Preparation method of sodium battery additive and application of sodium battery additive in sodium battery

Abstract

The invention relates to the technical field of sodium ion batteries, and discloses a preparation method of a sodium battery additive and application of the sodium battery additive in a sodium battery, and the preparation method comprises the following steps: a) a reaction step: in an isopropanol solvent, enabling pyromellitic acid and sodium hydroxide to react under heating and stirring; after the reaction is finished, filtering a reaction product to obtain a benzene tetracarboxylic acid sodium crude product; b) a purification step: dissolving the benzene tetracarboxylic acid sodium crude product in water, and heating for rotary evaporation until the solution reaches a saturated state; adding methanol into the solution in the saturated state to separate out a solid, and filtering a mixture containing the solid while the mixture is hot; and carrying out vacuum drying on the solid obtained by filtering to obtain the sodium electric additive. According to the invention, the high-purity product is used as the sodium-ion battery additive, and the comprehensive performances of high-temperature circulation, high magnification, low temperature and the like of the battery can be comprehensively and obviously improved through a unique mechanism of synchronously forming a stable protective film on a positive electrode and a negative electrode.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a preparation method of a sodium battery additive and application of the sodium battery additive in a sodium battery. BACKGROUND

[0002] With the continuous growth of industries such as electric vehicles, renewable energy and smart grids, people's demand for sustainable energy and environmental protection solutions is increasing. Under this background, sodium ion batteries gradually entered people's field of vision and became a hot topic in the global energy storage industry. Sodium ion batteries are a kind of secondary batteries, which mainly rely on sodium ions to move between the positive electrode and the negative electrode to work, similar to the working principle of lithium ion batteries. Compared with lithium ion batteries, sodium ion batteries can achieve lower cost, higher cost performance and better environmental protection, and have broad prospects in the fields of energy storage and two-wheeled vehicles.

[0003] Sodium electrolyte is a carrier for transmitting sodium ions, which is composed of electrolyte, solvent and additive. When charging, sodium ions are released from the positive electrode, pass through the pore of the diaphragm and are embedded in the negative electrode through the electrolyte; when discharging, sodium ions are released from the negative electrode, pass through the pore of the diaphragm and are embedded in the positive electrode through the electrolyte. The additive of sodium battery electrolyte is similar to that of lithium battery. Vinylene carbonate is a representative of the additive, which is basically used in high-voltage electrolyte formula, and the addition amount is 1.5-3%. For a long time, the mechanism of VC is considered to be that, in the battery formation process, it is reduced on the negative electrode surface before vinylene carbonate to form a solid-state electrolyte interface film. However, more than 1.5% VC will cause the impedance of the battery to increase, affecting the rate performance and low-temperature performance of the battery, and the interface film of VC is unstable under high temperature and high voltage conditions, so FEC, NaPO2F2 and 1,3-PS additives are added for compounding in practical application, but the compounded system also has the defects of high-temperature instability or low-temperature low efficiency. Moreover, the existing preparation methods of sodium battery additives such as vinylene carbonate, sodium difluorophosphate and sodium bisfluorosulfonylimide have the problems of low purity of the obtained product, narrow application range, complex reaction, many by-products and difficult process separation.

[0004] A Chinese patent document with publication number CN115140715A discloses a preparation method of a double fluorosulfonyl imide alkali metal salt. First, halogenated sulfuryl isocyanate and halogenated sulfonic acid are reacted to prepare a double halogenated sulfuryl imide acid; then the double halogenated sulfuryl imide acid is reacted with an alkali metal fluorohydride to produce a double fluorosulfonyl imide alkali metal salt. However, the halogenated sulfuryl isocyanate and halogenated sulfonic acid used in this method are brominated or iodinated, which are not easy to obtain and expensive. Moreover, the reaction with the alkali metal fluorohydride generates toxic gases such as hydrogen chloride and hydrogen fluoride. A Chinese patent document with publication number CN115028146A discloses a preparation method of a double fluorosulfonyl imide sodium. Amino sulfonic acid and fluorosulfonic acid are added to a reaction kettle, and carbonyl fluoride is introduced to prepare a double fluorosulfonyl imide, which is then reacted with sodium alcoholate to obtain a double fluorosulfonyl imide sodium. This method uses toxic carbonyl fluoride as a raw material, which is not easy to obtain, and uses sodium alcoholate as a raw material, which is dangerous. A Chinese patent document with publication number CN116101996A discloses a combined preparation method of difluorophosphate and monofluorophosphate. Hydrofluoric acid is used in the first step, which is dangerous. Both the first and second steps need to be purified, which is complicated. A Chinese patent document with publication number CN115947351A discloses a method for co-production of sodium hexafluorophosphate and sodium difluorophosphate. However, this process first needs to react anhydrous hydrofluoric acid with phosphorus, then generates phosphorus oxytrifluoride with oleum, and then generates sodium difluorophosphate with phosphorus oxytrifluoride, sodium source and silicon oxide. The whole process is complicated, uses dangerous hydrofluoric acid and oleum as raw materials, and the silicon oxide used in the second step is expensive. The generated phosphorus oxytrifluoride and phosphorus pentafluoride are also toxic gases. The whole process is expensive and not environmentally friendly.

