A sodium ion electrolyte suitable for high temperature and preparation method thereof

Abstract

The present invention discloses a sodium ion electrolyte suitable for high temperature and a preparation method thereof, and relates to the technical field of sodium ion batteries. The preparation method of the present invention comprises the following steps: (1) dissolving a sodium salt in a highly thermally stable solvent, and dissolving the sodium salt in an oxygen-free environment to obtain a mixed solution; (2) adding a high temperature enhancer, a film-forming agent and a flame retardant to the mixed solution in step (1), and mixing them uniformly to obtain the sodium ion electrolyte suitable for high temperature; wherein the high temperature enhancer is a benzothiazole containing piperidine. The sodium ion electrolyte of the present invention has good ionic conductivity, electrochemical stability and thermal stability under high temperature (80°C) conditions. By improving the stability of the SEI film and reducing the oxidation loss of the electrolyte, the number of cycles and the overall life of the battery in a high temperature environment can be significantly increased (the capacity retention rate after 500 cycles is up to 95.9%).

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion electrolyte suitable for high temperatures and a preparation method thereof. Background Art

[0002] With the growth of global energy demand and the improvement of environmental protection awareness, renewable energy and energy storage technologies have developed rapidly, and battery technology has received widespread attention as the core technology for energy storage and management. Lithium-ion batteries have become the mainstream of the market due to their high energy density and excellent cycle performance. However, the limited lithium resources and their high mining costs have prompted researchers to explore other alternative technologies. Sodium-ion batteries are seen as a powerful alternative to lithium-ion batteries due to their abundant sodium resources and low cost, especially in large-scale energy storage and low-cost battery applications.

[0003] Sodium-ion batteries are similar to lithium-ion batteries in principle, but due to the larger ionic radius of sodium ions, there are certain differences in electrochemical performance. Research on sodium-ion batteries covers the optimization of electrode materials, electrolytes, diaphragms, and the overall battery structure. Among them, the electrolyte, as a medium for the conduction of ions between the positive and negative electrodes, plays a vital role in the overall performance of the battery. The main function of the sodium-ion battery electrolyte is to dissolve sodium salts, provide sufficient ionic conductivity, and maintain chemical and electrochemical stability during battery operation.

[0004] Traditional sodium ion electrolytes are usually formed by dissolving sodium salts (such as sodium hexafluorophosphate) in organic solvents (such as carbonate compounds) to form electrolyte solutions. These electrolytes were originally designed mainly for room temperature working environments and can provide good conductivity and stability at room temperature. For example, the patent application with publication number CN116885283A discloses a sodium ion battery ultra-low temperature resistant electrolyte, a preparation method and a sodium ion battery, which belongs to the field of sodium ion battery technology; the sodium ion battery electrolyte provided by the application introduces compounds with amide groups, epoxybutyl groups, sulfoxide groups and halogen groups as additives, thereby improving the kinetic process of sodium ions in the sodium ion battery electrolyte and the uniform deposition of the interface layer, thereby improving the performance of the electrolyte in an ultra-low temperature (-40°C) environment.

[0005] However, in many practical applications, such as electric vehicles and industrial energy storage devices, batteries need to work in high temperature environments, and the temperature may even reach 60℃-100℃. Under these high temperature conditions, traditional electrolytes are prone to decomposition or evaporation, resulting in decreased ion conductivity and increased electrolyte viscosity, which in turn affects battery performance and life. In addition, some organic solvents may produce flammable gases at high temperatures, increasing battery safety risks.

[0006] Therefore, it is particularly important to develop a sodium ion electrolyte suitable for high temperature environments. Such an electrolyte not only needs to maintain high ionic conductivity and electrochemical stability at high temperatures, but also needs to have good thermal stability and flame retardancy to ensure the safety and long-life cycle performance of the battery under high temperature conditions. Summary of the invention

[0007] In view of this, the present application provides a sodium ion electrolyte suitable for high temperature and a preparation method thereof, which is used to solve the technical problem of the lack of sodium ion battery electrolyte for high temperature in the prior art.

[0008] To achieve the above-mentioned purpose, the specific technical scheme of the present invention is as follows:

[0009] The present invention provides a method for preparing a sodium ion electrolyte suitable for high temperature, comprising the following steps:

[0010] (1) dissolving the sodium salt in a highly thermally stable solvent, and fully dissolving the sodium salt in an oxygen-free environment to obtain a mixed solution;

[0011] (2) adding a high temperature enhancer, a film-forming agent and a flame retardant to the mixed solution in step (1), mixing them evenly, and obtaining the sodium ion electrolyte suitable for high temperature;

[0012] Wherein, the high temperature enhancer is benzothiazole containing piperidine.

