Non-aqueous electrolyte and non-aqueous electrolyte secondary battery

Abstract

To provide a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery in which a battery cell hardly expands even when a negative electrode material such as a silicon material is used.SOLUTION: A non-aqueous electrolyte used for a non-aqueous electrolyte secondary battery in which a negative electrode contains at least any of a silicon compound, a germanium compound and a tin compound as a negative electrode active material particle, the non-aqueous electrolyte including at least one or more silane compounds selected from silane compounds represented by the following general formulas (1), (2), etc.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, small electronic devices such as mobile terminals have become widespread, and there is a strong demand for further miniaturization, weight reduction, and longer life. In response to such market demands, development of secondary batteries that are particularly small and lightweight and capable of achieving high energy density has been progressing. The application of these secondary batteries is being considered not only for small electronic devices but also for large electronic devices such as automobiles and power storage systems such as those for homes.

[0003] Among these, lithium-ion secondary batteries are attracting great attention because they are easy to make small and have high capacity, and can provide higher energy density than lead batteries and nickel-cadmium batteries.

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

[0005] While carbon-based active materials are widely used as negative electrode active materials, recent market demands have called for further improvements in battery capacity. To improve battery capacity, the use of silicon as a negative electrode active material is being considered. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times greater than that of graphite (372 mAh / g), and a significant improvement in battery capacity can be expected. The development of silicon materials as negative electrode active materials is being considered not only for silicon itself, but also for alloys and compounds such as oxides. Furthermore, the shape of the negative electrode active material is being considered, ranging from the standard coated type used for carbon-based active materials to an integrated type deposited directly on the current collector.

[0006] However, when silicon is used as the primary raw material for the negative electrode active material, the negative electrode active material expands and contracts during charging and discharging, making it prone to cracking, primarily near the surface. Furthermore, ionic substances are generated within the negative electrode active material, making it prone to cracking. When the surface layer of the negative electrode active material cracks, a new surface is created, increasing the reactive area of ​​the negative electrode active material. At this time, the electrolyte decomposes on the new surface, and a coating of the electrolyte decomposition product is formed on the new surface, consuming the electrolyte and potentially reducing cycle performance.

[0007] To date, various studies have been conducted on negative electrode materials and electrode configurations for lithium-ion secondary batteries that use silicon materials as the main material in order to improve the initial battery efficiency and cycle characteristics.

[0008] Specifically, to achieve good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see, for example, Patent Document 1). Furthermore, to achieve high battery capacity and safety, a carbon material (electron-conductive material) is provided on the surface layer of silicon oxide particles (see, for example, Patent Document 2). Furthermore, to improve cycle characteristics and achieve high input / output characteristics, an active material containing silicon and oxygen is prepared, and an active material layer with a high oxygen ratio near the current collector is formed (see, for example, Patent Document 3). Furthermore, to improve cycle characteristics, oxygen is incorporated into the silicon active material, and the silicon active material is formed so that the average oxygen content is 40 at% or less and the oxygen content is higher near the current collector (see, for example, Patent Document 4).

[0009] There are also reports of using fluoroethylene carbonate (FEC) as an electrolyte additive to suppress the decomposition reaction of the electrolyte accompanying the charge and discharge of silicon active materials (see, for example, Patent Document 5). Fluorine-based electrolytes form a stable solid electrolyte interphase (SEI) film on the silicon surface, making it possible to suppress the deterioration of silicon materials. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-185127 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-042806 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-164954 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-114454 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-134719 Summary of the Invention [Problem to be solved by the invention]

[0011] As mentioned above, compact electronic devices, such as mobile terminals, have become increasingly sophisticated and multifunctional in recent years, necessitating increased battery capacity for their primary power source: lithium-ion secondary batteries. One solution to this problem is the development of lithium-ion secondary batteries with anodes primarily made of silicon materials. Furthermore, lithium-ion secondary batteries using silicon materials are expected to have cycle characteristics comparable to those of lithium-ion secondary batteries using carbon-based active materials. To address this issue, fluorine-based additives have been developed, which have tended to improve battery performance. However, repeated charge-discharge cycles consume the fluorine-based solvent, increasing the amount of electrolyte decomposition products that accumulate on the silicon material surface. This deactivates the reversibly mobile lithium by trapping it in the decomposition products, resulting in poor battery cycle performance and cell expansion due to swelling, which are insufficient compared to batteries using carbon-based active materials.

