A high-voltage ether electrolyte containing an electric field coupling agent, its preparation method and application

Abstract

This invention relates to a high-voltage ether electrolyte containing an electric field coupling agent, its preparation method, and its applications, specifically in sodium-ion battery technology. It aims to address the technical problems of limited oxidation stability and unstable cathode / electrolyte interface films in existing ether electrolytes at high voltages, leading to performance degradation during cycling. The high-voltage ether electrolyte of this invention involves adding an electric field coupling agent containing voltage-sensitive groups and beneficial components for the interface film to a sodium salt ether solution. This electrolyte is activated by high voltage, promoting the directional migration of the electric field coupling agent and inducing the decomposition of beneficial components, forming a dense and stable cathode / electrolyte interface film. This enhances the oxidation resistance and chemical stability of the interface film, and suppresses solvent side reactions and transition metal dissolution. A sodium layered oxide / sodium metal battery using this electrolyte maintains a capacity retention of approximately 87.9% and a coulombic efficiency consistently above 99% after 1000 cycles at 4.5 V, making it suitable for energy storage systems and power batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a high-voltage electrolyte that optimizes the performance of sodium-ion batteries through a high-temperature activation mechanism, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, with their abundant resources and low cost, have broad application prospects in large-scale energy storage. Using sodium layered transition metal oxides with high theoretical specific capacity as the positive electrode and increasing its charging cut-off voltage are key ways to improve the energy density of sodium-ion batteries. Currently, ether-based electrolytes have good compatibility with sodium metal anodes, which is beneficial to the cycle stability of the battery. However, conventional ether solvent molecules have poor intrinsic oxidation resistance and are prone to severe oxidative decomposition under high voltage conditions. This leads to repeated breakage and reconstruction of the cathode / electrolyte interface (CEI) film, accompanied by transition metal dissolution and bulk structure degradation, ultimately resulting in a continuous decline in battery performance. Therefore, how to construct a stable CEI structure under high voltage to fundamentally inhibit electrolyte decomposition and material degradation, and improve the oxidation limit and cycle performance of the battery, has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0003] This invention aims to address the technical problems of insufficient antioxidant properties and performance degradation caused by instability of the cathode / electrolyte interface (CEI) film in existing sodium-ion battery electrolytes. It provides a high-voltage ether-based electrolyte containing an electric field coupling agent, its preparation method, and its applications. This invention introduces compounds containing voltage-sensitive groups and beneficial interfacial film components as electric field coupling agents into the electrolyte, constructing a novel electrolyte system with high-voltage response characteristics, suitable for high-voltage environments of 4.3 V and above.

[0004] The high-voltage ether electrolyte containing an electric field coupling agent of the present invention is: a mixture of a sodium salt ether organic solvent solution and an electric field coupling agent; wherein the sodium salt ether organic solvent solution is obtained by dissolving the sodium salt in the ether organic solvent at a sodium salt concentration of 0.5–3.0 mol / L; the mass of the electric field coupling agent is 1%–5.0% of the mass of the sodium salt ether organic solvent solution; the electric field coupling agent is a compound whose molecular structure simultaneously contains a voltage-sensitive group and a beneficial interfacial film component; wherein the voltage-sensitive group is an organic active group that readily undergoes oxidative decarboxylation, ring-opening, or electropolymerization reactions under high voltage, and is oxalate (C2O4). 2- ), malonate (C3H2O4) 2- The preferred interfacial film component is one or two of vinyl (CH≡C-), allyl (H₂C=CH-CH₂-), propargyl (HC≡CCH₂-), and cyano (-CN); the preferred interfacial film component is an inorganic or organic group containing heteroatoms, such as sulfonyl (RS(=O)₂).- ), sulfonylimide group (-SO) 2- One or more of the following: N-SO2-, difluoroboronyl (-BF2), tetrafluorophosphoryl (-PF4), difluorophosphoryl (-PF2), sulfonic acid (-SO3H), and sulfate ester (-O-SO2-O-).