[0013] In some embodiments of the present invention, in step (1), the high thermal stability solvent is first heated to 50°C-80°C and kept warm, and then the sodium salt is added and stirred to dissolve, which helps to accelerate the dissolution process of the sodium salt and improve the dissolution efficiency; the stirring speed is 300-450 rpm.

[0014] In some embodiments of the present invention, the sodium salt is at least one of sodium hexafluorophosphate, sodium difluorooxyphosphate, and sodium trifluoromethanesulfonate, which salts have high thermal stability and electrochemical properties and are suitable for use in high-temperature electrolytes;

[0015] The highly thermally stable solvent is at least one of propylene carbonate, dimethyl carbonate, and trifluoroethyl phosphate, which can effectively improve the thermal stability and safety of the electrolyte;

[0016] The mass ratio of the sodium salt, the high thermal stability solvent, the film former and the flame retardant is 9-15:80-120:0.7-1.2:0.5-1.5.

[0017] Preferably, in step (2), the method for preparing the high temperature enhancer comprises the following steps:

[0018] Excess 3-allyl-1-boc-piperidine-3-carboxylic acid is neutralized with a base to obtain 3-allyl-1-boc-piperidine-3-carboxylate, which is then subjected to an addition reaction with 6-amino-2-mercaptobenzothiazole (CAS: 7442-07-1) at a high temperature to obtain a piperidine-containing benzothiazole, i.e., the high-temperature enhancer.

[0019] Specifically, the specific preparation method of the high temperature enhancer is:

[0020] Step 1: Add 24-48 parts of 3-allyl-1-boc-piperidine-3-carboxylic acid to 10-16 parts of sodium hydroxide and 200-300 parts of anhydrous ethanol by weight, and stir at room temperature for 100-130 minutes to generate sodium 3-allyl-1-boc-piperidine-3-carboxylate;

[0021] Step 2: Add 19-38 parts of 6-amino-2-mercaptobenzothiazole, mix and react for 70-120 minutes at a temperature of 60-70° C., and distill off anhydrous ethanol to obtain piperidine-containing benzothiazole, namely the high temperature enhancer.

[0022] Preferably, the amount of the high temperature enhancer added is 2%-5% of the mass of the high thermal stability solvent.

[0023] The mechanism of action of piperidine-containing benzothiazole as a sodium ion electrolyte additive in improving high temperature performance mainly includes the following points:

[0024] 1. Enhance the stability of SEI film: Under high temperature environment, more heat will be generated inside the battery, which will accelerate the decomposition of electrolyte, thus destroying the stability of solid electrolyte interface (SEI) film. Benzothiazole containing piperidine can promote the formation of a more uniform and stable SEI film by participating in the formation of SEI film. This film can effectively prevent further reaction between electrode materials and electrolytes, reduce the continuous decomposition of electrolytes, and thus improve the cycle stability and service life of batteries at high temperatures.

[0025] 2. Improve the antioxidant capacity of electrolyte: Under high temperature conditions, the organic solvent in the electrolyte is prone to oxidation reaction, which not only consumes the electrolyte, but also may produce harmful gases and additional heat, further reducing the safety performance of the battery. Benzothiazole containing piperidine has antioxidant properties, which can inhibit the oxidation of the solvent to a certain extent, protect the electrolyte from being consumed prematurely, and maintain the stability of the battery performance.

[0026] 3. Improve the thermal stability of the electrolyte: The structural characteristics of this compound enable it to maintain the stability of its chemical structure at higher temperatures and is not easily decomposed. This thermal stability helps prevent the rapid degradation of electrolyte components under high temperature working conditions, ensures that the electrolyte works normally over a wide temperature range, and supports the reliability of the battery in extreme temperature environments.

[0027] In some embodiments of the present invention, in step (2), the film-forming agent is at least one of ethylene glycol diethyl ether (DEE), methoxyethoxy methyl ether (MEM), ethylene glycol dimethyl ether carbonate (DEC), and vinylene carbonate (VEC).

[0028] The flame retardant is at least one of triethyl phosphate (TEP), trimethyl phosphate (TMP), triethylphosphonic acid (TEPi), and fluorophosphate ester (FPE).

[0029] In some embodiments of the present invention, during mixing, the stirring speed is 450-600 rpm and the stirring time is 30-40 min.

