A hard-carbon negative electrode material for fast-charging sodium-ion batteries and a preparation method thereof

Abstract

The present application relates to the field of sodium ion battery, in particular to a kind of hard carbon negative material of fast charging sodium ion battery and preparation method thereof, for solving the shortcomings of existing hard carbon negative material of fast charging sodium ion battery, capacity is low, cycle performance is poor, limit the popularization of sodium ion battery in practical application problem;The present application can improve the conductivity and reaction kinetics of the material by doping nickel-cobalt metal oxide into nitrogen-containing hard carbon microspheres, thereby improving the theoretical capacity of the material, can significantly improve the charge-discharge rate of sodium ion battery, enhance the electrochemical performance of battery, and after being coated by composite gel structure, the structural stability of the material can be effectively improved, the volume change of the material in the cycle process is reduced, the cycle stability of sodium ion battery can be significantly improved, long cycle life and high capacity retention rate can be maintained while realizing fast charging, prolong the service life of battery.

Description

TECHNICAL FIELD

[0001] The application relates to the field of sodium ion batteries, in particular to a fast-charging sodium ion battery hard carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of new energy industries such as electric vehicles and energy storage power stations, the demand for high-performance, low-cost and long-life energy storage devices is increasing. Sodium ion batteries, due to their abundant resources and low cost, have become an important supplement to lithium ion batteries and play an increasingly important role in promoting energy transformation. As a key component of the battery, the performance of the negative electrode material directly affects the charging and discharging efficiency, capacity and cycle life of the battery. Hard carbon, as a potential negative electrode material for sodium ion batteries, has good safety and low cost advantages, but its electrochemical performance is not ideal, resulting in limited capacity and rate performance, which is difficult to meet the fast-charging demand. By loading other metal oxides into the hard carbon structure, the electrochemical performance can be adjusted, and the electrical conductivity and capacitance can be improved. However, the loading of metal oxides in the cycle process shows obvious volume expansion / contraction, which leads to the powdering of the electrode material structure, and the specific capacity of the battery also decreases rapidly, resulting in poor cycle performance.

[0003] Therefore, it is of great significance to develop a fast-charging sodium ion battery hard carbon negative electrode material with high capacity and excellent cycle stability and a preparation method thereof. SUMMARY

[0004] In order to overcome the above technical problems, the purpose of the present application is to provide a fast-charging sodium ion battery hard carbon negative electrode material and a preparation method thereof, which solves the problem of low capacity and poor cycle performance of the existing fast-charging sodium ion battery hard carbon negative electrode material, and limits the promotion of sodium ion batteries in practical applications.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] A preparation method of a fast-charging sodium ion battery hard carbon negative electrode material, comprising the following steps:

[0007] Step one: melamine and formaldehyde solution is added to a three-necked flask equipped with a stirrer, thermometer and gas inlet tube, and protected by nitrogen, stirred at a temperature of 20-25℃ and a stirring rate of 300-400r / min for 20-25min, then heated to a temperature of 60-65℃ and continued to stir for 2-3h, then polyvinyl alcohol, deionized water and anhydrous acetic acid are added and continued to stir for 1-1.5h, the reaction is completed, the reaction product is cooled to room temperature, then centrifuged, the precipitate is washed with distilled water and anhydrous ethanol for 2-3 times, then placed in a vacuum drying oven and dried at a temperature of 50-55℃ for 2-3h to obtain melamine formaldehyde resin;

[0008] Step two: the melamine formaldehyde resin and urea are mixed uniformly and placed in a tube furnace, protected by nitrogen, and calcined at a heating rate of 1-2℃ / min to 700-800℃ for 5-6h, then cooled in the furnace to obtain high-nitrogen hard carbon microspheres;

[0009] Step three: the high-nitrogen hard carbon microspheres and hydrochloric acid solution are added to a three-necked flask equipped with a stirrer and thermometer, and treated with ultrasonic power of 200-250W for 30-40min, then stirred at a temperature of 40-45℃ and a stirring rate of 300-400r / min for 2-3h, the reaction is completed, the reaction product is cooled to room temperature, then placed for 2-3h, then centrifuged, the precipitate is washed with distilled water for 2-3 times, then placed in a vacuum drying oven and dried at a temperature of 70-75℃ for 4-5h to obtain expanded hard carbon microspheres;

