Ultrasonic-enhanced pre-sodium-modified hard carbon negative electrode plate, preparation method and sodium ion battery

Abstract

The invention discloses an ultrasonic-enhanced pre-sodium-modified hard carbon negative pole piece, a preparation method and a sodium ion battery, and the ultrasonic-enhanced pre-sodium-modified hard carbon negative pole piece is obtained by soaking, cleaning and drying a mixture of a hard carbon negative pole piece and a pre-sodium-modified reagent under ultrasonic waves. The reaction efficiency of the system is enhanced by introducing an external physical field, a pre-sodium modification reagent is in contact with a deeper hard carbon negative electrode material in a short time by utilizing an ultrasonic method, so that the mass transfer of the system is enhanced, and meanwhile, the first coulombic efficiency and the cycling stability of the sodium ion total battery are improved. In the same time, electron transfer in the pre-sodium-modification reaction is accelerated by the ultrasonic cavitation effect, so that the first coulombic efficiency of a total battery assembled by the ultrasonic-assisted pre-sodium-modification hard carbon negative electrode is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet, a preparation method thereof, and a sodium ion battery. Background Art

[0002] At present, due to its excellent performance, low cost, and wide sources, hard carbon materials have gradually become the main force of the negative electrode materials for industrialization of sodium ion batteries. However, limited by the special microstructure of hard carbon materials themselves, the first Coulombic efficiency of sodium ion batteries is generally lower than that of lithium ion batteries. To change this situation, researchers have proposed various pre-sodiation methods, including the positive electrode sodium supplementation method of adding sacrificial sodium salts such as sodium oxalate and sodium acetate, and the negative electrode sodium supplementation method of introducing metallic sodium. These methods can all improve the first Coulombic efficiency of sodium ion batteries, but they will have some negative impacts: directly introducing sacrificial salts will produce by-products such as gas and reduce the conductivity of the positive electrode system; introducing metallic sodium may also pose a safety hazard.

[0003] Therefore, it is necessary to provide a method that can solve the problem of low first Coulombic efficiency of sodium ion batteries while reducing the influence of the pre-sodiation process on the positive electrode material and system. Summary of the Invention

[0004] To overcome the problem of low first Coulombic efficiency of sodium ion batteries in the prior art, the purpose of the present invention is to provide an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet, a preparation method thereof, and a sodium ion battery. This method improves the first Coulombic efficiency of the battery and also provides new possibilities for the industrial application of pre-sodiation technology.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] A preparation method of an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet, comprising the following steps:

[0007] Soak, wash, and dry the mixture of the hard carbon negative electrode sheet and the pre-sodiation reagent under ultrasonic waves to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet.

[0008] Further, the ultrasonic power is set to 40 - 100 W, and the working frequency is 40 - 100 KHz.

[0009] Further, the soaking time is 30 s - 20 min.

[0010] Further, the heating temperature is 60 - 100 °C, and the time is 20 - 40 min.

[0011] Further, the pre-sodiation reagent is prepared through the following process:

[0012] Dissolve polycyclic aromatic hydrocarbons in an aprotic polar solvent, then add metallic sodium and react under stirring to form sodium polycyclic aromatic hydrocarbons, wherein the molar ratio of polycyclic aromatic hydrocarbons to sodium is 1:1.

[0013] Further, the stirring time is 12 - 24 h.

[0014] Further, the polycyclic aromatic hydrocarbons are selected from one or more of biphenyl, dimethylbiphenyl, naphthalene, dimethylnaphthalene, phenanthrene and anthracene;

[0015] The aprotic solvent is selected from one or more of diethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, dimethyltetrahydrofuran, tetrahydropyran and N,N - dimethylformamide.

[0016] Further, dissolve hard carbon, conductive carbon black and sodium carboxymethylcellulose in water, mix evenly, then add styrene - butadiene rubber and mix evenly to obtain a negative electrode slurry;

[0017] Coat the negative electrode slurry on a copper foil current collector and dry it to obtain a hard carbon negative electrode sheet.

[0018] An ultrasonically enhanced pre - sodiated hard carbon negative electrode sheet.

