Method for improving air stability of pre-sodium-modified hard carbon negative electrode plate and sodium ion battery

Abstract

The invention discloses a method for improving air stability of a pre-sodium-modified hard carbon negative pole piece and a sodium ion battery, and the method comprises the following steps: soaking, cleaning and drying a mixture of the pre-sodium-modified hard carbon negative pole piece and a quenching reagent to obtain the air-stable pre-sodium-modified hard carbon negative pole piece. By utilizing the characteristic that ester electrolyte and metal sodium are subjected to spontaneous reaction, electrolyte components are regulated and controlled, a boron-rich passivation layer is grown on the surface of pre-sodium-modified hard carbon by utilizing boron-containing electrolyte, the nanoscale compact components can play a role in isolating water and oxygen, the oxidation rate of metalloid sodium adsorbed in the hard carbon is delayed, and the corrosion resistance of the hard carbon is improved. According to the preparation method, NaF and B-O bonds are combined, the mechanical property and ion transmission kinetics of the SEI membrane are optimized, the B-O bonds with high stability and NaF synergistically enhance the mechanical stability of the SEI membrane, the application feasibility of a pre-sodium-modification soft package process is improved, and the sodium ion battery with high first discharge specific capacity is prepared.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a method for improving air stability of a pre-sodiumized hard carbon negative electrode sheet and a sodium ion battery. BACKGROUND

[0002] At present, sodium ion batteries have entered the initial stage of industrialization, and gradually become a new force in the energy storage field due to the advantages of low price and wide source. However, the intrinsic defects of hard carbon materials in the negative electrode of the sodium ion battery limit the first coulomb efficiency, resulting in limited energy density. In order to change this situation, researchers have proposed various pre-sodiumization methods, including positive electrode sodium supplement method, negative electrode sodium supplement method, electrolyte sodium supplement method and separator sodium supplement method. These methods can improve the first coulomb efficiency of the sodium ion battery, especially the negative electrode sodium supplement method. However, the process flow of the negative electrode sodium supplement method is relatively complex, and the structural stability of the pre-sodiumized hard carbon negative electrode in the air is affected by water and oxygen.

[0003] Therefore, it is necessary to provide a method for solving the problem of low energy density of the sodium ion battery and improving the structural stability of the pre-sodiumized hard carbon negative electrode in the air. SUMMARY

[0004] In order to overcome the problem of the structural stability of the pre-sodiumized hard carbon negative electrode in the air in the prior art, the purpose of the application is to provide a method for improving the air stability of the pre-sodiumized hard carbon negative electrode sheet and a sodium ion battery. The method can solve the problem of low energy density of the sodium ion battery, improve the structural stability of the pre-sodiumized hard carbon negative electrode in the air, delay the deterioration speed of the pre-sodiumized hard carbon negative electrode sheet, and provide a new possibility for the industrial application of the negative electrode pre-sodiumization technology.

[0005] In order to solve the above technical problems, the application provides the following technical scheme: A method for improving the air stability of a pre-sodiumized hard carbon negative electrode sheet, comprising the following steps: The pre-sodiumized hard carbon negative electrode sheet is soaked in a quenching reagent containing a boron electrolyte, then washed, dried, and an air stable pre-sodiumized hard carbon negative electrode sheet is obtained.

[0006] Further, the quenching reagent containing the boron electrolyte is prepared by the following process: A fluorinated ethylene carbonate is added to a carbonate solution of NaPF6, mixed uniformly to obtain an electrolyte, and a boron-containing electrolyte is added to the electrolyte to obtain a quenching reagent containing a boron electrolyte.

[0007] Further, the concentration of NaPF6 in the carbonate solution is 1 mol / L, the mass concentration of fluoroethylene carbonate in the electrolyte is 5%, and the dosage ratio of the electrolyte to the boron-containing electrolyte is 20-500 mL:0.08-2 g.

[0008] Further, the boron-containing electrolyte is selected from one or more of sodium borate, sodium tetrafluoroborate, sodium oxalate borate and sodium difluoro oxalate borate.

[0009] Further, the carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0010] Further, the soaking temperature is 20-40 DEG C, and the soaking time is 3 s-5 min.

[0011] Further, the cleaning is performed using one or more of diethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydro pyran and N,N-dimethyl formamide.

[0012] Further, the drying temperature is 60-80 DEG C, and the time is 10-40 min.

[0013] An air-stable pre-sodiumized hard carbon negative electrode sheet.

[0014] A sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and an electrolyte, and the negative electrode sheet is an air-stable pre-sodiumized hard carbon negative electrode sheet.