[0005] Furthermore, the electric field coupling agent is sodium difluoromalonoborate (NaDFMB), diphenylmethylenesulfonyl fluoride (DPMSF), p-toluenesulfonyl isocyanate (PTSI), or 4-fluorobenzenesulfonyl isocyanate (FBSI); or the electric field coupling agent is one or more of sodium difluorooxalate borate, sodium tetrafluorooxalate phosphate (NaTFOP), and diphenylmethylenesulfonyl fluoride (DPMSF) combined with sodium difluoromalonoborate (NaDFMB).

[0006] Furthermore, the sodium salt is one or more of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0007] Furthermore, the ether organic solvent is one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TEGDME), diethylene glycol monobutyl ether (DEE), and 1,3-dioxolane (DOL).

[0008] The preparation method of the above-mentioned high-voltage ether electrolyte containing an electric field coupling agent is carried out according to the following steps:

[0009] 1. Under an oxygen-free and anhydrous environment, add sodium salt to an ether-based organic solvent at a concentration of 0.5–3.0 mol / L, and stir until the sodium salt is completely dissolved to obtain a sodium salt solution.

[0010] 2. Under an oxygen-free and anhydrous environment, weigh out an electric field coupling agent at 1% to 5.0% of the total mass of the sodium salt solution. Add the electric field coupling agent to the sodium salt solution and mix thoroughly until the solution becomes transparent and clear, thus obtaining a high-voltage ether electrolyte containing the electric field coupling agent. Store this electrolyte in a sealed container to avoid contact with air.

[0011] Furthermore, the oxygen-free and water-free environment described in steps one and two is a glove box filled with high-purity argon gas, with an oxygen concentration of less than 0.1 ppm and a moisture concentration of less than 0.1 ppm. This ensures that there is no interference from moisture and oxygen during the preparation of the electrolyte.

[0012] Furthermore, the stirring described in step one is carried out at a temperature of 25℃~30℃ and a stirring speed of 200~400rpm for 30~40 minutes.

[0013] Furthermore, the mixing described in step two is performed using ultrasonic treatment. Ultrasonic treatment is carried out at a frequency of 40kHz-60kHz for 10-20 minutes to ensure that the electric field coupling agent is thoroughly and uniformly dispersed in the ether solvent.

[0014] The aforementioned application of high-voltage ether electrolytes containing electric field coupling agents involves using these electrolytes in sodium-ion battery systems that use sodium layered transition metal oxides as the positive electrode material.

[0015] Furthermore, the aforementioned sodium layered transition metal oxide cathode material is a P2-type sodium manganese ferrite layered oxide (Na... 0.67 Fe 0.1 Mn 0.9 O2). This cathode material has advantages such as high theoretical specific capacity and adjustable voltage and structure.

[0016] The above-mentioned activation method for high-voltage ether electrolyte containing an electric field coupling agent involves injecting the high-voltage ether electrolyte containing the electric field coupling agent into a sodium-ion battery, setting the battery's charging cutoff voltage to 4.3~4.5 V, and charging at 0.02 A g. -1 The current density is charged and discharged three times to complete the activation, so as to promote the preferential migration of the electric field coupling agent and the decomposition of the functional groups of the interface film components, forming a dense and stable CEI film.

