Non-aqueous electrolyte and power storage device

Abstract

This non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt, wherein the electrolyte salt includes a first lithium salt, a second lithium salt, and a third lithium salt. The first lithium salt is at least one selected from the group consisting of LiPF6, LiSbF6 and LiAsF6, the second lithium salt is at least one selected from the group of imide salts represented by LiN(SO2R1)(SO2R2) (R1 and R2 are each independently represented by CnF2n+1, and n is an integer of 0 or more), and the third lithium salt is at least one selected from the group consisting of oxalate complex salts and lithium nitrate. The shift value from a reference peak (the peak in the 7Li-NMR spectrum of a 1 mol / L LiCl solution in D2O) in the 7Li-NMR spectrum of the non-aqueous electrolyte is -1.15 ppm or more.

Description

Nonaqueous electrolyte and power storage device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-023997, filed on February 20, 2024 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a non-aqueous electrolyte and an electricity storage device.

[0003] Patent Document 1 describes a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and the electrolyte salt is LiPF ６ , LiBF ４ , LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ , and LiN(SO ２ C ２ F ５ ) ２ and at least one second lithium salt selected from lithium salts having an oxalic acid skeleton, lithium salts having a phosphate skeleton, and lithium salts having an S═O group, wherein the first lithium salt and the second lithium salt are four or more in total.

[0004] International Publication No. 2016 / 009994

[0005] Although efforts to improve the high-temperature and low-temperature performance of batteries by mixing multiple types of lithium salts in a non-aqueous electrolyte have been reported, further improvements are needed to ensure reversibility of charge / discharge cycles and output characteristics at low temperatures, as the trend toward higher battery capacities has led to higher electrode densities and thicker electrode mixture layers.

[0006] One aspect of the present disclosure is a non-aqueous electrolyte solution including a non-aqueous solvent and an electrolyte salt, the electrolyte salt including a first lithium salt, a second lithium salt, and a third lithium salt, the first lithium salt being LiPF ６ , LiSbF ６ and LiAsF ６and the second lithium salt is at least one selected from the group consisting of LiN(SO ２ R1) (SO ２ R2) (wherein R1 and R2 are each independently C ｎ F ２ｎ＋１ wherein n is an integer of 0 or more; the third lithium salt is at least one selected from the group consisting of an oxalate complex salt and lithium nitrate; and ７ The shift value from the base peak in the Li-NMR spectrum is −1.15 ppm or more, and the base peak is the D peak of LiCl at a concentration of 1 mol / L measured at 25° C. ２ O solution ７ This relates to the non-aqueous electrolyte, which is a peak in the Li-NMR spectrum.

[0007] By using the nonaqueous electrolyte according to the present disclosure, an electrochemical device with excellent high-temperature and low-temperature performance can be realized. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0008] 1 is a longitudinal sectional view schematically illustrating a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0009] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0010] The present disclosure encompasses any combination of two or more claims arbitrarily selected from the appended claims, i.e., any combination of two or more claims arbitrarily selected from the appended claims may be combined unless a technical contradiction arises.

[0011] [Non-aqueous electrolyte] The present disclosure relates to a non-aqueous electrolyte used in a non-aqueous electrochemical device such as a lithium ion secondary battery. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte may further contain an additive. The electrolyte salt contains the following first lithium salt, second lithium salt, and third lithium salt. The non-aqueous electrolyte contains: ７ The Li-NMR spectrum is designed to meet certain conditions.

[0012] Specifically, the nonaqueous electrolyte solution according to the present disclosure (hereinafter also referred to as "electrolyte solution (L)") has a specific resistance measured at 25°C. ７ The shift value from the base peak in the Li-NMR spectrum (hereinafter also referred to as "shift value (S)") is designed to be -1.15 ppm or more. The base peak is the D of LiCl at a concentration of 1 mol / L measured at 25°C. ２ O solution ７ These are peaks in the Li-NMR spectrum.

[0013] The shift value (S) may be in the range of -1.15 ppm or more and -0.90 ppm or less, or in the range of -1.15 ppm or more and -1.00 ppm or less.

[0014] The electrolyte solution (L) is in a high entropy state due to the mixture of multiple lithium salts, and it is believed that dissociation of the lithium salts is suppressed, and the solvation of the lithium ions is in a state in which the anions are coordinated. By adopting such a solution structure with high entropy in the desolvation reaction, it is believed that the energy required for desolvation is reduced, making it easier to achieve high output even at low temperatures.

[0015] On the other hand, by changing the solvation of lithium ions to a state where anions are coordinated, the active centers for the reductive decomposition of the solvent, which is the main cause of capacity degradation, are reduced, improving cycle characteristics at high temperatures. In addition, the interaction between the anions of the lithium salt and the lithium ions is relatively strong, making it easier for a high-quality inorganic coating derived from the anions of the lithium salt to form on the electrode surface.

