Ether-based sodium metal battery electrolyte with wide temperature range based on ionic liquid regulation and application thereof

Abstract

The application discloses a kind of ether group sodium metal battery electrolyte based on ion liquid regulation of wide temperature range and application thereof, belong to sodium metal battery technical field;The sodium metal battery electrolyte includes sodium salt, ether solvent, fluorinated additive and ion liquid;Wherein the concentration of sodium salt is 0.5-1.5mol / L;Sodium salt is sodium hexafluorophosphate, ether solvent is diethylene glycol dimethyl ether, fluorinated additive is fluorinated ethylene carbonate, and ion liquid is 1-ethyl-3-methyl imidazole tetrafluoroborate salt. Wherein, the volume ratio of diethylene glycol dimethyl ether and fluorinated ethylene carbonate is 9:1, and the volume fraction of 1-ethyl-3-methyl imidazole tetrafluoroborate salt in electrolyte is 1-25vol%. The application introduces ion liquid containing BF4 ‑ , regulates Na + solvent structure, and constructs stable positive and negative electrode interface film, so as to improve the cycle stability of sodium metal battery under the condition of wide temperature, high rate and high voltage.

Description

Technical Field

[0001] This invention relates to the field of sodium metal battery technology, and in particular to a wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation and its application. Background Technology

[0002] Sodium metal batteries are considered a promising new type of rechargeable battery system due to the abundance of sodium resources, low cost, and high theoretical specific capacity of sodium metal anodes. The electrolyte, as a key component connecting the positive and negative electrodes, directly affects sodium ion transport behavior, electrode / electrolyte interface stability, and battery cycle life and safety performance. Ether electrolytes, due to their good interfacial compatibility with sodium metal anodes, low viscosity, and good low-temperature ion transport capabilities, are often used in sodium metal batteries, contributing to better rate performance and low-temperature cycling performance. However, existing ether electrolytes still have significant shortcomings. First, ether solvents are generally flammable, posing certain safety hazards under thermal runaway or high-temperature conditions. Second, ether electrolytes have limited antioxidant stability, easily undergoing continuous oxidative decomposition under high-voltage positive electrode conditions, leading to instability of the positive electrode / electrolyte interface film and rapid capacity decay. Furthermore, under high-rate and wide-temperature operating conditions, the sodium metal anode surface is prone to uneven deposition, sodium dendrite growth, and repeated rupture and regeneration of the unstable solid electrolyte interphase (SEI); at the same time, the positive electrode side is also prone to aggravated side reactions and continuous deterioration of the positive electrode electrolyte interphase (CEI), which seriously affects the cycle stability and safety of the battery.

[0003] To address these issues, various electrolyte optimization strategies have been proposed in existing technologies, such as fluorinated molecule design, high-concentration electrolytes, locally high-concentration electrolytes, and ionic liquid modification. Fluorinated solvents or additives help form fluorinated interfacial films and improve electrode interfacial stability; however, excessive introduction of fluorinated groups may reduce the solvent's ability to dissolve and dissociate sodium salts, thereby affecting ionic conductivity and low-temperature transport kinetics. High-concentration electrolytes and locally high-concentration electrolytes can increase the participation of anions in the sodium ion solvation structure and promote the formation of anion-derived inorganic enriched SEI / CEI, but they typically suffer from high viscosity, large salt consumption, high cost, insufficient wettability, or dependence on fluorinated diluents, which are detrimental to practical applications.

