Electrolyte and electrochemical device and electronic device comprising same

Abstract

The invention provides an electrolyte, and an electrochemical device and an electronic device comprising the same. The electrolyte includes LiFSI and a compound of formula I # imgabs0 # wherein R1 and R3 are selected from the group consisting of substituted or unsubstituted alkyl groups containing heteroatoms, R2 is selected from the group consisting of substituted or unsubstituted alkyl groups containing or not containing heteroatoms, the heteroatoms including O, S, and N. Therefore, by adding the compound as shown in the formula I into the electrolyte, continuous corrosion of lithium salts such as LiFSI to aluminum foil can be prevented, application of LiFSI as a main lithium salt in a high-voltage battery system is realized, and the safety performance of a high-voltage battery is improved. In addition, the electrolyte has excellent thermal stability, and the high temperature resistance of the battery is further improved.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical devices, and specifically provides an electrolyte and an electrochemical device and an electronic device containing the electrolyte. Background Art

[0002] In electrochemical devices, especially lithium batteries, lithium hexafluorophosphate (LiPF6) has become the main lithium salt in current commercial use due to its high ionic conductivity, wide electrochemical window, and good film-forming properties on the positive and negative electrode surfaces. However, since LiPF6 is easily decomposed at high temperatures and is extremely sensitive to moisture, it produces highly toxic PF5 and HF after decomposition, so there are serious safety hazards when using LiPF6 as the main lithium salt. In addition, for high-nickel ternary and lithium-rich manganese-based high-voltage and high-capacity cathode systems, the presence of HF in the electrolyte will cause Mn 2+ Dissolution destroys the structural integrity of the positive electrode material and the stability of the SEI film on the negative electrode surface, thereby accelerating the attenuation of battery capacity and the deterioration of cycle stability. Therefore, LiPF6 is difficult to apply to special battery systems with high energy density.

[0003] Currently, lithium bis(fluorosulfonyl)imide (LiFSI) is widely studied as a substitute for LiPF6. The price of this lithium salt is similar to that of LiPF6, and it has higher ionic conductivity than LiPF6 when dissolved in carbonate solvents. In addition, LiFSI has better thermal stability and water stability than LiPF6. LiFSI can form an interface protection film with lower impedance on the surface of the positive and negative electrodes, which is beneficial to the improvement of battery rate performance. However, LiFSI easily corrodes the positive current collector aluminum foil under high voltage, which limits the application of LiFSI in high-voltage battery systems.

[0004] In addition, carbonate solvents commonly used in commercial lithium-ion batteries have safety risks, especially at high temperatures, ethylene carbonate (EC) will react with the oxygen released by the high-nickel NCM (nickel-cobalt-manganese) ternary cathode to generate a large amount of heat, thereby causing thermal runaway of the battery. Although new solvents, such as ethers and fluorinated ethers, can improve the cycle stability of metal lithium electrodes, most of these solvents are volatile, have low flash points, and have low electrochemical windows, and are not suitable for high-voltage and high-safety power battery systems.

[0005] In summary, there is a need in the art for an electrolyte that is conducive to the application of LiFSI. Summary of the invention

[0006] In order to solve the above problems, the object of the present invention is to provide an electrolyte, which includes LiFSI and a compound of formula I.

[0007]

[0008] Wherein R1 and R3 are selected from heteroatom-containing, substituted or unsubstituted alkyl groups, and R2 is selected from heteroatom-containing or non-heteroatom-containing, substituted or unsubstituted alkyl groups, wherein the heteroatom includes O, S and N.

[0009] According to one embodiment of the present invention, the compound of formula I comprises at least one selected from the following:

[0010]

[0011] Among them, R 12 and R 31 Independently selected from O, S and

[0012] R 11 and R 32 independently selected from substituted or unsubstituted C1 to C4 alkyl groups,

[0013] R 21 is selected from substituted or unsubstituted C1 to C4 alkyl groups, such as C1 to C4 alkyl groups containing or not containing heteroatoms,

[0014] R 22 Selected from O, S and

[0015] R4 is selected from substituted or unsubstituted C1 to C4 alkyl groups.

[0016] According to one embodiment of the present invention, at least one of R1, R2 and R3 is substituted by a fluorine atom.

[0017] According to one embodiment of the present invention, R4 is methyl or ethyl.

