] First, for battery stabilization, charge-discharge was performed at 0.2C for 2 cycles in an atmosphere of 25°C, and thereafter, up to the 500th cycle, charge-discharge was performed at 0.7C for charging and 0.5C for discharging. At this time, the charging voltage was 4.3V, the discharging termination voltage was 2.5V, and the charging termination rate was 0.07C.

[0118] At the time of discharging at the 500th cycle, the thickness of the battery cell was measured. Based on the thickness of the initial battery cell (thickness 5.5 mm, width 34 mm, length 36 mm), the expansion rate of the battery cell was determined as follows. Expansion rate (%) = (thickness at the 500th cycle / 5.5 mm) × 100

[0119] [Examples 2 to 28] The procedure of Example 1 was repeated except that the type (silane compound) and amount of the additive were changed as shown in Table 2. The structural formulas of the silane compounds are as shown in Table 1. Si-2 in Table 1 is the case where, in General Formula (2), R 1 is a vinyl group, X is a vinylene group, l = 3, and m = 2. Si-3 in Table 1 is the case where, in General Formula (3), R 1 is a vinyl group, X is a vinylene group, l = 3, and m = 2. Si-4 in Table 1 is the case where, in General Formula (1), R 1 is a vinyl group, X is an ethylene group, and l = 3. Si-5 in Table 1 is the case where, in General Formula (2), R 1 is a vinyl group, R 2 is a methyl group, X is a methylene group, l = 3, and m = 1. Si-6 in Table 1 is the case where, in General Formula (4), R 1 is a vinyl group, X is a methylene group, and l = 3. Si-7 in Table 1 is the case where, in General Formula (5), R 1 is a vinyl group, R 2 is a methyl group, X is a methylene group, and l = 3.

[0120] [Examples 29 to 40] Additional heat treatment was performed on the silicon material to control the crystallinity of Si and Li 2 SiO 3 and confirm the battery characteristics. The temperature was adjusted in the range of 600 to 700°C. Otherwise, the procedure of Example 1 was repeated except that the type (silane compound) and amount of the additive were changed as shown in Table 2.

[0121] [Comparative Example 1] The procedure of Example 1 was repeated except that no additive (silane compound) was added.

[0122] [Comparative Examples 2 to 4] Except for changing the type of additive (silane compound) and the addition amount as shown in Table 2, the procedure was the same as in Example 1. The silane compound used here was MTVS (methyltrivinylsilane), and its structural formula was as shown in Table 1. MTVS does not fall under any of the general formulas (1) to (5).

[0123]

Table 1

[0124]

Table 2

[0125] [Examples 41 - 42] As the negative electrode active material, SIE23PB (metallic Si, high - purity science) was used, and the negative electrode was fabricated in the same procedure as in Example 1. Except for changing the type of additive (silane compound) and the addition amount as shown in Table 3, the procedure was the same as in Example 1.

[0126] [Examples 43 - 44] As the negative electrode active material, GEE05PB (germanium, high - purity science) was sieved with a mesh size of 20 μm, and the recovered powder was used to fabricate the negative electrode in the same procedure as in Example 1. Except for changing the type of additive (silane compound) and the addition amount as shown in Table 3, the procedure was the same as in Example 1.

[0127] [Examples 45 - 46] As the negative electrode active material, SNE08PB (tin, high - purity science) was sieved with a mesh size of 20 μm, and the recovered powder was used to fabricate the negative electrode in the same procedure as in Example 1. Except for changing the type of additive (silane compound) and the addition amount as shown in Table 3, the procedure was the same as in Example 1.

[0128] [Examples 47 - 48] As the negative electrode active material, SNO07PB (tin oxide, high-purity science) was sieved with a mesh size of 20 μm, and the recovered powder was used to fabricate the negative electrode in the same procedure as in Example 1. Otherwise, it was carried out in the same manner as in Example 1 except that the type (silane compound) and the addition amount of the additive were changed as shown in Table 3.

[0129] [Comparative Examples 5 - 6] As the negative electrode active material, artificial graphite (median diameter 15 μm) was used to fabricate the negative electrode in the same procedure as in Example 1. Otherwise, it was carried out in the same manner as in Example 1 except that the type (silane compound) and the addition amount of the additive were changed as shown in Table 3.

[0130] [Comparative Examples 7 - 11] The negative electrode active material was changed as shown in Table 3, and it was carried out in the same manner as in Example 1 except that the additive (silane compound) was not added.