[0005] A patent with publication number CN117199527A reports a sodium electrolyte additive of boroxin derivative, which is claimed to improve the high-temperature and low-temperature performance of sodium batteries. However, the data from its examples show that the capacity retention rate at 45℃ is only 79.5%, and the discharge capacity retention rate at -20℃ is only 75.7%-82.6%. The improvement in high and low temperature performance of the battery is not significant. A patent with publication number CN117096435A reports a sodium battery additive containing sulfur. However, its effect on the initial efficiency and cycle performance of sodium batteries is limited. A patent with publication number CN1168057114A reports a sodium battery additive containing sulfonic acid group, amino group and nitrile group. However, the capacity of the battery using this additive is only about 120 mAh / g, which is at a low level. A patent with publication number CN113921907A reports a silicon-based / boron-based sodium battery additive. However, its rate performance in sodium batteries is low. A patent with publication number CN116207350A reports an acetylsulfanilic acid sodium additive. However, the capacity recovery rate of the battery using this additive is not high at room temperature, high temperature cycling, and high temperature storage.

[0006] Patent with publication number CN202411351280.0 reports a preparation method of lithium benzene tetra carboxylate, but the purification condition is to heat the crude lithium benzene tetra carboxylate and dissolve it in ethanol for recrystallization, and the efficiency of purification still needs to be improved, and the battery performance of the obtained product still needs to be improved. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a preparation method of a sodium battery additive and its application in a sodium battery, which solves the problems of complex preparation process, environmental pollution, high cost and difficulty in effectively improving the high-temperature, low-temperature and rate performance of sodium ion batteries of the sodium battery additive in the prior art.

[0008] To achieve the above object, the present application is implemented by the following technical scheme: a preparation method of a sodium battery additive and its application in a sodium battery, comprising the following steps: a) reaction step: in isopropanol solvent, uniform benzene tetra carboxylic acid is reacted with sodium hydroxide under heating and stirring; after the reaction is completed, the reaction product is filtered to obtain sodium benzene tetra carboxylate crude product; b) purification step: the sodium benzene tetra carboxylate crude product is dissolved in water and heated for rotary evaporation until the solution reaches a saturated state; methanol is added to the saturated solution to precipitate a solid, and the mixture containing the solid is filtered while hot; and the solid obtained by filtration is vacuum dried to obtain a sodium battery additive.

[0009] Preferably, in a), the concentration of uniform benzene tetra carboxylic acid in isopropanol solvent is 0.1 mol / L to 0.3 mol / L; the molar ratio of uniform benzene tetra carboxylic acid to sodium hydroxide is 1:3.8 to 1:4.2; the reaction temperature is 60℃ to 120℃, and the reaction time is 28 hours to 44 hours.

[0010] Preferably, the reaction temperature is 80℃ to 100℃, and the reaction time is 32 hours to 40 hours.

[0011] Preferably, in b), the mass-volume ratio of sodium benzene tetra carboxylate crude product to water is 1g:(10-20)ml; the temperature of heating and rotary evaporation is 60℃ to 80℃; the volume-mass ratio of methanol to sodium benzene tetra carboxylate crude product is (2-3)ml:1g; the temperature of vacuum drying is 70℃ to 90℃, and the time is 16 hours to 24 hours.

[0012] The application of a sodium battery additive in a sodium battery, the application of the sodium battery additive prepared by any one of claims 1 to 4 in the preparation of an electrolyte for a sodium ion battery.

