Electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to an electrolyte and a preparation method and application thereof. The electrolyte comprises an organic solvent, a lithium salt and an additive, the organic solvent is a first solvent or a first solvent and a second solvent; the first solvent is a p-fluoroalkyl alkenyl ester compound as shown in a formula (1), and the second solvent is linear carbonate and / or cyclic acid ester. The electrolyte provided by the invention can simultaneously stabilize transmission of an electrode interface and a lithium ion interface at a wide temperature range so as to overcome the limitation of the traditional electrolyte, so that the lithium ion battery can normally work in a wider temperature range, and the application requirements under different environmental conditions are met.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to an electrolyte and a preparation method and application thereof. Background Art

[0002] With the growing demand for energy storage in modern society, the application scenarios of lithium-ion batteries are becoming increasingly extensive, from consumer electronics to electric vehicles, to high-end fields such as aerospace. Although lithium-ion batteries have excellent cycle life and high energy density, in some special environments, such as outdoor operations in cold areas or high temperature environments, higher requirements are placed on the wide temperature performance of lithium-ion batteries. However, traditional lithium-ion battery electrolytes will have problems such as reduced ion conductivity, slowed electrode reaction kinetics, and poor stability of solid electrolyte interface film (SEI) under wide temperature conditions, which seriously restrict the practical application of lithium-ion batteries in wide temperature environments. In high temperature environments, high temperatures will accelerate the interface decomposition of the electrolyte, leading to the collapse of the positive electrode material structure and a sharp drop in battery capacity. In order to solve these problems, improve the performance of lithium-ion batteries in wide temperature environments, and promote the application of lithium-ion batteries in a wider range of fields, it is of great significance to study wide temperature electrolytes.

[0003] In recent years, there have been many reports on the problem of poor performance of lithium batteries over a wide temperature range. For example, by optimizing the composition of the electrolyte, at low temperatures, co-solvents with low freezing points and low viscosity are used to replace part of the EC solvent to improve ionic conductivity; fluorinated electrolytes, new solvents with weak solvation affinity, or adjusting the molecular structure of the solvent are selected to accelerate the desolvation process; suitable electrolyte formulations are designed to optimize the properties of the SEI film and promote the transmission of lithium ions in the film. In high temperature environments, suitable additives are selected to inhibit the dissolution of the positive electrode metal, reduce material structure damage and active material loss, while alleviating the intensification of electrolyte side reactions, reducing the risk of internal short circuits and thermal runaway, and improving the problem of battery performance degradation.

[0004] Previous studies on low-temperature electrolytes believed that the main reason for the poor low-temperature cycle performance of lithium-ion batteries is the reduced conductivity of the electrolyte. However, in-depth studies have shown that low conductivity is not the dominant factor leading to the poor low-temperature performance of lithium-ion batteries. At low temperatures, the cycle performance of lithium-ion batteries is closely related to the stability of the electrode interface and the difficulty of the lithium ion desolvation structure process. Solvated lithium ions need to strip off the solvation sheath before embedding into the electrode. However, the strong interaction between polar solvents and lithium ions makes this process energy-intensive, and as the temperature decreases, the coordination number of the solvent in the first solvation sheath of lithium ions increases, resulting in a slower desolvation process at low temperatures. In addition, the slow ion transport in the electrolyte under low-temperature conditions will aggravate the electrochemical polarization of the electrode, promote the growth of lithium dendrites, hinder the lithium ion interface transport, lead to a decrease in battery discharge capacity, shorten the cycle life, and severely limit the practical application of lithium-ion batteries. At high temperatures, excess energy will increase the reaction rate of the entire system, accelerate the decomposition of the electrolyte, cause the dissolution of transition metals, collapse the positive electrode structure, and uncontrolled thermal decomposition of lithium salts, severely reduce the stability of the electrode interface and accelerate the battery capacity decay. Therefore, it is necessary to develop new lithium-ion electrolytes that can stabilize the electrode interface and lithium-ion interface transport at a wide temperature range, so as to overcome the limitations of traditional electrolytes and enable lithium-ion batteries to operate normally in a wider temperature range and meet application requirements under different environmental conditions.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] An object of the present invention is to provide an electrolyte to solve the technical problems in the prior art that the ion conductivity of the electrolyte decreases, the electrode reaction kinetics slows down, and the stability of the solid electrolyte interface membrane deteriorates under a wide temperature range.