[0017] This invention introduces a compound containing voltage-sensitive groups and beneficial interfacial film components as an electric field coupling agent to construct a novel electrolyte system with high-voltage response characteristics. This invention utilizes the electric field coupling agent additive, whose voltage-sensitive groups respond to the strong electric field under high voltage, preferentially and directionally adsorbing onto the positive electrode surface. This guides the in-situ decomposition reaction of beneficial components in the interfacial film, forming a highly stable and dense CEI film, enhancing the mechanical strength and chemical stability of the CEI film. This effectively inhibits the continuous oxidative decomposition of ether solvents under high voltage, reduces side reactions and gas production, and improves the high-voltage cycle life of the battery. Furthermore, this electric field coupling agent can significantly improve the structural stability of the P2-type sodium manganese ferrite layered oxide positive electrode in a deeply desodium-free state, inhibiting transition metal dissolution and migration, further enhancing the overall electrochemical performance of the battery. Based on the synergistic introduction of two types of functional groups within the molecule, this high-voltage ether electrolyte containing the electric field coupling agent has a unique high-voltage activation method. The system after high-voltage activation can achieve a long cycle life at a high voltage of 4.5 V. This invention, by rationally selecting and optimizing the types of these two types of groups and the specific compound addition ratios in the electric field coupling agent, can significantly overcome the inherent high-voltage defects of conventional ether electrolytes and enhance the overall stability and ultra-high-voltage long-cycle performance of the battery.

[0018] The electrolyte system of this invention should be stored in a sealed container to avoid contact with air, preventing the volatilization of additives and electrolyte contamination. The container should be inspected regularly to ensure it is properly sealed and prevent the entry of external moisture or gas. During use, the electrolyte system is first activated under high pressure to fully utilize the performance of the electric field coupling agent additive.

[0019] Compared with traditional methods, the electrolyte of the present invention has the following beneficial effects:

[0020] (1) Proposing the concept of electric field coupling agent electrolyte additive: This invention innovatively proposes the concept of electric field coupling agent additive, defining an electrolyte additive that simultaneously contains voltage-sensitive groups and interface film beneficial component groups as an electric field coupling agent. Utilizing the synergistic effect of functional groups, ether electrolytes containing electric field coupling agents all exhibit significantly improved cycle stability and a special high-voltage working mechanism.

[0021] (2) Adopting a unique high-voltage activation mechanism: This invention adopts a unique high-voltage activation strategy. By setting the battery charging cutoff voltage to 4.3 V or above for initial activation, the electric field coupling agent is preferentially migrated and oxidized and cross-linked before the solvent, thus constructing a stable gradient interface film in situ. This breaks through the technical bottleneck that traditional ether electrolytes are difficult to work stably in high-voltage systems.

[0022] (3) Significantly enhances the high-voltage stability of the cathode / electrolyte interface film: By introducing an electric field coupling agent additive into the sodium salt ether solution, and utilizing the favorable interface film components containing atoms such as fluorine, boron, phosphorus, sulfur, and / or nitrogen in its molecular structure, a dense interface protective layer with high mechanical strength and chemical stability is constructed on the cathode surface. This interface layer can effectively shield the highly active cathode surface from direct contact with ether solvent molecules, fundamentally inhibiting the intrinsic oxidative decomposition of ether electrolytes under high voltage, increasing the withstand voltage of ether electrolytes to 4.5 V, and significantly reducing the dissolution of transition metals in the layered oxide cathode, thus maintaining the long-term stability of the cathode interface.

[0023] (4) Synergistic optimization of interface and bulk structure: The electrolyte containing the electric field coupling agent generates a stable interface film through a unique working mechanism. This interface film not only ensures its own high voltage resistance, but also effectively anchors the lattice on the positive electrode surface, reducing structural collapse and transition metal dissolution caused by extreme high voltage, and significantly improving the electrochemical performance of sodium layered oxides over a wide voltage range.

[0024] (5) Improved high-voltage cycle stability of the battery: Thanks to the dual protection of the positive electrode interface and bulk structure by the ether electrolyte containing electric field coupling agent, the sodium-ion battery using the electrolyte of this invention can work normally at a high cutoff voltage of 4.5 V, and can obtain more stable cycle performance. After 1000 cycles, the capacity retention rate is about 87.9% and the coulombic efficiency is stable at over 99%, which solves the technical problem that ether electrolyte is difficult to match with high-voltage positive electrode materials. Attached Figure Description

[0025] Figure 1 The cycle performance of the sodium-ion half-cell assembled in Comparative Example 1;

[0026] Figure 2 Cyclic performance of the sodium-ion half-cell assembled in Example 1;

[0027] Figure 3 Cyclic performance of the sodium-ion half-cell assembled in Example 2;

[0028] Figure 4 The constant current charge-discharge curves of the sodium-ion half-cells assembled in Example 1 and Comparative Example 1 in the voltage range of 1.5-4.5 V are shown.

