A wide-temperature-range, long-life sodium-ion battery electrolyte, its preparation method, and its application.

Abstract

This invention discloses a wide-temperature-range, long-life sodium-ion battery electrolyte, its preparation method, and its applications. The invention uses sodium perchlorate as the sodium salt, synergistically with low-viscosity, low-melting-point methyl acetate to ensure high ionic conductivity of the electrolyte over a wide temperature range. Simultaneously, dimethyl sulfite and fluoroethylene carbonate synergistically construct an inorganic-rich SEI film, significantly improving interfacial stability and cycle performance. The Na||NVP battery, after reversible charge-discharge at 60°C, maintained a discharge specific capacity retention of 88.33% of the initial capacity after 400 stable cycles. Under low-temperature conditions, reversible charge-discharge at currents of 0.1C and 0.3C resulted in stable cycles of 300 and 380 cycles, respectively. The preparation method of this invention is simple, low-cost, easy to implement, requires minimal equipment investment, and is suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of sodium battery technology, specifically relating to a wide-temperature-range, long-life sodium-ion battery electrolyte, its preparation method, and its application. Background Technology

[0002] As an emerging energy storage system, room-temperature sodium-ion batteries have largely followed the development path of lithium-ion batteries in terms of electrolytes, generally employing formulations composed of carbonate solvents such as ethylene carbonate and dimethyl carbonate, combined with sodium hexafluorophosphate. However, this traditional electrolyte system faces a fundamental contradiction when expanding the battery's operating temperature range: on the one hand, the high dielectric constant solvents (typically with high melting points and viscosities) introduced to ensure sufficient salt dissociation lead to a sharp decline in ionic conductivity at low temperatures, severely degrading battery performance; on the other hand, at high temperatures, the electrode / electrolyte interface (especially the negative electrode SEI film) lacks stability, easily triggering continuous electrolyte decomposition, gas generation, and sodium dendrite growth, resulting in rapid capacity decay and safety risks. Although some studies have attempted to improve interface performance by introducing additives such as fluoroethylene carbonate or using ether solvents to enhance low-temperature conductivity, it is often difficult to simultaneously achieve comprehensive performance at both high and low temperatures and long-term cycle stability. Therefore, developing a new electrolyte system that can maintain high ionic conductivity and form a stable interfacial film over a wide temperature range is a key technical problem that urgently needs to be solved to promote the practical application of sodium-ion batteries. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a wide-temperature-range, long-life sodium-ion battery electrolyte, its preparation method and application, which are in contrast to the prior art. The purpose of this technology is to improve the cycle performance of sodium-ion batteries under extreme environments.

[0004] Low-viscosity linear esters introduced to ensure low-temperature ionic conductivity often fail to form stable electrode interface films; while components that can effectively construct stable solid electrolyte interfaces (SEIs) are often accompanied by high melting points or high viscosity, limiting low-temperature performance. Existing improvement schemes, such as using high-concentration electrolytes or adding various organophosphorus compounds, can improve performance to some extent in a certain temperature range, but they are often accompanied by problems such as soaring costs, excessively high viscosity, or poor compatibility with electrode materials, making it difficult to achieve a comprehensive performance balance over a wide temperature range.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a wide temperature range and long life sodium-ion battery electrolyte, the electrolyte comprising a sodium salt and a solvent, wherein the sodium salt comprises sodium perchlorate; and the solvent comprises dimethyl sulfite, methyl acetate and fluoroethylene carbonate.

[0006] The electrolyte prepared above specifically includes the following steps:

[0007] 1) Under the argon atmosphere of the glove box, weigh a certain amount of sodium perchlorate (1M-3M) and place it in a bottle.

[0008] 2) Add a certain amount of dimethyl sulfite, methyl acetate and fluoroethylene carbonate to the bottle, and stir at room temperature to form a homogeneous solution to obtain the above electrolyte.

