Sodium-ion battery electrolyte of low-fluorophosphate system and sodium-ion battery
By combining a low-fluorinated phosphate ester system with appropriate additives, the problem of poor compatibility of sodium-ion battery electrolytes on hard carbon anodes was solved, resulting in sodium-ion batteries with high conductivity, low cost, and good safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-21
- Publication Date
- 2026-04-21
AI Technical Summary
Existing sodium-ion battery electrolytes have difficulty forming a stable and dense SEI film on hard carbon anodes, leading to electrolyte reduction and decomposition, poor compatibility, high salt concentration electrolytes are expensive and have high viscosity, and high fluorinated phosphate solvents reduce sodium salt solubility and conductivity.
A sodium-ion battery electrolyte with a low-fluorinated phosphate ester system is used, combined with appropriate electrolyte additives to regulate the degree of fluorination, promote the formation of a stable AI-ISC structure and a NaF-rich SEI film, and improve compatibility and conductivity.
This technology achieves sodium-ion batteries with high conductivity, good compatibility, and low cost, reducing battery internal resistance and improving battery safety and electrochemical performance.
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Figure CN121905968A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery technology, specifically to a sodium-ion battery electrolyte based on a low-fluorinated phosphate ester system and a sodium-ion battery. Background Technology
[0002] The development of human society requires the continuous consumption of Earth's energy resources. Secondary energy sources such as solar, wind, and tidal energy are characterized by being clean and producing little pollution. However, these clean energy sources cannot be utilized in real time and require energy storage technologies of a certain scale to be effectively developed and utilized.
[0003] Lithium-ion batteries are currently the most commonly used energy storage technology in portable electronic devices, but the Earth's lithium resources are limited and cannot meet the demand for lithium resources for large-scale energy storage technologies.
[0004] Sodium-ion batteries share a similar energy storage mechanism with lithium-ion batteries, and sodium resources are abundant on Earth, making them a promising candidate for large-scale energy storage. However, large-scale energy storage technologies place much stricter safety requirements on batteries.
[0005] In the electrolyte of sodium-ion batteries, phosphate esters are a type of solvent with flame-retardant properties. Common phosphate ester solvents include trimethyl phosphate (TMP), triethyl phosphate (TEP), tripropyl phosphate, and tributyl phosphate (TBP). Using phosphate esters as battery electrolytes can greatly improve the safety performance of sodium-ion batteries.
[0006] However, pure phosphate ester electrolyte and hard carbon anode are incompatible because phosphate ester solvent is difficult to form a stable and dense SEI film on the surface of hard carbon anode. Therefore, during battery operation, the electrolyte will continuously reduce and decompose, causing the hard carbon anode to irreversibly deintercalate and deintercalate sodium ions.
[0007] Recent studies have shown that increasing the concentration of sodium salt in the electrolyte (generally >3 mol / L) can effectively improve the compatibility of phosphate ester electrolytes and hard carbon anodes. This is because at high salt concentrations, anions will participate in sodium ion coordination to generate a more reduction-resistant anion-involved solvation structure (AI-ISC). At the same time, the anions in the AI-ISC structure will participate in the formation of a stable SEI film rich in NaF inorganic matter.
[0008] High-salt-concentration electrolytes have high costs and viscosity due to their high salt concentration, making them difficult to use in practical batteries.
[0009] Meanwhile, to improve the compatibility between the electrolyte and the negative electrode material, phosphate esters are generally fluorinated. For example, tri-(2,2,2-trifluoroethyl)-phosphate (TFEP)-based electrolytes are compatible with hard carbon because fluorination can effectively reduce the solvation ability of phosphate esters and sodium ions, allowing anions to enter the solvation layer even at low salt concentrations to generate a more reduction-resistant AI-ISC structure. At the same time, TFEP itself can also preferentially reduce and decompose to generate an SEI film with a higher NaF content.
