Ether-based electrolyte for improving high-voltage and long-period operation stability of sodium ion battery and preparation method and application thereof

Abstract

This invention provides an ether-based electrolyte for improving the high-voltage and long-cycle stability of sodium-ion batteries, its preparation method, and its application. The ether-based electrolyte comprises a base electrolyte and additives; the additives include aromatic isocyanates and alkoxysilanes. The aromatic isocyanates are a combination of one of the following: 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate, 3,4-dihydro-1,5-benzodioxane-7-isocyanate, or 3,4-(methylenedioxy)phenyl isocyanate, and 4-trifluoromethoxyphenyl isocyanate; the alkoxysilanes are 2-cyanoethyltriethoxysilane or 3,3,3-trifluoropropyltriethoxysilane. The electrolyte of this invention achieves synergistic regulation of interfacial reactions and interfacial film evolution, is suitable for sodium-ion half-cells or full-cells, and can improve overall stability and operating efficiency under high-voltage and long-cycle operating conditions.

Description

Technical Field

[0001] This invention relates to an ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries, its preparation method and application, and belongs to the field of sodium-ion battery technology. Background Technology

[0002] Sodium-ion batteries have attracted widespread attention due to their abundant resources, relatively low cost, and potential application in low- to medium-cost energy storage scenarios. With the increasing demand for high energy density, sodium-ion batteries are gradually evolving towards higher upper voltage limits, longer cycle life, and more stringent operating conditions (such as higher temperatures and higher rate capabilities). Against this backdrop, the electrolyte, as a key medium connecting the positive and negative electrode reactions and ion transport, has become a significant factor limiting battery performance improvement due to its chemical / electrochemical stability under high voltage and long-cycle operating conditions.

[0003] In existing sodium-ion electrolyte systems, ether solvents (such as diethylene glycol dimethyl ether, DGM) exhibit good low-temperature performance, wettability, and ion solvation capability, and can show low interfacial polarization in some systems, thus making them suitable for constructing sodium-ion battery electrolytes. Meanwhile, sodium salts, represented by NaPF6, can form a usable ion-conducting environment in ether systems. However, when the battery operating voltage is further increased and long-cycle operation is carried out, the NaPF6 / DGM system may still face the following problems: First, under high voltage conditions, solvent and salt-related side reactions are prone to occur and accumulate, manifested as electrolyte oxidative decomposition, interfacial byproduct generation, and electrolyte consumption; Second, the film layer formed at the electrode / electrolyte interface (usually including CEI / SEI) may have complex composition, loose structure, or non-uniformity, which are prone to thickening, cracking, peeling, and redeposition during cycling, resulting in uncontrollable interfacial film evolution; Third, as the side reactions and film layer evolution proceed, the interfacial impedance often shows a continuous increasing trend, leading to intensified polarization, decreased energy efficiency, and accelerated capacity decay, thereby limiting the stability and lifespan of sodium-ion batteries under high voltage and long-cycle operation conditions.

[0004] To address these issues, existing technologies typically employ an additive strategy, introducing small amounts of functional components into the electrolyte to regulate interfacial reactions, promote the formation of a more stable interfacial film, and improve high-voltage stability. However, single additives often struggle to simultaneously achieve both "interfacial protection" and "interfacial transport / impedance control": additives with strong film-forming capabilities may inhibit decomposition while simultaneously leading to excessive film growth or restricted ion transport, resulting in increased impedance; while additives primarily improving solvation or wetting / transport, although reducing initial polarization, may not be sufficient to sustainably suppress high-voltage side reactions and interfacial film instability, resulting in limited long-cycle performance. Furthermore, the mechanism of action and optimal formulation of additives often differ under different electrode materials, temperature, and voltage windows, making it difficult for existing electrolytes to simultaneously achieve the combined goals of a stable interfacial film and controllable impedance growth under high-voltage and long-cycle conditions.

