CN111584936A - Electrolyte and preparation method thereof - Google Patents

Electrolyte and preparation method thereof Download PDF

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Publication number
CN111584936A
CN111584936A CN202010603868.6A CN202010603868A CN111584936A CN 111584936 A CN111584936 A CN 111584936A CN 202010603868 A CN202010603868 A CN 202010603868A CN 111584936 A CN111584936 A CN 111584936A
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lithium
electrolyte
ether
solvent
additive
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杨春晖
何伟东
东立伟
陈宁
周梅
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Sichuan Dongwei Hydrogen Energy Technology Co ltd
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Sichuan Dongwei Hydrogen Energy Technology Co ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/056Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566Liquid materials
    • H01M10/0567Liquid materials characterised by the additives
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00Electrolytes
    • H01M2300/0017Non-aqueous electrolytes
    • H01M2300/0025Organic electrolyte
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

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Abstract

The invention relates to an electrolyte and a preparation method thereof, belonging to the technical field of batteries. The electrolyte comprises a solvent and an additive, wherein the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether. The electrolyte disclosed by the invention is good in affinity to lithium ions, strong in wetting capacity to a diaphragm and strong in thermal stability. The growth of lithium dendrites can be inhibited, and simultaneously, because the dispersion of oxygen and sulfur in the electrolyte is reduced, the dissolution of polysulfide and the related shuttle effect are inhibited, and the rate capability and the long cycle performance of the battery are greatly improved.

Description

Electrolyte and preparation method thereof
Technical Field
The invention relates to an electrolyte and a preparation method thereof, belonging to the technical field of batteries.
Background
Lithium ion batteries have attracted extensive attention due to their advantages of high energy density, long service life, low self-discharge degree, environmental friendliness, and the like, and are widely used in mobile phones, notebook computers, cameras, electric vehicles, and the like. However, in recent years, lithium ion batteries have been developed to meet bottlenecks, the inherent safety problem of the lithium ion batteries brings huge hidden dangers to users, and the conventional lithium ion batteries are close to the capacity density limit of intercalation chemistry, while the lithium sulfur batteries are one of the most effective schemes for improving energy density and meeting people demands under the existing lithium battery system due to the very high abundance of sulfur on the earth and the theoretical capacity of 1675 mAh/g. Four main materials of the lithium battery are respectively a positive electrode, a negative electrode, a diaphragm and electrolyte, and under the condition that the current positive and negative electrode materials cannot bring great improvement, the electrolyte is widely researched as a carrier for ion transmission.
Lithium hexafluorophosphate is mainly used in the current lithium ion battery electrolyte to be dissolved in organic carbonate solvents of Ethylene Carbonate (EC) and dimethyl carbonate (DMC), and the solvents have strong oxidation resistance but poor compatibility with a negative electrode, and are easy to generate dendrites to pierce a diaphragm to cause short circuit. Due to such limitations, ether solvents such as Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) have certain compatibility with the negative electrode and low solubility for polysulfides, and thus can suppress the shuttle effect to a certain extent, and thus are used as commercial electrolyte solvents for lithium sulfur batteries.
In order to develop lithium ion battery electrolyte with more excellent performance and higher safety, a large amount of organic solvents are developed and researched, wherein the fluorinated solvents show wide application prospects by virtue of excellent performance. The outermost layer of the electron orbitals of fluorine atoms has 7 electrons, with strong electronegativity and weaker polarity. The selective fluorination of anions reduces the interaction of anions and cations, thereby improving the dissociation capability of salts in electrolyte solutions, fluorinated organic solvents generally have the characteristics of low freezing point, high flash point and high oxidation resistance, and the fluorination also facilitates the contact between the electrolyte and electrodes, and the importance of fluorine lies not only in the presence of fluorine but also in molecular structure factors which are considered to be functional electrolyte components. Therefore, fluorination is expected to improve the oxidation resistance, flame retardant property and the like of the ether organic solvent, thereby realizing the application of the ether organic solvent in the lithium ion battery. Fluorinated ethers such as 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE) and 1,1, 5-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether (OFE) have been developed, and after the TTE and the OFE are introduced, the combustibility of the electrolyte is remarkably reduced, the safety of the battery is effectively improved, and the wettability of the electrolyte is improved to a certain extent.