[0029] Figure 5 Cyclic performance of the sodium-ion half-cell assembled in Example 1 within a voltage range of 1.5 to 4.5 V;

[0030] Figure 6 Cyclic performance of sodium-ion half-cells assembled in Example 1 and Comparative Example 2;

[0031] Figure 7 These are high-resolution transmission electron microscope images of the positive electrode surfaces after 5 cycles of Example 1 and Comparative Example 2. Detailed Implementation

[0032] The beneficial effects of the present invention will be verified using the following examples.

[0033] Example 1: The preparation method of the high-voltage ether electrolyte containing an electric field coupling agent in this example is carried out according to the following steps:

[0034] 1. In an oxygen-free and anhydrous glove box where both oxygen and moisture concentrations are below 0.1 ppm,

[0035] First, weigh out diethylene glycol dimethyl ether (DEGDME) and ethylene glycol dimethyl ether (DME) in a volume ratio of 6:4.

[0036] Then, calculate and weigh sodium perchlorate (NaClO4) based on the total volume of diethylene glycol dimethyl ether and ethylene glycol dimethyl ether solvents, wherein the concentration of sodium perchlorate is 1.0 mol / L;

[0037] Then, calculate and weigh sodium difluoromalonide borate (NaDFMB) based on 1% of the total mass of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether and sodium perchlorate.

[0038] Weigh out sodium difluorooxalate borate (NaDFOB) at 0.5% of the total mass of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether and sodium perchlorate.

[0039] Sodium perchlorate was placed in a container, and diethylene glycol dimethyl ether was added first, followed by diethylene glycol dimethyl ether. The mixture was stirred continuously for 30 minutes at a temperature of 25°C and a stirring speed of 300 rpm. At this point, the sodium perchlorate was completely dissolved, and a clear and transparent sodium perchlorate solution was obtained.

[0040] 2. In an oxygen-free and anhydrous glove box where both oxygen and moisture concentrations are below 0.1 ppm, weighed sodium difluoromalonate borate and sodium difluorooxalate borate are added to a sodium perchlorate solution. The solution is ultrasonically treated for 15 minutes at a temperature of 25°C and an ultrasonic frequency of 40 kHz. At this point, the solution is transparent and clear, and a high-voltage ether electrolyte containing an electric field coupling agent is obtained.

[0041] The high-voltage ether electrolyte containing the electric field coupling agent prepared in Example 1 needs to be transferred to a sealed container and stored in a glove box to achieve physical isolation from the external environment's water and oxygen. The electrolyte also needs to be stored in a dark, cool, and dry place in the glove box, and the ambient temperature should be strictly controlled within the range of 25~30℃.

[0042] The battery was assembled and activated at high voltage using the high-voltage ether electrolyte containing an electric field coupling agent prepared in Example 1. The specific steps were as follows: using P2 type sodium manganese ferrite layered oxide Na... 0.67 Fe 0.1 Mn 0.9 Using O2 as the positive electrode active material, sodium metal as the negative electrode, and the high-voltage ether electrolyte containing an electric field coupling agent prepared in Example 1 as the electrolyte, coin cells were assembled in an argon-filled glove box. The assembled cells were then placed in a constant temperature chamber and allowed to stand for 12 hours to allow the electrolyte to fully wet the separator and electrode plates. The stood cells were then placed in a battery testing system with the charging cut-off voltage set to 4.3 V and the discharging cut-off voltage set to 1.5 V, using 0.02 A g... -1 The high-voltage activation was completed by three constant current charge-discharge cycles.