[0016] As a result of the above, by using the electrolytic solution (L), an electrochemical device can be realized which has excellent charge-discharge cycle characteristics at high and low temperatures and which has reduced internal resistance at low temperatures.

[0017] (Electrolyte Salt) The first lithium salt is LiPF ６ , LiSbF ６ and LiAsF ６ The first lithium salt is at least one selected from the group consisting of: The first lithium salt has a relatively excellent lithium ion dissociation property, and has a function of promoting ion transport in the electrolyte solution (L) in a high-entropy state.

[0018] The first lithium salt is at least LiPF ６ It is preferable that the material contains LiPF ６ has excellent lithium ion dissociation properties. ６ The molar fraction of is preferably 0.5 or more, may be 0.7 or more, or may be 0.9 or more and 1.0 or less.

[0019] The second lithium salt is LiN(SO ２ R1) (SO ２ R2) (wherein R1 and R2 are each independently C ｎ F ２ｎ＋１ where n is an integer of 0 or more. The second lithium salt is at least one selected from the group of imide salts represented by the formula: ６ They tend to exhibit high ionic conductivity compared to other salts. In imide salts, the anions are relatively weakly coordinated to the lithium ions, making it easy to form a high-quality anion-derived coating on the surface of the electrode (especially the negative electrode). Imide salts are suitable for achieving good liquid properties, such as high ionic conductivity and low viscosity.

[0020] The imide salt alone tends to corrode Al during high potential sweeps, whereas the electrolyte (L) containing the first to third lithium salts and having a shift value (S) that satisfies the above condition suppresses Al corrosion.

[0021] The second lithium salt is, for example, LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ and LiN(SO ２ F) (SO ２ CF ３ These second lithium salts have excellent lithium ion dissociation properties and are likely to form a high-quality coating on the surface of the electrode.

[0022] The second lithium salt preferably contains at least two salts. In this case, one of the two salts is LiN(SO ２ F) ２ It is preferable that:

[0023] An example of a preferred combination of second lithium salts is LiN(SO ２ F) ２ and LiN (SO ２ CF ３ ) ２ Combination with LiN(SO ２ F) ２ and LiN (SO ２ F) (SO ２ CF ３ ) combination, LiN(SO ２ F) ２ and LiN (SO ２ CF ３ ) ２ Combination with LiN(SO ２ F) ２ and LiN (SO ２ CF ３ ) ２ and LiN (SO ２ F) (SO ２ CF ３ ) can be combined.

[0024] When the second lithium salt contains at least two kinds of salts, LiN(SO ２ F) ２ The mole fraction of is preferably greater than 0.5, may be 0.5 to 0.8, or may be 0.5 to 0.75.

[0025] The third lithium salt is at least one selected from the group consisting of an oxalate complex salt and lithium nitrate. In the third lithium salt, the anion is relatively weakly coordinated to the lithium ion. Therefore, the third lithium salt improves low-temperature and high-temperature operating performance.

[0026] The third lithium salt alone has a low degree of dissociation, and tends to increase the viscosity of the non-aqueous electrolyte, increase the internal resistance, and decrease the ionic conductivity. On the other hand, an electrolyte (L) containing the first to third lithium salts and having a shift value (S) that satisfies the above condition reduces the internal resistance at low temperatures. The third lithium salt is ７ This contributes to the magnitude of the specific shift in the Li-NMR spectrum.

[0027] The third lithium salt may be, for example, at least one selected from the group consisting of lithium bis(oxalato)borate (hereinafter also referred to as "LiBOB"), lithium difluoro(oxalato)borate (hereinafter also referred to as "LiDFOB"), lithium tetrafluoro(oxalato)phosphate (hereinafter also referred to as "LiTFOP"), lithium difluorobis(oxalato)phosphate (hereinafter also referred to as "LiDFBOP"), and lithium nitrate.

[0028] The third lithium salt preferably contains at least LiDFOB. LiDFOB has excellent lithium ion dissociation properties and, among the third lithium salts, is more likely to maintain a low viscosity of the nonaqueous electrolyte. The mole fraction of LiDFOB in the third lithium salt is preferably 0.5 or more, and may be 0.7 or more, or may be 0.9 to 1.0.

[0029] The total molar concentration of the first lithium salt, the second lithium salt, and the third lithium salt may be in the range of 1.2 mol / L to 2.0 mol / L, may be in the range of 1.2 mol / L to 1.8 mol / L, or may be in the range of 1.2 mol / L to 1.6 mol / L.