Disclosure of Invention
The first technical problem to be solved by the invention is to provide a novel electrolyte.
In order to solve the first technical problem, the electrolyte solution of the present invention includes a solvent and an additive, wherein the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether.
In a specific embodiment, the solvent is at least one of dioxolane, ethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate, and methylethyl carbonate.
In a specific embodiment, the volume ratio of the solvent to the additive is 2-8: 2 to 8.
In a specific embodiment, the electrolyte further contains a lithium salt, and the lithium salt preferably has a lithium ion concentration of 0 to 5 mol/L.
In a specific embodiment, the lithium salt is lithium bistrifluoromethylsulfonyl imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium oxalyldifluoroborate, lithium bistrifluorosulfonimide, and lithium difluorophosphate.
The second technical problem to be solved by the invention is to provide a preparation method of the electrolyte, which comprises the following steps:
(1) drying lithium salt in vacuum at 50-80 ℃ for more than one week, and storing the dried lithium salt in an environment with the water oxygen value less than 0.01 ppm;
(2) uniformly mixing a solvent, an additive and lithium salt in an environment with the water oxygen value less than 0.01ppm, and stirring for 24-48 hours at normal temperature to obtain an electrolyte;
the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether.
In a specific embodiment, the solvent is at least one of dioxolane, ethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate and methylethyl carbonate, and preferably the solvent is: mixing dioxolane and glycol dimethyl ether according to the volume ratio of 1-9: 1-9 in the environment with the water oxygen value of less than 0.01ppm, and stirring for 5-10 min at normal temperature to obtain the composition.
In a specific embodiment, the volume ratio of the solvent to the additive is 2-8: 2 to 8.
In a specific embodiment, the mixing in step (2) is carried out at 20-40 ℃ for 1-2 h.
In a specific embodiment, the lithium salt is added in an amount such that the concentration of lithium ions in the electrolyte is 0 to 5 mol/L; the lithium salt is preferably lithium bistrifluoromethanesulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium oxalyldifluoroborate, lithium bistrifluorosulfonimide and lithium difluorophosphate.
Has the advantages that:
the electrolyte disclosed by the invention is good in affinity to lithium ions, strong in wetting capacity to a diaphragm and strong in thermal stability. The growth of lithium dendrites can be inhibited, and simultaneously, because the dispersion of oxygen and sulfur in the electrolyte is reduced, the dissolution of polysulfide and related shuttle effect are inhibited, and the rate capability and long cycle performance of the battery are greatly improved. The requirements of electronic equipment on high capacity, high multiplying power, long service life and low attenuation of the lithium ion battery are met.
The electrolyte provided by the invention effectively improves the flame retardance of the electrolyte, and finally greatly improves the safety of the battery.
The invention provides a preparation method of electrolyte, which has simple process and easy realization and is easy to realize direct matching with a new improved scheme of an electrode or a diaphragm.
Drawings
FIG. 1: (a) THE contact angle test result graphs of a plurality of groups of home-made electrolytes and commercial electrolytes with different volume contents of THE THE additives in THE embodiment of THE invention are shown; (b) selecting a liquid absorption rate test result graph of a self-made electrolyte and a commercial electrolyte with THE volume content of THE THE additive of 60 vt% in THE embodiment of THE invention;
FIG. 2: THE lithium ion migration number test result graphs of THE self-made electrolyte and THE commercial electrolyte with different volume contents of THE THE additives in THE several groups of THE electrolyte are shown in THE embodiment of THE invention;
FIG. 3: THE self-made electrolyte and THE commercial electrolyte with THE volume content of THE THE additive of 60 vt% in THE embodiment of THE invention are combustion test charts;
FIG. 4: THE lithium iron phosphate half-cell respectively uses a cycle performance and rate performance test chart of a self-made electrolyte and a commercial electrolyte with THE volume content of THE THE additive being 60 vt%;
(a) circulating for 5000 circles under the multiplying power of 10C; (b) testing the multiplying power;
(c) circulating for 50 circles at 0.5C multiplying power; (d) testing the multiplying power;
FIG. 5: THE lithium-sulfur battery respectively uses a cycle performance and rate performance test chart of a self-made electrolyte and a commercial electrolyte with THE volume content of THE THE additive being 60 vt%;
(a) circulating for 100 circles at 0.5C multiplying power; (b) testing the multiplying power; (c) self-discharge testing;
(d) and (5) testing open circuit voltage change.
