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: The invention provides 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 a silane compound represented by the following general formula (1): Si(R1)l(R2)m(R3)4-l-m (1). In the general formula (1), R1 represents an aryl group in which some or all of hydrogen atoms in an aryl group having 6 to 20 carbon atoms are substituted with a fluorine atom or a fluoroalkyl group; R2 represents an alkenyl group or alkynyl group having 2 to 20 carbon atoms; R3 represents an alkyl group having 1 to 20 carbon atoms; and l and m each independently represent an integer of 1 to 3, provided that 2≤l+m≤4 is satisfied.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 been widely spread, 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 high energy density has been promoted. Application of this secondary battery is being studied not only for small electronic devices but also for large electronic devices typified by automobiles and for power storage systems typified by houses.

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

[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, while 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 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, an ionic substance is generated inside the negative electrode active material, making the negative electrode active material a substance prone to cracking. When the surface layer of the negative electrode active material cracks, a new surface is thereby generated, increasing the reaction area of the negative electrode active material. At this time, a decomposition reaction of the electrolyte occurs on the new surface, and a film that is a decomposition product of the electrolyte is formed on the new surface, so the electrolyte is consumed and the cycle characteristics are likely to deteriorate.

[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 materials in order to improve the initial efficiency and cycle characteristics of the battery.

[0008] Specifically, for the purpose of obtaining 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). In addition, in order to obtain a 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, 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 a place close to 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 there is a demand for an increase in the battery capacity of lithium-ion secondary batteries, which are their main power sources. As one method of 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 comparable to those of a lithium-ion secondary battery using a carbon-based active material. Therefore, fluorine-based additives have been developed, and the battery characteristics tend to improve. However, by repeatedly charging and discharging, 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 the form of being 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 are 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 a 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 a silane compound represented by the following general formula (1). Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In general formula (1), R 1 is an aryl group in which some or all of the hydrogen atoms of an aryl group having 6 to 20 carbon atoms are substituted with fluorine atoms or fluoroalkyl groups, R 2 is an alkenyl group or alkynyl group having 2 to 20 carbon atoms, and R 3 is an alkyl group having 1 to 20 carbon atoms. Also, l and m each independently represent an integer of 1 to 3, and are integers satisfying 2 ≤ l + m ≤ 4.)

[0014] Such a silane compound has high electron accepting property and excellent reductive decomposability on the negative electrode surface, and thus has a feature 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, sufficient battery cycle characteristics can be realized while using these negative electrode materials, and battery swelling can be suppressed.

[0015] At this time, it is preferable that the energy level of the lowest unoccupied molecular orbital of the silane compound represented by the general formula (1) is -0.40 eV or lower.

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

[0017] Also, it is preferable that the energy level of the highest occupied molecular orbital of the silane compound represented by the general formula (1) is -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 represented by the general formula (1) contained in the non-aqueous electrolyte is preferably 0.1% by mass to 10.0% by mass.

[0020] With such a content, a sufficient film (SEI film) is easily formed, and the expansion 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, the silicon oxide particles contain Li2SiO3, and the Li2SiO3 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 Li2SiO3(111) crystal plane is the following formula (2) 0.4 ≦ A / B ≦ 1.0 ···(2) is preferably 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 non-aqueous electrolyte of the present invention can be preferably used for a non-aqueous 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, when the potential of Li / Li + is taken as the 0V reference, in the range of 0.23V or more, it is preferable that the silane compound represented by the general formula (1) decomposes to form a film on the negative electrode.

[0026] Such a silane compound decomposes at a high potential of 0.23V or more and has the characteristic of forming a film (SEI film) on the surface of the negative electrode. Therefore, it can be suitably used for a non-aqueous electrolyte secondary battery containing at least 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] In addition, it is preferable that the film formed by the decomposition of the silane compound represented by the general formula (1) is in a stable state in the range of 0.70V or more when the potential of Li / Li + is taken as the 0V reference.