[0010] However, the high degree of fluorination (nonafluoro) in TFEP significantly reduces the solubility of sodium salts. For example, the solubility of NaClO4 and NaPF6 in TFEP is less than 0.5 mol / L. It also greatly reduces the ionic conductivity of the electrolyte (< 0.7 mS / cm). These drawbacks of high-fluorination TFEP necessitate the use of expensive sodium bis(fluorosulfonyl)imide (NaFSI) in TFEP-based electrolytes to increase the solubility of sodium salts to 0.9 M, but the conductivity is still not ideal (0.9 mS / cm). Summary of the Invention The purpose of this invention is to provide a sodium-ion battery electrolyte and a sodium-ion battery based on a low-fluorinated phosphate ester system, which has the characteristics of high conductivity, strong compatibility and good safety.
[0011] This invention can be achieved through the following technical solutions: This invention discloses a sodium-ion battery electrolyte based on a low-fluorinated phosphate ester system, comprising a sodium salt, a solvent, and an electrolyte additive. The solvent is a low-fluorinated phosphate ester solvent, which is one or more of trimethyl phosphate, triethyl phosphate, and / or tripropyl phosphate.
[0012] Furthermore, the electrolyte additive is one or more of the following: fluoroethylene carbonate, vinylene carbonate, 1,3-propanediol cyclosulfonate, ethylene sulfite, and 1,3-propanesulfonate lactone.
[0013] Furthermore, the mass content of the electrolyte additive is 0.01-10 wt%.
[0014] Furthermore, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorosulfonamide, sodium ditrifluorosulfonamide, sodium tetrafluoroborate, sodium dioxolane-borate, and sodium difluorooxolane-borate.
[0015] Furthermore, the concentration of sodium salt is between 0.01 and 3.0 mol / L.
[0016] Another aspect of the present invention is to protect a sodium-ion battery that uses the above-mentioned sodium-ion electrolyte.
[0017] Furthermore, the cathode material of the sodium-ion battery is sodium vanadium phosphate, sodium iron pyrophosphate, layered oxide cathode material and / or Prussian blue cathode material.
[0018] Furthermore, the negative electrode material of the sodium-ion battery is one or more of hard carbon, soft carbon, graphite, sodium-antimony alloy and / or sodium-tin alloy.
[0019] This invention provides a sodium-ion battery electrolyte based on a low-fluorinated phosphate ester system and a sodium-ion battery, which have the following beneficial effects: First, it has high conductivity. In this invention, after the degree of fluorination of the phosphate ester solvent is reduced (from mono- to penta-fluorination), the phosphate ester solvent still has a low solvation energy, which can promote the entry of anions into the solvation layer at low salt concentration to generate a more stable AI-ISC structure. At the same time, the phosphate ester with some fluorinated substituents can also be reduced and decomposed to generate a stable SEI film rich in NaF. The low degree of fluorination retains the high degree of dissociation of phosphate ester to sodium salt, so that the low-fluorinated phosphate ester electrolyte has a high ionic conductivity (>2.5 mS / cm).
[0020] Secondly, it exhibits strong compatibility. In this invention, the sodium-ion battery electrolyte of the low-fluorinated phosphate ester system achieves good compatibility by rationally controlling the degree of fluorination. Although the degree of fluorination is reduced, fluorination can effectively reduce the solubilization ability of phosphate ester and sodium ion. For fluorinated phosphate ester electrolytes, unfluorinated phosphate esters cannot form a stable SEI film, resulting in poor compatibility. On the other hand, excessively fluorinated phosphate esters have extremely low conductivity, which leads to a significant increase in charge and discharge polarization of the electrode materials, resulting in poor compatibility. Appropriately low-fluorinated phosphate esters can ensure that the electrolyte still has excellent electrochemical compatibility with hard carbon anodes, sodium tin alloy anodes, and positive electrodes such as sodium iron pyrophosphate, sodium vanadium phosphate, and oxide positive electrodes. Various electrode materials can achieve stable high-efficiency cycling and good rate performance in this electrolyte.
[0021] Third, it has good safety. The sodium-ion battery in this invention improves the solubility of sodium salt and ionic conductivity of the electrolyte by reducing the degree of fluorination of phosphate ester. Fluorinated phosphate ester electrolyte has the characteristic of being non-flammable, which ensures the safety performance of the battery.