[0018] According to one embodiment of the present invention, R 11 , R 21 , R 22 and R 32 At least one of them is substituted by a fluorine atom.

[0019] According to one embodiment of the present invention, the content of LiFSI is in the range of 9 wt % to 25 wt % based on the total weight of the electrolyte.

[0020] According to one embodiment of the present invention, the content of the compound of formula I is in the range of 5 wt % to 60 wt %, based on the total weight of the electrolyte.

[0021] According to one embodiment of the present invention, the content of LiFSI is in the range of 12 wt % to 17 wt % based on the total weight of the electrolyte.

[0022] According to one embodiment of the present invention, the content of the compound of formula I is in the range of 15 wt % to 25 wt % based on the total weight of the electrolyte.

[0023] According to one embodiment of the present invention, the compound of formula I comprises at least one selected from the following:

[0024]

[0025] According to one embodiment of the present invention, the electrolyte further comprises an additive, and the additive comprises at least one of the following: vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, 1,3-propene sultone, vinyl sulfite, tris(trimethylsilane)phosphate, tris(trimethylsilane)borate and methylene methanedisulfonate.

[0026] According to one embodiment of the present invention, the electrolyte further includes an additional solvent, and the additional solvent includes at least one of the following: a linear carbonate, a cyclic carbonate and a carboxylic acid ester; wherein the linear carbonate is selected from at least one or a combination of two or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and a fluorinated linear carbonate; the cyclic carbonate is selected from at least one or a combination of two or more of ethylene carbonate, propylene carbonate, butylene carbonate, and a fluorinated cyclic carbonate; the carboxylic acid ester is selected from at least one or a combination of two or more of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and a fluorinated carboxylic acid ester.

[0027] According to one embodiment of the present invention, the electrolyte further includes an additional lithium salt, and the additional lithium salt includes at least one of the following: lithium hexafluorophosphate, lithium tetrafluoroborate, trifluorosulfonyl lithium, lithium bis(fluorosulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(pentafluoroethylsulfonic acid)imide, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole) and lithium difluorooxalatoborate.

[0028] According to one embodiment of the present invention, in the electrolyte, the weight content of the additional lithium salt is less than the weight content of LiFSI.

[0029] According to one embodiment of the present invention, based on the total weight of the electrolyte, the content of the additive is 0 wt % to 5 wt %, the content of the additional solvent is 5 wt % to 60 wt %, and the content of the additional lithium salt is 0 wt % to 8 wt %.

[0030] According to one embodiment of the present invention, the compound of formula I has a dielectric constant of 20 to 60.

[0031] According to one embodiment of the present invention, the compound of formula I has a DN value of 20 to 60 kcal / mol.

[0032] According to one embodiment of the present invention, the compound of formula I has a DN value of 40 to 60 kcal / mol.

[0033] According to one embodiment of the present invention, the electrolyte does not contain ethylene carbonate.

[0034] The present invention also aims to provide an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the electrochemical device comprises the electrolyte according to the present invention.

[0035] According to one embodiment of the present invention, the positive electrode plate includes a positive electrode current collector, and the positive electrode current collector includes aluminum, for example, the positive electrode current collector is aluminum metal or aluminum alloy.

[0036] Another object of the present invention is to provide an electronic device, wherein the electronic device comprises the electrochemical device according to the present invention.

[0037] The technical solution of this application has the following beneficial effects:

[0038] The present application uses LiFSI as the main lithium salt in the electrolyte, so that the electrolyte can form a LiF-rich inorganic CEI / SEI film on the surface of the electrode (for example, the surface of the high-nickel NCM ternary positive electrode and the high-capacity silicon-carbon negative electrode material), thereby reducing the direct current resistance (DCR) of the battery after formation, and can inhibit the interfacial side reactions between the electrolyte and the electrode, thereby significantly improving the cycle performance and rate capability of the high-voltage battery.

[0039] The present application can prevent the continuous corrosion of aluminum foil by lithium salts such as LiFSI by adding the compound of formula I to the electrolyte, realize the application of LiFSI as the main lithium salt in the high-voltage battery system, and improve the safety performance of the high-voltage battery. In addition, the electrolyte has excellent thermal stability, which further improves the high temperature resistance of the battery. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described in conjunction with the embodiments below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present invention. The embodiments of the present invention should not be interpreted as limiting the present invention. All other embodiments obtained by those skilled in the art based on the technical scheme provided by the present invention and the embodiments given belong to the scope of protection of the present invention.