[0013] The present application provides a preparation method of a sodium battery additive and its application in a sodium battery. The present application has the following beneficial effects: 1. The preparation method of sodium benzene-1,2,4,5-tetracarboxylate provided by the present application has a simplified process flow, mild reaction conditions, is green and environmentally friendly, has a high total yield of product, is easy to realize industrial production, and reduces the preparation cost.

[0014] 2. The sodium benzene-1,2,4,5-tetracarboxylate product prepared by the present application has high purity, and the content of key impurities such as free acid, moisture, chloride ions and sulfate ions, which have a negative impact on the electrochemical performance of batteries, can be effectively controlled at a very low level, thereby fundamentally ensuring the quality and performance stability of the product as an electrolyte additive.

[0015] 3. The high-purity sodium benzene-1,2,4,5-tetracarboxylate prepared by the present application is used as an electrolyte additive for sodium-ion batteries, and compared with VC or its complex system commonly used in the prior art, can cooperatively build a more stable and denser interface protection film on the surface of the positive electrode and the negative electrode. Therefore, the sodium-ion battery using the additive of the present application is significantly improved in terms of comprehensive electrochemical performance such as high-temperature cycle stability, high-rate performance and low-temperature performance, and solves the problem of incomplete performance improvement of the existing additive system. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the specification of the present application. Obviously, the described embodiments are only 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.

[0017] The present application provides a preparation method of a sodium battery additive, comprising the following steps: a) reaction step: reacting pyromellitic acid and sodium hydroxide in an isopropanol solvent under heating and stirring; after the reaction is completed, the reaction product is filtered to obtain a sodium benzene-1,2,4,5-tetracarboxylate crude product; This step is a salt formation reaction stage. Isopropanol is selected as the reaction solvent because pyromellitic acid has moderate solubility in it, and the boiling point of isopropanol is relatively high, allowing the reaction to be carried out in a relatively wide temperature range of 60-120℃, thereby effectively improving the reaction rate.

[0018] First, pyromellitic acid is dissolved in isopropanol to prepare a solution with a concentration of 0.1-0.3 mol / L to ensure that the reactants can fully contact in the liquid phase. Subsequently, sodium hydroxide is added under continuous heating and stirring. The molar ratio of sodium hydroxide to pyromellitic acid is controlled between 1:3.8 and 1:4.2, and the slightly excessive sodium hydroxide is intended to ensure that the four carboxyl groups on the pyromellitic acid can be completely reacted to form the target product sodium benzene-1,2,4,5-tetracarboxylate, avoiding the production of by-products such as sodium benzene-1,2,4,5-tetracarboxylate monosodium, disodium or trisodium due to incomplete reaction of the acid radical.

[0019] The reaction temperature is preferably controlled at 80-100°C, and the reaction time is maintained at 28-44 hours, preferably 32-40 hours, which combination of conditions ensures that the salt formation reaction can be carried out fully and completely. After the reaction is completed, the target product sodium benzotetramine will exist in the reaction system in solid form due to its low solubility in isopropyl alcohol. Therefore, the crude sodium benzotetramine can be easily separated from the reaction mother liquor by simple solid-liquid separation operation, i.e. filtration, and the process is simple b) purification step: dissolving the crude sodium benzotetramine in water and heating for rotary evaporation until the solution reaches a saturated state; adding methanol to the saturated solution to precipitate a solid, and performing hot filtration on the mixture containing the solid; and vacuum drying the solid obtained by filtration to obtain a sodium battery additive; This step is the key to obtaining a product with high purity and low impurity content. The principle is to use the significant difference in solubility of sodium benzotetramine in different solvents and temperatures for recrystallization purification.

[0020] First, the crude product obtained in the previous step is dissolved in water. Water is chosen as the solvent because sodium benzotetramine has a high solubility in water, while some organic by-products or unreacted raw materials that may be produced in the reaction step have relatively low solubility in water. The mass-to-volume ratio of the crude product to water is controlled at 1 g:(10-20) ml to form a solution concentration suitable for recrystallization.

[0021] Subsequently, the aqueous solution is heated and rotary evaporated at a temperature of 60-80°C. The purpose of this operation is to accurately remove part of the water solvent without introducing new impurities, so that the solution reaches a saturated state, creating the necessary supersaturation conditions for subsequent crystallization.

[0022] When the solution reaches a hot saturated state, methanol is added as a crystallization inducer or anti-solvent. The solubility of sodium benzotetramine in a water-methanol mixed solvent is much lower than its solubility in pure water, so the addition of methanol will quickly break the solubility balance, causing high-purity sodium benzotetramine to precipitate from the solution in the form of solid crystals. Impurities such as inorganic salts are effectively retained in the mother liquor due to their different solubility characteristics. The volume-to-mass ratio of methanol to crude product is controlled at (2-3) ml:1 g to ensure complete crystallization and pure product.