[0019] A sodium - ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet, characterized in that the negative electrode sheet uses the ultrasonically enhanced pre - sodiated hard carbon negative electrode sheet.

[0020] Compared with the existing technology, the present invention has the following beneficial effects:

[0021] The present invention provides a method and application for ultrasonically enhancing the pre - sodiation effect of a hard carbon negative electrode of a sodium - ion battery. Considering the problems of insufficient reaction due to short - time contact between the pre - sodiation reagent and the hard carbon electrode sheet and long - time influence on the stripping strength of the electrode sheet, the mixture of the hard carbon negative electrode sheet and the pre - sodiation reagent is soaked under ultrasonic waves. Through ultrasonic induction or acceleration, the quasi - metallic sodium in the pre - sodiation reagent is adsorbed by the defects in the hard carbon electrode sheet, enhancing the mass transfer of the system and achieving the purpose of sufficient pre - sodiation in a short time. In addition, the quasi - metallic sodium further reacts with the oxygen - containing functional groups on the surface defects of the hard carbon, reducing the sodium ion loss during the first charge - discharge process. Within the same treatment time, the sodium - ion battery assembled with the pre - sodiated hard carbon negative electrode of the present invention has a higher initial Coulomb efficiency and more excellent cycle performance.

[0022] Further, under the action of ultrasonic cavitation, adjust the ultrasonic power to 40 - 100 W and the frequency to 40 - 100 KHz, causing a contact electro - catalytic reaction to occur at the hard carbon interface, accelerating electron transfer, and enabling the sodium - ion battery under the ultrasonically enhanced treatment mode to have a higher initial Coulomb efficiency critical value. Description of the Drawings

[0023] Figure 1 It is the micrograph of the ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet prepared in Example 1 of the present invention;

[0024] Figure 2 It is the performance graph of the batteries prepared in Example 3 and Comparative Example 1 of the present invention. Detailed implementation manners

[0025] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present invention can be understood more thoroughly and comprehensively.

[0026] The present invention first provides a pre-sodiation reagent. The pre-sodiation reagent is prepared by dissolving polycyclic aromatic hydrocarbons in an aprotic polar solvent, and then adding a corresponding proportion of metallic sodium to react the polycyclic aromatic hydrocarbons to generate sodium polycyclic aromatic hydrocarbons, and fully stirring for 12 - 24 h to obtain a solution with a concentration of sodium polycyclic aromatic hydrocarbons of 0.05 - 2 mol / L. The molar ratio of polycyclic aromatic hydrocarbons to sodium is 1:1.

[0027] Further, the polycyclic aromatic hydrocarbons are selected from one or more of biphenyl, dimethylbiphenyl, naphthalene, dimethylnaphthalene, phenanthrene, and anthracene.

[0028] Further, the aprotic solvent is selected from one or more of diethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, dimethyltetrahydrofuran, tetrahydropyran, and N,N-dimethylformamide.

[0029] The present invention further provides a method for preparing an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet, comprising the following steps:

[0030] Preparing a hard carbon negative electrode sheet: Mixing hard carbon, conductive carbon black, and sodium carboxymethylcellulose in parts by weight of 90.5 parts, 5 parts, and 1.5 parts, dissolving them in deionized water to obtain a mixture, then adding the mixture to a polytetrafluoroethylene mixing tank, starting a planetary mixer and maintaining it at 800 revolutions per minute for 5 minutes for dry mixing, adding an appropriate amount of deionized water, and continuing to mix at the same speed for 1.5 hours to ensure the uniformity of the obtained slurry. Finally, adding 3 parts of styrene-butadiene rubber and performing vacuum mixing at 600 revolutions per minute for 1 minute to obtain a negative electrode slurry.

[0031] Adjust the thickness of the doctor blade to 0.2 mm, and lay a copper foil current collector on the flat plate of the coater. Subsequently, pour the negative electrode slurry on the flat plate, start the coater to push the doctor blade to coat the slurry, and then transfer the obtained sheet to a vacuum oven at 70 °C and store it for 12 hours. After the sheet is completely dehydrated, cut it to obtain a hard carbon negative electrode sheet for standby.

