Ether-based electrolyte, lithium secondary battery and electric equipment

Abstract

The embodiment of the invention discloses an ether-based electrolyte, a lithium secondary battery and electric equipment, the ether-based electrolyte comprises a lithium salt and a solvent, the solvent comprises a chain ether compound shown as a formula (I): # imgabs0 #, R1 and R4 are independently selected from alkyl, halogenated alkyl, phenyl or halogenated phenyl, and R2 and R3 are independently selected from alkyl, halogenated alkyl, phenyl or halogenated phenyl. R2 and R3 are independently selected from hydrogen, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, phenyl, halogenated phenyl, phenoxyl or halogenated phenoxyl, and n is greater than or equal to 1 and less than or equal to 5. According to the embodiment of the invention, a large steric hindrance group is introduced to an oxygen atom site of a chain ether-based compound molecule, so that the solvation effect between a solvent and lithium ions is effectively weakened, the boiling point, the flash point and the oxidation stability of the ether-based electrolyte are improved, the ether-based electrolyte is applied to a lithium secondary battery, and the service life of the lithium secondary battery is prolonged. The electrochemical performance and the safety performance of the battery can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium secondary batteries, and in particular to an ether-based electrolyte, a lithium secondary battery and electrical equipment. Background Art

[0002] Lithium metal is considered to be one of the most ideal choices for lithium battery negative electrode materials, with a high theoretical capacity (3860mAh g -1 ) and a lower negative reduction potential (-3.040V vs standard hydrogen electrode). However, due to the extremely strong chemical activity of the lithium metal anode, it is very easy to react with the organic solvent in the electrolyte, resulting in significant deterioration of the interface, rapid consumption of the electrolyte, and rapid degradation of battery performance.

[0003] In order to improve the stability of the electrolyte to lithium metal, a high concentration electrolyte (HCE) can be used. HCE greatly reduces the content of free solvent molecules by enhancing the interaction between the cations and anions of the salt and the solvent, thereby preventing the co-intercalation of solvent molecules and forming a solid electrolyte interface (SEI) with low impedance and high inorganic salt content to improve lithium deposition. At present, the commonly used solvents for HCE include ethers, carbonates, nitriles, sulfones and phosphates. Among them, ether solvents have good compatibility with metal lithium negative electrodes and are the most commonly used solvents for HCE. However, the existing ether solvents have strong solvation ability, low boiling point and flash point, and poor oxidation stability, which can easily cause problems such as low coulombic efficiency, poor safety and low cycle life. Therefore, it is necessary to provide an electrolyte with high coulombic efficiency, high safety and long cycle life. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides an ether-based electrolyte, a lithium secondary battery and an electrical device. The ether-based electrolyte includes a lithium salt and a chain ether-based compound. The chain ether-based compound has a weak solvation effect with lithium ions, a high boiling point and a flash point, and good oxidation stability. When applied to a lithium secondary battery, it can effectively improve the electrochemical performance and safety performance of the battery.

[0005] In a first aspect, an embodiment of the present invention provides an ether-based electrolyte, wherein the ether-based electrolyte comprises a lithium salt and a solvent, wherein the solvent comprises a chain ether-based compound represented by formula (I),

[0006]

[0007] Wherein, R1 and R4 are independently selected from alkyl, haloalkyl, phenyl or halophenyl, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl, alkoxy, haloalkoxy, phenyl, halophenyl, phenoxy or halophenoxy, and at least one of R1, R2, R3 and R4 is a branched alkyl, a polysubstituted haloalkyl, phenyl or halophenyl, or at least one of R2 and R3 is an alkoxy, a haloalkoxy, phenoxy or halophenoxy; 1≤n≤5.

[0008] In the embodiment of the present invention, at least one of R1, R2, R3 and R4 is selected from C4-C 12 A branched alkyl group, a polyfluoroalkyl group, a phenyl group or a fluorophenyl group.

[0009] In an embodiment of the present invention, the chain ether compound includes at least one of 1,1,1-trifluoro-2,3-dimethoxypropane, 1-ethoxy-2-[2-(trifluoromethoxy)ethoxy]ethane, 1-(trifluoromethoxy)-2-(2-(trifluoromethoxy)ethoxy)ethane, 1,2-di-tert-butoxyethane, diethylene glycol ethyl tert-butyl ether, 2-methoxyethoxybenzene, (1,2-dimethoxyethyl)benzene, 1-tert-butoxy-2-ethoxyethane, (2,2-diethoxyethoxy)benzene and 1-ethoxy-2(2,2,2-trifluoroethoxy)ethane.

[0010] In the embodiment of the present invention, the relative molecular mass of the chain ether compound is 130-260.

[0011] In the embodiment of the present invention, the boiling point of the chain ether-based compound is ≥90°C, and the flash point of the chain ether-based compound is ≥20°C.