[0023] To maximize the purification efficiency and prevent impurities from precipitating with the product during the cooling process, hot filtration is used to quickly separate the precipitated sodium benzotetramine solid. Finally, the obtained solid is vacuum dried at a temperature of 70-90°C for 16-24 hours, with the purpose of completely removing the residual water and methanol, and finally obtaining a high-purity, dry, powdered sodium battery additive that meets the requirements of battery applications.

[0024] Example 1 Reaction Step: 1 mol of pyromellitic acid was dissolved in isopropyl alcohol to prepare a 0.1 mol / L pyromellitic acid isopropyl alcohol solution. 3.8 mol of sodium hydroxide was added under stirring at 60°C, and the reaction was continued for 28 hours. After the reaction was completed, the product was filtered to obtain a crude sodium pyromellitate with a yield of 96%.

[0025] Purification Step: 100 g of the crude product was taken and 1000 ml of water was added. The mixture was stirred at 60°C for 5 minutes to dissolve the product. The aqueous solution was subjected to rotary evaporation at 60°C until it reached a saturated state, and then methanol was added along the wall of the vessel to precipitate the solid. The mixture was hot-filtered, and the obtained solid was collected and vacuum-dried at 70°C for 16 hours to obtain purified sodium pyromellitate crystals with a purification yield of 97%.

[0026] Example 2 Reaction Step: 1 mol of pyromellitic acid was dissolved in isopropyl alcohol to prepare a 0.2 mol / L solution. 4.0 mol of sodium hydroxide was added under stirring at 80°C, and the reaction was continued for 32 hours. The product was filtered to obtain a crude sodium pyromellitate with a yield of 98%.

[0027] Purification Step: 100 g of the crude product was taken and 1500 ml of water was added. The mixture was stirred at 70°C for 4 minutes to dissolve the product. The aqueous solution was subjected to rotary evaporation at 70°C until it reached a saturated state, and then methanol was added to precipitate the solid. After hot-filtration, the obtained solid was vacuum-dried at 80°C for 20 hours to obtain purified sodium pyromellitate crystals with a purification yield of 99%.

[0028] Example 3 Reaction Step: 1 mol of pyromellitic acid was dissolved in isopropyl alcohol to prepare a 0.2 mol / L solution. 3.9 mol of sodium hydroxide was added under stirring at 100°C, and the reaction was continued for 40 hours. The product was filtered to obtain a crude sodium pyromellitate with a yield of 97%.

[0029] Purification Step: 100 g of the crude product was taken and 1600 ml of water was added. The mixture was stirred at 75°C for 3 minutes to dissolve the product. The aqueous solution was subjected to rotary evaporation at 75°C until it reached a saturated state, and then methanol was added to precipitate the solid. After hot-filtration, the obtained solid was vacuum-dried at 85°C for 22 hours to obtain purified sodium pyromellitate crystals with a purification yield of 98%.

[0030] Example 4 Reaction Step: 1 mol of pyromellitic acid was dissolved in isopropyl alcohol to prepare a 0.2 mol / L solution. 4.1 mol of sodium hydroxide was added under stirring at 90°C, and the reaction was continued for 36 hours. The product was filtered to obtain a crude sodium pyromellitate with a yield of 97%.

[0031] Purification step: Take 100 g of the crude product and add 1800 ml of water. Stir at 75°C for 3 minutes to dissolve. Evaporate the solution at 65°C until saturated and add methanol to precipitate the solid. Filter while hot and dry the solid obtained at 75°C under vacuum for 21 hours to obtain purified sodium pyromellitate crystals with a purification yield of 98%.

[0032] Example 5 Reaction step: Dissolve 1 mol of pyromellitic acid in isopropyl alcohol to make a 0.3 mol / L solution. Add 4.2 mol of sodium hydroxide under stirring at 120°C and continue the reaction for 44 hours. Filter to obtain the crude sodium pyromellitate with a yield of 96%.

[0033] Purification step: Take 100 g of the crude product and add 2000 ml of water. Stir at 80°C for 2 minutes to dissolve. Evaporate the solution at 80°C until saturated and add methanol to precipitate the solid. Filter while hot and dry the solid obtained at 90°C under vacuum for 24 hours to obtain purified sodium pyromellitate crystals with a purification yield of 96%.

