Electrolyte for sodium-ion battery and preparation method of electrolyte

Abstract

The invention relates to the field of sodium ion batteries, and discloses an electrolyte for a sodium ion battery and a preparation method thereof, the electrolyte for the sodium ion battery comprises a sodium salt, an organic solvent and a composite additive; the composite additive is formed by mixing fluoroethylene carbonate and a modified additive according to the mass ratio of (1-3): 1; the modified additive is prepared by the following steps: reacting 2-cyano-6-hydroxybenzothiazole with liquid bromine to generate 2-cyano-6-hydroxy-5-bromobenzothiazole, then carrying out substitution reaction on phenolic hydroxyl group in the 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate, and then under the catalysis of bis (triphenylphosphine) palladium dichloride and cuprous iodide, carrying out substitution reaction on the phenolic hydroxyl group in the 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate to obtain the modified additive. According to the invention, the electrolyte with a good flame retardant effect is prepared by adding the modified additive, and the sodium-ion battery is endowed with good capacity performance and cycle performance by carrying out a coupling reaction on the prepared 2-cyano-6-diethyl phosphate 5-bromobenzothiazole and trimethylsilylacetylene.

Description

Technical Field

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

[0002] Sodium-ion batteries have a similar operating principle to lithium-ion batteries and are relatively inexpensive to develop, showing great potential for development in large-scale energy storage applications. Sodium-ion batteries are composed of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging, sodium ions are released from the positive electrode, transported through the electrolyte, and embedded into the negative electrode material. During discharge, sodium ions are released from the negative electrode material and transported through the electrolyte to the positive electrode material. Their operating principle is similar to that of a rocking chair. The electrolyte, the "blood" of the battery, transports sodium ions during the charge and discharge process. Its properties, such as conductivity and ion diffusion rate, have a significant impact on the overall performance of the battery.

[0003] Existing sodium-ion batteries, when subjected to certain abuses (such as overcharging, heating, penetration, and crushing), can cause internal temperature and pressure to rise, leading to the release of volatile, flammable solvents that can ignite, posing a serious fire hazard. Therefore, existing technologies aim to improve the safety of sodium-ion batteries by modifying the electrolyte. Flame retardants are typically introduced to reduce the electrolyte's flammability. However, trimethyl phosphate, the most commonly used flame retardant, has poor reduction stability and decomposes strongly on the surface of the hard carbon anode, producing phosphoric acid that dissolves in the electrolyte, as well as large amounts of methane and ethylene gases. This degrades battery performance. Excess trimethyl phosphate, combined with sodium ions, enters the interlayers of the hard carbon, disrupting the mechanical structure and causing a decrease in sodium storage capacity, which in turn impacts the electrochemical performance of the sodium-ion battery. Summary of the Invention

[0004] In order to address the deficiencies mentioned in the above background technology, the object of the present invention is to provide an electrolyte for a sodium ion battery and a preparation method thereof. By adding a modifying additive, an electrolyte with good flame retardant effect is prepared, and the sodium ion battery is given good capacity performance and cycle performance.

[0005] The purpose of the present invention can be achieved through the following technical solutions: An electrolyte for a sodium ion battery, comprising the following components in parts by weight: 20-40 parts of a sodium salt, 100-120 parts of an organic solvent, and 10-20 parts of a composite additive; the composite additive is a mixture of fluoroethylene carbonate and a modifying additive in a mass ratio of 1-3:1; The modified additive is prepared by reacting 2-cyano-6-hydroxybenzothiazole with liquid bromine to generate 2-cyano-6-hydroxy-5-bromobenzothiazole, then subjecting the phenolic hydroxyl group in the 2-cyano-6-hydroxy-5-bromobenzothiazole to a substitution reaction with diethyl chlorophosphate, and subsequently subjecting the prepared 2-cyano-6-diethyl phosphate-5-bromobenzothiazole to a coupling reaction with trimethylsilylacetylene under the catalysis of bistriphenylphosphine palladium dichloride and cuprous iodide.

[0006] Preferably, the sodium salt is one or more combinations of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, and sodium perchlorate.

[0007] Preferably, the organic solvent is one or more combinations of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0008] Preferably, the preparation method of the modified additive comprises the following steps: A. Take 2-cyano-6-hydroxybenzothiazole and dichloromethane in a reactor, place it in an ice-water bath, add a mixture of liquid bromine and dichloromethane, and stir the reaction for 1.5 to 2 hours. After the reaction is completed, add saturated sodium thiosulfate aqueous solution, then add dichloromethane, stir, stand and separate, collect the organic phase, dry it with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole; B. Place a reactor containing tetrahydrofuran in an ice-water bath, add 60% sodium hydride immersed in mineral oil, 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate in sequence, and stir the reaction at room temperature for 1-1.5 hours. After the reaction is completed, add saturated ammonium chloride solution, then add ether and saturated brine, and allow to stand for separation. Collect the organic phase, dry it with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole; C. Take triethylamine in a reactor, pass argon protection, add 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, bistriphenylphosphine palladium dichloride and cuprous iodide, maintain the argon atmosphere, slowly add trimethylsilyl acetylene dropwise, then raise the temperature to 70-80℃ and react for 4-6h. After the reaction is completed, it is rotary evaporated, washed and dried to prepare the modified additive.