Detailed Description
In order to solve the first technical problem, the electrolyte solution of the present invention includes a solvent and an additive, wherein the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether.
In a specific embodiment, the solvent is at least one of dioxolane, ethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate, and methylethyl carbonate.
In a specific embodiment, the volume ratio of the solvent to the additive is 2-8: 2 to 8.
In a specific embodiment, the electrolyte further contains a lithium salt, and the lithium salt preferably has a lithium ion concentration of 0 to 5 mol/L.
In a specific embodiment, the lithium salt is lithium bistrifluoromethylsulfonyl imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium oxalyldifluoroborate, lithium bistrifluorosulfonimide, and lithium difluorophosphate.
The second technical problem to be solved by the invention is to provide a preparation method of the electrolyte, which comprises the following steps:
(1) drying lithium salt in vacuum at 50-80 ℃ for more than one week, and storing the dried lithium salt in an environment with the water oxygen value less than 0.01 ppm;
(2) uniformly mixing a solvent, an additive and lithium salt in an environment with the water oxygen value less than 0.01ppm, and stirring for 24-48 hours at normal temperature to obtain an electrolyte;
the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether.
In a specific embodiment, the solvent is at least one of dioxolane, ethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate and methylethyl carbonate, and preferably the solvent is: mixing dioxolane and glycol dimethyl ether according to the volume ratio of 1-9: 1-9 in the environment with the water oxygen value of less than 0.01ppm, and stirring for 5-10 min at normal temperature to obtain the composition.
In a specific embodiment, the volume ratio of the solvent to the additive is 2-8: 2 to 8.
In a specific embodiment, the mixing in step (2) is carried out at 20-40 ℃ for 1-2 h.
In a specific embodiment, the lithium salt is added in an amount such that the concentration of lithium ions in the electrolyte is 0 to 5 mol/L; the lithium salt is preferably lithium bistrifluoromethanesulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium oxalyldifluoroborate, lithium bistrifluorosulfonimide and lithium difluorophosphate.
The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.
Example 1
THE embodiment provides an electrolyte, which includes 1mol/L of lithium salt, 80 vt% by volume of an ether electrolyte solvent and 20 vt% by volume of an additive, wherein THE lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI), THE ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and THE additive is 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether (tee).
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the temperature is 50 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
step 3, under the environment that the water oxygen value is less than 0.01ppm, carrying out the reaction of Dioxolane (DOL) and ethylene glycol dimethyl ether (DME) according to the weight ratio of 1: 1, stirring the solution for 5min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether (THE) into THE ether solvent mixed solution obtained in THE step 3 in an environment with THE water oxygen value less than 0.01ppm, and stirring for 1h at 20 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 80vt percent, and the volume percentage of the fluorinated ether additive is 20vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4 to enable the concentration of lithium ions to be 1mol/L, and stirring at normal temperature for 24 hours to obtain the electrolyte.
Example 2
THE embodiment provides an electrolyte, which includes 1mol/L of lithium salt, 60 vt% by volume of ether electrolyte solvent and 40 vt% by volume of additive, wherein THE lithium salt is lithium bistrifluoromethanesulfonylimide (LiTFSI), THE ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and THE additive is 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether (tee).