[0034] Example 6 Reaction step: Dissolve 1 mol of pyromellitic acid in isopropyl alcohol to make a 0.3 mol / L solution. Add 4.1 mol of sodium hydroxide under stirring at 110°C and continue the reaction for 42 hours. Filter to obtain the crude sodium pyromellitate with a yield of 96%.

[0035] Purification step: Take 100 g of the crude product and add 1200 ml of water. Stir at 60°C for 10 minutes to dissolve. Evaporate the solution at 60°C until saturated and add methanol to precipitate the solid. Filter while hot and dry the solid obtained at 80°C under vacuum for 18 hours to obtain purified sodium pyromellitate crystals with a purification yield of 97%.

[0036] Comparative Example 1 The same purification step as in Example 1 was used. The reaction step was: Dissolve 1 mol of pyromellitic acid in isopropyl alcohol to make a 0.1 mol / L solution. Add 3.8 mol of sodium hydroxide under stirring at 50°C and continue the reaction for 24 hours. Filter to obtain the crude product. The final overall yield was 93%.

[0037] Comparative Example 2 The same purification step as in Example 1 was used. The reaction step was: Dissolve 1 mol of pyromellitic acid in isopropyl alcohol to make a 0.1 mol / L solution. Add 3.8 mol of sodium hydroxide under stirring at 40°C and continue the reaction for 20 hours. Filter to obtain the crude product. The final overall yield was 92%.

[0038] Comparative Example 3 The same purification procedure as Example 1 was used. The reaction procedure was as follows: 1 mol of pyromellitic acid was dissolved in isopropanol to make a 0.1 mol / L solution, 3.8 mol of sodium hydroxide was added under stirring at 140 °C, and the reaction was allowed to proceed for 48 h. The crude product was obtained by filtration. The final overall yield was 94%.

[0039] Comparative Example 4 The same purification procedure as Example 1 was used. The reaction procedure was as follows: 1 mol of pyromellitic acid was dissolved in isopropanol to make a 0.1 mol / L solution, 3.8 mol of sodium hydroxide was added under stirring at 160 °C, and the reaction was allowed to proceed for 60 h. The crude product was obtained by filtration. The final overall yield was 91%.

[0040] Comparative Example 5 This comparative example was not prepared, and commercially available vinylene carbonate was directly used as an additive for battery performance testing. VC was purchased from Macklin Company, with a purity of 98%, and a CAS number of 872-36-6.

[0041] Comparative Example 6 This comparative example was not prepared, and commercially available VC and fluoroethylene carbonate were directly used as a composite additive for battery performance testing. FEC was purchased from Shanghui Technology, with a purity of 99%, and a CAS number of 114435-02-8.

[0042] Comparative Example 7 This comparative example was not prepared, and commercially available VC and 1,3-propane sultone (1,3-PS) were directly used as a composite additive for battery performance testing. 1,3-PS was purchased from Jihua Chang Company, with a purity of 99.9%, and a CAS number of 1120-71-4.

[0043] Test Example: Product Characterization and Electrochemical Performance Testing 1. Product Purity and Impurity Content Testing The sodium pyromellitate samples prepared in Examples 1-6 and Comparative Examples 1-4 were analyzed for purity and impurity content.

[0044] Purity Testing: Nuclear magnetic resonance internal standard method was used. Deuterium oxide (D2O) was used as the solvent, and tetramethylsilane was used as the internal standard. The purity of sodium pyromellitate was calculated based on the peak area integral value of the test substance and the internal standard, the number of protons, the sample weight, and the purity of the internal standard.

[0045] Impurity Testing: The contents of free acid, moisture, chloride ion, sulfate ion, and other impurities were determined by conventional chemical analysis methods. The test results are shown in Table 1.

[0046] 2. Electrochemical Performance Testing Battery System: 3.3 V Na 0·83 Li 0·25 Mn 0·75Sodium battery soft package battery of O2 / hard carbon system.

[0047] Electrolyte preparation: Reference electrolyte: composed of 30wt% dimethyl carbonate (DMC) + 25wt% diethyl carbonate (DEC) as mixed solvent, and 30wt%-40wt% sodium hexafluorophosphate (NaPF6) as electrolyte salt.