[0012] In an embodiment of the present invention, the chain ether compound accounts for 10%-70% of the total volume of the solvent.

[0013] In an embodiment of the present invention, the concentration of the lithium salt in the ether-based electrolyte is 0.5 mol / L-4 mol / L.

[0014] In an embodiment of the present invention, the solvent further comprises a diluent, and the diluent accounts for 30%-90% of the total volume of the solvent.

[0015] In an embodiment of the present invention, the diluent includes a fluoroalkyl ether, and the fluoroalkyl ether includes bis(2,2,2-trifluoroethyl) ether, 1,1,1,2,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, nonafluorobutyl methyl ether, nonafluorobutyl ethyl ether, 1,1,1,2,2,3,3,4,4-nonafluoroisobutyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,3 ,3,3-pentafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, hexafluoroisopropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, tris(2,2,2-trifluoroethyl)orthoformate, 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether and 1,1,2,2-tetrafluoroethyl ethyl ether.

[0016] In an embodiment of the present invention, the lithium salt includes one or more of lithium phosphates, borates, boron cluster compounds, imine salts, aluminates, heterocyclic anion salts, halides, arsenates and sulfonates.

[0017] The ether-based electrolyte provided by the embodiment of the present invention includes a lithium salt and a chain ether-based compound. On the one hand, the solvation effect between the chain ether-based compound and lithium ions is weak, which is beneficial to improving the ion conductivity and charge and discharge efficiency of the electrolyte, and the chain ether-based compound has good compatibility with lithium metal, which can reduce the occurrence of side reactions and improve the compatibility of the electrolyte with the lithium metal negative electrode; on the other hand, the chain ether-based compound has a high boiling point and flash point and good oxidation stability, which is beneficial to improving the safety and cycle life of the electrolyte.

[0018] In a second aspect, an embodiment of the present invention provides a lithium secondary battery, comprising the ether-based electrolyte described in the first aspect.

[0019] In an embodiment of the present invention, the lithium secondary battery includes a lithium metal battery.

[0020] The lithium secondary battery provided by the embodiment of the present invention has an ether-based electrolyte, which has low solvation ability, high boiling point, high flash point, high oxidation stability and high safety, which helps to improve the ion conductivity, charge and discharge efficiency, safety and cycle life of the lithium secondary battery, and is beneficial to the long-term use of the lithium secondary battery.

[0021] In a third aspect, an embodiment of the present invention provides an electrical device, wherein the electrical device comprises the lithium secondary battery described in the second aspect.

[0022] The electric device provided in the embodiment of the present invention has a lithium secondary battery, which has high charge and discharge efficiency, good safety and long cycle life, helps to improve the safety and cycle stability of the electric device, and is conducive to the long-term use of the electric device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention, the accompanying drawings required for use in the embodiments of the present invention will be described below.

[0024] Figure 1 is a schematic structural diagram of a lithium secondary battery 100 in one embodiment of the present invention. DETAILED DESCRIPTION

[0025] The embodiments of the present invention will be described below in conjunction with some specific implementation methods of the present invention.

[0026] Lithium metal batteries (LMBs) are considered to be the most promising and feasible high-energy-density rechargeable battery technology in the future, but their application is limited by the high reactivity of the negative electrode lithium, which will continuously consume electrolyte and lithium salts during the cycle. High-concentration electrolytes (HCEs) have been developed for high-energy-density lithium metal batteries. HCEs effectively reduce the content of free solvent molecules by adding high-concentration lithium salts, which helps to prevent the co-intercalation of solvent molecules and form a solid electrolyte interface (SEI) with low impedance and high inorganic content to improve lithium deposition.

[0027] At present, the commonly used solvents for HCE are ether solvents with good stability to lithium metal. Among them, ether solvents usually use ethylene glycol dimethyl ether (DME). The electrolyte composed of DME has the following problems: 1) DME has a strong solvation effect with lithium ions, resulting in a weakened desolvation ability of lithium ions. The solvent will participate in the lithium negative electrode reduction process and the SEI film formation process, continuously consuming the solvent, causing irreversible loss of active lithium and low coulomb efficiency, and also causing uneven lithium deposition and growth of lithium dendrites, shortening the cycle life of the electrolyte; 2) Under high voltage and high temperature conditions, DME is easily oxidized and decomposed, and the electrolyte is consumed in large quantities, resulting in a decrease in its cycle life and serious gas production; 3) DME has a low flash point (-3°C) and boiling point (85°C), is flammable and explosive, and has poor safety of the electrolyte, and has a greater risk of industrial application. Therefore, it is necessary to provide an electrolyte with high coulomb efficiency, high safety and long cycle life.