[0009] Preferably, the molar ratio of 2-cyano-6-hydroxybenzothiazole to liquid bromine in step A is 1:1-1.02.

[0010] Preferably, in step B, the molar ratio of 2-cyano-6-hydroxy-5-bromobenzothiazole to diethyl chlorophosphate is 1:1 to 1.1.

[0011] Preferably, in step C, the molar ratio of 2-cyano-6-diethyl phosphate-5-bromobenzothiazole to trimethylsilylacetylene is 1:1 to 1.1.

[0012] A method for preparing an electrolyte for a sodium ion battery comprises the following steps: S1. Weigh each component by weight; S2. After mixing the organic solvent evenly, add the composite additive, stir and mix evenly to prepare an electrolyte matrix; S3. Add sodium salt to the electrolyte matrix, stir and mix evenly, and prepare an electrolyte for sodium ion battery.

[0013] Beneficial effects of the present invention: The invention uses 2-cyano-6-hydroxybenzothiazole and liquid bromine to react to generate 2-cyano-6-hydroxy-5-bromobenzothiazole, then carries out a substitution reaction between the phenolic hydroxyl group in the 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, and then carries out a coupling reaction between the 2-cyano-6-diethyl phosphate-5-bromobenzothiazole and trimethylsilylacetylene under the catalysis of bistriphenylphosphine palladium dichloride and cuprous iodide to prepare a modified additive. The -C≡N group contained in the modified additive can attract sodium ions to form solvation clusters, change the solvation structure, and then change the formation path of the solid electrolyte interface (SEI), construct a more stable SEI on the hard carbon surface, and improve the compatibility between the electrolyte and the hard carbon negative electrode. At the same time, the -C≡N group and diethyl phosphate participate in the construction of a more stable SEI, which is beneficial to improving the capacity performance and cycle performance of sodium ion batteries. In addition, the modified additive contains four flame retardant elements, N, S, P and Si, which can greatly improve the flame retardant effect through synergistic action, reduce the demand for flame retardants, and prevent excessive flame retardants from having a negative impact on the battery. DETAILED DESCRIPTION

[0014] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0015] Example 1 A method for preparing a modified additive comprises the following steps: A. Take 4.26g 2-cyano-6-hydroxybenzothiazole and 50mL dichloromethane in a reactor, place in an ice-water bath, add a mixed solution of 1.26mL liquid bromine and 5mL dichloromethane, stir and react for 2h, after the reaction is completed, add 50mL saturated sodium thiosulfate aqueous solution, then add 50mL dichloromethane, stir, static layering, collect the organic phase, dry over anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole; B. The reactor filled with 50mL tetrahydrofuran was placed in an ice-water bath, 0.7g 60% sodium hydride, 4.46g 2-cyano-6-hydroxy-5-bromobenzothiazole and 3.02g diethyl chlorophosphate were added successively, the reaction was stirred for 1h at room temperature, 10mL saturated ammonium chloride solution was added after the reaction was completed, 50mL ether and 50mL saturated aqueous common salt were added, static layering, the organic phase was collected, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole; C. Take 50 mL of triethylamine in a reactor, pass argon protection, add 3.9 g of 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, 0.07 g of bistriphenylphosphine palladium dichloride and 0.038 g of cuprous iodide, maintain the argon atmosphere, slowly add 1.08 g of trimethylsilyl acetylene, then raise the temperature to 75 ° C and react for 5 hours. After the reaction is completed, it is rotary evaporated, washed and dried to prepare a modified additive.

[0016] Example 2 An electrolyte for a sodium ion battery comprises the following components in parts by weight: 22 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of ethyl methyl carbonate, and 11 parts of a composite additive, wherein the composite additive is a mixture of fluoroethylene carbonate and the modified additive prepared in Example 1 in a mass ratio of 1:1.

[0017] The method for preparing the above-mentioned sodium ion battery electrolyte comprises the following steps: S1. Weigh each component by weight; S2. Ethylene carbonate, propylene carbonate, and ethyl methyl carbonate are mixed evenly, and then a composite additive is added, and the mixture is stirred and mixed evenly to prepare an electrolyte matrix; S3. Add sodium hexafluorophosphate to the electrolyte matrix, stir and mix evenly, and prepare an electrolyte for a sodium ion battery.

