Sodium ion battery and liquid injection method thereof
By using a phased electrolyte injection method, a base electrolyte is injected first for formation, followed by the injection of a phosphate ester flame retardant. This solves the problem of decomposition of the flame retardant electrolyte during the first formation cycle of sodium-ion batteries, thereby improving the performance and safety of high-efficiency batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-16
- Publication Date
- 2026-03-13
AI Technical Summary
Phosphorus-containing materials in existing flame-retardant electrolytes are prone to decomposition after the first formation cycle of sodium-ion batteries, leading to a surge in electrolyte polarization, which affects battery performance and safety, and is also costly.
A staged injection method is adopted. First, the basic electrolyte is injected for formation, and then the flame retardant containing phosphate esters is injected. The injection sequence is adjusted to avoid the decomposition of the flame retardant during the first formation process.
It forms a stable solid electrolyte interface film, improves the efficiency of the first charge and discharge, reduces energy loss, extends battery cycle life, reduces production costs, and improves battery safety.
Smart Images
Figure SMS_1 
Figure SMS_2
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a method for injecting sodium-ion batteries and the sodium-ion battery thereof. Background Technology
[0002] With the continuous expansion of applications such as electric vehicles and energy storage power stations, modern battery technology has placed more stringent requirements on the safety of sodium-ion batteries. Flame-retardant electrolytes, as a core material for improving battery safety, have become a focus of extensive research and attention in the industry.
[0003] Currently, most mainstream flame-retardant electrolytes rely on phosphorus to achieve their flame-retardant function. The principle is to form an insulating layer during combustion, blocking other components from contacting oxygen to terminate the combustion reaction. However, existing flame-retardant technologies still face two major challenges: First, commonly used high-performance phosphorus-containing flame-retardant materials are expensive due to complex synthesis processes and scarce raw materials, significantly increasing the production cost of sodium-ion batteries and limiting their large-scale application. This makes sodium-ion batteries using these flame retardants lack a price advantage in market competition. Second, although there are relatively inexpensive phosphorus-containing materials such as trimethoxysilane (TMSP), tricresyl phosphate (TMP), and triethyl phosphate (TEP), in practical applications, these materials will catalyze the breakage of organic phosphorus ester CO bonds after the first formation cycle of the sodium-ion battery due to the strong reducing properties of the lithium / sodium intercalated negative electrode. This leads to a surge in battery polarization, which not only reduces charge and discharge efficiency but also increases battery internal resistance, severely degrading cycle performance and making it unable to meet the actual use requirements of sodium-ion batteries.
[0004] Despite numerous attempts by researchers to develop novel flame retardants and optimize electrolyte formulations, an ideal solution that can effectively reduce costs while ensuring unaffected battery performance has yet to be found. Therefore, developing an electrolyte injection method that allows for the application of high-volume, inexpensive flame retardants without compromising sodium-ion battery performance, and a corresponding sodium-ion battery, has significant practical importance and value. Summary of the Invention
[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem that phosphorus-containing materials in existing flame-retardant electrolytes are prone to negative electrode decomposition after the first formation, which leads to a surge in electrolyte polarization and ultimately fails to meet the needs of practical applications.
[0006] To address the aforementioned technical problems, this invention provides a method for injecting electrolyte into a sodium-ion battery and the sodium-ion battery thereof. The method employs a staged injection approach. In the first injection stage, a basic electrolyte is injected to ensure the smooth initial formation of the sodium-ion battery and to provide a stable environment for subsequent chemical reactions. After the sodium-ion battery has completed formation, a second injection is performed, injecting a flame-retardant electrolyte containing phosphate ester flame retardants. By adjusting the injection sequence of the phosphate ester flame retardants, the decomposition of the phosphate ester flame retardants at the negative electrode during the first formation cycle is effectively prevented.
[0007] The first objective of this invention is to provide a method for injecting electrolyte into a sodium-ion battery, comprising the following steps: S1. After injecting the basic electrolyte into the cell, side sealing is performed and the cell is left to stand; the basic electrolyte includes a first electrolyte salt and a first solvent; S2. Perform stepped charging on the side-encapsulated battery cells; S3. After injecting flame-retardant electrolyte into the battery cell after step charging, let it stand to obtain the sodium-ion battery; the flame-retardant electrolyte includes phosphate ester flame retardant, second electrolyte salt and second solvent.