[0043] Example 2: The preparation method of the high-voltage ether electrolyte containing an electric field coupling agent in this example is carried out according to the following steps:

[0044] 1. In an oxygen-free and anhydrous glove box where both oxygen and moisture concentrations are below 0.1 ppm,

[0045] First, weigh out diethylene glycol dimethyl ether (DEGDME) and ethylene glycol dimethyl ether (DME) in a volume ratio of 6:4.

[0046] Then, calculate and weigh sodium perchlorate (NaClO4) based on the total volume of diethylene glycol dimethyl ether and ethylene glycol dimethyl ether solvents, wherein the concentration of sodium perchlorate is 1.0 mol / L;

[0047] Weigh out sodium difluoromalonate borate (NaDFMB) at 1% of the total mass of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether and sodium perchlorate.

[0048] Weigh out sodium tetrafluorooxalate phosphate (NaTFOP) at 0.5% of the total mass of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and sodium perchlorate.

[0049] Weigh out 0.5% of the total mass of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether and sodium perchlorate, and then weigh out diphenylmethylene sulfonyl fluoride (DPMSF).

[0050] Sodium perchlorate was placed in a container, and diethylene glycol dimethyl ether was added first, followed by diethylene glycol dimethyl ether. The mixture was stirred continuously for 30 minutes at a temperature of 25°C and a stirring speed of 300 rpm. At this point, the sodium perchlorate was completely dissolved, and a clear and transparent sodium perchlorate solution was obtained.

[0051] 2. In an oxygen-free and anhydrous glove box where both oxygen and moisture concentrations are below 0.1 ppm, weighed sodium difluoromalonate borate, sodium tetrafluorooxalate phosphate, and diphenylmethylene sulfonyl fluoride are added to a sodium perchlorate solution. The solution is ultrasonically treated for 20 minutes at a temperature of 25°C and an ultrasonic frequency of 40 kHz. The solution becomes transparent and clear, yielding a high-voltage ether electrolyte containing an electric field coupling agent.

[0052] The high-voltage ether electrolyte containing the electric field coupling agent prepared in Example 2 needs to be transferred to a sealed container and stored in a glove box to achieve physical isolation from the external environment's water and oxygen. The electrolyte also needs to be stored in a dark, cool, and dry place in the glove box, and the ambient temperature should be strictly controlled within the range of 25~30℃.

[0053] The battery was assembled and activated at high voltage using the high-voltage ether electrolyte containing an electric field coupling agent prepared in Example 2. The specific steps were as follows: using P2 type sodium manganese ferrite layered oxide Na... 0.67 Fe 0.1 Mn 0.9Using O2 as the positive electrode active material, sodium metal as the negative electrode, and the high-voltage ether electrolyte containing an electric field coupling agent prepared in Example 2 as the electrolyte, coin cells were assembled in an argon-filled glove box. The assembled cells were then placed in a constant temperature chamber and allowed to stand for 12 hours to allow the electrolyte to fully wet the separator and electrode plates. The stood cells were then placed in a battery testing system with the charging cut-off voltage set to 4.3 V and the discharging cut-off voltage set to 1.5 V, using 0.02 A g... -1 The high-voltage activation was completed by three constant current charge-discharge cycles.

[0054] Comparative Example 1: The electrolyte in this comparative example is a conventional sodium-ion battery ether electrolyte without an electric field coupling agent, and its preparation method is carried out according to the following steps:

[0055] In an oxygen- and anhydrous glove box where both oxygen and moisture concentrations are below 0.1 ppm, 60% diethylene glycol dimethyl ether (DEGDME) and 40% ethylene glycol dimethyl ether (DME) were weighed by volume. Sodium perchlorate (NaClO4) with a concentration of 1.0 mol / L was then weighed, with the total volume of DEGDME and DME as the solvent volume. The sodium perchlorate was placed in a container, and DEGDME was added, followed by DME. The mixture was stirred continuously for 30 minutes at 25°C and 300 rpm until it was completely dissolved, yielding a clear and transparent conventional sodium-ion battery ether electrolyte.

