Secondary batteries

Abstract

Provided is a secondary battery capable of suppressing corrosion of a current corrector due to lithium bis(fluorosulfonyl)imide and of charging / discharging stably. This secondary battery comprises a positive electrode, a negative electrode, a separator and an electrolyte solution, and the electrolyte solution contains an acetamide derivative represented by formula (1) and lithium bis(fluorosulfonyl)imide. (In formula (1), R1 and R2 respectively independently represent an alkyl group or alkoxy group having 1-5 carbon atoms and optionally having a substituent or a trimethylsilyl group and R1 and R2 may be bound to each other to form a fused ring.)

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] In secondary batteries, lithium bis(fluorosulfonyl)imide (LiFSI) is sometimes used as the electrolyte salt of the electrolyte. In this case, the electrolyte may corrode metals such as aluminum used as the positive electrode current collector. Therefore, it is necessary to suppress the corrosion of the current collector by LiFSI.

[0003] Patent Document 1 describes the addition of an asymmetric borate ester, an asymmetric phosphate ester, or the like to an electrolyte solution for the purpose of suppressing corrosion of a current collector or the like by LiFSI. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2017-504145 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for a secondary battery that uses LiFSI as the electrolyte salt of the electrolyte solution, and that can be stably charged and discharged while suppressing corrosion of the current collector and the like.

[0006] The present invention has been made in view of the above problems, and aims to provide a secondary battery that can be stably charged and discharged while suppressing corrosion of a current collector and the like by lithium bis(fluorosulfonyl)imide. [Means for solving the problem]

[0007] A secondary battery according to one embodiment of the present invention is a secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution, and the electrolyte solution contains an acetamide derivative represented by formula (1) and lithium bis(fluorosulfonyl)imide. [ka] (In formula (1), R1 and R2 each independently represent an alkyl group or alkoxy group having 1 to 5 carbon atoms, which may have a substituent, or a trimethylsilyl group, and R1 and R2 may be bonded to each other to form a fused ring.) [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a secondary battery that can be stably charged and discharged while suppressing corrosion of the current collector and the like caused by lithium bis(fluorosulfonyl)imide. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 2] FIG. 2 is an enlarged view of region A in FIG. [Figure 3] FIG. 3 is a cutaway view showing another example of the secondary battery according to this embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line VI-VI in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0011] (Secondary battery) Fig. 1 is a cross-sectional view showing an example of a secondary battery according to this embodiment. The secondary battery 1 shown in Fig. 1 is a cylindrical lithium-ion secondary battery. As shown in Fig. 1, the secondary battery 1 includes a casing 10 and an electrode assembly 200.

[0012] The casing 10 is a case that houses the electrode assembly 200 and an electrolyte (not shown) inside. The casing 10 includes a battery can 11, a lid 12, a thermosensitive resistor element 13, a safety valve mechanism 14, a gasket 15, a positive electrode lead 16, a negative electrode lead 17, a center pin 19, and an insulating plate 18.

[0013] The battery can 11 is a cylindrical member that includes an end face that serves as the negative electrode of the secondary battery 1. That is, the battery can 11 is a cylinder with one end face closed and the other end face open. The battery can 11 is a conductor, and is made of, for example, iron (Fe) whose surface is plated with nickel (Ni).

[0014] The lid body 12 is a disk-shaped member including a protrusion that serves as the positive electrode of the secondary battery 1. The lid body 12 is provided on the end face on the open side of the battery can 11. The lid body 12 is made of a conductor, for example, made of the same material as the battery can 11.

[0015] In the following description, the direction in which the cylindrical portion of the battery can 11 extends may be referred to as the length direction of the secondary battery 1. In the following description, the positive electrode of the secondary battery 1 refers to the protrusion of the lid 12, and the negative electrode of the secondary battery 1 refers to the closed end surface of the battery can 11.

[0016] The thermosensitive resistor 13 is an element whose resistance increases with an increase in temperature. The thermosensitive resistor 13 is provided on the negative electrode side of the lid 12. When the secondary battery 1 becomes hot due to a short circuit or the like, the resistance of the thermosensitive resistor 13 increases and limits the current.

[0017] The safety valve mechanism 14 is a mechanism that changes shape in response to the gas pressure inside the casing 10. The safety valve mechanism 14 is provided on the negative electrode side with respect to the thermosensitive resistor element 13. The safety valve mechanism 14 is electrically connected to the lid 12 via the thermosensitive resistor element 13. The safety valve mechanism 14 has a protrusion on the negative electrode side, and when the gas pressure inside the casing 10 is normal, the safety valve mechanism 14 is in contact with and electrically connected to the positive electrode lead 16 via the protrusion. On the other hand, when the gas pressure inside the casing 10 increases, the protrusion of the safety valve mechanism 14 flips to the positive electrode side and moves away from the positive electrode lead 16. This electrically disconnects the positive electrode lead 16 from the lid 12.