[0008] In one embodiment of the present invention, in S1, the concentration of the basic electrolyte is 1.0 mol / L-1.2 mol / L, and the amount used is 85%-95% of the total electrolyte mass.
[0009] In one embodiment of the present invention, in S1, the injection rate is 80 mL / min-120 mL / min; And / or, the settling time is more than 4 hours.
[0010] In one embodiment of the present invention, in S1, the battery cell includes a positive electrode, a negative electrode, and a separator; The positive electrode sheet includes a positive electrode active material; the positive electrode active material is sodium iron pyrophosphate. The negative electrode sheet includes a negative electrode active material, which is selected from one or more of sodium titanium phosphate, sodium titanate, iron carbide, titanium carbide, and hard carbon. The diaphragm is selected from one or more of polypropylene (PP), polyethylene (PE), and polytetrafluoroethylene (PTFE).
[0011] In one embodiment of the present invention, when the negative electrode active material is sodium titanium phosphate, the step charging specifically includes: in a constant temperature environment of 40℃-50℃, first charging at a charging rate of 0.05C-0.2C to 80%-90% of the cutoff voltage, and then charging at a charging rate of 0.2C-0.45C to the cutoff voltage. When the negative electrode active material is one or more of sodium titanate, iron carbide, titanium carbide and hard carbon, in a constant temperature environment of 23℃-27℃, it is first charged at a constant current rate of 0.08C-0.12C to the cutoff voltage of 3.0V-3.8V, and then charged at the cutoff voltage at a constant voltage until the current drops to 0.01C-0.025C.
[0012] In one embodiment of the present invention, in S3, the phosphate ester flame retardant is selected from one or more of tris(trimethylsilyl)phosphate (TMSP), trimethyl phosphate (TMP), and triethyl phosphate (TEP).
[0013] Furthermore, the purity of the tris(trimethylsilyl)phosphate (TMSP) is ≥99.9%, and the moisture content is ≤10ppm; The trimethyl phosphate (TMP) has a phosphate content of ≥99.5%; The viscosity of the triethyl phosphate (TEP) is 2 cP-5 cP.
[0014] In one embodiment of the present invention, in S3, the concentration of the phosphate ester flame retardant in the flame retardant electrolyte is 10wt%-30wt%, the concentration of the second electrolyte salt is 3mol / L-5mol / L, and the amount used is 5%-15% of the total electrolyte mass.
[0015] In one embodiment of the present invention, in S3, the injection rate is 80 mL / min-120 mL / min; And / or, the settling time is 30 min to 40 min.
[0016] In one embodiment of the present invention, the first electrolyte salt and the second electrolyte salt are independently selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalate-borate), sodium difluorooxalate-borate, sodium difluorophosphate, sodium difluorosulfonylimide, and sodium bis(trifluoromethylsulfonyl)imide. And / or, the first solvent and the second solvent are independently selected from one or more of ethylene carbonate (EC), propylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate (EMC), dimethyl carbonate and diethyl carbonate (DEC).
[0017] Further, the first solvent and the second solvent comprise ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC); the volume ratio of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) is (5-7):(9-11):(3-5).
[0018] A second objective of this invention is to provide a sodium-ion battery prepared by the liquid injection method described above.
[0019] The technical solution of the present invention has the following advantages compared with the prior art: (1) The electrolyte injection method described in this invention performs formation treatment after injecting the base electrolyte once, which enables the sodium-ion battery to form a well-structured solid electrolyte interface film (SEI film) (first-time efficiency > 85%) in the initial stage, thereby ensuring excellent interfacial contact between the electrode and the electrolyte, effectively improving the battery's first charge and discharge efficiency, allowing the sodium-ion battery to achieve more efficient storage and release of electrical energy during first use, reducing energy loss, and optimizing its initial performance.
