Electrolyte, lithium ion battery and electronic equipment

Abstract

The invention discloses an electrolyte, a lithium ion battery and electronic equipment. The electrolyte is prepared from fluoroether, cyclic fluorocarbonate and linear fluorocarbonate; wherein the fluoroether is one or more of compounds as shown in a formula I and a formula II; in the formula I, R1 and R2 are respectively and independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R2 is not less than 3. When the electrolyte provided by the invention is applied to the lithium ion battery, the high-temperature cycling stability and the fast charging performance of the battery can be synchronously improved.

Description

Technical Field

[0001] The present invention provides an electrolyte, a lithium ion battery and an electronic device. Background Art

[0002] In recent years, the new energy vehicle market has rapidly developed, driving explosive growth in the market for power batteries, primarily secondary alkali metal ion batteries. However, the energy density of commercial secondary alkali metal ion batteries is currently approaching its theoretical upper limit. To fundamentally address the range anxiety and fast charging demands of electric vehicle buyers, it is necessary to increase the energy density of current batteries. Increasing the battery voltage is a straightforward and feasible approach. However, as the battery voltage increases, higher requirements are placed on the electrolyte's high-voltage resistance and fast-charging performance.

[0003] Fluorinated solvents, such as 2,2,2-trifluoroethyl methyl carbonate (FEMC), are commonly used in the prior art to address these issues. Due to the high electron-withdrawing capacity of fluorine atoms, they significantly enhance the oxidative stability of conventional carbonates, enabling their widespread use as primary solvents in high-voltage batteries. They significantly improve the high-voltage resistance of lithium battery electrolytes, making them a crucial solvent component in high-voltage battery systems. However, fluorine substitution reduces the solvent's reduction stability, which can easily lead to severe side reactions in the electrolyte, particularly with oxidation intermediates, on the negative electrode side. This ultimately manifests as a series of problems, including high-temperature capacity loss and increased DCR, severely deteriorating the battery's high-temperature performance. Furthermore, fluorinated solvents have low polarity, poor dissociation ability with lithium salts, and high viscosity. This results in reduced electrolyte conductivity, increased viscosity, increased impedance, degraded battery kinetics, and poor fast-charging performance.

[0004] In view of this, the development of electrolyte solutions suitable for high-voltage lithium-ion battery systems, taking into account the stability and dynamics of the battery at high temperatures, is of great significance for the development of fast charging performance of future high-energy-density lithium battery systems. Summary of the Invention

[0005] The present invention primarily aims to overcome the drawbacks of prior art batteries, which struggle to balance high-temperature stability and dynamics, by providing an electrolyte, a lithium-ion battery, and an electronic device. The electrolyte provided by the present invention, when applied to a lithium-ion battery, can simultaneously improve the battery's high-temperature cycling stability and fast-charging performance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A first aspect of the present invention provides an electrolyte comprising a fluoroether, a cyclic fluorocarbonate, and a linear fluorocarbonate; wherein the fluoroether is one or more compounds represented by Formula I and Formula II;

[0008] , ,

[0009] In Formula I, R1 and R2 are each independently a methyl group or a fluoromethyl group, and the total number of fluorine atoms in R1 and R2 is not less than 3.

[0010] A second aspect of the present invention provides a lithium-ion battery, comprising the electrolyte described above.

[0011] A third aspect of the present invention provides an electronic device comprising the lithium-ion battery described above.

[0012] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0013] The reagents and raw materials used in the present invention are commercially available.

[0014] The positive progress effect of the present invention is:

[0015] By adding specific fluoroethers to the electrolyte in combination with cyclic fluorocarbonates and linear fluorocarbonates, the present invention can ensure the oxidative stability of the electrolyte during the use of the lithium-ion battery, reduce the interference of side reaction products between the positive and negative electrodes, and simultaneously improve the high-temperature stability and fast-charging performance of the battery. DETAILED DESCRIPTION

[0016] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0017] In the electrolyte described in the first aspect of the present invention, the electrolyte comprises a fluoroether, a cyclic fluorocarbonate and a linear fluorocarbonate; wherein the fluoroether is one or more compounds represented by Formula I and Formula II;

[0018] , ,

[0019] In Formula I, R1 and R2 are each independently a methyl group or a fluoromethyl group, and the total number of fluorine atoms in R1 and R2 is not less than 3.