[0028] In view of this, an embodiment of the present invention provides an ether-based electrolyte, the ether-based electrolyte comprising a lithium salt and a solvent, wherein the solvent comprises a chain ether-based compound represented by formula (I):

[0029]

[0030] Wherein, R1 and R4 are independently selected from alkyl, haloalkyl, phenyl or halophenyl, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl, alkoxy, haloalkoxy, phenyl, halophenyl, phenoxy or halophenoxy, and at least one of R1, R2, R3 and R4 is a branched alkyl, a polysubstituted haloalkyl, phenyl or halophenyl, or at least one of R2 and R3 is an alkoxy, a haloalkoxy, phenoxy or halophenoxy; 1≤n≤5.

[0031] The ether-based electrolyte provided by the embodiment of the present invention includes a lithium salt and a chain ether-based compound, and the chain ether-based compound has the characteristics of low solvation ability, high boiling point, high flash point and high oxidation stability, which is helpful to improve the coulombic efficiency, safety and cycle life of the ether-based electrolyte. Specifically, compared with conventional ether solvents, a large steric hindered group (such as a branched alkyl group, a benzene ring, etc.) is introduced into the oxygen atom site in the molecule of the chain ether-based compound, which can reduce the electron cloud density at the oxygen atom site, thereby effectively weakening the binding force between the solvent and the lithium ion, and promoting the rapid desolvation process of the lithium ion on the electrode surface. The weakly solvated ether-based electrolyte using the chain ether-based compound as a solvent can effectively increase the number of lithium ion migration, so that the lithium ion has a higher mass transfer flux, which is conducive to the uniform material exchange on the metal lithium negative electrode interface, and can effectively suppress the space charge layer generated by the consumption of the interface anion, thereby reducing the electric field driving force of the non-uniform deposition of metal lithium, reducing the generation of lithium dendrites, and improving the coulombic efficiency. Moreover, the large steric hindrance group in the chain ether-based compound has good compatibility with lithium metal, which can reduce the occurrence of side reactions, thereby improving the compatibility of the electrolyte with the lithium metal negative electrode. The use of the weakly solvated ether-based electrolyte can also allow anions to participate in the first solvation sheath layer, forming a stable SEI film on the electrode surface, effectively reducing the interfacial impedance and improving the uniformity of lithium deposition. Furthermore, the large steric hindrance group in the chain ether-based compound improves its oxidation stability, flash point and boiling point. The high oxidation stability can inhibit its oxidative decomposition and gas production under high voltage and high temperature conditions, and improve the cycle life of the electrolyte. At the same time, the high flash point and high boiling point can prevent the combustion and explosion of the electrolyte, improve the safety of the electrolyte, and facilitate the industrial application of the electrolyte.

[0032] In the embodiment of the present invention, the alkyl group is a saturated hydrocarbon group formed by removing a hydrogen atom from a chain alkane molecule, and can be a straight-chain alkyl group or a branched-chain alkyl group. 18The alkyl group of the present invention is alkyl, that is, the number of carbon atoms of the alkyl group is 1-18, which is conducive to the preparation and use of chain ether compounds. In some embodiments, the number of carbon atoms of the alkyl group can be 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 15 or 18. Specifically, the alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 4-methylbutyl, 2,2-dimethylpropyl, n-hexyl, heptyl, 2-methylhexyl, 3-methylhexyl, 4-methylpentyl, 5-methylpentyl, 2-ethylbutyl, 3-ethylbutyl, heptyl, octyl, nonyl or decyl.

[0033] In the embodiment of the present invention, the haloalkyl group may be a monosubstituted haloalkyl group in which a single hydrogen atom in the alkyl molecule is replaced by a halogen atom, or may be a polysubstituted haloalkyl group in which multiple (two or more) hydrogen atoms in the alkyl molecule are replaced by halogen atoms. The halogen atom may be at least one of fluorine, chlorine, bromine and iodine. In some embodiments, the haloalkyl group may be C1-C 18 The haloalkyl group may be a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a trifluoroethyl group, a tetrafluoroethyl group, a pentafluoroethyl group, a trifluoropropyl group, a tetrafluoropropyl group, a hexafluoroisopropyl group, a nonafluorobutyl group, a chloromethyl group, a dichloromethyl group, a trichloromethyl group, a chloroethyl group, a dichloroethyl group, a trichloroethyl group, a chloropropyl group, a dichloropropyl group, a dichloroisopropyl group, a chlorobutyl group, a bromomethyl group, a tribromomethyl group, a bromoethyl group, a dibromoethyl group, a bromopropyl group, a bromoisopropyl group, a dibromopropyl group or a bromobutyl group.

[0034] In the present invention, the alkoxy group is an alkyl group bonded to an oxygen atom. In some embodiments, the alkoxy group can be C1-C 18 In some embodiments, the alkoxy group may be 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 15 or 18. Specifically, the alkoxy group may be methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentoxy, isopentyloxy or neopentyloxy.

