Lithium ion battery electrolyte and preparation method thereof

Abstract

The invention discloses a lithium ion battery electrolyte and a preparation method thereof. The lithium ion battery electrolyte comprises the following raw materials in parts by weight: 85-95 parts of an organic solvent, 15-25 parts of lithium salt, 1-2 parts of an additive A and 1-2 parts of an additive B. The synthesized additive A contains acylamino, a thiourea structure, trifluoromethyl and the like. Hydrofluoric acid and trace water in the electrolyte are removed by acylamino, formation of lithium dendrites is inhibited by a thiourea structure, and trifluoromethyl forms a solid electrolyte phase (SEI) film prior to the electrolyte, so that the electrolyte is protected. The synthesized additive B contains an allyl phenyl sulfone structure, an amide group and a siloxane structure. The allyl phenyl sulfone structure is beneficial to formation of an SEI film with excellent lithium ion diffusion dynamics performance; and a siloxane structure is beneficial to formation of SEI which is thinner, lower in impedance, rich in LiF and extremely high in thermal stability, so that continuous loss of metal lithium is prevented. The electrolyte provided by the invention enables the battery to have excellent cycle performance and high capacity retention rate.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a lithium-ion battery electrolyte and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in electronic products due to their high specific energy, no memory effect, small size, light weight, short charging time, long cycle life and other characteristics. However, with the continuous development of technology, users have put forward higher requirements for the cycle performance, fast charge and discharge ability and environmental adaptability of lithium batteries, and the impedance of lithium-ion batteries is an important indicator to measure the excellent performance of the above. Generally speaking, by adding functional additives to the electrolyte of lithium-ion batteries and adjusting the composition of the solid electrolyte interphase (SEI) film to make it more conducive to the penetration of lithium ions, the impedance of lithium-ion batteries can be effectively reduced, thereby improving the cycle performance of lithium-ion batteries. However, since the electrolyte of lithium-ion batteries uses fluorinated lithium salts such as lithium hexafluorophosphate as electrolytes, hydrofluoric acid will inevitably be introduced into the lithium-ion batteries. During the storage and use of the electrolyte, the content of hydrofluoric acid will increase. When the content of hydrofluoric acid in the lithium-ion battery exceeds a certain concentration, it will consume the active lithium ions on the surface of the negative electrode and also corrode the positive electrode material, resulting in an increase in the impedance of the lithium-ion battery and a decline in the cycle performance. In view of this, it is necessary to develop new additives to improve the comprehensive performance of the electrolyte to meet the use requirements. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a lithium-ion battery electrolyte and a preparation method thereof.

[0004] The object of the present invention can be achieved by the following technical solutions: A lithium-ion battery electrolyte, comprising the following raw materials in parts by weight: 85-95 parts of an organic solvent, 15-25 parts of a lithium salt, 1-2 parts of additive A and 1-2 parts of additive B.

[0005] The organic solvent is prepared by mixing ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile in a volume ratio of 1:1:1:1:1.

[0006] The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium hexafluorophosphate in the lithium-ion battery electrolyte is 0.90-1.10 mol / L.

[0007] The additive A is prepared by the following steps: Step A1: Add 3-(1H-imidazol-1-yl)propanoic acid into DMF, add thionyl chloride under stirring, reflux and stir the reaction at 50 °C for 4 - 5 h, filter, extract, and dry to obtain Intermediate 1. The dosage ratio of 3-(1H-imidazol-1-yl)propanoic acid, DMF, and thionyl chloride is 0.1 mol : 150 mL : 0.2 - 0.3 mol; During the reaction, 3-(1H-imidazol-1-yl)propanoic acid reacts with thionyl chloride to form Intermediate 1, and the structure of Intermediate 1 is shown as follows:

[0008] Step A2: Add N-(2-hydroxyethyl)-N ， -2-propenylthiourea, potassium carbonate, and dimethyl sulfoxide into a flask to obtain mixture a, and then add Intermediate 1 into dimethyl sulfoxide to obtain mixture b. Under an ice bath at 0 °C, slowly add mixture b dropwise to mixture a. After the addition is complete, raise the temperature to 40 °C and keep the temperature constant for reaction for 8 - 10 h, then perform vacuum distillation to obtain Intermediate 2. The dosage ratio of Intermediate 1, N-(2-hydroxyethyl)-N ， -2-propenylthiourea, potassium carbonate, and dimethyl sulfoxide is 0.1 mol : 0.1 mol : 0.01 - 0.015 mol : 100 mL; During the reaction, N-(2-hydroxyethyl)-N ， -2-propenylthiourea reacts with Intermediate 1 to form an esterification product, namely Intermediate 2, and the structure of Intermediate 2 is shown as follows:

[0009] Step A3: Add Intermediate 2 and 3-chloropropionamide into acetonitrile. Under nitrogen protection, start stirring, stir at 50 °C for 30 - 35 min, then raise the temperature to 75 - 80 °C and keep the temperature constant for reaction for 72 h. Cool to room temperature, extract with acetonitrile, and then perform vacuum drying at 80 °C for 2 - 2.5 h to obtain Intermediate 3. The dosage ratio of Intermediate 2, 3-chloropropionamide, and acetonitrile is 0.1 mol : 0.1 mol : 120 - 130 mL; During the reaction, Intermediate 2 reacts with 3-chloropropionamide to form Intermediate 3, and the structure of Intermediate 3 is shown as follows:

[0010] Step A4: Add intermediate 3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) into deionized water, stir and react at room temperature for 2.5 - 3 h to obtain a reaction solution. The reaction solution is divided into upper and lower layers. Wash the reaction solution with deionized water until no white turbidity is produced when the upper layer is detected with silver nitrate solution, then separate the lower layer liquid. The lower layer liquid is subjected to reduced pressure distillation and vacuum dried at 70 - 80 °C for 48 - 72 h to obtain an additive. The dosage ratio of intermediate 3, lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) and deionized water is 0.1 mol : 0.1 mol : 120 - 130 mL, and the molar concentration of the silver nitrate solution is 0.1 mol / L.

[0011] During the reaction process, intermediate 3 and lithium bis(trifluoromethanesulfonyl)imide react to generate a multifunctional ionic liquid additive A. Additive A contains an amide group, a thiourea structure, a trifluoromethyl group, etc. The amide group is a basic group that can combine with hydrofluoric acid and trace water in the electrolyte, enabling additive A to have the ability to remove hydrofluoric acid and trace water. Different from traditional electrolyte additives, the thiourea group exhibits a catalytic effect in lithium metal plating. It only adsorbs on the surface of the lithium metal, promotes the deposition of lithium ions, and does not react and decompose with the lithium metal, ensuring the stability of additive A to exert its efficacy. The electrolyte additive A containing a trifluoromethyl group can preferentially form a solid electrolyte interphase (SEI) rich in LiF at the negative electrode prior to the electrolyte, making additive A contribute to the construction of a strong and stable interfacial film.

[0012] The structure of additive A is as follows:

[0013] The said additive B is prepared through the following steps: Step B1: Add p-chloromethylbenzoic acid into DMF, add thionyl chloride under stirring, reflux and stir at 50 °C for 4 - 5 h, filter, extract, and dry to obtain intermediate a. The dosage ratio of p-chloromethylbenzoic acid, DMF and thionyl chloride is 0.1 mol : 160 mL : 0.2 - 0.3 mol; During the reaction process, p-chloromethylbenzoic acid reacts with thionyl chloride to generate intermediate a. The structure of intermediate a is as follows:

[0014] Step B2: Add 3-aminopropyltriethoxysilane, potassium carbonate, and dimethyl sulfoxide into a flask to obtain mixture c. Then add intermediate a into dimethyl sulfoxide to obtain mixture d. Under an ice-water bath at 0 °C, slowly drip mixture d into mixture c. After the dripping is completed, raise the temperature to 40 °C and carry out a constant-temperature reaction for 8 - 10 h. Then perform vacuum distillation to obtain intermediate b. The dosage ratio of intermediate a, 3-aminopropyltriethoxysilane, potassium carbonate, and dimethyl sulfoxide is 0.1 mol : 0.1 mol : 0.01 - 0.015 mol : 120 mL; During the reaction process, 3-aminopropyltriethoxysilane reacts with intermediate a to generate an amidation product, namely intermediate b. The structure of intermediate b is as follows:

[0015] Step B3: Add 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF, and THF into a flask, stir at room temperature for 0.5 - 1 h, then add intermediate b, and stir and react at 50 °C for 4 - 5 h. Wash with deionized water and extract with chloroform to obtain additive B. The dosage ratio of intermediate b, 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF, and THF is 0.01 mol : 0.01 - 0.015 mol : 4.6 g : 1.6 g : 30 mL : 15 mL; During the reaction process, 2-(2-butene sulfonyl)phenol reacts with intermediate 2 to generate an etherification product, namely additive B. The molecule of additive B contains an allyl phenyl sulfone structure, an amide group, and a siloxane structure. The allyl phenyl sulfone structure enables additive B to contribute to the formation of a dense and firm solid electrolyte interphase (SEI) film; the amide group can combine with trace amounts of water and acid in the electrolyte, enabling additive B to have the ability to remove trace amounts of water and acid; the siloxane structure enables additive B to form a siloxane network on the surface, improving the thermal stability of additive B.

[0016] The structure of additive B is as follows:

[0017] Advantages of the present invention: The lithium-ion battery electrolyte prepared by the present invention includes organic solvents, lithium salts, additive A, and additive B as raw materials. The synthesized additive A molecule contains an amide group, a thiourea structure, a trifluoromethyl group, etc. The amide group is a basic group that can combine with hydrofluoric acid and trace water in the electrolyte, thereby removing hydrofluoric acid and trace water, avoiding damage to the solid electrolyte interphase (SEI) film caused by hydrofluoric acid, resulting in shortened battery life, and being beneficial to solving the problems of increased impedance and decreased cycle performance of lithium-ion batteries; different from traditional electrolyte additives, the thiourea group exhibits a catalytic effect in lithium metal plating, only adsorbing on the surface of the lithium metal, promoting lithium ion deposition, and not reacting with the lithium metal and decomposing. At an ultra-high current density, the battery can stably cycle, effectively inhibit dendrite formation, and maintain a high battery capacity; the additive A containing a trifluoromethyl group can preferentially form a solid electrolyte interphase (SEI) rich in lithium fluoride at the negative electrode prior to the electrolyte, which will help build a strong and stable interfacial film and prevent further reaction between the electrolyte and the lithium metal, preventing the occurrence of electrolyte depletion and continuous loss of active lithium.

[0018] The synthesized additive B molecule contains an allyl phenyl sulfone structure, an amide group, and a siloxane structure. The allyl phenyl sulfone structure helps to form a dense and strong SEI film, and the formed SEI film has high mechanical strength and excellent lithium ion diffusion kinetics performance, which can effectively inhibit parasitic side reactions at the electrode-electrolyte interface; the amide group can remove trace water and acid in the electrolyte, further improving the interfacial stability of the SEI film; the siloxane structure enables additive B to form a siloxane network on the surface, forming a thinner, lower impedance, LiF-rich, and extremely thermally stable SEI, thereby preventing continuous reaction between metallic lithium and the electrolyte, and enabling the battery to exhibit good reversible capacity and cycle stability. Detailed implementation manners