[0022] Fourth, the cost is lower. The production process of low-fluorinated phosphate esters is more controllable, and fewer fluorinated raw materials are required, thus resulting in lower costs. Attached Figure Description
[0023] Figure 1 The first-week charge-discharge curves of the hard carbon / sodium half-cells of Example 1 and Comparative Example 1 are shown. Figure 2The graph shows the specific capacity and coulombic efficiency of the hard carbon / sodium half-cell during cycling in Example 2. Figure 3 The rate performance of sodium vanadium phosphate / sodium half-cells in Example 4 and Comparative Example 2; Figure 4 The first-cycle charge-discharge curves of sodium pyrophosphate / sodium half-cells in Example 5 and Comparative Example 3 are shown. Figure 5 The diagram shows the specific capacity and coulombic efficiency of the sodium iron pyrophosphate / hard carbon pouch full cell in Example 6 during cycling.
[0024] Figure 6 The first-week charge-discharge curves of the hard carbon / sodium half-cells in Example 1, Comparative Examples 5 and 6 are shown. Detailed Implementation
[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.
[0026] This invention discloses a sodium-ion battery electrolyte based on a low-fluorinated phosphate ester system, comprising a sodium salt, a solvent, and electrolyte additives. The solvent is a low-fluorinated phosphate ester solvent, specifically one or more of mono- to hexafluorotrimethyl phosphate, mono- to hexafluorotriethyl phosphate, and / or mono- to hexafluorotripropyl phosphate. When the degree of fluorination is zero, the phosphate ester electrolyte cannot form a stable SEI film, thus resulting in incompatibility. When the degree of fluorination is greater than six, the extremely low conductivity of the phosphate ester electrolyte leads to a significant increase in charge-discharge polarization of the electrode material, resulting in poor compatibility.
[0027] Furthermore, the electrolyte additives are one or more of the following: fluoroethylene carbonate, vinylene carbonate, 1,3-propanediol cyclosulfonate, ethylene sulfite, and 1,3-propanesulfonate lactone. Combining additives such as fluoroethylene carbonate and vinylene carbonate with fluorophosphates of slightly lower fluorination degree (mono- to trifluoro) can further improve compatibility. Combining additives such as 1,3-propanediol cyclosulfonate, ethylene sulfite, and 1,3-propanesulfonate lactone with fluorophosphates of slightly lower fluorination degree (tetra- to hexafluoro) can reduce electrolyte impedance and improve rate performance.
[0028] Furthermore, the mass content of the electrolyte additive is 0.01-10wt%. When the additive content is less than 0.01%, it cannot effectively play a film-forming role. When the additive content is higher than 10%, the generated SEI film is too thick, which will increase the polarization of the electrode during charging and discharging.
[0029] Furthermore, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorosulfonamide, sodium ditrifluorosulfonamide, sodium tetrafluoroborate, sodium dioxalate borate, and sodium difluorooxalate borate.
[0030] Furthermore, the sodium salt concentration is between 0.01 and 3.0 mol / L. When the sodium salt concentration is below 0.01 mol / L, the electrolyte cannot provide sufficient ionic conductivity (ionic conductivity < 0.3 mS / cm when sodium salt concentration is 0.01 M). When the sodium salt concentration is above 3 mol / L, the electrolyte viscosity increases significantly, which also reduces ionic conductivity (ionic conductivity is only 1.2 mS / cm when sodium salt concentration is 3.0 M), further leading to an increase in battery internal resistance.
[0031] Another aspect of the present invention is to protect a sodium-ion battery that uses the above-mentioned sodium-ion electrolyte.
[0032] Furthermore, the cathode material of the sodium-ion battery is sodium vanadium phosphate, sodium iron pyrophosphate, layered oxide cathode material and / or Prussian blue cathode material.
[0033] Furthermore, the negative electrode material of the sodium-ion battery is one or more of hard carbon, soft carbon, graphite, sodium-antimony alloy and / or sodium-tin alloy.
