Electrolyte for sodium-ion battery and preparation method thereof

Abstract

The application 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 fluorinated ethylene carbonate and a modified additive at a mass ratio of 1-3:1. The modified additive is prepared by the following steps: 2-cyano-6-hydroxybenzothiazole is reacted with liquid bromine to generate 2-cyano-6-hydroxy-5-bromobenzothiazole, then a substitution reaction is performed on the 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, a coupling reaction is performed on the prepared 2-cyano-6-diethyl phosphate-5-bromobenzothiazole and trimethylsilylethine to generate the modified additive. The electrolyte with good flame-retardant effect is prepared by adding the modified additive, and the sodium ion battery has good capacity performance and cycle performance.

Description

TECHNICAL FIELD

[0001] The application 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

[0002] Sodium ion batteries have similar working principles to lithium ion batteries and relatively low development costs, and show great development potential in large-scale energy storage applications. A sodium ion battery is composed of a positive electrode, a negative electrode, a separator and an electrolyte. In the charging process, sodium ions are released from the positive electrode, transported through the electrolyte and embedded into the negative electrode material. In the discharging process, sodium ions are released from the negative electrode material, transported through the electrolyte and embedded into the positive electrode material. The working principle is similar to that of a rocking chair. The electrolyte, as the "blood" of the battery, plays a role in transporting sodium ions during charging and discharging. The conductivity, ion diffusion rate and other characteristics of the electrolyte have a great influence on the overall performance of the battery.

[0003] When the temperature and pressure inside the existing sodium ion battery increase due to some abuses (such as overcharging, heating, penetration, crushing, etc.), volatile flammable solvents are easily discharged and ignited, causing serious fire hazards. Therefore, the prior art improves the safety of sodium ion batteries by modifying the electrolyte. Generally, a flame retardant is introduced into the electrolyte to reduce the flammability of the electrolyte. The most commonly used flame retardant is trimethyl phosphate, which has poor reduction stability and will decompose strongly on the surface of the hard carbon negative electrode, generating phosphoric acid dissolved in the electrolyte, as well as a large amount of methane and ethylene gas, resulting in deterioration of battery performance. Excess trimethyl phosphate combined with sodium ions enters the interlayer of hard carbon, damaging the mechanical structure of hard carbon and causing a decrease in sodium storage capacity, which affects the electrochemical performance of the sodium ion battery. SUMMARY

[0004] To solve the problems mentioned in the background, the purpose of the present application is to provide an electrolyte for a sodium ion battery and a preparation method thereof. By adding a modified additive, an electrolyte with good flame retardant effect is prepared, and the sodium ion battery has good capacity performance and cycle performance.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] An electrolyte for a sodium ion battery comprises the following components 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 modified additive in a mass ratio of 1-3:1.

[0007] The modified additive is prepared by reacting 2-cyano-6-hydroxybenzothiazole and liquid bromine to form 2-cyano-6-hydroxy-5-bromobenzothiazole, then substituting the phenolic hydroxyl group in 2-cyano-6-hydroxy-5-bromobenzothiazole with diethyl chlorophosphate, and then coupling the prepared 2-cyano-6-diethyl phosphate-5-bromobenzothiazole with trimethylsilacetylene in the presence of dichlorobis(triphenylphosphine)palladium and cuprous iodide.

[0008] Preferably, the sodium salt is one or more of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium perchlorate.

[0009] Preferably, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate.

[0010] Preferably, the method for preparing the modified additive comprises the following steps:

[0011] A. 2-cyano-6-hydroxybenzothiazole and dichloromethane are taken into a reactor, which is placed in an ice water bath, and a mixture of liquid bromine and dichloromethane is added, and stirred for 1.5-2 hours. After the reaction is completed, saturated aqueous sodium thiosulfate solution is added, followed by dichloromethane, stirring, static layering, collection of the organic phase, drying with anhydrous sodium sulfate, and rotary evaporation to remove the solvent, to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole;

[0012] B. The reactor containing tetrahydrofuran is placed in an ice water bath, and 60% sodium hydride immersed in mineral oil, 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate are added in sequence, and stirred at room temperature for 1-1.5 hours. After the reaction is completed, saturated ammonium chloride solution is added, followed by addition of diethyl ether and saturated brine, static layering, collection of the organic phase, drying with anhydrous sodium sulfate, and rotary evaporation to remove the solvent, to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole;

[0013] C. Triethylamine is taken into a reactor, which is protected by argon, and 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, dichlorobis(triphenylphosphine)palladium and cuprous iodide are added, argon atmosphere is maintained, and trimethylsilacetylene is slowly added dropwise, and then the temperature is raised to 70-80°C for 4-6 hours of reaction. After the reaction is completed, rotary evaporation, washing and drying are performed to prepare the modified additive.

