Electrolyte and lithium ion battery

Abstract

The application discloses an electrolyte and a lithium ion battery, wherein the electrolyte comprises a lithium salt, a nonaqueous organic solvent, and a 2,4-dimercapto pyrimidine alkali metal salt additive; the 2,4-dimercapto pyrimidine alkali metal salt additive comprises at least one of a structural formula I and a structural formula II; wherein M is an alkali metal cation. ⊕ The 2,4-dimercapto pyrimidine alkali metal salt additive of the application contains a 2,4-dimercapto pyrimidine anion with stable structure, so that the additive has excellent thermal stability below 500 DEG C; meanwhile, the additive contains two exposed nitrogen and sulfur atoms, and has strong bonding capacity with metal ions, so that the additive can also prevent the structure of a positive electrode material from being destroyed under high temperature and high voltage; in addition, the additive participates in the formation of an SEI film in the formation stage of the battery, so that the SEI film is more stable. Therefore, the electrolyte of the application can improve the high-temperature storage and high-temperature fast-charging cycle performance of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to an electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, aerospace, military, power tools, and electric vehicles due to their high energy density, long lifespan, and environmental friendliness. However, with the growing market demand for energy storage devices with higher energy density, the requirements for the energy density of lithium-ion batteries are becoming increasingly stringent.

[0003] Lithium cobalt oxide batteries were first developed by Sony in 1990. As the positive electrode of lithium-ion batteries, lithium cobalt oxide possesses advantages such as high specific capacity, high mass and volumetric energy density. In particular, when the charging cutoff voltage is increased from 4.2V to 4.5V, the specific capacity of lithium cobalt oxide can increase by more than 25%. Therefore, developing high-voltage lithium cobalt oxide has become one of the important paths to improve energy density. However, a series of problems have been encountered in the development of high-voltage lithium cobalt oxide. Traditional electrolytes are prone to oxidative decomposition at the positive electrode under high voltage, especially after repeated high-temperature cycles. The carbonate solvent in the electrolyte will be oxidized and decomposed to produce gases such as carbon dioxide and carbon monoxide, causing battery volume expansion and capacity decay.

[0004] Therefore, there is an urgent need for an electrolyte and lithium-ion battery to address the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide an electrolyte that can improve the high-temperature storage and high-temperature fast-charge cycle performance of lithium-ion batteries at high voltage (4.53V).

[0006] Another object of the present invention is to provide a lithium-ion battery that has good high-temperature storage performance and high-temperature fast-charge cycle performance at high voltage (4.53V).

[0007] To achieve the above objectives, the present invention provides an electrolyte comprising a lithium salt, a non-aqueous organic solvent, and a 2,4-dimercaptopyrimidine alkali metal salt additive, wherein the 2,4-dimercaptopyrimidine alkali metal salt additive comprises at least one of structural formula I and structural formula II.

[0008]

[0009] Where M ⊕ It is an alkali metal cation.

[0010] Compared with the prior art, the electrolyte of the present invention contains a 2,4-dimercaptopyrimidine alkali metal salt additive. This additive has a structurally stable 2,4-dimercaptopyrimidine anion, which gives it excellent thermal stability below 500°C. Therefore, the electrolyte of the present invention can improve the high-temperature storage and high-temperature fast-charge cycle performance of lithium-ion batteries at high voltage (4.53V). Simultaneously, the additive structure contains two exposed nitrogen and sulfur atoms, which have strong bonding capabilities with metal ions (such as Li, Na, K, Cs, Co, Cu, Mn). Therefore, the additive can also stabilize the cathode material, preventing its structure from being damaged under high temperature and high voltage, thereby improving the high-temperature storage and high-temperature fast-charge cycle performance of lithium-ion batteries at high voltage (4.53V). Furthermore, the additive of the present invention participates in the formation of the SEI film during the battery formation stage, making the SEI film more stable, thereby improving the high-temperature storage and high-temperature fast-charge cycle performance of lithium-ion batteries.

