Nonaqueous electrolyte solution, additive for nonaqueous electrolyte solution, method for manufacturing nonaqueous electrolyte solution, and power storage device

Abstract

Disclosed is a nonaqueous electrolyte solution which contains: a compound represented by formula (1), wherein R is a direct bond, an alkylene group having 1-4 carbon atoms, or a halogenated alkylene group having 1-4 carbon atoms; LiBF4; a nonaqueous solvent; and an electrolyte. The electrolyte is a compound that is different from the compound represented by formula (1) and LiBF4. The content of LiBF4 is 3.0 mass% or less based on the total amount of the nonaqueous electrolyte solution.

Description

Nonaqueous electrolyte, additive for nonaqueous electrolyte, method for producing nonaqueous electrolyte, and electricity storage device

[0001] The present disclosure relates to a non-aqueous electrolyte, an additive for a non-aqueous electrolyte, a method for producing a non-aqueous electrolyte, and an electricity storage device.

[0002] Additives are sometimes added to non-aqueous electrolytes for the purpose of improving the performance of electricity storage devices such as lithium ion batteries. For example, Patent Document 1 discloses an electrolyte for lithium ion secondary batteries containing an additive including lithium oxalatoborate and a fluorine-containing cyclic carbonate, with the aim of providing an electrolyte for lithium ion batteries that can exhibit good cycle characteristics even at low temperatures.

[0003] Japanese Patent Application Laid-Open No. 2020-155378

[0004] On the other hand, electricity storage devices are also required to withstand temperatures of, for example, approximately 60° C. for lithium ion batteries and approximately 80° C. for lithium ion capacitors. However, there is a problem that the performance of electricity storage devices deteriorates in high-temperature environments.

[0005] The present disclosure relates to suppressing performance degradation of an electricity storage device having a non-aqueous electrolyte, and particularly to suppressing degradation of battery performance in a high-temperature environment.

[0006] The present disclosure includes at least the following: [1] Formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms; and LiBF ４ a non-aqueous solvent; and an electrolyte, wherein the electrolyte contains the compound represented by formula (1) and LiBF ４ is a different compound from LiBF ４ [2] A non-aqueous electrolyte solution in which the content of the compound represented by formula (1) is 3.0 mass % or less based on the total amount of the non-aqueous electrolyte solution. ４[3] The nonaqueous electrolyte solution according to [1], wherein the compound represented by formula (1) and LiBF are present in an amount of 10 mass % to 90 mass % based on the total amount of the compound represented by formula (1) and LiBF. ４ [4] The non-aqueous electrolyte solution according to [1] or [2], wherein the total content of LiBF is 3.0 mass% or less based on the total amount of the non-aqueous electrolyte solution. ４ [5] The non-aqueous electrolyte solution according to any one of [1] to [3], wherein the content of the compound represented by formula (1) is 0.9 mass % or less based on the total amount of the non-aqueous electrolyte solution. [6] The nonaqueous electrolyte solution according to any one of [1] to [4], wherein the compound is represented by formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms; and LiBF ４ [7] An additive for a non-aqueous electrolyte solution, comprising: the compound represented by formula (1) and LiBF ４ [8] The additive for a non-aqueous electrolyte solution according to [6], wherein the content of LiBF is 10 mass % or more and 90 mass % or less based on the total amount of ４ and formula (1): [9] A non-aqueous electrolyte additive used for adding to a non-aqueous electrolyte in combination with a compound represented by the formula (I) and wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms. ４ and dissolving a compound represented by formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms; and dissolving an electrolyte in the nonaqueous solvent, wherein the electrolyte comprises the compound represented by formula (1) and LiBF ４ and LiBF is a compound different from the compound ４

[10] An electricity storage device comprising the nonaqueous electrolyte solution according to any one of [1] to [5], a positive electrode, and a negative electrode.

[0007] According to the present disclosure, it is possible to suppress the deterioration of performance of an electricity storage device having a nonaqueous electrolyte, particularly the deterioration of battery performance under high-temperature environments. For example, it is possible to suppress an increase in resistance when the electricity storage device is stored or used at high temperatures. It is also possible to suppress gas generation during storage of the electricity storage device.