[0035] In the embodiment of the present invention, the haloalkoxy group is a substituted alkoxy group in which one or more hydrogen atoms in the alkoxy molecule are replaced by a halogen atom. The halogen atom may be at least one of fluorine, chlorine, bromine and iodine. In some embodiments, the haloalkoxy group may be C1-C 18The halogenated alkoxy group is a halogenated alkoxy group, that is, the number of carbon atoms of the halogenated alkoxy group is 1-18. In some embodiments, the number of carbon atoms of the halogenated alkoxy group can be 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 15 or 18. Specifically, the halogenated alkoxy group can be a fluoromethoxy group, a trifluoromethoxy group, a trifluoroethoxy group, a heptafluorobutoxy group, an octafluoropentyloxy group, a chloromethoxy group, a trichloromethoxy group, a chloroethoxy group, a trichloroethoxy group, a chlorobutoxy group, a chloropentyloxy group, a bromomethoxy group, a bromoethoxy group, a dibromopropoxy group or an iodoethoxy group.

[0036] In the embodiment of the present invention, halophenyl is a substituted phenyl in which one or more hydrogen atoms in the phenyl molecule are replaced by a halogen atom. Wherein, the halogen atom can be at least one of fluorine, chlorine, bromine and iodine. In some embodiments, halophenyl can be a fluorophenyl, a trifluorophenyl, a pentafluorophenyl, a chlorophenyl, a dichlorophenyl, a trichlorophenyl, a bromophenyl or an iodophenyl.

[0037] In the embodiment of the present invention, the halogenated phenoxy group is a substituted phenoxy group in which one or more hydrogen atoms in the phenoxy group molecule are replaced by a halogen atom. The halogen atom may be at least one of fluorine, chlorine, bromine and iodine. In some embodiments, the halogenated phenoxy group may be a fluorophenoxy group, a chlorophenoxy group, a dichlorophenoxy group, a bromophenoxy group, a tribromophenoxy group or an iodophenoxy group.

[0038] In the embodiment of the present invention, at least one of R1, R2, R3 and R4 is selected from C4-C 12 The branched alkyl, polyfluoroalkyl, phenyl or fluorophenyl groups are not only conducive to the synthesis of chain ether compounds, but also further increase the steric hindrance of the oxygen atom sites in the chain ether compound molecules, making lithium ions easier to desolvate, thereby improving the electrochemical performance of ether-based electrolytes. 12 The branched alkyl group may be isobutyl, sec-butyl, tert-butyl, neopentyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, 2-methylbutyl, 3-methylbutyl, 4-methylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl or 1,3-dimethylbutyl, the polyfluoroalkyl group may be trifluoromethyl, trifluoroethyl, pentafluoroethyl, trifluoropropyl, tetrafluoropropyl, hexafluoroisopropyl or nonafluorobutyl, and the fluorophenyl group may be 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 2,4-difluorophenyl, 3,5-difluorophenyl, 2,5-difluorophenyl, 2,4,5-trifluorophenyl, 2,4,6-trifluorophenyl, 2,3,4,5-tetrafluorophenyl or pentafluorophenyl.

[0039] In the embodiment of the present invention, R1, R2, R3 and R4 may be the same or different groups.

[0040] In the implementation manner of the present invention, n is a positive integer greater than or equal to 1 and less than or equal to 5. Specifically, n can be 1, 2, 3, 4 or 5.

[0041] In an embodiment of the present invention, the chain ether compound includes at least one of the compounds shown in formula (I-1) to (I-8), and the compounds shown in formula (I-1) to (I-8) are 1,1,1-trifluoro-2,3-dimethoxypropane, 1-ethoxy-2-[2-(trifluoromethoxy)ethoxy]ethane, 1-(trifluoromethoxy)-2-(2-(trifluoromethoxy)ethoxy)ethane, 1,2-di-tert-butoxyethane, diethylene glycol ethyl tert-butyl ether, 2-methoxyethoxybenzene, (1,2-dimethoxyethyl)benzene, 1-tert-butoxy-2-ethoxyethane, (2,2-diethoxyethoxy)benzene and 1-ethoxy-2(2,2,2-trifluoroethoxy)ethane.

[0042]

[0043] In the embodiment of the present invention, the relative molecular mass of the chain ether-based compound can be 130-260, which not only ensures that the boiling point and flash point of the chain ether-based compound are in a higher range, but also ensures that its viscosity is in a lower range, so that the prepared ether-based electrolyte has good safety and conductivity. In some embodiments, the relative molecular mass of the chain ether-based compound can be 132, 140, 146, 152, 158, 160, 170, 174, 180, 190, 200, 216, 210, 220, 230, 240, 250, 256 or 260.