[0005] Therefore, there is an urgent need to provide a modified NaPF6 / DGM ether electrolyte that can effectively suppress the continuous decomposition of the electrolyte and the accumulation of interfacial side reactions under high voltage and long-cycle operation conditions, promote the formation of a stable and more adhesive interfacial film, and achieve controllable growth of interfacial impedance, thereby improving the overall operational stability and energy efficiency of sodium-ion batteries under harsh operating conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, particularly the problems encountered with NaPF6 / DGM (DGM being diethylene glycol dimethyl ether) ether-based electrolytes under high-voltage, long-cycle operation conditions, such as continuous electrolyte oxidation and decomposition, accumulation of interfacial side reactions, insufficient interfacial film (CEI / SEI) stability, and rapid increase in interfacial impedance, this invention provides an ether-based electrolyte for improving the high-voltage and long-cycle operation stability of sodium-ion batteries, along with its preparation method and applications. This invention utilizes two types of additives—aromatic isocyanates and alkoxysilanes—to achieve a synergistic effect through a combination of "suppressing side reactions + optimizing the film layer + controlling impedance growth." This synergistic regulation of interfacial reactions and interfacial film evolution results in a better balance between "interfacial stability, impedance growth, and transmission efficiency," thereby improving the stability and adaptability of the battery under high-voltage operation.

[0007] The technical solution of the present invention is as follows:

[0008] An ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries includes a base electrolyte and additives; the additives include aromatic isocyanate compounds and alkoxysilanes.

[0009] According to a preferred embodiment of the present invention, the aromatic isocyanate compound is a combination of one of 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate (CAS No.: 321309-30-2), 3,4-dihydro-1,5-benzodioxane-7-isocyanate (CAS No.: 368869-87-8), or 3,4-(methylenedioxy)phenyl isocyanate (CAS No.: 69922-28-7) with 4-trifluoromethoxyphenyl isocyanate; more preferably, the mass ratio of 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate, 3,4-dihydro-1,5-benzodioxane-7-isocyanate, or 3,4-(methylenedioxy)phenyl isocyanate to 4-trifluoromethoxyphenyl isocyanate is 1-3:1, more preferably 2:1.

[0010] According to a preferred embodiment of the present invention, the alkoxysilane is 2-cyanoethyltriethoxysilane or 3,3,3-trifluoropropyltriethoxysilane.

[0011] According to a preferred embodiment of the present invention, the mass ratio of aromatic isocyanate compound to alkoxysilane in the additive is 6:4-4:6, and more preferably 5:5.

[0012] According to a preferred embodiment of the present invention, the mass of the additive is 0.05-5% of the mass of the base electrolyte, more preferably 0.2-2%, and even more preferably 1%.

[0013] According to a preferred embodiment of the present invention, the basic electrolyte is a NaPF6 / DGM electrolyte, which is prepared by dissolving NaPF6 in diethylene glycol dimethyl ether (DGM) and stirring until homogeneous. The concentration of NaPF6 in the NaPF6 / DGM electrolyte is 0.1-2.0 mol / L, more preferably 0.5-1.5 mol / L, and even more preferably 1.0 mol / L.

[0014] According to the present invention, the method for preparing the ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries includes the following steps:

[0015] Adding the additive to the base electrolyte and stirring until homogeneous yields an ether-based electrolyte that improves the high voltage and long-cycle operation stability of sodium-ion batteries.

[0016] The present invention also provides a sodium-ion battery, comprising the above-mentioned ether-based electrolyte, negative electrode, positive electrode and separator for improving the high voltage and long-cycle operation stability of sodium-ion batteries.

[0017] According to a preferred embodiment of the present invention, the negative electrode sheet is prepared by the following method: A negative electrode active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose are mixed in a mass ratio of 7:2:1, deionized water is added, and the mixture is ball-milled at 300-400 r / min for 3-5 hours to obtain a slurry. The obtained slurry is coated onto copper foil, vacuum dried at 60°C for 10-15 hours, and then cut into negative electrode sheets after rolling. The volume ratio of the deionized water to the total mass of the negative electrode active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose is 9-11 mL:1 g. The loading of the active material on the negative electrode sheet is 1-2 mg / cm³. 2 When forming a sodium-ion half-cell, the active material on the negative electrode is sodium (Na) plate; when forming a sodium-ion full-cell, the active material on the negative electrode is hard carbon.