[0007] Another object of the present invention is to provide a method for preparing the electrolyte, which is simple, easy to operate and environmentally friendly.

[0008] Another object of the present invention is to provide a battery.

[0009] Another object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] An electrolyte comprising an organic solvent, a lithium salt and an additive;

[0012] The organic solvent is a first solvent, or a first solvent and a second solvent; the first solvent is a para-fluoroalkyl alkenyl ester compound represented by formula (1), and the second solvent is a linear carbonate and / or a cyclic acid ester;

[0013]

[0014] Wherein, Rf is a fluorine substituent -(CF2) n CF3, n≥1, or Rf is a C6-C10 aryl group substituted with a fluorine atom or a fluoroalkyl group, or Rf is -SiR1R2R3, R1, R2, and R3 are independently selected from C1-C8 fluoroalkyl groups, or Rf is -POR4R5, R4 and R5 are independently selected from C1-C4 fluoroalkyl groups or fluorine atoms, or Rf is -SR6R7R8, R6, R7, and R8 are independently selected from C1-C4 fluoroalkyl groups or fluorine atoms, or Rf is -NSR9R 10 R 11 , R9, R 10 and R 11 independently selected from C1-C3 fluoroalkyl groups or fluorine atoms.

[0015] In some embodiments, the para-fluoroalkyl alkenyl ester compound includes at least one of the following compounds 1 to 10:

[0016] Compound 1: Compound 2: Compound 3: Compound 4: Compound 5: Compound 6: Compound 7:

[0017] Compound 8:

[0018] Compound 9:

[0019] Compound 10:

[0020] In some embodiments, the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, and propyl acetate.

[0021] In some embodiments, the cyclic acid ester includes at least one of ethylene carbonate, propylene carbonate, caprolactone, and γ-butyrolactone.

[0022] In some embodiments, the mass ratio of the linear carbonate, the cyclic acid ester and the para-fluoroalkyl alkenyl ester compound is (5-10):(10-20):(70-85).

[0023] In some embodiments, the additive includes at least one of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, and a borate compound.

[0024] In some embodiments, the lithium salt includes at least one of LiF, Li2O, Li2O2, LiPF6, LiBF4, LiClO4, LiBOB, LiODFB, LiAsF6, LiCF3SO3, LiN(SO2CF3)2 and LiBF3C2F5.

[0025] In some embodiments, the mass content of the additive in the electrolyte is 1% to 3%, and the mass content of the lithium salt in the electrolyte is 10% to 15%.

[0026] The method for preparing the electrolyte as described above comprises the following steps:

[0027] obtaining an organic solvent, wherein the organic solvent is the first solvent, or the first solvent and the second solvent;

[0028] The organic solvent, lithium salt and additive are mixed to obtain an electrolyte.

[0029] A battery comprises the electrolyte.

[0030] In some embodiments, a positive electrode sheet and a negative electrode sheet are also included; the positive electrode sheet includes a positive electrode collector and a positive electrode layer located on at least one side of the positive electrode collector, the positive electrode layer contains a positive electrode active material, and the positive electrode active material includes a transition metal oxide of lithium and / or a transition metal phosphate compound of lithium; the negative electrode sheet includes a negative electrode collector and a negative electrode layer located on at least one side of the negative electrode collector, the negative electrode layer contains a negative electrode active material, and the negative electrode active material includes at least one of a carbonaceous material, an alloy material, a metal composite material containing lithium, and metallic lithium.