[0012] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a nonaqueous electrolyte and a nonaqueous electrolyte secondary battery in which battery cells are less likely to expand even when a negative electrode material such as a silicon material is used. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a nonaqueous electrolyte for use in a nonaqueous electrolyte secondary battery in which the negative electrode contains, as negative electrode active material particles, at least one of a silicon compound, a germanium compound, and a tin compound, wherein the nonaqueous electrolyte contains at least one silane compound selected from silane compounds represented by the following general formulas (1) to (5): [ka] [ka] [ka] [ka] [ka] (In the formula, R 1 are each independently an alkenyl or alkynyl group having 2 to 20 carbon atoms, and R 2 are each independently an alkyl group having 1 to 20 carbon atoms, and each X is independently an alkylene group having 1 to 20 carbon atoms or an alkenylene or alkynylene group having 2 to 20 carbon atoms. Each 1 is independently an integer of 1 to 3, and each m is independently an integer of 1 or 2.

[0014] Such silane compounds have high electron-accepting properties and excellent reductive decomposition properties on the negative electrode surface, and therefore have the characteristic of forming a coating (SEI film) on the negative electrode surface. Therefore, when the nonaqueous electrolyte of the present invention is used in a nonaqueous electrolyte secondary battery having 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] In this case, the energy level of the lowest unoccupied molecular orbital (LUMO) of the silane compound is preferably −0.40 eV or less.

[0016] At such an energy level, the silane compound is more likely to be reductively decomposed.

[0017] The silane compound preferably has a highest occupied molecular orbital (HOMO) energy level of −8.8 eV or higher.

[0018] Such an energy level improves the reactivity after reductive decomposition, particularly the radical reactivity, making it easier to obtain a high-quality coating (SEI film).

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

[0020] At such a content, a sufficient coating (SEI film) is easily formed, which makes it easy to suppress the expansion of the battery cell, and also makes it easy to prevent high resistance due to the formation of an excessive coating (SEI film).

[0021] In the nonaqueous electrolyte of the present invention, the negative electrode active material particles in the negative electrode may contain silicon oxide particles coated with a carbon layer, the silicon oxide particles may contain Li2SiO3, and the Li2SiO3 may be crystalline.

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

[0023] In this case, the negative electrode active material particles have a peak attributable to a Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation 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 attributable to the Si(111) crystal plane to the intensity B of the peak attributable to the Li2SiO3(111) crystal plane satisfies the following formula (6): 0.4≦A / B≦1.0 (6) It is preferable that the following is satisfied.

[0024] Such negative electrode active material particles can exhibit high slurry stability without impairing the ease of conversion from Li2SiO3 to Li4SiO4. Therefore, the nonaqueous electrolyte of the present invention can be suitably used in a nonaqueous electrolyte secondary battery using a negative electrode containing such negative electrode active material particles.

[0025] In addition, in the non-aqueous electrolyte of the present invention, Li / Li + When the potential of the negative electrode is set to 0 V as a reference potential, the silane compound preferably decomposes to form a coating on the negative electrode in a range of 0.23 V or more.

[0026] Such silane compounds are characterized by decomposing at a high potential of 0.23 V or higher and forming a coating (SEI film) on the surface of the negative electrode, and therefore can be suitably used in non-aqueous electrolyte secondary batteries containing at least one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles having capacity on the high potential side.

[0027] The coating formed by decomposition of the silane compound is Li / Li + When the potential of the compound is set to 0 V as a reference potential, the compound is preferably in a stable state in the range of 0.70 V or more.

[0028] Thus, if the coating, which is a decomposition product of the silane compound, is stable and does not decompose in the range of 0.70 V or higher, it is easy to obtain the effect of suppressing expansion of the battery cell even when a negative electrode with capacity on the high potential side is used.

[0029] The present invention also provides a non-aqueous electrolyte secondary battery comprising the above-described non-aqueous electrolyte together with a positive electrode and a negative electrode.

[0030] Such a non-aqueous electrolyte secondary battery includes the non-aqueous electrolyte of the present invention, and therefore, battery swelling can be suppressed. [Effects of the Invention]

[0031] The silane compounds represented by the general formulas (1) to (5) contained in the nonaqueous electrolyte of the present invention have high electron-accepting properties and excellent reductive decomposition properties on the surface of a negative electrode, and therefore have the characteristic of forming a coating (SEI film) on the surface of the negative electrode. Therefore, when the nonaqueous electrolyte of the present invention is used in a nonaqueous electrolyte secondary battery having 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. DETAILED DESCRIPTION OF THE INVENTION

[0032] As described above, there has been a demand for a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery that are less likely to cause battery cell expansion even when using a negative electrode material such as a silicon material.