[0030] The molar concentration of the first lithium salt (hereinafter also referred to as "first molar concentration Ma") may be, for example, in the range of 0.2 mol / L to 1.0 mol / L, in the range of 0.3 mol / L to 0.9 mol / L, or in the range of 0.4 mol / L to 0.8 mol / L.

[0031] The molar concentration of the second lithium salt (hereinafter also referred to as "second molar concentration Mb") may be, for example, in the range of 0.2 mol / L to 1.0 mol / L, in the range of 0.3 mol / L to 0.9 mol / L, or in the range of 0.4 mol / L to 0.8 mol / L.

[0032] The molar concentration of the third lithium salt, "third molar concentration Mc," may be in the range of 0.1 mol / L to 0.5 mol / L, may be in the range of 0.1 mol / L to 0.4 mol / L, may be in the range of 0.2 mol / L to 0.5 mol / L, or may be in the range of 0.2 mol / L to 0.4 mol / L.

[0033] From the viewpoint of increasing the entropy of the nonaqueous electrolyte as much as possible, it is preferable that the first molar concentration Ma, the second molar concentration Mb, and the third molar concentration Mc satisfy the following relationships (1) to (3): (1) 0.2≦Ma / (Ma+Mb+Mc)≦0.8 (preferably 0.3≦Mc / (Ma+Mb+Mc)≦0.7) (2) 0.2≦Mb / (Ma+Mb+Mc)≦0.8 (preferably 0.3≦Mc / (Ma+Mb+Mc)≦0.7) (3) 0.1≦Mc / (Ma+Mb+Mc)≦0.5 (preferably 0.2≦Mc / (Ma+Mb+Mc)≦0.4)

[0034] The first molar concentration Ma, the second molar concentration Mb, and the third molar concentration Mc may further satisfy at least one of the following relationships (4) to (6). It is particularly preferable that the relationships (4) and (5) are satisfied: (4) Mc<Ma (5) Mc<Mb (6) Ma≦Mb

[0035] The electrolyte salt may contain a salt other than the first to third lithium salts. However, from the viewpoint of maintaining a low viscosity and a high ionic conductivity of the nonaqueous electrolyte solution, the molar concentration of the other salt is preferably 0.2 mol / L or less, and more preferably 0.1 mol / L or less.

[0036] (Non-aqueous solvent) The non-aqueous solvent is not particularly limited as long as it is a solvent that can be used in a non-aqueous electrochemical device. Examples of non-aqueous solvents include carbonate esters, carboxylic acid esters, and ethers. The non-aqueous solvent may contain a halogen atom. The halogen atom is preferably a fluorine atom. Only one type of non-aqueous solvent may be used, but it is preferable to use a mixture of two or more types.

[0037] The carbonate ester may be a cyclic carbonate or a chain carbonate. Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), vinylene carbonate (VC), and vinyl ethyl carbonate. Examples of the chain carbonate include symmetric chain carbonates such as dimethyl carbonate (DMC) and diethyl carbonate, and asymmetric chain carbonates such as ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate.

[0038] The carboxylic acid ester may be a cyclic carboxylic acid ester or a chain carboxylic acid ester. Examples of the cyclic carboxylic acid ester that can be used include γ-butyrolactone and γ-valerolactone. Examples of the chain carboxylic acid ester that can be used include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and methyl fluoropropionate.

[0039] The ether may be a cyclic ether or a chain ether. Examples of the cyclic ether that can be used include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ether. Examples of the chain ether that can be used include diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,1-dimethoxymethane, 1,1-diethoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0040] However, the non-aqueous solvent is not limited to these.

[0041] A preferred example of the non-aqueous solvent includes a cyclic carbonate and a chain ester. The chain ester may be a chain carbonate or a chain carboxylic acid ester.

[0042] The volume ratio of the cyclic carbonate in the nonaqueous solvent may be, for example, in the range of 0.01% to 30% by volume, 3% to 30% by volume, or 5% to 20% by volume. A composition containing a reduced proportion of cyclic carbonate, which readily participates in the solvation of lithium ions, is suitable for forming a high-quality coating derived from the anions of the lithium salt. However, during its reductive decomposition, the cyclic carbonate forms a coating derived from, for example, lithium ethylene dicarbonate (LEDC), which is used to realize reversible operation of the graphite negative electrode. Therefore, it is preferable to contain the cyclic carbonate in an amount within the above range.

[0043] The cyclic carbonate may include, for example, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, and preferably includes ethylene carbonate and fluoroethylene carbonate. The proportion of fluoroethylene carbonate in the cyclic carbonate is, for example, 20% by volume to 100% by volume, and may be, for example, 30% by volume to 70% by volume.