[0020] (2) The liquid injection method described in this invention optimizes the injection time of the flame retardant electrolyte, which can prevent the decomposition of cheap phosphate ester flame retardants at the negative electrode during the first formation stage, thereby preventing the surge in battery polarization. The stability of the polarization state makes the internal resistance of the sodium-ion battery change less during multiple charge-discharge cycles, and the charge-discharge efficiency can be maintained at a high level, which ultimately significantly extends the battery cycle life, enabling it to meet the needs of more charge-discharge cycles and reduce the frequency of battery replacement and usage costs.
[0021] (3) The solvent and electrolyte of the base electrolyte and flame retardant electrolyte used in the liquid injection method of the present invention are consistent, and the only difference is in the addition of phosphate ester flame retardants, which significantly reduces the difficulty of the process. Detailed Implementation
[0022] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.
[0023] In this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0024] In this invention, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0025] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.
[0026] In this invention, unless otherwise stated, the diaphragm used in the embodiments of this invention is a PP / PE / PP three-layer composite diaphragm.
[0027] In this invention, unless otherwise stated, the basic electrolyte used in the embodiments of this invention includes NaPF6 with a concentration of 1.1 mol / L and a mixed solvent of EC, EM and DEC with a volume ratio of 6:10:4.
[0028] In this invention, unless otherwise stated, the flame-retardant electrolyte used in the embodiments of this invention includes 15wt% TMP (phosphate ester content of 99.5%), 3mol / L NaPF6, and a mixed solvent of EC, EM and DEC in a volume ratio of 6:10:4. Example 1
[0029] The sodium-ion battery and its electrolyte injection method in this embodiment specifically include the following steps: S1, Cell fabrication S11. Preparation of positive and negative electrode slurries: Weigh 920g each of sodium iron pyrophosphate (positive electrode active material) and sodium titanium phosphate (negative electrode active material), 40g of conductive carbon black (conductive agent), 10g of carbon nanotube powder (conductive agent), 30g of polyvinylidene fluoride powder (binder), and 1500g of N-methyl-2-pyrrolidone (solvent). Add the above components to a ball mill jar and ball mill at 40 rpm for 180 min to obtain positive and negative electrode slurries. S12. Preparation of positive and negative electrode sheets: Positive and negative electrode slurries are poured into the material tank of a transfer coating machine, and the transfer die head is controlled to coat the front and back sides of a 14μm thick carbon-coated aluminum foil in sequence. After drying in an oven at 130℃, positive and negative electrode rolls are obtained respectively. Then, the positive and negative electrode rolls are compacted by a roller press with a roller pressure of 4.0MPa. The compacted positive and negative electrode rolls are then die-cut to obtain a positive electrode sheet with a size of 99.5mm*152mm and a negative electrode sheet with a size of 102.5mm*154mm. S13. Cell preparation: The cells are stacked in a Z-shape in the order of "positive electrode, separator, negative electrode, separator". The stacked cells are then placed into a square aluminum shell to obtain a dry cell with a set capacity of 45Ah. The dry cell is then placed in a vacuum oven with a vacuum degree of -0.095MPa and a temperature of 120℃ and baked for 12 hours to obtain the cell. S2, Electrolyte injection into the battery cell S21. After injecting 400g of basic electrolyte (90wt% of the total electrolyte mass) into the cell at a rate of 100mL / min, side seal it and let it stand for 4 hours. S22. In a constant temperature environment of 45℃, perform stepped charging on the side-encapsulated battery cell; first charge at a charging rate of 0.1C to 0.8V (about 83% of the cutoff voltage), and then charge at a charging rate of 0.25C to the cutoff voltage of 0.96V. S23. After injecting flame-retardant electrolyte (10% of the total electrolyte mass) into the cell after step charging at a rate of 100 mL / min, let it stand for 35 min to obtain a sodium-ion battery. Comparative Example 1
[0030] The process is basically the same as in Example 1, except that the base electrolyte is replaced with a flame-retardant electrolyte, meaning that both injections use a flame-retardant electrolyte. Comparative Example 2
[0031] The process is basically the same as in Example 1, except that the flame-retardant electrolyte is replaced with the basic electrolyte, meaning that the basic electrolyte is injected in both cases. Comparative Example 3
[0032] It is basically the same as Example 1, except that only one injection is performed, and it is the base electrolyte. Comparative Example 4
[0033] It is basically the same as Example 1, except that only one injection is performed, and the electrolyte is flame-retardant. Test Example 1