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

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

[0030] Such a non-aqueous electrolyte secondary battery is a non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte of the present invention, so it can exhibit sufficient battery cycle characteristics and can suppress battery swelling.

Effects of the Invention

[0031] The silane compound represented by the general formula (1) contained in such a non-aqueous electrolyte of the present invention has high electron acceptability and excellent reductive decomposability on the surface of the negative electrode, and thus has 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, sufficient battery cycle characteristics can be realized while using these negative electrode materials, and battery swelling can be suppressed.

Embodiments for Carrying Out the Invention

[0032] As described above, even when a silicon-based negative electrode material is used, a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery capable of realizing sufficient battery cycle characteristics have been demanded.

[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 a functional group containing a fluorine aromatic compound into a silane compound and further introducing an alkenyl group or an alkynyl group, and 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, The non-aqueous electrolyte is characterized in that it contains a silane compound represented by the following general formula (1). Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1) (In the general formula (1), R 1 is an aryl group in which part or all of the hydrogen atoms of an aryl group having 6 to 20 carbon atoms are substituted with fluorine atoms or fluoroalkyl groups, R 2 is an alkenyl group or an alkynyl group having 2 to 20 carbon atoms, R 3is an alkyl group having 1 to 20 carbon atoms. Also, l and m each independently represent an integer of 1 to 3, and are integers satisfying 2 ≦ l + m ≦ 4.)

[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 represented by the following general formula (1) (hereinafter, also referred to as "compound (1)"). Si(R 1 ) l (R 2 ) m (R 3 ) 4-l-m (1)

[0037] In the general formula (1), R 1 is an aryl group in which part or all of the hydrogen atoms of an aryl group having 6 to 20 carbon atoms, preferably 6 to 12 carbon atoms, more preferably 6 to 8 carbon atoms are substituted with fluorine atoms or fluoroalkyl groups.

[0038] R 1Specific examples of the aryl group in which some or all of the hydrogen atoms of the aryl group are substituted with fluorine atoms or fluoroalkyl groups include 2-fluorophenyl group, 3-fluorophenyl group, 4-fluorophenyl group, 2,3-difluorophenyl group, 2,4-difluorophenyl group, 2,5-difluorophenyl group, 2,6-difluorophenyl group, 3,4-difluorophenyl group, 3,5-difluorophenyl group, 2,3,4-trifluorophenyl group, 2,3,5-trifluorophenyl group, 2,3,6-trifluorophenyl group, 2,4,5-trifluorophenyl group, 2,4,6-trifluorophenyl group, 2,3,4,5-tetrafluorophenyl group, 2,3,4,6-tetrafluorophenyl group, 2,3,5,6-tetrafluorophenyl group, pentafluorophenyl group and other aryl groups in which some or all of the hydrogen atoms are substituted with fluorine atoms; 2-trifluoromethylphenyl group, 3-trifluoromethylphenyl group, 4-trifluoromethylphenyl group, 2,3-bis(trifluoromethyl)phenyl group, 2,4-bis(trifluoromethyl)phenyl group, 2,5-bis(trifluoromethyl)phenyl group, 2,6-bis(trifluoromethyl)phenyl group, 3,4-bis(trifluoromethyl)phenyl group, 3,5-bis(trifluoromethyl)phenyl group, 2,3,4-tris(trifluoromethyl)phenyl group, 2,3,5-tris(trifluoromethyl)phenyl group, 2,3,6-tris(trifluoromethyl)phenyl group, 2,4,5-tris(trifluoromethyl)phenyl group, 2,4,6-tris(trifluoromethyl)phenyl group and other aryl groups in which some or all of the hydrogen atoms are substituted with fluoroalkyl groups.

[0039] Among these, from the viewpoint of significantly increasing the electron-accepting property and enhancing the reductive decomposability of the silane compound, 2-fluorophenyl group, 3-fluorophenyl group, 4-fluorophenyl group, 2-trifluoromethylphenyl group, 3-trifluoromethylphenyl group, 4-trifluoromethylphenyl group are preferred.