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the drying temperature is 80 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
and 3, in an environment with the water oxygen value less than 0.01ppm, mixing two ether electrolyte solvents, namely Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), according to the ratio of 1: 1, stirring the solution for 10min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive into the ether solvent mixed solution obtained in the step 3 in an environment with the water oxygen value less than 0.01ppm, and stirring for 2 hours at 40 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 60vt percent, and the volume percentage of the fluorinated ether additive is 40vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4, and stirring for 48 hours at normal temperature to obtain the electrolyte, wherein the concentration of lithium ions is 1 mol/L.
Example 3
THE embodiment provides an electrolyte, which includes 1mol/L of lithium salt, 40 vt% by volume of ether electrolyte solvent and 60 vt% by volume of additive, wherein THE lithium salt is lithium bistrifluoromethanesulfonylimide (LiTFSI), THE ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and THE additive is 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether (tee).
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the temperature is 70 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
and 3, in an environment with the water oxygen value less than 0.01ppm, mixing two ether electrolyte solvents according to the ratio of 1: 1, stirring for 7min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive into the ether solvent mixed solution obtained in the step 3 in an environment with the water oxygen value less than 0.01ppm, and stirring for 1.5 hours at the temperature of 30 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 40vt percent, and the volume percentage of the fluorinated ether additive is 60vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4, and stirring at normal temperature for 36 hours to obtain the electrolyte, wherein the concentration of lithium ions is 1 mol/L.
Example 4
THE embodiment provides an electrolyte, which includes 1mol/L lithium salt, 20 vt% by volume of an ether electrolyte solvent and 80 vt% by volume of an additive, wherein THE lithium salt is lithium bistrifluoromethanesulfonylimide (LiTFSI), THE ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and THE additive is 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether (tee).
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the temperature is 65 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
and 3, in an environment with the water oxygen value less than 0.01ppm, mixing two ether electrolyte solvents according to the ratio of 1: 1, stirring for 6min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive into the ether solvent mixed solution obtained in the step 3 in an environment with the water oxygen value less than 0.01ppm, and stirring for 1.5 hours at 25 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 20vt percent, and the volume percentage of the fluorinated ether additive is 80vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4, and stirring for 40 hours at normal temperature to obtain the electrolyte, wherein the concentration of lithium ions is 1 mol/L.
Comparative example 1 this example provides an electrolyte comprising 1mol/L of lithium salt, 50 vt% by volume of an ether electrolyte solvent and 50 vt% by volume of an additive, wherein the lithium salt is lithium bistrifluoromethylsulfonimide (LiTFSI), the ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and the additive is 1,1, 5-octafluoropentyl-1, 1,2, 2-tetrafluoroethane (OFE).
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the temperature is 60 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
and 3, in an environment with the water oxygen value less than 0.01ppm, mixing two ether electrolyte solvents according to the ratio of 1: 1, stirring the solution for 10min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive into the ether solvent mixed solution obtained in the step 3 in an environment with the water oxygen value less than 0.01ppm, and stirring for 1.5 hours at 35 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 50vt percent, and the volume percentage of the fluorinated ether additive is 50vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4, and stirring at normal temperature for 36 hours to obtain the electrolyte, wherein the concentration of lithium ions is 1 mol/L.
Comparative example 1
This example provides an electrolyte, including 1mol/L lithium salt, 40 vt% by volume of ether electrolyte solvent, and 60 vt% by volume of additive, where the lithium salt is lithium bistrifluoromethylsulfonyl imide (LiTFSI), the ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and the additive is 1,1, 5-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether (OFE)
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the temperature is 70 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
and 3, in an environment with the water oxygen value less than 0.01ppm, mixing two ether electrolyte solvents according to the ratio of 1: 1, stirring for 7min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive into the ether solvent mixed solution obtained in the step 3 in an environment with the water oxygen value less than 0.01ppm, and stirring for 1.5 hours at the temperature of 30 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 40vt percent, and the volume percentage of the fluorinated ether additive is 60vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4, and stirring at normal temperature for 36 hours to obtain the electrolyte, wherein the concentration of lithium ions is 1 mol/L.