[0008] FIG. 1 is a cross-sectional view illustrating an example of an electricity storage device.

[0009] The present invention is not limited to the following examples.

[0010] <Non-aqueous electrolyte> An example of a non-aqueous electrolyte is a mixture of a compound represented by formula (1) and LiBF ４ The compound represented by formula (1) and LiBF are included. R in formula (1) is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms. ４ The combination of can function as an additive for a non-aqueous electrolyte to improve the performance of an electricity storage device.

[0011] LiBF in non-aqueous electrolyte ４ The content of LiBF is 3.0 mass % or less based on the total amount of the nonaqueous electrolyte. ４ By including a relatively small amount of LiBF as an additive together with the compound represented by formula (1), the storage stability of the electricity storage device at high temperatures can be improved. ４ The content of LiBF in the nonaqueous electrolyte may be 2.5 mass% or less, 2.0 mass% or less, 1.5 mass% or less, 1.0 mass% or less, 0.8 mass% or less, 0.6 mass% or less, 0.5 mass% or less, 0.4 mass% or less, or 0.3 mass% or less, based on the total amount of the nonaqueous electrolyte. ４may have a content of 0.1% by mass or more and 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, 1.5% by mass or less, 1.0% by mass or less, 0.8% by mass or less, 0.6% by mass or less, 0.5% by mass or less, 0.4% by mass or less, or 0.3% by mass or less, based on the total amount of the non-aqueous electrolyte solution.

[0012] The content of the compound represented by formula (1) is the compound represented by formula (1) and LiBF ４ When the content of the compound represented by formula (1) is within this range, a particularly significant effect is likely to be obtained in terms of suppressing an increase in the resistance of the electricity storage device in a high-temperature environment. From the same viewpoint, the content of the compound represented by formula (1) may be 10 mass % or more and 90 mass % or less based on the total amount of the compound represented by formula (1) and LiBF. ４ may be 10% by mass or more and 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less, based on the total amount of

[0013] The content of the compound represented by formula (1) in the non-aqueous electrolyte may be 0.1% by mass or more and 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.9% by mass or less, based on the total amount of the non-aqueous electrolyte, or 0.2% by mass or more and 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.9% by mass or less, or 0.3% by mass or more and 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less It may be 0.4% by mass or more and 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.9% by mass or less, it may be 0.5% by mass or more and 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.9% by mass or less, it may be 0.6% by mass or more and 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.9% by mass or less.

[0014] A compound represented by formula (1) and LiBF ４ The total content of the compound represented by formula (1) and LiBF may be 3.0 mass % or less based on the total amount of the nonaqueous electrolyte solution. ４ When the total content of the compound represented by formula (1) and LiBF is within this range, a particularly significant effect is likely to be obtained in terms of suppressing an increase in the resistance of the electricity storage device in a high-temperature environment. ４ The total content of the compound represented by formula (1) and LiBF may be 0.2 mass% or more, or 0.5 mass% or more, and may be 2.5 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, based on the total amount of the nonaqueous electrolyte solution. ４ The total content may be 0.2% by mass or more and 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, or 1.5% by mass or less, or may be 0.5% by mass or more and 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, or 1.5% by mass or less.

[0015] R in formula (1) may be, for example, a single bond, a methylene group, an ethane-1,2-diyl group, a propane-1,3-diyl group, an n-butane-1,4-diyl group, or a halogenated alkylene group in which one or more hydrogen atoms in these groups have been substituted with halogen atoms (for example, fluorine atoms). The compound represented by formula (1) may also be a compound represented by the following formula (1A). This compound is lithium difluoro(oxalato)borate, and may be abbreviated as LiDFOB.

[0016] The non-aqueous solvent constituting the non-aqueous electrolyte may be an aprotic solvent. For example, the non-aqueous solvent may contain at least one aprotic solvent selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, lactones, lactams, cyclic ethers, chain ethers, sulfones, nitriles, and halogenated derivatives thereof. The non-aqueous solvent may contain a cyclic carbonate or a chain carbonate, or may contain a combination of a cyclic carbonate and a chain carbonate.