[0034] Example 1 In this embodiment, the electrolyte used contains NaClO4 as the sodium salt, trifluoromethyl phosphate as the solvent (specifically, (trifluoromethyl)-dimethyl phosphate), and FEC as the electrolyte additive. The sodium salt concentration is 1.5 mol / L, and the additive content is 2% wt. The battery is a hard carbon / sodium half-cell. The hard carbon / sodium half-cell is tested using a 20 mA g... -1 The current density was charged and discharged within the voltage range of 0V to 2V, and the coulombic efficiency of the first cycle was compared, followed by a charge-discharge cycle at 20 mA g. -1 The current density circulates continuously.
[0035] Example 2 In this embodiment, the electrolyte used contains NaPF6 as the sodium salt, triethyl hexafluorophosphate as the solvent, specifically di-(2,2,2-trifluoroethyl)-ethyl phosphate, and DTD as the electrolyte additive. The sodium salt concentration is 0.9 mol / L M, and the additive content is 2% wt. The battery is a hard carbon / sodium half-cell. The hard carbon / sodium half-cell is tested using a 20 mAg... -1 The current density was charged and discharged within the voltage range of 0V to 2V, and the coulombic efficiency of the first week was compared.
[0036] Example 3 In this embodiment, the electrolyte used contains NaClO4 as the sodium salt, trifluoropropyl phosphate as the solvent, specifically (3,3,3-trifluoropropyl)-dipropyl phosphate, and FEC as the electrolyte additive. The sodium salt concentration is 0.4 mol / L, and the additive content is 5% wt. The battery is a hard carbon / sodium half-cell. The hard carbon / sodium half-cell is tested using a 20 mAg... -1 The current density was charged and discharged within the voltage range of 0V to 2V, and the coulombic efficiency of the first week was compared.
[0037] Example 4 In this embodiment, the electrolyte used contains NaClO4 as the sodium salt, trifluoroethyl phosphate as the solvent (specifically, (2,2,2-trifluoroethyl)-diethyl phosphate), and FEC as the electrolyte additive. The sodium salt concentration is 0.9 mol / L, and the additive content is 2% wt. The battery is a sodium vanadium phosphate / sodium half-cell. The rate performance test method for the sodium vanadium phosphate / sodium half-cell is as follows: first, activate it at a current density of 0.2C for three weeks, then cycle it for five weeks at current densities of 0.5C, 1C, 2C, 5C, 10C, and 0.5C respectively, where 1C = 120 mAh / g. The capacity retention rate of the sodium vanadium phosphate cathode under different current densities is observed and compared.
[0038] Example 5 In this embodiment, the electrolyte used contains NaPF6 as the sodium salt, tripropyl hexafluorophosphate as the solvent, specifically di(3,3,3-trifluoropropyl)-propyl phosphate, and PS as the electrolyte additive. The sodium salt concentration is 0.5 mol / L, and the additive content is 5% wt. The battery is a sodium iron pyrophosphate / sodium half-cell. The test method for the sodium iron pyrophosphate / sodium half-cell is as follows: at 50 mA g... -1 The current density was first activated for three weeks between 2V and 3.8V, and then at 100mA g. -1 The current density was continuously cycled between 2V and 3.8V. The coulombic efficiency in the first cycle and the capacity retention rate of the sodium vanadium phosphate anode during the cycle were compared. The coulombic efficiency in the first cycle and the capacity retention rate of the sodium iron pyrophosphate cathode during the cycle were also compared.
[0039] Example 6 In this embodiment, the electrolyte used contains NaClO4 as the sodium salt and trifluorotriethyl phosphate as the solvent, specifically (2,2,2-trifluoroethyl)-diethyl phosphate. The electrolyte additives are FEC and DTD, with a sodium salt concentration of 0.9 mol / L M and an additive content of 2% wt. The battery is a sodium iron pyrophosphate / hard carbon pouch cell with a capacity of approximately 1 Ah. The testing method for the sodium iron pyrophosphate / hard carbon pouch cell involves first activating it for one week at a current of 500 mA between 1.5 V and 3.5 V, then continuously cycling it at a density of 1000 mA between 1.5 V and 3.5 V. The capacity retention and average cycle efficiency of the pouch cell during the cycling process are compared.