[0044] When a chain carboxylic acid ester is used as the chain ester, the chain carboxylic acid ester is preferably methyl acetate, propyl acetate, or the like.

[0045] When a chain carbonate is used as the chain ester, it is preferable to contain an asymmetric chain carbonate and a symmetric chain carbonate having a volume greater than that of the asymmetric chain carbonate. As the asymmetric chain carbonate, for example, ethyl methyl carbonate is preferable. As the symmetric chain carbonate, dimethyl carbonate or diethyl carbonate is preferable.

[0046] Preferable examples of the nonaqueous solvent include ethylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. The proportion of ethylene carbonate in such a nonaqueous solvent may be, for example, 3 to 10% by volume, the proportion of fluoroethylene carbonate may be, for example, 3 to 10% by volume, the proportion of ethyl methyl carbonate may be, for example, 10 to 30% by volume, and the proportion of dimethyl carbonate may be, for example, 50 to 80% by volume.

[0047] The non-aqueous electrolyte may be gelled. For example, the non-aqueous electrolyte may be gelled by being combined with a matrix polymer. The matrix polymer may be any polymer that absorbs the non-aqueous solvent and gels. Examples of such polymer materials include fluororesins, acrylic resins, and polyether resins.

[0048] [Electrochemical Device] An electrochemical device according to an embodiment of the present disclosure includes a pair of electrodes and the nonaqueous electrolyte. One of the pair of electrodes is a positive electrode, and the other of the pair of electrodes is a negative electrode. Examples of the electrochemical device include nonaqueous electrolyte secondary batteries (lithium ion secondary batteries, lithium metal secondary batteries, etc.), electric double layer capacitors, and lithium ion capacitors.

[0049] The configuration of the nonaqueous electrolyte secondary battery will be described below.

[0050] A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. A separator is usually disposed between the positive electrode and the negative electrode.

[0051] [Negative Electrode] The negative electrode includes at least a negative electrode current collector, and may include a negative electrode mixture layer formed on the surface of the negative electrode current collector and containing a negative electrode active material. Lithium metal secondary batteries do not need to have a negative electrode mixture layer. Lithium ion secondary batteries include a negative electrode mixture layer. The negative electrode mixture layer can be formed by applying a negative electrode slurry, in which the negative electrode mixture is dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying it. The dried coating may be rolled as necessary. The negative electrode mixture layer may be formed on one surface or both surfaces of the negative electrode current collector.

[0052] The negative electrode mixture contains a negative electrode active material as an essential component, and may contain optional components such as a binder, a conductive agent, and a thickener. The negative electrode active material contains a material that electrochemically absorbs and releases lithium ions. Examples of the material that electrochemically absorbs and releases lithium ions include carbon materials and Si-containing materials. Examples of the Si-containing material include silicon oxide (SiO ｘ : 0.5≦x≦1.5), and composite materials containing a silicate phase and silicon particles dispersed within the silicate phase.

[0053] Examples of carbon materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). Among these, graphite is preferred because of its excellent charge / discharge stability and low irreversible capacity. Graphite refers to a material having a graphite-type crystal structure, and includes natural graphite, artificial graphite, graphitized mesophase carbon particles, and the like. One type of carbon material may be used alone, or two or more types may be used in combination.

[0054] The negative electrode current collector may be a metal foil, a mesh, a net, a punched sheet, etc. Examples of the material for the negative electrode current collector include stainless steel, nickel, a nickel alloy, copper, and a copper alloy.

[0055] 1 m on one side of the negative electrode current collector ２ The mass of the negative electrode mixture layer formed per unit area may be, for example, 50 g or more, and is preferably 100 g or more. By making the mass 100 g or more, it is possible to increase the capacity of the lithium ion battery. The mass can be increased by thickening the negative electrode mixture layer or increasing the density of the negative electrode mixture layer. There is no particular limitation on the thickness of the negative electrode mixture layer, but for example, the total thickness of both sides may be in the range of 50 μm to 200 μm. By using the nonaqueous electrolyte according to the present disclosure, an increase in internal resistance can be suppressed even if the negative electrode mixture layer is thickened. The density of the negative electrode mixture layer is, for example, 1.1 g / cm ３ ~1.7g / cm ３ It may be in the range of

[0056] [Positive Electrode] The positive electrode comprises, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector and containing a positive electrode active material. The positive electrode mixture layer can be formed by applying a positive electrode slurry, in which the positive electrode mixture is dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying it. The dried coating may be rolled as necessary. The positive electrode mixture layer may be formed on one surface or both surfaces of the positive electrode current collector.

