High-voltage-resistant non-flammable sodium ion battery electrolyte and sodium ion battery containing electrolyte
By combining phosphate ester solvent, sodium borate salt and fluorine-containing functional additives, a sodium ion battery electrolyte with high safety, high stability and high performance is solved, and the problem of traditional electrolytes is flammable and explosive under extreme conditions is suitable for large-scale energy storage and high safety requirements.
Patent Information
- Application Number
- CN202510239405.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-03
- Publication Date
- 2025-05-02
AI Technical Summary
Traditional sodium ion battery electrolytes are prone to burning or even explode under extreme conditions such as high temperature or overcharging, and their chemical stability and electrochemical window performance are insufficient, which limits the practical application of the battery.
The combination of pure phosphate solvents, boric acid electrolyte sodium salts (such as sodium difluoroxalic acid borate and sodium tetrafluoroborate) and fluorine-containing functional additives (such as fluorovinyl carbonate) is used to form a high safety, high stability and high performance electrolyte through the synergistic action of a variety of flame retardant and functional components.
It achieves a balance of high safety, high stability and high performance of sodium ion batteries, especially in application scenarios with extremely high requirements for large-scale energy storage and safety.
Smart Images
Figure BDA0005293629390000051 
Figure HDA0005293629400000011 
Figure HDA0005293629400000012
Abstract
Description
Technical Field
[0001] The invention relates to an organic flame-retardant electrolyte for a sodium ion battery, in particular to a sodium ion battery electrolyte which is resistant to high voltage and non-flammable and a sodium ion battery containing the electrolyte, belonging to the technical field of secondary sodium ion batteries. Background Art
[0002] With the rapid development of new energy technologies, sodium-ion batteries have become an important direction of the next generation of energy storage technology after lithium-ion batteries due to their advantages such as abundant raw materials, low cost, and excellent cycle performance. Sodium-ion batteries have shown broad application prospects in energy storage equipment, electric vehicles, and smart grids. However, the safety of traditional sodium-ion battery electrolytes is still an important bottleneck restricting their practical application.
[0003] At present, commercial sodium-ion battery electrolytes are mainly composed of carbonate solvents and sodium salts. However, due to the low flash point and flammability of carbonate solvents, they are prone to combustion or even explosion under extreme conditions such as high temperature or overcharge, which seriously threatens the safety of the battery system. In addition, the chemical stability and electrochemical window of sodium salts and electrolytes directly affect the energy density and cycle life of the battery. Therefore, the development of sodium-ion battery electrolytes with high safety and excellent electrochemical performance is of great research value.
[0004] Among the many existing modification technologies, the introduction of organic flame retardant solvents, fluorine-containing functional additives and high-efficiency sodium salts is considered to be an effective means to improve the safety and electrochemical performance of electrolytes. Among them, phosphate solvents have become an ideal solvent choice due to their excellent flame retardant properties and high chemical stability. However, for example, the literature: MA Y, QIN B, DU X, et al. Delicately Tailored Ternary Phosphate Electrolyte Promotes Ultrastable Cycling of Na3V2(PO4)2F3-Based Sodium Metal Batteries[J]. ACS Applied Materials & Interfaces, 2022, 14(15): 17444-53. and CHEN H, CHEN K, YANG J, et al. Designing Advanced Electrolytes for High-Safety and Long-Lifetime Sodium-Ion Batteries via Anion-Cation Interaction Modulation[J]. Journal of the American Chemical Society, 2024, 146(23): 15751-60. discloses that phosphate electrolytes are difficult to be compatible with carbon-based and sodium metal negative electrodes because they cannot form a stable and dense solid electrolyte interface (SEI) film. Fluorine-containing additives can effectively improve the battery's cycle and rate performance by generating a stable solid electrolyte interface film (SEI film) at the electrode interface; sodium difluorooxalatoborate as the main salt has a wide electrochemical window, high thermal stability and low side reaction activity, which can further improve the overall performance of sodium-ion batteries. However, sodium difluorooxalatoborate has a low solubility, and there are few reports on its use as a main salt in electrolytes and its compatibility with different sodium-ion battery electrodes, which still requires further exploration.