[0034] Performance tests, including first-efficiency and DC internal resistance, were conducted based on Example 1 and Comparative Examples 1-4. (1) First Coulombic Efficiency (%): The first efficiency test focuses on the activation process. During the activation process, the first charge capacity and the first discharge capacity of the battery are measured respectively. Then, the first coulombic efficiency (%) is calculated according to the formula: first coulombic efficiency = first discharge capacity / first charge capacity. (2) DC internal resistance (mΩ): After the battery is left to stand, at the instant the discharge begins, record the voltage difference (ΔV) before and after the current is applied. Then, according to Ohm's law (R=ΔV / I, where R is the DC internal resistance, ΔV is the voltage difference, and I is the applied current), calculate the DC internal resistance of the battery. (3) Thermal runaway temperature T3 (°C): First, the battery is initialized and charged until it reaches 100% SOC (fully charged state); suitable heating components and temperature sensors are selected and placed on the battery surface, and the battery with initial setup is placed in the ARC device; the ARC adopts the "heating-waiting-searching" working mode, the sampling frequency is set to 0.1s, and after adjusting to the initial temperature, the adiabatic process is calibrated to ensure that there is no heat exchange between the battery and the environment, and the battery surface temperature is made uniform by letting it stand; then, the battery is searched for whether it is releasing heat, the adiabatic process is calibrated again to confirm, and then the battery is heated in 5°C increments, with the chamber tracking the temperature rise synchronously. After standing, the battery heat release is searched and the heat release rate dT / dt is monitored. The above heating, waiting, and searching process is repeated until the battery fails. Finally, the highest temperature during the thermal runaway process is recorded, which is the thermal runaway temperature T3 (°C); (4) Polarization voltage change (mV): After cycling the battery 10 times, let it stand at the set test temperature (25℃) until the open circuit voltage change is ≤1mV / min (usually it needs to stand for more than 2 hours) to ensure that the battery reaches a balanced state; then record the stable open circuit voltage V0 at this time as the reference voltage; then apply the rated current (1C) for 10s constant current charge and discharge, and record the voltage V during charging at the moment the pulse ends. chg and the voltage V during discharge dis Finally, according to the formula, the charging polarization ΔV chg =V chg -V0, discharge polarization ΔV dis =V0-V dis The polarization voltage change under charging and discharging conditions was calculated. Table 1 shows the final measured performance parameters: Table 1
[0035] As shown in Table 1, the electrolyte injection method in Example 1 achieves an optimal balance in key performance indicators of sodium-ion batteries, including initial coulombic efficiency, DC internal resistance, thermal runaway temperature, and polarization voltage variation. This is because Example 1 employs a staged electrolyte injection strategy. First, formation is completed using a base electrolyte to form a stable solid electrolyte interphase (SEI) film. Then, an electrolyte containing inexpensive phosphate ester flame retardants is injected. These flame retardants preferentially adsorb onto the electrode surface and form a gradient-distributed flame retardant layer, which can both delay heat transfer and prevent excessive flame retardant from participating in SEI film formation. This strategy avoids the decomposition problem of flame retardants during the formation stage and the risk of polarization surge, while ensuring that the high amount of phosphate ester flame retardants can more efficiently exert their flame retardant effect, significantly improving battery safety. At the same time, because the solvent and electrolyte systems of the base electrolyte and the flame retardant electrolyte are consistent, the risk of interface compatibility is effectively reduced, ultimately achieving synergistic optimization of battery cost, safety, and performance.
[0036] Comparing Example 1 and Comparative Example 1, it can be seen that Example 1 has a significantly higher initial coulombic efficiency, significantly lower DC internal resistance and polarization voltage changes, and a better thermal runaway temperature. This is because Comparative Example 1 used flame-retardant electrolyte in both injections, causing the flame retardant to encounter a strongly reducing environment at the negative electrode during the initial formation stage, resulting in an irreversible reduction reaction to generate PO3. - Free radicals disrupt the integrity of the SEI film, triggering continuous interfacial side reactions that increase charge transfer resistance and cause a surge in polarization. In contrast, Example 1, by adjusting the injection timing and injecting the flame-retardant electrolyte after formation, ensures that the stable SEI film isolates the flame retardant from the direct reaction between the flame retardant and the negative electrode, thus avoiding the aforementioned problems.