[0041] Unless otherwise specified, the terms used in the present invention have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in the present invention can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of the present invention).

[0042] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0043] In the context of the present invention, "heteroatom-containing alkyl" and "heteroalkyl" refer to an alkyl group in which at least one carbon atom is replaced with a heteroatom, wherein the heteroatom includes O, S and N.

[0044] 1. Negative electrode

[0045] According to some embodiments of the present invention, a negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0046] In some embodiments, the negative electrode active material may be a commonly used negative electrode active material, including but not limited to: graphite, carbon material, silicon-based material, metal oxide, tin-based material. For example, silicon-based composite materials include but are not limited to silicon-carbon composite materials, silicon-metal oxide composite materials, silicon alloy composite materials. For example, metal oxides include but are not limited to iron oxide, lithium titanate, copper oxide, etc., which are regarded as all metal oxides that can be used for lithium extraction and storage.

[0047] In some embodiments, the conductive agent can be a commonly used conductive agent, including but not limited to: metal-based materials, carbon-based materials, conductive polymers and mixtures thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, nickel, copper, aluminum or silver. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, acetylene black, Ketjen black, carbon black, carbon fiber or any combination thereof. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0048] In some embodiments, the binder can be a commonly used binder, including but not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, ethylene oxide-containing polymers, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyurethane, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

[0049] 2. Positive electrode

[0050] The materials, composition and manufacturing method of the positive electrode that can be used in the embodiments of the present invention include any technology disclosed in the prior art.

[0051] According to some embodiments of the present invention, the positive electrode includes a current collector and a positive electrode active material layer located on the current collector. According to some embodiments of the present invention, the positive electrode active material includes, but is not limited to: lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese (NCM) ternary material, lithium nickel cobalt aluminum (NCA) ternary material, lithium iron phosphate (LiFePO4), lithium iron manganese phosphate (LiMn x Fe 1- x PO4) or lithium manganate (LiMn2O4).

[0052] According to some embodiments of the present invention, the positive electrode current collector includes aluminum.

[0053] According to some embodiments of the present invention, the positive electrode current collector is an aluminum foil.

[0054] According to a preferred embodiment of the present invention, the positive electrode active material is a high-nickel ternary positive electrode material and / or a lithium-rich manganese-based positive electrode material.

[0055] According to one embodiment of the present invention, the positive electrode active material is Li[Ni 1-x-y Co x M y ]O2(M=Mn, Al, etc., such as lithium nickel cobalt manganese oxide Li[Ni 1-x-y Co x Mn y ]O2, 1-xy ≥ 0.5, lithium nickel cobalt aluminum oxide Li[Ni 1-x-y Co x Al y ]O2, 1-xy≥0.5).

[0056] According to some embodiments of the present invention, the positive electrode active material layer further includes a binder and optionally includes a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector. In some embodiments, the binder includes: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

[0057] According to some embodiments of the present invention, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0058] 3. Diaphragm

[0059] The material and shape of the separator used in the embodiments of the present invention are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present invention.

[0060] For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene and polyethylene terephthalate. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0061] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0062] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0063] The polymer layer contains polymers, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0064] In a preferred embodiment according to the present invention, the separator is a polyethylene (PE) separator coated with ceramic layers on both sides, wherein the PE layer thickness is in the range of 5 to 20 μm, and the coating thickness of each ceramic layer is in the range of 0 to 5 μm.

[0065] 4. Electrolyte

[0066] In some embodiments, the electrolyte includes LiFSI and a compound of formula I,

[0067]

[0068] Wherein R1 and R3 are selected from heteroatom-containing, substituted or unsubstituted alkyl groups, and R2 is selected from heteroatom-containing or non-heteroatom-containing, substituted or unsubstituted alkyl groups, wherein the heteroatom includes O, S and N.

[0069] In some embodiments, the compound of Formula I comprises at least one selected from the following:

[0070]

[0071] Among them, R 12 and R 31 Independently selected from O, S and

[0072] R 11 and R 32 independently selected from substituted or unsubstituted C1 to C4 alkyl groups,

[0073] R 21 is selected from substituted or unsubstituted C1 to C4 alkyl groups containing or not containing heteroatoms,

[0074] R 22 Selected from O, S and

[0075] R4 is selected from substituted or unsubstituted C1 to C4 alkyl groups.