[0044] In the embodiment of the present invention, the boiling point of the chain ether-based compound is ≥90°C, and the flash point of the chain ether-based compound is ≥20°C, which further reduces the risk of spontaneous combustion or explosion of the ether-based electrolyte, and is conducive to the industrial application of the ether-based electrolyte. In some embodiments, the boiling point of the chain ether-based compound can be 90°C, 95°C, 100°C, 105°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 180°C, 200°C, 220°C, 250°C, 280°C or 300°C, and the flash point of the chain ether-based compound can be 20°C, 25°C, 30°C, 35°C, 40°C, 50°C, 60°C, 70°C or 80°C. The boiling points of some chain ether-based compounds in the embodiments of the present application are shown in Table 1, and the flash points of some chain ether-based compounds in the embodiments of the present application are shown in Table 2.

[0045] Table 1 Boiling points of different chain ether compounds

[0046] Chain ether compounds Boiling point(℃) 1,1,1-Trifluoro-2,3-dimethoxypropane 92 1-Ethoxy-2-[2-(trifluoromethoxy)ethoxyethane 145.6 1-(Trifluoromethoxy)-2-(2-(trifluoromethoxy)ethoxy)ethane 101.2 1,2-Di-tert-butoxyethane 169.5 Diethylene glycol ethyl tert-butyl ether 195 2-Methoxyethoxybenzene 218 1-tert-Butoxy-2-ethoxyethane 146.8 (2,2-diethoxyethoxy)benzene 290.4 1-Ethoxy-2(2,2,2-trifluoroethoxy)ethane 127.7

[0047] Table 2 Flash points of different chain ether compounds

[0048] Chain ether compounds Flash point(℃) 1,2-Di-tert-butoxyethane 30 Diethylene glycol ethyl tert-butyl ether 77.7 2-Methoxyethoxybenzene 79.1 1-tert-Butoxy-2-ethoxyethane 41 (2,2-diethoxyethoxy)benzene 96.4

[0049] In an embodiment of the present invention, the chain ether-based compound may account for 10%-70% of the total volume of the solvent, which can not only ensure the electrochemical performance and safety of the ether-based electrolyte, but also avoid the waste of the chain ether-based compound, which is beneficial to control costs. In some embodiments, the chain ether-based compound may account for 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70% of the total volume of the solvent.

[0050] In an embodiment of the present invention, the concentration of the lithium salt in the ether-based electrolyte may be 0.5 mol / L-4 mol / L, which can ensure the electrochemical performance and safety of the ether-based electrolyte, avoid waste of lithium salt, and help control costs. In some embodiments, the concentration of the lithium salt in the ether-based electrolyte may be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L.

[0051] In an embodiment of the present invention, the solvent further includes a diluent, which cannot dissolve the lithium salt but is miscible with the above-mentioned chain ether compound to form ((Li +-chain ether-based compound) diluent) state, will not affect the coordination of the original lithium salt-chain ether-based compound in the ether-based electrolyte, but can significantly reduce the content of lithium salt in unit volume, thereby reducing the cost of lithium salt, while retaining or even enhancing the electrochemical performance and safety of the original ether-based electrolyte, which is more conducive to practical application. In some embodiments, the diluent can be a fluoroalkyl ether. Specifically, the fluoroalkyl ether can include bis (2,2,2-trifluoroethyl) ether (CAS No.: 333-36-8), 1,1,1,2,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether (CAS No.: 993-95-3), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (CAS No.: 16627-68-2), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (CAS No.: 406-78-0), nonafluorobutyl methyl ether (CAS No.: 163702-07-6), nonafluorobutyl ethyl ether (CAS No.: 163702-05-4), 1,1,1,2,2,3,3,4,4-nonafluoroisobutyl methyl ether (CAS No.: 163702-08-7), 1,1,2,2-tetrafluoroethyl ethyl ether (CAS No.: 512-51-6), 2,2,3,3,3-pentafluoropropyl methyl ether (CAS No.: 378-1 6-5), 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether (CAS No.: 993-95-3), 1,1,2,2-tetrafluoroethyl ethyl ether (CAS No.: 512-51-6), 1,1,2,2-tetrafluoroethyl methyl ether (CAS No.: 425-88-7), 2,2,3,3-tetrafluoropropyl difluoromethyl ether (CAS No.: 35042-99-0), hexafluoroisopropyl methyl ether (CAS No.: 1317 1-18-1), 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether (CAS No.: 382-34-3), tris(2,2,2-trifluoroethyl)orthoformate (CAS No.: 58244-27-2), 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether (CAS No.: 16627-71-7) and 1,1,2,2-tetrafluoroethyl ether (CAS No.: 512-51-6) One or more.