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0020] An additive A is prepared by the following steps: Step A1: Add 3-(1H-imidazol-1-yl)propionic acid to DMF, add thionyl chloride under stirring, reflux and stir at 50 °C for 4 h, filter, extract, and dry to obtain intermediate 1. The dosage ratio of 3-(1H-imidazol-1-yl)propionic acid, DMF, and thionyl chloride is 0.1 mol: 150 mL: 0.2 mol; Step A2: Add N-(2-hydroxyethyl)-N ， -2-propenylthiourea, potassium carbonate and dimethyl sulfoxide into a flask to obtain a mixed solution a. Then add Intermediate 1 into the dimethyl sulfoxide solution to obtain a mixed solution b. Under an ice-water bath at 0 °C, slowly add the mixed solution b dropwise to the mixed solution a. After the addition is complete, raise the temperature to 40 °C and carry out a constant-temperature reaction for 8 h. Then carry out reduced-pressure distillation to obtain Intermediate 2. The dosage ratio of Intermediate 1, N-(2-hydroxyethyl)-N ， -2-propenylthiourea, potassium carbonate and dimethyl sulfoxide is 0.1 mol:0.1 mol:0.01 mol:100 mL; Step A3: Add Intermediate 2 and 3-chloropropionamide into acetonitrile. Under nitrogen protection, start stirring and stir at 50 °C for 30 min. Then raise the temperature to 75 °C and carry out a constant-temperature stirring reaction for 72 h. Cool to room temperature, extract with acetonitrile, and then carry out vacuum drying at 80 °C for 2 h to obtain Intermediate 3. The dosage ratio of Intermediate 2, 3-chloropropionamide and acetonitrile is 0.1 mol:0.1 mol:120 mL; Step A4: Add Intermediate 3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) into deionized water. Stir and react at room temperature for 2.5 h to obtain a reaction solution. The reaction solution is divided into upper and lower layers. Wash the reaction solution with deionized water until no white turbidity appears when the upper layer is detected with silver nitrate solution. Then separate the lower layer liquid. After the lower layer liquid is subjected to reduced-pressure distillation and vacuum drying at 70 °C for 48 h, Additive A is obtained. The dosage ratio of Intermediate 3, lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) and deionized water is 0.1 mol:0.1 mol:120 mL, and the molar concentration of the silver nitrate solution is 0.1 mol / L. Example

[0021] An Additive A is prepared by the following steps: Step A1: Add 3-(1H-imidazol-1-yl)propionic acid into DMF, add thionyl chloride under stirring, and carry out a reflux stirring reaction at 50 °C for 4.5 h. Then filter, extract and dry to obtain Intermediate 1. The dosage ratio of 3-(1H-imidazol-1-yl)propionic acid, DMF and thionyl chloride is 0.1 mol:150 mL:0.25 mol; Step A2: Add N-(2-hydroxyethyl)-N ， -2-propenylthiourea, potassium carbonate and dimethyl sulfoxide into a flask to obtain a mixed solution a. Then add Intermediate 1 into the dimethyl sulfoxide solution to obtain a mixed solution b. Under an ice-water bath at 0 °C, slowly add the mixed solution b dropwise to the mixed solution a. After the addition is complete, raise the temperature to 40 °C and carry out a constant-temperature reaction for 9 h. Then carry out reduced-pressure distillation to obtain Intermediate 2. The dosage ratio of Intermediate 1, N-(2-hydroxyethyl)-N ，The dosage ratio of -2-propenylthiourea, potassium carbonate and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.012 mol: 100 mL; Step A3: Add intermediate 2 and 3-chloropropionamide into acetonitrile. Under nitrogen protection, start stirring, stir at 50 °C for 32 min, then raise the temperature to 75 °C, and stir and react at a constant temperature for 72 h. Cool to room temperature, extract with acetonitrile, and then vacuum dry at 80 °C for 2.2 h to obtain intermediate 3. The dosage ratio of intermediate 2, 3-chloropropionamide and acetonitrile is 0.1 mol: 0.1 mol: 125 mL; Step A4: Add intermediate 3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) into deionized water. Stir and react at room temperature for 2.8 h to obtain a reaction solution. The reaction solution is divided into upper and lower layers. Wash the reaction solution with deionized water until no white turbidity appears when the upper layer is detected with silver nitrate solution. Then separate the lower layer liquid. After the lower layer liquid is distilled under reduced pressure and vacuum dried at 75 °C for 60 h, additive A is obtained. The dosage ratio of intermediate 3, lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) and deionized water is 0.1 mol: 0.1 mol: 125 mL, and the molar concentration of the silver nitrate solution is 0.1 mol / L. Example