[0005] Therefore, there is an urgent need to develop an efficient and safe sodium-ion battery electrolyte, which has important technical significance and application value. Summary of the invention
[0006] The purpose of the present invention is to solve the problems existing in the prior art, provide a high-voltage resistant and non-flammable sodium ion battery electrolyte and a sodium ion battery containing the electrolyte, combine a phosphate solvent, a fluorine-containing additive and a sodium borate salt, and achieve a balance of high safety, high stability and high performance through the synergistic effect of multiple flame retardant and functional components. The present invention is particularly suitable for large-scale energy storage and sodium ion battery application scenarios with extremely high safety requirements.
[0007] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a high-voltage resistant and non-flammable sodium ion battery electrolyte and a sodium ion battery containing the electrolyte, wherein the electrolyte comprises a pure phosphate ester solvent, a boric acid electrolyte sodium salt and a fluorine-containing functional additive; the pure phosphate ester solvent is one or more of trimethyl phosphate (TMP) and triethyl phosphate (TEP); the boric acid electrolyte sodium salt is sodium difluorooxalatoborate (NaDFOB) or a mixture of sodium difluorooxalatoborate (NaDFOB) and sodium tetrafluoroborate (NaBF4); the fluorine-containing functional additive is fluoroethylene carbonate (FEC), and its addition amount is 2.5% to 10% of the volume of the electrolyte.
[0008] When the boric acid electrolyte sodium salt is sodium difluorooxalate borate (NaDFOB), the concentration of sodium difluorooxalate borate (NaDFOB) in the electrolyte is 0.8 to 1.2 mol L -1 .
[0009] When the boric acid electrolyte sodium salt is a mixture of sodium difluorooxalate borate (NaDFOB) and sodium tetrafluoroborate (NaBF4), sodium difluorooxalate borate (NaDFOB) is used as the main salt, and the concentration of the sodium difluorooxalate borate (NaDFOB) in the electrolyte is 0.8-1.2 mol L -1 The concentration of sodium tetrafluoroborate (NaBF4) in the electrolyte is 0.05-0.2 mol L -1 .
[0010] The present invention also discloses a sodium ion battery containing the electrolyte, wherein the positive electrode material of the sodium ion battery is one of sodium vanadium phosphate and sodium vanadium fluorophosphate, and the negative electrode material is one of sodium metal or hard carbon.
[0011] The beneficial effects of the present invention are:
[0012] 1) In the sodium ion battery of the present invention, a phosphate solvent, a fluorine-containing additive and a sodium borate salt are combined, and a balance of high safety, high stability and high performance is achieved through the synergistic effect of a variety of flame retardant and functional components, which is particularly suitable for large-scale energy storage and sodium ion battery application scenarios with extremely high safety requirements.
[0013] 2) The sodium ion battery of the present invention uses sodium difluorooxalate borate as the main salt, which not only has a wide electrochemical window and excellent antioxidant properties, but also has good solubility and ionic conductivity. Its decomposition products can inhibit the oxidative decomposition of the electrode interface, reduce the corrosion rate of the electrode material, and effectively improve the capacity retention rate of the sodium ion battery; at the same time, it has high thermal stability at high temperatures and is not easy to thermally decompose, while traditional sodium salts such as sodium perchlorate have poor thermal stability and cannot effectively protect the electrode under high temperature and high pressure conditions, causing the battery capacity to decay rapidly. The introduction of NaBF4 can further improve the high voltage resistance and cycle stability of the electrolyte.
[0014] 3) In the sodium ion battery of the present invention, phosphate ester solvents are used as electrolyte solvents. When phosphate ester decomposes at high temperature, it releases phosphorus-containing gas (such as phosphoric acid and phosphate ester). These phosphorus compounds react with free radicals to inhibit the important free radical chain reaction in the combustion process, which can prevent the combustion of the electrolyte, significantly improve the flame retardant properties and thermal stability of the electrolyte, and effectively avoid the flammable and explosive safety hazards of traditional carbonate solvents. The high flash point and low volatility of phosphate ester solvents greatly reduce the risk of thermal runaway of the battery under high temperature or overcharge conditions. At the same time, the phosphorus-containing substances produced by its decomposition can also form a protective interface layer on the electrode surface, improving the cycle life and safety of the battery.