[0040] In general formula (1), R 2is 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.

[0041] R 2 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; and branched alkenyl groups such as isopropenyl group, isobutenyl group, isopentenyl group, isohexenyl group, isoheptenyl group, isooctenyl group, isononyl group, isodecenyl group, isoundecyl 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), a vinyl group and an n-propenyl group are preferred.

[0043] R 2 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; and 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.

[0044] 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, 1-propynyl group, and 1-butynyl group are preferred.

[0045] In general formula (1), R 3is an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms.

[0046] R 3 Specific examples of the alkyl group of

[0047] 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.

[0048] In the general formula (1), l and m each independently represent an integer of 1 to 3, and l and m are integers satisfying 2 ≦ l + m ≦ 4. From the viewpoint of improving the reductive decomposability of the silane compound, in the general formula (1), it is more preferable that l and m each independently represent an integer of 1 to 3 and l and m are integers satisfying l + m = 4.

[0049] Specific examples of the compound (1) include 2-fluorophenyltrivinylsilane, bis(2-fluorophenyl)divinylsilane, tris(2-fluorophenyl)vinylsilane, 3-fluorophenyltrivinylsilane, bis(3-fluorophenyl)divinylsilane, tris(3-fluorophenyl)vinylsilane, 4-fluorophenyltrivinylsilane, bis(4-fluorophenyl)divinylsilane, tris(4-fluorophenyl)vinylsilane, 2-fluorophenyltriethynylsilane, bis(2-fluorophenyl)diethynylsilane, ethynyltris(2-fluorophenyl)silane, 3-fluorophenyltriethynylsilane, bis(3-fluorophenyl)diethynylsilane, ethynyltris(3-fluorophenyl)silane, 4-fluorophenyltriethynylsilane, bis(4-fluorophenyl)diethynylsilane, ethynyltris(4-fluorophenyl)silane, 2-trifluoromethylphenyltrivinylsilane, bis(2-trifluoromethylphenyl)divinylsilane, tris(2-trifluoromethylphenyl)vinylsilane, 3-trifluoromethylphenyltrivinylsilane, bis(3-trifluoromethylphenyl)divinylsilane, tris(3-trifluoromethylphenyl)vinylsilane, 4-trifluoromethylphenyltrivinylsilane, bis(4-trifluoromethylphenyl)divinylsilane, tris(4-trifluoromethylphenyl)vinylsilane, triethynyl-2-trifluoromethylphenylsilane, bis(2-trifluoromethylphenyl)diethynylsilane, ethynyltris(2-trifluoromethylphenyl)silane, triethynyl-3-trifluoromethylphenylsilane, bis(3-trifluoromethylphenyl)diethynylsilane, ethynyltris(3-trifluoromethylphenyl)silane, triethynyl-4-trifluoromethylphenylsilane, bis(4-trifluoromethylphenyl)diethynylsilane, ethynyltris(4-trifluoromethylphenyl)silane, 2-fluorophenyldivinylmethylsilane, bis(2-fluorophenyl)methylvinylsilane, 3-fluorophenyldivinylmethylsilane, bis(3-fluorophenyl)methylvinylsilane, 4-fluorophenyldivinylmethylsilane,Examples include bis(4-fluorophenyl)methylvinylsilane, divinylmethyl-2-trifluoromethylphenylsilane, bis(2-trifluoromethylphenyl)methylvinylsilane, divinylmethyl-3-trifluoromethylphenylsilane, bis(3-trifluoromethylphenyl)methylvinylsilane, divinylmethyl-4-trifluoromethylphenylsilane, bis(4-trifluoromethylphenyl)methylvinylsilane, and the like.

[0050] The silane compound represented by the general formula (1) can be obtained, for example, by reacting vinyl halosilane with fluoroaryl magnesium halide or fluoroaryl lithium.