[0032] Place 10 - 50 mL of the pre-sodiumation reagent in an ultrasonic reactor, soak the hard carbon negative electrode plate in the ultrasonic assistance of the pre-sodiumation reagent for 30 s - 20 min, maintain the treatment temperature at 25°C - 40°C, wash the hard carbon negative electrode plate soaked by ultrasonic assistance twice with the aprotic polar solvent, wash it for 10 - 30 s in an ultrasonic environment for the first time and 5 - 20 s in an ultrasonic environment for the second time, and then place it on a heating platform to heat and dry to obtain an ultrasonically enhanced pre-sodiumated hard carbon negative electrode plate;

[0033] Further, the ultrasonic power is set to 40 - 100 W, and the working frequency is 40 - 100 KHz.

[0034] Further, the heating temperature of the heating platform is maintained at 60 - 100°C for 20 - 40 min.

[0035] All the above preparation steps are carried out in a glove box filled with argon.

[0036] The present invention further provides a sodium-ion battery, which is composed of a positive electrode plate, a negative electrode plate, a separator and an electrolyte placed between the positive electrode plate and the negative electrode plate, and the negative electrode plate uses the ultrasonically enhanced pre-sodiumated hard carbon negative electrode plate of the sodium-ion battery.

[0037] The following are specific examples.

[0038] Example 1

[0039] Provide a method for enhancing the pre-sodiumation effect of the hard carbon negative electrode plate of a sodium-ion battery by ultrasonic waves, including the following steps:

[0040] Prepare the hard carbon negative electrode plate: Mix hard carbon, conductive carbon black and sodium carboxymethyl cellulose according to 90.5 parts, 5 parts and 1.5 parts by weight, dissolve them in deionized water to obtain a mixture, then add the mixture to a polytetrafluoroethylene mixing tank, start the planetary mixer and maintain it at 800 revolutions per minute for 5 minutes of dry mixing, add an appropriate amount of deionized water, and continue to mix at the same speed for 1.5 hours to ensure the uniformity of the obtained slurry. Finally, add 3 parts of styrene-butadiene rubber and perform 1 minute of vacuum mixing at 600 revolutions per minute to obtain the negative electrode slurry.

[0041] Adjust the blade thickness to 0.2 mm, lay the copper foil current collector on the coating machine flat plate, then pour the negative electrode slurry on the flat plate, start the coating machine to push the blade to coat the slurry, and then transfer the obtained electrode plate to a 70°C vacuum oven for 12 hours. After the electrode plate is completely dehydrated, cut it to obtain the hard carbon negative electrode plate.

[0042] In a glove box filled with argon gas, naphthalene and sodium were mixed in an equimolar ratio and then co-dissolved in tetrahydropyran (THP). After stirring for 15 h, a 1 mol / L THP solution of sodium naphthalide was prepared. The hard carbon negative electrode was immersed in the 30 mL THP solution for 1 min under ultrasonic assistance. The ultrasonic power was set at 60 W and the working frequency was 60 KHz. During the treatment, the temperature was maintained at 30 °C. The hard carbon negative electrode after ultrasonic-assisted immersion was washed twice with THP. The first wash was for 15 s in an ultrasonic environment, and the second wash was for 10 s in an ultrasonic environment. Then it was placed on a heating platform at 60 °C for 30 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode;

[0043] See Figure 1 , it can be seen that the surface of the hard carbon becomes rougher after the ultrasonically enhanced pre-sodiation treatment, indicating that it has been modified by the pre-sodiation reagent.

[0044] Using the ultrasonically enhanced pre-sodiated hard carbon negative electrode as the negative electrode, NaNi 0.33 Fe 0.33 Mn 0.33 O 2 as the positive electrode, and 1 mol / L NaPF 6 in EC:PC:DEC = 1:1:1 Vol% with 5% FEC as the electrolyte, a sodium-ion full battery was assembled and charged and discharged.

[0045] Example 2

[0046] The difference from Example 1 is that the immersion time under ultrasonic assistance was changed to 3 min. The rest is the same as in Example 1 and will not be elaborated here.