[0057] The positive electrode mixture contains a positive electrode active material as an essential component, and may contain optional components such as a binder and a conductive agent. The positive electrode active material contains a material that electrochemically absorbs and releases lithium ions. A lithium transition metal composite oxide is preferred as the material that electrochemically absorbs and releases lithium ions. Examples of the lithium transition metal composite oxide that can be used include layered compounds with a rock salt crystal structure, spinel compounds, and polyanion compounds. Among these, a layered compound containing Ni, in which the proportion of Ni relative to all metal elements other than Li is 90 mol % or more, is preferred in terms of achieving high capacity.

[0058] An example of a preferred layered compound is a compound having the composition of formula (C): Li α Ni(1-x1-x2-x3-y)Co ｘ１ Mn ｘ２ Al ｘ３ M ｙ O ２＋β and a lithium transition metal composite oxide represented by the formula (C) where 0.95≦α≦1.05, 0.8≦1-x1-x2-x3-y≦0.99, 0≦x1≦0.1, 0≦x2≦0.1, 0≦x3≦0.1, 0≦y≦0.1, and −0.05≦β≦0.05. M is at least one element selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, and Y.

[0059] The positive electrode current collector is, for example, a metal foil, and examples of the material include stainless steel, aluminum, aluminum alloy, and titanium.

[0060] 1 m on one side of the positive electrode current collector ２The mass of the positive electrode mixture layer formed per unit area may be, for example, 200 g or more, and preferably 250 g or more. By setting the mass to 250 g or more, it is possible to increase the capacity of the lithium-ion battery. The mass can be increased by thickening the positive electrode mixture layer or increasing the density of the positive electrode mixture layer. There are no particular limitations on the thickness of the positive electrode mixture layer, but for example, the total thickness of both sides may be in the range of 50 μm to 250 μm. By using the nonaqueous electrolyte according to the present disclosure, an increase in internal resistance can be suppressed even if the positive electrode mixture layer is thickened. The density of the positive electrode mixture layer is, for example, 3.3 g / cm ３ ~3.7g / cm ３ It may be in the range of

[0061] Examples of binders for each electrode include resin materials, such as fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride (PVDF); polyolefin resins such as polyethylene and polypropylene; polyamide resins such as aramid resin; polyimide and polyamideimide; acrylic resins such as polyacrylic acid, polyacrylates (e.g., lithium polyacrylate), polymethyl acrylate, and ethylene-acrylic acid copolymers; vinyl resins such as polyacrylonitrile and polyvinyl acetate; polyvinylpyrrolidone; polyethersulfone; and rubber-like materials such as styrene-butadiene copolymer rubber (SBR). These may be used alone or in combination of two or more.

[0062] Examples of conductive agents include carbon blacks such as acetylene black, conductive fibers such as carbon fibers and metal fibers, carbon fluoride, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene derivatives. These may be used alone or in combination of two or more.

[0063] The dispersion medium is not particularly limited, but examples thereof include water, alcohol, and N-methyl-2-pyrrolidone (NMP).

[0064] [Separator] A separator is usually interposed between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. The separator can be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. The separator is preferably made of polyolefin such as polypropylene or polyethylene.

[0065] An example of the structure of a secondary battery is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween and an electrolyte are housed in an outer casing. Alternatively, instead of a wound electrode group, other types of electrode groups may be used, such as a stacked electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween. The secondary battery may be in any shape, such as a cylindrical shape, a prismatic shape, a coin shape, a button shape, or a laminate shape.

[0066] The structure of the secondary battery will be described below with reference to Fig. 1. Fig. 1 is a longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 that is an example of this embodiment. However, the present disclosure is not limited to the following configuration.

[0067] The secondary battery 10 includes an electrode group 18, an electrolyte (not shown), and a cylindrical battery can 22 with a bottom that accommodates these. A sealing body 11 is crimped to the opening of the battery can 22 via a gasket 21, thereby sealing the battery. The sealing body 11 includes a valve body 12, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are connected to each other at their respective centers. A positive electrode lead 15a extending from a positive electrode plate 15 is connected to the metal plate 13. Thus, the valve body 12 functions as an external terminal for the positive electrode. A negative electrode lead 16a extending from a negative electrode plate 16 is connected to the inner bottom surface of the battery can 22. An annular groove 22a is formed near the open end of the battery can 22. A first insulating plate 23 is disposed between one end face of the electrode group 18 and the annular groove portion 22a. A second insulating plate 24 is disposed between the other end face of the electrode group 18 and the bottom of the battery can 22. The electrode group 18 is formed by winding a positive electrode plate 15 and a negative electrode plate 16 with a separator 17 interposed therebetween.

[0068] [Method for Analyzing Nonaqueous Electrolyte] The sample to be measured may be a nonaqueous electrolyte extracted by disassembling a battery, or may be a nonaqueous electrolyte that is a raw material used in the manufacture of a battery.