[0022] An additive A is prepared by the following steps: Step A1: Add 3-(1H-imidazol-1-yl)propionic acid into DMF, add thionyl chloride under stirring, and reflux and stir at 50 °C for 5 h. Filter, extract, and dry to obtain intermediate 1. The dosage ratio of 3-(1H-imidazol-1-yl)propionic acid, DMF and thionyl chloride is 0.1 mol: 150 mL: 0.3 mol; Step A2: Add N-(2-hydroxyethyl)-N,-2-propenylthiourea, potassium carbonate and dimethyl sulfoxide into a flask to obtain a mixed solution a, and then add intermediate 1 into a dimethyl sulfoxide solution to obtain a mixed solution b. Under an ice-water bath at 0 °C, slowly drop the mixed solution b into the mixed solution a. After dropping, raise the temperature to 40 °C and react at a constant temperature for 10 h. Distill under reduced pressure to obtain intermediate 2. The dosage ratio of intermediate 1, N-(2-hydroxyethyl)-N,-2-propenylthiourea, potassium carbonate and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.015 mol: 100 mL; Step A3: Add intermediate 2 and 3-chloropropionamide into acetonitrile. Under nitrogen protection, start stirring, stir at 50 °C for 35 min, then raise the temperature to 80 °C, and stir and react at a constant temperature for 72 h. Cool to room temperature, extract with acetonitrile, and then vacuum dry at 80 °C for 2.5 h to obtain intermediate 3. The dosage ratio of intermediate 2, 3-chloropropionamide and acetonitrile is 0.1 mol: 0.1 mol: 130 mL; Step A4: Add intermediate 3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) into deionized water, stir the reaction at room temperature for 3 h to obtain a reaction solution. The reaction solution is divided into upper and lower layers. Wash the reaction solution with deionized water until no white turbidity is produced when the upper layer is detected with silver nitrate solution. Then separate the lower layer liquid. The lower layer liquid is subjected to reduced pressure distillation and vacuum drying at 80 °C for 72 h to obtain additive A. The dosage ratio of intermediate 3, lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) and deionized water is 0.1 mol: 0.1 mol: 130 mL, and the molar concentration of the silver nitrate solution is 0.1 mol / L. Example

[0023] An additive B is prepared by the following steps: Step B1: Add p-chloromethylbenzoic acid into DMF, add thionyl chloride under stirring, reflux and stir the reaction at 50 °C for 4 h, filter, extract, and dry to obtain intermediate a. The dosage ratio of p-chloromethylbenzoic acid, DMF and thionyl chloride is 0.1 mol: 160 mL: 0.2 mol; Step B2: Add 3-aminopropyltriethoxysilane, potassium carbonate and dimethyl sulfoxide into a flask to obtain a mixed solution c, and then add intermediate a into dimethyl sulfoxide to obtain a mixed solution d. Under an ice bath at 0 °C, slowly drop the mixed solution d into the mixed solution c. After the dropping is completed, raise the temperature to 40 °C and keep the temperature constant for reaction for 8 h, and then perform reduced pressure distillation to obtain intermediate b. The dosage ratio of intermediate a, 3-aminopropyltriethoxysilane, potassium carbonate and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.01 mol: 120 mL; Step B3: Add 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF and THF into a flask, stir at room temperature for 0.5 h, then add intermediate b, and stir the reaction at 50 °C for 4 h. Wash with deionized water and extract with chloroform to obtain additive B. The dosage ratio of intermediate b, 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF and THF is 0.01 mol: 0.01 mol: 4.6 g: 1.6 g: 30 mL: 15 mL. Example

[0024] An additive B is prepared by the following steps: Step B1: Add p-chloromethylbenzoic acid into DMF, add thionyl chloride under stirring, reflux and stir the reaction at 50 °C for 4.5 h, filter, extract, and dry to obtain intermediate a. The dosage ratio of p-chloromethylbenzoic acid, DMF and thionyl chloride is 0.1 mol: 160 mL: 0.25 mol; Step B2: Add 3-aminopropyltriethoxysilane, potassium carbonate, and dimethyl sulfoxide into a flask to obtain mixture c. Then add intermediate a into dimethyl sulfoxide to obtain mixture d. Under an ice bath at 0 °C, slowly add mixture d dropwise to mixture c. After the addition is complete, raise the temperature to 40 °C and carry out a constant-temperature reaction for 9 h. Then perform vacuum distillation to obtain intermediate b. The dosage ratio of intermediate a, 3-aminopropyltriethoxysilane, potassium carbonate, and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.012 mol: 120 mL; Step B3: Add 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF, and THF into a flask and stir at room temperature for 0.8 h. Then add intermediate b and stir and react at 50 °C for 4.5 h. Wash with deionized water and extract with chloroform to obtain additive B. The dosage ratio of intermediate b, 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF, and THF is 0.01 mol: 0.012 mol: 4.6 g: 1.6 g: 30 mL: 15 mL. Example