[0020] In the present invention, the compounds represented by Formula I and Formula II are both fluorine-substituted ether solvents. Due to the significant improvement in their oxidative stability after fluorine substitution, they can ensure the interfacial stability of the lithium-ion battery positive electrode and reduce the generation of oxidation products. They can also maintain good negative electrode stability and slow the growth rate of battery system impedance. Furthermore, their low viscosity can improve the conductivity of the electrolyte.

[0021] In some preferred embodiments, the compound represented by formula I may be one or more selected from compounds 1-5;

[0022] 、 、 、 and

[0023] .

[0024] In some embodiments, the mass ratio of the fluoroether, the cyclic fluorocarbonate, and the linear fluorocarbonate may be (3-6.5):(2-3):(1.5-5), for example, 4:2:4, 3:2:5, 5.3:2:2.7, 3:3:4, or 6.2:2:1.8.

[0025] In some embodiments, the content of the fluoroether may be 25 wt.%-45 wt.%, where wt.% is the mass percentage of the fluoroether in the electrolyte.

[0026] In some embodiments, the content of the fluoroether may be 25 wt.%, 25.95 wt.%, 34.6 wt.%, 35 wt.%, 45 wt.%, 45.845 wt.%, or 53.63 wt.%, where wt.% is the mass percentage of the fluoroether in the electrolyte.

[0027] In some embodiments, the cyclic fluorocarbonate may be fluoroethylene carbonate.

[0028] In some embodiments, the content of the cyclic fluorinated carbonate may be 5 wt.%-20 wt.%, for example, 15 wt.% or 25 wt.%, where wt.% is the mass percentage of the cyclic fluorinated carbonate in the electrolyte.

[0029] In some embodiments, the content of the cyclic fluorinated carbonate may be 17.3 wt.% or 25.95 wt.%, where wt.% is the mass percentage of the cyclic fluorinated carbonate in the electrolyte.

[0030] In some embodiments, the linear fluorocarbonate may be 2,2,2-trifluoroethyl methyl carbonate.

[0031] In some embodiments, the content of the linear fluorocarbonate may be 25 wt.%-40 wt.%, for example, 15 wt.% or 35 wt.%, where wt.% is the mass percentage of the linear fluorocarbonate in the electrolyte.

[0032] In some embodiments, the content of the linear fluorinated carbonate may be 15.57 wt.%, 23.355 wt.%, 34.6 wt.%, or 43.25 wt.%, where wt.% is the mass percentage of the linear fluorinated carbonate in the electrolyte.

[0033] In some specific embodiments, the fluoroether is Compound 1, the cyclic fluorocarbonate is fluoroethylene carbonate, and the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate.

[0034] In some specific embodiments, the fluoroether is compound 1, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 34.6 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 34.6 wt.%.

[0035] In some specific embodiments, the fluoroether is compound 1, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 25.95 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 43.25 wt.%.

[0036] In some specific embodiments, the fluoroether is compound 1, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 45.845 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 23.355 wt.%.

[0037] In some specific embodiments, the fluoroether is compound 1, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 25.95 wt.%, the content of fluoroethylene carbonate is 25.95 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 34.6 wt.%.

[0038] In some specific embodiments, the fluoroether is compound 1, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 53.63 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 15.57 wt.%.

[0039] In some specific embodiments, the fluoroether is compound 2, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 34.6 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 34.6 wt.%.

[0040] In some specific embodiments, the fluoroether is compound 3, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 34.6 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 34.6 wt.%.

[0041] In some specific embodiments, the fluoroether is a compound represented by formula II, the cyclic fluorocarbonate is fluoroethylene carbonate, the linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate, the content of compound 1 is 34.6 wt.%, the content of fluoroethylene carbonate is 17.3 wt.%, and the content of 2,2,2-trifluoroethyl methyl carbonate is 34.6 wt.%.