[0030] In some embodiments of the present invention, the obtained high-temperature applicable sodium ion electrolyte is filtered using a polytetrafluoroethylene filter membrane to remove possible tiny impurities and undissolved particles to obtain a high-purity electrolyte; the pore size of the polytetrafluoroethylene filter membrane is 0.18-0.22 μm.

[0031] The present invention also provides a sodium ion electrolyte prepared by the preparation method.

[0032] Compared with the traditional method, the present invention has the following beneficial effects:

[0033] 1. Extend battery life: By improving the stability of the SEI film and reducing the oxidation loss of the electrolyte, the number of cycles and overall life of the battery in a high temperature environment can be significantly increased.

[0034] 2. Improve battery safety: Enhanced anti-oxidation ability and thermal stability reduce the risk of thermal runaway of the battery at high temperatures and improve safety during use.

[0035] 3. Optimize battery performance: Keeping the performance of the electrolyte stable under high temperature conditions helps maintain the battery's energy output and charging efficiency, allowing the battery to work properly under a wider range of environmental conditions. DETAILED DESCRIPTION

[0036] The following specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, such modifications are protected by the patent law as long as they are within the scope of the claims of the present invention.

[0037] It should be noted that the parts without indicating the detailed steps and amounts of materials are routine experimental operations and recognized common sense in the field and will not be elaborated on.

[0038] Example 1

[0039] The preparation method of the high temperature enhancer in this embodiment is:

[0040] Step 1: Add 24 g of 3-allyl-1-boc-piperidine-3-carboxylic acid to 10 g of sodium hydroxide and 200 g of anhydrous ethanol, and stir at room temperature for 100 min at a rotation speed of 200 rpm to generate sodium 3-allyl-1-boc-piperidine-3-carboxylate;

[0041] Step 2: Add 19g of 6-amino-2-mercaptobenzothiazole (CAS: 7442-07-1), mix and react for 70 minutes at 60°C, and distill off anhydrous ethanol to obtain benzothiazole containing piperidine, i.e., a high temperature enhancer, with the following structural formula:

[0042] .

[0043] A method for preparing a high temperature suitable sodium ion electrolyte, the operating steps of which are:

[0044] Step 1: Add 80 g of propylene carbonate into a reactor, keep warm in a water bath at 50°C, then add 9 g of sodium hexafluorophosphate, and stir and dissolve at a stirring speed of 300 rpm in an anaerobic environment;

[0045] Step 2: Add 1.6g high temperature enhancer, 1g DEE and 1g TEP, increase the stirring speed to 450rpm, and continue stirring for 30min to ensure that the additives are evenly distributed;

[0046] Step 3: The uniformly mixed electrolyte is cooled to room temperature, and then filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.18 μm to remove possible tiny impurities and undissolved particles to obtain a high-purity electrolyte.

[0047] Example 2

[0048] The preparation method of the high temperature enhancer in this embodiment is:

[0049] Step 1: Add 32 g of 3-allyl-1-boc-piperidine-3-carboxylic acid to 12 g of sodium hydroxide and 250 g of anhydrous ethanol, and stir at room temperature for 110 min at a rotation speed of 200 rpm to generate sodium 3-allyl-1-boc-piperidine-3-carboxylate;

[0050] Step 2: Add 24 g of 6-amino-2-mercaptobenzothiazole, mix and react at 65° C. for 85 min, and distill off anhydrous ethanol to obtain piperidine-containing benzothiazole, i.e., a high-temperature enhancer.

[0051] A method for preparing a high temperature suitable sodium ion electrolyte, the operating steps of which are:

[0052] Step 1: Add 90 g of dimethyl carbonate to a reactor, keep it warm in a water bath at 60° C., then add 12 g of sodium difluorooxyphosphate, and stir and dissolve it at a stirring speed of 350 rpm in an anaerobic environment;

[0053] Step 2: Add 2.7 g of high temperature enhancer, 1 g of MEM and 1 g of TMP, increase the stirring speed to 500 rpm, and continue stirring for 35 min to ensure that the additives are evenly distributed;

[0054] Step 3: The uniformly mixed electrolyte is cooled to room temperature, and then filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.20 μm to remove possible tiny impurities and undissolved particles to obtain a high-purity electrolyte.