[0004] Ionic liquids, with their characteristics of low volatility, high thermal stability, and non-flammability, have been used in recent years to improve the safety and interfacial stability of electrolytes in metal batteries. Anions or cations in some ionic liquids can participate in electrode interfacial reactions, inducing the formation of an interfacial film rich in inorganic components, which is beneficial for suppressing dendrite growth and side reactions. However, existing ionic liquid electrolyte systems still face problems such as high viscosity, low ion transport rate, insufficient low-temperature kinetics, and difficulty in precisely controlling interfacial decomposition behavior. Furthermore, existing solutions often focus on improving a single interface of the sodium metal anode or cathode, with insufficient attention paid to the reconstruction of the sodium ion solvation structure and the synergistic stability of the positive and negative electrode interfaces under high voltage, high rate, and wide temperature conditions. Therefore, there is an urgent need to develop a new ether-based sodium metal battery electrolyte system that can maintain the good ion transport capacity and compatibility of ether solvents with the sodium metal anode, while also using ionic liquids to control the sodium ion solvation structure, increasing the degree of anion participation, and inducing the formation of a stable positive and negative electrode interfacial film, thereby meeting the requirements for stable operation of sodium metal batteries under wide temperature, high rate, and high voltage conditions. Summary of the Invention

[0005] To address the problems of insufficient interfacial stability, uneven sodium deposition, and limited cycle performance of existing ether-based sodium metal battery electrolytes under high voltage, wide temperature range, and high rate conditions, this invention provides an ether-based sodium metal battery electrolyte based on ionic liquid solvation control and its application. This electrolyte is prepared by introducing BF4-containing compounds into an ether-based solvent system. - Ionic liquids are used as solvation structure modulators to regulate Na+. + Local coordination environment enhances the role of anions in Na+ + The participation level in the first solvation shell is increased, thereby constructing a stable SEI on the sodium metal anode side and a stable CEI on the cathode side. This reduces side reactions at the electrode / electrolyte interface, promotes uniform sodium deposition, improves the high-voltage interface stability of the cathode, and ultimately improves the cycle stability of sodium metal batteries under wide temperature, high rate, and high voltage conditions.

[0006] To achieve the above objectives, the present invention employs the following technical solution: a wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation, comprising a sodium salt, an ether solvent, a fluorinated carbonate additive, and an ionic liquid component. The concentration of the sodium salt is 0.5-1.5 mol / L, and the sodium salt is sodium hexafluorophosphate; the ether solvent is diethylene glycol dimethyl ether; the fluorinated additive is fluoroethylene carbonate; and the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0007] This invention also discloses a method for preparing a wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid control, as described above, comprising the following steps: under an inert atmosphere, mixing an ether solvent and a fluorocarbonate additive at a preset volume ratio to obtain a mixed solvent; adding a sodium salt to the mixed solvent and stirring until the sodium salt is completely dissolved to obtain a basic ether-based electrolyte; subsequently adding a preset volume fraction of an ionic liquid component to the basic ether-based electrolyte and continuing to stir until the system is uniform and transparent to obtain the wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid control.

[0008] The present invention also discloses an application of the wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid control as described above. The sodium metal battery further includes a positive electrode, a negative electrode, and a separator. The positive electrode is obtained by mixing sodium vanadium phosphate, conductive carbon black, and polyvinylidene fluoride in an N-methylpyrrolidone solvent at a mass ratio of 8:1:1 and grinding them into a uniform slurry. The negative electrode uses a sodium metal sheet as the counter electrode and reference electrode, and the separator is a glass fiber separator.

[0009] The beneficial effects of this invention are: 1) This invention achieves effective regulation of the solvation structure of sodium ions by introducing ionic liquid components into ether-based solvent electrolytes, which work synergistically with sodium salts and fluorocarbonate additives. The anions in the ionic liquid can participate in the solvation structure construction of sodium ions, altering the coordination environment around the sodium ions, thereby optimizing the ion transport behavior and electrochemical properties of the electrolyte system.

[0010] 2) The ether-based sodium metal electrolyte system constructed in this invention induces the formation of a stable interfacial film structure on the electrode surface by regulating the solvation structure and interfacial reaction pathway. On the sodium metal anode side, it promotes the formation of a stable SEI; on the cathode side, it promotes the formation of a stable CEI, effectively reducing the oxidative decomposition of the electrolyte under high voltage conditions, expanding the electrochemical stability window of the ether-based electrolyte, and providing support for the application of high-voltage cathode materials, thereby improving the energy density of sodium metal batteries. This inorganically enriched interfacial film structure can effectively suppress side reactions at the electrode / electrolyte interface and reduce the increase in interfacial impedance.