[0076] By using LiFSI as the main lithium salt in the electrolyte, the electrolyte can form a LiF-rich inorganic CEI / SEI film on the surface of the electrode (such as high-nickel NCM ternary positive electrode and high-capacity silicon-carbon negative electrode), thereby reducing the direct current resistance (DCR) of the battery after formation, and can inhibit the interfacial side reactions between the electrolyte and the electrode, thereby significantly improving the cycle performance and rate capability of the high-voltage battery.

[0077] By adding the compound of formula I to the electrolyte, the continuous corrosion of aluminum foil by lithium salts such as LiFSI can be prevented, the application of LiFSI as the main lithium salt in the high-voltage battery system can be realized, and the safety performance of the high-voltage battery can be improved. In addition, the electrolyte according to the present invention has excellent thermal stability, which further improves the high temperature resistance of the battery.

[0078] In some embodiments, the content of LiFSI is in the range of 9 wt % to 25 wt %, preferably in the range of 12 wt % to 17 wt %, based on the total weight of the electrolyte.

[0079] In some embodiments, the content of the compound of formula I is in the range of 5 wt % to 60 wt %, preferably in the range of 15 wt % to 25 wt %, based on the total weight of the electrolyte.

[0080] In some embodiments, the compound of Formula I comprises at least one selected from the following:

[0081]

[0082] In some embodiments, the electrolyte further includes an additive, wherein the additive includes at least one of the following: vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), diethylene sulfate (DTD), 1,3-propene sultone (1,3-PST), vinyl sulfite (ES), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB) and methylene methane disulfonate (MMDS).

[0083] When ethylene carbonate (EC) is included in the electrolyte, since EC has a dielectric constant of up to 90 and a DN value of about 15, it may lead to the dissolution of Al(FSI)3 formed by LiFSI on the surface of the aluminum foil. Therefore, in some embodiments of the present invention, the electrolyte does not contain ethylene carbonate (EC).

[0084] In some embodiments, the electrolyte further includes an additional solvent, and the additional solvent includes at least one of the following: a linear carbonate, a cyclic carbonate and a carboxylic acid ester; wherein the linear carbonate is selected from at least one or a combination of two or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and a fluorinated linear carbonate; the cyclic carbonate is selected from at least one or a combination of two or more of ethylene carbonate, propylene carbonate, butylene carbonate, and a fluorinated cyclic carbonate; the carboxylic acid ester is selected from at least one or a combination of two or more of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and a fluorinated carboxylic acid ester.

[0085] In a preferred embodiment, the additional solvent is selected from one or more of propylene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0086] Based on the total weight of the electrolyte, the content of the additive is 0 wt % to 5 wt %, and the content of the additional solvent is 5 wt % to 60 wt %.

[0087] In some embodiments, the electrolyte further includes an additional lithium salt, including but not limited to lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), trifluorosulfonyl lithium (LiOTf), lithium bis(fluorosulfonyl)imide (LiFSI), (trifluoromethylsulfonyl) (perfluorobutylsulfonyl) imide lithium (LiFNFSI), bis(pentafluoroethylsulfonic acid) imide lithium (LiBETI), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate) borate (LiBFMB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazole) (LiTDI), and lithium difluorooxalatoborate (LiDFOB).

[0088] In some embodiments, in the electrolyte, the weight content of the additional lithium salt is less than the weight content of LiFSI.

[0089] In some embodiments, the content of the additional lithium salt is in the range of 0 wt % to 8 wt % based on the total weight of the electrolyte.

[0090] In some embodiments, the compound of formula I in the electrolyte has a dielectric constant of 20 to 60, and in some embodiments, the compound of formula I has a DN value of 20 kcal / mol to 60 kcal / mol, preferably 40 kcal / mol to 60 kcal / mol.

[0091] In some embodiments, the compound of formula I has a DN value of 40 kcal / mol or more, preferably 45 kcal / mol or more. This can further prevent the continuous corrosion of aluminum foil by lithium salts such as LiFSI, while ensuring the dissolution and dissociation of the lithium salt, thereby realizing the application of LiFSI as the main lithium salt in a high-voltage battery system.