[0055] Example 3

[0056] The preparation method of the high temperature enhancer in this embodiment is:

[0057] Step 1: Add 40 g of 3-allyl-1-boc-piperidine-3-carboxylic acid to 14 g of sodium hydroxide and 250 g of anhydrous ethanol, and stir at room temperature for 120 min at a rotation speed of 200 rpm to generate sodium 3-allyl-1-boc-piperidine-3-carboxylate;

[0058] Step 2: Add 32 g of 6-amino-2-mercaptobenzothiazole, mix and react at 65° C. for 100 min, and distill off anhydrous ethanol to obtain piperidine-containing benzothiazole, i.e., a high-temperature enhancer.

[0059] A method for preparing a high temperature suitable sodium ion electrolyte, the operating steps of which are:

[0060] Step 1: Add 110 g of trifluoroethyl phosphate to a reactor, keep warm in a water bath at 70° C., then add 13 g of sodium trifluoromethanesulfonate, and stir and dissolve at a stirring speed of 400 rpm in an anaerobic environment;

[0061] Step 2: Add 4.4 g of high temperature enhancer, 1 g of DEC and 1 g of TEPi, increase the stirring speed to 550 rpm, and continue stirring for 35 min to ensure that the additives are evenly distributed;

[0062] Step 3: The uniformly mixed electrolyte is cooled to room temperature, and then filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.2 μm to remove possible tiny impurities and undissolved particles to obtain a high-purity electrolyte.

[0063] Example 4

[0064] The preparation method of the high temperature enhancer in this embodiment is:

[0065] Step 1: Add 48 g of 3-allyl-1-boc-piperidine-3-carboxylic acid to 16 g of sodium hydroxide and 300 g of anhydrous ethanol, and stir at room temperature for 130 min at a rotation speed of 200 rpm to generate sodium 3-allyl-1-boc-piperidine-3-carboxylate;

[0066] Step 2: Add 38 g of 6-amino-2-mercaptobenzothiazole, mix and react at 70° C. for 120 min, and distill off anhydrous ethanol to obtain piperidine-containing benzothiazole, i.e., a high-temperature enhancer.

[0067] A method for preparing a high temperature suitable sodium ion electrolyte, the operating steps of which are:

[0068] Step 1: Add 120 g of trifluoroethyl phosphate into a reactor, keep warm in a water bath at 80° C., then add 15 g of sodium trifluoromethanesulfonate, and stir and dissolve at a stirring speed of 450 rpm in an anaerobic environment;

[0069] Step 2: Add 6 g of high temperature enhancer, 1 g of VEC and 1 g of FPE, increase the stirring speed to 600 rpm, and continue stirring for 40 min to ensure that the additives are evenly distributed;

[0070] Step 3: The uniformly mixed electrolyte is cooled to room temperature, and then filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm to remove possible tiny impurities and undissolved particles to obtain a high-purity electrolyte.

[0071] Comparative Example 1

[0072] This comparative example is the same as Example 1 except that no high temperature enhancer is added.

[0073] Comparative Example 2

[0074] This comparative example is the same as Example 1 except that 6-amino-2-mercaptobenzothiazole is not added during the preparation of the high temperature enhancer.

[0075] Comparative Example 3

[0076] This comparative example is the same as Example 1 except that 3-allyl-1-boc-piperidine-3-carboxylic acid is not added during the preparation of the high temperature enhancer.

[0077] Test Example 1

[0078] 1. Conductivity test

[0079] The ionic conductivity of the electrolyte was measured using a conductivity meter (such as an EIS module in an electrochemical workstation). The sodium ion electrolyte prepared in the embodiment and the comparative example was injected into a standard conductivity cell. The conductivity of the electrolyte was measured at different temperatures (25°C, 60°C, 80°C). The measurement at each temperature was repeated three times and the average value was taken.

[0080] 2. Electrochemical stability test

[0081] The electrochemical window of the electrolyte was tested using cyclic voltammetry (CV). The electrolyte prepared in the examples and comparative examples was injected into a button cell equipped with a sodium metal electrode and a stainless steel counter electrode. The scanning voltage range was set to 2.0V to 4.5V, and the scanning rate was 0.5 mV / s. The electrochemical window of the electrolyte was tested at different temperatures (25°C, 60°C, 80°C).

[0082] 3. Cycle performance test

[0083] The sodium ion electrolyte prepared in the embodiment and the comparative example was used in a button cell to assemble a sodium ion battery. The battery was subjected to a constant current charge and discharge test in a constant temperature box at 80°C, with a charge and discharge current density of 1C and a voltage range of 2.5V to 4.2V. The cycle life of the battery was tested, that is, the capacity retention rate was measured after 500 cycles.