[0056] The conventional sodium-ion battery ether electrolyte prepared in Comparative Example 1 needs to be transferred to a sealed container and stored in a glove box to achieve physical isolation from the external environment's water and oxygen. The electrolyte should also be stored in a cool, dry place away from light in the glove box, and the ambient temperature should be strictly controlled within the range of 25~30℃.

[0057] A battery was assembled using the conventional sodium-ion battery ether electrolyte prepared in Comparative Example 1 and activated at high voltage. The specific steps were as follows: using a P2-type layered transition metal oxide Na... 0.67 Fe 0.1 Mn 0.9 Using O2 as the positive electrode active material and sodium metal as the negative electrode, and the conventional sodium-ion battery ether electrolyte prepared in Comparative Example 1 as the electrolyte, coin cells were assembled in an argon-filled glove box. The assembled cells were then placed in a constant temperature chamber and allowed to stand for 12 hours to allow the electrolyte to fully wet the separator and electrode plates. The stood cells were then placed in a battery testing system with the charging cut-off voltage set to 4.3 V and the discharging cut-off voltage set to 1.5 V, using 0.02 A g... -1 The high-voltage activation was completed by three constant current charge-discharge cycles.

[0058] Comparative Example 2: This comparative example uses the high-voltage ether electrolyte containing an electric field coupling agent prepared in Example 1 as the electrolyte to assemble a battery, but performs low-voltage activation. The specific battery assembly method is the same as in Example 1. The settled battery is placed in the battery testing system, with the charging cut-off voltage set to 4.0 V and the discharging cut-off voltage set to 1.5 V, using 0.02 Ag... -1 The current density constant current charge-discharge cycle was repeated 3 times.

[0059] Figure 1 The sodium-ion half-cell assembled for Comparative Example 1 was used at 1.5–4.3 V and 0.2 A g. -1 Cyclic performance at current density. Figure 1 It can be seen that Comparative Example 1 exhibits poor cycling stability, showing a continuous decrease in capacity during cycling, with a capacity retention rate of only 58.1% after 200 cycles.

[0060] Figure 2 The sodium-ion half-cell assembled for Example 1 was tested at 1.5–4.3 V and 0.2 A g. -1 Cyclic performance at current density. Figure 2 As can be seen, Example 1 exhibits excellent cycling stability, with almost no capacity decay after 200 cycles, and its stability is higher than that of Comparative Example 1. This is because the introduction of the electric field coupling agent additive enhances the intrinsic antioxidant properties of the electrolyte. At the same time, the induced stable interfacial film suppresses side reactions during cycling. Therefore, Example 1 exhibits significantly improved cycling stability, with a capacity retention of 85.1% after 500 cycles.

[0061] Figure 3 The sodium-ion half-cell assembled for Example 2 was tested at 1.5-4.3 V and 0.2 A g. -1 Cyclic performance at current density. Figure 3 As can be seen, Example 2 also exhibits superior cycle stability compared to Comparative Example 1, with a capacity retention rate of 97.8% after 200 cycles and 80.5% after 400 cycles. The stability is significantly higher than that of Comparative Example 1, indicating that the high-voltage cycle stability of the cathode material is effectively improved after the introduction of the electric field coupling agent additive. At the same time, it proves the effectiveness of the electric field coupling agent proposed in this invention in improving the intrinsic antioxidant stability of ether electrolytes.

[0062] Figure 4 The sodium-ion half-cells assembled for Example 1 and Comparative Example 1 were tested at 1.5–4.5 V and 0.02 A g. -1 Constant current charge-discharge curves at current density. Figure 4It can be seen that Comparative Example 1 could not perform normal charge and discharge operations, and its charging curve exhibited a long voltage plateau characteristic near 4.46 V, indicating that the electrolyte underwent a severe and continuous oxidative decomposition reaction. In contrast, Example 1 could exhibit normal charge and discharge behavior at a high voltage of 4.5 V, and the continuous decomposition plateau of the electrolyte in Comparative Example 1 completely disappeared, indicating that the use of the electric field coupling agent additive successfully extended the actual usable voltage window of the ether-based electrolyte to above 4.5 V.