[0031] An electrical device comprises the battery.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) In the electrolyte of the present invention, the above-mentioned fluoroalkyl alkenyl ester compounds can participate in the lithium ion solvation structure in priority to other traditional ester solvent molecules, reduce the energy barrier of lithium ion desolvation under low temperature environment, and effectively promote the lithium ion desolvation process, thereby improving the low temperature cycle stability of the battery. And the alkenyl-containing fluorine solvent has good reactivity, which is conducive to the formation of a fluoride-rich positive electrode electrolyte interface (CEI) film. This CEI film has high ionic conductivity and mechanical strength, and can effectively prevent the further reaction of solvent molecules with electrodes at high temperature and reduce the material structure destruction and active material loss caused by the dissolution of positive electrode metals, thereby effectively improving the battery performance under high temperature environment. In addition, the fluorine solvent has a certain rigidity due to the double bond contained therein, and can maintain the relative stability of the molecular structure at high temperature. And the double bond can form a certain coordination bond with the cation in the lithium salt, so that the lithium salt is more stably present in the electrolyte at high temperature, reducing the electrolyte performance degradation caused by problems such as lithium salt decomposition at high temperature. The electrolyte of the present invention also has excellent high temperature application potential.

[0034] (2) The preparation method of the electrolyte of the present invention is simple, easy and environmentally friendly. The electrolyte obtained by the method can stabilize the electrode interface and lithium ion interface transmission at a wide temperature, thereby overcoming the limitations of traditional electrolytes and enabling the battery to work normally in a wider temperature range (-40°C to 55°C) to meet application requirements under different environmental conditions.

[0035] (3) The battery of the present invention has both excellent high-temperature performance and low-temperature performance, excellent cycle stability under wide temperature conditions, and good safety. DETAILED DESCRIPTION

[0036] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0037] According to one aspect of the present invention, the present invention relates to an electrolyte, comprising an organic solvent, a lithium salt and an additive; the organic solvent is a first solvent, or a first solvent and a second solvent; the first solvent is a para-fluoroalkyl alkenyl ester compound represented by formula (1), and the second solvent is a linear carbonate and / or a cyclic acid ester;

[0038]

[0039] Wherein, Rf is a fluorine substituent -(CF2) nCF3, n≥1, or Rf is a C6-C10 aryl group substituted with a fluorine atom or a fluoroalkyl group, or Rf is -SiR1R2R3, R1, R2, and R3 are independently selected from C1-C8 fluoroalkyl groups, or Rf is -POR4R5, R4 and R5 are independently selected from C1-C4 fluoroalkyl groups or fluorine atoms, or Rf is -SR6R7R8, R6, R7, and R8 are independently selected from C1-C4 fluoroalkyl groups or fluorine atoms, or Rf is -NSR9R 10 R 11 , R9, R 10 and R 11 independently selected from C1-C3 fluoroalkyl groups or fluorine atoms.

[0040] In the electrolyte of the present invention, the above-mentioned fluoroalkyl alkenyl ester compounds can participate in the lithium ion solvation structure in preference to other traditional ester solvent molecules, reduce the energy barrier of lithium ion desolvation under low temperature environment, and can effectively promote the lithium ion desolvation process, thereby improving the low temperature cycle stability of the battery. And the alkenyl-containing fluorine solvent has good reactivity, which is conducive to the formation of a fluoride-rich cathode electrolyte interface (CEI) film, which has high ionic conductivity and mechanical strength, and can effectively prevent further reaction of solvent molecules with electrodes at high temperature and reduce material structure destruction and active material loss caused by dissolution of positive electrode metal, thereby effectively improving battery performance under high temperature environment. In addition, the fluorine solvent has a certain rigidity due to the double bond contained therein, and can maintain the relative stability of the molecular structure at high temperature. And the double bond can form a certain coordination bond with the cation in the lithium salt, so that the lithium salt is more stably present in the electrolyte at high temperature, reducing the electrolyte performance degradation caused by problems such as lithium salt decomposition at high temperature, and the electrolyte of the present invention also has excellent high temperature application potential. The electrolyte of the present invention enables the battery to have excellent electrochemical performance within a wide temperature range (-40° C. to 55° C.), meeting application requirements under different environmental conditions.

[0041] In some embodiments, the fluoroalkyl alkenyl ester compound includes at least one of the following compounds 1 to 10:

[0042] Compound 1: Compound 2: Compound 3: Compound 4: Compound 5: Compound 6:

[0043] Compound 7:

[0044] Compound 8:

[0045] Compound 9:

[0046] Compound 10:

[0047] The para-fluoroalkyl alkenyl ester compound of the present invention can be selected from any one of the above-mentioned compounds 1 to 10, or a combination of multiple ones, such as a combination of compound 1 and compound 2, a combination of compound 5 and compound 6, a combination of compound 8, compound 9 and compound 10, etc.