[0040] Example 7 In this embodiment, the electrolyte used contains NaClO4 as the sodium salt, (2-fluoroethyl)-diethyl phosphate as the solvent, and FEC as the electrolyte additive. The sodium salt concentration is 0.9 mol / L, and the additive content is 5%wt. An ignition test was performed on the electrolyte to verify its flammability.
[0041] Comparative Example 1 In this comparative example, the electrolyte used contained NaClO4 as the sodium salt, and the solvent was unfluorinated triethyl phosphate solvent, with a sodium salt concentration of 0.9 mol / L. The battery was a hard carbon / sodium half-cell. The test method for the hard carbon / sodium half-cell was consistent with that in Example 1, comparing the coulombic efficiency in the first cycle and the capacity retention of the hard carbon anode during cycling.
[0042] Comparative Example 2 In this comparative example, the electrolyte used contained NaClO4 as the sodium salt, and the solvent was a superfluorinated tri-(2,2,2-trifluoroethyl) phosphate solvent, with a sodium salt concentration of 0.4 mol / L. The battery was a sodium vanadium phosphate / sodium half-cell. The test method for the sodium vanadium phosphate / sodium half-cell was consistent with that in Example 4. The capacity retention rate of the sodium vanadium phosphate cathode at different current densities was observed and compared, which represents the rate performance of the electrolyte.
[0043] Comparative Example 3 In this comparative example, the electrolyte used contained NaClO4 as the sodium salt, and the solvent was unfluorinated triethyl phosphate solvent, with a sodium salt concentration of 0.9 mol / L. The battery was a sodium iron pyrophosphate / sodium half-cell. The test method for the sodium iron pyrophosphate / sodium half-cell was consistent with that in Example 5, comparing the coulombic efficiency in the first cycle and the capacity retention of the sodium iron pyrophosphate cathode during cycling.
[0044] Comparative Example 4 In this embodiment, the electrolyte used contains NaClO4 as the sodium salt, a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:1), and FEC as the electrolyte additive, wherein the sodium salt concentration is 1M and the additive content is 5%wt. An ignition test was performed on the electrolyte to verify its flammability.
[0045] Comparative Example 5 In this comparative example, the electrolyte used contained NaClO4 as the sodium salt, trifluoromethyl phosphate as the solvent (specifically, (trifluoromethyl)-dimethyl phosphate), and FEC as the electrolyte additive. The sodium salt concentration was 1.5 mol / L, and the additive content was 0.005% wt. The battery was a hard carbon / sodium half-cell. The test method for the hard carbon / sodium half-cell was as follows: at 20 mA g... -1 The current density was charged and discharged within the voltage range of 0V to 2V, and the coulombic efficiency of the first cycle was compared, followed by a charge-discharge cycle at 20 mA g. -1 The current density circulates continuously.
[0046] Comparative Example 6 In this comparative example, the electrolyte used contained NaClO4 as the sodium salt, trifluoromethyl phosphate as the solvent (specifically, (trifluoromethyl)-dimethyl phosphate), and FEC as the electrolyte additive. The sodium salt concentration was 1.5 mol / L, and the additive content was 12% wt. The battery was a hard carbon / sodium half-cell. The test method for the hard carbon / sodium half-cell was as follows: at 20 mA g... -1 The current density was charged and discharged within the voltage range of 0V to 2V, and the coulombic efficiency of the first cycle was compared, followed by a charge-discharge cycle at 20 mA g. -1 The current density circulates continuously.