[0063] Figure 5 The sodium-ion half-cell assembled for Example 1 was tested at 1.5–4.5 V and 1.0 A g. -1 Cyclic performance at current density. Figure 5 It can be seen that in Example 1, after 1000 cycles at a high cutoff voltage of 4.5 V, the capacity retention rate is still 87.9%, and the coulombic efficiency of the battery remains stable. This indicates that the introduction of electric field coupling agent additive can induce the formation of a stable CEI layer, which not only improves the cycle stability, but also raises the upper voltage limit of the ether-based electrolyte to 4.5 V, achieving a synergistic breakthrough in high voltage and stability.

[0064] Figure 6 The sodium-ion half-cells assembled for Example 1 and Comparative Example 2 were tested at 1.5–4.0 V and 0.2 A g. -1 Cycling performance at current density. The long-cycle charging cutoff voltage was set to 4.0 V to verify the unique high-voltage activation mechanism of the high-voltage ether electrolyte containing the electric field coupling agent of this invention. Example 1 was high-voltage activated, while Comparative Example 2 was not. Figure 6 It can be seen that Comparative Example 2, which did not undergo high-voltage activation, exhibited poor cycling performance, with a capacity retention of only 65.6% after 300 cycles. In contrast, Example 1, which underwent high-voltage activation, achieved a capacity retention of 96.0% after 300 cycles, demonstrating significantly improved cycling stability. This indicates that the high-voltage ether electrolyte containing the field coupling agent has a unique working mechanism, where higher voltage actually drives it to perform better. High-voltage activation causes the field coupling agent to undergo directional migration and favorable oxidative decomposition, forming a dense and stable interfacial film, thereby stabilizing the battery's long-term cycling operation.

[0065] Figure 7 These are high-resolution transmission electron microscope images of Example 1 and Comparative Example 2 after 5 cycles. Example 1 underwent high-voltage activation, while Comparative Example 2 was not. Figure 7It can be seen that the CEI in Comparative Example 2 exhibits a thin region of 6.1 nm and a thick region of 13.3 nm, showing significant inhomogeneity. In contrast, the electrode surface of Example 1 shows a more uniform and dense CEI layer, indicating that high-voltage activation induces the formation of a more dense passivation film, which helps to stabilize the crystal structure.

[0066] This invention's ether-based electrolyte system innovatively optimizes the film-forming kinetics and chemical stability of the cathode / electrolyte interface (CEI) by introducing an electric field coupling agent composed of voltage-sensitive groups and beneficial interfacial components into the electrolyte. This successfully extends the working voltage of the ether-based electrolyte to 4.5 V and significantly improves the cycle stability and coulombic efficiency of sodium-ion batteries under ultra-high voltage. The ether-based electrolyte of this invention exhibits a unique voltage-activated working mechanism. Utilizing the strong electric field driving effect of a high cutoff voltage, it induces the directional adsorption of additive molecules and the in-situ construction of a dense and stable CEI film rich in inorganic components. This effectively suppresses repeated rupture and recombination of the interfacial film under high sodium desodium states and provides sufficient protection for the bulk structure. Through this innovative electrolyte system and activation strategy, this invention successfully overcomes the high-voltage intrinsic limitations of conventional ether-based electrolytes, providing core technical support for the long-life operation of high-energy-density sodium-ion batteries.