[0025] An additive B is prepared through the following steps: Step B1: Add p-chloromethylbenzoic acid into DMF, add thionyl chloride with stirring, and reflux and stir at 50 °C for 5 h. Then filter, extract, and dry to obtain intermediate a. The dosage ratio of p-chloromethylbenzoic acid, DMF, and thionyl chloride is 0.1 mol: 160 mL: 0.3 mol; Step B2: Add 3-aminopropyltriethoxysilane, potassium carbonate, and dimethyl sulfoxide into a flask to obtain mixture c. Then add intermediate a into dimethyl sulfoxide to obtain mixture d. Under an ice bath at 0 °C, slowly add mixture d dropwise to mixture c. After the addition is complete, raise the temperature to 40 °C and carry out a constant-temperature reaction for 10 h. Then perform vacuum distillation to obtain intermediate b. The dosage ratio of intermediate a, 3-aminopropyltriethoxysilane, potassium carbonate, and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.015 mol: 120 mL; Step B3: Add 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF, and THF into a flask and stir at room temperature for 1 h. Then add intermediate b and stir and react at 50 °C for 5 h. Wash with deionized water and extract with chloroform to obtain additive B. The dosage ratio of intermediate b, 2-(2-butene sulfonyl)phenol, potassium carbonate, potassium iodide, DMF, and THF is 0.01 mol: 0.015 mol: 4.6 g: 1.6 g: 30 mL: 15 mL. Example

[0026] A lithium-ion battery electrolyte comprises the following raw materials in parts by weight: 85 parts of an organic solvent, 15 parts of a lithium salt, 1 part of additive A, and 1 part of additive B; the organic solvent is prepared from ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile in a volume ratio of 1:1:1:1:1; the lithium salt is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the lithium-ion battery electrolyte is 0.90 mol / L; The lithium-ion battery electrolyte is prepared by the following steps: Lithium hexafluorophosphate is vacuum dried at 80 °C for 4 h and then the dried lithium hexafluorophosphate is reserved for use; under the conditions of less than 1 ppm of water and less than 1 ppm of oxygen in an argon glove box, ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile are fully mixed in a volume ratio of 1:1:1:1:1 to obtain an organic solvent, and then the dried lithium hexafluorophosphate is dissolved in the organic solvent, and then additive A obtained in Example 1 and additive B obtained in Example 4 are added thereto, and after stirring for 15 min, the lithium-ion battery electrolyte is obtained. Example

[0027] A lithium-ion battery electrolyte comprises the following raw materials in parts by weight: 90 parts of an organic solvent, 20 parts of a lithium salt, 1.5 parts of additive A, and 1.5 parts of additive B; the organic solvent is prepared from ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile in a volume ratio of 1:1:1:1:1; the lithium salt is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the lithium-ion battery electrolyte is 1.00 mol / L; The lithium-ion battery electrolyte is prepared by the following steps: Lithium hexafluorophosphate is vacuum dried at 80 °C for 4.2 h and then the dried lithium hexafluorophosphate is reserved for use; under the conditions of less than 1 ppm of water and less than 1 ppm of oxygen in an argon glove box, ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile are fully mixed in a volume ratio of 1:1:1:1:1 to obtain an organic solvent, and then the dried lithium hexafluorophosphate is dissolved in the organic solvent, and then additive A obtained in Example 2 and additive B obtained in Example 5 are added thereto, and after stirring for 18 min, the lithium-ion battery electrolyte is obtained. Example

[0028] A lithium-ion battery electrolyte includes the following raw materials in parts by weight: 95 parts of an organic solvent, 25 parts of a lithium salt, 2 parts of additive A, and 2 parts of additive B; the organic solvent is prepared from ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile in a volume ratio of 1:1:1:1:1; the lithium salt is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the lithium-ion battery electrolyte is 1.10 mol / L. The lithium-ion battery electrolyte is prepared by the following steps: After vacuum drying lithium hexafluorophosphate at 80 °C for 4.5 h, the dried lithium hexafluorophosphate is reserved. In an argon glove box under the conditions of moisture less than 1 ppm and oxygen less than 1 ppm, ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone, and succinonitrile are fully mixed in a volume ratio of 1:1:1:1:1 to obtain an organic solvent. Then, the dried lithium hexafluorophosphate is dissolved in the organic solvent, and then additive A obtained in Example 3 and additive B obtained in Example 6 are added thereto. After stirring for 20 min, the lithium-ion battery electrolyte is obtained.