[0052] In an embodiment of the present invention, the diluent may account for 30%-90% of the total volume of the solvent, which can effectively reduce the amount of lithium salt used, thereby reducing costs, and does not affect the electrochemical properties and safety of the ether-based electrolyte. In some embodiments, the diluent may account for 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90% of the total volume of the solvent.

[0053] In the present invention, the main function of the lithium salt is to provide lithium ions to ensure that the battery has enough lithium ions during the charge and discharge process. These lithium ions are transmitted between the positive and negative electrodes and are embedded and de-embedded in the negative electrode material during the charge and discharge process. In some embodiments, the lithium salt may include one or more of lithium phosphates, borates, boron cluster compounds, imide salts, aluminates, heterocyclic anion salts, halides, arsenates and sulfonates. Specifically, the lithium salt may include lithium trifluoromethylsulfonate (LiTFA), lithium bistrifluoromethylsulfonyl imide (LiTFSI), lithium bisfluorosulfonyl imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenide (LiAsF6), lithium difluorophosphate (LiPOF2), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiODFB), lithium dioxalatoborate (LiBOB), lithium perchlorate (LiClO4), lithium tetrafluoroaluminate (LiAlF4), lithium perfluoropinacol aluminate (LiFPA), Li2B 12 F 12 and one or more of lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA).

[0054] The embodiment of the present invention also provides a lithium secondary battery, including the ether-based electrolyte in any of the above embodiments. In some embodiments, the lithium secondary battery may be composed of a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte includes the ether-based electrolyte in any of the above embodiments. The lithium secondary battery provided by the embodiment of the present invention has an ether-based electrolyte, which has low solvation ability, high boiling point, high flash point, high oxidation stability and high safety, which helps to improve the ion conductivity, charge and discharge efficiency, safety and cycle life of the lithium secondary battery, and is conducive to the long-term use of the lithium secondary battery.

[0055] In a specific embodiment, Figure 1 As shown, the lithium secondary battery 100 includes a negative electrode 10, an ether-based electrolyte 20, a separator 30, a positive electrode 40 and a battery case 50, wherein the ether-based electrolyte 20 and the separator 30 are located between the negative electrode 10 and the positive electrode 40, and the battery case 50 is used to encapsulate the negative electrode 10, the ether-based electrolyte 20, the separator 30 and the positive electrode 40.

[0056] In the embodiment of the present invention, the lithium secondary battery includes a lithium metal battery. A lithium metal battery is a battery that uses lithium metal or lithium alloy as the negative electrode material and uses a non-aqueous electrolyte solution. The ether-based electrolyte provided in the embodiment of the present invention has good compatibility with lithium metal. Applying it to a lithium metal battery can improve the coulombic efficiency and cycle stability of the battery.

[0057] The embodiment of the present invention further provides an electric device, which includes the lithium secondary battery in any of the above embodiments. Specifically, the electric device can be an electric car, an electric motorcycle, an electric bicycle, a mobile power supply, an unmanned aerial vehicle, a mobile phone, a computer, a camera, an electric tool, a smart home or a wearable device.

[0058] The electric device provided in the embodiment of the present invention has a lithium secondary battery, which has high charge and discharge efficiency, good safety and long cycle life, helps to improve the safety and cycle stability of the electric device, and is conducive to the long-term use of the electric device.

[0059] The technical solution of the present invention is further illustrated below through specific embodiments and comparative examples.

[0060] Example 1

[0061] First, 4 mol of lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 1 L of 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1), and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain a mixed solution A. Then, 2 L of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was added to the mixed solution A, and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain an ether-based electrolyte A.

[0062] Example 2

[0063] Ether-based electrolyte B was prepared in the same manner as in Example 1, except that an equal amount of 2-methoxyethoxybenzene represented by formula (I-6) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1).

[0064] Example 3

[0065] Ether-based electrolyte C was prepared in the same manner as in Example 1, except that an equal amount of 1-ethoxy-2-[2-(trifluoromethoxy)ethoxyethane of formula (I-2) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent of formula (I-1).

[0066] Example 4

[0067] Ether-based electrolyte D was prepared in the same manner as in Example 1, except that an equal amount of 1-(trifluoromethoxy)-2-(2-(trifluoromethoxy)ethoxy)ethane shown in formula (I-3) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent shown in formula (I-1).

[0068] Example 5

[0069] Ether-based electrolyte E was prepared in the same manner as in Example 1, except that an equal amount of 1,2-di-tert-butoxyethane of formula (I-4) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent of formula (I-1).

[0070] Example 6

[0071] Ether-based electrolyte F was prepared in the same manner as in Example 1, except that an equal amount of (1,2-dimethoxyethyl)benzene represented by formula (I-7) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1).