[0048] Test electrolyte: in the reference electrolyte, respectively add sodium benzenetetracarboxylate prepared in examples 1-6 and comparative examples 1-4, the addition amount is 1.5wt%; or add the commercial additives of comparative examples 5-7, the specific addition amount is: comparative example 5 (1.5% VC), comparative example 6 (1.5% VC+1.5% FEC), comparative example 7 (1.5% VC+2% 1,3-PS).

[0049] Test items: High temperature cycle performance: the battery is subjected to 1C / 1C rate charge-discharge cycle for 300 times under the condition of 50℃ constant temperature, and the capacity retention rate is recorded.

[0050] Rate performance: the battery is discharged at 5C rate at room temperature, and the discharge specific capacity (mAh / g) is recorded.

[0051] Low temperature performance: the battery is discharged at 0.5C rate under the condition of-20℃ constant temperature, and the retention rate of the discharge capacity relative to the 0.5C discharge capacity at room temperature is recorded. The test results are shown in table 2.

[0052] Results and analysis Table 1 purity and impurity content of each sample

[0053] As shown in table 1, the purity of sodium benzenetetracarboxylate obtained in examples 1-6 is all higher than 99.9%, and the impurity contents of free acid, moisture, chloride ion, sulfate ion and the like are all controlled at a very low level. In contrast, the products of comparative examples 1-4 which do not use the preferred process conditions (reaction temperature and time) of the present application have lower purity and significantly higher impurity content. This fully shows that the reaction conditions and time range defined in the present application are crucial for obtaining high-quality products, and the effect is better.

[0054] Table 2 comparison of electrochemical performance of each sample

[0055] From Table 2, (1) compared with commercially available additives (Comparative Examples 5-7), the batteries using sodium benzene-1,2,4,5-tetracarboxylate prepared by the method of the application (Examples 1-6) all show overwhelming advantages in high-temperature cycling, high-rate and low-temperature performance. Taking the best performance Example 2 as an example, all three key performance indicators (91.5%, 196.7 mAh / g, 90.5%) are much higher than all commercially available additive systems. (2) Compared with the additives prepared by non-optimal process (Comparative Examples 1-4), the battery performance of Examples 1-6 is also more comprehensive. This proves that sodium benzene-1,2,4,5-tetracarboxylate prepared by the method of the application as a sodium battery additive can more effectively and more comprehensively improve the overall performance of the battery than the commonly used additives on the market.

[0056] Although embodiments of the application have been shown and described, it is to be understood that various modifications, substitutions, combinations and variations can be made to these embodiments without departing from the principles and spirit of the application. The scope of the application is not to be understood as being limited to the embodiments shown and described, but is to be understood as being limited only by the claims and their equivalents.

Claims

1. A method for preparing a sodium electricity additive, characterized by, The method comprises the following steps: a) a reaction step: reacting pyromellitic acid with sodium hydroxide in isopropyl alcohol solvent under heating and stirring; after the reaction is completed, the reaction product is filtered to obtain a sodium pyromellitate crude product; b) a purification step: dissolving the sodium pyromellitate crude product in water and heating to perform rotary evaporation until the solution reaches a saturated state; adding methanol to the saturated solution to precipitate a solid, and performing hot filtration on the mixture containing the solid; and vacuum drying the solid obtained by filtration to obtain the sodium battery additive.

2. The method for preparing a sodium electrolyte additive according to claim 1, characterized in that, In the a), the concentration of the pyromellitic acid in the isopropyl alcohol solvent is 0.1 mol / L to 0.3 mol / L; the molar ratio of the pyromellitic acid to the sodium hydroxide is 1:3.8 to 1:4.2; the reaction temperature is 60°C to 120°C, and the reaction time is 28 hours to 44 hours.

3. The method for preparing a sodium electrolyte additive according to claim 2, characterized in that, The reaction temperature is 80°C to 100°C, and the reaction time is 32 hours to 40 hours.

4. The method for preparing a sodium electrolyte additive according to claim 1, characterized in that, In the b), the mass-volume ratio of the sodium pyromellitate crude product to water is 1g:10-20ml; the heating and rotary evaporation temperature is 60°C to 80°C; the volume-mass ratio of the methanol to the sodium pyromellitate crude product is 2-3ml:1g; and the vacuum drying temperature is 70°C to 90°C, and the time is 16 hours to 24 hours.

5. Use of a sodium battery additive in a sodium battery, the sodium battery additive being prepared according to the method of any one of claims 1 to 4 for preparing an electrolyte of a sodium ion battery.

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