[0033] As a result of extensive research into achieving the above object, the present inventors discovered that the above object can be achieved by introducing at least one alkenyl or alkynyl group into a silane compound containing at least two silicon atoms, and thus completed the present invention.

[0034] That is, the present invention provides a non-aqueous electrolyte for use in a non-aqueous electrolyte secondary battery in which a negative electrode contains, as negative electrode active material particles, at least one of a silicon compound, a germanium compound, and a tin compound, wherein the non-aqueous electrolyte contains at least one silane compound selected from silane compounds represented by the following general formulas (1) to (5): [ka] [ka] [ka] [ka] [ka] (In the formula, R1 are each independently an alkenyl or alkynyl group having 2 to 20 carbon atoms, and R 2 are each independently an alkyl group having 1 to 20 carbon atoms, and each X is independently an alkylene group having 1 to 20 carbon atoms or an alkenylene or alkynylene group having 2 to 20 carbon atoms. Each 1 is independently an integer of 1 to 3, and each m is independently an integer of 1 or 2.

[0035] Hereinafter, the present invention will be described in detail with reference to the preferred embodiments, but the present invention is not limited to these.

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

[0037] The nonaqueous electrolyte of the present invention contains a silane compound having 2 to 4 silicon atoms, as represented by the general formulas (1) to (5). When the compound has 2 to 4 silicon atoms, the molecular weight of the coating (SEI film) after reductive decomposition tends to be high, and a coating (SEI film) having excellent strength and decomposition resistance is likely to be obtained. On the other hand, when the compound has 5 or more silicon atoms, the solubility in nonaqueous electrolytes decreases.

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

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

[0040] Among these, vinyl groups and n-propenyl groups are preferred from the viewpoints of improving the reductive decomposition properties of silane compounds, promoting polymerization reactions between silane compounds or between silane compounds and other additives, and improving the strength and decomposition resistance of the coating (SEI film).

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

[0042] Among these, ethynyl, 1-propynyl, and 1-butynyl groups are preferred from the viewpoints of improving the reductive decomposition properties of the silane compound, promoting polymerization reactions between silane compounds or between a silane compound and another additive, and improving the strength and decomposition resistance of the coating (SEI film).

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

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

[0045] Among these, a methyl group is preferred from the viewpoint of less steric hindrance and facilitating the reaction between silane compounds.

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

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

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

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

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

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

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

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

[0054] Specific examples of the 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, and bis[2-(dimethylvinylsilyl)ethenyl]divinylsilane. Nylsilane, 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-(di [2-(vinylmethylsilyl)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 general formulas (1) to (3) can be obtained, for example, by reacting vinylsilane in the presence of a metathesis catalyst. The silane compounds represented by the general formulas (4) and (5) can be obtained, for example, by reacting vinylhalosilane with an organometallic reagent prepared from haloalkylvinylsilane and magnesium.

[0056] [Content in non-aqueous electrolyte] The content of the general formulas (1) to (5) in the nonaqueous electrolyte is preferably 0.1% to 5.0% by mass, more preferably 0.1% to 4.0% by mass, and even more preferably 0.1% to 2.0% by mass. This content facilitates the formation of a sufficient coating (SEI film), making it easy to suppress battery cell expansion. It also facilitates preventing high resistance due to excessive coating (SEI film) formation.

[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, even more preferably −0.60 eV or less, and particularly preferably −0.65 eV or less, which facilitates reductive decomposition of the silane compound.

[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 higher, more preferably −8.0 eV or higher, more preferably −7.5 eV or higher, and particularly preferably −7.3 eV or higher. Such an energy level improves reactivity after reductive decomposition, particularly radical reactivity, and makes it easier to obtain a high-quality coating (SEI film).

[0059] [Energy level calculation method] The energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) can be determined by quantum chemical calculations. Quantum chemical calculation software such as Gaussian and GAMESS can be used. From the viewpoints of calculation accuracy and calculation cost, density functional theory 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 compounds] The silane compound contained in the non-aqueous electrolyte of the present invention has the characteristic of decomposing at a relatively high potential. Therefore, in order to obtain a sufficient effect of suppressing expansion of the battery cell, it is necessary to use a negative electrode containing a silicon compound, a germanium compound, or a tin compound, which has a capacity on the high potential side. Li / Li + With a graphite negative electrode that does not have a capacity above 0.24 V, the silane compound does not decompose sufficiently, and the battery cell expansion suppression effect cannot be obtained. Therefore, the present invention is premised on the negative electrode being a non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery, which contains at least one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles. Note that, hereinafter, the potential is expressed as Li / Li + The potential is set to 0V.