[0018] According to a preferred embodiment of the present invention, the positive electrode sheet is prepared by the following method: positive electrode active material, conductive agent, and binder are mixed in a mass ratio of 8:1:1, N-methylpyrrolidone (NMP) is added, the mixture is ball-milled into a slurry, coated onto aluminum foil, dried at 100°C, rolled, and cut into positive electrode sheets; the volume ratio of N-methylpyrrolidone (NMP) to the total mass of the positive electrode active material, conductive agent, and binder is 8-10 mL:1 g; the loading of active material on the positive electrode sheet is 7-8 mg / cm³. 2 The conductive agent is acetylene black, the binder is polyvinylidene fluoride (PVDF), and the positive electrode active material is Na3(VOPO4)2F.

[0019] According to a preferred embodiment of the present invention, the diaphragm is a Whatman GF / F glass fiber membrane.

[0020] The technical features and beneficial effects of this invention are as follows:

[0021] 1. The electrolyte of this invention incorporates aromatic isocyanate compounds, which exhibit a strong tendency to participate in interfacial reactions under high voltage conditions. These compounds preferentially participate in reactions or compete for side reaction pathways at the electrode / electrolyte interface, thereby helping to reduce the continuous occurrence rate of DGM and salt-related decomposition, and promoting the formation of an earlier and more stable interfacial protective layer. This reduces the direct erosion of the interface by the subsequent electrolyte and the accumulation of parasitic reactions. The electrolyte of this invention also incorporates 4-trifluoromethoxyphenyl isocyanate, whose -OCF3 strong electron-withdrawing structure and fluorine-containing structure provide a "dual upgrade": on the one hand, it enhances the priority of interfacial reactions under high voltage through electronic structure regulation, more effectively suppressing the oxidative decomposition of the main electrolyte; on the other hand, based on the in-situ cross-linking of isocyanates to form an organic framework, the introduction of fluorine-containing components to participate in film formation and reinforcement makes the CEI denser, more antioxidant, and more mechanically stable. Therefore, it can complement the "rapid cross-linking film formation" mechanism of aromatic isocyanates, significantly improving the problems of uncontrollable film formation, insufficient film antioxidantity, and weak suppression of high-voltage side reactions that exist with ordinary aromatic isocyanates in high-voltage systems.

[0022] 2. The electrolyte of the present invention contains alkoxysilane, which has the ability to regulate interface and film composition. Its structural features help to improve the compactness and continuity of the interface film, reduce electrolyte penetration and local side reaction concentration caused by film defects (pores, cracks, local weak areas), and improve interface wetting and local microenvironment, thereby delaying the nonlinear growth of interface impedance and reducing the risk of polarization aggravation.

[0023] 3. The electrolyte of this invention incorporates a specific ratio of aromatic isocyanate compounds and alkoxysilanes. This avoids the situation where aromatic isocyanate compounds alone dominate film formation, leading to excessively thick film layers and a rapid increase in impedance. It also avoids the situation where alkoxysilanes alone improve wetting / transport, but the interface continues to decompose. This improves the overall stability and adaptability of the system under high voltage and long-cycle conditions. Therefore, this invention achieves synergistic regulation of the interface reaction and film evolution of the NaPF6 / DGM system through the synergistic effect of aromatic isocyanate compounds and alkoxysilanes, thereby improving the overall stability and operating efficiency of sodium-ion batteries under high voltage and long-cycle operating conditions.