[0048] In some embodiments, the linear carbonate comprises one or more combinations of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate and propyl acetate, such as a combination of dimethyl carbonate and diethyl carbonate, a combination of ethyl methyl carbonate and methyl propyl carbonate, a combination of ethyl propyl carbonate and methyl formate, a combination of methyl formate and ethyl formate, a combination of propyl formate and methyl acetate, a combination of ethyl acetate and propyl acetate, and the like.

[0049] In some embodiments, the cyclic acid ester includes a combination of one or more of ethylene carbonate, propylene carbonate, caprolactone, and gamma-butyrolactone.

[0050] In some embodiments, the organic solvent is a composition of a linear carbonate, a cyclic acid ester and a fluoroalkyl alkenyl ester compound, and the mass ratio of the linear carbonate, the cyclic acid ester and the fluoroalkyl alkenyl ester compound is (5-10):(10-20):(70-85), including but not limited to 5:10:85, 10:10:80, 10:15:75 or 10:20:70, etc.

[0051] In some embodiments, the additive includes one or more combinations of cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sultone compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate compounds and lithium salt additives.

[0052] In some embodiments, the lithium salt includes one or more of LiF, Li2O, Li2O2, LiPF6, LiBF4, LiClO4, LiBOB, LiODFB, LiAsF6, LiCF3SO3, LiN(SO2CF3)2 and LiBF3C2F5, such as a combination of LiPF6 and LiBF4, a combination of LiAsF6 and LiCF3SO3, a combination of LiCF3SO3, LiN(SO2CF3)2 and LiBF3C2F5, etc.

[0053] In some embodiments, the mass content of the additive in the electrolyte is 1% to 3%, including but not limited to 1%, 1.5%, 2%, 2.5%, 3%, etc., preferably 1.5% to 2%. The mass content of the lithium salt in the electrolyte is 10% to 15%, including but not limited to 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, etc.

[0054] According to another aspect of the present invention, the present invention also relates to a method for preparing the electrolyte as described above, comprising the following steps:

[0055] An organic solvent is obtained, where the organic solvent is the first solvent, or the first solvent and the second solvent; the organic solvent, a lithium salt and an additive are mixed to obtain an electrolyte.

[0056] The preparation method of the electrolyte of the present invention is simple and easy, and is environmentally friendly. The electrolyte has both excellent high-temperature performance and low-temperature performance, and can stabilize the electrode interface and lithium ion interface transmission at a wide temperature to overcome the limitations of traditional electrolytes, so that lithium-ion batteries can work normally in a wider temperature range and meet application requirements under different environmental conditions.

[0057] According to another aspect of the present invention, the present invention also relates to a battery comprising an electrolyte.

[0058] The battery of the present invention has excellent high-temperature performance and low-temperature performance, excellent cycle stability under wide temperature conditions, and good safety performance.

[0059] In some embodiments, the battery further includes a positive electrode sheet and a negative electrode sheet.

[0060] In some embodiments, the positive electrode sheet includes a positive electrode collector and a positive electrode layer located on at least one side of the positive electrode collector, the positive electrode layer contains a positive electrode active material, and the positive electrode active material includes a lithium transition metal oxide and / or a lithium transition metal phosphate compound; in some embodiments, the positive electrode material includes any one of Li2MnO4, LiFePO4, LiCoO2, LiMn2O4, LiMnO2, LiNixMnyO2, LiNixCoyMnzO2, LiMnPO4 and LiCoPO4, or a combination of at least two of them, wherein 0≤x≤1, 0≤y≤1, and 0≤z≤1.

[0061] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode layer located on at least one side of the negative electrode current collector, the negative electrode layer contains a negative electrode active material, and the negative electrode active material includes one or more of a carbonaceous material, an alloy material, a metal composite material containing lithium, and metallic lithium.