[0015] Compared with the prior art, the present application has the following beneficial effects: The present application provides a method for improving the air stability of a pre-sodiumized hard carbon negative electrode sheet and an application. Considering that the sodium-carbon alloy phase formed after the pre-sodiumization process of the pre-sodiumization reagent and the hard carbon electrode sheet has a high water and oxygen sensitivity, by utilizing the spontaneous reaction between the ester electrolyte and metallic sodium, the electrolyte composition is adjusted, and a boron-rich passivation layer is grown on the surface of the pre-sodiumized hard carbon by using the boron-containing electrolyte. This nanoscale dense composition can isolate water and oxygen, slow down the oxidation rate of the quasi-metallic sodium adsorbed in the hard carbon, and also optimize the mechanical properties and ion transport kinetics of the SEI film. The B-O bond with high stability and NaF synergistically enhance the mechanical stability of the SEI film, improve the feasibility of the pre-sodiumization soft package process application, and thus prepare a sodium ion battery with high initial discharge specific capacity. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 An HRTEM image of an air-stable pre-sodiumized hard carbon negative electrode prepared for Example 5 of the present application; Figure 2Performance chart of the battery prepared for the embodiment 5 and the comparative example 2 of the present application. DETAILED DESCRIPTION

[0017] For the purpose of promoting the understanding of the present application, the present application will be more fully described by reference to the accompanying drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. It is noted that the scope of the present application is defined by the appended claims and not by the description of the embodiments.

[0018] The present application first provides a quenching reagent, which is prepared in a glove box, fluoroethylene carbonate (FEC) is added into a carbonate solution of NaPF6, and mixed uniformly to obtain an electrolyte, the concentration of NaPF6 in the carbonate solution is 1 mol / L, and the mass concentration of fluoroethylene carbonate in the electrolyte is 5%. Further, the carbonate is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0019] A boron-containing electrolyte is added into the electrolyte to obtain the quenching reagent; the dosage ratio of the electrolyte to the boron-containing electrolyte is 20-500 mL: 0.08-2 g.

[0020] Further, the boron-containing electrolyte is selected from one or more of sodium borate, sodium tetrafluoroborate, sodium oxalate borate and sodium difluoro oxalate borate. A method for improving the air stability of a pre-sodiumized hard carbon negative electrode sheet, comprising the following steps: Preparation of a pre-sodiumized hard carbon negative electrode sheet: hard carbon, conductive carbon black and sodium carboxymethyl cellulose are dissolved in water, butadiene styrene rubber is added after uniform mixing, and the mixture is uniformly mixed to obtain a negative electrode slurry. The copper foil current collector is coated with the negative electrode slurry, dried, and a hard carbon negative electrode sheet is obtained. The mixture of the hard carbon negative electrode sheet and the pre-sodiumization reagent is soaked under ultrasonic, washed, and dried to obtain an ultrasonic-enhanced pre-sodiumized hard carbon negative electrode sheet, i.e. a pre-sodiumized hard carbon negative electrode sheet. The preparation process of the pre-sodiumized hard carbon negative electrode sheet is carried out by the method in patent CN120048847A, "Ultrasonic-enhanced pre-sodiumized hard carbon negative electrode sheet and preparation method and sodium ion battery". 10-40 mL of the quenching reagent is placed in a beaker, and then the pre-sodiumized hard carbon negative electrode sheet is soaked in the quenching reagent for 3 s-5 min, the treatment temperature is maintained at 20-40°C, the hard carbon negative electrode sheet after ultrasonic-assisted soaking is washed once with the aprotic polar solvent, and then it is placed on a heating platform for heating and drying to obtain an air-stable pre-sodiumized hard carbon negative electrode sheet.

[0021] Further, the aprotic polar solvent is selected from one or more of diethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran and N,N-dimethylformamide.

[0022] Further, the heating platform heating temperature is maintained at 60-80℃, and the heating time is 10-40min.

[0023] Further, the obtained air-stable pre-sodium hard carbon negative electrode sheet is placed in a dry air environment for 0.5-8h.

[0024] All the above preparation steps are carried out in an argon-filled glove box.

[0025] The application further provides a sodium ion battery composed of a positive electrode sheet, a negative electrode sheet, a separator placed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the negative electrode sheet adopts the air-stable pre-sodium hard carbon negative electrode sheet.

[0026] The application forms a passivation layer by introducing a boron-containing electrolyte, which not only effectively isolates water and oxygen, but also optimizes the mechanical properties and ion transport kinetics of the SEI film, and the high-stability B-O bond cooperates with NaF to synergistically enhance the mechanical stability of the SEI film, thereby providing a key technical path for the application of pre-sodium technology.