[0061] The decomposition potential (Li / Li + The potential (reference potential (0 V)) is preferably 0.23 to 0.70 V, more preferably 0.25 to 0.60 V, even more preferably 0.27 to 0.55 V, and particularly preferably 0.30 to 0.50 V. Such a decomposition potential makes it easy to obtain a coating (SEI film) that suppresses expansion of the battery cell. The decomposition potential of the silane compound can be measured, for example, by cyclic voltammetry (CV).

[0062] [Decomposition potential of silane compound decomposition product (coating)] The silane compound contained in the nonaqueous electrolyte of the present invention decomposes to form a coating (SEI film). Such decomposition products (coatings) are preferably stable (do not decompose) at 0.70 V or higher. If they do not decompose at the above potential, the expansion suppression effect of the battery cell can be easily achieved even when a negative electrode with a capacity on the high potential side is used. In particular, negative electrodes containing silicon oxide have a large capacity at 0.7 V or higher, and are therefore compatible with the silane compound contained in the nonaqueous electrolyte of the present invention.

[0063] The silane compound contained in the nonaqueous electrolyte of the present invention has high electron-accepting properties and excellent reductive decomposition properties on the surface of the negative electrode, and is characterized in that it decomposes at a high potential of 0.23 V or higher to form a coating (SEI film) on the surface of the negative electrode. Therefore, it is used to protect negative electrodes that have a capacity on the high potential side of 0.23 V or higher, and is particularly compatible with negative electrodes that use a silicon material as the main material.

[0064] Furthermore, the silane compound contained in the nonaqueous electrolyte of the present invention has a structure that is highly reactive with multiple silicon atoms, and therefore is likely to form a high-quality coating (SEI film) after reductive decomposition, particularly a coating (SEI film) that is excellent in strength and decomposition resistance.

[0065] This type of coating (SEI film) is resistant to repeated charge and discharge and can suppress further decomposition of the electrolyte (e.g., solvent, additives, etc.), thereby making it possible to suppress expansion of the battery cell due to the swelling phenomenon.

[0066] The silane compound contained in the nonaqueous electrolyte of the present invention effectively protects the Li silicate portion that constitutes the silicon-based negative electrode active material, and can form a stable coating (SEI film) with Li2SiO3 and Li4SiO4, which is formed by conversion of Li2SiO3.

[0067] It is known that the Li silicate moiety decomposes at a high potential of 0.7 V or more. However, the coating (SEI film) formed by the silane compound contained in the nonaqueous electrolyte of the present invention has excellent resistance to decomposition at high potentials, and therefore can suppress the decomposition of the Li silicate.

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

[0069] Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. Among these, from the viewpoint of obtaining better properties, it is desirable to use at least one 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 or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate, the dissociation property and ion mobility of the electrolyte salt are improved, resulting in more advantageous properties.

[0070] When using an alloy-based negative electrode containing a silicon-based negative electrode material, it is particularly desirable to use a solvent containing at least one of a halogenated chain carbonate or a halogenated cyclic carbonate. This allows a stable coating to be formed on the surface of the negative electrode active material during charge and discharge, particularly during charging. Here, the halogenated chain carbonate is a chain carbonate having a halogen as a constituent element (i.e., at least one hydrogen atom is substituted with a halogen). Furthermore, the halogenated cyclic carbonate is a cyclic carbonate having a halogen as a constituent element (i.e., at least one hydrogen atom is substituted with a halogen).

[0071] Although the type of halogen is not particularly limited, fluorine is preferred from the viewpoint of forming a coating film of better quality than other halogens. Furthermore, the number of halogens is preferably as large as possible, since the resulting coating film is more stable and the decomposition reaction of the electrolyte is reduced.

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

[0073] The electrolyte salt may include, for example, one or more light metal salts such as lithium salts, for example, lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

[0074] From the viewpoint of obtaining high ionic conductivity, the content of the electrolyte salt relative to the non-aqueous solvent 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, and even more preferably 0.8 mol / kg or more and 1.5 mol / kg or less.