[0042] In some preferred embodiments, the electrolyte further comprises tripropynyl phosphate (TPP) and / or 1,3-propane sultone.

[0043] The content of the tripropynyl phosphate is preferably 0.01 wt.%-1 wt.%, for example, 0.1 wt.%, 0.5 wt.% or 1 wt.%, where wt.% is the mass percentage of the tripropynyl phosphate in the electrolyte.

[0044] The content of the 1,3-propane sultone is preferably 0.01 wt.%-3 wt.%, for example, 0.1 wt.%, 1.5 wt.% or 3 wt.%, where wt.% is the mass percentage of the 1,3-propane sultone in the electrolyte.

[0045] The electrolyte preferably comprises tripropynyl phosphate and 1,3-propane sultone, and the mass ratio of the 1,3-propane sultone to the tripropynyl phosphate is (2-4):1.

[0046] In some embodiments, the electrolyte includes tripropynyl phosphate and 1,3-propane sultone, and the mass ratio of the 1,3-propane sultone to the tripropynyl phosphate is 0.2:1, 3:1, or 6:1.

[0047] In some specific embodiments, the electrolyte includes 34.6 wt.% Compound 1, 17.3 wt.% fluoroethylene carbonate, 34.6 wt.% 2,2,2-trifluoroethyl methyl carbonate, and 0.5 wt.% tripropynyl phosphate.

[0048] In some specific embodiments, the electrolyte includes 34.6 wt.% Compound 1, 17.3 wt.% fluoroethylene carbonate, 34.6 wt.% 2,2,2-trifluoroethyl methyl carbonate, and 0.1 wt.% tripropynyl phosphate.

[0049] In some specific embodiments, the electrolyte includes 34.6 wt.% Compound 1, 17.3 wt.% fluoroethylene carbonate, 34.6 wt.% 2,2,2-trifluoroethyl methyl carbonate, and 1 wt.% tripropynyl phosphate.

[0050] In some specific embodiments, the electrolyte includes 34.6 wt.% Compound 1, 17.3 wt.% fluoroethylene carbonate, 34.6 wt.% 2,2,2-trifluoroethyl methyl carbonate, 0.5 wt.% tripropynyl phosphate, and 0.1 wt.% 1,3-propane sultone.

[0051] In some specific embodiments, the electrolyte includes 34.6 wt.% Compound 1, 17.3 wt.% fluoroethylene carbonate, 34.6 wt.% 2,2,2-trifluoroethyl methyl carbonate, 0.5 wt.% tripropynyl phosphate, and 1.5 wt.% 1,3-propane sultone.

[0052] In some specific embodiments, the electrolyte includes 34.6 wt.% Compound 1, 17.3 wt.% fluoroethylene carbonate, 34.6 wt.% 2,2,2-trifluoroethyl methyl carbonate, 0.5 wt.% tripropynyl phosphate, and 3 wt.% 1,3-propane sultone.

[0053] The tripropynyl phosphate used in the present invention is an additive that helps to generate a fluorine / phosphorus-rich cross-linked compound at the electrode interface, which can effectively inhibit the side reactions of the electrode / electrolyte and significantly improve the high-temperature stability of the electrolyte, thereby improving the high-temperature cycle performance and the temperature rise caused by fast charging. This may be because TPP easily undergoes an ester exchange reaction with cyclic fluorocarbonates or linear fluorocarbonates, cross-linking to form a fluorine / phosphorus-containing organic compound, which can not only form a stable and uniform film at the interface, but also effectively repair the damage to the membrane during the cycle. Therefore, under the combined action of fluorocarbonates and TPP, the high-temperature cycle and fast charging performance of the battery are comprehensively improved.

[0054] In some embodiments, the electrolyte further comprises a lithium salt comprising lithium hexafluorophosphate.

[0055] The lithium salt preferably further includes one or more of lithium bis(fluoromethyl)sulfonyl imide (LiFSI), lithium bis(trifluoromethyl)sulfonyl imide, lithium acetate, lithium methanesulfonate and lithium trifluoromethylsulfonate.

[0056] The content of lithium salt in the electrolyte is preferably 10 wt.%-20 wt.%, for example, 13 wt.%, where wt.% is the mass percentage of the lithium salt in the electrolyte.

