Electrolyte additive and method for its preparation

Abstract

This invention relates to the field of lithium-ion battery technology and discloses an electrolyte additive and its preparation method. When the electrolyte additive prepared by this invention is added to the electrolyte of a lithium battery, it can improve the cycle performance and safety performance of the lithium battery. This is because in this electrolyte additive, the maleimide ring constructs a flexible and stable CEI / SEI through electrochemical polymerization and removes acidic impurities; the thiourea structure improves ion transport and lithium deposition uniformity by coordinating Li+ and adsorbing onto the metal surface; the fluorine group generates a dense LiF-rich layer to enhance high-voltage stability and safety; and the benzene ring enhances thermal stability and film-forming durability through conjugated rigidity and π-π interaction. The synergistic effect of these four components improves the overall performance of the lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to an electrolyte additive and its preparation method. Background Technology

[0002] Currently, as lithium-ion and lithium-metal batteries are developing towards higher energy density, higher voltage (≥4.5V), and longer cycle life, the interfacial stability between the electrolyte and electrode materials has become a key technological bottleneck. Traditional carbonate electrolytes are prone to oxidative decomposition on the positive electrode surface under high voltage, while problems such as transition metal dissolution, gas generation, and increased interfacial impedance severely restrict battery performance.

[0003] To address these issues, researchers have widely employed electrolyte additives to suppress side reactions by forming stable solid electrolyte interphase (SEI) or cathode electrolyte interphase (CEI) films on the electrode surface. While common additives such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), or 1,3-propane sulpholactone (PS) can improve cycle performance to some extent, single-function additives often struggle to simultaneously meet the demands for high voltage tolerance, lithium dendrite suppression, and thermal safety. Especially for high-nickel ternary cathode or lithium metal anode systems, existing additives still have significant shortcomings in suppressing interfacial side reactions, regulating lithium deposition morphology, and improving battery safety under abuse conditions. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an electrolyte additive and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] On one hand, the present invention provides a method for preparing an electrolyte additive, comprising the following steps:

[0007] Step S1: Add isothiocyano-4-nitrobenzene ester to a mixed solvent and stir until homogeneous. Add dibutyltin dilaurate and stir until homogeneous. Then, slowly add diethylenetriamine dropwise under continuous stirring and heat to 35-45℃ for 2-3 hours. Filter under reduced pressure, wash, and dry to obtain the terminal nitrothiourea benzene derivative.

[0008] Further, the mixed solvent in step S1 is a mixture of anhydrous ethanol and tetrahydrofuran, and the volume ratio of the two is 3:1;

[0009] Furthermore, in step S1, the molar ratio of isothiocyano-4-nitrobenzene ester to diethylenetriamine is 2-2.01:1;

[0010] Furthermore, in step S1, the amount of dibutyltin dilaurate used is 0.2wt%-0.5wt% of the total reactants;

[0011] Step S2: Add the thiourea nitrobenzene derivative and Pd / C to ethanol and mix thoroughly. Then, slowly add hydrazine hydrate at a rate of 1-2 drops / second for 20-30 minutes. Heat to 80°C and reflux for 6 hours. Filter to remove Pd / C, add deionized water and stir for 30 minutes. Filter, dry, and recrystallize to obtain the terminal amino thiourea benzene derivative.

[0012] Furthermore, in step S2, the ratio of the amount of thiourea nitrobenzene derivative, Pd / C, hydrazine hydrate, and deionized water is 0.008 mol: 0.2-0.4 g: 2-2.5 g: 100 mL;

[0013] Step S3: Mix the terminal aminothiourea benzene derivative and anhydrous tetrahydrofuran until homogeneous, then add triethylamine, 4-dimethylaminopyridine and ditert-butyl dicarbonate (Boc) in sequence, purge with nitrogen, stir at room temperature for 4-8 hours, monitor with TLC, and after the reaction is complete, perform post-processing to obtain the Boc protected terminal aminothiourea benzene derivative.

[0014] Further, the specific post-processing steps in step S3 are as follows: concentration under reduced pressure, then adding 100 mL of saturated sodium bicarbonate solution, extraction with 240 mL of ethyl acetate, combining the organic phases, washing with 100 mL of saturated brine, drying with 10 g of anhydrous sodium sulfate, filtration, concentration under reduced pressure, and recrystallization.