[0051] [Content in non-aqueous electrolyte] The content of the compound (1) in the non-aqueous electrolyte is preferably 0.1% by mass to 10.0% by mass, more preferably 0.1% by mass to 8.0% by mass, still more preferably 0.1% by mass to 6.0% by mass, and particularly preferably 1.0% by mass to 5.0% by mass. With such a content, a sufficient film (SEI film) is easily formed, and the expansion of the battery cell is easily suppressed. Also, it is easy to prevent the increase in resistance due to excessive film (SEI film) formation.

[0052] [Lowest unoccupied molecular orbital (LUMO) energy level] The lowest unoccupied molecular orbital (LUMO) energy level of the silane compound (compound (1)) is preferably -0.40 eV or lower, more preferably -0.70 eV or lower, still more preferably -0.90 eV or lower, and particularly preferably -1.0 eV or lower. With such an energy level, the silane compound is likely to undergo reductive decomposition.

[0053] [Highest occupied molecular orbital (HOMO) energy level] The highest occupied molecular orbital (HOMO) energy level of the silane compound (compound (1)) is preferably -8.8 eV or higher, more preferably -8.5 eV or higher, still more preferably -8.0 eV or higher, and particularly preferably -7.8 eV or higher. With such an energy level, the reactivity after reductive decomposition, particularly the radical reactivity, is improved, and a high-quality film (SEI film) can be easily obtained.

[0054] [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. As software for quantum chemical calculations, Gaussian, GAMESS, etc. 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.

[0055] [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 effect of suppressing the swelling of the battery cell, 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. With the potential of 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 effect of suppressing the swelling of the battery cell cannot be obtained. Therefore, the present invention is premised on a non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery in which the negative electrode contains 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 + being 0 V.

[0056] The decomposition potential (Li / Li +The potential of [[ID=]] 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 with respect to the reference (0 V). With such a decomposition potential, a film (SEI film) that suppresses the swelling of the battery cell is easily obtained. The decomposition potential of the silane compound can be measured, for example, by cyclic voltammetry (CV).

[0057] [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 capacity 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 capacity at 0.7 V or higher, so it has good compatibility with the silane compound contained in the non-aqueous electrolyte of the present invention.

[0058] The silane compound represented by the general formula (1) contained in the non-aqueous electrolyte of the present invention has high electron acceptability 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 capacity on the high potential side of 0.23 V or higher, and particularly has good compatibility with a negative electrode mainly made of a silicon material.

[0059] In addition, 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, so it easily forms a high-quality film (SEI film), particularly a film (SEI film) excellent in strength and decomposition resistance, after reductive decomposition.

[0060] 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.

[0061] Since the silane compound contained in the non-aqueous electrolyte of the present invention has a fluoro group that strongly interacts with silicon, it can effectively protect the Li silicate part that constitutes the silicon-based negative electrode active material, and can also form a stable film (SEI film) with Li2SiO3 and Li4SiO4 formed by the conversion of Li2SiO3.

[0062] The Li silicate part is known to decompose at a high potential of 0.7 V or more. 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 the decomposition of Li silicate can be suppressed.

[0063] <Non-aqueous electrolyte secondary battery> [Non-aqueous electrolyte] The non-aqueous electrolyte of the present invention has an electrolyte salt dissolved in a non-aqueous solvent and contains the compound (1), and may also contain other materials as additives. At least a part of the active material layer or the separator is impregnated with the non-aqueous electrolyte.

[0064] 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 or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate, the dissociation property of the electrolyte salt and the ion mobility can be improved, and more excellent characteristics can be obtained.

[0065] When using an alloy negative electrode containing a silicon-based negative electrode material, it is particularly desirable that the solvent contains at least one of a halogenated linear 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 linear carbonate is a linear carbonate having a halogen as a constituent element (at least one hydrogen is substituted by a halogen). Also, 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).