[0057] The content of the lithium hexafluorophosphate is preferably 8 wt.%-20 wt.%, for example, 13 wt.%, where wt.% is the mass percentage of the lithium hexafluorophosphate in the electrolyte.

[0058] In some embodiments, the electrolyte further includes a lithium salt, wherein the lithium salt is lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide, and the content of the lithium hexafluorophosphate is 13 wt.%, and the content of the lithium bis(fluorosulfonyl)imide is 1 wt.%.

[0059] In the lithium ion battery according to the second aspect of the present invention, the lithium ion battery includes the electrolyte described above.

[0060] In the present invention, the lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte as described above.

[0061] positive electrode

[0062] In the present invention, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector; and the positive electrode active material layer includes a positive electrode active material.

[0063] In some embodiments, the positive electrode active material is lithium cobalt oxide or carbon-coated lithium nickel manganese oxide or.

[0064] Wherein, the chemical formula of the lithium nickel manganese oxide is preferably Li a Ni x Mn y O 4-z M z , wherein 0.90≤a≤1.10, 0.4≤x≤0.6, 1.4≤y≤1.6, 0≤z≤0.1, and the element M is one or more of Cl, Br, I, S, Se, Te or F, such as Li 1.01 Ni 0.5 Mn 1.5 O 3.9 F 0.1 .

[0065] Wherein, in the carbon-coated lithium nickel manganese oxide, preferably, the mass of the carbon coating layer is 1.0 wt%-3.0 wt% of the mass of the lithium nickel manganese oxide, for example, 1.5 wt%.

[0066] Wherein, the carbon-coated lithium nickel manganese oxide is preferably prepared by the following preparation method:

[0067] The carbon source is pre-sintered to obtain component B; the component B is mixed with the lithium nickel manganese oxide and subjected to secondary sintering to obtain the carbon-coated lithium nickel manganese oxide.

[0068] The carbon source is preferably one or more of fructose, polyethylene glycol, galactose, polyvinyl pyrrolidone and tannic acid, such as tannic acid.

[0069] The pre-sintering temperature is preferably 500°C-650°C, for example 520°C.

[0070] The pre-sintering time is preferably 3 h to 6 h, for example 4 h.

[0071] The secondary sintering temperature is preferably 400°C-500°C, for example 420°C.

[0072] The secondary sintering time is preferably 14 hours to 18 hours, for example 16 hours.

[0073] In some embodiments, the positive electrode active material layer further includes a conductive agent. The conductive agent is an agent used to ensure that the electrode has good charge and discharge performance. The conductive agent can be selected from graphite materials such as natural graphite and artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and other carbon black materials, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder and other metal powders, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives, for example, conductive carbon black.

[0074] In some embodiments, the positive electrode active material layer further includes a binder. The binder may be a component that facilitates bonding between the positive electrode material and the conductive agent, and facilitates bonding between the positive electrode material and the positive electrode current collector. Typically, the binder may be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0075] In some embodiments, the positive electrode active material layer includes a positive electrode active material, polyvinylidene fluoride, and conductive carbon black.

[0076] In some specific embodiments, the mass ratio of the positive electrode active material, polyvinylidene fluoride and conductive carbon black is 98:1:1.

[0077] In the present invention, the positive electrode current collector may be a conventional positive electrode current collector in the art. For the positive electrode current collector, any material that does not cause chemical changes and has high conductivity may be used without restriction. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel materials that have been surface-treated with carbon, nickel, titanium, silver, or the like may be commonly used. To enhance adhesion, micro-embossing may be formed on the surface of the positive electrode current collector. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, or porous body.

[0078] In some optional embodiments, the positive electrode current collector is aluminum foil.

[0079] In some optional embodiments, the thickness of the positive electrode current collector may be 8-16 μm, for example, 10 μm.

[0080] In the present invention, the positive electrode sheet can be prepared by conventional methods in the art.