Claims

1. A high-voltage ether electrolyte containing an electric field coupling agent, characterized in that, The electrolyte is a mixture of a sodium salt ether-based organic solvent solution and an electric field coupling agent. The sodium salt ether-based organic solvent solution is obtained by dissolving the sodium salt in the ether-based organic solvent at a concentration of 0.5–3.0 mol / L. The mass of the electric field coupling agent is 1%–5.0% of the mass of the sodium salt ether-based organic solvent solution. The electric field coupling agent is a compound whose molecular structure simultaneously contains a voltage-sensitive group and a beneficial interfacial film component. The voltage-sensitive group is an organic active group that readily undergoes oxidative decarboxylation, ring-opening, or electropolymerization reactions under high voltage, and is one or two of oxalate, malonate, vinyl, allyl, propargyl, and cyano groups. The beneficial interfacial film component is an inorganic or organic group containing heteroatoms, and is one or more of sulfonyl, sulfonimide, difluoroboron, tetrafluorophosphoric, difluorophosphoric, sulfonic acid, and sulfate ester groups.

2. The high-voltage ether electrolyte containing an electric field coupling agent according to claim 1, characterized in that, The electric field coupling agent is sodium difluoromalonoborate, diphenylmethylenesulfonyl fluoride, p-toluenesulfonyl isocyanate, or 4-fluorobenzenesulfonyl isocyanate; or the electric field coupling agent is one or more of sodium difluorooxalateborate, sodium tetrafluorooxalate phosphate, and diphenylmethylenesulfonyl fluoride combined with sodium difluoromalonoborate.

3. A high-voltage ether electrolyte containing an electric field coupling agent according to claim 1 or 2, characterized in that, The sodium salt is one or more of sodium perchlorate, sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(fluorosulfonyl)imide.

4. A high-voltage ether electrolyte containing an electric field coupling agent according to claim 1 or 2, characterized in that, The ether organic solvent is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol monobutyl ether, and 1,3-dioxolane.

5. The method for preparing the high-voltage ether electrolyte containing an electric field coupling agent according to claim 1, characterized in that, This method is performed in the following steps:

1. Under an oxygen-free and anhydrous environment, add sodium salt to an ether-based organic solvent at a concentration of 0.5–3.0 mol / L, and stir until the sodium salt is completely dissolved to obtain a sodium salt solution.

2. Under an oxygen-free and anhydrous environment, weigh out an electric field coupling agent at 1% to 5.0% of the total mass of the sodium salt solution. Add the electric field coupling agent to the sodium salt solution and mix thoroughly until the solution becomes transparent and clear, thus obtaining a high-voltage ether electrolyte containing the electric field coupling agent. Store this electrolyte in a sealed container to avoid contact with air.

6. The method for preparing the high-voltage ether electrolyte containing an electric field coupling agent according to claim 5, characterized in that, The oxygen-free and water-free environment described in steps one and two is a glove box filled with high-purity argon gas, with an oxygen concentration of less than 0.1 ppm and a moisture concentration of less than 0.1 ppm.

7. The method for preparing a high-voltage ether electrolyte containing an electric field coupling agent according to claim 5 or 6, characterized in that, The stirring described in step one is carried out at a temperature of 25℃~30℃ and a stirring speed of 200~400 rpm for 30~40 minutes.

8. The application of the high-voltage ether electrolyte containing an electric field coupling agent as described in claim 1, characterized in that, This application involves using high-voltage ether electrolytes containing electric field coupling agents in sodium-ion battery systems with sodium layered transition metal oxides as the positive electrode material.

9. The application of a high-voltage ether electrolyte containing an electric field coupling agent according to claim 8, characterized in that, The sodium layered transition metal oxide cathode material is P2 type sodium manganese ferrite layered oxide Na. 0.67 Fe 0.1 Mn 0.9 O2.

10. The activation method for a high-voltage ether electrolyte containing an electric field coupling agent as described in claim 1, characterized in that, This method involves injecting a high-voltage ether-based electrolyte containing an electric field coupling agent into a sodium-ion battery, setting the battery's charging cutoff voltage to 4.3~4.5 V, and charging at 0.02 A g. -1 The current density is charged and discharged three times to complete the activation.

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