[0011] 3) The electrolyte system described in this invention can effectively suppress sodium dendrite growth and improve the uniformity of sodium deposition. By forming a stable SEI film, the deposition behavior of sodium ions is regulated, reducing irreversible losses of the sodium metal anode during cycling, thereby improving the cycle life and safety performance of the sodium metal battery. Attached Figure Description

[0012] Figure 1 This is a comparison chart showing the cycle performance of Na||NVP batteries assembled with the electrolytes of Examples 1-5 of the present invention and Comparative Example 1 at a high rate of 20C and 25°C. Figure 2 A comparison graph showing the long-cycle performance of batteries assembled with electrolytes from Example 1 and Control Example 1 at 25°C and 20C high rate. Figure 3 A comparison graph showing the cycle performance of batteries assembled with the electrolytes of Example 1 and Control Example 1 at 25°C, 2.5V~4.3V high voltage, and 5C rate. Figure 4 A comparison graph showing the cycle performance of batteries assembled with the electrolytes of Example 1 and Control Example 1 at -30°C. Figure 5 The constant current charge-discharge curves of the battery assembled with the electrolyte of Example 1 at 60°C and 0.1C are shown. Figure 6 The graph shows the cycle performance of the battery assembled with the electrolyte of Example 1 under high-rate conditions of 60°C and 20C. Detailed Implementation

[0013] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0014] I. Preparation of Electrolyte Example 1: In an argon atmosphere glove box (water and oxygen content both below 0.01 ppm), diethylene glycol dimethyl ether and fluoroethylene carbonate were mixed at a volume ratio of 9:1 to obtain a mixed solvent; sodium hexafluorophosphate was added to the mixed solvent and stirred until completely dissolved, so that the concentration of sodium hexafluorophosphate was 1 mol / L. -1 Then, 1 vol% of 1-ethyl-3-methylimidazolium tetrafluoroborate was added, and the mixture was stirred until it was uniform and transparent, thus obtaining an ether-based sodium metal battery electrolyte controlled by ionic liquid.

[0015] Example 2: The difference between this example and Example 1 is that the volume fraction of 1-ethyl-3-methylimidazolium tetrafluoroborate in the electrolyte is 5 vol%, and the remaining components, proportions and preparation methods are the same as in Example 1.

[0016] Example 3: The difference between this example and Example 1 is that the volume fraction of 1-ethyl-3-methylimidazolium tetrafluoroborate in the electrolyte is 10 vol%, and the remaining components, proportions and preparation methods are the same as in Example 1.

[0017] Example 4: The difference between this example and Example 1 is that the volume fraction of 1-ethyl-3-methylimidazolium tetrafluoroborate in the electrolyte is 20 vol%, and the remaining components, proportions and preparation methods are the same as in Example 1.

[0018] Example 5: The difference between this example and Example 1 is that the volume fraction of 1-ethyl-3-methylimidazolium tetrafluoroborate in the electrolyte is 25 vol%, and the remaining components, proportions and preparation methods are the same as in Example 1.

[0019] Comparative Example 1: In an argon-atmospheric glove box, diethylene glycol dimethyl ether and fluoroethylene carbonate were mixed at a volume ratio of 9:1 to obtain a mixed solvent; sodium hexafluorophosphate was added to the mixed solvent and stirred until completely dissolved, so that the concentration of sodium hexafluorophosphate was 1 mol / L. -1 This yields a basic ether-based electrolyte that does not contain ionic liquid components.

[0020] II. Assembly of Sodium Metal Batteries To evaluate the performance of the electrolyte, the electrolytes prepared in Examples 1-5 and Comparative Example 1 were assembled into CR2032 coin cells.