[0014] Preferably, the molar ratio of 2-cyano-6-hydroxybenzothiazole to liquid bromine in step A is 1:1-1.02.

[0015] Preferably, the molar ratio of 2-cyano-6-hydroxy-5-bromobenzothiazole to diethyl chlorophosphate in step B is 1:1-1.1.

[0016] Preferably, the molar ratio of 2-cyano-6-diethyl phosphate-5-bromobenzothiazole and trimethylsilylacetylene in step C is 1:1~1.1.

[0017] A preparation method of an electrolyte for a sodium ion battery, comprising the following steps:

[0018] S1, each component is weighed by parts by weight;

[0019] S2, after the organic solvent is mixed uniformly, the composite additive is added, and stirred and mixed uniformly to prepare an electrolyte matrix;

[0020] S3, the sodium salt is added to the electrolyte matrix, and stirred and mixed uniformly to prepare the electrolyte for the sodium ion battery.

[0021] The beneficial effects of the present application are:

[0022] The present application utilizes the reaction of 2-cyano-6-hydroxybenzothiazole and liquid bromine to generate 2-cyano-6-hydroxy-5-bromobenzothiazole, then the phenolic hydroxyl group in 2-cyano-6-hydroxy-5-bromobenzothiazole and diethyl chlorophosphate undergo substitution reaction to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, and then under the catalysis of bis-triphenylphosphine palladium dichloride and cuprous iodide, 2-cyano-6-diethyl phosphate-5-bromobenzothiazole and trimethylsilylacetylene undergo coupling reaction to prepare the modified additive. The -C≡N group contained in the modified additive can attract sodium ions to form solvated clusters, change the solvation structure, and then change the formation path of the solid electrolyte interface (SEI), build a more stable SEI on the surface of hard carbon, and improve the compatibility of the electrolyte with the hard carbon negative electrode. At the same time, the -C≡N group and diethyl phosphate participate in building a more stable SEI, which is conducive to improving the capacity performance and cycle performance of the sodium ion battery. In addition, the modified additive contains four flame-retardant elements of N, S, P and Si, which can greatly improve the flame-retardant effect through synergistic effect, reduce the demand for flame retardants, and prevent the negative impact of excessive flame retardants on the battery. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] The preparation method of the modified additive in embodiment 1 comprises the following steps:

[0025] A. Take 4.26g 2-cyano-6-hydroxybenzothiazole and 50mL dichloromethane in a reactor, place in ice water bath, add 1.26mL liquid bromine and 5mL dichloromethane mixture, stir for 2h, after the reaction is completed, add 50mL saturated sodium thiosulfate aqueous solution, then add 50mL dichloromethane, stir, separate the layers, collect the organic phase, dry with anhydrous sodium sulfate, rotary evaporation to remove the solvent, to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole;

[0026] B. Put the reactor containing 50mL tetrahydrofuran in an ice water bath, add 0.7g 60% sodium hydride immersed in mineral oil, 4.46g 2-cyano-6-hydroxy-5-bromobenzothiazole and 3.02g diethyl chlorophosphate in turn, stir at room temperature for 1h, after the reaction is completed, add 10mL saturated ammonium chloride solution, then add 50mL ether and 50mL saturated brine, separate the layers, collect the organic phase, dry with anhydrous sodium sulfate, rotary evaporation to remove the solvent, to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole;

[0027] C. Take 50mL triethylamine in a reactor, protect with argon, add 3.9g 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, 0.07g dichlorobis(triphenylphosphine)palladium and 0.038g cuprous iodide, maintain argon atmosphere, slowly add 1.08g trimethylsilylacetylene, then heat to 75℃ for 5h, after the reaction is completed, rotary evaporation, washing, drying, to prepare the modified additive.

[0028] Example 2 An electrolyte for sodium ion battery, comprising the following components by weight: 22 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of methyl ethyl carbonate, 11 parts of 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.

[0029] The preparation method of the above-mentioned electrolyte for sodium ion battery, comprising the following steps:

[0030] S1. Weigh each component by weight;

[0031] S2. Mix ethylene carbonate, propylene carbonate and methyl ethyl carbonate uniformly, then add the composite additive, stir and mix uniformly, to prepare the electrolyte base;

[0032] S3. Add sodium hexafluorophosphate to the electrolyte base, stir and mix uniformly, to prepare the electrolyte for sodium ion battery.