[0037] Comparing Example 1 and Comparative Example 2, it can be seen that Example 1 has a significantly lower thermal runaway temperature and better flame retardant safety, but its initial coulombic efficiency and DC internal resistance are basically the same as those of Comparative Example 2. This is because Comparative Example 2 does not contain any flame retardant, and the solvent in its electrolyte will undergo violent decomposition at high temperatures, subsequently triggering a chain reaction such as binder carbonization and positive electrode oxygen evolution, resulting in an extremely high heat release rate and a significant increase in thermal runaway temperature, leading to extremely poor battery safety. In contrast, the flame-retardant electrolyte of Example 1 contains 15 wt% TMP, and the resulting gradient flame-retardant layer can effectively delay heat transfer, improve the thermal stability of the battery, and does not have a significant negative impact on the basic electrochemical performance of the battery.
[0038] Comparing Example 1 and Comparative Example 3, it can be seen that Example 1 has a higher initial coulombic efficiency and lower changes in DC internal resistance and polarization voltage. This is because Comparative Example 3 only performed one basic electrolyte injection, and the insufficient injection volume led to the formation of a "dry zone" inside the electrode, making the sodium ion transport path tortuous, reducing charge transfer efficiency, increasing energy loss during the first charge and discharge process, lowering the initial efficiency, and increasing internal resistance. In contrast, Example 1, through two injections, ensured that the electrolyte fully wetted the electrode, especially with the basic electrolyte accounting for 90% of the total mass, meeting the ion transport requirements during the formation stage. The flame-retardant electrolyte added in the second injection further filled any possible gaps, ensuring good interfacial contact between the electrode and the electrolyte.
[0039] Comparing Example 1 and Comparative Example 4, it can be seen that the battery performance of Example 1 fully meets the standards and is stable, while the battery of Comparative Example 4 fails and cannot be charged and discharged normally. Its initial coulombic efficiency, DC internal resistance, and polarization voltage changes are all significantly different. This is because in Comparative Example 4, a single injection of high-concentration flame-retardant electrolyte occurs. During the formation stage, the high-concentration flame retardant is catalytically decomposed by the strong reducing environment of the negative electrode, producing corrosive substances such as HF. This not only corrodes the active material on the electrode surface but also causes a surge in electrolyte viscosity, severely hindering sodium ion migration and causing a sharp increase in polarization, ultimately causing the battery to lose its charge and discharge function. In contrast, Example 1 delays the injection of the flame retardant until after formation and controls its concentration within a reasonable range, thus avoiding decomposition and corrosion problems while fully exerting the flame-retardant effect. Example 2
[0040] The process is basically the same as in Example 1, except that the negative electrode active material is hard carbon and the liquid injection method is different. The liquid injection method specifically includes the following steps: S21. After injecting 400g of basic electrolyte (90wt% of the total electrolyte mass) into the cell at a rate of 100mL / min, side seal it and let it stand for 4 hours. S22. In a constant temperature environment of 25℃, perform stepped charging on the side-encapsulated battery cell; first, charge at a constant current rate of 0.1C to the cutoff voltage of 3.6V, and then charge at the cutoff voltage at a constant voltage until the current drops to 0.02C. S23. After injecting flame-retardant electrolyte (10% of the total electrolyte mass) into the cell after step charging at a rate of 100 mL / min, let it stand for 35 min to obtain a sodium-ion battery. Comparative Example 5
[0041] The process is basically the same as in Example 2, except that the base electrolyte is replaced with a flame-retardant electrolyte, meaning that both injections use a flame-retardant electrolyte. Comparative Example 6
[0042] The process is basically the same as in Example 2, except that the flame-retardant electrolyte is replaced with the basic electrolyte, meaning that the basic electrolyte is injected in both instances. Comparative Example 7
[0043] It is basically the same as Example 2, except that only one injection is performed, and it is the base electrolyte. Comparative Example 8
[0044] It is basically the same as Example 2, except that only one injection is performed, and the electrolyte is flame-retardant. Test Example 2
[0045] Referring to Test Example 1, performance tests such as first-efficiency and DC internal resistance were conducted based on Example 2 and Comparative Examples 5-8: Table 2 shows the final measured performance parameters: Table 2
[0046] As can be seen from Table 2, the test results are consistent with the overall trend in Table 1. This is because the electrochemical deposition voltage of hard carbon is close to the redox potential of metallic sodium, and it forms a solid electrolyte interphase (SEI) film during cycling. Therefore, under the same test conditions, the initial coulombic efficiency of the battery with hard carbon as the negative electrode is lower than that of Example 1 with sodium titanium phosphate as the negative electrode. At the same time, due to the side effects of metallic sodium precipitation, its thermal runaway temperature is also significantly higher than that of the sodium titanium phosphate negative electrode system.