[0018] Example 3 An electrolyte for a sodium ion battery comprises the following components in parts by weight: 30 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of ethyl methyl carbonate, and 14 parts of a composite additive, wherein the composite additive is a mixture of fluoroethylene carbonate and the modified additive prepared in Example 1 in a mass ratio of 2:1.

[0019] The preparation method of the electrolyte for sodium ion battery is the same as that in Example 2.

[0020] Example 4 An electrolyte for a sodium ion battery comprises the following components in parts by weight: 37 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of ethyl methyl carbonate, and 18 parts of a composite additive, wherein the composite additive is a mixture of fluoroethylene carbonate and the modified additive prepared in Example 1 in a mass ratio of 3:1.

[0021] The preparation method of the electrolyte for sodium ion battery is the same as that in Example 2.

[0022] Comparative Example 1 A method for preparing a modified additive comprises the following steps: A. Take 4.26g 2-cyano-6-hydroxybenzothiazole and 50mL dichloromethane in a reactor, place in an ice-water bath, add a mixed solution of 1.26mL liquid bromine and 5mL dichloromethane, stir and react for 2h, after the reaction is completed, add 50mL saturated sodium thiosulfate aqueous solution, then add 50mL dichloromethane, stir, static layering, collect the organic phase, dry over anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole; B. Place a reactor containing 50 mL of tetrahydrofuran in an ice-water bath, add 0.7 g of 60% sodium hydride immersed in mineral oil, 4.46 g of 2-cyano-6-hydroxy-5-bromobenzothiazole and 3.02 g of diethyl chlorophosphate in sequence, and stir the reaction at room temperature for 1 hour. After the reaction is completed, add 10 mL of saturated ammonium chloride solution, then add 50 mL of ether and 50 mL of saturated brine, let it stand and separate, collect the organic phase, dry it with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare a modified additive.

[0023] Comparative Example 2 An electrolyte for a sodium ion battery comprises the following components in parts by weight: 30 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of ethyl methyl carbonate, and 9 parts of fluoroethylene carbonate.

[0024] The method for preparing the above-mentioned sodium ion battery electrolyte comprises the following steps: S1. Weigh each component by weight; S2. Ethylene carbonate, propylene carbonate, and ethyl methyl carbonate are mixed evenly, and then fluoroethylene carbonate is added, and the mixture is stirred and mixed evenly to prepare an electrolyte matrix; S3. Add sodium hexafluorophosphate to the electrolyte matrix, stir and mix evenly, and prepare an electrolyte for a sodium ion battery.

[0025] Comparative Example 3 An electrolyte for a sodium ion battery comprises the following components in parts by weight: 30 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of ethyl methyl carbonate, and 14 parts of a composite additive, wherein the composite additive is a mixture of fluoroethylene carbonate and trimethyl phosphate in a mass ratio of 2:1.

[0026] The preparation method of the electrolyte for sodium ion battery is the same as that in Example 2.

[0027] Comparative Example 4 An electrolyte for a sodium ion battery comprises the following components in parts by weight: 30 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of ethyl methyl carbonate, and 14 parts of a composite additive, wherein the composite additive is a mixture of fluoroethylene carbonate and the modified additive prepared in Comparative Example 1 in a mass ratio of 2:1.

[0028] The preparation method of the electrolyte for sodium ion battery is the same as that in Example 2.

[0029] Performance testing A. The electrolytes prepared in Examples 2-4 and Comparative Examples 2-4 were subjected to flammability testing: The prepared electrolytes were subjected to a flammability test using a direct ignition method. 0.15 g of the electrolyte to be tested was dropped into a battery shell with a diameter of 20 mm, and ignited with a lighter. The burning time was recorded. The above process was repeated multiple times and the average value was taken. The data results are shown in Table 1.

[0030] Table 1 Electrolyte flammability test results As can be seen from the data in Table 1, the electrolytes prepared in Examples 2-4 of the present invention have good flame retardant effects. In Comparative Example 2, no modifying additive was added, while in Comparative Example 3, an equal amount of the modifying additive was replaced with trimethyl phosphate. The self-extinguishing time of Comparative Example 2-3 was significantly longer than that of Examples 2-4. This is because the presence of four flame retardant elements, N, S, P, and Si, in the modifying additive structure greatly enhances the flame retardant effect of the electrolyte. In Comparative Example 4, the modifying additive component was not grafted with trimethylsilyl acetylene, and the self-extinguishing time measured was slightly longer than that of Examples 2-4, indicating that the grafting of trimethylsilyl acetylene further enhances the flame retardant effect of the electrolyte to a certain extent.