[0018] The gasket 15 is an annular member that fixes the lid 12, the thermosensitive resistor 13, and the safety valve mechanism 14 to the battery can 11. The gasket 15 is provided on the open end surface of the battery can 11. The gasket 15 tightly seals the battery can 11 and the lid 12, making the inside of the casing 10 airtight. The gasket 15 is an insulator.

[0019] The positive electrode lead 16 is a terminal connected to a positive electrode 210 of the electrode body 200, which will be described later. The positive electrode lead 16 is electrically connected to the lid body 12 via a safety valve mechanism 14 and a thermosensitive resistor element 13. The positive electrode lead 16 is a conductor, and is made of, for example, aluminum.

[0020] The negative electrode lead 17 is a terminal connected to the negative electrode 220 of the electrode body 200, which will be described later. The negative electrode lead 17 is electrically connected to the battery can 11. The negative electrode lead 17 is a conductor, and is made of, for example, nickel.

[0021] The insulating plate 18 is an insulating plate-shaped member. One insulating plate 18 is provided so as to cover the positive electrode side of the secondary battery 1 and the negative electrode side of the secondary battery 1 of the electrode body 200 described later.

[0022] The center pin 19 is provided on the central axis of the electrode body 200. The center pin 19 is a linear member having a length in the longitudinal direction of the secondary battery 1. The material of the center pin 19 is not particularly limited, and may be, for example, a metal.

[0023] FIG. 2 is an enlarged view of region A in FIG. 1. As shown in FIG. 2, the electrode assembly 200 includes a positive electrode 210, a negative electrode 220, and a separator 230. In the secondary battery 1, the electrode assembly 200 has a structure in which the positive electrode 210 and the negative electrode 220 are stacked with the separator 230 interposed therebetween. In the example of FIG. 1, the electrode assembly 200 is provided inside a battery can 11 and has a structure in which the electrode assembly 200 is wound around a center pin 19. In other words, in the electrode assembly 200, the positive electrode 210, the negative electrode 220, and the separator 230 are stacked in the radial direction of the secondary battery 1 with the center pin 19 at the center. The positive electrode 210 and the negative electrode 220 included in the electrode assembly 200 are layered members for the charge / discharge reaction of the secondary battery according to this embodiment.

[0024] The positive electrode 210 includes a positive electrode current collector layer 211 and a positive electrode active material layer 212. In the positive electrode 210, the positive electrode current collector layer 211 is laminated between the positive electrode active material layers 212.

[0025] The positive electrode current collector layer 211 is a conductive layer, and for example, aluminum foil or the like can be used.

[0026] The positive electrode active material layer 212 is a layer containing a positive electrode active material. The positive electrode active material layer 212 includes a positive electrode active material, a binder, and a conductive additive. The positive electrode active material layer 212 is not limited to the materials listed above, and may further include, for example, a dispersant.

[0027] The positive electrode active material is preferably a lithium-containing compound such as a lithium-containing composite oxide or a lithium-containing phosphate compound. The lithium-containing composite oxide is an oxide containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing composite oxide has, for example, a layered rock salt type or a spinel type crystal structure. Specific examples of the lithium-containing composite oxide include LiNiO2, LiCoO2, and LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2, LiMn2O4, etc. The lithium-containing phosphate compound is a phosphate compound containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing phosphate compound has, for example, an olivine-type crystal structure. Specific examples of the lithium-containing phosphate compound are LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 PO4, etc.

[0028] The binder contained in the positive electrode active material layer 212 may be any material, and may include, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride and polyimide.

[0029] The conductive additive contained in the positive electrode active material layer 212 may be any material, including, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and ketjen black. However, the conductive additive is not limited to these materials, and may also be a metal material, a conductive polymer, or the like, as long as it is a conductive material.

[0030] The negative electrode 220 includes a negative electrode current collector layer 221 and a negative electrode active material layer 222. In the negative electrode 220, the negative electrode current collector layer 221 is laminated between the negative electrode active material layers 222.

[0031] The negative electrode current collector layer 221 is a conductor, and for example, copper foil or the like can be used.

[0032] The negative electrode active material layer 222 is a layer containing a negative electrode active material. The negative electrode active material layer 222 is not limited to being made of only a negative electrode active material, and may also contain, for example, a conductive additive and a binder.

[0033] The negative electrode active material includes a material capable of absorbing and releasing lithium, such as a carbon material, a metal, a metalloid, an alloy or compound of silicon, or an alloy or compound of tin (Sn).

[0034] Examples of carbon materials that can be used as the negative electrode active material include graphite, non-graphitizable carbon, and graphitizable carbon. More specifically, carbon materials include pyrolytic carbons, cokes, glassy carbon fiber, fired organic polymer compounds, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Here, fired organic polymer compounds are carbonized by firing a polymer compound such as a phenolic resin or a furan resin at an appropriate temperature.