[0011] Preferably, structural formula I of the present invention is selected from at least one of compounds 1 to 5:

[0012]

[0013] Preferably, structural formula II of the present invention is selected from at least one of compounds 6 to 10:

[0014]

[0015] Preferably, the 2,4-dimercaptopyrimidine alkali metal salt additive of the present invention accounts for 0.01 to 2% of the total mass of the electrolyte; specifically, it may be, but is not limited to, 0.01%, 0.05%, 0.08%, 0.1%, 0.14%, 0.18%, 1%, 1.3%, 1.5%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0016] Preferably, the lithium salt of the present invention is selected from at least one of lithium hexafluorophosphate (LiFP6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium difluorophosphate (LiPO2F2), and lithium difluorobis(oxalate phosphate) (LiDFOP). Specifically, the lithium salt accounts for 5% to 25% of the total mass of the electrolyte, and may be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%.

[0017] Preferably, the non-aqueous organic solvent of the present invention is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butyl acetate (EB), γ-butyrolactone (GBL), propyl propionate (PP), butyl propionate (EP), and ethyl butyrate (EB). Specifically, the non-aqueous organic solvent of the present invention accounts for 70-90% of the total mass of the electrolyte, and may be, but is not limited to, 70%, 72%, 74%, 75%, 77%, 78%, 80%, 82%, 83%, 84%, 86%, 88%, and 90%.

[0018] Preferably, the preparation method of the 2,4-dimercaptopyrimidine alkali metal salt additive of the present invention includes:

[0019] (1) Mix 2,4-dimercaptopyrimidine with a solvent and stir at a certain temperature to obtain a suspension;

[0020] (2) Add the alkali metal compound to the suspension in batches to react and obtain a mixture;

[0021] (3) Adjust the pH value of the mixture and continue the reaction for a certain period of time;

[0022] (4) After the reaction in step (3) is completed, the product is cooled, crystallized, filtered, and dried to obtain 2,4-dimercaptopyrimidine alkali metal salt additive.

[0023] Preferably, the solvent of the present invention is at least one selected from polar protic solvents, halogenated hydrocarbons, aliphatic hydrocarbons, ethers, ketones, esters, and nitrile solvents. Specifically, the polar protic solvent may be water, methanol, ethanol, isopropanol, n-propanol, or n-butanol; the halogenated hydrocarbon solvent may be dichloromethane, trichloromethane, 1,2-dichloroethane, or tetrachloroethane; the aliphatic hydrocarbon solvent may be n-hexane or cyclohexane; the ether solvent may be diethyl ether, methyl tert-butyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, or dioxane; the ketone solvent may be acetone, cyclohexanone, or 4-methyl-2-pentanone; the ester solvent may be dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, or propyl acetate; and the nitrile solvent may be acetonitrile. Preferably, the solvent of the present invention is methanol or water.

[0024] Preferably, step (1) of the present invention includes stirring at 0–90°C to obtain a suspension. More preferably, step (1) of the present invention includes stirring at 35–60°C to obtain a suspension.

[0025] Preferably, the molar ratio of 2,4-dimercaptopyrimidine to the alkali metal compound of the present invention is 1:1 to 1.1. More preferably, the molar ratio of 2,4-dimercaptopyrimidine to the alkali metal compound of the present invention is 1:1 to 1.05.

[0026] Preferably, the alkali metal compound of the present invention is a lithium compound, a sodium compound, a potassium compound, a rubidium compound, or a cesium compound. Specifically, the lithium compound is lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium methoxide, lithium ethoxide, or lithium tert-butoxide; the sodium compound is sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium methoxide, sodium ethoxide, or sodium tert-butoxide; the potassium compound is potassium hydroxide, potassium carbonate, potassium bicarbonate, potassium methoxide, or potassium tert-butoxide; the rubidium compound is rubidium hydroxide or rubidium carbonate; and the cesium compound is cesium hydroxide, cesium hydroxide monohydrate, cesium carbonate, or cesium bicarbonate. More preferably, the alkali metal compound is lithium hydroxide, lithium hydroxide monohydrate, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, or cesium hydroxide monohydrate.

[0027] Preferably, step (3) of the present invention includes adjusting the pH of the mixture to 7-8. More preferably, the pH of the mixture is adjusted to 7-7.5.

[0028] Preferably, in step (4) of the present invention, the cooling crystallization temperature is -20 to 25°C, the time is 2 to 4 hours, and the drying temperature is 60 to 200°C. More preferably, in step (4) of the present invention, the cooling crystallization temperature is 0 to 5°C, the time is 2 hours, and the drying temperature is 120 to 150°C.