[0069] (Content of Each Component in Non-Aqueous Electrolyte) The content of each component (concentration of each Li salt, volume ratio of solvent, additives, etc.) in the non-aqueous electrolyte can be determined, for example, using gas chromatography under the following conditions: Measuring device: GC-2010 Plus manufactured by Shimadzu Corporation Column: HP-1 (1 μm×60 m) manufactured by J&W (Agilent Technologies, Inc.) Linear velocity: 30.0 cm / sec Injection port temperature: 270° C. Detector: FID 290° C. (ses.10 １ )

[0070] ( ７ Li-NMR measurement) Non-aqueous electrolyte ７ Li-NMR measurement is carried out, for example, using the following apparatus under the following conditions: Sampling: A double tube is used, with the sample in the outer tube and the measurement solvent D-Acetone (hexadeuteroacetone) in the inner tube Temperature: 25°C Measurement apparatus: JNM-ECX400 manufactured by JEOL Ltd. Shift reference material: 1 mol / L LiCl / D ２ O solution (0 ppm) Observation frequency: 153.855 MHz Pulse width: 6.95 usec (45°C) Signal acquisition time: 10.6 sec Pulse repetition time: 15.6 sec Number of integrations: 32 Observation width: 20 ppm Observation center: near 0 ppm

[0071] (Additional Note) The above description discloses the following technology: (Technology 1) A non-aqueous electrolyte solution including a non-aqueous solvent and an electrolyte salt, wherein the electrolyte salt includes a first lithium salt, a second lithium salt, and a third lithium salt, and the first lithium salt is LiPF ６ , LiSbF ６ and LiAsF ６ The second lithium salt is at least one selected from the group consisting of LiN(SO ２ R1) (SO ２ R2) (wherein R1 and R2 are each independently C ｎ F ２ｎ＋１wherein n is an integer of 0 or more; the third lithium salt is at least one selected from the group consisting of an oxalate complex salt and a lithium nitrate; and ７ The shift value from the base peak in the Li-NMR spectrum is −1.15 ppm or more, and the base peak is the D peak of LiCl at a concentration of 1 mol / L measured at 25° C. ２ O solution ７ A non-aqueous electrolyte solution, wherein the shift value is a peak in a Li-NMR spectrum. (Technology 2) The non-aqueous electrolyte solution according to Technology 1, wherein the shift value is in the range of -1.15 ppm or more and -0.90 ppm or less. (Technology 3) The non-aqueous electrolyte solution according to Technology 1 or 2, wherein the total molar concentration of the first lithium salt, the second lithium salt, and the third lithium salt is in the range of 1.2 mol / L to 2.0 mol / L. (Technology 4) The non-aqueous electrolyte solution according to any one of Technology 1 to 3, wherein the molar concentration of the first lithium salt is in the range of 0.2 mol / L to 1.0 mol / L. (Technology 5) The first lithium salt is LiPF ６ (Technology 6) The nonaqueous electrolyte according to any one of Techniques 1 to 5, wherein the molar concentration of the second lithium salt is in the range of 0.2 mol / L to 1.0 mol / L. (Technology 7) The nonaqueous electrolyte according to any one of Techniques 1 to 5, wherein the second lithium salt is LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ and LiN(SO ２ F) (SO ２ CF ３ (Technology 8) The nonaqueous electrolyte solution according to any one of Techniques 1 to 6, which contains at least two types of the second lithium salt and at least LiN(SO ２ F) ２ The LiN(SO) in the second lithium salt ２ F) ２The nonaqueous electrolyte according to any one of Techniques 1 to 7, wherein the molar fraction of the third lithium salt is greater than 0.5. (Technology 9) The nonaqueous electrolyte according to any one of Techniques 1 to 8, wherein the molar concentration of the third lithium salt is in the range of 0.1 mol / L to 0.5 mol / L. (Technology 10) The nonaqueous electrolyte according to any one of Techniques 1 to 9, wherein the third lithium salt is at least one selected from the group consisting of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoro(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium nitrate. (Technology 11) The nonaqueous electrolyte according to any one of Techniques 1 to 10, wherein the nonaqueous solvent contains a cyclic carbonate and a chain ester. (Technology 12) The nonaqueous electrolyte according to Technique 11, wherein the volume fraction of the cyclic carbonate in the nonaqueous solvent is in the range of 0.001% by volume to 30% by volume. (Technology 13) The nonaqueous electrolyte according to Technology 11 or 12, wherein the chain ester comprises a chain carboxylic acid ester. (Technology 14) The nonaqueous electrolyte according to any one of Technology 11 to 13, wherein the chain ester comprises an asymmetric chain carbonate and a symmetric chain carbonate having a volume greater than that of the asymmetric chain carbonate. (Technology 15) The nonaqueous electrolyte according to any one of Technology 11 to 14, wherein the cyclic carbonate comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. (Technology 16) An electricity storage device comprising a positive electrode, a negative electrode, and the nonaqueous electrolyte according to any one of Technology 1 to 15.