[0024] 4. The electrolyte of the present invention improves electrolyte / interface stability and reduces the accumulation rate of side reactions under high voltage conditions; optimizes the interfacial film structure and composition, making the increase of interfacial impedance more controllable and the increase of polarization more gradual; and helps to improve capacity retention, coulombic efficiency stability and energy efficiency during long-cycle processes. Attached Figure Description

[0025] Figure 1The figures show the cycle performance of sodium-ion half-cells assembled with the electrolytes of Examples 1-4; where a is the cycle performance of the sodium-ion half-cell assembled with the electrolyte of Example 1; b is the cycle performance of the sodium-ion half-cell assembled with the electrolyte of Example 2; c is the cycle performance of the sodium-ion half-cell assembled with the electrolyte of Example 3; and d is the cycle performance of the sodium-ion half-cell assembled with the electrolyte of Example 1.

[0026] Figure 2 The diagram shows the cycle performance of sodium-ion half-cells assembled with the electrolytes of Examples 1 and Comparative Examples 1-6.

[0027] Figure 3 The images show scanning electron microscope (SEM) images of the positive electrode of sodium-ion half-cells assembled with the electrolytes of Example 1 and Comparative Example 2 after 100 cycles, where a is Example 1 and b is Comparative Example 2.

[0028] Figure 4 These are comparative photographs of the electrolytes of Example 1 and Comparative Example 6 after standing at 60°C for 1 day, 3 days, and 10 days; where a, b, and c are Comparative Example 6, and d, e, and f are Example 1. Detailed Implementation

[0029] The present invention will now be described in more detail with reference to the accompanying drawings and embodiments, but is not limited thereto.

[0030] All raw materials used in the examples are commercially available products.

[0031] Example 1

[0032] An ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries includes a base electrolyte and an additive; the additive includes aromatic isocyanate compounds and alkoxysilanes; the mass of the additive is 1% of the mass of the base electrolyte; the mass ratio of the aromatic isocyanate compound to the alkoxysilane in the additive is 5:5.

[0033] Among them, the aromatic isocyanate compound is a combination of 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate and 4-trifluoromethoxyphenyl isocyanate, wherein the mass ratio of 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate to 4-trifluoromethoxyphenyl isocyanate is 2:1; the alkoxysilane is 2-cyanoethyltriethoxysilane;

[0034] The basic electrolyte is NaPF6 / DGM electrolyte, which is obtained by dissolving NaPF6 in diethylene glycol dimethyl ether (DGM, Diglyme) and stirring until homogeneous. The concentration of NaPF6 in the NaPF6 / DGM electrolyte is 1 mol / L.

[0035] The preparation method of the ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries includes the following steps:

[0036] Add the additive to the base electrolyte and stir until homogeneous to obtain the final product.

[0037] Example 2

[0038] An ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries is described in Example 1, except that 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate is replaced with 3,4-(methylenedioxy)phenyl isocyanate, and other conditions are as described in Example 1.

[0039] Example 3

[0040] An ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries is described in Example 1, except that 2-cyanoethyltriethoxysilane is replaced with 3,3,3-trifluoropropyltriethoxysilane, while other conditions are the same as described in Example 1.

[0041] Example 4

[0042] An ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries is described in Example 1, except that the mass ratio of aromatic isocyanate compound to alkoxysilane in the additive is 6:4, and other conditions are as described in Example 1.

[0043] Comparative Example 1

[0044] An ether-based electrolyte is as described in Example 1, except that the additive is only an aromatic isocyanate compound, and the other conditions are as described in Example 1.

[0045] Comparative Example 2

[0046] An ether-based electrolyte is as described in Example 1, except that the additive is only alkoxysilane, and other conditions are as described in Example 1.

[0047] Comparative Example 3

[0048] An ether-based electrolyte is described in Example 1, except that the aromatic isocyanate compound is only 4-trifluoromethoxyphenyl isocyanate.

[0049] Comparative Example 4

[0050] An ether-based electrolyte is described in Example 1, except that the aromatic isocyanate compound is only 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate.

[0051] Comparative Example 5

[0052] An ether-based electrolyte is described in Example 1, except that the mass ratio of aromatic isocyanate compound to alkoxysilane in the additive is 2:8.