[0081] In some optional embodiments, the method for preparing the positive electrode sheet includes the following steps:

[0082] The positive electrode active material, binder and conductive agent are mixed in a certain mass ratio, and a solvent is added to mix evenly to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on at least one surface of the positive electrode current collector; and the positive electrode sheet is prepared after drying, rolling, slitting and other processes.

[0083] negative electrode

[0084] In the present invention, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer. The negative electrode material layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode material.

[0085] In the present invention, the negative electrode material in the negative electrode material layer may be a negative electrode material conventionally used in the art, such as a graphite-based negative electrode material, a silicon-oxygen-based negative electrode material, or a silicon-carbon-based negative electrode material.

[0086] In some embodiments, the negative electrode material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon monoxide, and silicon-carbon materials.

[0087] In some embodiments, the negative electrode material layer further includes a conductive agent.

[0088] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. Examples include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated SP), carbon nanotubes (CNTs), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0089] In some specific embodiments, the conductive agent in the negative electrode material layer is acetylene black.

[0090] In some embodiments, the negative electrode material layer further includes a binder.

[0091] The type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers, for example, SBR.

[0092] In some embodiments, the negative electrode material layer further includes a thickener.

[0093] The addition of the thickener can increase the system viscosity of the components in the negative electrode slurry, and the thickener can be a thickener conventionally used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0094] In the present invention, the negative electrode current collector may be a conventional negative electrode current collector in the art. The negative electrode current collector serves as a substrate supporting the negative electrode material layer, and is generally a metal foil having a thickness of 3-500 μm. There is no particular restriction on the material, as long as it has high electrical conductivity and does not produce chemical reactions in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector generally has a smooth surface, but fine lines may also be formed on its surface to increase the adhesion between the negative electrode material layer and the current collector. In addition to foil, the negative electrode current collector may also be in the form of a film, mesh, porous, foam or non-woven fabric, or any one or more combinations thereof. Generally, the negative electrode current collector is copper foil.

[0095] In some embodiments, the mass ratio of the negative electrode material, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber is 96:1:1:2.

[0096] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: thoroughly stirring and mixing the components of the negative electrode material layer in a solvent to obtain a negative electrode slurry, coating it on at least one surface of the negative electrode current collector, drying, cold pressing, and cutting.

[0097] diaphragm

[0098] In some optional embodiments, the separator may be a polypropylene film or a polyethylene film.

[0099] In the present invention, the preparation method of the lithium-ion battery can be a conventional preparation method in the field, which can be a process of winding a positive electrode sheet, a separator, and a negative electrode sheet in this order to obtain a battery cell, then packaging the battery cell in a packaging shell and injecting the electrolyte; or a process of stacking a positive electrode sheet, a separator, and a positive electrode sheet in this order to obtain a battery cell, then packaging the battery cell in a packaging shell and injecting the electrolyte; and then undergoing processes such as standing, hot and cold pressing, formation, clamping, and capacity separation to obtain a lithium-ion battery.

[0100] In the electronic device described in the third aspect of the present invention, the electronic device includes the lithium-ion battery.

[0101] Illustratively, the electronic devices described in the present invention may be, but are not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0102] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0103] Example 1

[0104] (1) Preparation of electrolyte

[0105] In a glove box with an argon content of 99.999%, an actual oxygen content of 0.1 ppm, and a moisture content of <10 ppm, compound 1, fluoroethylene carbonate (FEC), and 2,2,2-trifluoroethylmethyl carbonate (FEMC) were uniformly mixed according to the mass ratio (per 10) shown in the table, and then tripropynyl phosphate (TPP) and thoroughly dried lithium hexafluorophosphate were added to prepare an electrolyte. wherein, based on the total mass of the electrolyte as 100 wt.%, the total content of the fluoroether, FEC, and FMEC was 86.5 wt.%, the content of compound 1 was 34.6 wt.%, the content of FEC was 17.3 wt.%, the content of FEMC was 34.6 wt.%, the content of TPP was 0.5 wt.%, and the content of lithium hexafluorophosphate was 13 wt.%.