[0084] The above test results are shown in Tables 1 to 3.

[0085] Table 1 Conductivity test

[0086]

[0087] Table 2 Electrochemical stability test

[0088]

[0089] Table 3 Cyclic performance test

[0090]

[0091] It can be seen from the test results in Tables 1 to 3 that the sodium ion electrolyte of the present invention has good ionic conductivity, electrochemical stability and thermal stability under high temperature (80°C) conditions. In addition, in the long-term cycle test at high temperature (80°C), the electrolyte showed excellent cycle life, and the capacity retention rate was as high as 95.9% after 500 cycles. It proves that it is suitable for sodium ion batteries under high temperature conditions, effectively improving the safety and reliability of the battery.

[0092] The applicant declares that the present invention is further illustrated by the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a sodium ion electrolyte suitable for high temperature, characterized in that: The following steps are involved: (1) dissolving the sodium salt in a highly thermally stable solvent, and fully dissolving the sodium salt in an oxygen-free environment to obtain a mixed solution; (2) adding a high temperature enhancer, a film-forming agent and a flame retardant to the mixed solution in step (1), mixing them evenly, and obtaining the sodium ion electrolyte suitable for high temperature; Wherein, the high temperature enhancer is benzothiazole containing piperidine.

2. The method for preparing a sodium ion electrolyte according to claim 1, characterized in that: In step (1), the high thermal stability solvent is first heated to 50°C-80°C and kept warm, and then the sodium salt is added and stirred to dissolve; the stirring speed is 300-450rpm.

3. The method for preparing a sodium ion electrolyte according to claim 2, characterized in that: The sodium salt is at least one of sodium hexafluorophosphate, sodium difluorooxyphosphate, and sodium trifluoromethanesulfonate; The high thermal stability solvent is at least one of propylene carbonate, dimethyl carbonate, and trifluoroethyl phosphate; The mass ratio of the sodium salt, the high thermal stability solvent, the film former and the flame retardant is: 9-15: 80-120: 0.7-1.2: 0.5-1.

5.

4. The method for preparing the sodium ion electrolyte according to claim 1, characterized in that: In step (2), the method for preparing the high temperature enhancer comprises the following steps: Excess 3-allyl-1-boc-piperidine-3-carboxylic acid is reacted with a base to undergo a neutralization reaction to obtain 3-allyl-1-boc-piperidine-3-carboxylate, which is then reacted with 6-amino-2-mercaptobenzothiazole at a high temperature to obtain a piperidine-containing benzothiazole, namely the high-temperature enhancer.

5. The method for preparing the sodium ion electrolyte according to claim 4, characterized in that: The specific preparation method of the high temperature enhancer is: Step 1: Add 24-48 parts of 3-allyl-1-boc-piperidine-3-carboxylic acid to 10-16 parts of sodium hydroxide and 200-300 parts of anhydrous ethanol by weight, and stir at room temperature for 100-130 minutes to generate sodium 3-allyl-1-boc-piperidine-3-carboxylate; Step 2: Add 19-38 parts of 6-amino-2-mercaptobenzothiazole, mix and react for 70-120 minutes at a temperature of 60-70° C., and distill off anhydrous ethanol to obtain piperidine-containing benzothiazole, namely the high temperature enhancer.

6. The method for preparing the sodium ion electrolyte according to claim 5, characterized in that: The amount of the high temperature enhancer added is 2%-5% of the mass of the high thermal stability solvent.

7. The method for preparing the sodium ion electrolyte according to claim 1, characterized in that: In step (2), the film-forming agent is at least one of ethylene glycol diethyl ether, methoxyethoxy methyl ether, ethylene glycol dimethyl ether carbonate, and vinylene carbonate. The flame retardant is at least one of triethyl phosphate, trimethyl phosphate, triethyl phosphonic acid, and fluorophosphate.

8. The method for preparing the sodium ion electrolyte according to claim 7, characterized in that: When mixing, the stirring speed is 450-600 rpm and the stirring time is 30-40 minutes.

9. The method for preparing a sodium ion electrolyte according to claim 1, characterized in that: The obtained sodium ion electrolyte suitable for high temperature is filtered using a polytetrafluoroethylene filter membrane, and the pore size of the polytetrafluoroethylene filter membrane is 0.18-0.22 μm.

10. The sodium ion electrolyte prepared by the preparation method according to any one of claims 1 to 9.

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