[0047] Comparative Example 7 In this embodiment, the electrolyte used contains NaPF6 as the sodium salt, tripropyl hexafluorophosphate as the solvent, specifically di(3,3,3-trifluoropropyl)-propyl phosphate, and PS as the electrolyte additive. The sodium salt concentration is 3.1 mol / L, and the additive content is 5% wt. The battery is a sodium iron pyrophosphate / sodium half-cell. The test method for the sodium iron pyrophosphate / sodium half-cell is as follows: at 50 mA g... -1 The current density was first activated for three weeks between 2V and 3.8V, and then at 100mA g. -1 The current density was continuously cycled between 2V and 3.8V. The coulombic efficiency in the first cycle and the capacity retention rate of the sodium vanadium phosphate anode during the cycle were compared. The coulombic efficiency in the first cycle and the capacity retention rate of the sodium iron pyrophosphate cathode during the cycle were also compared.
[0048] like Figure 1As shown, the hard carbon / sodium half-cell using (trifluoromethyl)-dimethyl phosphate as the electrolyte in Example 1 exhibited a high first-cycle coulombic efficiency of 83.2% and a reversible specific capacity as high as 298.1 mAh / g. In contrast, the hard carbon / sodium half-cell using unfluorinated triethyl phosphate as the electrolyte (Comparative Example 1) had almost no reversible capacity, demonstrating that moderate fluorination of the phosphate solvent can effectively improve the electrochemical compatibility of the electrolyte. Moreover, as Figure 2 As shown, the hard carbon / sodium half-cell using the electrolyte in Example 2 retained 98.3% of its capacity after 100 cycles, demonstrating that the hard carbon anode has excellent cycle stability in the aforementioned low-fluorinated phosphate electrolyte.
[0049] like Figure 3 As shown, the sodium vanadium phosphate / sodium half-cell using the electrolyte with (2,2,2-trifluoroethyl)-diethyl phosphate as the single solvent in Example 4 exhibits excellent rate performance, maintaining a reversible specific capacity of up to 90.2 mAh / g even at a high current density of 10C. In contrast, the sodium vanadium phosphate / sodium half-cell using the over-fluorinated tri-(2,2,2-trifluoroethyl) phosphate electrolyte (Comparative Example 2) has almost no reversible specific capacity at a current density of 5C. This is because the room temperature ionic conductivity of the electrolyte in Example 4 is still 3.2 mS / cm, while the room temperature ionic conductivity of the over-fluorinated electrolyte in Comparative Example 2 is only 0.6 mS / cm. This demonstrates that reducing the degree of fluorination of the phosphate ester can improve the rate performance of the phosphate ester electrolyte, which is very helpful for the practical application of sodium-ion batteries.
[0050] like Figure 4 As shown, the sodium iron pyrophosphate / sodium half-cell using the electrolyte with di(3,3,3-trifluoropropyl)-propyl phosphate as the single solvent in Example 5 exhibits a high first-cycle coulombic efficiency of 94.2% and a reversible specific capacity of up to 95.1 mAh / g. In contrast, the sodium iron pyrophosphate / sodium half-cell using the electrolyte with unfluorinated triethyl phosphate as the single solvent (Comparative Example 3) has a lower reversible specific capacity and first-cycle coulombic efficiency, and the charging curve shows obvious voltage fluctuations, indicating that the unfluorinated phosphate electrolyte has poor interfacial stability, while the fluorinated phosphate solvent has excellent interfacial stability.
[0051] like Figure 5 The diagram shows the cycling performance of the Ah-level sodium-ion pouch cell in Example 6. It can be seen that the full cell using an electrolyte with (2,2,2-trifluoroethyl)-diethyl phosphate as a single solvent still retains 81.3% of its capacity after 300 cycles, and the average coulombic efficiency during the cycling process exceeds 99.9%. This demonstrates that electrolytes using a single fluorophosphate as a solvent have good electrochemical compatibility in practical batteries.