[0075] In addition to the silane compounds represented by the general formulas (1) to (5), the non-aqueous electrolyte of the present invention may further contain, as separate additives, unsaturated carbon-bonded cyclic carbonates, sultones (cyclic sulfonates), and acid anhydrides. Unsaturated carbon-bonded cyclic carbonates may be included from the viewpoint of forming a stable coating on the negative electrode surface during charge and discharge and suppressing decomposition reactions of the non-aqueous electrolyte, and examples thereof include vinylene carbonate and vinylethylene carbonate. Furthermore, sultones may be included from the viewpoint of improving the chemical stability of the battery, and examples thereof include propane sultone and propene sultone. Furthermore, acid anhydrides may be included from the viewpoint of improving the chemical stability of the electrolyte, and examples thereof include propane disulfonic acid anhydride.

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

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

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

[0079] On the other hand, the positive electrode active material layer contains one or more positive electrode materials capable of absorbing and releasing lithium ions, and may contain other materials such as a binder, a conductive additive, a dispersant, etc., depending on the design. In this case, the binder and conductive additive may be the same as the negative electrode binder and negative electrode conductive additive described below.

[0080] Positive electrode materials can be lithium-containing compounds, such as composite oxides containing lithium and transition metal elements or phosphate compounds containing lithium and transition metal elements, from the viewpoint of obtaining high battery capacity and excellent cycle characteristics. Preferred transition metal elements are nickel, iron, manganese, and cobalt, and the lithium-containing compounds are compounds containing at least one of these transition metal elements. The chemical formula of the lithium-containing compound is, for example, LixM1O2 or LiyM2PO4. In the formula, M1 and M2 represent at least one transition metal element. The values ​​of x and y vary depending on the battery's charge / discharge state, but generally satisfy the relationships 0.05≦x≦1.10 and 0.05≦y≦1.10.

[0081] Specific examples of composite oxides containing lithium and transition metal elements include lithium cobalt composite oxide (Li x CoO2, lithium nickel composite oxide (Li x NiO2), lithium nickel cobalt composite oxide, lithium nickel cobalt composite oxide (lithium nickel cobalt aluminum composite oxide; NCA, lithium nickel cobalt manganese composite oxide + NCM), etc.

[0082] Specific examples of the phosphate compound having lithium and a transition metal element include, for example, lithium iron phosphate compound (LiFePO4), lithium iron manganese phosphate compound (LiFe 1-u Mn u PO4, provided that 0 < u < 1), etc. can be mentioned. By using these cathode materials, a high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[0083] [Negative electrode] The negative electrode has a structure having a negative electrode active material layer on, for example, 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 made of an excellent conductive material and has 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 viewpoint of improving the physical strength of the negative electrode current collector, it is preferable to contain carbon (C) and sulfur (S) in addition to the copper (Cu) and nickel (Ni). In particular, when there is an active material layer that expands during charging, the inclusion of the above elements in the current collector 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 viewpoint 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 be roughened or may not be roughened. Examples of the roughened negative electrode current collector include a metal foil treated by electrolysis, embossing, or chemical etching. Examples of the non-roughened negative electrode current collector include a rolled metal foil.

[0087] [Negative electrode active material layer] The negative electrode active material layer contains a negative electrode active material capable of absorbing (inserting) and releasing lithium ions, and may further contain other materials such as a negative electrode binder, a conductive additive, etc. The negative electrode active material contains negative electrode active material particles, and the negative electrode active material particles contain at least any 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), and among these, silicon compound particles are preferred, and silicon compound particles containing a silicon compound containing oxygen are particularly preferred.

[0088] The negative electrode active material contains at least 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), and among these, it is preferable to contain silicon compound particles, and it is particularly preferable to contain silicon oxide material (silicon compound containing oxygen). This silicon compound, SiO x From the viewpoint of cycle characteristics and resistance of silicon oxide, it is preferable that x, which is the composition ratio of silicon to oxygen constituting SiO , is a number that satisfies 0.8≦x≦1.2. x In the composition, it is preferable that x is close to 1, since high cycle characteristics can be obtained. Note that the composition of the silicon compound in the present invention does not necessarily mean 100% purity, and may contain trace amounts of impurity elements.

[0089] It is preferable that the silicon compound contains as little crystalline Si as possible, which can prevent the reactivity with the electrolyte from becoming too high, and as a result, can prevent the battery characteristics from deteriorating.

[0090] The silicon compound contains Li, and it is desirable that some of it is in the form of silicate Li2SiO3. This Li2SiO3 is crystalline, but is active during charge and discharge. In the slurry state, it remains Li2SiO3, but changes to Li4SiO4 with repeated charge and discharge.