[0066] 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 decomposition reaction of the electrolyte is reduced.

[0067] Examples of the halogenated linear 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.

[0068] 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 (LiPF6), lithium tetrafluoroborate (LiBF4), and the like.

[0069] 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.

[0070] In addition to the compound (1), the non-aqueous electrolyte of the present invention can contain, as further separate additives, unsaturated carbon-bonded cyclic carbonates, sultones (cyclic sulfonic acid esters), and acid anhydrides. 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, the 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, the acid anhydride can be included from the viewpoint of improving the chemical stability of the electrolyte, and an example thereof is propane disulfonic anhydride.

[0071] 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.

[0072] [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.

[0073] Here, the positive electrode current collector is formed of a conductive material such as aluminum, for example.

[0074] On the other hand, the positive electrode active material layer contains any one or two or more kinds of positive electrode materials capable of occluding and releasing 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.

[0075] As the positive electrode material, from the viewpoint of obtaining a high battery capacity and excellent cycle characteristics, for example, lithium-containing compounds such as composite oxides containing lithium and transition metal elements or phosphate compounds containing lithium and transition metal elements can be mentioned. As the transition metal element, nickel, iron, manganese, and cobalt are preferable, and the lithium-containing compound is a compound having at least one of these transition metal elements. As the chemical formula of the thium-containing compound, for example, it is represented by LixM1O2 or LiyM2PO4. In the formula, M1 and M2 represent at least one transition metal element. The values of x and y represent different values depending on the battery charge and discharge state, but generally satisfy 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

[0076] Specific examples of the composite oxide containing lithium and transition metal elements include, for example, 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.

[0077] Specific examples of the phosphate compound containing lithium and transition metal elements 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. By using these positive electrode materials, a high battery capacity can be obtained and excellent cycle characteristics can also be obtained.

[0078] [Negative electrode] The negative electrode has, for example, a structure 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.

[0079] [Negative electrode current collector] The negative electrode current collector is composed of an excellent conductive material and has high 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).

[0080] From the perspective of improving the physical strength of the negative electrode current collector, in addition to the above-mentioned copper (Cu) and nickel (Ni), it is preferable that 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 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 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.

[0081] 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.

[0082] [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.

[0083] 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). Among them, it preferably contains silicon compound particles, and particularly preferably contains a silicon oxide material (silicon compound containing oxygen). This silicon compound SiO x The composition ratio x of silicon to oxygen constituting is preferably a number satisfying 0.8 ≦ x ≦ 1.2 from the viewpoints of cycle characteristics and the resistance of the silicon oxide. Among them, for the composition of SiO x , it is preferable that x is closer to 1 because higher cycle characteristics can be obtained. 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.

[0084] 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.

[0085] The silicon compound contains Li, and it is desirable that a part of it becomes Li2SiO3 as a silicate. This Li2SiO3 is crystalline but is active with respect to charge and discharge. In a slurry state, it remains as Li2SiO3, but changes to Li4SiO4 by repeating charge and discharge.

[0086] The higher the crystallinity of Li2SiO3, the more difficult it is to convert to Li4SiO4. On the other hand, in the case of low crystallinity, it is likely to elute into the slurry, so there is an optimal range.

[0087] Specifically, before charging and discharging the negative electrode active material particles, 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. The crystallite size corresponding to this 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 Li2SiO3(111) crystal plane is given by the following formula (2) 0.4 ≦ A / B ≦ 1.0 ···(2) It is preferable to satisfy this condition.

[0088] The degree of coarsening of the Li 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").

[0089] 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 is measured 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.

[0090] The peak caused by the Si(111) crystal plane appears near 2θ = 28.4° in the X-ray diffraction chart.

[0091] 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.

[0092] 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 Li2SiO3(111) crystal plane is preferably 0.40 ≦ A / B ≦ 1.00, more preferably 0.45 ≦ A / B ≦ 0.75, and still more preferably 0.50 ≦ A / B ≦ 0.70. Here, the peak caused by the Li2SiO3(111) crystal plane appears in the range of 2θ = 17° to 21° in the X-ray diffraction chart.