[0053] Comparative Example 6

[0054] An ether-based electrolyte is as described in Example 1, except that it does not contain additives.

[0055] Experimental Example 1

[0056] The electrolytes prepared in the examples and comparative examples were used to assemble sodium-ion batteries. The specific steps are as follows:

[0057] 1. Negative electrode preparation: Active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose were mixed in a mass ratio of 7:2:1. Deionized water was added (the volume ratio of deionized water to the total mass of active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose was 10 mL:1 g). The mixture was ball-milled at 300 r / min for 4 hours to obtain a slurry. The slurry was coated onto copper foil and vacuum-dried at 60℃ for 12 hours. After rolling, it was cut into electrode sheets. The loading of active material on the negative electrode sheet was 1.3 mg / cm³. 2 When forming a sodium-ion half-cell, the active material on the negative electrode is sodium (Na) plate; when forming a sodium-ion full-cell, the active material on the negative electrode is hard carbon.

[0058] 2. Preparation of the positive electrode sheet: Active material, conductive agent, and binder are mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) is then added, with the volume ratio of NMP to the total mass of active material, conductive agent, and binder being 9 mL:1 g. The mixture is ball-milled into a slurry and coated onto aluminum foil. After coating, it is vacuum-dried at 100℃ for 4 hours. After drying, it is rolled and cut into electrode sheets. The active material loading on the positive electrode sheet is 8 mg / cm³. 2 The conductive agent is acetylene black, the binder is polyvinylidene fluoride (PVDF), and the active material is Na3(VOPO4)2F.

[0059] 3. Assemble the positive electrode, negative electrode, Whatman GF / F glass fiber separator, electrolyte prepared in the examples or comparative examples, and casing (model 2025) into a sodium-ion half cell or sodium-ion full cell. The battery assembly is carried out in a glove box.

[0060] Electrochemical performance testing of the assembled battery

[0061] 1. Electrochemical performance of half-cells

[0062] The test conditions were: voltage 2-4.4V, current density 0.5A·g. -1The temperature is 25℃.

[0063] Figure 1-2 The figures show a comparison of the cycle performance of sodium-ion half-cells assembled with the electrolytes of the examples and comparative examples. Figure 1 It can be seen that the sodium-ion half-cell assembled with the electrolyte in Example 1 has a performance of 0.5 A·g -1 The discharge capacity remained stable at approximately 110 mAh·g during 400 cycles at the current density. -1 The capacity curve remained stable with no significant decay during cycling, and the coulombic efficiency remained close to 100%. The sodium-ion half-cells assembled with the electrolytes from Examples 2-3 also exhibited stable cycling behavior under the same test conditions, with the overall capacity maintained at approximately 100 mAh·g. -1 Around 100%, the coulombic efficiency remained close to 100%; the sodium-ion half-cell assembled with the electrolyte in Example 4 achieved a coulombic efficiency of 0.5 A·g. -1 The discharge capacity remained stable at approximately 100 mAh·g during 300 cycles at the current density. -1 Around 100%, no significant decay trend was observed during the cycling process, the capacity curve remained stable, and the coulombic efficiency remained close to 100%. This indicates that the electrolyte of this embodiment exhibits good electrochemical reversibility and interfacial stability in the high-voltage range. In contrast, [the following text appears to be incomplete and requires further context: "by..."] Figure 2 It can be seen that Comparative Examples 1-6 all exhibited varying degrees of capacity decay under the same conditions, with some examples showing significant failure (marked "dead" in the figure). Comparative Example 6 showed significant failure (marked "dead" in the figure) at approximately 150 cycles, Comparative Example 1 showed significant failure at approximately 300 cycles, and Comparative Example 2 had a lower capacity than Example 1 and showed significant failure at 260 cycles, indicating that additives can significantly improve battery performance, and both types of additives are indispensable. Comparative Examples 3 and 4 showed capacity decay compared to Example 1 during cycling, indicating that batteries containing only one type of aromatic isocyanate compound have insufficient electrode / electrolyte interface stability, making it difficult to maintain high capacity and long-term stable operation in the high-voltage range. Their coulombic efficiency also fluctuated or showed a decreasing trend with cycling, reflecting more serious side reactions. Furthermore, as can be seen from Example 1 and Comparative Example 5, when aromatic isocyanate compounds are compounded with alkoxysilanes in a 5:5 ratio, a more effective synergistic film-forming effect can be achieved, constructing a denser and more stable interface layer, thereby significantly improving the capacity level and cycle stability. However, at a 2:8 ratio, the content of aromatic isocyanate compounds is relatively low, the interface regulation ability is weakened, resulting in a decrease in electrochemical performance and a certain capacity decay.