[0091] The higher the crystallinity of Li2SiO3, the more difficult it is to convert to Li4SiO4. On the other hand, if the crystallinity is low, it becomes more likely to dissolve in the slurry, so there is an optimum range.

[0092] Specifically, the negative electrode active material particles have a peak attributable to the Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation 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 attributable to the Si(111) crystal plane to the intensity B of the peak attributable to the Li2SiO3(111) crystal plane satisfies the following formula (6): 0.4≦A / B≦1.0 (6) It is preferable that the following is satisfied.

[0093] The degree of Li silicate enlargement and the degree of Si crystallization (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] The X-ray diffraction device used can be a Bruker D8 ADVANCE. The X-ray source is Cu Kα radiation and a Ni filter, and measurements are taken from 10 to 40° with 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 due to the Si(111) crystal plane appears near 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, and even more preferably 2.5 nm or less, and is desirably substantially amorphous.

[0097] The ratio A / B of the intensity A of the peak due to the Si(111) crystal plane to the intensity B of the peak due to the Li2SiO3(111) crystal plane is preferably 0.40≦A / B≦1.00, more preferably 0.45≦A / B≦0.75, and even more preferably 0.50≦A / B≦0.70. Here, the peak due to the Li2SiO3(111) crystal plane appears in the range of 2θ=17° to 21° in an X-ray diffraction chart.

[0098] The median diameter of the negative electrode active material, as measured by a 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, and even 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 expansion of the negative electrode active material during charge and discharge.

[0099] The negative electrode active material layer may contain a mixed negative electrode active material containing the silicon-based negative electrode active material and a carbon-based active material. This reduces the electrical resistance of the negative electrode active material layer and alleviates expansion stress caused by charging. Examples of carbon-based active materials include natural graphite, artificial graphite, hard carbon, and soft carbon.

[0100] The negative electrode active material layer of the present invention contains the negative electrode active material of the present invention that can absorb and release lithium ions, and may further contain other materials such as a negative electrode binder and a conductive additive from the viewpoint of battery design.

[0101] The negative electrode binder may be, for example, one or more of polymer materials, synthetic rubber, etc. Examples of polymer materials include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxymethyl cellulose, etc. Examples of synthetic rubbers include styrene-butadiene rubber, fluorine-based rubber, ethylene propylene diene, etc.

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

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

[0104] [Separator] The separator separates the lithium metal or positive electrode from the negative electrode, preventing current short-circuiting due to contact between the two electrodes while allowing lithium ions to pass through. This separator is formed, for example, from a porous film made of synthetic resin or ceramic, and may have a laminate structure in which two or more types of porous film are laminated. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene. [Example]

[0105] EXAMPLES The present invention will be explained in more detail below by showing examples and comparative examples of the present invention, but the present invention is not limited to these examples.

[0106] <Common features between Examples and Comparative Examples> [HOMO and LUMO energy levels] After structural optimization of the silane compound, the HOMO and LUMO energy levels were calculated. Gaussian 16 was used as the quantum chemistry calculation software. The calculation was performed using density functional theory with B3LYP as the exchange-correlation functional and 6-311+G(d,p) as the basis set.

[0107] [Cyclic Voltammetry] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed, and then a silane compound was dissolved to prepare an electrolyte solution. The volume ratio of EC to DMC was 30:70, and the mass ratio of the EC / DMC mixed solvent to the silane compound was 95:5. Cyclic voltammetry (CV) measurements were performed on the obtained electrolyte solution. A SUS304 plate (immersion area 3 cm) was used as the working electrode. 2 ), platinum wire as counter electrode, Ag / Ag as reference electrode + (Internal solution: acetonitrile, 0.1 mol / L silver nitrate, 0.1 mol / L tetrabutylammonium perchlorate) was used. The scan rate was 50 mV / sec.

[0108] [Example 1] [Preparation of negative electrode] The negative electrode current collector was an electrolytic copper foil having a thickness of 15 μm, which contained carbon and sulfur at concentrations of 70 ppm by mass each.

[0109] The silicon-based negative electrode active material was KSC-7130 ("Li-SiO-C", silicon oxide particles containing Li2SiO3 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), and artificial graphite (median diameter 15 μm). The negative electrode conductive additive was carbon nanotubes and carbon microparticles with a median diameter of approximately 50 nm. The negative electrode binders were sodium polyacrylate and carboxymethyl cellulose, which were mixed in a dry mass ratio of 9.3:83.7:1:1:4:1, respectively, 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. After drying, the deposition amount (area density) of the negative electrode active material layer per unit area on one surface of the negative electrode was 7.0 mg / cm. 2 It was.