[0029] To achieve the above objectives, the present invention also provides a lithium-ion battery, including a positive electrode and a negative electrode, and further including the electrolyte described above, wherein the positive electrode is made of lithium cobalt oxide material.

[0030] Compared with the prior art, the electrolyte of the lithium-ion battery of the present invention contains a 2,4-dimercaptopyrimidine alkali metal salt additive. The structure of this additive contains a 2,4-dimercaptopyrimidine anion, which gives the additive excellent thermal stability below 500°C. Therefore, the electrolyte of the present invention can improve the high-temperature storage and high-temperature fast-charge cycle performance of lithium-ion batteries at high voltage (4.53V). At the same time, the additive structure contains two exposed nitrogen and sulfur atoms, which have a good complexing effect on cobalt ions, slowing down the dissolution of cobalt ions and stabilizing the structure of the lithium cobalt oxide cathode material. This protects the dissolved cobalt ions from catalytic decomposition of the electrolyte, thereby improving the high-temperature fast-charge cycle and high-temperature storage performance of lithium batteries under high voltage systems. In addition, the additive of the present invention participates in the formation of the SEI film during the battery formation stage, making the SEI film more stable, thereby improving the high-temperature storage and high-temperature fast-charge cycle performance of lithium-ion batteries.

[0031] Preferably, the negative electrode of the present invention is selected from any one of artificial graphite, natural graphite, silicon-carbon composite material and lithium titanate. Attached Figure Description

[0032] Figure 1 H is the 2,4-dimercaptopyrimidine dilithium salt in Example 1 of the present invention. 1NMR spectrum. Detailed Implementation

[0033] To further illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below in conjunction with specific embodiments. It should be noted that, unless specific conditions are specified in the embodiments and comparative examples, conventional conditions or conditions recommended by the manufacturer can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0034] The reaction route for preparing the 2,4-dimercaptopyrimidine alkali metal salt additive of the present invention will be explained below, as follows:

[0035]

[0036] Where M ⊕ This represents an alkali metal cation, specifically a monovalent cation of lithium, sodium, potassium, rubidium, or cesium; L - This refers to anions that counteract alkali metal ions, specifically hydroxide ions, carbonate ions, bicarbonate ions, methoxy, ethoxy, and tert-butoxy ions. Structural formulas I and II represent tautomers of the same substance: 2,4-dimercaptopyrimidine dilithium salt includes two tautomers, compounds 1 and 6; 2,4-dimercaptopyrimidine disodium salt includes two tautomers, compounds 2 and 7; 2,4-dimercaptopyrimidine dipotassium salt includes two tautomers, compounds 3 and 8; 2,4-dimercaptopyrimidine dirubidium salt includes two tautomers, compounds 4 and 9; and 2,4-dimercaptopyrimidine dicesium salt includes two tautomers, compounds 5 and 10. More specifically, in weakly polar or nonpolar solutions, because nitrogen atoms are more electronegative than sulfur atoms, N- atoms are more likely to coordinate with alkali metal cations. Therefore, 2,4-dimercaptopyrimidine alkali metal salt additives mainly exist in the form of structural formula II in conventional electrolytes, with a small portion existing in the form of structural formula I. However, in strongly polar protic solvents or in the presence of cations with stronger binding ability to nitrogen ions, 2,4-dimercaptopyrimidine alkali metal salt additives mainly exist in the form of structural formula I, with a small portion existing in the form of structural formula II. More specifically, the ratio of structural formula I to structural formula II in 2,4-dimercaptopyrimidine alkali metal salt additives can be adjusted by controlling the polarity of the electrolyte.

[0037] Example 1

[0038] This invention provides a 2,4-dimercaptopyrimidine dilithium salt, the preparation method of which includes:

[0039] (1) 28g (0.194mol) of 2,4-dimercaptopyrimidine and 120ml of methanol were placed into a 500ml three-necked flask and stirred at 50℃ for 10min to obtain a slightly yellow suspension.