[0027] The following are specific examples.

[0028] Example 1 A method for improving the air stability of a pre-sodium hard carbon negative electrode sheet, comprising the following steps: A pre-sodium hard carbon negative electrode sheet is prepared and reserved for use.

[0029] In the glove box, the quenching reagent is prepared: NaPF6 is added to a mixture of diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1 to obtain a carbonate solution of NaPF6, and fluoroethylene carbonate (FEC) is added to the carbonate solution of NaPF6, mixed uniformly to obtain an electrolyte, the concentration of NaPF6 in the carbonate solution is 1mol / L, and the mass concentration of fluoroethylene carbonate in the electrolyte is 5%; that is, 1mol / L NaPF6in EC: DEC=1:1 Vol% with 5%FEC. In an argon atmosphere glove box, 20mL of electrolyte is taken, 0.08g of sodium difluoroborate is added, and stirred for 12h to prepare the quenching reagent.

[0030] The pre-sodiumized hard carbon negative electrode sheet was soaked in 20 mL quenching solution for 5 s, the temperature was maintained at 30°C during the treatment process, and the soaked pre-sodiumized hard carbon negative electrode sheet was cleaned with tetrahydropyran (THP), and then placed on a heating platform at 60°C for 30 min to obtain an air-stable pre-sodiumized hard carbon negative electrode sheet.

[0031] In order to verify the water oxygen resistance in a dry air environment, the air-stable pre-sodiumized hard carbon negative electrode sheet was placed in a dry air environment for 1 h, and the dew point temperature of the dry air environment should be controlled below -25°C.

[0032] Referring to Figure 1 It can be seen that a passivation layer is grown on the surface of the pre-sodiumized hard carbon after quenching treatment, indicating that the pre-sodiumized reagent has been modified.

[0033] The air-stable pre-sodiumized hard carbon negative electrode sheet after standing for 1 h was used as the negative electrode, NaNi 0.33 Fe 0.33 Mn 0.33 O2 as the positive electrode, 1 mol / L NaPF6 in EC:PC:DEC=1:1:1 Vol% with 5% FEC as the electrolyte to assemble a sodium ion full cell, and perform charge and discharge test.

[0034] Example 2 Different from example 1: the 1 h standing time in a dry air environment is changed to 2 h, and the rest is the same as example 1, which is not repeated here.

[0035] Example 3 Different from example 1: the 1 h standing time in a dry air environment is changed to 4 h, and the rest is the same as example 1, which is not repeated here.

[0036] Example 4 Different from example 1: the 1 h standing time in a dry air environment is changed to 6 h, and the rest is the same as example 1, which is not repeated here.

[0037] Example 5 Different from example 1: the 1 h standing time in a dry air environment is changed to 0, and the rest is the same as example 1, which is not repeated here.

[0038] Example 6 Different from example 1: 0.08 g of sodium difluoroborate is changed to 0.04 g of sodium difluoroborate, and the rest is the same as example 1, which is not repeated here.

[0039] Example 7 Different from example 1: 0.08g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC was changed to 0.04g NaBF2and 0.04g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0040] Example 8 Different from example 1: 0.08g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC was changed to 0.04g NaBF2and 0.04g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0041] Example 9 Different from example 1: 0.08g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC was changed to 0.04g NaBF2and 0.04g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0042] Example 10 Different from example 1: 0.08g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC was changed to 0.04g NaBF2and 0.04g NaBF2in EC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0043] Example 11 Different from example 1: 1 mol / L NaPF6in EC: DEC = 1:1 Vol% with 5% FEC was changed to 1 mol / L NaPF6in PC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0044] Example 12 Different from example 1: 1 mol / L NaPF6in EC: DEC = 1:1 Vol% with 5% FEC was changed to 1 mol / L NaPF6in DMC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0045] Example 13 Different from example 1: 1 mol / L NaPF6in EC: DEC = 1:1 Vol% with 5% FEC was changed to 1 mol / L NaPF6in EMC: DEC = 1:1 Vol% with 5% FEC, the rest was the same as example 1, here will not repeat.

[0046] Example 14 The difference from Example 1 is that 1 mol / L NaPF6 in EC: DEC=1:1 Vol% with 5% FEC is changed to 1 mol / L NaPF6 in EMC: PC=1:1 Vol% with 5% FEC. The rest is the same as in Example 1, and will not be repeated here.

[0047] Example 15 The difference from Example 1 is that the 1mol / L NaPF6in EC: DEC=1:1 Vol% with 5% FEC is changed to 1mol / L NaPF6in EMC: PC: DMC=1:1:1 Vol% with 5% FEC. The rest is the same as in Example 1, and will not be repeated here.