[0015] Further, in step S3, the ratio of the amount of the terminal aminothiourea benzene derivative, triethylamine, 4-dimethylaminopyridine, and ditert-butyl dicarbonate is 0.01 mol: 1.5-3 mL: 0.06-0.012 g: 5-6 g;

[0016] Step S4: Add solution 2 dropwise to solution 1 over 15-30 min and react at room temperature for 2 h. Then add anhydrous sodium acetate and hydroquinone and stir for 30 min. Next, add acetic anhydride and heat to 50 °C and react for 1.5-2.5 h. After cooling to room temperature, slowly add the reaction solution dropwise to a large amount of ice-water mixture under vigorous stirring. Filter, wash, and dry to collect the intermediate product. Add dichloromethane to the intermediate product and stir well. Place in an ice-water bath and slowly add trifluoroacetic acid. After the addition is complete, remove the ice bath and stir at room temperature for 1-3 h. Monitor with TLC and perform post-processing to obtain the maleimide thiourea benzene derivative.

[0017] Further, in step S4, solution 1 is prepared by mixing and stirring maleic anhydride in DMF until homogeneous, and solution 2 is prepared by mixing and stirring Boc protected-terminal aminothiourea benzene derivative in DMF until homogeneous.

[0018] Further, the specific post-processing steps in step S4 are as follows: concentration under reduced pressure, adjustment of pH to 7-8 (using saturated sodium bicarbonate solution), filtration, extraction with ethyl acetate, washing with ethanol, and vacuum drying;

[0019] Further, in step S4, the ratio of maleic anhydride, Boc protected-terminal aminothiourea benzene derivative, anhydrous sodium acetate, hydroquinone, and acetic anhydride is 0.1-0.12 mol: 0.05 mol: 1-1.5 g: 0.8-1.2 g: 5-6 mL;

[0020] Furthermore, in step S4, the ratio of the intermediate product, dichloromethane, and trifluoroacetic acid is 0.04 mol: 20-30 mL: 20-30 mL;

[0021] Step S5: Add maleimide thiourea benzene derivative and fluorinated acrylate compound to a mixture of methanol and water, stir until homogeneous, and then mix. Transfer the mixed solution to an oil bath, stir at room temperature for 3-5 minutes, then heat to 60°C and react for 2-3 hours. Distill under reduced pressure, wash and dry to obtain electrolyte additive.

[0022] Further, the fluorinated acrylate compound in step S5 is one of perfluoroalkyl ethyl acrylate, perfluoroalkyl ethyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate or 1H,1H-perfluoropropyl methacrylate.

[0023] Furthermore, in step S5, the molar ratio of maleimide thiourea benzene derivative and fluorinated acrylate compound is 0.7-0.8:1;

[0024] Furthermore, in step S5, the volume ratio of methanol and water in the mixture is 1:1.

[0025] On the other hand, the present invention provides an electrolyte additive prepared by the above preparation method.

[0026] The beneficial effects of this invention are:

[0027] The electrolyte additive prepared in this invention, when added to lithium battery electrolytes, can improve the cycle performance and safety performance of lithium batteries. This is because in this electrolyte additive, the maleimide ring constructs a flexible and stable CEI / SEI through electrochemical polymerization and removes acidic impurities, while the thiourea structure coordinates with Li... + The adsorption of metal surfaces improves ion transport and lithium deposition uniformity, while fluorine groups generate a dense LiF-rich layer to enhance high-voltage stability and safety. Benzene rings enhance thermal stability and film durability through conjugated rigidity and π-π interaction. The synergistic effect of these four factors improves the overall performance of lithium batteries.

[0028] The maleimide ring of this additive has a high electron density in its C=C double bond, allowing for electrochemically induced anionic or free radical polymerization on the positive or negative electrode surface. This results in a cross-linked polymer network, forming a flexible and thermally stable polymer film that can adapt to volume changes during charging and discharging of the positive electrode, hindering the dissolution and diffusion of transition metal ions from the positive electrode surface to the negative electrode. The strong Lewis acid PF5 from LiPF6 decomposition attacks the solvent, but maleimide can react with it, removing acidic impurities and inhibiting the autocatalytic decomposition of the electrolyte. The sulfur atom in the thiourea structure (–NH–CS–NH–) has a lone pair of electrons, which can react with Li… + Forming temporary coordinate bonds reduces Li + The desolvation energy improves interfacial kinetics, and it also spontaneously chemisorbs exposed metal atoms or defect sites on the surface of the positive electrode (such as LCO, NCM), forming a molecular-level protective barrier and reducing direct contact between the electrolyte and the positive electrode. Furthermore, thiourea can decompose to generate Li₂S, Li₂S₂, or nitrogen-containing oligomers; Li₂S is a good source of Li₂. + The conductive and moderately mechanically strong components improve the ionic conductivity and density of the SEI (Sediment Injection). Fluorine groups typically enhance the flash point and flame retardancy of the electrolyte. Furthermore, on the negative electrode surface, fluorine groups can decompose under reducing conditions to generate LiF. LiF possesses extremely low electronic conductivity, high interfacial energy, and high mechanical strength, making it one of the most effective SEI components for suppressing lithium dendrite penetration. Finally, the benzene rings utilize conjugated rigidity and π-π interactions to promote the pre-arrangement of additive molecules into an ordered layer on the electrode surface, thereby guiding film uniformity. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: A method for preparing an electrolyte additive, comprising the following steps:

[0031] Step S1: Add 0.2 mol of isothiocyano-4-nitrobenzene to 200 mL of mixed solvent and stir until homogeneous. Add dibutyltin dilaurate and stir until homogeneous. Then, slowly add 0.1 mol of diethylenetriamine dropwise under continuous stirring and heat to 35 °C for 2 h. Filter under reduced pressure, wash, and dry to obtain the terminal nitrothiourea benzene derivative. The amount of dibutyltin dilaurate is 0.2 wt% of the total reactants. The mixed solvent is a mixture of anhydrous ethanol and tetrahydrofuran in a volume ratio of 3:1.

[0032] Step S2: Add 0.008 mol of thiourea nitrobenzene derivative and 0.2 g of Pd / C to 50 mL of ethanol and mix and stir evenly. Then slowly add 2 g of hydrazine hydrate at a rate of 1 drop / second for 20 min. Heat to 80 °C and reflux and stir for 6 h. Filter to remove Pd / C, add 100 mL of deionized water and stir for 30 min. Filter, dry, and recrystallize to obtain the terminal aminothiourea benzene derivative.

[0033] Step S3: Mix 0.01 mol of terminal aminothiourea benzene derivative with 50 mL of anhydrous tetrahydrofuran and stir until homogeneous. Then add 1.5 mL of triethylamine, 0.06 g of 4-dimethylaminopyridine and 5 g of ditert-butyl dicarbonate in sequence. Purge with nitrogen and stir at room temperature for 4 h. Monitor the reaction by TLC. After the reaction is complete, concentrate under reduced pressure, add 100 mL of saturated sodium bicarbonate solution, extract with 240 mL of ethyl acetate, combine the organic phases, wash with 100 mL of saturated brine, dry with 10 g of anhydrous sodium sulfate, filter, concentrate under reduced pressure, and recrystallize to obtain Boc protected terminal aminothiourea benzene derivative.

[0034] Step S4: Add solution 2 dropwise to solution 1 over 15 min and react at room temperature for 2 h. Then add 1 g of anhydrous sodium acetate and 0.8 g of hydroquinone and stir for 30 min. Subsequently, add 5 mL of acetic anhydride and heat to 50 °C and react for 1.5 h. After cooling to room temperature, slowly add the reaction solution dropwise to a large amount of ice-water mixture under vigorous stirring. Filter, wash, and dry to collect the intermediate product. Add 20 mL of dichloromethane to 0.04 mol of the intermediate product and stir well. Place in an ice-water bath and slowly add 20 mL of trifluoroacetic acid. After the addition is complete, remove the ice bath and stir at room temperature for 1 h. Monitor by TLC, concentrate under reduced pressure, adjust the pH to 7 (using saturated sodium bicarbonate solution), filter, extract with ethyl acetate, wash with ethanol, and dry under vacuum to obtain the maleimide thiourea benzene derivative. Solution 1 is prepared by mixing 0.1 mol of maleic anhydride in 50 mL of DMF and stirring until homogeneous. Solution 2 is prepared by mixing 0.05 mol of Boc-protected aminothiourea benzene derivative in 50 mL of DMF. The mixture is prepared by thoroughly stirring in DMF.

[0035] Step S5: Add 0.07 mol maleimide thiourea benzene derivative and 0.1 mol perfluoroalkyl ethyl acrylate to 50 mL of a mixture of methanol and water (volume ratio 1:1), stir until homogeneous, and then mix. Transfer the mixed solution to an oil bath, stir at room temperature for 3-5 min, then heat to 60 °C and react for 2 h. Distill under reduced pressure, wash and dry to obtain the electrolyte additive.