[0062] According to another aspect of the present invention, the present invention also relates to an electric device, comprising the above-mentioned battery. The electric device includes an electric car and the like.

[0063] The following is further explained in conjunction with specific embodiments and comparative examples.

[0064] Example 1

[0065] An electrolyte comprises a lithium salt, an organic solvent and an additive; the mass fraction of the lithium salt in the electrolyte is 8%, and the lithium salt is lithium hexafluorophosphate; the mass fraction of the organic solvent in the electrolyte is 90%, and the organic solvent comprises dimethyl carbonate, ethylene carbonate and a fluoroalkyl alkenyl ester compound, the mass ratio of dimethyl carbonate, ethylene carbonate and the fluoroalkyl alkenyl ester compound is 10:20:70, and the fluoroalkyl alkenyl ester compound is compound 1; the mass fraction of the additive in the electrolyte is 2%, and the additive is fluoroethylene carbonate.

[0066] Among them, compound 1:

[0067] The synthesis method of compound 1 comprises: preparing the compound 1 by reflux reaction of a corresponding fluorine-containing alcohol precursor with p-toluenesulfonic acid monohydrate and maleic anhydride, and the specific reaction chemical formula is as follows:

[0068]

[0069] Example 2

[0070] An electrolyte, which differs from Example 1 in that:

[0071] The fluoroalkyl alkenyl ester compound is compound 4.

[0072] Compound 4:

[0073] The synthesis method of compound 4 comprises:

[0074] S1: Preparation of Grignard reagent. Under anhydrous and oxygen-free conditions, magnesium chips are added to dry tetrahydrofuran (THF), and then a THF solution of m-trifluoromethyl bromobenzene is slowly added dropwise. After the reaction is initiated, the addition is continued to complete the reaction to obtain m-trifluoromethylphenylmagnesium bromide Grignard reagent.

[0075] S2: Reaction with ethylene oxide. Slowly drop the cooled ethylene oxide into the prepared Grignard reagent. After the dropwise addition is complete, heat and stir to react for a period of time.

[0076] S3: Hydrolysis and post-treatment. After the reaction is completed, dilute acid is added to the reaction system for hydrolysis, and then the organic phase is separated, the aqueous phase is extracted with an organic solvent, and the organic phases are combined. The organic phase is washed, dried, distilled, etc. to obtain the precursor trifluorophenyl ring alcohol.

[0077] S4: The final product is prepared according to the following reaction path, and the reaction chemical formula is as follows:

[0078]

[0079] Example 3

[0080] An electrolyte, which differs from Example 1 in that:

[0081] The fluoroalkyl alkenyl ester compound is compound 7.

[0082] Compound 7:

[0083] The synthesis method of compound 7 comprises:

[0084] S1: Catalytic reaction. Under the protection of inert gas, add trifluorosilane and ethylene oxide into a reaction vessel while controlling the reaction temperature within a certain range (eg, 0-50° C.), add an appropriate amount of metal catalyst or Lewis acid catalyst, and stir the reaction for a period of time.

[0085] S2: Separating and purifying the reaction mixture. Unreacted raw materials and by-products can be removed by distillation, extraction, etc. to obtain a relatively pure precursor trifluorosilane ethanol.

[0086] S3: The final product is obtained according to the following reaction path, and the chemical reaction formula is as follows:

[0087]

[0088] Example 4

[0089] An electrolyte, which differs from Example 1 in that:

[0090] The mass ratio of dimethyl carbonate, ethylene carbonate and p-fluoroalkyl alkenyl ester compound is 10:10:80.

[0091] Example 5

[0092] An electrolyte, which differs from Example 1 in that:

[0093] The mass ratio of dimethyl carbonate, ethylene carbonate and p-fluoroalkyl alkenyl ester compound is 5:10:85.

[0094] Example 6

[0095] An electrolyte, which differs from Example 1 in that:

[0096] The mass ratio of dimethyl carbonate, ethylene carbonate and p-fluoroalkyl alkenyl ester compound is 5:5:90.