[0048] Example 16 A method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets includes the following steps: Prepare pre-sodium-treated hard carbon negative electrode sheets for later use.

[0049] The quenching reagent was prepared in a glove box: NaPF6 was added to diethyl carbonate (DEC) to obtain a NaPF6 carbonate solution. Fluoroethylene carbonate (FEC) was then added to the NaPF6 carbonate solution and mixed thoroughly to obtain an electrolyte. The concentration of NaPF6 in the carbonate solution was 1 mol / L, and the mass concentration of FEC in the electrolyte was 5%; that is, 1 mol / L NaPF6 in DEC with 5% FEC. In an argon-atmosphere glove box, 20 mL of the electrolyte was taken, and 0.08 g of sodium difluorooxalate borate was added. The mixture was stirred for 24 h to obtain the quenching reagent.

[0050] The pre-sodium-treated hard carbon negative electrode sheet was immersed in 20 mL of quenching solution for 5 min, and the temperature was maintained at 20 °C during the treatment. The immersed pre-sodium-treated hard carbon negative electrode sheet was cleaned with ether and then placed on a heating platform at 70 °C for 20 min to obtain an air-stable pre-sodium-treated hard carbon negative electrode sheet.

[0051] Example 17 A method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets includes the following steps: Prepare pre-sodium-treated hard carbon negative electrode sheets for later use.

[0052] The quenching reagent was prepared in a glove box: NaPF6 was added to a 1:1 volume ratio mixture of diethyl carbonate (DEC) and ethylene carbonate (EC) to obtain a NaPF6 carbonate solution. Fluoroethylene carbonate (FEC) was then added to the NaPF6 carbonate solution and mixed thoroughly to obtain the electrolyte. The concentration of NaPF6 in the carbonate solution was 1 mol / L, and the mass concentration of fluoroethylene carbonate in the electrolyte was 5%; that is, 1 mol / L NaPF6 in EC: DEC = 1:1 Vol% with 5% FEC. In an argon-atmosphere glove box, 200 mL of the electrolyte was taken, 1 g of sodium difluorooxalate borate was added, and the mixture was stirred for 16 h to obtain the quenching reagent.

[0053] The pre-sodium-treated hard carbon negative electrode sheet was immersed in 20 mL of quenching solution for 3 seconds, and the temperature was maintained at 40 °C during the treatment. The immersed pre-sodium-treated hard carbon negative electrode sheet was cleaned with ethylene glycol dimethyl ether, and then placed on a heating platform at 80 °C for 10 minutes to obtain an air-stable pre-sodium-treated hard carbon negative electrode sheet.

[0054] Example 18 A method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets includes the following steps: Prepare pre-sodium-treated hard carbon negative electrode sheets for later use.

[0055] The quenching reagent was prepared in a glove box: NaPF6 was added to a 1:1 volume ratio mixture of diethyl carbonate (DEC) and ethylene carbonate (EC) to obtain a NaPF6 carbonate solution. Fluoroethylene carbonate (FEC) was then added to the NaPF6 carbonate solution and mixed thoroughly to obtain the electrolyte. The concentration of NaPF6 in the carbonate solution was 1 mol / L, and the mass concentration of fluoroethylene carbonate in the electrolyte was 5%; that is, 1 mol / L NaPF6 in EC: DEC = 1:1 Vol% with 5% FEC. In an argon-atmosphere glove box, 500 mL of the electrolyte was taken, 2 g of sodium difluorooxalate borate was added, and the mixture was stirred for 12 h to obtain the quenching reagent.

[0056] The pre-sodium-treated hard carbon negative electrode sheet was immersed in 20 mL of quenching solution for 2 min, and the temperature was maintained at 25 °C during the treatment. The immersed pre-sodium-treated hard carbon negative electrode sheet was cleaned with N,N-dimethylformamide, and then placed on a heating platform at 60 °C for 40 min to obtain an air-stable pre-sodium-treated hard carbon negative electrode sheet.

[0057] Comparative Example 1 The difference from Example 1 is that the prepared pre-sodium hard carbon negative electrode sheet is not quenched (i.e., it is not soaked, cleaned and dried with quenching reagents), but is left to stand in a dry air environment for 0.5 hours before being directly assembled into a full cell. The rest is the same as in Example 1, and will not be repeated here.

[0058] Comparative Example 2 Only normal, untreated hard carbon negative electrode sheets are used, without any pre-sodium treatment or quenching process.

[0059] Table 1. Initial coulombic efficiency and open-circuit voltage of the full cells in Examples 1-5 and Comparative Examples 1-2.