[0017] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate. Examples of linear carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of aliphatic carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, and methyl trimethylacetate. An example of a lactone is γ-butyrolactone. Examples of lactams include ε-caprolactam and N-methylpyrrolidone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, and 1,3-dioxolane. Examples of linear ethers include 1,2-diethoxyethane and ethoxymethoxyethane. An example of a sulfone is sulfolane. An example of a nitrile is acetonitrile. Examples of the halogen derivative include halogen derivatives of cyclic carbonates such as 4-fluoro-1,3-dioxolan-2-one, 4-chloro-1,3-dioxolan-2-one, and 4,5-difluoro-1,3-dioxolan-2-one. These may be used alone or in combination of two or more.

[0018] The content of the nonaqueous solvent in the nonaqueous electrolyte may be, for example, 70 mass % or more and 99 mass % or less based on the total amount of the nonaqueous electrolyte.

[0019] In this specification, the term "electrolyte" refers to a compound represented by formula (1) and LiBF ４ The term "electrolyte" is used to refer to an electrolyte that is a compound different from both of the above. The electrolyte may include a lithium salt that is a source of lithium ions. The electrolyte may be LiAlCl ４ , LiPF ６ , LiClO ４ , LiTFSI (lithium bistrifluoromethanesulfonimide), LiFSI (lithium bisfluorosulfonimide), LiAsF ６ and LiSbF ６ The electrolyte may contain at least one selected from the group consisting of LiPF ６may include:

[0020] The content of the electrolyte in the non-aqueous electrolyte may be 0.1 mol / L or more and 2.0 mol / L or less, based on the total volume of the non-aqueous electrolyte. The content of the electrolyte may be 0.2 mol / L or more, 0.4 mol / L or more, 0.6 mol / L or more, or 0.8 mol / L or more and 2.0 mol / L or less, based on the total volume of the non-aqueous electrolyte. The content of the electrolyte may be more than 3.0 mass%, 5.0 mass% or more, 7.5 mass% or more, or 10 mass% or more, based on the total amount of the non-aqueous electrolyte. The content of the electrolyte may be 30 mass% or less, based on the total amount of the non-aqueous electrolyte. The content of the electrolyte may be more than 3.0 mass%, 5.0 mass% or more, 7.5 mass% or more, or 10 mass% or more, and 30 mass% or less, based on the total amount of the non-aqueous electrolyte.

[0021] The non-aqueous electrolyte solution is prepared by, for example, preparing a non-aqueous solvent and dissolving LiBF in the non-aqueous solvent. ４ LiBF can be produced by a method including dissolving the compound represented by formula (1) in a non-aqueous solvent, dissolving the compound represented by formula (1) in a non-aqueous solvent, and dissolving an electrolyte in a non-aqueous solvent. ４ The order in which the compound represented by formula (1) and the electrolyte are dissolved in the non-aqueous solvent is not particularly limited and can be selected arbitrarily. Two or more components selected from these may be simultaneously dissolved in the non-aqueous solvent. In the formed non-aqueous electrolyte, the compound represented by formula (1) and LiBF ４ A part or all of the compounds represented by formula (1), LiBF, which are dissolved in a non-aqueous solvent, may interact with each other to form a complex. ４ The amount of the electrolyte may be in the ranges described above as examples of the content of each component in the non-aqueous electrolyte solution.

[0022] To form a non-aqueous electrolyte, a compound represented by formula (1) and LiBF ４ The additive may be in the form of a powder, and may be a mixture of particles containing the compound represented by formula (1) and LiBF. ４Alternatively, the non-aqueous electrolyte may be a powder mixture containing a first additive containing a compound represented by formula (1) and a particle containing LiBF ４ and a second additive containing the above may be prepared, and these may be dissolved in the non-aqueous solvent simultaneously or sequentially.