Comparative example 2
THE embodiment provides an electrolyte, which includes 1mol/L of lithium salt, 90 vt% by volume of ether electrolyte solvent and 10 vt% by volume of additive, wherein THE lithium salt is lithium bistrifluoromethanesulfonylimide (LiTFSI), THE ether electrolyte solvent is Dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and THE additive is 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether (tee).
The preparation method of the electrolyte specifically comprises the following steps:
step 1, drying the lithium salt in vacuum for at least one week. Wherein the temperature is 75 ℃;
step 2, storing the dried lithium salt obtained in the step 1 in an environment with the water oxygen value less than 0.01 ppm;
and 3, in an environment with the water oxygen value less than 0.01ppm, mixing two ether electrolyte solvents according to the ratio of 1: 1, stirring for 9min at normal temperature to obtain an ether solvent mixed solution;
step 4, adding a fluorinated ether additive into the ether solvent mixed solution obtained in the step 3 in an environment with the water oxygen value less than 0.01ppm, and stirring for 1 hour at 30 ℃ to uniformly mix to obtain a fluorinated ether solvent; wherein, the volume percentage of the ether solvent mixed solution in the step 3 is 90vt percent, and the volume percentage of the fluorinated ether additive is 10vt percent;
and 5, in an environment with the water oxygen value less than 0.01ppm, adding a certain amount of lithium salt into the fluorinated ether solvent obtained in the step 4, and stirring at normal temperature for 36 hours to obtain the electrolyte, wherein the concentration of lithium ions is 1 mol/L.
FIG. 1: (a) for THE contact angle test result graphs of THE self-made electrolyte and THE commercial electrolyte (namely, THE content of THE THE is 0 vt%) with different volume contents of THE THE additives in THE groups of THE embodiments of THE invention, THE comparison result shows that THE contact angle of THE electrolyte added with THE THE is obviously reduced, which is attributed to that THE introduction of THE fluorinated ether THE reduces THE surface tension of THE electrolyte; (b) selecting a liquid absorption rate test result graph of a self-made electrolyte and a commercial electrolyte with THE volume content of THE THE additive of 60 vt% in THE embodiment of THE invention; THE test result shows that THE electrolyte added with THE THE obviously improves THE wettability with THE diaphragm and is beneficial to improving THE rate capability of THE battery.
FIG. 2: in THE embodiment of THE invention, THE lithium ion migration number test result graphs of THE self-made electrolyte and THE commercial electrolyte (namely THE content of THE THE is 0 vt%) with different THE additive volume contents show that THE lithium ion migration number is gradually increased along with THE increase of THE volume ratio of THE fluorinated ether THE, and THE lithium ion migration number is higher than that of THE commercial electrolyte.
FIG. 3: THE self-made electrolyte and THE commercial electrolyte with THE volume content of THE THE additive of 60 vt% in THE embodiment of THE invention are selected, 200ml of THE two electrolytes are respectively dripped on THE glass fiber membrane for combustion test, and it can be observed from THE figure that THE 60 vt% THE self-made electrolyte can not be ignited, and THE ignited glass fiber membrane has no combustion trace due to fluorine substitution on THE THE alkyl part, so that THE diffusion of oxygen free radicals in THE combustion process is inhibited, and on THE contrary, THE commercial electrolyte burns violently, and THE glass fiber membrane has obvious combustion trace after combustion, which shows that THE introduction of THE fluorinated ether THE can obviously improve THE safety of THE battery.