[0064] A comprehensive comparison shows that the electrolyte in the embodiments, especially in Example 1, maintains high capacity output and near 100% coulombic efficiency under high voltage (e.g., 4.4V) and high current density conditions. Its cycle life is significantly better than that of the comparative examples. This indicates that the electrolyte system of the present invention, under the synergistic effect of aromatic isocyanate compounds and alkoxysilanes, can effectively construct a stable electrode interface structure, inhibit electrolyte decomposition and structural degradation, thereby significantly improving the high-voltage cycle stability and long-term operational reliability of sodium-ion batteries.

[0065] Figure 3 The images are scanning electron microscope (SEM) images of the positive electrode of the sodium-ion half-cells assembled with the electrolytes of Example 1 and Comparative Example 2 after 100 cycles. Figure 3 As can be seen, the electrode of the sodium-ion half-cell assembled with the electrolyte of Example 1 remained generally flat and dense after 100 cycles, with no obvious cracks or structural damage observed. The surface morphology was uniform, and the particles were tightly bonded, indicating that the electrode structure maintained good integrity and the interface remained stable during cycling. In contrast, the electrode of the sodium-ion half-cell assembled with the electrolyte of Comparative Example 2 showed obvious cracks on its surface under the same cycling conditions, with localized structural cracking and discontinuities, indicating that the electrode experienced severe volumetric stress accumulation and structural degradation during cycling. Based on the above results, it can be seen that Example 1 can effectively maintain the integrity of the electrode structure during cycling. Aromatic isocyanates can inhibit crack formation, alleviate volumetric expansion stress, and significantly improve the structural and interfacial stability of the electrode. This advantage provides a strong guarantee for the battery to maintain excellent electrochemical performance under high voltage and long-term cycling conditions, demonstrating the significant superiority of Example 1 in terms of structural stability.

[0066] Experimental Example 2

[0067] The stability of the electrolytes in Example 1 and Comparative Example 6 was evaluated by the following steps: 2 mL of electrolyte was placed in a sealed glass bottle and kept at a constant temperature of 60°C. The appearance changes were observed periodically.

[0068] Figure 4 These are comparative photographs of the electrolytes of Example 1 and Comparative Example 6 after standing at 60°C for 1 day, 3 days, and 10 days. Figure 4It can be seen that the electrolyte of Comparative Example 6 remained basically clear and transparent after 1 day; slight turbidity began to appear after 3 days; and by 10 days, the solution had darkened significantly and even showed black sediment, indicating that significant side reactions or decomposition reactions occurred in the system under high temperature conditions, and the electrolyte's chemical stability was insufficient. In contrast, the electrolyte of Example 1 remained clear and transparent after 1, 3, and 10 days at 60°C, with no obvious turbidity, discoloration, or precipitation observed, indicating that this electrolyte system has excellent thermal and chemical stability under high temperature conditions.

[0069] The comparison shows that Example 1 is significantly superior to Comparative Example 6 under high-temperature storage conditions, effectively suppressing electrolyte decomposition and side reactions caused by high temperatures. This provides an important guarantee for the safe operation of sodium-ion batteries and the maintenance of excellent electrochemical performance in high-temperature environments, demonstrating the significant advantages of the electrolyte system of this invention in practical applications.