[0023] <Electricity Storage Device> Examples of electricity storage devices are mainly composed of the nonaqueous electrolyte solution exemplified above, a positive electrode, and a negative electrode. Specific examples of electricity storage devices include nonaqueous electrolyte secondary batteries (particularly lithium ion batteries) and electric double layer capacitors (particularly lithium ion capacitors).

[0024] FIG. 1 is a cross-sectional view schematically illustrating an example of a nonaqueous electrolyte secondary battery (e.g., a lithium-ion battery) that is an electricity storage device. The nonaqueous electrolyte secondary battery 1 shown in FIG. 1 includes alternately stacked negative electrodes 4 and positive electrodes 9, a nonaqueous electrolyte 5 disposed between the negative electrodes 4 and the positive electrodes 9, and a separator 6 disposed in the nonaqueous electrolyte 5. The multiple negative electrodes 4 and positive electrodes 9 are stacked such that a major surface of the negative electrode 4 faces a major surface of the positive electrode 9 via the separator 6. The nonaqueous electrolyte secondary battery 1 includes seven layers of negative electrodes 4 and six layers of positive electrodes 9, although some of the repeated structures are omitted in FIG. 1. The negative electrode 4 includes a negative electrode current collector 3 and negative electrode active material layers 2 disposed on both sides of the negative electrode current collector 3. The positive electrode 9 includes a positive electrode current collector 8 and positive electrode active material layers 7 disposed on both sides of the positive electrode current collector 8. The nonaqueous electrolyte 5 is the nonaqueous electrolyte described above.

[0025] The positive electrode current collector 8 and the negative electrode current collector 3 may be, for example, a metal foil containing one or more metals selected from aluminum, copper, nickel, stainless steel, and the like.

[0026] The positive electrode active material layer 7 contains a positive electrode active material. The positive electrode active material may be a lithium-containing composite oxide, which is a composite oxide containing lithium, or a lithium-containing phosphate compound, which is a phosphate compound containing lithium. Examples of lithium-containing composite oxides include LiMnO ２ , LiFeO ２ , LiCoO ２ , LiMn ２ O ４ , LiNi１／３ Co １／３ Mn １／３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．８ Co ０．１ Mn ０．１ O ２、 LiNi ｘ Co ｙ M ｚ O ２ (wherein 0.01<x<1, 0≦y<1, 0≦z<1, and x+y+z=1, and M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, Fe, Cu, and Al), Li ｚ Ni （１－ｘ－ｙ） Co ｘ M ｙ O ２ (wherein 0≦x≦0.40, 0≦y≦0.40, and 0.90≦z≦1.20, and M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, and Al), and Li ｚ Co （１－ｘ） M ｘ O ２ (wherein 0≦x≦0.1 and 0.97≦z≦1.20, and M is at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb, and Al.) Examples of lithium-containing phosphate compounds include LiFePO ４ , LiCoPO ４ , LiMnPO ４ , LiNiPO ４ When the lithium-containing phosphate compound contains a transition element (such as Fe, Co, Mn, or Ni), the transition element may be substituted or doped with another element.

[0027] The positive electrode active material is Li ｚ Ni （１－ｘ－ｙ） Co ｘ M ｙ O ２(wherein 0.01≦x≦0.20, 0≦y≦0.30, and 0.90≦z≦1.20, and M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, and Al), Li ｚ Ni （１－ｘ－ｙ） Co ｘ M ｙ O ２ (wherein 0.01≦x≦0.15, 0≦y≦0.15, and 0.97≦z≦1.20, and M is at least one element selected from Mn, V, Mg, Mo, Nb, and Al), or Li ｚ Co （１－ｘ） M ｘ O ２ (wherein 0≦x≦0.1 and 0.97≦z≦1.20, and M is at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb, and Al.) These positive electrode active materials can further improve battery performance.

[0028] The negative electrode active material layer 2 includes a negative electrode active material. The negative electrode active material may be, for example, a material capable of absorbing and releasing lithium. Examples of negative electrode active materials include carbon materials such as graphite and amorphous carbon, oxide materials such as indium oxide, silicon oxide, tin oxide, lithium titanate, zinc oxide, and lithium oxide, lithium metal, and metal materials capable of forming an alloy with lithium. Examples of metal materials capable of forming an alloy with lithium include Cu, Sn, Si, Co, Mn, Fe, Sb, and Ag. The negative electrode active material may also include an alloy containing two or three metals including these metals and lithium. These exemplified negative electrode active materials may be used alone or in combination of two or more.