[0047] Example 3

[0048] The difference from Example 1 is that the immersion time under ultrasonic assistance was changed to 5 min. The rest is the same as in Example 1 and will not be elaborated here.

[0049] Example 4

[0050] The difference from Example 1 is that the immersion time under ultrasonic assistance was changed to 10 min. The rest is the same as in Example 1 and will not be elaborated here.

[0051] Example 5

[0052] The difference from Example 1 is that the immersion time under ultrasonic assistance was changed to 15 min. The rest is the same as in Example 1 and will not be elaborated here.

[0053] Example 6

[0054] Differences from Example 1: The immersion under ultrasonic assistance was changed to ordinary immersion (i.e., without ultrasonic). The rest is the same as in Example 1 and will not be elaborated here.

[0055] Example 7

[0056] Differences from Example 6: The ordinary immersion time was changed to 3 min. The rest is the same as in Example 6 and will not be elaborated here.

[0057] Example 8

[0058] Differences from Example 6: The ordinary immersion time was changed to 5 min. The rest is the same as in Example 6 and will not be elaborated here.

[0059] Example 9

[0060] Differences from Example 6: The ordinary immersion time was changed to 10 min. The rest is the same as in Example 6 and will not be elaborated here.

[0061] Example 10

[0062] Differences from Example 6: The ordinary immersion time was changed to 15 min. The rest is the same as in Example 6 and will not be elaborated here.

[0063] Example 11

[0064] Same as Example 1, except that in a glove box under an argon atmosphere, biphenyl and sodium were mixed in an equimolar ratio, then co-dissolved in diethyl ether, and after stirring for 18 h, a 0.05 mol / L solution of sodium biphenyl was prepared. The hard carbon negative electrode sheet was immersed in the sodium biphenyl solution for 30 s under ultrasonic assistance, the ultrasonic power was set to 40 W, and the working frequency was 50 KHz. The hard carbon negative electrode sheet immersed under ultrasonic assistance was washed twice with biphenyl. The first wash was for 15 s in an ultrasonic environment, and the second wash was for 10 s in an ultrasonic environment. Then it was placed on a heating platform at 75 °C for 30 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet.

[0065] Example 12

[0066] Same as Example 1, except that in a glove box under an argon atmosphere, dimethylbiphenyl and sodium were mixed in an equimolar ratio, then co-dissolved in ethylene glycol dimethyl ether, and after stirring for 18 h, a 0.1 mol / L solution of sodium dimethylbiphenyl was prepared. The hard carbon negative electrode sheet was immersed in the sodium dimethylbiphenyl solution for 20 min under ultrasonic assistance, the ultrasonic power was set to 100 W, and the working frequency was 40 KHz. The hard carbon negative electrode sheet immersed under ultrasonic assistance was washed multiple times with dimethylbiphenyl. The first wash was for 15 s in an ultrasonic environment, and the second wash was for 10 s in an ultrasonic environment. Then it was placed on a heating platform at 65 °C for 30 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet.

[0067] Example 13

[0068] Same as Example 1, except that in a glove box under an argon atmosphere, dimethylnaphthalene and sodium were mixed in an equimolar ratio and then co-dissolved in tetraethylene glycol dimethyl ether. After stirring for 20 h, a 0.5 mol / L solution of sodium dimethylnaphthalene was prepared. The hard carbon negative electrode sheet was immersed in the sodium dimethylnaphthalene solution for 10 min under ultrasonic assistance, and the hard carbon negative electrode sheet immersed under ultrasonic assistance was washed repeatedly with dimethylnaphthalene. The first washing was for 15 s in an ultrasonic environment, the second washing was for 10 s in an ultrasonic environment, and then it was placed on a heating platform at 60 °C for 35 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet.