[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A method for injecting electrolyte into a sodium-ion battery, characterized in that, Includes the following steps: S1. After injecting the basic electrolyte into the cell, side sealing is performed and the cell is left to stand; the basic electrolyte includes a first electrolyte salt and a first solvent; S2. Perform stepped charging on the side-encapsulated battery cells; S3. After injecting flame-retardant electrolyte into the battery cell after step charging, let it stand to obtain the sodium-ion battery; the flame-retardant electrolyte includes phosphate ester flame retardant, second electrolyte salt and second solvent.
2. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, In S1, the concentration of the basic electrolyte is 1.0 mol / L-1.2 mol / L, and the amount used is 85%-95% of the total electrolyte mass.
3. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, In S1, the injection rate is 80 mL / min - 120 mL / min; And / or, the settling time is more than 4 hours.
4. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, In S1, the battery cell includes a positive electrode, a negative electrode, and a separator; The positive electrode sheet includes a positive electrode active material; the positive electrode active material is sodium iron pyrophosphate. The negative electrode sheet includes a negative electrode active material, which is selected from one or more of sodium titanium phosphate, sodium titanate, iron carbide, titanium carbide, and hard carbon. The diaphragm is selected from one or more of polypropylene, polyethylene, and polytetrafluoroethylene.
5. The method for injecting electrolyte into a sodium-ion battery according to claim 4, characterized in that, When the negative electrode active material is sodium titanium phosphate, the step charging specifically includes: in a constant temperature environment of 40℃-50℃, first charging at a charging rate of 0.05C-0.2C to 80%-90% of the cutoff voltage, and then charging at a charging rate of 0.2C-0.45C to the cutoff voltage. When the negative electrode active material is one or more of sodium titanate, iron carbide, titanium carbide and hard carbon, in a constant temperature environment of 23℃-27℃, it is first charged at a constant current rate of 0.08C-0.12C to the cutoff voltage of 3.0V-3.8V, and then charged at the cutoff voltage at a constant voltage until the current drops to 0.01C-0.025C.
6. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, In S3, the phosphate ester flame retardant is selected from one or more of tris(trimethylsilyl) phosphate, trimethyl phosphate, and triethyl phosphate.
7. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, In S3, the concentration of phosphate ester flame retardant in the flame retardant electrolyte is 10wt%-30wt%, the concentration of the second electrolyte salt is 3mol / L-5mol / L, and the amount used is 5%-15% of the total electrolyte mass.
8. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, In S3, the injection rate is 80 mL / min - 120 mL / min; And / or, the settling time is 30 min to 40 min.
9. The method for injecting electrolyte into a sodium-ion battery according to claim 1, characterized in that, The first electrolyte salt and the second electrolyte salt are independently selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalate-borate), sodium difluorooxalate-borate, sodium difluorophosphate, sodium difluorosulfonylimide, and sodium bis(trifluoromethylsulfonyl)imide. And / or, the first solvent and the second solvent are independently selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate.
10. A sodium-ion battery, characterized in that, The sodium-ion battery is prepared by the liquid injection method of the sodium-ion battery according to any one of claims 1-9.