[0036] Example 2: A method for preparing an electrolyte additive, comprising the following steps:

[0037] Step S1: Add 0.2005 mol of isothiocyano-4-nitrobenzene to 200 mL of mixed solvent and stir until homogeneous. Add dibutyltin dilaurate and stir until homogeneous. Then, slowly add 0.1 mol of diethylenetriamine dropwise under continuous stirring and heat to 40 °C for 2.5 h. Filter under reduced pressure, wash, and dry to obtain the terminal nitrothiourea benzene derivative. The amount of dibutyltin dilaurate is 0.35 wt% of the total reactants. The mixed solvent is a mixture of anhydrous ethanol and tetrahydrofuran in a volume ratio of 3:1.

[0038] Step S2: Add 0.008 mol of thiourea nitrobenzene derivative and 0.3 g of Pd / C to 50 mL of ethanol and mix and stir evenly. Then, slowly add 2.3 g of hydrazine hydrate at a rate of 1.5 drops / second for 25 min. Heat to 80 °C and reflux and stir for 6 h. Filter to remove Pd / C, add 100 mL of deionized water and stir for 30 min. Filter, dry, and recrystallize to obtain the terminal aminothiourea benzene derivative.

[0039] Step S3: Mix 0.01 mol of terminal aminothiourea benzene derivative and 50 mL of anhydrous tetrahydrofuran until homogeneous. Then add 2.2 mL of triethylamine, 0.09 g of 4-dimethylaminopyridine and 5.5 g of ditert-butyl dicarbonate in sequence. Purge with nitrogen and stir at room temperature for 6 h. Monitor the reaction by TLC. After the reaction is complete, concentrate under reduced pressure, add 100 mL of saturated sodium bicarbonate solution, extract with 240 mL of ethyl acetate, combine the organic phases, wash with 100 mL of saturated brine, dry with 10 g of anhydrous sodium sulfate, filter, concentrate under reduced pressure, and recrystallize to obtain Boc protected terminal aminothiourea benzene derivative.

[0040] Step S4: Add solution 2 dropwise to solution 1 over 25 min and react at room temperature for 2 h. Then add 1.2 g anhydrous sodium acetate and 1 g hydroquinone and stir for 30 min. Next, add 5.5 mL acetic anhydride and heat to 50 °C and react for 2 h. After cooling to room temperature, slowly add the reaction solution dropwise to a large amount of ice-water mixture under vigorous stirring. Filter, wash, and dry to collect the intermediate product. Add 25 mL dichloromethane to 0.04 mol of the intermediate product and stir well. Place in an ice-water bath and slowly add 25 mL trifluoroacetic acid. After the addition is complete, remove the ice bath and stir at room temperature for 2 h. Monitor by TLC, concentrate under reduced pressure, adjust the pH to 7.5 (using saturated sodium bicarbonate solution), filter, extract with ethyl acetate, wash with ethanol, and dry under vacuum to obtain the maleimide thiourea benzene derivative. Solution 1 is prepared by mixing 0.115 mol maleic anhydride in 50 mL DMF and stirring until homogeneous. Solution 2 is prepared by mixing 0.05 mol Boc-protected aminothiourea benzene derivative in 50 mL DMF. The mixture is prepared by thoroughly stirring in DMF.

[0041] Step S5: Add 0.075 mol maleimide thiourea benzene derivative and 0.1 mol perfluoroalkyl ethyl methacrylate to 50 mL of a mixture of methanol and water (volume ratio 1:1), stir until homogeneous, and then mix. Transfer the mixed solution to an oil bath, stir at room temperature for 4 min, then heat to 60 °C and react for 2.5 h. Distill under reduced pressure, wash and dry to obtain the electrolyte additive.

[0042] Example 3: A method for preparing an electrolyte additive, comprising the following steps:

[0043] Step S1: Add 0.201 mol of isothiocyano-4-nitrobenzene ester to 200 mL of mixed solvent and stir until homogeneous. Add dibutyltin dilaurate and stir until homogeneous. Then, slowly add 0.1 mol of diethylenetriamine dropwise under continuous stirring and heat to 45 °C for 3 h. Filter under reduced pressure, wash, and dry to obtain the terminal nitrothiourea benzene derivative. The amount of dibutyltin dilaurate used is 0.4 wt% of the total reactants. The mixed solvent is a mixture of anhydrous ethanol and tetrahydrofuran, with a volume ratio of 3:1.