[0029] From the viewpoint of achieving a high energy density, the negative electrode active material may include a carbon material such as graphite and a Si-based active material selected from Si, a Si alloy, a Si oxide, etc. From the viewpoint of enabling a higher energy density, the negative electrode active material may include graphite and a Si-based active material. In these cases, the ratio of the mass of the Si-based active material to the total mass of the carbon material and the Si-based active material may be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, or may be 95% by mass or less, 50% by mass or less, or 40% by mass or less.

[0030] The positive electrode active material layer 7 and the negative electrode active material layer 2 may further contain a binder. Examples of binders include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, carboxymethyl cellulose, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide-imide, polyacrylic acid, polyvinyl alcohol, metal polyacrylate, acrylic acid-polyacrylonitrile, polyacrylamide, polymethacrylic acid, and copolymers thereof. The positive electrode active material layer and the negative electrode active material layer may contain the same or different binders.

[0031] The positive electrode active material layer 7 and the negative electrode active material layer 2 may further contain a conductive additive. Examples of the conductive additive include carbonaceous fine particles such as graphite, carbon black, acetylene black, and ketjen black, and carbon fiber.

[0032] The separator 6 may be, for example, a porous film. The porous film may be a film containing a resin selected from polyethylene, polypropylene, fluororesin, etc. The porous film may be a single layer or may have multiple layers.

[0033] The specific configuration of each member constituting the electricity storage device, such as the shape and thickness, can be appropriately determined by a person skilled in the art. The configuration of the electricity storage device is not limited to the embodiment shown in FIG. 1 and can be appropriately changed.

[0034] The present invention is not limited to the following examples. 1. Preparation of non-aqueous electrolyte solution Production Example 1 Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:EMC = 30:70 to obtain a mixed non-aqueous solvent. LiPF as an electrolyte was added to the obtained mixed non-aqueous solvent. ６ 151.91 g of LiPF was dissolved to obtain a solution of LiPF with a concentration of 1.0 mol / L (13 mass%). ６ A solution was obtained.

[0035] Example 1 LiPF obtained in Production Example 1 ６ To 9.90 g of the solution, 0.073 g of the compound represented by formula (1A) (LiDFOB) and LiBF ４ 0.027 g of LiDFOB was further dissolved in the nonaqueous electrolyte to prepare a nonaqueous electrolyte solution. In the nonaqueous electrolyte solution, the concentration of LiDFOB was 0.73 mass % based on the total mass of the nonaqueous electrolyte solution, and LiBF ４ The concentration of was 0.27 mass % based on the total mass of the nonaqueous electrolyte.

[0036] Comparative Example 1 LiPF obtained in Production Example 1 ６ 0.10 g of LiDFOB alone was further dissolved in 9.90 g of the solution to prepare a non-aqueous electrolyte solution having a LiDFOB concentration of 1.0 mass % based on the total mass of the non-aqueous electrolyte solution.

[0037] Comparative Example 2 LiPF obtained in Production Example 1 ６ To 9.90 g of the solution, LiBF was added as an additive. ４ 0.10 g of LiBF was further dissolved to prepare a non-aqueous electrolyte solution. ４ The concentration of was 1.0 mass % based on the total mass of the nonaqueous electrolyte solution.

[0038] Comparative Example 3 LiPF obtained in Production Example 1 ６ The solution was used as it was as a non-aqueous electrolyte.