[0106] (2) Preparation of positive electrode

[0107] The carbon source is pre-sintered in a nitrogen atmosphere at a temperature of 520°C for 4 hours to obtain component B, wherein the carbon source is tannic acid; component B is then mixed with component A and subjected to a secondary sintering treatment at a temperature of 420°C for 16 hours, so that component B is coated on at least part of the surface of component A to obtain a positive electrode active material; wherein the mass of component B is 1.5 wt % of the mass of component A, and the chemical formula of component A is Li 1.01 Ni 0.5 Mn 1.5 O 3.9 F 0.1 .

[0108] The positive electrode active material prepared above, the binder polyvinylidene fluoride and the conductive agent Super P were mixed in a mass ratio of 98:1:1, N-methylpyrrolidone (NMP) was added, and the mixture was stirred under the action of a vacuum mixer until the system became uniform and transparent to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on aluminum foil, and then dried at room temperature and transferred to an oven for drying, and then cold pressed and slit to obtain positive electrode sheets.

[0109] (3) Preparation of negative electrode sheet

[0110] The negative electrode active material artificial graphite, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC-Na) and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96:1:1:2, deionized water was added, and the negative electrode slurry was obtained under the action of a vacuum mixer; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil, then dried at room temperature and transferred to an oven for drying, and then cold pressed and cut to obtain the negative electrode sheet.

[0111] (4) Preparation of diaphragm

[0112] A polypropylene film with a thickness of 12 μm was used as the separator.

[0113] (5) Assembly of lithium-ion batteries

[0114] The positive electrode sheet, separator and negative electrode sheet prepared in the above steps are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, to obtain a bare cell. Then the bare cell is placed in an aluminum-plastic film and then placed in a vacuum oven at 120 o After baking and removing water at 400 °C, 3.0 g / Ah of the electrolyte prepared in step (1) was injected and sealed. After that, the lithium-ion battery was obtained through the processes of standing, hot and cold pressing, forming, clamping, and capacity separation.

[0115] Examples 2-16 and Comparative Examples 1-4

[0116] Examples 2-16 Comparative Examples 1-4, except that the types or contents of some components in the electrolyte or the positive electrode active materials are different from those in Example 1, the remaining steps and conditions are the same as those in Example 1.

[0117] The types and contents of the components in the electrolytes of Examples 1-16 and Comparative Examples 1-4 are shown in Table 1.

[0118] The positive electrode active material used in Examples 2-14, 16 and Comparative Examples 1-2 and 4 is the same as that in Example 1, and the positive electrode active material used in Example 15 and Comparative Example 3 is LiCoO2.

[0119] Table 1

[0120] serial number Types of fluoroethers Mass ratio of fluoroether, FEC and FEMC Total content of fluoroether, FEC and FEMC / wt.% TPP / wt.% 1,3-Propane sultone / wt.% Lithium salt and content wt.% Example 1 Compound 1 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 2 Compound 1 4:2:4 86.9 0.1 / <![CDATA[13 wt.% LiPF6]]> Example 3 Compound 1 4:2:4 86 1 / <![CDATA[13 wt.% LiPF6]]> Example 4 Compound 2 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 5 Compound 3 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 6 Formula II 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 7 Compound 1 3:2:5 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 8 Compound 1 5.3:2:2.7 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 9 Compound 1 4:2:4 86.4 0.5 0.1 <![CDATA[13 wt.% LiPF6]]> Example 10 Compound 1 4:2:4 85 0.5 1.5 <![CDATA[13 wt.% LiPF6]]> Example 11 Compound 1 4:2:4 83.5 0.5 3 <![CDATA[13 wt.% LiPF6]]> Example 12 Compound 1 3:3:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 13 Compound 1 6.2:2:1.8 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 14 Compound 1 4:2:4 85.5 0.5 / <![CDATA[13 wt.% LiPF6+1wt.% LiFSI]]> Example 15 Compound 1 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Example 16 Compound 1 4:2:4 87 / / <![CDATA[13 wt.% LiPF6]]> Comparative Example 1 TTE 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Comparative Example 2 / / 86.5 0.5 / <![CDATA[13 wt.% LiPF6 <!-- 8 -->]]> Comparative Example 3 TTE 4:2:4 86.5 0.5 / <![CDATA[13 wt.% LiPF6]]> Comparative Example 4 TTE 4:2:4 87 / / <![CDATA[13 wt.% LiPF6]]>