Claims

1. An ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries, characterized in that, It includes a base electrolyte and additives; the additives include aromatic isocyanates and alkoxysilanes.

2. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to claim 1, characterized in that, The aromatic isocyanate compound is a combination of one of 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate, 3,4-dihydro-1,5-benzodioxane-7-isocyanate, or 3,4-(methylenedioxy)phenyl isocyanate with 4-trifluoromethoxyphenyl isocyanate.

3. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to claim 2, characterized in that, The mass ratio of 6-fluoro-1H-1,3-benzodioxane-8-yl isocyanate, 3,4-dihydro-1,5-benzodioxane-7-isocyanate or 3,4-(methylenedioxy)phenyl isocyanate to 4-trifluoromethoxyphenyl isocyanate is 1-3:1, preferably 2:

1.

4. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to claim 1, characterized in that, The alkoxysilane is 2-cyanoethyltriethoxysilane or 3,3,3-trifluoropropyltriethoxysilane.

5. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to claim 1, characterized in that, The mass ratio of aromatic isocyanate compounds to alkoxysilanes in the additive is 6:4-4:6, preferably 5:

5.

6. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to claim 1, characterized in that, The mass of the additive is 0.05-5% of the mass of the base electrolyte, preferably 0.2-2%, and more preferably 1%.

7. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to claim 1, characterized in that, The basic electrolyte is a NaPF6 / DGM electrolyte, which is prepared by dissolving NaPF6 in diethylene glycol dimethyl ether and stirring until homogeneous. The concentration of NaPF6 in the NaPF6 / DGM electrolyte is 0.1-2.0 mol / L, preferably 0.5-1.5 mol / L, and more preferably 1.0 mol / L.

8. The ether-based electrolyte for improving the high voltage and long-cycle operation stability of sodium-ion batteries according to any one of claims 1-7, characterized in that, The method for preparing the ether-based electrolyte that improves the high voltage and long-cycle operation stability of sodium-ion batteries includes the following steps: Adding the additive to the base electrolyte and stirring until homogeneous yields an ether-based electrolyte that improves the high voltage and long-cycle operation stability of sodium-ion batteries.

9. A sodium-ion battery, characterized in that, Includes the ether-based electrolyte, negative electrode, positive electrode, and separator described in any one of claims 1-7 for improving the high voltage and long-cycle operation stability of sodium-ion batteries.

10. The sodium-ion battery according to claim 9, characterized in that, The negative electrode sheet is prepared by the following method: A negative electrode active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose are mixed in a mass ratio of 7:2:1, deionized water is added, and the mixture is ball-milled at 300-400 r / min for 3-5 hours to obtain a slurry. The slurry is coated onto copper foil, vacuum dried at 60℃ for 10-15 hours, and then cut into negative electrode sheets after rolling. The volume ratio of the deionized water to the total mass of the negative electrode active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose is 9-11 mL:1 g. The loading of the active material on the negative electrode sheet is 1-2 mg / cm³. 2 When forming a sodium-ion half-cell, the active material on the negative electrode is sodium (Na) plate; when forming a sodium-ion full-cell, the active material on the negative electrode is hard carbon. The positive electrode sheet is prepared by the following method: Positive electrode active material, conductive agent, and binder are mixed in a mass ratio of 8:1:1, N-methylpyrrolidone is added, the mixture is ball-milled into a slurry, coated onto aluminum foil, dried at 100°C, rolled, and cut into positive electrode sheets; the volume ratio of N-methylpyrrolidone to the total mass of the positive electrode active material, conductive agent, and binder is 8-10 mL:1 g; the loading of active material on the positive electrode sheet is 7-8 mg / cm³. 2 The conductive agent is acetylene black, the binder is polyvinylidene fluoride, and the positive electrode active material is Na3(VOPO4)2F; The diaphragm is a Whatman GF / F glass fiber membrane.

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