[0093] From the viewpoint of controlling the reaction with the electrolyte or suppressing the expansion of the negative electrode active material accompanying charge and discharge, 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, and still more preferably 6.0 μm or more and 8.0 μm or less.

[0094] The negative electrode active material layer may contain a mixed negative electrode active 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.

[0095] 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 from the viewpoint of battery design, may further contain other materials such as a negative electrode binder (binder) and a conductive assistant.

[0096] As the negative electrode binder, for example, any one or more of a polymer material, a synthetic rubber, and the like 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.

[0097] Examples of the negative electrode conductive assistant include carbon fine particles, carbon black, acetylene black, graphite, ketjen black, carbon nanotubes, carbon nanofibers, and the like, and any one or more of these can be used.

[0098] 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 and a binder are mixed with a negative electrode conductive assistant and a carbon-based active material as necessary, and then dispersed in an organic solvent or water and coated.

[0099] [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.

Examples

[0100] Hereinafter, the present invention will be described more specifically by showing examples and comparative examples of the present invention, but the present invention is not limited to these examples.

[0101] <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 6 - 311+G(d,p) basis function were used, and the calculation was performed using the density functional method.

[0102] [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.

[0103] [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.

[0104] As the silicon-based negative electrode active material, KSC-7130 (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), 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.

[0105] 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 It was.

[0106] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed as non-aqueous solvents, and then lithium hexafluorophosphate: LiPF6 was dissolved in this mixed solvent as an electrolyte salt to prepare an electrolyte. 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.

[0107] Vinylene carbonate (VC) and bis(4-fluorophenyl)divinylsilane (hereinafter referred to as "BFDVS") were added to the prepared electrolyte as additives for film formation at 1.0% by mass and 0.1% by mass, respectively, to prepare a non-aqueous electrolyte. The structural formula of BFDVS is shown in Table 1.

[0108] [Fabrication of non-aqueous electrolyte secondary battery] Next, the 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.

[0109] [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 discharge termination voltage was set to 1.2V, and CC discharge (first discharge) was performed.

[0110] In order to examine the initial charge-discharge characteristics, the initial efficiency (hereinafter also referred to as "initial efficiency") was calculated as follows. Initial efficiency (%) = (first discharge capacity / first charge capacity) × 100

[0111] Based on the obtained initial efficiency data, the counter electrode was designed and the following battery evaluations were performed.

[0112] [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 then charge-discharge was performed at 0.7C for charging and 0.5C for discharging up to the 500th cycle. At this time, the charging voltage was 4.3V, the discharge termination voltage was 2.5V, and the charging termination rate was 0.07C.

[0113] 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

[0114] [Examples 2 to 20] It was carried out in the same manner as in Example 1 except that the type of additive (silane compound) and the addition amount were changed as shown in Table 2. The structural formula of the silane compound is as shown in Table 1.

[0115] [Examples 21 - 32] Additional heat treatment was performed on the silicon material to control the crystallinity of Si and Li2SiO3 and confirm the battery characteristics. The temperature was adjusted in the range of 600 - 700°C. Otherwise, it was carried out in the same manner as in Example 1 except that the type of additive (silane compound) and the addition amount were changed as shown in Table 2.

[0116] [Comparative Example 1] It was carried out in the same manner as in Example 1 except that no additive (silane compound) was added.

[0117] [Comparative Examples 2 - 4] It was carried out in the same manner as in Example 1 except that the type of additive (silane compound) and the addition amount were changed as shown in Table 2.

[0118]

Table 1

[0119]

Table 2

[0120] [Examples 33 - 34] 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. Otherwise, it was carried out in the same manner as in Example 1 except that the type of additive (silane compound) and the addition amount were changed as shown in Table 3.