[0015] 4) The sodium ion battery of the present invention introduces fluorine-containing functional additives, which can construct a stable solid electrolyte interface (SEI) film on the electrode surface, significantly improve the chemical stability of the electrode / electrolyte interface, effectively reduce the occurrence of side reactions, inhibit the decomposition of the electrolyte and the growth of sodium dendrites, thereby improving the coulombic efficiency and rate performance of the battery. In addition, the gas generated by the decomposition of the fluorine-containing additive has a fire-suppressing effect, which can further improve the overall safety of the system. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 This is a combustion state diagram of the electrolyte prepared in Example 1 of the present invention;
[0017] Figure 2 This is the combustion state diagram of the conventional carbonate electrolyte Commercial;
[0018] Figure 3 The graph is a cycle data diagram of a sodium ion battery prepared using different concentrations of fluorinated functional additive FEC in an embodiment of the present invention at 2.0-4.3V;
[0019] Figure 4 This is a comparison chart of cycle data of sodium ion batteries prepared using Example 1, Example 6 and commercial electrolytes at 2.0-4.3V of the present invention;
[0020] Figure 5This is a comparison chart of cycle data of the sodium ion batteries prepared using Example 1 and Example 6 of the present invention at 60° C. and 2.0 to 4.3 V;
[0021] Figure 6 This is a comparison chart of the cycle data of the sodium ion batteries prepared using Example 1 and Example 6 at 2.0-4.5V of the present invention;
[0022] Figure 7 A comparison of the sodium metal negative electrode deposition morphology of the battery prepared by Example 1 of the present invention and Commercial after cycling;
[0023] Figure 8 This is a comparison of the positive electrode morphologies of sodium vanadium fluorophosphate prepared in Example 1, Example 6 and Commercial after battery cycling. DETAILED DESCRIPTION
[0024] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.
[0025] The preparation of the electrolyte and the assembly of the battery are all carried out in a glove box filled with high-purity argon (water and oxygen content are all less than 1ppm). In the glove box, the required mass of NaDFOB and NaBF4 are weighed and dissolved in the required phosphate solution, and then the required volume of FEC additive is added, and then stirred at room temperature for 1 hour until the solution is evenly mixed to obtain a sodium ion battery electrolyte with flame retardant function.
[0026] According to the above method and by selecting solvents with different contents or materials, sodium ion electrolytes of Examples 1 to 10, Comparative Example 1 and Commercial group were prepared. The component relationships and measured performance results are shown in Table 1 below.
[0027] Table 1
[0028]
[0029] Finally, the electrolytes prepared in the above different embodiments were loaded into button-type half-cells whose positive electrode material was sodium vanadium fluorophosphate (Na3V2(PO4)2F3, NVPF) and whose negative electrode material was sodium metal sheet, and tested.
[0030] In the test, all batteries were activated for 2 cycles at a current density of 0.2C, and then long cycled at a current density of 1C, where 1C = 128mA / g.
[0031] The results of Examples 1 to 10 were as follows: Figure 1 As shown in the figure, it is extremely difficult to ignite, and will immediately self-extinguish after ignition, and has good flame retardant properties, while commercial electrolytes are as follows Figure 2As shown, upon contact with an open flame it will burn immediately until the electrolyte is consumed.
[0032] It can be seen from Examples 1 to 3 that the best effect is achieved when the sodium salt concentration is 1 M. Figure 3 As shown, from Examples 1, 4, 5 and Comparative Example 1, it can be seen that the fluorinated functional additive effectively stabilizes the system and maintains the cycle stability. This is because FEC can build a stable solid electrolyte interface (SEI) film on the electrode surface, significantly improve the chemical stability of the electrode / electrolyte interface, and effectively reduce the occurrence of side reactions. 5% is the optimal dosage of the fluorinated functional additive FEC.
[0033] like Figure 4 As shown, it can be seen from Example 1 and Example 6 that the capacity retention rates are better than those of commercial electrolytes, and the introduction of NaBF4 further improves the capacity retention rate of the battery cycle.
[0034] like Figure 5 As shown, Example 1 and Example 6 were further tested at a higher cut-off voltage (2.0-4.5V). The electrolyte of the present invention still has excellent cycle stability and capacity retention after 300 cycles at a high voltage of 4.5V. Example 6 has an excellent performance of 98.9% capacity retention after 300 cycles.