[0111] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed as a non-aqueous solvent, and then lithium hexafluorophosphate (LiPF6) was dissolved as an electrolyte salt in this mixed solvent to prepare an electrolyte solution. In this case, the solvent composition was EC:DMC = 30:70 in volume ratio, and the content of the electrolyte salt was 1 mol / kg relative to the solvent.

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

[0113] [Fabrication of non-aqueous electrolyte secondary battery] Next, a coin battery was assembled as follows: First, a 1 mm thick Li foil 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, and the Li foil was placed face-to-face with a separator between them. After the non-aqueous electrolyte obtained by the above method was poured into the negative electrode, a 2032 coin battery, which is a non-aqueous electrolyte secondary battery, was fabricated.

[0114] [Battery evaluation] The coin battery was charged (initial charge) in CCCV mode at a charge rate equivalent to 0.03 C. The CV was set to 0 V and the cut-off current was 0.04 mA. Next, CC discharge (initial discharge) was performed at a discharge rate of 0.03 C and a discharge cut-off voltage of 1.2 V.

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

[0116] Based on the obtained initial efficiency data, a counter positive electrode was designed and the following battery evaluation was carried out.

[0117] [Expansion rate of battery cells (swelling evaluation)] First, to stabilize the battery, two cycles of charge and discharge were performed at 0.2 C in an atmosphere of 25 °C, and then up to the 500th cycle, charge and discharge were performed at 0.7 C and 0.5 C. In this case, the charge voltage was 4.3 V, the discharge cut-off voltage was 2.5 V, and the charge cut-off rate was 0.07 C.

[0118] The thickness of the battery cell was measured at the 500th discharge cycle. The expansion rate of the battery cell was calculated as follows, using the initial thickness of the battery cell (5.5 mm thick, 34 mm wide, 36 mm long) as the reference. Expansion rate (%) = (thickness at 500th cycle / 5.5 mm) x 100

[0119] [Examples 2 to 28] The same procedure as in Example 1 was carried out except that the type of additive (silane compound) and the amount added were changed as shown in Table 2. The structural formula of the silane compound is as shown in Table 1. Si-2 in Table 1 represents the silane compound represented by the general formula (2) with R 1 is a vinyl group, X is a vinylene group, l=3, and m=2. Si-3 in Table 1 is a compound represented by the general formula (3) where R 1 is a vinyl group, X is a vinylene group, l=3, and m=2. Si-4 in Table 1 is a compound represented by the general formula (1) where R 1 is a vinyl group, X is an ethylene group, and l=3. Si-5 in Table 1 is a compound in which 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 a compound in which R 1 is a vinyl group, X is a methylene group, and l=3. Si-7 in Table 1 is a compound in which 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] The silicon material was subjected to additional heat treatment to control the crystallinity of Si and Li2SiO3 and confirm the battery characteristics. The temperature was adjusted within the range of 600 to 700°C. Other than that, the type of additive (silane compound) and the amount added were changed as shown in Table 2, and the same procedure was followed as in Example 1.

[0121] [Comparative Example 1] The same procedure as in Example 1 was carried out except that the additive (silane compound) was not added.

[0122] [Comparative Examples 2 to 4] The same procedure as in Example 1 was carried out, except that the type of additive (silane compound) and the amount added were changed as shown in Table 2. The silane compound used here was MTVS (methyltrivinylsilane), and its structural formula is as shown in Table 1. MTVS does not fall under any of the general formulae (1) to (5).

[0123] [Table 1]

[0124] [Table 2]

[0125] [Examples 41 to 42] Using SIE23PB (metal Si, Kojundo Kagaku) ​​as the negative electrode active material, a negative electrode was prepared in the same manner as in Example 1. The same procedure was followed as in Example 1, except that the type of additive (silane compound) and the amount added were changed as shown in Table 3.

[0126] [Examples 43 to 44] As the negative electrode active material, GEE05PB (germanium, Kojundo Kagaku) ​​was sieved with a mesh size of 20 μm and the collected powder was used to prepare a negative electrode in the same manner as in Example 1. The same procedure was followed as in Example 1, except that the type of additive (silane compound) and the amount added were changed as shown in Table 3.