[0097] Example 7

[0098] An electrolyte, which differs from Example 1 in that:

[0099] The organic solvent is a 4-fluoroalkyl alkenyl ester compound, and the 4-fluoroalkyl alkenyl ester compound is compound 4.

[0100] Example 8

[0101] An electrolyte, which differs from Example 1 in that:

[0102] The organic solvent is a 4-fluoroalkyl alkenyl ester compound and γ-butyrolactone, the mass ratio of γ-butyrolactone to the 4-fluoroalkyl alkenyl ester compound is 30:70, and the 4-fluoroalkyl alkenyl ester compound is compound 4.

[0103] Comparative Example 1

[0104] An electrolyte, which differs from Example 1 in that:

[0105] Does not contain 4-fluoroalkylene ester compounds.

[0106] Experimental example

[0107] The electrolytes of the embodiments and comparative examples are assembled into lithium-ion batteries, comprising the following steps:

[0108] (1) Preparation of positive electrode sheets for lithium-ion batteries: The positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1O2), conductive agent Super-P, and adhesive PVDF were dissolved in solvent N-methylpyrrolidone at a mass ratio of 95.8:2.2:2.0 and mixed evenly to form positive electrode slurry. The positive electrode slurry was evenly coated on the current collector aluminum foil with a coating amount of 18 mg / cm 2 Then, after drying at 90°C, cold pressing, trimming, cutting, and striping are performed, and then drying is performed at 90°C under vacuum conditions for 4 hours, and the tabs are welded to produce a positive electrode sheet for a lithium-ion secondary battery that meets the requirements.

[0109] (2) Preparation of negative electrode sheets for lithium-ion batteries: The negative electrode active material artificial graphite, conductive agent Super-P, thickener CMC, and binder SBR were dissolved in solvent deionized water at a mass ratio of 96.5:1.0:1.0:1.5 and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on the current collector copper foil with a coating amount of 8.0 mg / cm 2 Then, after drying at 90°C, cold pressing, trimming, cutting, and striping are performed, and then drying is performed at 110°C under vacuum conditions for 4 hours, and the tabs are welded to produce a negative electrode sheet for a lithium-ion secondary battery that meets the requirements.

[0110] (3) Preparation of lithium-ion batteries: The positive electrode sheet, negative electrode sheet and isolation film (PE film) of the lithium-ion secondary battery prepared above were laminated to form a battery with a thickness of 8 mm, a width of 60 mm and a length of 130 mm, and vacuum-baked at 90°C for 10 h. The electrolytes in the embodiments and comparative examples were injected into each battery, and the lithium-ion batteries were obtained after standing, pre-charging, formation and degassing and sealing.

[0111] The lithium ion batteries prepared in the examples and comparative examples were tested for room temperature cycle performance, high temperature and low temperature cycle performance, and high temperature and low temperature capacity retention rate. The specific test methods are as follows:

[0112] 1. Test of the conductivity of electrolyte at low temperature (-20℃, -40℃)

[0113] Use low temperature test box, conductivity meter and low temperature resistant container and other equipment and materials. Set the low temperature test box to -20℃ and -40℃ respectively and wait for the temperature to stabilize. Install the electrode in the container in the low temperature box, pour in an appropriate amount of electrolyte to ensure that the electrode is immersed. After turning on the conductivity meter for calibration, wait for the reading to stabilize and record the conductivity value at the corresponding temperature. Repeat the test several times to get the conductivity average value.

[0114] The test results of the low temperature ionic conductivity of the electrolyte are shown in Table 1.

[0115] Table 1 Low temperature ionic conductivity of electrolyte

[0116]

[0117]

[0118] 2. Test of battery capacity retention and capacity recovery rate at 55℃ high temperature storage

[0119] Perform an initial capacity test on the battery and record the initial capacity value C0 of each battery. Place the battery in a high-temperature test chamber, set the temperature to 55°C, and store for 7 days. Perform a capacity test on the battery under the same charge and discharge conditions, and record the capacity value C1 after storage. Calculate the capacity retention rate: Capacity retention rate = (C1 / C0) × 100%; Perform a complete charge and discharge cycle on the battery that has been stored at high temperature and tested for capacity retention to activate battery performance. Use the battery charge and discharge test equipment again to perform a capacity test on the battery under the same charge and discharge conditions, and record the capacity value C2 after recovery. Calculate the capacity recovery rate: Capacity recovery rate = (C2 / C0) × 100%.