[0035] Examples of metals and metalloids that can be used as negative electrode active materials include tin, lead (Pb), aluminum, indium (In), silicon, zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y), and hafnium (Hf). Among these, silicon, germanium, tin, and lead are preferred. Silicon and tin are more preferred because they have a high ability to absorb and release lithium and can achieve a high energy density.

[0036] Examples of silicon alloys that can be used as the negative electrode active material include those containing at least one element selected from the group consisting of tin, nickel, copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony, and chromium (Cr) as a second constituent element other than silicon. Examples of silicon compounds that can be used as the negative electrode active material include those containing oxygen (O) or carbon (C), and may contain the above-mentioned second constituent element in addition to silicon.

[0037] Examples of tin alloys that can be used as the negative electrode active material include those containing at least one element selected from the group consisting of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as a second constituent element other than tin. Examples of tin compounds that can be used as the negative electrode active material include those containing oxygen or carbon, and may contain the above-mentioned second constituent element in addition to tin.

[0038] The separator 230 is a film that insulates the positive electrode 210 and the negative electrode 220. The separator 230 is laminated between the positive electrode 210 and the negative electrode 220 to prevent direct contact between the positive electrode 210 and the negative electrode 220. The material of the separator 230 is preferably electrically stable, chemically stable against the positive electrode active material, the negative electrode active material, and the electrolyte, and has insulating properties. The separator 230 can be, for example, a polymer nonwoven fabric, a porous film, or a layer made of glass or ceramic fibers. The material of the separator 230 more preferably includes a porous polyolefin film. The separator 230 may be composed of multiple layers, or a composite of a porous polyolefin film and a heat-resistant film containing polyimide, glass, or ceramic fibers may be used.

[0039] The electrolyte is an electrolyte that is filled into the space surrounded by the insulating plate 18 and the battery can 11. The electrolyte is, for example, an electrolyte that contains an electrolyte salt and a solvent that dissolves the electrolyte salt.

[0040] The electrolyte salt contains lithium bis(fluorosulfonyl)imide (LiN(SO2F2)2). This can improve the charge / discharge characteristics. The electrolyte salt may contain other electrolyte salts used as electrolyte salts for lithium ion batteries. The mass of the other electrolyte salt is preferably 1 / 3 or less, more preferably 1 / 4 or less, of the mass of lithium bis(fluorosulfonyl)imide (LiN(SO2F2)2). The other electrolyte salt is, for example, a light metal salt such as a lithium salt. Specific examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), lithium tris(trifluoromethanesulfonyl)methide (LiC(CFSO)), lithium bis(oxalato)borate (LiB(C0)), lithium monofluorophosphate (LiPFO), and lithium difluorophosphate (LiPF0).

[0041] The solvent contains an acetamide derivative represented by formula (1), which can suppress corrosion of the positive electrode current collector layer 211 and the like caused by lithium bis(fluorosulfonyl)imide. [ka] (In formula (1), R1 and R2 each independently represent an alkyl group or alkoxy group having 1 to 5 carbon atoms, which may have a substituent, or a trimethylsilyl group, and R1 and R2 may be bonded to each other to form a fused ring.) The term "optionally substituted" means that the group has no substituents or that the hydrogen groups are substituted with one or more substituents. Examples of the substituents include hydrocarbon groups and halogen groups such as fluorine groups.

[0042] Examples of the compound represented by formula (1) include compounds represented by formulas (1-1) to (1-5). [ka]

[0043] In this embodiment, the molar ratio of the acetamide derivative to lithium bis(fluorosulfonyl)imide is 2 or more and 4 or less. By setting the molar ratio to 2 or more, corrosion of the positive electrode current collector layer 211 and the like by lithium bis(fluorosulfonyl)imide can be effectively suppressed. Furthermore, by setting the molar ratio to 4 or less, the viscosity of the electrolyte solution decreases, thereby improving the discharge rate characteristics.

[0044] The solvent may contain other non-aqueous solvents used as electrolyte salts in lithium-ion batteries. The mass of the other non-aqueous solvent is preferably ⅓ or less, more preferably ¼ or less, of the mass of the acetamide derivative represented by Formula (1). The other non-aqueous solvents include esters, ethers, etc. More specifically, the other non-aqueous solvents include carbonate ester compounds, carboxylic acid ester compounds, lactone compounds, etc. The carbonate ester compounds include cyclic carbonate esters and chain carbonate esters. Specific examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate. Specific examples of chain carbonate esters include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The carboxylic acid ester compounds include chain carboxylic acid esters. Specific examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl trimethyl acetate, ethyl trimethyl ethyl acetate, methyl butyrate, and ethyl butyrate. The lactone compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone. Specific examples of ethers include 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc. The ethers may be compounds in which some or all of the hydrogen atoms have been substituted with fluorine atoms, such as 1,1,2-tetrafluoroethyl 2,2,2,3,3-tetrafluoropropyl ether.

[0045] The electrolytic solution may contain substances other than the electrolyte salt and the solvent, such as additives, etc. The mass of the substances other than the electrolyte salt and the solvent is preferably 0.1% by mass or more and 20% by mass or less relative to the mass of the electrolyte salt and the solvent additive.