[0040] (2) 8.23 ​​g (0.196 mol) of lithium hydroxide monohydrate was added to the suspension in batches to react and obtain a mixture;

[0041] (3) Adjust the pH of the mixture to 7.0 and continue the reaction for 3 hours;

[0042] (4) After the product from step (3) is naturally cooled to room temperature, a suspension with precipitate is obtained. The suspension with precipitate is filtered to obtain a filter cake. The filter cake is washed 1-2 times with fresh methanol. The filter cake is dried under vacuum at 120°C for 12 hours to obtain 26g of 2,4-dimercaptopyrimidine dilithium salt, with a yield of 85.8%. The H of the obtained 2,4-dimercaptopyrimidine dilithium salt is... 1 NMR spectrum as follows Figure 1 As shown.

[0043] Example 2

[0044] This invention provides a 2,4-dimercaptopyrimidine dilithium salt, the preparation method of which includes:

[0045] (1) 28g (0.194mol) of 2,4-dimercaptopyrimidine and 120ml of deionized water were placed into a 500ml three-necked flask and stirred at 60℃ for 10min to obtain a slightly yellow suspension.

[0046] (2) 8.23 ​​g (0.196 mol) of lithium hydroxide monohydrate was added to the suspension in batches to react and obtain a mixture;

[0047] (3) Adjust the pH of the mixture to 7.0 and continue the reaction for 2 hours;

[0048] (4) After the product of step (3) is naturally cooled to room temperature, a clear and transparent solution is obtained. Then the solution is concentrated and cooled to 5°C for crystallization for 2 hours. Then the solution is filtered to obtain a filter cake. The filter cake is washed with cold water 1 to 2 times and dried under vacuum at 150°C for 24 hours to obtain 27.1 g of 2,4-dimercaptopyrimidine dilithium salt, with a yield of 89.4%.

[0049] Example 3

[0050] This invention provides a disodium salt of 2,4-dimercaptopyrimidine, the preparation method of which includes:

[0051] (1) 28g (0.194mol) of 2,4-dimercaptopyrimidine and 120ml of methanol were placed into a 500ml three-necked flask and stirred at 50℃ for 10min to obtain a slightly yellow suspension.

[0052] (2) 7.84 g (0.196 mol) of sodium hydroxide was added to the suspension in batches to react and obtain a mixture;

[0053] (3) Adjust the pH of the mixture to 7.3 and continue the reaction for 3 hours;

[0054] (4) After the product of step (3) is cooled to room temperature, a suspension with precipitate is obtained. The suspension with precipitate is filtered to obtain a filter cake. The filter cake is washed with fresh methanol 1-2 times. The filter cake is dried under vacuum at 120°C for 12 hours to obtain 32.9 g of 2,4-dimercaptopyrimidine disodium salt, with a yield of 90%.

[0055] Example 4

[0056] This invention provides a 2,4-dimercaptopyrimidine dipotassium salt, the preparation method of which includes:

[0057] (1) 28g (0.194mol) of 2,4-dimercaptopyrimidine and 120ml of methanol were placed into a 500ml three-necked flask and stirred at 50℃ for 10min to obtain a slightly yellow suspension.

[0058] (2) 10.89 g (0.195 mol) of potassium hydroxide was added to the suspension in batches to react and obtain a mixture;

[0059] (3) Adjust the pH of the mixture to 7.4 and continue the reaction for 3 hours;

[0060] (4) After the product of step (3) is cooled to room temperature, a suspension with precipitate is obtained. The suspension with precipitate is filtered to obtain a filter cake. The filter cake is washed with fresh methanol 1-2 times. The filter cake is dried under vacuum at 120°C for 12 hours to obtain 39.3g of 2,4-dimercaptopyrimidine dipotassium salt, with a yield of 92%.

[0061] Example 5

[0062] This invention provides a 2,4-dimercaptopyrimidine dicesium salt, the preparation method of which includes:

[0063] (1) 28g (0.194mol) of 2,4-dimercaptopyrimidine and 120ml of methanol were placed into a 500ml three-necked flask and stirred at 50℃ for 10min to obtain a slightly yellow suspension.

[0064] (2) 29.08 g (0.194 mol) of cesium hydroxide was added to the suspension in batches to carry out the reaction and obtain a mixture;

[0065] (3) Adjust the pH of the mixture to 7.5 and continue the reaction for 3 hours;

[0066] (4) After the product of step (3) is naturally cooled to room temperature, a suspension with precipitate is obtained. The suspension with precipitate is filtered to obtain a filter cake. The filter cake is washed 1-2 times with fresh methanol. The filter cake is dried under vacuum at 150°C for 24 hours to obtain 75.2g of 2,4-dimercaptopyrimidine dicesium salt, with a yield of 95%.