[0072] [Examples] The present disclosure will be specifically described below based on examples and comparative examples relating to lithium ion secondary batteries, but the present disclosure is not limited to the following examples.

[0073] Examples 1 to 10, Comparative Examples 1 to 9 Non-aqueous electrolyte secondary batteries (batteries A1 to A10 of Examples 1 to 10, batteries B1 to B9 of Comparative Examples 1 to 9) were fabricated and evaluated according to the following procedure.

[0074] (1) Preparation of Negative Electrode 92 parts by mass of graphite powder and 8 parts by mass of SiO powder as negative electrode active materials, 0.8 parts by mass of carboxymethyl cellulose (CMC), 1.2 parts by mass of styrene butadiene rubber (SBR), and an appropriate amount of water were mixed to obtain a negative electrode mixture slurry. Next, the negative electrode slurry was applied to the surface of a copper foil, the coating was dried, and then rolled to form a negative electrode mixture layer (total thickness 160 μm, density 1.6 g / cm ) on both sides of the copper foil. ３ ) was formed to obtain a negative electrode.

[0075] (2) Preparation of the positive electrode: Lithium-containing composite oxide (LiNi ０．８８ Co ０．０７ Mn ０．０５ O ２ 95 parts by mass of acetylene black, 2.5 parts by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed with 95 parts by mass of acetylene black, 2.5 parts by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. Next, the positive electrode slurry was applied to the surface of an aluminum foil, the coating was dried, and then rolled to form a positive electrode mixture layer (total thickness 160 μm, density 3.6 g / cm ) on both sides of the aluminum foil. ３ ) was formed to obtain a positive electrode.

[0076] (3) Preparation of non-aqueous electrolyte: LiPF as the first lithium salt ６ was used at the molar concentrations shown in Table 1.

[0077] As the second lithium salt, LiN(SO ２ F) ２ :LiFSI LiN(SO ２ CF ３ ) ２ :LiTFSI LiN(SO ２ F) (SO ２ CF ３ ): LiFTFSI was used at the molar concentrations shown in Table 1.

[0078] As the third lithium salt, lithium difluoro(oxalato)borate: LiDFOB, lithium tetrafluoro(oxalato)phosphate: LiTFOP, and lithium difluorobis(oxalato)phosphate: LiDFBOP were used in the molar concentrations shown in Table 1.

[0079] As the non-aqueous solvent, ethylene carbonate: EC, fluoroethylene carbonate: FEC, ethyl methyl carbonate: EMC, and dimethyl carbonate: DMC were used in the volume ratios shown in Table 1.

[0080] The non-aqueous electrolyte contained VC at a concentration of 1.5 mass %.

[0081] (4) Fabrication of a Non-Aqueous Electrolyte Secondary Battery An Al positive electrode lead was attached to the positive electrode obtained above, and a Ni negative electrode lead was attached to the negative electrode obtained above. The positive electrode and negative electrode were spirally wound with a polyethylene thin film (separator) in between in an inert gas atmosphere to fabricate a wound electrode assembly. The electrode assembly was housed in a cylindrical outer can, and the non-aqueous electrolyte was injected. The outer can was then sealed to fabricate a cylindrical 2170 battery with a rated capacity of 5 Ah.

[0082]

[0083] Evaluation [0°C / SOC 10% Resistance (DCIR)] After constant current charging at 1.5 A from a discharged state to 3.4 V (corresponding to a 10% state of charge (SOC)), the battery was held at a constant voltage of 3.4 V until the charging current fell to 10 mA or less, and then left in an open circuit state for 2 hours. The DCIR of the battery was measured at 0°C (low temperature). The voltage drop (ΔV) when a current of 2.5 A was applied for 10 seconds was divided by the current value, and this was taken as the DCIR. The results are shown in Table 2.

[0084] [Charge-Discharge Cycle Test] Charge-discharge cycle tests were conducted under the following conditions: 45°C (high temperature), 0°C (low temperature), and 25°C (room temperature). Charge and discharge were conducted under the following conditions: A 20-minute break was allowed between charge and discharge. 200 charge-discharge cycles were repeated, and the capacity retention rate was calculated using the formula "Capacity retention rate (%) = (200th cycle discharge capacity / 1st cycle discharge capacity) × 100". The results are shown in Table 2.