[0092] In some embodiments, the electrolyte includes a solvent, and the solvent includes at least one of a linear carbonate, a cyclic carbonate, and a carboxylic acid ester. The linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and a fluorinated linear carbonate; the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, and a fluorinated cyclic carbonate; the carboxylic acid ester includes at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and a fluorinated carboxylic acid ester.

[0093] 5. Electrochemical Device

[0094] The electrochemical device according to the present invention can be a secondary battery, such as a lithium secondary battery or a sodium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a sodium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device of the present invention includes a positive electrode, a negative electrode, a separator and an electrolyte. In some embodiments, the electrochemical device of the present invention includes a high nickel ternary positive electrode material and / or a lithium-rich manganese-based positive electrode material.

[0095] The electrochemical device according to the present invention can be used in electronic devices, including but not limited to laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0096] 6. Testing

[0097] Solvent DN value test

[0098] Under adiabatic conditions, the solvent substance is reacted with a standard Lewis acid in a calorimeter. The thermal effect value of the reaction is calculated through the temperature change of the reaction system before and after the reaction and the mass and specific heat of the relevant substances to obtain the DN value of the solvent substance.

[0099] Solvent dielectric constant ε test

[0100] The dielectric constant is obtained with the aid of a capacitance meter. The dielectric constant is a dimensionless value, and its calculation formula is ε=C / C0, where C0 is the capacitance value of the capacitor when air is the medium, and C is the capacitance value of the solvent.

[0101] Positive leakage current test

[0102] Charge the battery to 4.3V, remove the battery, and use an electrochemical workstation to test the current-time curve of the battery at a constant voltage of 4.3V. After 12 hours, read the output current value, which is the leakage current of the battery positive electrode.

[0103] Example 1

[0104] Positive electrode: LiNi 0.9 Co 0.05 Mn 0.05 O2, carbon nanotubes, acetylene black, polyvinylidene fluoride PVDF, LiNi by weight 0.9 Co 0.05 Mn 0.05 O2:CNT:Super-P:PVDF=95:2.0:1.0:2 was fully slurried in N-methylpyrrolidone NMP solvent system, coated on a 12 μm thick aluminum current collector, and dried and roll-pressed to obtain a positive electrode sheet.

[0105] Negative electrode sheet: artificial graphite, conductive agent acetylene black, styrene-butadiene rubber SBR, sodium carboxymethyl cellulose CMCNa, and polyacrylic acid PAA are fully homogenized in a deionized water solvent in a weight ratio of 96:2:1.5:1:0.5, coated on the surface of a 8 μm thick copper current collector, dried and rolled to obtain a negative electrode sheet.

[0106] Electrolyte: In a glove box filled with argon (H2O <0.1ppm, O2 <0.1ppm), ethyl methyl carbonate and the compound of formula I-1 are mixed in a mass ratio of EMC:I-1=56:25, and then 17 wt% of lithium bis(fluorosulfonylimide) salt LiFSI based on the total weight of the electrolyte, as well as additives of 0.5% VC and 1.5% DTD are slowly added to the mixed solution, and the electrolyte is obtained after stirring evenly.

[0107] Diaphragm: Use commercially available PP / PE / PP three-layer composite diaphragm.

[0108] Lithium-ion battery: stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, and wind them to obtain a bare cell; place the bare cell in an aluminum-plastic film outer package, and inject the above-mentioned electrolyte into the bare cell that has been fully dried to form a lithium-ion battery.

[0109] Example 2 to Example 15

[0110] Examples 2 to 15 were carried out using substantially the same method as Example 1, except that the electrolyte was prepared according to the electrolyte components shown in Table 1.

[0111] Comparative Example 1 to Comparative Example 10

[0112] Comparative Examples 1 to 10 were carried out using substantially the same method as Example 1, except that the electrolyte was prepared according to the electrolyte components shown in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] The batteries obtained from Examples 1 to 16 and Comparative Examples 1 to 10 were subjected to a positive electrode leakage current test, a direct current resistance (DCR) test, a capacity retention rate test after 500 1C / 1C cycles at 25°C, a capacity retention rate test after 300 1C / 1C cycles at 45°C, and an aluminum foil corrosion test. The test results are shown in Table 2, wherein the capacity retention rate after 300 cycles = the 300th discharge capacity / the first discharge capacity, and the capacity retention rate after 500 cycles = the 500th discharge capacity / the first discharge capacity. The aluminum foil corrosion test was carried out by using the electrolytes of Examples 1 to 16 and Comparative Examples 1 to 10 in a Li / Al half-cell battery, and the test results were observed using SEM after the test.