[0067] Furthermore, the following are specific implementation methods for using 2,4-dimercaptopyrimidine alkali metal salts in lithium-ion batteries:

[0068] Example 6

[0069] Electrolyte preparation:

[0070] In a nitrogen-filled glove box (water content ≤1ppm, oxygen content ≤1ppm), the raw materials ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were dehydrated to a solution moisture content ≤1ppm (5% activated 4A molecular sieve was added). Then, 87g of mixed solution A was prepared according to the mass ratio of EC:EMC:DEC = 1:1:1. 12.9g of lithium hexafluorophosphate was then slowly added to solution A and stirred until it was completely dissolved. Then, 0.1g of 2,4-dimercaptopyrimidine dilithium salt prepared in Example 1 was added and stirred until it was completely dissolved to form an electrolyte.

[0071] Preparation of cathode materials:

[0072] Lithium cobalt oxide material, PVDF binder and Super P conductive agent are mixed evenly at a mass ratio of 95:1.5:3.5 to prepare a slurry. The slurry is then coated on both sides of aluminum foil, and after drying and rolling, a positive electrode sheet is obtained.

[0073] Preparation of negative electrode materials:

[0074] Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) are mixed evenly in a mass ratio of 95:2:1:2 to prepare a slurry. The slurry is then coated on both sides of a copper foil, dried, and rolled to obtain the negative electrode sheet.

[0075] The fabrication of lithium-ion batteries:

[0076] The positive electrode, separator, and negative electrode are stacked to form a square cell, which is then packaged with polymer and vacuum dried at 60°C for 12 hours. Electrolyte is then injected into the cell in a glove box, and the cell is then processed through formation, capacity grading, and other processes to produce a lithium-ion battery with a capacity of 1000mAh.

[0077] The composition of the lithium-ion battery electrolytes in Examples 6-12 and Comparative Example 1 is shown in Table 1. The preparation processes of the lithium-ion battery electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries in Examples 7-12 and Comparative Example 1 are the same as those in Example 6. The 2,4-dimercaptopyrimidine dilithium salt was prepared in Example 1, and the 2,4-dimercaptopyrimidine dicesium salt was prepared in Example 5.

[0078] Table 1. Composition of the electrolytes in the examples and comparative examples.

[0079] Example 6 EC:EMC:DEC = 1:1:1 / 87g <![CDATA[LiPF6 / 12.9g]]> 2,4-Dimercaptopyrimidine dilithium salt / 0.1g Example 7 EC:EMC:DEC = 1:1:1 / 87g <![CDATA[LiPF6 / 12.7g]]> 2,4-Dithiopyrimidine dilithium salt / 0.3g Example 8 EC:EMC:DEC = 1:1:1 / 87g <![CDATA[LiPF6 / 12.5g]]> 2,4-Dithiopyrimidine dilithium salt / 0.5g Example 9 EC:EMC:DEC = 1:1:1 / 87g <![CDATA[LiPF6 / 11.2g]]> 2,4-Dimercaptopyrimidine dilithium salt / 1.8g Example 10 EC:EMC:DEC = 1:1:1 / 87g <![CDATA[LiPF6 / 12.9g]]> 0.1 g of 2,4-dimercaptopyrimidine dicesium salt Example 11 EC:EMC:DEC = 1:1:1 / 87g <![CDATA[LiPF6 / 12.7g]]> 2,4-Dimercaptopyrimidine dicesium salt / 0.3g Example 12 PC:EMC:DEC = 1:2:1 / 87g <![CDATA[LiPF6 / 12.5g]]> 2,4-Dimercaptopyrimidine dicesium salt / 0.5g Comparative Example 1 EC:EMC:DEC = 1:1:1 87g <![CDATA[LiPF6 13.0g]]> /

[0080] The lithium-ion batteries prepared with the electrolytes from Examples 6 to 12 and Comparative Example 1 were subjected to high-temperature storage performance tests and high-temperature fast-charge cycle performance tests. The test conditions are as follows, and the test results are shown in Table 2. High-temperature storage performance test:

[0081] At room temperature (25℃) and an upper limit voltage of 4.53V, the lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle, and the discharge capacity was recorded as C0. Then, the battery was placed in a 60℃ oven and left to stand for 7 days. After the battery temperature dropped to 25℃, it was discharged at 0.3C, and the discharge capacity was recorded as C1. Then, the lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle, and the discharge capacity was recorded as C2. The capacity retention rate = C1 / C0*100%, and the capacity recovery rate = C2 / C0*100%.