[0021] 1. Electrode preparation: Positive electrode: Sodium vanadium phosphate (NVP) positive electrode active material, conductive agent and binder are mixed according to a preset mass ratio, and an appropriate amount of solvent is added to grind or stir to form a uniform slurry; then the slurry is coated on aluminum foil current collector, and after drying, rolling and cutting, NVP positive electrode sheet is obtained.

[0022] Negative electrode: A sodium metal sheet is used as both the counter electrode and the reference electrode.

[0023] 2. The battery assembly method is as follows: Inside the glove box, place the battery negative electrode shell, sodium metal sheet, glass fiber separator, appropriate amount of electrolyte (approximately 150 μL), positive electrode sheet, gasket, spring clip, and positive electrode shell in sequence, and seal them using a sealing machine. Let the assembled battery stand for 24 hours to ensure sufficient electrolyte saturation.

[0024] III. Battery Performance Testing The assembled battery was then evaluated for its electrochemical performance using the Blue Battery Testing System.

[0025] like Figure 1 As shown, this invention demonstrates a comparison of the cycling performance of Examples 1-5 and Control Example 1 under high-rate conditions of 25°C and 20°C. The results show that different ionic liquid contents have a significant impact on battery cycle stability. Among them, Example 4 exhibits the most outstanding cycle performance, maintaining 80.28 mAh g⁻¹ after 1000 cycles. -1 The discharge capacity retained at 99.9%; in Example 5, the discharge capacity after 1000 cycles was 77.34 mAh g. -1The capacity retention rate was 99.2%, also demonstrating excellent cycle stability. In comparison, the discharge capacities after 1000 cycles for Examples 1, 2, and 3 were 67.88, 63.24, and 59.16 mAh g, respectively. -1 The corresponding capacity retention rates were 83.2%, 77.0%, and 73.1%, respectively. Control Example 1 showed the most significant capacity decay, with a discharge capacity of only 36.11 mAh g after cycling. -1 The capacity retention rate was 47.1%. These results demonstrate that introducing an appropriate amount of ionic liquid component into the ether-based electrolyte can significantly improve the cycle stability of sodium metal batteries under high-rate conditions, with the ionic liquid content corresponding to Example 4 being the preferred option.

[0026] like Figure 2 As shown, this invention demonstrates a comparison of the cycling performance of Example 4 and Control Example 1 under conditions of 25°C and 20°C. The results show that the full cell of Example 4 maintained a relatively stable capacity before 5000 cycles, and achieved a capacity retention of 95.3% after 3000 cycles; in contrast, Control Example 1, without the addition of the ionic liquid component, showed a significant capacity decrease after approximately 700 cycles. These results indicate that by introducing an appropriate amount of ionic liquid component into the ether-based electrolyte, this invention can significantly improve the cycling stability of sodium metal batteries under high-rate and wide-temperature conditions.

[0027] like Figure 3 As shown, this invention demonstrates a comparison of the cycling performance of Example 4 and Control Example 1 under conditions of 25°C, 2.5–4.3V, and 5C. The results show that Example 4 exhibits more stable cycling performance under high cutoff voltage and high rate conditions, with a capacity retention of 97.2% after 700 cycles. In contrast, Control Example 1, without the addition of the ionic liquid component, shows more significant capacity decay under the same test conditions, with a capacity retention of 90.8% after 700 cycles. These results indicate that by introducing an appropriate amount of ionic liquid component, this invention can effectively improve the interfacial stability and cycle durability of ether-based sodium metal battery electrolytes under high voltage conditions.

[0028] like Figure 4 As shown, this invention demonstrates a comparison of the cycling performance of Example 4 and Control Example 1 under a low-temperature condition of -30°C. The results show that Example 4 can maintain stable charge-discharge cycles at low temperatures, with minimal fluctuations in discharge capacity and stable coulombic efficiency. In contrast, Control Example 1, without the addition of the ionic liquid component, exhibits rapid capacity decay during low-temperature cycling and shows significant failure within a short number of cycles. These results indicate that by introducing an appropriate amount of ionic liquid component, this invention can improve the ion transport capability and interfacial stability of the ether-based sodium metal battery electrolyte under low-temperature conditions, thereby enhancing the low-temperature cycling performance of sodium metal batteries.