[0031] B. Hard carbon, conductive carbon black, carboxymethyl cellulose, and styrene-butadiene rubber were added to deionized water in a mass ratio of 96:1.5:1.5:1 and stirred evenly to form a slurry. The prepared slurry was coated on a carbon-coated aluminum foil with a thickness of 100 μm. The coated aluminum foil was placed in a vacuum drying oven and dried at 120°C for 12 h. The discs were cut into 14 mm diameter wafers to obtain electrode sheets. The electrode materials were assembled into a half-cell using a button battery case (CR2016 type) for testing. The positive electrode was the prepared electrode sheet, the counter electrode was a metal sodium sheet (diameter 16 mm), the separator was a Whatman GF / D (diameter 19 mm), and the electrolytes prepared in Example 2-4 and Comparative Example 2-4 were used as the electrolyte. After the components were assembled, they were packaged and the constant current charge and discharge performance test was performed: the measurement was performed using a CT3002A blue electric test system with a voltage window of 0-2 V and a current density of 30 mA / g. The data results are shown in Table 2.

[0032] Table 2 Electrochemical performance test results of sodium ion batteries As can be seen from the data in Table 2, the sodium-ion batteries prepared in Examples 2-4 of the present invention have high first-cycle reversible specific capacity and first-cycle coulombic efficiency, and exhibit good capacity performance and cycle performance. The capacity performance and cycle performance measured in Comparative Examples 2-3 are lower than those in Examples 2-4, indicating that the addition of the modifying additive can improve the capacity performance and cycle performance of the battery.

[0033] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0034] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. An electrolyte for a sodium ion battery, characterized in that The invention comprises the following components in parts by weight: 20-40 parts of sodium salt, 100-120 parts of organic solvent, and 10-20 parts of composite additive; the composite additive is a mixture of fluoroethylene carbonate and a modifying additive in a mass ratio of 1-3:1; The modified additive is prepared by reacting 2-cyano-6-hydroxybenzothiazole with liquid bromine to generate 2-cyano-6-hydroxy-5-bromobenzothiazole, then subjecting the phenolic hydroxyl group in the 2-cyano-6-hydroxy-5-bromobenzothiazole to a substitution reaction with diethyl chlorophosphate, and subsequently subjecting the prepared 2-cyano-6-diethyl phosphate-5-bromobenzothiazole to a coupling reaction with trimethylsilylacetylene under the catalysis of bistriphenylphosphine palladium dichloride and cuprous iodide.

2. The sodium ion battery electrolyte according to claim 1, wherein The sodium salt is one or more combinations of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, and sodium perchlorate.

3. The sodium ion battery electrolyte according to claim 1, wherein The organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

4. The sodium ion battery electrolyte according to claim 1, wherein The preparation method of the modified additive comprises the following steps: A. Take 2-cyano-6-hydroxybenzothiazole and dichloromethane in a reactor, place it in an ice-water bath, add a mixture of liquid bromine and dichloromethane, and stir the reaction for 1.5 to 2 hours. After the reaction is completed, add saturated sodium thiosulfate aqueous solution, then add dichloromethane, stir, stand and separate, collect the organic phase, dry it with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole; B. Place a reactor containing tetrahydrofuran in an ice-water bath, add 60% sodium hydride immersed in mineral oil, 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate in sequence, and stir the reaction at room temperature for 1-1.5 hours. After the reaction is completed, add saturated ammonium chloride solution, then add ether and saturated brine, and allow to stand for separation. Collect the organic phase, dry it with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole; C. Take triethylamine in a reactor, pass argon protection, add 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, bistriphenylphosphine palladium dichloride and cuprous iodide, maintain the argon atmosphere, slowly add trimethylsilyl acetylene dropwise, then raise the temperature to 70-80℃ and react for 4-6h. After the reaction is completed, it is rotary evaporated, washed and dried to prepare the modified additive.

5. The electrolyte for sodium ion batteries according to claim 4, characterized in that In step A, the molar ratio of 2-cyano-6-hydroxybenzothiazole to liquid bromine is 1:1-1.

02.

6. The electrolyte for sodium ion batteries according to claim 4, characterized in that In the step B, the molar ratio of 2-cyano-6-hydroxy-5-bromobenzothiazole to diethyl chlorophosphate is 1:1-1.

1.

7. The electrolyte for sodium ion batteries according to claim 4, characterized in that In the step C, the molar ratio of 2-cyano-6-diethyl phosphate-5-bromobenzothiazole to trimethylsilylacetylene is 1:1-1.

1.

8. A method for preparing an electrolyte for a sodium ion battery according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Weigh each component by weight; S2. After mixing the organic solvent evenly, add the composite additive, stir and mix evenly to prepare an electrolyte matrix; S3. Add sodium salt to the electrolyte matrix, stir and mix evenly, and prepare an electrolyte for sodium ion battery.

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