[0121] [Examples 35 - 36] 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. Otherwise, it was carried out in the same manner as in Example 1 except that the type of additive (silane compound) and the addition amount were changed as shown in Table 3.

[0122] [Examples 37 - 38] 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. Otherwise, it was carried out in the same manner as in Example 1 except that the type (silane compound) and amount of the additive were changed as shown in Table 3.

[0123] [Examples 39 - 40] 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 amount of the additive were changed as shown in Table 3.

[0124] [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 amount of the additive were changed as shown in Table 3.

[0125] [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.

[0126]

Table 3

[0127] 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 containing a fluorine - containing aromatic compound, the swelling of the battery cell was suppressed. In particular, it is excellent in that a sufficient swelling - suppressing effect can be obtained even without adding fluoroethylene carbonate (FEC). Also, when the heat treatment temperature of the silicon material was lowered, the crystallization of Si was suppressed, and the swelling - suppressing effect tended to improve.

[0128] As is clear from the results in Table 3, it was confirmed that the expansion of the battery cell was suppressed even in the negative electrode containing metal Si, germanium, tin, and tin oxide. On the other hand, in the graphite negative electrode, the expansion of the battery cell was not suppressed.

[0129] Regarding the silane compounds contained in the non-aqueous electrolyte of the present invention, when cyclic voltammetry (CV) was measured, it was revealed that all of the compounds decomposed around 0.4V. Since the graphite negative electrode does not have a capacity of 0.24V or more, it is considered that the positive decomposition and film formation of the silane compound were not performed, and the effect of suppressing the expansion of the battery cell was not obtained.

[0130] In addition, the graphite negative electrode has a problem that the capacity does not increase when made into a battery because it has less capacity than silicon, germanium, and tin-based negative electrodes.

[0131] 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 PHITVS and is excellent in reductive decomposability at the negative electrode. Also, the HOMO also tends to be higher than that of FEC (HOMO: -8.9715 eV), 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

[0132] According to the present invention, a non-aqueous electrolyte capable of suppressing the expansion of a battery cell can be provided.

[0133] Note that the present invention is not limited to the above-described embodiment. The above-described embodiment is an example, 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 one of a silicon compound, a germanium compound, and a tin compound as negative electrode active material particles, wherein the non-aqueous electrolyte contains a silane compound represented by the following general formula (1). A non-aqueous electrolyte characterized by this. Si(R １ ) ｌ (R ２ ) ｍ (R ３ ) ４－ｌ－ｍ (1) (In general formula (1), R １ is an aryl group in which some or all of the hydrogen atoms of an aryl group having 6 to 20 carbon atoms are substituted with fluorine atoms or fluoroalkyl groups, and R ２ is an alkenyl group or an alkynyl group having 2 to 20 carbon atoms, and R ３ is an alkyl group having 1 to 20 carbon atoms. Also, l and m each independently represent an integer of 1 to 3, and are integers satisfying 2 ≤ l + m ≤ 4.)

2. The non-aqueous electrolyte according to Claim 1, wherein the energy level of the lowest unoccupied molecular orbital of the silane compound represented by the general formula (1) 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 represented by the general formula (1) 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 represented by the general formula (1) contained in the non-aqueous electrolyte is 0.1% by mass to 10.0% 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 contain Li ２ SiO ３ and The Li ２ SiO ３ is crystalline, and the non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that.

6. 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, 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 (2) 0.4 ≦ A / B ≦ 1.0 ··· (2) The non-aqueous electrolyte according to Claim 5, characterized by satisfying the above.

7. 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 represented by the general formula (1) decomposes to form a film on the negative electrode. The non-aqueous electrolyte according to any one of claims 1 to 6, characterized in that.

8. The film formed by the decomposition of the silane compound represented by the general formula (1) is stable in the range of 0.70 V or more when the potential of Li / Li ＋ is taken as the reference of 0 V. The non-aqueous electrolyte according to claim 7, characterized in that it is in a stable state.

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

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