[0029] like Figure 5 As shown, this invention demonstrates the charging process characteristics of Comparative Example 1 at 60°C and 0.1C. The curves show that the voltage rapidly rises to a plateau voltage during the initial charging phase, but begins to decline significantly in the middle of the charging process, accompanied by unstable fluctuations, indicating rapid electrolyte decomposition. This phenomenon illustrates that the electrolyte without added ionic liquid components has insufficient charging stability at high temperatures, easily leading to exacerbated side reactions and capacity decay, making it difficult to maintain the stability of the interfacial film, thereby limiting the cycle life and high-temperature performance of sodium metal batteries.

[0030] like Figure 6 As shown, this invention demonstrates the long-cycle performance of Example 4 at 60°C and 20°C. The results show that Example 4 retains 64.98 mAh g⁻¹ after 1000 cycles. -1 The discharge capacity of the sample was 78.73%, with a coulombic efficiency consistently close to 100%. In contrast, Control Example 1 could barely cycle normally at 60°C, exhibiting significant overcharging from the first charge cycle, accompanied by rapid electrolyte decomposition. This indicates that the electrolyte without the added ionic liquid component has extremely poor cycle stability at high temperatures. These results further demonstrate that introducing an appropriate amount of ionic liquid component into the ether-based electrolyte can significantly improve the cycle stability and interfacial durability of sodium metal batteries under high-temperature conditions.

[0031] The above experimental results indicate that the introduction of 1-ethyl-3-methylimidazolium tetrafluoroborate plays a role in regulating Na+. + The solvation structure, the stable sodium metal anode interface, and the high-voltage cathode interface are crucial and are key to achieving stable operation of this system over a wide temperature range, high rate, and high voltage over long cycles.

[0032] The sodium metal battery electrolyte of this invention constructs an ether-based electrolyte system based on ionic liquid solvation regulation through a combination design of sodium hexafluorophosphate, ether solvents, fluorocarbonate additives, and ionic liquid components. This system can improve the performance of anions in Na+. + The degree of participation in the first solvation shell and the induction of the formation of a stable positive and negative electrode interface film enable sodium metal batteries to have good cycle stability and interface durability under wide temperature, high rate and high voltage conditions.

[0033] The above description is for illustrative purposes only and is not intended to limit the scope of the invention. Any modifications, equivalent substitutions, or conventional variations made by those skilled in the art to the technical solutions of this invention without departing from the spirit and scope thereof should be covered within the scope of the claims of this invention.

Claims

1. A wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation, characterized in that, It includes the following components: sodium salt, ether solvent, fluorocarbonate additives, and ionic liquid.

2. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The sodium salt is sodium hexafluorophosphate.

3. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The concentration of the sodium salt is 0.5~1.5 mol / L. -1 .

4. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The ether solvent is diethylene glycol dimethyl ether.

5. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The fluorocarbonate additive is fluoroethylene carbonate.

6. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The volume ratio of the ether solvent to the fluorocarbonate additive is 9:

1.

7. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The ionic liquid component includes an organic cation and a fluoroborate anion, wherein the organic cation is an imidazole cation.

8. The wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation according to claim 1, characterized in that, The volume fraction of the ionic liquid in the electrolyte is 1-25 vol.

9. A method for preparing a wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid control as described in claim 1, characterized in that, Includes the following steps: Under an inert atmosphere, ether solvents and fluorocarbonate additives are mixed at a preset volume ratio to obtain a mixed solvent; sodium salt is added to the mixed solvent and stirred until completely dissolved to obtain a basic ether-based electrolyte; a preset volume fraction of ionic liquid is added to the basic ether-based electrolyte and stirred until the system is uniform and transparent to prepare a sodium metal battery electrolyte.

10. The application of the wide-temperature-range ether-based sodium metal battery electrolyte based on ionic liquid regulation as described in claim 1 in sodium metal batteries.

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