[0039] 2. Fabrication of a non-aqueous electrolyte secondary battery A positive electrode sheet (manufactured by Yayama Co., Ltd.) containing a lithium-containing composite oxide and a negative electrode sheet (manufactured by Yayama Co., Ltd.) containing graphite were prepared. The positive electrode sheet had an aluminum foil (thickness: 20 μm) as a positive electrode current collector and positive electrode active material layers formed on both sides of the aluminum foil. The positive electrode active material layer contained a lithium-containing composite oxide (LiNi) as a positive electrode active material. ０．５ Co ０．２ Mn ０．３ O ２ The negative electrode sheet contained carbon black (CB) and carbon (KS) as conductivity imparting agents, and polyvinylidene fluoride (PVDF) as a binder. The mass ratio of these was lithium-containing composite oxide:CB:KS:PVDF = 92:2.5:2.5:3. The negative electrode sheet had copper foil (thickness 10 μm) as a negative electrode current collector and negative electrode active material layers formed on both sides thereof. The negative electrode active material layer contained graphite (Gr) as a negative electrode active material, and sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as binders. The mass ratio of these was Gr:CMC:SBR = 98:1:1. The negative electrode sheets and positive electrode sheets were alternately stacked with propylene separators interposed between them to produce a battery element having a total of 13 layers as electrodes: 7 layers of negative electrode sheets and 6 layers of positive electrode sheets.

[0040] The fabricated battery element was inserted into a bag formed from a laminate film having aluminum (40 μm thick) and resin layers covering both sides thereof, with the ends of the positive electrode sheet and negative electrode sheet protruding from the bag. Next, each of the nonaqueous electrolyte solutions obtained in Example 1 or Comparative Examples 1 to 3 was added to the bag. The bag was vacuum-sealed to obtain a sheet-like nonaqueous electrolyte secondary battery. To enhance adhesion between the electrodes, the sheet-like nonaqueous electrolyte secondary battery was sandwiched between glass plates and pressure was applied.

[0041] 3. Evaluation of Battery Performance Battery performance was evaluated by the following method. The evaluation results are shown in Table 1.

[0042] Aging (initial volume and initial capacity of battery) Each nonaqueous electrolyte secondary battery was charged at 25°C for 1 hour at a current equivalent to 0.1 C and then held at 25°C for 10 hours. Subsequently, each nonaqueous electrolyte secondary battery was charged at a current equivalent to 0.1 C for 5 hours and held at 45°C for 24 hours. Thereafter, the battery was discharged to 3 V at 25°C at a current equivalent to 0.1 C, and then degassed. After degassing, the volume of each nonaqueous electrolyte secondary battery was measured by Archimedes' method, and the measured value was defined as the "initial volume of the battery." Thereafter, each nonaqueous electrolyte secondary battery was aged by repeating three cycles of charging to 4.2 V at a current corresponding to 0.2 C and discharging to 3 V at a current corresponding to 0.2 C, three cycles of charging to 4.2 V at a current corresponding to 0.5 C and discharging to 3.0 V at a current corresponding to 0.5 C, and three cycles of charging to 4.2 V at a current corresponding to 1 C and discharging to 3.0 V at a current corresponding to 1 C, thereby stabilizing each nonaqueous electrolyte secondary battery. During this aging, the battery was charged to 4.2 V at a current corresponding to 1 C and discharged to 3.0 V at a current corresponding to 1 C, and the discharge capacity measured at the third cycle was designated as the "initial capacity."

[0043] Initial DCR Each nonaqueous electrolyte secondary battery after aging was charged to 50% of its initial capacity and then discharged at a current equivalent to 0.2 C, and the change in battery voltage during this period was measured. After that, with a 10-minute pause, the battery was repeatedly charged and discharged while changing the discharge current (discharge rate) to 0.5 C, 1.0 C, and 2.0 C, and the change in voltage was measured. From this value, the DCR (Ω) was calculated as "initial DCR (Ω)." The DCR is a value equivalent to the resistance value of the battery, and it can be said that the lower the DCR value, the higher the battery's output characteristics.