[0069] Example 14

[0070] Same as Example 1, except that in a glove box under an argon atmosphere, phenanthrene and sodium were mixed in an equimolar ratio and then co-dissolved in dimethyltetrahydrofuran. After stirring for 15 h, a 15 mol / L solution of sodium phenanthrene was prepared. The hard carbon negative electrode sheet was immersed in the sodium phenanthrene solution for 1 min under ultrasonic assistance, the ultrasonic power was set to 60 W, and the working frequency was 100 KHz. The hard carbon negative electrode sheet immersed under ultrasonic assistance was washed repeatedly with phenanthrene. The first washing was for 15 s in an ultrasonic environment, the second washing was for 10 s in an ultrasonic environment, and then it was placed on a heating platform at 100 °C for 30 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet.

[0071] Example 15

[0072] Same as Example 1, except that in a glove box under an argon atmosphere, polycyclic aromatic hydrocarbons and sodium were mixed in an equimolar ratio. The polycyclic aromatic hydrocarbons were a mixture of biphenyl and anthracene with a molar ratio of 1:1, and then they were co-dissolved in tetrahydropyran. After stirring for 12 h, a solution of sodium biphenyl and sodium anthracene with a total concentration of 2 mol / L of sodium biphenyl and sodium anthracene was prepared. The hard carbon negative electrode sheet was immersed in the solution of sodium biphenyl and sodium anthracene for 5 min under ultrasonic assistance, the ultrasonic power was set to 80 W, and the working frequency was 70 KHz. The hard carbon negative electrode sheet immersed under ultrasonic assistance was washed repeatedly with tetrahydropyran. The first washing was for 15 s in an ultrasonic environment, the second washing was for 10 s in an ultrasonic environment, and then it was placed on a heating platform at 60 °C for 40 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode sheet.

[0073] Example 16

[0074] Same as Example 1, except that in a glove box under an argon atmosphere, naphthalene and sodium were mixed in an equimolar ratio and then co-dissolved in an aprotic solvent, which was a mixed solution of tetrahydropyran and N,N-dimethylformamide with a volume ratio of 1:1. After stirring for 24 h, a 1 mol / L solution of sodium naphthalide was prepared. The hard carbon negative electrode was immersed in the sodium naphthalide solution for 3 min under ultrasonic assistance, with the ultrasonic power set at 70 W and the working frequency at 60 KHz. Tetrahydropyran was used to wash the ultrasonically assisted immersed hard carbon negative electrode multiple times, washing it for 15 s in an ultrasonic environment for the first time and 10 s in an ultrasonic environment for the second time, and then placing it on a heating platform at 80 °C for 20 min to obtain an ultrasonically enhanced pre-sodiated hard carbon negative electrode.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that after the prepared hard carbon negative electrode was not pre-sodiated (i.e., not subjected to treatments such as ultrasonic-assisted solution immersion, washing, and drying), the full cell was directly assembled. The rest was the same as in Example 1 and will not be elaborated here.

[0077] Table 1 First Coulombic efficiency and open-circuit voltage of the full cells in Examples 1-10 and Comparative Example 1

[0078]

[0079]

[0080] From the data analysis in Table 1, it can be obtained that:

[0081] (1) For the sodium-ion full cells assembled with the hard carbon electrodes after ultrasonic enhanced pre-sodiation treatment in Examples 1-5, there was an obvious overall improvement in the first Coulombic efficiency and open-circuit voltage compared to those after ordinary immersion pre-sodiation treatment in Examples 6-10. The hard carbon electrodes pre-sodiated by ordinary immersion in Examples 6-10 could reach the best first Coulombic efficiency of 92.56% at 10 min, while the hard carbon electrodes pre-sodiated by ordinary immersion in Examples 1-5 only needed 5 min to reach the best first Coulombic efficiency of 93.8%. This shows that the introduction of the external physical field improvement technology of ultrasound not only shortens the contact time of the solid-liquid interface reaction but also realizes deeper sodium compensation of the hard carbon electrodes, improves the best first Coulombic efficiency, and further shortens the time to reach the best efficiency.