[0121] Note: “ / ” indicates that the component is not contained; “TTE” indicates 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0122] Effect embodiment

[0123] 1. Initial DC resistance (DCR) test of the battery

[0124] At 25°C, discharge the battery at 1C to 50% SOC (state of charge, reflecting the battery's remaining capacity). Then, increase the current to 4C and maintain it for 30 seconds. Measure the difference between the updated stable voltage and the original platform voltage. The ratio of this value to the 4C current value is the battery's DC resistance. The DCR test result after the battery is fully charged for the first time is the battery's initial DCR.

[0125] 2. 25℃ fast charge capacity retention rate:

[0126] At 25°C, the lithium-ion battery was charged at different rates (0.33C, 1C, 2C, 3C) to the upper cutoff voltage. After standing for 10 minutes, it was discharged at a constant current of 0.33C to the lower cutoff voltage to obtain the charge capacity at different rates. The charge capacity of the lithium-ion battery at 0.33C and 3C was taken, and the capacity retention rate of 3C charging was calculated according to the following formula:

[0127] Fast charge capacity retention rate (%) = (3C charge capacity / 0.33C charge capacity) × 100%

[0128] 3. 45℃ high temperature stability test:

[0129] Examples 1-14, 16 and Comparative Examples 1-2, 4:

[0130] In an oven at 45°C, cyclic charge and discharge were carried out in the range of 3.4V-4.85V: specifically, the battery was charged from the open circuit voltage to 4.85V with a current of 1C, and then charged to 0.05C at a constant voltage. The battery was discharged from 4.85V to 3.4V with a current of 1C, and then discharged to 0.05C at a constant voltage. The above process was counted as one charge and discharge cycle, and the discharge capacity of each cycle was recorded. The test was terminated when the battery capacity reached 80% of the first cycle capacity. The number of cycles recorded was the high-temperature cycle performance effect data, which is recorded in Table 2.

[0131] Example 15 and Comparative Example 3

[0132] In an oven at 45°C, cyclic charge and discharge were performed in the range of 2.8V-4.45V: specifically, the battery was charged from the open circuit voltage to 4.45V with a current of 1C, and then charged to 0.05C at a constant voltage. The battery was discharged from 4.45V to 2.8V with a current of 1C, and then discharged to 0.05C at a constant voltage. The above process was counted as one charge and discharge cycle, and the discharge capacity of each cycle was recorded. The test was terminated when the battery capacity reached 80% of the first cycle capacity. The number of cycles recorded was the high-temperature cycle performance effect data, which is recorded in Table 2.

[0133] Table 2

[0134] serial number 25℃DCR / mΩ Fast charge capacity retention rate / % 45℃ cycle times Example 1 85 56 530 Example 2 82 54 498 Example 3 91 45 554 Example 4 80 61 511 Example 5 89 49 561 Example 6 88 50 569 Example 7 101 41 559 Example 8 72 53 521 Example 9 86 54 548 Example 10 89 50 571 Example 11 93 44 584 Example 12 95 48 563 Example 13 68 46 489 Example 14 76 63 518 Example 15 96 34 459 Example 16 80 53 489 Comparative Example 1 157 28 522 Comparative Example 2 128 40 519 Comparative Example 3 137 25 425 Comparative Example 4 151 25 465

[0135] As can be seen from Table 2, the lithium-ion battery prepared using the electrolyte of the present invention has excellent fast charging performance and high-temperature cycling performance. The DCR at 25°C is lower than 101mΩ, the fast charging capacity retention rate of 3C charging is above 34%, and the number of cycles to 80SOH% at a high temperature of 45°C is more than 459.

[0136] In Comparative Example 1, the fluoroether added was TTE, whose fluorine atom substitution position is outside the scope of the present invention, and whose structure has only one ether bond. When used in a battery with the same other conditions as in Example 1, the DCR, fast-charge performance, and high-temperature cycling performance at 25°C failed to simultaneously achieve the performance of the present invention. In particular, the DCR at 25°C was much greater than that of Example 1.