[0046] The electrolyte preferably further contains, as an additive, at least one of unsaturated cyclic carbonates such as vinylene carbonate, 4-methylene-1,3-dioxolan-2-one (methyleneethylene carbonate), and vinylethylene carbonate, and halogenated cyclic carbonates such as fluoroethylene carbonate (monofluoroethylene carbonate) and difluoroethylene carbonate. This allows for the formation of coatings with high ion conductivity at the interfaces between the electrolyte and the positive electrode 210 and the negative electrode 220, thereby further improving the discharge rate characteristics.

[0047] The additives are not limited to those listed above, and other additives may also be used. The other additives are not particularly limited, but may specifically include sulfonic acid esters, phosphate esters, acid anhydrides, isocyanates, etc. Specific examples of sulfonic acid esters include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of isocyanates include hexamethylene diisocyanate.

[0048] The electrolyte preferably further contains a hydrofluoroether as an additive. Examples of hydrofluoroethers include 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. This reduces the viscosity of the electrolyte, improving the ionic conductivity of the electrolyte and further improving the discharge rate characteristics.

[0049] Although the battery according to this embodiment has been described above, the secondary battery according to this embodiment is not limited to the one shown in Fig. 1. Other examples will be described below using the drawings, but the same components as those in Fig. 1 and Fig. 2 will be denoted by reference numerals and will not be described again.

[0050] Fig. 3 is a cutaway view showing another example of the secondary battery according to the present embodiment. The secondary battery 1A shown in Fig. 3 is a laminated lithium-ion secondary battery. As shown in Fig. 3, the secondary battery 1A includes a battery element 20, an exterior member 31, and an adhesive 32.

[0051] FIG. 4 is a schematic cross-sectional view taken along line VI-VI in FIG. 3. The battery element 20 is provided inside an exterior member 31. As shown in FIG. 4, the battery element 20 includes an electrode body 200A, a positive electrode lead 21, a negative electrode lead 22, and a protective material 23. The positive electrode lead 21 is a terminal extending from inside the battery element 20 to the outside of the exterior member 31. That is, the positive electrode lead 21 is a terminal serving as the positive electrode of the secondary battery 1A. In FIG. 4, the positive electrode lead 21 is provided near the center of the battery element 20. The negative electrode lead 22 is a terminal extending from inside the battery element 20 to the outside of the exterior member 31. That is, the negative electrode lead 22 is a terminal serving as the negative electrode of the secondary battery 1A. In FIG. 4, the negative electrode lead 22 is provided near the center of the battery element 20. The protective material 23 is a member that protects the exterior of the battery element 20. The protective material 23 is provided so as to be wrapped around the electrode body 200A. The protective material 23 is, for example, an insulating tape.

[0052] The exterior member 31 is a case that houses the battery element 20. The exterior member 31 includes an insulating layer, a metal layer, and an outermost layer. The exterior member 31 is constructed by laminating the insulating layer, metal layer, and outermost layer in this order from the inside, i.e., the side where the battery element 20 is provided, and then bonding them together by lamination or other processing. The insulating layer of the exterior member 31 is made of a resin such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, or a polyolefin resin containing ethylene or propylene as a monomer. This allows the exterior member 31 to reduce the moisture permeability of the secondary battery 1A and improve its airtightness. The metal layer of the exterior member 31 is a metal plate or foil material such as aluminum, stainless steel, nickel, or iron. The outermost layer may be made of any material, but is preferably made of the same resin as the insulating layer or a material that is highly resistant to tearing and punctures, such as nylon.

[0053] The adhesive 32 is a member for making the exterior member 31 airtight. The adhesive 32 is provided between the exterior member 31 and the positive electrode lead 21 and the negative electrode lead 22. The material of the adhesive 32 preferably has adhesion to the positive electrode lead 21 and the negative electrode lead 22. For example, when the positive electrode lead 21 and the negative electrode lead 22 are made of a metal material, the adhesive 32 is made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. This allows the adhesive 32 to seal the gap between the exterior member 31 and the positive electrode lead 21 and the negative electrode lead 22, thereby making the interior of the exterior member 31 airtight.

[0054] 4, the electrode assembly 200A is a laminate for charge / discharge reactions of the secondary battery according to this embodiment. The electrode assembly 200A includes a positive electrode 210A including a positive electrode current collector layer 211A and a positive electrode active material layer 212A, a negative electrode 220A including a negative electrode current collector layer 221A and a negative electrode active material layer 222A, and a separator 230A. The electrode assembly 200A has a structure in which the positive electrode lead 21 and the negative electrode lead 22 are wound around the center, and is laminated in the following order from the outside, i.e., from the protective material 23 side: the negative electrode current collector layer 221A, the negative electrode active material layer 222A, the separator 230A, the positive electrode active material layer 212A, the positive electrode current collector layer 211A, the positive electrode active material layer 212A, the separator 230A, and the negative electrode active material layer 222A. In the electrode body 200A, no layers other than the negative electrode current collector layer 221A, the separator 230A, and the positive electrode current collector layer 211A are provided near the positive electrode lead 21 and the negative electrode lead 22. With this structure, the positive electrode current collector layer 211A is connected to the positive electrode lead 21, and the negative electrode current collector layer 221A is connected to the negative electrode lead 22.