[0052] like Figure 6 As shown, Example 1, with the addition of 2% FEC additive by mass, exhibited good electrochemical compatibility between the hard carbon anode and the low-fluorinated phosphate electrolyte. The hard carbon / sodium half-cell demonstrated a high first-cycle coulombic efficiency of 83.2% and a reversible specific capacity of up to 298.1 mAh / g. In contrast, in Comparative Example 5, with only 0.005% FEC additive by mass, the hard carbon / sodium half-cell showed severe electrolyte decomposition and almost no reversible specific capacity. In Comparative Example 6, with 12% FEC additive by mass, although the hard carbon anode could reversibly intercalate and deintercalate some sodium ions, the excessive FEC additive decomposition led to significant charge-discharge polarization, resulting in a reversible specific capacity of only 152 mAh / g for the hard carbon anode. This demonstrates that appropriate additive content can significantly improve the compatibility between the low-fluorinated phosphate electrolyte and the electrode material.
[0053] As shown in Table 1, in Example 5, the sodium salt concentration used in the low-fluoride electrolyte was 0.5 mol / L, the ionic conductivity of the electrolyte was 3.1 mS / cm, and the internal resistance of the sodium iron pyrophosphate / sodium half-cell was only 12.6 Ω. In contrast, in Comparative Example 7, the sodium salt concentration was 3.1 mol / L, the ionic conductivity of the electrolyte was 3.1 mS / cm, and the internal resistance of the sodium iron pyrophosphate / sodium half-cell increased to 593.1 Ω. This demonstrates that a suitable sodium salt concentration is beneficial for improving the ionic conductivity of the electrolyte and reducing the internal resistance of the battery.
[0054] Based on the above examples and comparative examples, it is evident that reducing the degree of fluorination of phosphate esters can improve the solubility of phosphate esters for sodium salts and the ionic conductivity of the electrolyte. Electrolytes using low-fluorinated phosphate esters exhibit excellent rate performance. Furthermore, because low-fluorinated phosphate esters still possess low solvation energies, they can promote the entry of anions into the solvation layer at low salt concentrations, forming a more stable Al-ISC structure. Low-fluorinated phosphate esters can also be reduced and decomposed to generate a stable SEI film rich in NaF, resulting in good electrochemical compatibility between the electrolyte and electrode materials. Due to the intrinsically non-flammable nature of fluorinated phosphate ester solvents, sodium-ion batteries using this electrolyte exhibit excellent safety, which is beneficial for promoting the application of sodium-ion batteries in large-scale energy storage.
[0055] Table 1 Performance Test Results The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.
Claims
1. A sodium-ion battery electrolyte based on a low-fluorinated phosphate ester system, comprising a sodium salt, a solvent, and electrolyte additives, characterized in that: The solvent is a low-fluorinated phosphate solvent, which is one or more of the following: mono- to hexafluorotrimethyl phosphate, mono- to hexafluorotriethyl phosphate, and / or mono- to hexafluorotripropyl phosphate.
2. The sodium-ion battery electrolyte of the low-fluorinated phosphate ester system according to claim 1, characterized in that: The electrolyte additive is one or more of the following: fluoroethylene carbonate, ethylene carbonate, 1,3-propanediol cyclosulfonate, ethylene sulfite, and 1,3-propanesulfonate lactone.
3. The sodium-ion battery electrolyte of the low-fluorinated phosphate ester system according to claim 2, characterized in that: The electrolyte additive has a mass content of 0.01-10 wt%.
4. The sodium-ion battery electrolyte of the low-fluorinated phosphate ester system according to claim 3, characterized in that: The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorosulfonamide, sodium ditrifluorosulfonamide, sodium tetrafluoroborate, sodium dioxolane-borate, and sodium difluorooxolane-borate.
5. The sodium-ion battery electrolyte of the low-fluorinated phosphate ester system according to claim 4, characterized in that: The concentration of the sodium salt is between 0.01 and 3.0 mol / L.
6. A sodium-ion battery, characterized in that: The sodium ion electrolyte according to any one of claims 1-5 is used.
7. The sodium-ion battery according to claim 6, characterized in that: The positive electrode material of the sodium-ion battery is sodium vanadium phosphate, sodium iron pyrophosphate, layered oxide positive electrode material and / or Prussian blue type positive electrode material.
8. The sodium-ion battery according to claim 6, characterized in that: The negative electrode material of the sodium-ion battery is one or more of hard carbon, soft carbon, graphite, sodium-antimony alloy and / or sodium-tin alloy.