[0044] Step S2: Add 0.008 mol of thiourea nitrobenzene derivative and 0.4 g of Pd / C to 50 mL of ethanol and mix thoroughly. Then, slowly add 2.5 g of hydrazine hydrate at a rate of 2 drops / second for 30 min. Heat to 80 °C and reflux for 6 h. Filter to remove Pd / C, add 100 mL of deionized water and stir for 30 min. Filter, dry, and recrystallize to obtain the terminal aminothiourea benzene derivative.

[0045] Step S3: Mix 0.01 mol of the terminal aminothiourea benzene derivative with 50 mL of anhydrous tetrahydrofuran and stir until homogeneous. Then, add 3 mL of triethylamine, 0.012 g of 4-dimethylaminopyridine and 6 g of ditert-butyl dicarbonate in sequence. Purge with nitrogen and stir at room temperature for 8 h. Monitor the reaction by TLC. After the reaction is complete, concentrate under reduced pressure, add 100 mL of saturated sodium bicarbonate solution, extract with 240 mL of ethyl acetate, combine the organic phases, wash with 100 mL of saturated brine, dry with 10 g of anhydrous sodium sulfate, filter, concentrate under reduced pressure, and recrystallize to obtain the Boc protected terminal aminothiourea benzene derivative.

[0046] Step S4: Add solution 2 dropwise to solution 1 over 30 min and react at room temperature for 2 h. Then add 1.5 g anhydrous sodium acetate and 1.2 g hydroquinone and stir for 30 min. Subsequently, add 6 mL acetic anhydride and heat to 50 °C and react for 2.5 h. After cooling to room temperature, slowly add the reaction solution dropwise to a large amount of ice-water mixture under vigorous stirring. Filter, wash, and dry to collect the intermediate product. Add 30 mL dichloromethane to 0.04 mol of the intermediate product and stir well. Place in an ice-water bath and slowly add 30 mL trifluoroacetic acid. After the addition is complete, remove the ice bath and stir at room temperature for 3 h. Monitor by TLC, concentrate under reduced pressure, adjust the pH to 8 (using saturated sodium bicarbonate solution), filter, extract with ethyl acetate, wash with ethanol, and vacuum dry to obtain the maleimide thiourea benzene derivative. Solution 1 is prepared by mixing 0.12 mol maleic anhydride in 50 mL DMF and stirring until homogeneous. Solution 2 is prepared by mixing 0.05 mol Boc-protected aminothiourea benzene derivative in 50 mL DMF. The mixture is prepared by thoroughly stirring in DMF.

[0047] Step S5: Add 0.08 mol maleimide thiourea benzene derivative and 0.1 mol 2,2,3,3-tetrafluoropropyl acrylate to 50 mL of a mixture of methanol and water (volume ratio 1:1), stir until homogeneous, and then mix. Transfer the mixed solution to an oil bath, stir at room temperature for 5 min, then heat to 60 °C and react for 3 h. Distill under reduced pressure, wash and dry to obtain the electrolyte additive.

[0048] Comparative Example 1: This comparative example is an electrolyte additive. The difference between this example and Example 3 is that step S5 was not performed, but all other steps are the same.

[0049] Comparative Example 2: This comparative example is an electrolyte additive. The difference between this example and Example 3 is that steps S3, S4 and S5 were not performed, but the rest are the same.

[0050] The electrolyte additives of Examples 1-3 and Comparative Examples 1-2 were added at 5 wt% to a commercial electrolyte (1.0 M LiPF6 in ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate (1:1:1)). This electrolyte system was tested in a lithium battery with lithium metal as the negative electrode, NCM811 as the positive electrode, and Celgard 2320 separator.

[0051] Cyclic performance was tested under the following conditions: the battery was charged to 4.2V at a constant current of 1C under a constant temperature of 25℃, then charged to the cutoff current of 0.05C at a constant voltage, and then discharged to 3.0V at a constant current of 1C. This was recorded as one charge-discharge cycle. The same conditions were then applied for 100 and 500 cycles. The capacity retention rate (%) of the lithium battery after 100 or 500 cycles was recorded as (discharge capacity of the 100th or 500th cycle / initial discharge capacity) × 100%.

[0052] To test safety performance, the test conditions were as follows: the battery was completely discharged once, and then charged at a constant current of 1C until it reached 1.5 times the termination voltage (4.2V) or the charging time reached 1 hour. The battery status was then observed for 1 hour and recorded.

[0053] The test results are shown in Table 1:

[0054] Table 1: Performance Test Results

[0055]

[0056] As can be seen from Table 1, the electrolyte additive prepared in this invention can improve the cycle performance and safety performance of lithium batteries when added to the electrolyte.