[0033] Example 3 An electrolyte for a sodium ion battery, comprising the following components by weight: 30 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of methyl ethyl 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.

[0034] The preparation method of the above-mentioned electrolyte for a sodium ion battery is the same as that of Example 2.

[0035] Example 4 An electrolyte for a sodium ion battery, comprising the following components by weight: 37 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of methyl ethyl 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.

[0036] The preparation method of the above-mentioned electrolyte for a sodium ion battery is the same as that of Example 2.

[0037] Preparation method of the modified additive in Comparative Example 1, comprising the following steps:

[0038] A. Take 4.26g 2-cyano-6-hydroxybenzothiazole and 50mL dichloromethane in a reactor, place in an ice water bath, add 1.26mL liquid bromine and 5mL dichloromethane mixture, stir for 2h, after the reaction is completed, add 50mL saturated sodium thiosulfate aqueous solution, then add 50mL dichloromethane, stir, separate the layers, collect the organic phase, dry with anhydrous sodium sulfate, rotary evaporation to remove the solvent, to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole;

[0039] B. Place the reactor containing 50mL tetrahydrofuran in an ice water bath, add 0.7g 60% sodium hydride immersed in mineral oil, 4.46g 2-cyano-6-hydroxy-5-bromobenzothiazole and 3.02g diethyl chlorophosphate in sequence, stir at room temperature for 1h, after the reaction is completed, add 10mL saturated ammonium chloride solution, then add 50mL ether and 50mL saturated brine, separate the layers, collect the organic phase, dry with anhydrous sodium sulfate, rotary evaporation to remove the solvent, to prepare the modified additive.

[0040] Comparative Example 2 An electrolyte for a sodium ion battery, comprising the following components by weight: 30 parts of sodium hexafluorophosphate, 15 parts of ethylene carbonate, 15 parts of propylene carbonate, 70 parts of methyl ethyl carbonate, and 9 parts of fluoroethylene carbonate.

[0041] The preparation method of the above-mentioned electrolyte for a sodium ion battery, comprising the following steps:

[0042] S1, weigh each component by weight;

[0043] S2, ethylene carbonate, propylene carbonate and methyl ethyl carbonate were mixed uniformly, then fluorinated ethylene carbonate was added, and stirring was performed to mix uniformly, to prepare an electrolyte matrix;

[0044] S3, sodium hexafluorophosphate was added to the electrolyte matrix, and stirring was performed to mix uniformly, to prepare the electrolyte for sodium ion batteries.

[0045] Comparative Example 3: An electrolyte for sodium ion batteries, comprising the following components in parts by weight: sodium hexafluorophosphate 30 parts, ethylene carbonate 15 parts, propylene carbonate 15 parts, methyl ethyl carbonate 70 parts, and a composite additive 14 parts, wherein the composite additive is a mixture of fluorinated ethylene carbonate and trimethyl phosphate in a mass ratio of 2:1.

[0046] The preparation method of the electrolyte for sodium ion batteries is the same as that in Example 2.

[0047] Comparative Example 4: An electrolyte for sodium ion batteries, comprising the following components in parts by weight: sodium hexafluorophosphate 30 parts, ethylene carbonate 15 parts, propylene carbonate 15 parts, methyl ethyl carbonate 70 parts, and a composite additive 14 parts, wherein the composite additive is a mixture of fluorinated ethylene carbonate and the modified additive prepared in Comparative Example 1 in a mass ratio of 2:1.

[0048] The preparation method of the electrolyte for sodium ion batteries is the same as that in Example 2.

[0049] Performance detection

[0050] A, flammability detection was performed on the electrolytes prepared in Examples 2-4 and Comparative Examples 2-4: 0.15 g of the electrolyte to be tested was dropped into a battery shell with a diameter of 20 mm, and a lighter was used to ignite it, and the burning time was recorded. The above process was repeated several times to obtain an average value, and the data results are shown in Table 1.

[0051] Table 1: Flammability detection results of electrolytes

[0052]

[0053] As can be seen from the data results in Table 1, the electrolyte prepared in Example 2-4 has good flame retardant effect. In Comparative Example 2, no modified additive is added, and in Comparative Example 3, the modified additive is replaced by an equal amount of trimethyl phosphate, and the self-extinguishing time of Comparative Examples 2-3 is significantly increased compared with Example 2-4, because the modified additive structure contains four flame-retardant elements of N, S, P and Si, which greatly improves the flame-retardant effect of the electrolyte. In Comparative Example 4, the modified additive component is not grafted with trimethylsilylethynyl, and the self-extinguishing time is slightly higher than that of Example 2-4, which shows that the grafting of trimethylsilylethynyl further improves the flame-retardant effect of the electrolyte to a certain extent.