[0060] From the data analysis in Table 1, we can conclude that: (1) The sodium-ion full cells assembled from the pre-sodium hard carbon electrodes of Examples 1-4 after quenching treatment and standing in a dry environment for a certain period of time showed a significant overall improvement in initial coulombic efficiency (ICE) and open-circuit voltage (OCV) after standing for 0.5 h after pre-sodium treatment compared to the ordinary immersion of Comparative Example 1. Examples 1-4 underwent drying chamber standing tests for 1 h, 2 h, 4 h, and 6 h, with ICE values ​​of 85.94%, 84.22%, 81.47%, and 79.38%, and OCV values ​​of 2.09 V, 1.87 V, 1.81 V, and 1.48 V, respectively. It can be clearly seen that the hard carbon grown and passivated after quenching treatment still has better ICE and OCV than Comparative Example 1 after standing in a dry chamber for 6 h. This dense, sheet-like passivation layer can effectively isolate water and oxygen, delaying the corrosion of metallic sodium by dry air.

[0061] (2) This quenching mode can effectively maintain the stability of pre-sodium hard carbon, further improve the pre-sodiumization performance and consistency of hard carbon after quenching, and shorten the industrialization process of pre-sodiumization process.

[0062] (3) Through the study of Example 5 ( Figure 2 UBHC (abbreviated as UBHC) and Comparative Example 2 ( Figure 2 (HC) assembled soft-pack batteries and subjected to charge-discharge cycle testing, such as Figure 2 As shown, the first-cycle discharge specific capacity of the HC pouch battery is 114.9 mA·g. -1 The UBHC pouch battery has a first-cycle discharge specific capacity of 124 mA·g. -1 The HC pouch cell underwent 150 charge-discharge cycle tests at a current density of 0.1C. The current density was 118.3 mA·g. -1 Decay to 109 mA·g -1 The capacity retention rate after cycling was 92.14%. Meanwhile, the UBHC pouch cell's capacity retention rate increased from 129.1 mA·g.-1 The battery's capacity decayed to 120.3 mA·g⁻¹, and the capacity retention after cycling was 95.27%. This demonstrates that the quenching process not only slows down the degradation rate of hard carbon after pre-sodiumization and maintains structural stability, but also improves the battery's cycle performance.

[0063] This invention introduces a boron-containing electrolyte (boron-rich substance) and uses an immersion method to construct a boron-rich passivation layer on the surface of hard carbon in situ within a short time. This not only effectively isolates water and oxygen and slows down the rate of deterioration of pre-sodium-treated hard carbon in a dry air environment, but also optimizes the mechanical properties and ion transport kinetics of the SEI film. The highly stable BO bonds and NaF synergistically enhance the mechanical stability of the SEI film, providing a key technical path for the application of pre-sodium treatment technology.

[0064] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0065] Unless otherwise defined, all 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. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets, characterized in that, Includes the following steps: The pre-sodium-treated hard carbon anode sheet is immersed in a quenching reagent containing boron electrolyte, then cleaned and dried to obtain an air-stable pre-sodium-treated hard carbon anode sheet.

2. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 1, characterized in that, The quenching reagent containing boron electrolyte is prepared by the following process: Add fluoroethylene carbonate to a NaPF6 carbonate solution and mix thoroughly to obtain an electrolyte. Add a boron-containing electrolyte to the electrolyte to obtain a quenching reagent containing boron electrolyte.

3. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 2, characterized in that, The concentration of NaPF6 in the carbonate solution is 1 mol / L, the mass concentration of fluoroethylene carbonate in the electrolyte is 5%, and the ratio of electrolyte to boron-containing electrolyte is 20-500 mL: 0.08-2 g.

4. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 2, characterized in that, The boron-containing electrolyte is selected from one or more of sodium borate, sodium tetrafluoroborate, sodium oxalate borate, and sodium difluorooxalate borate.

5. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 2, characterized in that, The carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

6. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 1, characterized in that, The soaking temperature is 20℃-40℃, and the soaking time is 3s-5min.

7. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 1, characterized in that, The cleaning is performed using one or more of the following: diethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, dimethyltetrahydrofuran, tetrahydropyran, and N,N-dimethylformamide.

8. The method for improving the air stability of pre-sodium-treated hard carbon negative electrode sheets according to claim 1, characterized in that, The drying temperature is 60-80℃ and the time is 10-40 minutes.

9. An air-stabilized pre-sodium hard carbon negative electrode sheet prepared by the method according to any one of claims 1-8.

10. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrode, and an electrolyte, characterized in that, The negative electrode is an air-stabilized pre-sodium hard carbon negative electrode prepared by the method described in any one of claims 1-8.

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