[0072] Example 7

[0073] 4 mol of lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 1 L of 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1), and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain an ether-based electrolyte G.

[0074] Example 8

[0075] First, 4 mol of lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 1 L of 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1), and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain a mixed solution H. Then, 9 L of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was added to the mixed solution H, and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain an ether-based electrolyte H.

[0076] Example 9

[0077] First, 4 mol of lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 1 L of 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1), and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain a mixed solution I. Then, 1.5 L of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was added to the mixed solution I, and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain an ether-based electrolyte I.

[0078] Example 10

[0079] First, 4 mol of lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 1 L of 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1), and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain a mixed solution J. Then, 0.5 L of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was added to the mixed solution I, and the mixture was stirred at 500 rpm for 24 hours at room temperature to obtain an ether-based electrolyte J.

[0080] Comparative Example 1

[0081] The ether-based electrolyte K was prepared in the same manner as in Example 1, except that an equal amount of ethylene glycol dimethyl ether (DME) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1).

[0082] Comparative Example 2

[0083] The ether-based electrolyte L was prepared in the same manner as in Example 8, except that an equal amount of ethylene glycol dimethyl ether (DME) was used to replace the 1,1,1-trifluoro-2,3-dimethoxypropane solvent represented by formula (I-1).

[0084] Performance Testing

[0085] (1) Determination of oxidation potential

[0086] Linear sweep voltammetry was used to detect the high voltage resistance of the ether-based electrolyte. The specific method is: in an environment where the water oxygen value is less than 0.01ppm, a stainless steel sheet, a lithium sheet and the ether-based electrolyte of Examples 1-10 and Comparative Examples 1-2 are assembled into a button cell, wherein the stainless steel sheet is a working electrode and the lithium sheet is a reference electrode and a counter electrode; an electrochemical workstation is used to test the electrochemical stability window at 25°C, the test voltage range is 0-6V, and the scanning speed is 1mV / s. The oxidation potential test results of the ether-based electrolyte are shown in Table 1.

[0087] (2) 45℃ high temperature cycle test

[0088] The ether-based electrolytes provided in Examples 1-10 and Comparative Examples 1-2 of the present invention were assembled into lithium metal full batteries according to the following methods and subjected to 45° C. high-temperature cycle tests:

[0089] Positive electrode preparation: N-methyl-2-pyrrolidone (NMP) was used as solvent to prepare the positive electrode active material Li(Ni 0.7 Co 0.1 Mn 0.2)O2, conductive agent carbon black and binder polyvinylidene fluoride (PVDF) are added to the solvent in a weight ratio of 98:1:1 and mixed to obtain a positive electrode slurry. The positive electrode slurry is coated on an aluminum (Al) current collector with a thickness of about 50 μm to form a positive electrode film, which is then dried and rolled to obtain a positive electrode;

[0090] Negative electrode preparation: Lithium metal was coated on a copper (Cu) film as a negative electrode current collector with a thickness of 25 μm, and then the negative electrode was prepared by roller pressing;

[0091] Diaphragm preparation: A polyethylene (PE) diaphragm with a thickness of 12 μm was cut into the required size to obtain a diaphragm;

[0092] Lithium metal battery assembly: The positive electrode, negative electrode and separator prepared as above are assembled into a lithium metal battery by a lamination method, and then the ether-based electrolytes of Examples 1-10 and Comparative Examples 1-2 are respectively injected into the lithium metal batteries in a glove box (water, oxygen ≤ 0.1 ppm), and the lithium metal full batteries of Examples 1-10 and Comparative Examples 1-2 are obtained after packaging.

[0093] The lithium metal full batteries of Examples 1-10 and Comparative Examples 1-2 were tested on a battery testing system. The process is as follows: at 45°C, charge to 4.3V at a constant current of 0.2C, and then discharge to 3.6V at a constant current of 0.5C. This is one cycle, and three cycles are used as an activation cycle. When the battery is cycled to a capacity retention rate of 80%, the coulombic efficiency and gas production of each battery at this time are measured, and the number of cycles of each battery at this time is recorded. The coulombic efficiency, gas production, and the number of cycles to 80% of the capacity obtained by the above test method are shown in Table 3, where the coulombic efficiency is the ratio of the discharge capacity to the charging capacity in the same cycle.

[0094] Table 3 Oxidation potential, coulombic efficiency and gas production of lithium metal full cells with different ether-based electrolyte compositions

[0095]

[0096] From the test results in Table 3, it can be concluded that the oxidation potentials of Examples 1-10 are all higher than those of Comparative Examples 1-2, indicating that the use of the chain ether-based compound with a large steric hindrance group provided in the embodiments of the present invention to prepare an ether-based electrolyte can improve the oxidation stability of the electrolyte, which is beneficial to the application of the ether-based electrolyte in lithium metal batteries of high voltage systems.