[0009] Furthermore, this invention also provides the application of the aforementioned wide-temperature-range, long-life sodium-ion battery electrolyte. This electrolyte, used as a wide-temperature-range electrolyte for sodium batteries with sodium vanadium phosphate (NVP) as the positive electrode, is employed to improve battery performance, including capacity and cycle life, under both high-temperature (above 40°C) and low-temperature (below 0°C) conditions. Under high-temperature conditions of 60°C and a 1C charge / discharge rate (1C = 111.6 mAh g⁻¹), [the following is observed]. 1 The battery underwent charge-discharge testing and yielded a capacity of 109.7 mAh g. 1 The initial discharge specific capacity was maintained at 88.33% after 400 stable cycles. Under low-temperature conditions, at a charge / discharge rate of 0.1C (1C = 111.6 mAh g⁻¹), the discharge specific capacity was... 1 The battery underwent charge-discharge testing and measured a capacity of 65.6 mAh g. 1 The initial discharge specific capacity is stable after 300 cycles. At a low temperature of 40℃, with a charge / discharge rate of 0.3C (1C = 111.6 mAh g⁻¹), 1 The battery underwent charge-discharge testing, and after activation, it had a capacity of 42.8 mAh g. 1 The initial discharge specific capacity, after 25 stable cycles, the temperature rises to At 30℃, it can still cycle through temperatures 380 times. At room temperature, with a charge / discharge rate of 1C (1C = 111.6 mAhg), it can achieve [performance / performance / etc.]. 1 The battery underwent charge-discharge testing and yielded a capacity of 103.9 mAh g. 1 The initial discharge specific capacity, after 800 stable cycles, retained 86.52% of the initial capacity. After activation, at a charge / discharge rate of 5C (1C = 111.6 mAh g⁻¹), 1 The battery underwent charge-discharge testing and yielded a capacity of 97.4 mAh g. 1 The initial discharge specific capacity, after 1000 stable cycles, the discharge specific capacity retention rate is 85.83% of the initial capacity.

[0010] Compared with the prior art, the features of the present invention are as follows: In this invention, sodium perchlorate is used as the sodium salt to provide sodium ions; methyl acetate, with its low viscosity and low melting point, is used as the main solvent. Combined with sodium perchlorate, which has high dissociation and good solubility in sodium perchlorate, this significantly reduces the overall viscosity of the electrolyte while maintaining high conductivity. Dimethyl sulfite and fluoroethylene carbonate undergo synergistic reduction on the negative electrode surface, jointly constructing a dense, uniform solid electrolyte interphase (SEI) film rich in inorganic components (such as sodium sulfide and sodium fluoride), which effectively inhibits the continuous decomposition of the electrolyte and the growth of sodium dendrites. This invention provides a wide-temperature-range, long-life sodium-ion battery electrolyte based on sodium vanadium phosphate as the positive electrode material and sodium sheets as the negative electrode. After reversible charge-discharge at 60°C and stable cycling for 400 cycles, the battery retains 88.33% of its initial capacity. Under low-temperature conditions, reversible charge-discharge at a current of 0.1C can achieve stable cycling for over 300 cycles. Attached Figure Description

[0011] Figure 1 This is a charge-discharge cycle diagram of the 1C current at 60°C in a sodium battery with sodium vanadium phosphate (NVP) as the positive electrode, using a wide-temperature-range electrolyte in Embodiment 2 of the present invention. Figure 2 This is a charge-discharge cycle diagram of the wide-temperature-range electrolyte applied to a sodium battery with sodium vanadium phosphate (NVP) as the positive electrode at low temperature and a current of 0.1C. Figure 3 This is a charge-discharge cycle diagram of a sodium battery with sodium vanadium phosphate (NVP) as the positive electrode, using a wide-temperature-range electrolyte in Example 4 of the present invention at a low temperature and a current of 0.3C. Figure 4 This is a charge-discharge cycle diagram of the wide-temperature-range electrolyte applied in Example 5 of the present invention to a sodium battery with sodium vanadium phosphate (NVP) as the positive electrode at room temperature and the 1C current. Figure 5 This is a charge-discharge cycle diagram of the wide-temperature-range electrolyte applied in Example 6 of the present invention to a sodium battery with sodium vanadium phosphate (NVP) as the positive electrode at room temperature and a 5C current. Detailed Implementation The present invention will be further described in detail below with reference to the embodiments.