[0117] Table 2

[0118]

[0119]

[0120] As can be seen from Table 2, the electrolyte according to the present invention can not only improve the high temperature safety performance of the battery, but also significantly improve the cycle performance of the high voltage battery. In addition, the LiFSI lithium salt in the electrolyte according to the present invention will not continue to corrode the positive electrode current collector aluminum foil even at high voltage, which not only prolongs the life of the battery, but also improves the rate performance of the battery.

[0121] Although some exemplary embodiments of the present invention have been illustrated and described, the present invention is not limited to the disclosed embodiments. On the contrary, those of ordinary skill in the art will recognize that some combinations, modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present invention as described in the appended claims, and these combinations, modifications and changes also fall within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises LiFSI and a compound of formula I, Wherein R1 and R3 are selected from heteroatom-containing, substituted or unsubstituted alkyl groups, and R2 is selected from heteroatom-containing or non-heteroatom-containing, substituted or unsubstituted alkyl groups, wherein the heteroatom includes O, S and N.

2. The electrolyte according to claim 1, characterized in that The compound of formula I comprises at least one selected from the following: Among them, R 12 and R 31 Independently selected from O, S and R 11 and R 32 independently selected from substituted or unsubstituted C1 to C4 alkyl groups, R 21 is selected from substituted or unsubstituted C1 to C4 alkyl groups, R 22 Selected from O, S and R4 is selected from substituted or unsubstituted C1 to C4 alkyl groups.

3. The electrolyte according to claim 1, characterized in that The content of LiFSI is in the range of 9 wt % to 25 wt % based on the total weight of the electrolyte; and / or The content of the compound of formula I is in the range of 5 wt % to 60 wt % based on the total weight of the electrolyte.

4. The electrolyte according to claim 1, characterized in that The content of LiFSI is in the range of 12 wt % to 17 wt % based on the total weight of the electrolyte; and / or The content of the compound of formula I is in the range of 15 wt % to 25 wt % based on the total weight of the electrolyte.

5. The electrolyte according to claim 1, characterized in that The compound of formula I comprises at least one selected from the following:

6. The electrolyte according to claim 1, characterized in that The electrolyte further comprises at least one of an additive, an additional solvent and an additional lithium salt, wherein: The additive comprises at least one of the following: vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, vinyl sulfate, 1,3-propene sultone, vinyl sulfite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate and methylene methanedisulfonate; based on the total weight of the electrolyte, the content of the additive is 0 wt % to 5 wt %; The additional solvent includes at least one of the following: a linear carbonate, a cyclic carbonate and a carboxylic acid ester; wherein the linear carbonate is selected from at least one or a combination of two or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and a fluorinated linear carbonate; the cyclic carbonate is selected from at least one or a combination of two or more of ethylene carbonate, propylene carbonate, butylene carbonate, and a fluorinated cyclic carbonate; the carboxylic acid ester is selected from at least one or a combination of two or more of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and a fluorinated carboxylic acid ester; based on the total weight of the electrolyte, the content of the additional solvent is 5 wt% to 60 wt%; The additional lithium salt includes at least one of the following: lithium hexafluorophosphate, lithium tetrafluoroborate, trifluorosulfonyl lithium, lithium bis(fluorosulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(pentafluoroethylsulfonate)imide, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole) and lithium difluorooxalatoborate; wherein, in the electrolyte, the weight content of the additional lithium salt is less than the weight content of LiFSI; based on the total weight of the electrolyte, the content of the additional lithium salt is 0 wt % to 8 wt %.

7. The electrolyte according to claim 1, characterized in that The compound of formula I has a dielectric constant of 20 to 60; and / or The compound of formula I has a DN value of 20 kcal / mol to 60 kcal / mol.

8. The electrolyte according to claim 1, characterized in that The electrolyte does not contain ethylene carbonate.

9. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet and a separator, characterized in that: The electrochemical device further comprises an electrolyte according to any one of claims 1 to 8, wherein the positive electrode sheet comprises a positive electrode current collector, and the positive electrode current collector comprises aluminum.

10. An electronic device, characterized in that: The electronic device comprises the electrochemical device according to claim 9.

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