[0120] The test results of the battery's 55°C high temperature storage capacity retention rate and capacity recovery rate are shown in Table 2.

[0121] Table 2 Battery 55℃ high temperature storage capacity retention rate and capacity recovery rate

[0122]

[0123] 3. Test of discharge capacity retention rate at specific temperature

[0124] In a 25℃ test chamber, charge the battery to 4.3V at 0.2C, then charge at 4.3V constant voltage until the current drops to 0.05C, adjust the test chamber to a specific high or low temperature, and then discharge at 0.2C to 2.8V. Calculate the battery's discharge capacity retention rate at a specific temperature according to the following formula: room temperature discharge capacity retention rate at a specific temperature = discharge capacity at a specific temperature / 25℃ discharge capacity × 100%. When the battery's capacity retention rate is less than 80% and the coulomb efficiency is less than 90%, the battery test is stopped.

[0125] The specific temperature discharge capacity retention rates of lithium-ion batteries corresponding to different electrolytes are shown in Table 3.

[0126] Table 3 Specific temperature discharge capacity retention rate of lithium-ion batteries corresponding to different electrolytes

[0127]

[0128] 4. Wide temperature (-20℃, 25℃, 55℃) cycle performance test:

[0129] The temperature of the test box was adjusted to -20℃, 25℃, and 55℃ respectively. The battery was charged to 4.3V at a constant current of 0.1C, and then the voltage was maintained at 4.3V until the charging current dropped below 0.05C. The battery was discharged to 2.8V at a constant current of 0.1C, and the above charging and discharging steps were repeated for 500 cycles. The capacity retention rate of the battery after the 500th cycle was calculated, and the capacity retention rate = discharge capacity after the 200th cycle / discharge capacity of the first cycle.

[0130] The cycle capacity retention rate of the battery under a wide temperature range is shown in Table 4.

[0131] Table 4 Cyclic capacity retention of batteries at wide temperature

[0132]

[0133] By comparing Example 1 and Comparative Example 1 in Table 1, it can be seen that the fluorinated alkyl alkenyl ester compounds have a good effect on improving the conductivity of the electrolyte at low temperatures. The fluorinated solvent can weaken the interaction between other high-polarity solvent molecules and lithium ions by participating in the lithium ion solvation structure, thereby reducing the energy barrier of the lithium ion desolvation structure and promoting the lithium ion transfer kinetics.

[0134] By comparing Examples 1-6 and Comparative Example 1 in Tables 2 and 3, it can be seen that the fluoroalkyl alkenyl ester compounds can significantly improve the storage performance of lithium-ion batteries at high temperatures and the discharge capacity retention rate at specific high and low temperatures. Among them, the capacity retention rate of Example 2 after storage at a high temperature of 55°C for 7 days is as high as 99%, the discharge capacity retention rate at a low temperature of -20°C is 98.5%, and the discharge capacity retention rate at -60°C can still be maintained at 92.4%, which is much higher than Comparative Example 1 using a traditional carbonate electrolyte.

[0135] By comparing Examples 1-6 and Comparative Example 1 in Table 4, it can be seen that the fluoroalkyl alkenyl ester compounds have the effect of improving the cyclic stability of lithium-ion batteries at both high and low temperatures. The lithium-ion batteries containing the solvent have a high capacity retention rate after 500 cycles at -40°C and 55°C, among which Examples 2 and 3 show better wide temperature cycle performance than Example 1, which indicates that the structural formula of the fluoroalkyl alkenyl ester solvent can be further optimized to enable lithium-ion batteries to achieve better wide temperature use effects. Among them, the fluoroalkyl alkenyl ester compounds containing fluorinated benzene ring groups have a better effect of breaking the temperature limit of lithium-ion battery electrolyte use.