[0057] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing an electrolyte additive, characterized by, Includes the following steps: Step S1: Add isothiocyano-4-nitrobenzene ester to a mixed solvent and mix well. Add dibutyltin dilaurate, then slowly add diethylenetriamine and heat to 35-45℃ for 2-3 hours. Filter under reduced pressure, wash, and dry to obtain the terminal nitrothiourea benzene derivative. Step S2: Add the thiourea nitrobenzene derivative and Pd / C to ethanol and mix well. Then slowly add hydrazine hydrate and heat to 80°C and reflux for 6 hours. Filter, add deionized water and stir for 30 minutes. Filter, dry and recrystallize to obtain the terminal amino thiourea benzene derivative. Step S3: Mix the terminal aminothiourea benzene derivative and anhydrous tetrahydrofuran, then add triethylamine, 4-dimethylaminopyridine and ditert-butyl dicarbonate in sequence, purge with nitrogen, stir at room temperature for 4-8 h, monitor with TLC to obtain Boc protected terminal aminothiourea benzene derivative. Step S4: Add solution 2 dropwise to solution 1 and react at room temperature for 2 hours. Then add anhydrous sodium acetate and hydroquinone, followed by acetic anhydride. Heat to 50°C and react for 1.5-2.5 hours. After cooling to room temperature, slowly add the reaction solution dropwise to a large amount of ice-water mixture under vigorous stirring. Filter, wash, and dry to collect the intermediate product. Add dichloromethane to the intermediate product and stir well. Place in an ice-water bath and slowly add trifluoroacetic acid. After the addition is complete, remove the ice bath and stir at room temperature for 1-3 hours. Monitor with TLC to obtain the maleimide thiourea benzene derivative. Solution 1 is prepared by mixing maleic anhydride in DMF and stirring until homogeneous. Solution 2 is prepared by mixing Boc-protected aminothiourea benzene derivative in DMF and stirring until homogeneous. Step S5: Add maleimide thiourea benzene derivative and fluorinated acrylate compound to a mixture of methanol and water, stir until homogeneous, and then mix. Transfer the mixed solution to an oil bath, stir at room temperature for 3-5 minutes, then heat to 60°C and react for 2-3 hours. Distill under reduced pressure, wash and dry to obtain the electrolyte additive.

2. A method of preparing an electrolyte additive according to claim 1, characterized in that, The mixed solvent in step S1 is a mixture of anhydrous ethanol and tetrahydrofuran, with a volume ratio of 3:

1.

3. The method for preparing an electrolyte additive according to claim 1, characterized in that, In step S1, the molar ratio of thiocyano-4-nitrobenzene ester to diethylenetriamine is 2-2.01:1, and the amount of dibutyltin dilaurate is 0.2wt%-0.5wt% of the total reactants.

4. The method for preparing an electrolyte additive according to claim 1, characterized in that, In step S2, the ratio of thiourea nitrobenzene derivative, Pd / C, hydrazine hydrate, and deionized water is 0.008 mol: 0.2-0.4 g: 2-2.5 g: 100 mL.

5. The method for preparing an electrolyte additive according to claim 1, characterized in that, In step S3, the ratio of the amount of the terminal aminothiourea benzene derivative, triethylamine, 4-dimethylaminopyridine, and ditert-butyl dicarbonate is 0.01 mol: 1.5-3 mL: 0.06-0.012 g: 5-6 g.

6. The method for preparing an electrolyte additive according to claim 1, characterized in that, In step S4, the ratio of maleic anhydride, Boc-protected aminothiourea benzene derivative, anhydrous sodium acetate, hydroquinone, and acetic anhydride is 0.1-0.12 mol. 0.05mol:1-1.5g:0.8-1.2g:5-6mL.

7. The method for preparing an electrolyte additive according to claim 1, characterized in that, In step S4, the ratio of intermediate product, dichloromethane, and trifluoroacetic acid is 0.04 mol: 20-30 mL: 20-30 mL.

8. The method for preparing an electrolyte additive according to claim 1, characterized in that, The fluorinated acrylate compound in step S5 is one of perfluoroalkyl ethyl acrylate, perfluoroalkyl ethyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate, or 1H,1H-perfluoropropyl methacrylate.

9. The method for preparing an electrolyte additive according to claim 1, characterized in that, In step S5, the molar ratio of maleimide thiourea benzene derivative and fluorinated acrylate compound is 0.7-0.8:1, and the volume ratio of the two in the methanol and water mixture is 1:

1.

10. An electrolyte additive, prepared by the preparation method according to any one of claims 1-9.

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