TABLE 1 test results for electrolytes of examples and comparative examples
Figure BDA0002560171650000081
FIG. 4: lithium iron phosphate half cells (lithium ion cells CR2032 (lithium iron phosphate is used as a positive electrode material, and a lithium plate is used as a negative electrode material)) respectively use a home-made electrolyte with THE volume content of THE THE additive of 60vt percent and a commercial electrolyte (a) to cycle 5000 cycles (b) of multiplying power test under 10C multiplying power. And (C) circulating 50-circle (d) multiplying power test under 0.5C multiplying power of a self-made electrolyte and a commercial electrolyte (C) of which THE volume content of THE THE additive is 60% respectively in THE lithium iron phosphate/lithium titanate full cell (lithium iron phosphate is used as a positive electrode material and lithium titanate is used as a negative electrode material). From THE comparison of THE electrochemical results, it can be seen that THE lithium ion battery using THE THE additive electrolyte has more excellent cycle performance and rate capability.
Table 2 results of performance test of lithium iron phosphate batteries prepared by electrolytes of examples and comparative examples
Figure BDA0002560171650000082
Figure BDA0002560171650000091
FIG. 5: THE method comprises THE steps of (a) circulating 100 circles of a lithium sulfur battery (sulfur is used as a positive electrode material, and a lithium sheet is used as a negative electrode material) by using a self-made electrolyte and a commercial electrolyte respectively, wherein THE volume content of THE THE additive is 60vt percent, (b) carrying out a multiplying factor test at 0.5C, and (C) carrying out a self-discharge test, and (d) carrying out an open-circuit voltage change test. From THE comparison of THE electrochemical results, it can be seen that THE lithium-sulfur battery using THE che additive electrolyte has more excellent cycle performance and rate performance, and a lower self-discharge rate.

Claims (10)

1. The electrolyte is characterized by comprising a solvent and an additive, wherein the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether.
2. The electrolyte of claim 1, wherein the solvent is at least one of dioxolane, ethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate, and methylethyl carbonate.
3. The electrolyte according to claim 1 or 2, wherein the volume ratio of the solvent to the additive is 2-8: 2 to 8.
4. The electrolyte according to any one of claims 1 to 3, wherein the electrolyte further comprises a lithium salt, preferably wherein the lithium salt has a lithium ion concentration of 0 to 5 mol/L.
5. The electrolyte of claim 4, wherein the lithium salt is lithium bistrifluoromethanesulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium oxalyldifluoroborate, lithium bisfluorosulfonylimide, and lithium difluorophosphate.
6. A method of preparing an electrolyte, the method comprising:
(1) drying lithium salt in vacuum at 50-80 ℃ for more than one week, and storing the dried lithium salt in an environment with the water oxygen value less than 0.01 ppm;
(2) uniformly mixing a solvent, an additive and lithium salt in an environment with the water oxygen value less than 0.01ppm, and stirring for 24-48 hours at normal temperature to obtain an electrolyte;
the solvent is at least one of ethers and carbonates, and the additive is at least one of 2,2, 2-trifluoroethyl-1, 1,2,3,3, 3-hexafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2,3,3, 3-pentafluoropropyl difluoromethyl ether.
7. The method for preparing the electrolyte according to claim 6, wherein the solvent is at least one of dioxolane, ethylene glycol dimethyl ether, propylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate, and preferably the solvent is: mixing dioxolane and glycol dimethyl ether according to the volume ratio of 1-9: 1-9 in the environment with the water oxygen value of less than 0.01ppm, and stirring for 5-10 min at normal temperature to obtain the composition.
8. The method for preparing the electrolyte according to claim 6 or 7, wherein the volume ratio of the solvent to the additive is 2-8: 2 to 8.
9. The method for preparing the electrolyte according to any one of claims 6 to 8, wherein the mixing in (2) is performed at 20 to 40 ℃ for 1 to 2 hours with stirring.
10. The method of preparing the electrolyte according to any one of claims 6 to 9, wherein the lithium salt is added in an amount such that the lithium ion concentration in the electrolyte is 0 to 5 mol/L; the lithium salt is preferably lithium bistrifluoromethanesulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium oxalyldifluoroborate, lithium bistrifluorosulfonimide and lithium difluorophosphate.
CN202010603868.6A 2020-06-29 2020-06-29 Electrolyte and preparation method thereof Pending CN111584936A (en)

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