[0055] As described above, the secondary battery according to this embodiment is a secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution, and the electrolyte solution contains an acetamide derivative represented by formula (1) and lithium bis(fluorosulfonyl)imide. [ka] (In formula (1), R1 and R2 each independently represent an alkyl group or alkoxy group having 1 to 5 carbon atoms, which may have a substituent, or a trimethylsilyl group, and R1 and R2 may be bonded to each other to form a fused ring.)

[0056] This makes it possible to suppress corrosion of the current collector (positive electrode current collector layer 211) and the like caused by lithium bis(fluorosulfonyl)imide, and thus makes it possible to provide a secondary battery that can be stably charged and discharged.

[0057] In a preferred embodiment, the molar ratio of the acetamide derivative to the lithium bis(fluorosulfonyl)imide is 2 or more and 4 or less. By setting the molar ratio to 2 or more, corrosion of the current collector and the like by the lithium bis(fluorosulfonyl)imide can be effectively suppressed. Furthermore, by setting the molar ratio to 4 or less, the viscosity of the electrolyte solution is reduced, thereby improving the discharge rate characteristics.

[0058] In a preferred embodiment, the electrolyte solution further contains at least one of an unsaturated cyclic ester carbonate and a halogenated cyclic ester carbonate, which allows lithium ion conductive coatings to be formed at the interfaces between the electrolyte solution and the positive and negative electrodes, thereby further improving the discharge rate characteristics.

[0059] In a preferred embodiment, the electrolyte solution further contains a hydrofluoroether, which reduces the viscosity of the electrolyte solution and further improves the discharge rate characteristics.

[0060] EXAMPLES Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0061] In the following description, lithium bis(fluorosulfonyl)imide is referred to as LiFSI, and a mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1 is referred to as ECPC. Chemicals A to E in the following description are as follows.

[0062] Compound A: a compound represented by formula (1-1) [ka]

[0063] Compound B: Compound represented by formula (1-2) [ka]

[0064] Compound C: Compound represented by formula (1-3) [ka]

[0065] Compound D: Compound represented by formula (1-4) [ka]

[0066] Compound E: Compound represented by formula (1-5) [ka]

[0067] <Example 1-1> In Example 1-1, a battery for metal corrosion evaluation test was prepared by stacking aluminum foil, a polyethylene porous film, and metallic lithium, and injecting an electrolyte solution. Also, in Example 1-1, a battery for battery evaluation test was prepared by stacking a positive electrode, a polyethylene porous film as a separator, and a negative electrode, and injecting an electrolyte solution. Here, the battery for battery evaluation test was designed to have a design capacity of 5 mAh.

[0068] In Example 1-1, Chemical A was used as the solvent for the electrolyte solution, and LiFSI was used as the electrolyte salt. The electrolyte solution according to Example 1-1 was prepared by mixing Chemical A and LiFSI at a molar ratio of 3:1.

[0069] The positive electrode of the battery for battery evaluation test was fabricated by the following method. First, 91% by mass of lithium nickel oxide (LiNiO2) as a positive electrode active material, 3% by mass of polyvinylidene fluoride as a binder, and 6% by mass of acetylene black as a conductive additive were mixed together to form a positive electrode mixture. Next, the positive electrode mixture was added to an organic solvent, N-methyl-2-pyrrolidone, and stirred to prepare a paste-like positive electrode mixture slurry. Next, using a coating device, the positive electrode mixture slurry was applied to both sides of a 12 μm-thick strip of aluminum foil serving as a positive electrode current collector. Finally, the positive electrode mixture slurry was dried to form a positive electrode active material layer. Then, the positive electrode active material layer was compression-molded using a roll press to fabricate a positive electrode.

[0070] The negative electrode of the battery for battery evaluation test was fabricated by the following method. First, 93% by mass of graphite as the negative electrode active material and 7% by mass of polyvinylidene fluoride as the binder were mixed together to form a negative electrode mixture. Next, the negative electrode mixture was added to an organic solvent, N-methyl-2-pyrrolidone, and stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a 15 μm-thick strip of copper foil as a negative electrode current collector using a coating device. The negative electrode mixture slurry was then dried to form a negative electrode active material layer. Finally, the negative electrode active material layer was compression-molded using a roll press to fabricate a negative electrode.

[0071] <Metal corrosion evaluation test> The prepared metal corrosion evaluation test battery was charged with aluminum foil as the working electrode, and the voltage was increased from the open circuit potential to 4.2 V at a rate of 1 mV per second. After reaching 4.2 V, constant-potential electrolysis was performed at 4.2 V for 5 hours to evaluate the occurrence of corrosion of the aluminum foil. Specifically, it was determined that corrosion of the aluminum foil had occurred if discoloration of the aluminum foil or leakage of the electrolyte occurred.