[0136] The above results show that the electrolyte of the present invention has excellent wide temperature application potential. Under low temperature conditions, fluoroalkyl alkenyl ester compounds can promote the lithium ion interface transfer dynamics at low temperatures by regulating the lithium ion solvation structure, thereby improving the capacity retention performance of lithium ion batteries at low temperatures. Under high temperature conditions, fluoroalkyl alkenyl ester compounds contain double bonds and have good reactivity, which is conducive to the formation of a fluoride-rich positive electrode electrolyte interface film, which can effectively prevent further reaction between solvent molecules and electrodes at high temperatures, and reduce the material structure destruction and active material loss caused by the dissolution of positive electrode metals. In addition, the double bonds can form certain coordination bonds with the cations in the lithium salt, so that the lithium salt can be more stably present in the electrolyte at high temperatures, reducing the degradation of the electrolyte performance caused by problems such as lithium salt decomposition at high temperatures. Therefore, the electrolyte of the present invention has an excellent effect of stabilizing the high temperature discharge capacity retention rate of lithium ion batteries.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that: Including organic solvents, lithium salts and additives; The organic solvent is a first solvent, or a first solvent and a second solvent; the first solvent is a para-fluoroalkyl alkenyl ester compound represented by formula (1), and the second solvent is a linear carbonate and / or a cyclic acid ester; Wherein, Rf is a fluorine substituent -(CF2) n CF3, n≥1, or Rf is a C6-C10 aryl group substituted with a fluorine atom or a fluoroalkyl group, or Rf is -SiR1R2R3, R1, R2, and R3 are independently selected from C1-C8 fluoroalkyl groups, or Rf is -POR4R5, R4 and R5 are independently selected from C1-C4 fluoroalkyl groups or fluorine atoms, or Rf is -SR6R7R8, R6, R7, and R8 are independently selected from C1-C4 fluoroalkyl groups or fluorine atoms, or Rf is -NSR9R 10 R 11 , R9, R 10 and R 11 independently selected from C1-C3 fluoroalkyl groups or fluorine atoms.

2. The electrolyte according to claim 1, characterized in that The para-fluoroalkyl alkenyl ester compound includes at least one of the following compounds 1 to 10: Compound 1: Compound 2: Compound 3: Compound 4: Compound 5: Compound 6: Compound 7: Compound 8: Compound 9: Compound 10:

3. The electrolyte according to claim 1, characterized in that The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate and propyl acetate; and / or, the cyclic acid ester comprises at least one of ethylene carbonate, propylene carbonate, caprolactone and γ-butyrolactone; And / or, the mass ratio of the linear carbonate, the cyclic acid ester and the para-fluoroalkyl alkenyl ester compound is (5-10):(10-20):(70-85).

4. The electrolyte according to claim 1, characterized in that The additive includes at least one of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound and a borate compound.

5. The electrolyte according to claim 1, characterized in that The lithium salt includes at least one of LiF, Li2O, Li2O2, LiPF6, LiBF4, LiClO4, LiBOB, LiODFB, LiAsF6, LiCF3SO3, LiN(SO2CF3)2 and LiBF3C2F5.

6. The electrolyte according to claim 1, characterized in that The mass content of the additive in the electrolyte is 1% to 3%, and the mass content of the lithium salt in the electrolyte is 10% to 15%.

7. The method for preparing an electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: obtaining an organic solvent, wherein the organic solvent is the first solvent, or the first solvent and the second solvent; The organic solvent, lithium salt and additive are mixed to obtain an electrolyte.

8. A battery, characterized in that: An electrolyte solution comprising the electrolyte solution according to any one of claims 1 to 6.

9. The battery according to claim 8, characterized in that Also includes positive and negative electrodes; The positive electrode sheet comprises a positive electrode current collector and a positive electrode layer located on at least one side of the positive electrode current collector, wherein the positive electrode layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium transition metal oxide and / or a lithium transition metal phosphate compound; The negative electrode sheet includes a negative electrode current collector and a negative electrode layer located on at least one side of the negative electrode current collector. The negative electrode layer contains a negative electrode active material. The negative electrode active material includes at least one of a carbonaceous material, an alloy material, a metal composite material containing lithium, and metallic lithium.

10. An electrical device, characterized in that: A battery comprising the battery according to claim 8 or 9.

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