[0082] (2) It can be seen from the open-circuit voltage changes of the sodium-ion full battery assembled with the pre-sodiation-treated hard carbon electrode sheets in Examples 1-10 that the open-circuit voltage increases with the increase of the soaking time, which is also in line with the situation of sodium supplementation in hard carbon: with the accumulation of the soaking time, more metallic sodium binds to the surface and deep layer of the hard carbon negative electrode sheet. Since the electrode potential of metallic sodium is low, the potential difference between the positive and negative electrodes becomes larger, that is, the open-circuit voltage becomes larger. At the same time, the greater the increase in the open-circuit voltage, the higher the first Coulombic efficiency, which also provides great help for quickly distinguishing the pre-sodiation effect and accelerating the industrial process of the pre-sodiation technology.

[0083] (3) By performing charge-discharge cycle tests on Example 3 ( Figure 2 abbreviated as UHC in the text) and Comparative Example 1 ( Figure 2 abbreviated as HC in the text), as Figure 2 shown. The first discharge specific capacity of UHC is 122.8 mA g -1 , and after 100 cycles, the capacity decays to 93 mA g -1 , and the capacity retention rate is 75.73%. The first discharge specific capacity of HC is 102.5 mA g -1 , and after 100 cycles, the capacity decays to 71.5 mA g -1 , and the capacity retention rate is 69.76%. The first discharge specific capacity of UHC is overall increased by 32.04% compared with that of HC, and the capacity retention rate of UHC is overall increased by 8.56% compared with that of HC. The above shows that the sodium-ion full battery assembled with the hard carbon electrode sheet after ultrasonic-enhanced pre-sodiation treatment not only has a large increase in the first discharge capacity, but also improves the overall cycle performance of the battery.

[0084] In the present invention, by introducing an external physical field to enhance the reaction efficiency of the system, the ultrasonic method is used to contact the pre-sodiation reagent with the deeper hard carbon negative electrode material in a short time, realizing the enhancement of mass transfer in the system, and at the same time improving the first Coulombic efficiency and cycle stability of the sodium-ion full battery. In the same time, the interfacial electrocatalytic effect caused by ultrasonic cavitation accelerates the electron transfer of the pre-sodiation reaction, further improving the first Coulombic efficiency of the full battery assembled with the hard carbon negative electrode after ultrasonic-assisted treatment.

[0085] The above is only an illustration of the best embodiment of the present invention, but it should not be construed as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to change. Any changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0086] 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 belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present 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 preparing an ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet, characterized in that: The following steps are involved: The mixture of the hard carbon negative electrode sheet and the pre-sodiumization reagent is immersed in ultrasound, cleaned, and dried to obtain an ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet.

2. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 1, characterized in that: The ultrasonic power is set to 40-100W and the operating frequency is 40-100KHz.

3. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 1, characterized in that: The soaking time is 30s-20min.

4. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 1, characterized in that: The heating temperature is 60-100°C and the heating time is 20-40 minutes.

5. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 1, characterized in that: The pre-sodium reagent is prepared by the following process: The polycyclic aromatic hydrocarbons are dissolved in a non-protonic polar solvent, and then metallic sodium is added and reacted under stirring to generate sodium polycyclic aromatic hydrocarbons, wherein the molar ratio of the polycyclic aromatic hydrocarbons to the sodium is 1:

1.

6. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 5, characterized in that: The stirring time is 12-24h.

7. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 5, characterized in that: The polycyclic aromatic hydrocarbons are selected from one or more of biphenyl, dimethylbiphenyl, naphthalene, dimethylnaphthalene, phenanthrene and anthracene; The aprotic solvent is selected from one or more of diethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, dimethyltetrahydrofuran, tetrahydropyran and N,N-dimethylformamide.

8. The method for preparing the ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet according to claim 1, characterized in that: Dissolve hard carbon, conductive carbon black and sodium carboxymethyl cellulose in water, mix well, then add styrene-butadiene rubber, mix well, and obtain negative electrode slurry; The negative electrode slurry is coated on the copper foil current collector and dried to obtain a hard carbon negative electrode sheet.

9. An ultrasonically enhanced pre-sodiumized hard carbon negative electrode sheet prepared according to the method according to any one of claims 1 to 8.

10. A sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, characterized in that: The negative electrode sheet adopts the ultrasonic enhanced pre-sodiumized hard carbon negative electrode sheet as described in any one of claims 1-8.

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