[0131]

Table 3

[0132] As is clear from the results in Table 2, it was confirmed that by adding the silane compound contained in the non-aqueous electrolyte of the present invention having two or more silicon atoms, the swelling of the battery cell was suppressed. Further, when the heat treatment temperature of the silicon material was lowered, the crystallization of Si was suppressed, and the swelling suppression effect tended to improve.

[0133] As is clear from the results in Table 3, it was confirmed that the swelling of the battery cell was also suppressed in the negative electrodes containing metal Si, germanium, tin, and tin oxide. On the other hand, in the graphite negative electrode, the swelling of the battery cell was not suppressed. That is, there was almost no difference among Comparative Examples 5, 6, and 11.

[0134] When cyclic voltammetry (CV) was measured for the silane compounds contained in the non-aqueous electrolyte of the present invention, it was revealed that all of the compounds decomposed around 0.4 V. Since the graphite negative electrode does not have a capacity of 0.24 V or more, it is considered that the positive decomposition and film formation of the silane compound did not occur, and the effect of suppressing the expansion of the battery cell was not obtained.

[0135] In addition, the graphite negative electrode has a problem that the capacity does not increase when made into a battery because it has a smaller capacity than silicon, germanium, and tin-based negative electrodes.

[0136] It was suggested that the silane compound contained in the non-aqueous electrolyte of the present invention has a lower LUMO than FEC (LUMO: -0.3921 eV) and is excellent in reductive decomposability at the negative electrode. Also, the HOMO also tends to be higher than FEC (HOMO: -8.9715 eV) and MTVS, and it was also suggested that, combined with the low LUMO, it has a high film-forming ability to form a high-quality film after reductive decomposition.

Industrial Applicability

[0137] According to the present invention, it is possible to provide a non-aqueous electrolyte capable of suppressing the expansion of a battery cell.

[0138] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Claims

1. A non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery in which the negative electrode contains at least a silicon compound as negative electrode active material particles, wherein the negative electrode active material particles in the negative electrode contain silicon oxide particles coated with a carbon layer, The silicon oxide particles contain Li ２ SiO ３ and The Li ２ SiO ３ is crystalline, and the non-aqueous electrolyte contains at least one silane compound selected from silane compounds represented by the following general formulas (1) to (5). The non-aqueous electrolyte is characterized by this. 【Chemical 1】 【Chemical 2】 【Chemical Formula 3】 【Chemical Formula 4】 【Chemical Formula 5】 (wherein, R １ is each independently an alkenyl group or an alkynyl group having 2 to 20 carbon atoms, and R ２ is each independently an alkyl group having 1 to 20 carbon atoms, and X is each independently an alkylene group having 1 to 20 carbon atoms, an alkenylene group or an alkynylene group having 2 to 20 carbon atoms. Further, l is each independently an integer of 1 to 3, and m is each independently an integer of 1 to 2.)

2. The non-aqueous electrolyte according to Claim 1, wherein the energy level of the lowest unoccupied molecular orbital of the silane compound is -0.40 eV or less.

3. The non-aqueous electrolyte according to Claim 1 or 2, wherein the energy level of the highest occupied molecular orbital of the silane compound is -8.8 eV or more.

4. The non-aqueous electrolyte according to any one of Claims 1 to 3, wherein the content of the silane compound contained in the non-aqueous electrolyte is 0.1% by mass to 5.0% by mass.

5. Before the negative electrode active material particles are charged and discharged, the negative electrode active material particles have a peak resulting from the Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα rays, and the crystallite size corresponding to the crystal plane is 5.0 nm or less, and Li ２ SiO ３ The ratio A / B of the intensity A of the peak resulting from the Si(111) crystal plane to the intensity B of the peak resulting from the ２ SiO ３ (111) crystal plane is represented by the following formula (6) 0.4 ≦ A / B ≦ 1.0... (6) The non-aqueous electrolyte according to any one of Claims 1 to 4, characterized by satisfying this.

6. Li / Li ＋ When the potential of Li / Li is taken as the reference of 0 V, in the range of 0.23 V or more, the silane compound decomposes to form a film on the negative electrode. The non-aqueous electrolyte according to any one of claims 1 to 5, characterized in that.

7. The film formed by the decomposition of the silane compound is stable in the range of 0.70 V or more when the potential of Li / Li ＋ is taken as the 0 V reference. The non-aqueous electrolyte according to claim 6, characterized in that it is in a stable state.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode containing at least a silicon compound as negative electrode active material particles, together with the non-aqueous electrolyte according to any one of Claims 1 to 7, wherein the negative electrode active material particles in the negative electrode contain silicon oxide particles coated with a carbon layer, the silicon oxide particles contain Li₂SiO₃, and the Li₂SiO₃ is crystalline.

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