[0029] Comparative Example 1 This comparative example is a commercially available lithium-ion battery electrolyte.

[0030] Comparative Example 2 Compared with Example 6, thiourea is used instead of additive A, and the others are exactly the same as in Example 9 to prepare a lithium-ion battery electrolyte.

[0031] Comparative Example 3 Compared with Example 9, 2-(2-butene sulfonyl)phenol is used instead of additive B, and the others are exactly the same as in Example 9 to prepare a lithium-ion battery electrolyte.

[0032] The lithium-ion battery electrolyte prepared by the present invention is further subjected to an effect test, and the test results are as follows.

[0033] To test the lithium-ion battery electrolyte prepared by the present invention, the lithium-ion battery electrolytes of each example and comparative example are applied to a lithium-ion battery, and the capacity retention rates of the battery are measured at 25 °C and a 5.0 C rate for 650 cycles and at 25 °C and a 1.0 C rate for 800 cycles. The results are shown in Table 1.

[0034] Table 1:

[0035] According to the data in Table 1, comparing Examples 7, 8 and 9 with Comparative Example 1, it can be seen that compared with the commercially available lithium-ion battery electrolyte, the lithium-ion battery electrolyte prepared by the present invention is applied to a lithium-ion battery, making the lithium-ion battery have excellent cycle performance and capacity retention rate; comparing Example 9 with Comparative Example 2, it can be seen that when additive A is replaced with thiourea and the trifluoromethyl group is missing, the SEI film cannot be formed preferentially and rapidly over the electrolyte, and the cycle performance and capacity retention rate of the battery cannot be effectively improved; comparing Example 9 with Comparative Example 3, it can be seen that when additive B is replaced with 2-(2-butene sulfonyl)phenol and the siloxane structure is missing, the siloxane network cannot be formed, and the thermal stability of the SEI film decreases, so it is not conducive to the cycle stability and capacity retention rate of the battery.

[0036] The above content is only an example and illustration of the concept of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by this claim book, they should all belong to the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The invention comprises the following raw materials in parts by weight: 85-95 parts of an organic solvent, 15-25 parts of a lithium salt, 1-2 parts of an additive A and 1-2 parts of an additive B; the organic solvent is ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone and succinonitrile prepared in a volume ratio of 1:1:1:1:1; the lithium salt is lithium hexafluorophosphate, and the concentration of the lithium hexafluorophosphate in the lithium ion battery electrolyte is 0.90-1.10 mol / L; The additive A is prepared by the following steps: Step A1: Add 3-(1H-imidazol-1-yl)propionic acid to DMF, add dichlorothionyl under stirring, reflux and stir at 50°C for 4-5h, filter, extract and dry to obtain intermediate 1; Step A2: Add N-(2-hydroxyethyl)-N'-2-propenylthiourea, potassium carbonate and dimethyl sulfoxide into a flask to obtain a mixed solution a, then add the intermediate 1 into dimethyl sulfoxide to obtain a mixed solution b, slowly dropwise add the mixed solution b into the mixed solution a in a 0°C ice-water bath, after the dropwise addition is completed, heat to 40°C, react at a constant temperature for 8-10 hours, and distill under reduced pressure to obtain the intermediate 2; Step A3: Add intermediate 2, 3-chloropropionamide to acetonitrile, start stirring under nitrogen protection, stir at 50°C for 30-35min, then raise the temperature to 75-80°C, stir and react at constant temperature for 72h, cool to room temperature, extract with acetonitrile, and then vacuum dry at 80°C for 2-2.5h to obtain intermediate 3; Step A4: Add intermediate 3 and lithium bis(trifluoromethanesulfonyl)imide into deionized water, stir and react at room temperature for 2.5-3h to obtain a reaction solution, which is divided into an upper and lower layer. The reaction solution is washed with deionized water until the upper layer is free of white turbidity after detection with a silver nitrate solution, and the lower layer of liquid is separated. The lower layer of liquid is subjected to reduced pressure distillation and vacuum drying at 70-80°C for 48-72h to obtain additive A.