[0097] From the test results in Table 3, it can be concluded that the 45°C high-temperature cycle gas production of Examples 1-10 is less than that of Comparative Examples 1-2, indicating that the use of the chain ether-based compound with a large steric hindrance group provided in the embodiments of the present invention to prepare the ether-based electrolyte improves the stability and boiling point of the electrolyte, reduces the high-temperature decomposition of the solvent, and alleviates the problem of high-temperature gas production of the electrolyte.

[0098] From the test results in Table 3, it can be concluded that the coulombic efficiencies of Examples 1-10 are all higher than those of Comparative Examples 1-2, indicating that the use of the chain ether-based compound with a large steric hindrance group provided in the embodiments of the present invention to prepare an ether-based electrolyte can reduce the solvation effect, making lithium ions more easily desolvated, thereby improving the coulombic efficiency of the electrolyte.

[0099] From the test results in Table 3, it can be concluded that the number of cycles for the capacity decay to 80% of Examples 1-10 is higher than that of Comparative Examples 1-2, indicating that the use of the chain ether-based compound with a large steric hindrance group provided in the embodiments of the present invention to prepare an ether-based electrolyte can reduce the capacity decay rate, improve the cycle performance, and thus extend the cycle life of the electrolyte.

[0100] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. An ether-based electrolyte, characterized in that: The ether-based electrolyte comprises a lithium salt and a solvent, wherein the solvent comprises a chain ether-based compound represented by formula (I): Wherein, R1 and R4 are independently selected from alkyl, haloalkyl, phenyl or halophenyl, R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl, alkoxy, haloalkoxy, phenyl, halophenyl, phenoxy or halophenoxy, and at least one of R1, R2, R3 and R4 is a branched alkyl, a polysubstituted haloalkyl, phenyl or halophenyl, or at least one of R2 and R3 is an alkoxy, a haloalkoxy, phenoxy or halophenoxy; 1≤n≤5.

2. The ether-based electrolyte according to claim 1, characterized in that At least one of R1, R2, R3 and R4 is selected from C4-C 12 A branched alkyl group, a polyfluoroalkyl group, a phenyl group or a fluorophenyl group.

3. The ether-based electrolyte according to claim 1 or 2, characterized in that: The chain ether compound includes at least one of 1,1,1-trifluoro-2,3-dimethoxypropane, 1-ethoxy-2-[2-(trifluoromethoxy)ethoxy]ethane, 1-(trifluoromethoxy)-2-(2-(trifluoromethoxy)ethoxy)ethane, 1,2-di-tert-butoxyethane, diethylene glycol ethyl tert-butyl ether, 2-methoxyethoxybenzene, (1,2-dimethoxyethyl)benzene, 1-tert-butoxy-2-ethoxyethane, (2,2-diethoxyethoxy)benzene and 1-ethoxy-2(2,2,2-trifluoroethoxy)ethane.

4. The ether-based electrolyte according to claim 1, characterized in that The relative molecular mass of the chain ether compound is 130-260.

5. The ether-based electrolyte according to claim 1, characterized in that The boiling point of the chain ether compound is ≥90°C; the flash point of the chain ether compound is ≥20°C.

6. The ether-based electrolyte according to claim 1, characterized in that The chain ether compound accounts for 10%-70% of the total volume of the solvent.

7. The ether-based electrolyte according to claim 1, characterized in that The concentration of the lithium salt in the ether-based electrolyte is 0.5 mol / L-4 mol / L.

8. The ether-based electrolyte according to claim 1, characterized in that The solvent further comprises a diluent, and the diluent accounts for 30%-90% of the total volume of the solvent.

9. The ether-based electrolyte according to claim 8, characterized in that The diluent includes a fluoroalkyl ether, and the fluoroalkyl ether includes bis(2,2,2-trifluoroethyl) ether, 1,1,1,2,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, nonafluorobutyl methyl ether, nonafluorobutyl ethyl ether, 1,1,1,2,2,3,3,4,4-nonafluoroisobutyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,3,3,3 -pentafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, hexafluoroisopropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, tris(2,2,2-trifluoroethyl)orthoformate, 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether and 1,1,2,2-tetrafluoroethyl ethyl ether.

10. The ether-based electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium phosphates, borates, boron cluster compounds, imine salts, aluminates, heterocyclic anion salts, halides, arsenates and sulfonates.

11. A lithium secondary battery, characterized in that: The invention comprises the ether-based electrolyte according to any one of claims 1 to 10.

12. The lithium secondary battery according to claim 11, characterized in that: The lithium secondary battery includes a lithium metal battery.

13. An electrical equipment, characterized in that: The electrical equipment comprises the lithium secondary battery according to claim 11 or 12.

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