[0137] No fluoroether substances were added to the electrolyte of Comparative Example 2. When other conditions were the same as those in Example 1, its high-temperature cycle performance and fast charge performance were comparable to those of certain embodiments of the present invention, but significantly decreased compared to Example 1. However, the DCR at 25°C was greater than that achievable by the present invention and significantly increased compared to Example 1.

[0138] Comparative Example 3 differs from Example 15 only in the type of fluoroether added. TTE is used in Comparative Example 3, where the fluorine atom substitution position is outside the scope of this invention and the structure contains only one ether bond. Under the same conditions, when used in a battery, this battery exhibits high impedance and very poor fast-charge and high-temperature cycling performance.

[0139] Comparative Example 4 differs from Example 16 only in the type of fluoroether added. Comparative Example 4 uses TTE, whose fluorine atom substitution positions are outside the scope of this invention, and whose structure contains only one ether bond. When used in a battery with these batteries, all other conditions remaining the same, high-temperature cycling performance, while comparable to that of some embodiments of this invention, is lower than that of Example 16. Furthermore, both DCR and fast-charge performance at 25°C are poor.

[0140] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a fluoroether, a cyclic fluorocarbonate and a linear fluorocarbonate; wherein the fluoroether is one or more compounds represented by Formula I and Formula II; ， ， In Formula I, R1 and R2 are each independently a methyl group or a fluoromethyl group, and the total number of fluorine atoms in R1 and R2 is not less than 3.

2. The electrolyte according to claim 1, characterized in that The compound represented by formula I is selected from one or more of compounds 1-5; 、 、 、 and 。 3. The electrolyte according to claim 1, characterized in that The content of the fluoroether is 25wt.%-45wt.%, where wt.% is the mass percentage of the fluoroether in the electrolyte.

4. The electrolyte according to claim 1, characterized in that The electrolyte satisfies one or more of the following conditions ad: a. The cyclic fluorocarbonate is fluoroethylene carbonate; b. The content of the cyclic fluorinated carbonate is 5wt.%-20wt.%, wt.% is the mass percentage of the cyclic fluorinated carbonate in the electrolyte; c. The linear fluorocarbonate is 2,2,2-trifluoroethyl methyl carbonate; d. The content of the linear fluorinated carbonate is 25wt.%-45wt.%, where wt.% is the mass percentage of the linear fluorinated carbonate in the electrolyte.

5. The electrolyte according to claim 1, characterized in that The electrolyte further comprises tripropynyl phosphate and / or 1,3-propane sultone.

6. The electrolyte according to claim 5, characterized in that The electrolyte satisfies one or more of the following conditions ac: a. The content of tripropynyl phosphate is 0.01wt.%-1wt.%, wt.% is the mass percentage of tripropynyl phosphate in the electrolyte; b. The content of 1,3-propane sultone is 0.01wt.%-3wt.%, wt.% is the mass percentage of 1,3-propane sultone in the electrolyte; c. The electrolyte further comprises tripropynyl phosphate and 1,3-propane sultone, wherein the mass ratio of the 1,3-propane sultone to the tripropynyl phosphate is (2-4):

1.

7. The electrolyte according to claim 1, characterized in that The electrolyte further includes a lithium salt, wherein the lithium salt includes lithium hexafluorophosphate, and the lithium salt satisfies one or more of the following conditions ac: a. The lithium salt further comprises one or more of lithium bis(trifluoromethyl)sulfonyl imide, lithium bis(trifluoromethyl)sulfonyl imide, lithium acetate, lithium methanesulfonate and lithium trifluoromethanesulfonate; b. The content of lithium salt in the electrolyte is 10wt.%-20wt.%, wt.% is the mass percentage of the lithium salt in the electrolyte; c. The content of the lithium hexafluorophosphate is 8wt.%-20wt.%, where wt.% is the mass percentage of the lithium hexafluorophosphate in the electrolyte.

8. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that The positive electrode active material of the lithium ion battery is lithium nickel manganese oxide.

10. An electronic device, characterized in that: The electronic device comprises the lithium-ion battery according to claim 8 or 9.

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