[0072] <<Initial charge / discharge test>> As an initial charge / discharge test, the prepared battery for battery evaluation test was subjected to CCCV charging at a constant charge rate under the following conditions. After the charge control voltage was reached, the battery was charged at the charge control voltage. When the current value decreased to the charge cutoff, the battery was CC discharged at a constant discharge rate, and the discharge was terminated when the voltage reached the discharge end voltage. Charge rate: 0.05C Charge control voltage: 4.20V Charging cutoff: 0.01C Discharge rate: 0.05C Discharge end voltage: 2.5V

[0073] An initial charge-discharge test was performed on three battery evaluation test batteries. If the capacity measured in the initial charge-discharge test was 50% or more of the theoretical capacity calculated from the mass of the active material, the battery evaluation test battery was determined to be capable of being charged and discharged. If the capacity measured in the initial charge-discharge test was less than 50% of the theoretical capacity calculated from the mass of the active material, the battery evaluation test battery was determined to be incapable of being charged and discharged.

[0074] <Example 1-2> In Example 1-2, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 1-1, except that chemical B was used instead of chemical A as the solvent for the electrolyte solution, and a battery evaluation test battery was prepared and an initial charge / discharge test was performed.

[0075] <Examples 1-3> In Example 1-3, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 1-1, except that chemical C was used instead of chemical A as the solvent for the electrolyte solution, and a battery evaluation test battery was prepared and an initial charge / discharge test was performed.

[0076] <Examples 1-4> In Example 1-4, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 1-1, except that chemical D was used instead of chemical A as the solvent for the electrolyte solution, and a battery evaluation test battery was prepared and an initial charge / discharge test was performed.

[0077] <Examples 1-5> In Example 1-5, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 1-1, except that chemical E was used instead of chemical A as the solvent for the electrolyte solution, and a battery evaluation test battery was prepared and an initial charge / discharge test was performed.

[0078] <Comparative Example 1-1> In Comparative Example 1-1, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 1-1, except that ECPC was used instead of Chemical A as the solvent for the electrolyte solution, and a battery evaluation test battery was prepared and an initial charge / discharge test was performed.

[0079] Table 1 shows the results of the metal corrosion evaluation test and the initial charge-discharge test for Examples 1-1 to 1-5 and Comparative Example 1-1.

[0080] [Table 1]

[0081] As shown in Table 1, in Examples 1-1 to 1-5, an electrolyte containing any one of Chemicals A to E was used, which suppressed corrosion of the aluminum foil by LiFSI, and all three batteries subjected to the battery evaluation test were able to be charged and discharged. As a result, the secondary batteries according to Examples 1-1 to 1-5 were able to be stably charged and discharged.

[0082] On the other hand, in Comparative Example 1-1, the use of an electrolyte containing ECPC suppressed corrosion of the aluminum foil by LiFSI, but all three batteries subjected to the battery evaluation test were unable to be charged or discharged. This is thought to be because the high viscosity of the electrolyte in Comparative Example 1-1 prevented the electrolyte from sufficiently impregnating the separator, etc., or because the ionic conductivity of the electrolyte was reduced.

[0083] <Example 2-1> In Example 2-1, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 1-1, except that Compound A and LiFSI were mixed in a molar ratio of 2:1, and a battery evaluation test battery was prepared and an initial charge / discharge test was performed.

[0084] <Discharge rate characteristic evaluation test> In Example 2-1, in addition to the initial charge / discharge test performed in Example 1-1, a discharge rate characteristic evaluation test was performed. In the discharge rate characteristic evaluation test, the battery for battery evaluation test, which was determined to be chargeable / dischargeable in the initial charge / discharge test, was subjected to second to sixth charge / discharge cycles as described below to evaluate the discharge rate characteristic.

[0085] In the second charge / discharge, under the following conditions, the battery was CCCV charged at a constant charge rate, and after reaching the charge control voltage, it was charged at the charge control voltage. Charging was terminated when the current value decreased to the charge cutoff point, and CC discharge was performed at a constant discharge rate. Discharge capacity was measured during the second charge / discharge and was taken as the 0.2C discharge capacity. Charging rate: 0.2C Charge control voltage: 4.20V Charging cutoff: 0.05C Discharge rate: 0.2C Discharge end voltage: 2.5V

[0086] The third to sixth charge / discharge cycles were performed under the same conditions as the second charge / discharge test, except that the charge rates were set to 0.5 C, 1.0 C, 2.0 C, and 5.0 C. The discharge capacity was measured after the sixth charge / discharge cycle and designated as the 5 C discharge capacity.