[0035] like Figure 6 As shown, the batteries prepared in Example 1 and Example 6 were also tested for cycling at 60°C. They can still cycle stably and normally at high temperatures, indicating that the battery has good thermal stability and high temperature adaptability. Among them, Example 6 has a capacity retention rate of 89.3% after 300 cycles at 60°C, and has excellent performance under high temperature conditions; this is because NaBF4 has a low HOMO energy level and is not easily oxidized, and a low LUMO energy level that preferentially reduces and decomposes to form a film on the surface of sodium metal, further improving the interface stability.
[0036] like Figure 7 As shown, this scanning electron microscope (SEM) image shows two different sodium metal negative electrode deposition morphologies, namely "Example 1" and "Commercial" samples.
[0037] The graph of Example 1 shows that the deposition of sodium metal is relatively uniform, the surface is relatively smooth and there are no obvious particles or cracks, which may show good sodium metal electrodeposition behavior. Overall, the structure of the deposited layer is more stable and there is no significant dendrite growth, which is conducive to improving the cycle stability of the battery.
[0038] Commercial's graph shows that the sodium metal deposition of this sample is relatively irregular, with obvious cracks and granular structures on the surface, which may be caused by excessive electrodeposition or uneven current distribution. The instability of sodium metal deposition may lead to the growth of dendrites, thus affecting the safety and cycle life of the battery.
[0039] like Figure 8 As shown, this figure shows the solid electrolyte interface (CEI) morphology of different sodium vanadium fluorophosphate positive electrode materials.
[0040] The figures of Example 1 and Example 6 show that the CEI layer exhibits a relatively uniform and dense structure, and the connection between the interface and the electrode material is relatively smooth, showing good stability and good coverage. The thickness of the CEI layer is relatively thin and there are no obvious cracks or unevenness, indicating that the material may help improve the cycle stability of the battery and the protection performance of the interface.
[0041] Commercial's graph shows that the CEI layer shows obvious non-uniformity, with some areas being thin or cracked, indicating that the material's interface stability is poor, which may affect the long-term use of the battery. The non-uniformity of the interface layer may lead to a decline in battery performance, especially during long-term cycling or high-rate charge and discharge, which may accelerate interface degradation.
[0042] Combined with the above test results, it can be seen that the electrolyte of the present invention uses phosphate as a solvent, sodium difluorooxalatoborate and sodium tetrafluoroborate as sodium salts, and fluoroethylene carbonate as a fluorinated functional additive. The prepared electrolyte is suitable for phosphate positive electrode sodium ion batteries and has a higher capacity retention rate than commercial electrolytes.
[0043] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.
Claims
1. A high-voltage-resistant and non-flammable sodium ion battery electrolyte and a sodium ion battery containing the electrolyte, characterized in that: The electrolyte comprises a pure phosphate solvent, a boric acid electrolyte sodium salt and a fluorine-containing functional additive; The pure phosphate ester solvent is one or more of trimethyl phosphate (TMP) and triethyl phosphate (TEP); The boric acid electrolyte sodium salt is sodium difluorooxalate borate (NaDFOB) or a mixture of sodium difluorooxalate borate (NaDFOB) and sodium tetrafluoroborate (NaBF4); The fluorine-containing functional additive is fluoroethylene carbonate (FEC), and its addition amount is 2.5% to 10% of the volume of the electrolyte.
2. The high-voltage and non-flammable sodium ion battery electrolyte and the sodium ion battery containing the electrolyte according to claim 1, characterized in that: When the boric acid electrolyte sodium salt is sodium difluorooxalate borate (NaDFOB), the concentration of sodium difluorooxalate borate (NaDFOB) in the electrolyte is 0.8 to 1.2 mol L -1 .
3. The high-voltage and non-flammable sodium ion battery electrolyte and the sodium ion battery containing the electrolyte according to claim 1, characterized in that: When the boric acid electrolyte sodium salt is a mixture of sodium difluorooxalate borate (NaDFOB) and sodium tetrafluoroborate (NaBF4), sodium difluorooxalate borate (NaDFOB) is used as the main salt, and the concentration of the sodium difluorooxalate borate (NaDFOB) in the electrolyte is 0.8-1.2 mol L -1 The concentration of sodium tetrafluoroborate (NaBF4) in the electrolyte is 0.05-0.2 mol L -1 .
4. A sodium ion battery containing the electrolyte according to any one of claims 1 to 3, characterized in that: The positive electrode material in the sodium ion battery is one of sodium vanadium phosphate and sodium vanadium fluorophosphate, and the negative electrode material is one of sodium metal or hard carbon.