[0054] B, hard carbon, conductive carbon black, carboxymethyl cellulose, butadiene rubber were added into deionized water in a mass ratio of 96:1.5:1.5:1 to stir uniformly to prepare a slurry, the prepared slurry was coated on a carbon-coated aluminum foil with a thickness of 100 μm, and the coated aluminum foil was placed in a vacuum drying oven at 120°C for 12h, cut into a disc with a diameter of 14mm to obtain an electrode sheet, a button cell shell (CR2016 type) was used to assemble the electrode material into a half battery for testing, the positive electrode was the prepared electrode sheet, the counter electrode was a metal sodium sheet (diameter 16mm), the separator was Whatman GF / D (diameter 19mm), and the electrolyte was the electrolyte prepared in examples 2-4 and comparative examples 2-4. After assembling and packaging, the constant current charge-discharge performance test was carried out: the CT3002A type blue light test system was used for determination, the voltage window was 0-2V, and the current density was 30mA / g. The data results are shown in Table 2.

[0055] Table 2: Sodium ion battery electrochemical performance test results

[0056]

[0057] From the data results in Table 2, it can be seen that the sodium ion battery prepared in example 2-4 has high initial reversible specific capacity and initial coulombic efficiency, and has good capacity performance and cycle performance. The capacity performance and cycle performance measured in comparative example 2-3 are lower than those of example 2-4, indicating that the addition of the modified additive can improve the capacity performance and cycle performance of the battery.

[0058] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0059] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. An electrolyte for a sodium-ion battery, characterized by, The sodium salt is one or more combinations of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, and sodium perchlorate. The organic solvent is one or more combinations of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

2. The electrolyte for sodium-ion batteries according to claim 1, characterized in that, The preparation method of the modified additive comprises the following steps:

3. The electrolyte for sodium-ion batteries according to claim 1, characterized in that, A. 2-cyano-6-hydroxybenzothiazole and dichloromethane are taken in a reactor, placed in an ice water bath, and a mixture of liquid bromine and dichloromethane is added, stirred for 1.5-2 hours, saturated sodium thiosulfate aqueous solution is added after the reaction is completed, dichloromethane is then added, stirred, and static layering is performed, the organic phase is collected, dried with anhydrous sodium sulfate, and solvent is removed by rotary evaporation to prepare 2-cyano-6-hydroxy-5-bromobenzothiazole; 4. The electrolyte for sodium-ion batteries according to claim 1, characterized in that, B. The reactor containing tetrahydrofuran is placed in an ice water bath, 60% sodium hydride immersed in mineral oil, 2-cyano-6-hydroxy-5-bromobenzothiazole, and diethyl chlorophosphate are sequentially added, stirred at room temperature for 1-1.5 hours, saturated ammonium chloride solution is added after the reaction is completed, ether and saturated brine are then added, static layering is performed, the organic phase is collected, dried with anhydrous sodium sulfate, and solvent is removed by rotary evaporation to prepare 2-cyano-6-diethyl phosphate-5-bromobenzothiazole; C. Triethylamine is taken in a reactor, argon gas is introduced for protection, 2-cyano-6-diethyl phosphate-5-bromobenzothiazole, bis(triphenylphosphine)palladium dichloride, and cuprous iodide are added, an argon atmosphere is maintained, trimethylsilacetylene is slowly added dropwise, and then the temperature is increased to 70-80°C for 4-6 hours of reaction, and after the reaction is completed, rotary evaporation, washing, and drying are performed to prepare the modified additive. The molar ratio of 2-cyano-6-hydroxybenzothiazole to liquid bromine in step A is 1:1-1.

02. The molar ratio of 2-cyano-6-hydroxy-5-bromobenzothiazole to diethyl chlorophosphate in step B is 1:1-1.

1.

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

1.

6. The electrolyte for sodium-ion batteries according to claim 4, characterized in that, The method comprises the following steps:

7. The electrolyte for sodium-ion batteries according to claim 4, characterized in that, S1. The components are weighed according to the weight parts; 8. A method for preparing the electrolyte for sodium-ion batteries according to any one of claims 1 to 7, characterized in that, S2. The organic solvent is mixed uniformly, the modified additive is added, and stirring and mixing are performed to prepare an electrolyte base; S3. The sodium salt is added to the electrolyte base, stirring and mixing are performed, and an electrolyte for a sodium ion battery is prepared. ​ ​

Images