[0087] The 5C discharge capacity retention rate was calculated based on the measured 0.2C discharge capacity and 5C discharge capacity. Here, the 5C discharge capacity retention rate is the ratio of the 5C discharge capacity to the 0.2C discharge capacity. In other words, if the 5C discharge capacity retention rate is high, the discharge capacity can be increased even at a high discharge rate, which can be said to improve the discharge rate characteristics.

[0088] <Example 2-2> In Example 2-2, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that Compound A and LiFSI were mixed in a molar ratio of 3:1. A battery for battery evaluation test was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed. That is, the electrolyte solution according to Example 2-2 was the same as that in Example 1-1.

[0089] <Example 2-3> In Example 2-3, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that Compound A and LiFSI were mixed in a molar ratio of 4:1. A battery for battery evaluation test was also prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0090] <Example 2-4> In Example 2-4, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that Compound A and LiFSI were mixed in a molar ratio of 5:1. A battery for battery evaluation test was also prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0091] <Comparative Example 2-1> In Comparative Example 2-1, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that ECPC was used instead of Compound A as the solvent for the electrolyte, and the molar ratio of ECPC to LiFSI was 2:1. A battery for battery evaluation test was also prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0092] <Comparative Example 2-2> In Comparative Example 2-2, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that ECPC was used instead of Compound A as the solvent for the electrolyte, and the molar ratio of ECPC to LiFSI was 3:1. A battery for battery evaluation test was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed. That is, the electrolyte solution according to Comparative Example 2-2 was the same as that of Comparative Example 1-1.

[0093] <Comparative Example 2-3> In Comparative Example 2-3, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that ECPC was used instead of Compound A as the solvent for the electrolyte, and the molar ratio of ECPC to LiFSI was 4:1. A battery for battery evaluation test was also prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0094] <Comparative Example 2-4> In Comparative Example 2-4, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-1, except that ECPC was used instead of Compound A as the solvent for the electrolyte, and the molar ratio of ECPC to LiFSI was 5:1. A battery for battery evaluation test was also prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0095] Table 2 shows the results of the metal corrosion evaluation test and the battery evaluation test for Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-4.

[0096] [Table 2]

[0097] As shown in Table 2, in Examples 2-1 to 2-4, the use of an electrolyte containing Compound A suppressed corrosion of the aluminum foil by LiFSI, and all three batteries subjected to the battery evaluation test were able to be charged and discharged. As a result, the secondary batteries according to Examples 2-1 to 2-4 were able to be stably charged and discharged.

[0098] On the other hand, in Comparative Examples 2-1 and 2-2, since ECPC was contained, corrosion of the aluminum foil by LiFSI was suppressed, but all three batteries subjected to the battery evaluation test were unable to be charged or discharged. This is thought to be because in Comparative Examples 2-1 and 2-2, the electrolyte solution became highly viscous, so the electrolyte solution did not sufficiently impregnate the separator, etc., or the ionic conductivity of the electrolyte solution decreased.

[0099] In Comparative Example 2-3, since ECPC was contained, corrosion of the aluminum foil by LiFSI was suppressed, but two of the three batteries subjected to the battery evaluation test were unable to charge and discharge. As a result, the secondary battery according to Comparative Example 2-3 was unable to stably charge and discharge. This is thought to be because the viscosity of the electrolyte in Comparative Example 2-3 was not sufficiently reduced, making it difficult for the electrolyte to impregnate the separator, etc., or because the ionic conductivity of the electrolyte was reduced.

[0100] In Comparative Example 2-4, the concentration of ECPC relative to LiFSI was low, so corrosion of the aluminum foil by LiFSI could not be suppressed, and all three batteries subjected to the battery evaluation test were unable to be charged or discharged.

[0101] As shown in Table 2, in Examples 2-1 to 2-3, the molar ratio of compound A to LiFSI was 2 or more and 4 or less, and therefore the 5C discharge capacity retention rate was improved compared to Example 2-4, in which the molar ratio was more than 4. In Example 2-3, an electrolyte solution containing compound A was used, and therefore the 5C discharge capacity retention rate was improved compared to Comparative Example 2-3, in which the molar concentration of LiFSI in the electrolyte solution was the same.

[0102] <Example 3-1> Example 3-1 is an example similar to Example 2-2. That is, in Example 3-1, no additive was mixed into the electrolyte solution according to Example 2-2, and similarly to Example 2-2, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed, and a battery evaluation test battery was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0103] <Example 3-2> In Example 3-2, a battery for metal corrosion evaluation test was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-2, except that 1 mass % of vinylene carbonate (VC) was mixed as an additive into the electrolyte solution of Example 2-2, and a battery for battery evaluation test was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0104] <Example 3-3> In Example 3-3, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-2, except that 1 mass % of fluoroethylene carbonate (FEC) was mixed as an additive into the electrolyte solution of Example 2-2, and a battery evaluation test battery was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0105] <Example 3-4> In Example 3-4, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-2, except that 1 mass % of 4-methylene-1,3-dioxolan-2-one (MDO) was mixed as an additive into the electrolyte solution of Example 2-2, and a battery evaluation test battery was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0106] Table 3 shows the results of the metal corrosion evaluation test and the battery evaluation test for Examples 3-1 to 3-4.