[0085] (Charging) The battery was charged at a constant current of 1.5 A until the voltage reached 4.2 V, and then was charged at a constant voltage of 4.2 V until the current reached 0.1 A.

[0086] (Discharge) Discharge was carried out at a constant current of 2.5 A until the voltage reached 2.85 V.

[0087]

[0088] From Tables 1 and 2, it contains a first lithium salt, a second lithium salt, and a third lithium salt, and ７ It can be seen that only when the shift value (S) in the Li-NMR spectrum is −1.15 ppm or more, the resistance at low temperatures is small and excellent charge-discharge cycle characteristics can be obtained over a wide temperature range. Furthermore, it can be seen that from the viewpoint of further reducing the resistance at low temperatures, it is preferable to use two or more second lithium salts in combination.

[0089] The nonaqueous electrolyte solution according to the present disclosure is suitable for electrochemical devices used over a wide temperature range from low to high, and is useful in a variety of applications, including electronic devices such as mobile phones, smartphones, and tablet devices, hybrid vehicles, plug-in hybrid vehicles, and electric vehicles.

[0090] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0091] 10: Secondary battery, 11: Sealing body, 12: Valve body, 13: Metal plate, 14: Insulating member, 15: Positive electrode plate, 15a: Positive electrode lead, 16: Negative electrode plate, 16a: Negative electrode lead, 17: Separator, 18: Electrode group, 21: Gasket, 22: Battery can, 22a: Groove portion, 23: First insulating plate, 24: Second insulating plate

Claims

1. A non-aqueous electrolyte solution comprising a non-aqueous solvent and an electrolyte salt, wherein the electrolyte salt comprises a first lithium salt, a second lithium salt, and a third lithium salt, and the first lithium salt is LiPF ６ , LiSbF ６ and LiAsF ６ The second lithium salt is at least one selected from the group consisting of LiN(SO ２ R1) (SO ２ R2) (wherein R1 and R2 are each independently C ｎ F ２ｎ＋１ wherein n is an integer of 0 or more; the third lithium salt is at least one selected from the group consisting of an oxalate complex salt and lithium nitrate; and ７ The shift value from the base peak in the Li-NMR spectrum is −1.15 ppm or more, and the base peak is the D peak of LiCl at a concentration of 1 mol / L measured at 25° C. ２ O solution ７ Peaks in the Li-NMR spectrum of the non-aqueous electrolyte.

2. The nonaqueous electrolyte according to claim 1, wherein the shift value is in the range of -1.15 ppm or more and -0.90 ppm or less.

3. The nonaqueous electrolyte according to claim 1, wherein the total molar concentration of the first lithium salt, the second lithium salt, and the third lithium salt is in the range of 1.2 mol / L to 2.0 mol / L.

4. The nonaqueous electrolyte according to claim 1, wherein the molar concentration of the first lithium salt is in the range of 0.2 mol / L to 1.0 mol / L.

5. The first lithium salt is LiPF ６ The nonaqueous electrolyte according to claim 1 , 6. The nonaqueous electrolyte according to claim 1, wherein the molar concentration of the second lithium salt is in the range of 0.2 mol / L to 1.0 mol / L.

7. The second lithium salt is LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ and LiN(SO ２ F) (SO ２ CF ３ 2. The nonaqueous electrolyte solution according to claim 1, wherein the nonaqueous electrolyte solution is at least one selected from the group consisting of:

8. A solution containing at least two of the second lithium salts and at least LiN(SO ２ F) ２ The LiN(SO) in the second lithium salt ２ F) ２ The non-aqueous electrolyte solution according to claim 1 , wherein the molar fraction of 9. The nonaqueous electrolyte according to claim 1, wherein the molar concentration of the third lithium salt is in the range of 0.1 mol / L to 0.5 mol / L.

10. The nonaqueous electrolyte solution according to claim 1, wherein the third lithium salt is at least one selected from the group consisting of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoro(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium nitrate.

11. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent comprises a cyclic carbonate and a chain ester.

12. The non-aqueous electrolyte according to claim 11, wherein the volume ratio of the cyclic carbonate in the non-aqueous solvent is in the range of 0.001% by volume to 30% by volume.

13. The nonaqueous electrolyte according to claim 11, wherein the chain ester comprises a chain carboxylic acid ester.

14. The nonaqueous electrolyte according to claim 11, wherein the chain ester comprises an asymmetric chain carbonate and a symmetric chain carbonate in a volume greater than that of the asymmetric chain carbonate.

15. The nonaqueous electrolyte according to claim 11, wherein the cyclic carbonate comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

16. An electricity storage device comprising a positive electrode, a negative electrode, and the nonaqueous electrolyte solution according to claim 1.

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