[0127] [Examples 45 to 46] As the negative electrode active material, SNE08PB (tin, Kojundo Kagaku) ​​was sieved through a 20 μm mesh and the collected powder was used to prepare a negative electrode in the same manner as in Example 1. The same procedure was followed as in Example 1, except that the type of additive (silane compound) and the amount added were changed as shown in Table 3.

[0128] [Examples 47 to 48] As the negative electrode active material, SNO07PB (tin oxide, Kojundo Kagaku) ​​was sieved through a 20 μm mesh and the collected powder was used to prepare a negative electrode in the same manner as in Example 1. The procedure was the same as in Example 1, except that the type and amount of additive (silane compound) were changed as shown in Table 3.

[0129] [Comparative Examples 5 to 6] Artificial graphite (median diameter 15 μm) was used as the negative electrode active material, and a negative electrode was produced in the same manner as in Example 1. The same procedure was followed as in Example 1, except that the type of additive (silane compound) and the amount added were changed as shown in Table 3.

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

[0131] [Table 3]

[0132] As is clear from the results in Table 2, it was confirmed that the expansion of battery cells can be suppressed by adding a silane compound contained in the nonaqueous electrolyte of the present invention, which has a silicon number of 2 or more. Furthermore, lowering the heat treatment temperature of the silicon material tends to suppress Si crystallization and improve the expansion suppression effect.

[0133] As is clear from the results in Table 3, it was confirmed that battery cell expansion was suppressed even with anodes containing metallic Si, germanium, tin, or tin oxide. On the other hand, battery cell expansion was not suppressed with a graphite anode. That is, there was almost no difference between Comparative Examples 5 and 6 and 11.

[0134] Cyclic voltammetry (CV) measurements of the silane compounds contained in the nonaqueous electrolyte of the present invention revealed that all compounds decomposed at around 0.4 V. Because the graphite negative electrode does not have a capacity above 0.24 V, it is believed that the silane compounds did not actively decompose and form a coating, and therefore the expansion-suppressing effect of the battery cell was not obtained.

[0135] In addition, graphite anodes have a lower capacity than silicon, germanium, or tin-based anodes, so there is also the issue that the capacity does not increase when used in a battery.

[0136] The silane compounds contained in the nonaqueous electrolyte of the present invention have a lower LUMO than FEC (LUMO: -0.3921 eV), suggesting excellent reductive decomposition properties at the anode. Furthermore, their HOMO also tends to be higher than those of FEC (HOMO: -8.9715 eV) and MTVS, suggesting that, combined with the low LUMO, they have a high film-forming ability, forming a high-quality film after reductive decomposition. [Industrial Applicability]

[0137] According to the present invention, a non-aqueous electrolyte that can suppress expansion of a battery cell can be provided.

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

Claims

1. A non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery, wherein the negative electrode contains at least one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles, The non-aqueous electrolyte is characterized in that it contains at least one silane compound selected from the silane compounds represented by the following general formulas (1) to (5): 【Chemical 1】 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 (In the formula, R １ are each independently an alkenyl group or an alkynyl group having 2 to 20 carbon atoms, and R ２ are each independently an alkyl group having 1 to 20 carbon atoms, and each X is independently an alkylene group having 1 to 20 carbon atoms or an alkenylene or alkynylene group having 2 to 20 carbon atoms. In addition, each 1 is independently an integer of 1 to 3, and each m is independently an integer of 1 or 2.

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

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

5. the negative electrode active material particles in the negative electrode contain silicon oxide particles coated with a carbon layer, The silicon oxide particles are Li ２ SiO ３ Including, The Li ２ SiO ３ The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that

6. The negative electrode active material particles have a peak attributable to a Si (111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation 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 due to the Si (111) crystal plane to the intensity B of the peak due to the (111) crystal plane is expressed by the following formula (6): 0.4≦A / B≦1.0 (6) 6. The non-aqueous electrolyte according to claim 5, wherein the above formula (1) is satisfied.

7. Li / Li ＋ 7. The nonaqueous electrolyte according to claim 1, wherein the silane compound decomposes to form a coating on the negative electrode in a range of 0.23 V or more relative to a potential of 0 V.

8. The coating formed by decomposition of the silane compound is Li / Li ＋ 8. The non-aqueous electrolyte according to claim 7, which is stable in a range of 0.70 V or more when the potential of said electrolyte is set to 0 V as a reference potential.

9. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte according to any one of claims 1 to 8.

Images