[0044] High-Temperature Storage Test (Remaining Capacity Retention Rate, Gas Generation Amount) After the initial DCR measurement, each nonaqueous electrolyte secondary battery was charged to 4.2 V at 1 C at 25°C, and then subjected to a high-temperature storage test in which the battery was held at 60°C for 30 days. The voltage immediately after holding the battery at 60°C for 30 days was measured, and this measured value was designated as the "remaining voltage." Thereafter, each nonaqueous electrolyte secondary battery was cooled to 25°C and discharged to 3 V at a current equivalent to 1 C. The discharge capacity immediately after this discharge was measured, and this measured value was designated as the "remaining capacity." The remaining capacity retention rate and voltage drop amount after the high-temperature storage test were calculated using the following formulas: Remaining capacity retention rate (%) = (remaining capacity / initial capacity) × 100 Voltage drop amount (V) = 4.2 V - remaining voltage

[0045] The volume of each nonaqueous electrolyte secondary battery after the high-temperature storage test was measured by Archimedes' method, and the measured value was defined as the "volume after storage." The amount of gas generated after storage was calculated using the following formula: Amount of gas generated after storage (cm ３ ) = volume after storage - initial volume

[0046] The nonaqueous electrolyte secondary battery whose volume after storage had been measured was charged to 50% of the remaining capacity and then discharged at a current equivalent to 0.2 C, and the change in battery voltage during this period was measured. After that, with a 10-minute pause, the battery was repeatedly charged and discharged while the discharge current (discharge rate) was changed to 0.5 C, 1.0 C, and 2.0 C, and the change in voltage was measured, and the DCR (Ω) was calculated from this value as "DCR (Ω) after storage."

[0047]

[0048] By using the nonaqueous electrolyte solution according to one aspect of the present disclosure, it is possible to manufacture an electricity storage device having excellent storage stability and a long life. An electricity storage device having a long life can contribute to solving environmental problems by reducing waste, etc.

[0049] DESCRIPTION OF SYMBOLS 1... Non-aqueous electrolyte secondary battery, 2... Negative electrode active material layer, 3... Negative electrode current collector, 4... Negative electrode, 5... Non-aqueous electrolyte, 6... Separator, 7... Positive electrode active material layer, 8... Positive electrode current collector, 9... Positive electrode.

Claims

1. Formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms; and LiBF ４ a non-aqueous solvent; and an electrolyte, wherein the electrolyte contains the compound represented by formula (1) and LiBF ４ is a different compound from LiBF ４ The non-aqueous electrolyte solution has a content of 3.0 mass % or less based on the total amount of the non-aqueous electrolyte solution.

2. The content of the compound represented by formula (1) is the compound represented by formula (1) and LiBF ４ 2. The nonaqueous electrolyte solution according to claim 1, wherein the content of the nonaqueous electrolyte is 10% by mass or more and 90% by mass or less based on the total amount of the components.

3. The compound represented by formula (1) and LiBF ４ The non-aqueous electrolyte solution according to claim 1, wherein the total content of the above is 3.0 mass % or less based on the total amount of the non-aqueous electrolyte solution.

4. LiBF ４ The non-aqueous electrolyte solution according to claim 1, wherein the content of is 0.9 mass % or less based on the total amount of the non-aqueous electrolyte solution.

5. The compound represented by formula (1) is represented by the following formula (1A): The non-aqueous electrolyte according to claim 1, wherein the compound is represented by the formula:

6. Formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms; and LiBF ４ and an additive for a non-aqueous electrolyte, comprising:

7. The content of the compound represented by formula (1) is the compound represented by formula (1) and LiBF ４ The additive for a non-aqueous electrolyte according to claim 6, wherein the content is 10 mass % or more and 90 mass % or less based on the total amount of 8. LiBF ４ and formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms, and is used to add the compound to a non-aqueous electrolyte.

9. Preparing a non-aqueous solvent; and adding LiBF to the non-aqueous solvent. ４ and dissolving a compound represented by formula (1): wherein R is a direct bond, an alkylene group having 1 to 4 carbon atoms, or a halogenated alkylene group having 1 to 4 carbon atoms; and dissolving an electrolyte in the nonaqueous solvent, wherein the electrolyte comprises the compound represented by formula (1) and LiBF ４ and LiBF is a compound different from the compound ４ is 3.0 mass% or less based on the total amount of the nonaqueous electrolyte solution.

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

Images