[0107] [Table 3]

[0108] As shown in Table 3, in Examples 3-1 to 3-4, corrosion of the aluminum foil by LiFSI was suppressed, and all three batteries subjected to the battery evaluation test were able to be charged and discharged. As a result, the secondary batteries according to Examples 3-1 to 3-4 were able to be stably charged and discharged.

[0109] As shown in Table 3, in Examples 3-2 to 3-4, an electrolyte solution in which VC, FEC, or MDO was added to the electrolyte solution of Example 2-2 was used, and therefore the 5C discharge capacity retention rate was improved compared to Example 3-1 in which an electrolyte solution similar to the electrolyte solution of Example 2-2 was used. This is thought to be because the addition of an unsaturated cyclic carbonate or a halogenated cyclic carbonate to the electrolyte formed a coating with high ion conductivity at the interfaces between the positive electrode and the negative electrode and the electrolyte, thereby reducing the interfacial resistance.

[0110] <Example 4-1> Example 4-1 is an example similar to Example 2-2. That is, in Example 4-1, no additive was mixed into the electrolyte solution according to Example 2-2, and similarly to Example 2-2, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed, and a battery evaluation test battery was prepared and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0111] <Example 4-2> In Example 4-2, a metal corrosion evaluation test battery was prepared and a metal corrosion evaluation test was performed in the same manner as in Example 2-2, except that 10 mass% of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) was mixed as an additive into the electrolyte solution of Example 2-2, and an initial charge / discharge test and a discharge rate characteristic evaluation test were performed.

[0112] Table 4 shows the results of the metal corrosion evaluation test and the battery evaluation test for Examples 4-1 and 4-2.

[0113] [Table 4]

[0114] As shown in Table 4, in Examples 4-1 and 4-2, corrosion of the aluminum foil by LiFSI was suppressed, and all three batteries subjected to the battery evaluation test were able to be charged and discharged. As a result, the secondary batteries according to Examples 4-1 and 4-2 were able to be stably charged and discharged.

[0115] As shown in Table 4, Example 4-1 used an electrolyte solution obtained by adding TTE to the electrolyte solution of Example 2-2, and therefore the 5C discharge capacity retention rate was improved compared to Example 4-1, which used an electrolyte solution similar to that of Example 2-2. This is thought to be because the addition of hydrofluoroether to the electrolyte solution reduced the viscosity of the electrolyte solution and improved the ionic conductivity.

[0116] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present invention.

[0117] The present invention can take the following aspects. <1> A secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte, The secondary battery, wherein the electrolyte solution contains an acetamide derivative represented by formula (1) and lithium bis(fluorosulfonyl)imide. [ka] (In formula (1), R1 and R2 each independently represent an alkyl group or alkoxy group having 1 to 5 carbon atoms, which may have a substituent, or a trimethylsilyl group, and R1 and R2 may be bonded to each other to form a fused ring.) <2> the molar ratio of the acetamide derivative to the lithium bis(fluorosulfonyl)imide is 2 or more and 4 or less; <1> The secondary battery according to claim 1. <3> The electrolyte solution further contains at least one of an unsaturated cyclic carbonate and a halogenated cyclic carbonate. <1> or <2> The secondary battery according to claim 1. <4> The electrolyte solution further contains a hydrofluoroether. <1> from <3> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. [Explanation of symbols]

[0118] 1, 1A secondary battery 10 Casing 11 Battery can 12 Lid 13 Thermal Resistance Element 14 Safety valve mechanism 15 Gasket 16 Positive lead 17 Negative lead 18 Insulating plate 19 Center pin 20 Battery element 21 Positive lead 22 Negative lead 23 Protective materials 31 Exterior materials 32 Adhesive 200, 200A electrode body 210, 210A positive electrode 211, 211A Positive electrode current collector layer 212, 212A Cathode active material layer 220, 220A negative pole 221, 221A negative electrode current collector layer 222, 222A negative electrode active material layer 230, 230A separator

Claims

1. A secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte, The secondary battery, wherein the electrolyte solution contains an acetamide derivative represented by formula (1) and lithium bis(fluorosulfonyl)imide. 【Chemistry 1】 (In formula (1), R1 and R2 each independently represent an alkyl group or alkoxy group having 1 to 5 carbon atoms, which may have a substituent, or a trimethylsilyl group, and R1 and R2 may be bonded to each other to form a fused ring.)

2. 2. The secondary battery according to claim 1, wherein a molar ratio of the acetamide derivative to the lithium bis(fluorosulfonyl)imide is 2 or more and 4 or less.

3. The secondary battery according to claim 1 or 2, wherein the electrolyte solution further contains at least one of an unsaturated cyclic ester carbonate and a halogenated cyclic ester carbonate.

4. The secondary battery according to claim 1 , wherein the electrolyte solution further contains a hydrofluoroether.

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