2. A lithium ion battery electrolyte according to claim 1, characterized in that: The additive B is prepared by the following steps: Step B1: Add p-chloromethylbenzoic acid to DMF, add dichlorothionyl under stirring, reflux and stir at 50°C for 4-5h, filter, extract and dry to obtain intermediate a; Step B2: Add 3-aminopropyltriethoxysilane, potassium carbonate and dimethyl sulfoxide into a flask to obtain a mixed solution c, then add the intermediate a into dimethyl sulfoxide to obtain a mixed solution d, slowly dropwise add the mixed solution d into the mixed solution c in a 0°C ice-water bath, after the dropwise addition is completed, heat to 40°C, react at a constant temperature for 8-10 hours, and distill under reduced pressure to obtain the intermediate b; Step B3: Add 2-(2-butenesulfonyl)phenol, potassium carbonate, potassium iodide, DMF and THF into a flask, stir at room temperature for 0.5-1h, then add intermediate b, stir and react at 50°C for 4-5h, wash with deionized water, and extract with chloroform to obtain additive B.

3. A lithium ion battery electrolyte according to claim 1, characterized in that: In step A1, the usage ratio of 3-(1H-imidazol-1-yl)propionic acid, DMF and thionyl chloride is 0.1 mol:150 mL:0.2-0.3 mol.

4. A lithium ion battery electrolyte according to claim 1, characterized in that: In step A2, the usage ratio of intermediate 1, N-(2-hydroxyethyl)-N'-2-propenylthiourea, potassium carbonate and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.01-0.015 mol: 100 mL.

5. The lithium ion battery electrolyte according to claim 1, characterized in that: In step A3, the usage ratio of the intermediate 2,3-chloropropionamide and acetonitrile is 0.1 mol:0.1 mol:120-130 mL.

6. A lithium ion battery electrolyte according to claim 1, characterized in that: In step A4, the usage ratio of intermediate 3, lithium bis(trifluoromethanesulfonyl)imide and deionized water is 0.1 mol:0.1 mol:120-130 mL, and the molar concentration of the silver nitrate solution is 0.1 mol / L.

7. A lithium ion battery electrolyte according to claim 2, characterized in that: In step B1, the usage ratio of p-chloromethylbenzoic acid, DMF and dichlorothionyl is 0.1 mol:160 mL:0.2-0.3 mol.

8. A lithium ion battery electrolyte according to claim 2, characterized in that: In step B2, the usage ratio of intermediate a, 3-aminopropyltriethoxysilane, potassium carbonate and dimethyl sulfoxide is 0.1 mol: 0.1 mol: 0.01-0.015 mol: 120 mL.

9. A lithium ion battery electrolyte according to claim 2, characterized in that: In step B3, the usage ratio of intermediate b, 2-(2-butenesulfonyl)phenol, potassium carbonate, potassium iodide, DMF and THF is 0.01 mol: 0.01-0.015 mol: 4.6 g: 1.6 g: 30 mL: 15 mL.

10. The method for preparing a lithium ion battery electrolyte according to claim 1, characterized in that: Prepared by the following steps: The lithium hexafluorophosphate is vacuum dried at 80° C. for 4-4.5 hours to obtain dry lithium hexafluorophosphate for standby use; in an argon glove box, under the conditions of less than 1 ppm of moisture and less than 1 ppm of oxygen, ethylene carbonate, diethyl carbonate, ethyl acetate, 1,3-propane sultone and succinonitrile are fully mixed in a volume ratio of 1:1:1:1:1 to obtain an organic solvent, the dry lithium hexafluorophosphate is dissolved in the organic solvent, and then additives A and additive B are added thereto, and after stirring for 15-20 minutes, a lithium ion battery electrolyte is obtained.

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