[0012] Example 1 In an argon-filled glove box, prepare a 5mL glass bottle, weigh 0.24488g of sodium perchlorate and add it to the bottle. Then add 0.8mL of dimethyl sulfite, 1mL of methyl acetate and 0.2mL of fluoroethylene carbonate and stir evenly at room temperature to obtain a wide-temperature-range sodium battery electrolyte. Next, in an argon-filled glove box, assemble the positive electrode material, glass fiber (1820-090) separator and negative electrode material in the following order: positive electrode shell, positive electrode material, electrolyte, glass fiber (1820-090) separator, negative electrode material, gasket, spring, and negative electrode shell to obtain a button cell battery. The positive electrode material is sodium vanadium phosphate, and the negative electrode material is a sodium sheet.

[0013] Example 2 The obtained button batteries were placed in a 60°C high-temperature oven and left to stand for 8 hours. After standing, the button batteries were installed in the Blue Electric high-precision battery testing system and tested using a 1C charge-discharge rate (1C=111.6 mAh g). 1 Perform charge-discharge cycle testing, and the test results are as follows: Figure 1 As shown, after 400 stable charge-discharge cycles at 60℃, the discharge specific capacity reaches 109.7 mAh g. 1 The capacity retention rate is as high as 88.33%.

[0014] Example 3 The button cell battery obtained in Example 1 was placed in an ultra-low temperature freezer and left to stand for 8 hours. After standing, the button cell battery was installed in the Blue Electric high-precision battery testing system and charged and discharged at a rate of 0.1C (1C = 111.6 mAh g). 1 Perform charge-discharge cycle testing, and the test results are as follows: Figure 2 As shown, it can withstand stable charge-discharge cycles at low temperatures for over 300 cycles, with an initial discharge specific capacity of up to 65.6 mAh g. 1 .

[0015] Example 4 The button cell battery obtained in Example 1 was placed in an ultra-low temperature freezer and left to stand for 8 hours. After standing, the button cell battery was installed in the Blue Electric high-precision battery testing system and charged and discharged at a rate of 0.3C (1C=111.6 mAh g). 1 Perform charge-discharge cycle testing, and the test results are as follows: Figure 3 As shown, after 380 stable charge-discharge cycles at low temperature, the initial discharge specific capacity can reach 42.8 mAh g. 1 .

[0016] Example 5 The button cell battery obtained in Example 1 was left to stand at room temperature for 8 hours. After that, the button cell battery was installed in the Blue Electric high-precision battery testing system and charged and discharged at a 1C rate (1C = 111.6 mAh g). 1 Perform charge-discharge cycle testing, and the test results are as follows: Figure 4 As shown, after 800 stable cycles at room temperature, the initial discharge specific capacity reaches 103.9 mAh g⁻¹. 1 The capacity retention rate is as high as 86.52%.

[0017] Example 6 The button cell battery obtained in Example 1 was left to stand at room temperature for 8 hours. After that, the button cell battery was installed in the Blue Electric high-precision battery testing system and charged and discharged at a 5C rate (1C = 111.6 mAh g). 1 Perform charge-discharge cycle testing, and the test results are as follows: Figure 5 As shown, after 1000 stable cycles at room temperature, the initial discharge specific capacity reaches 97.4 mAh g⁻¹. 1 The capacity retention rate is as high as 85.83%.

Claims

1. A wide-temperature-range, long-life sodium-ion battery electrolyte, characterized in that, The electrolyte comprises a sodium salt and a solvent; the sodium salt is sodium perchlorate, and the solvent is dimethyl sulfite, methyl acetate, and fluoroethylene carbonate.

2. The electrolyte preparation method according to claim 1, characterized in that, The electrolyte preparation method includes the following steps: 1) Under an argon atmosphere in a glove box, weigh a certain mass of sodium perchlorate (0.5M-3M) and place it in a bottle; 2) Add the following organic solvents to the bottle: dimethyl sulfite, ethylene fluorocarbonate, and methyl acetate, and stir at room temperature to dissolve them to obtain the above electrolyte.

3. The electrolyte preparation method according to claim 1, characterized in that, The electrolyte in The ionic conductivity at 40℃ is not less than 0.3 mS / cm.

4. The use of the wide-temperature-range, long-life sodium-ion battery electrolyte according to claim 1, characterized in that, This electrolyte, as a wide-temperature-range electrolyte for sodium-ion batteries, can improve the retention time of the discharge specific capacity and the cycle life of sodium-ion batteries in high-temperature environments above 40°C and low-temperature environments below 0°C.

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