[0082] High-temperature fast charging cycle performance test:

[0083] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 2C until the voltage reached 4.53V, followed by constant voltage charging at 4.53V until the current reached 0.05C. Finally, it was discharged at a constant current of 1C until the voltage reached 3.0V. The first discharge capacity was recorded as C0. This constitutes one charge-discharge cycle. Then, 300 cycles of 2C / 1C charge and discharge were performed at 45°C, and the discharge capacity was recorded as C1. Capacity retention = C1 / C0 * 100%.

[0084] Table 2. Performance test results of lithium-ion batteries

[0085]

[0086] As shown in Table 2, compared with Comparative Example 1, the lithium-ion batteries of Examples 6-12 exhibit significantly improved high-temperature storage and high-temperature fast-charge cycle performance. This is because the electrolyte of the lithium-ion battery of the present invention contains a 2,4-dimercaptopyrimidine alkali metal salt additive. The structure of this additive contains a structurally stable 2,4-dimercaptopyrimidine anion, which gives the additive excellent thermal stability below 500°C. Therefore, the electrolyte of the present invention can improve the high-temperature storage and high-temperature fast-charge cycle performance of the lithium-ion battery at high voltage (4.53V). At the same time, the additive structure contains two exposed nitrogen and sulfur atoms, which have a good complexing effect on cobalt ions, slowing down the dissolution of cobalt ions and stabilizing the structure of the lithium cobalt oxide cathode material. This protects the dissolved cobalt ions from catalytic decomposition of the electrolyte, thereby improving the high-temperature fast-charge cycle and high-temperature storage performance of the lithium battery under high voltage system. In addition, the additive of the present invention participates in the formation of the SEI film during the battery formation stage, making the SEI film more stable, thereby improving the high-temperature storage and high-temperature fast-charge cycle performance of the lithium-ion battery.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to the embodiments listed above. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte comprising a lithium salt and a non-aqueous organic solvent, characterized in that, It also includes 2,4-dimercaptopyrimidine alkali metal salt additives, said 2,4-dimercaptopyrimidine alkali metal salt additives comprising at least one of structural formula I and structural formula II: Where M ⊕ It is an alkali metal cation.

2. The electrolyte as described in claim 1, characterized in that, The structural formula I is selected from at least one of compounds 1 to 5:

3. The electrolyte as described in claim 1, characterized in that, The structural formula II is selected from at least one of compounds 6 to 10:

4. The electrolyte as described in claim 1, characterized in that, The 2,4-dimercaptopyrimidine alkali metal salt additive accounts for 0.01 to 2% of the total mass of the electrolyte.

5. The electrolyte as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, and lithium difluorobis(oxalate) phosphate.

6. The electrolyte as described in claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, butyl propionate, and ethyl butyrate.

7. The electrolyte as described in claim 1, characterized in that, The preparation method of the 2,4-dimercaptopyrimidine alkali metal salt additive includes: (1) Mix 2,4-dimercaptopyrimidine with a solvent and stir at a certain temperature to obtain a suspension; (2) Add the alkali metal compound to the suspension in batches to react and obtain a mixture; (3) Adjust the pH value of the mixture and continue the reaction for a certain period of time; (4) After the reaction in step (3) is completed, the product is cooled, crystallized, filtered, and dried to obtain 2,4-dimercaptopyrimidine alkali metal salt additive.

8. The electrolyte as described in claim 7, characterized in that, The molar ratio of the 2,4-dimercaptopyrimidine to the alkali metal compound is 1:1 to 1.

1.

9. The electrolyte as described in claim 7, characterized in that, Step (1) includes stirring at 0–90°C to obtain a suspension.

10. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, It also includes the electrolyte as described in any one of claims 1 to 9, wherein the positive electrode is made of lithium cobalt oxide material.

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