[0010] Step four: nickel nitrate hexahydrate, cobalt acetate tetrahydrate and deionized water are added to a three-necked flask equipped with a stirrer, thermometer, gas inlet tube and reflux condenser, and protected by nitrogen, stirred at a temperature of 20-25℃ and a stirring rate of 300-400r / min for 25-30min, then expanded hard carbon microspheres, polyvinylpyrrolidone and ethylenediamine are added and continued to stir for 5-10min, then heated to a temperature of 150-160℃ and continued to stir for 5-6h, the reaction is completed, the reaction product is cooled to room temperature, then centrifuged, the precipitate is washed with distilled water for 2-3 times, then placed in a vacuum drying oven and dried at a temperature of 80-85℃ for 6-8h, then placed in a tube furnace and calcined at a heating rate of 1-2℃ / min to 450-550℃ for 3-4h, then cooled in the furnace to obtain supported hard carbon microspheres;

[0011] Step five: sodium alginate, deionized water were added into a three-necked flask equipped with a stirrer, thermometer, gas inlet tube and constant pressure dropping funnel, and then nitrogen was introduced for protection, and then the reaction was stirred at a temperature of-5-0℃ and a stirring speed of 300-400r / min for 1-2h, and then calcium chloride solution was added and the reaction was stirred for 20-30min, and then the supported hard carbon microspheres, aniline and sodium dodecyl sulfate were added and the reaction was stirred for 40-50min, and then ammonium persulfate solution was added dropwise while stirring, and the dropping speed was controlled at 1-2 drops / s, and after the addition was completed, the reaction was stirred for 6-8h, and then freeze-drying was performed to obtain the hard carbon anode material for fast-charging sodium ion batteries.

[0012] As a further scheme of the present application: the amount ratio of the melamine, formaldehyde solution, polyvinyl alcohol, deionized water and anhydrous acetic acid in step one is 10-12g: 50-55mL: 2-5g: 100-120mL: 6-8mL.

[0013] As a further scheme of the present application: the mass fraction of the formaldehyde solution in step one is 37-40%.

[0014] As a further scheme of the present application: the amount ratio of the melamine formaldehyde resin, urea in step two is 10g: 0.3-1.9g.

[0015] As a further scheme of the present application: the amount ratio of the high-nitrogen hard carbon microspheres, hydrochloric acid solution in step three is 5g: 80-100mL.

[0016] As a further scheme of the present application: the mass fraction of the hydrochloric acid solution in step three is 5-15%.

[0017] As a further scheme of the present application: the amount ratio of the nickel nitrate hexahydrate, cobalt acetate tetrahydrate, deionized water, expanded hard carbon microspheres, polyvinylpyrrolidone and ethylenediamine in step four is 10mmol: 10mmol: 150-180mL: 8-10g: 0.1-0.15g: 0.2-0.6mL.

[0018] As a further scheme of the present application: the amount ratio of the sodium alginate, deionized water, calcium chloride solution, supported hard carbon microspheres, aniline, sodium dodecyl sulfate and ammonium persulfate solution in step five is 0.25-0.75g: 45-50mL: 20-30mL: 10g: 0.42-0.88g: 0.02-0.04g: 10-15mL.

[0019] As a further scheme of the present application: the molar concentration of the calcium chloride solution in step five is 0.2-0.6mol / L.

[0020] As a further scheme of the present application: the mass fraction of the ammonium persulfate solution is 1.5-2.5%.

[0021] As a further scheme of the present application: the hard carbon negative electrode material for fast-charging sodium ion battery is prepared according to the preparation method of the hard carbon negative electrode material for fast-charging sodium ion battery.

[0022] The beneficial effects of the present application are:

[0023] The hard carbon negative electrode material for fast-charging sodium ion battery and the preparation method thereof, through the nucleophilic addition reaction of melamine and formaldehyde, hydroxymethylated melamine is generated, then through polycondensation reaction, polymer is formed, melamine formaldehyde resin is obtained, then the melamine formaldehyde resin is mixed with urea and calcined, the nitrogen element content of the melamine formaldehyde resin is high, the nitrogen element content of the calcined hard carbon is high, and the nitrogen element is further doped in the hard carbon after calcination with urea, thereby increasing the active sites, improving the conductivity, obtaining high-nitrogen hard carbon microspheres, then the high-nitrogen hard carbon microspheres are treated with hydrochloric acid solution to remove impurities in the high-nitrogen hard carbon microspheres, which plays a pore expanding and pore increasing effect, and obtains pore expanded hard carbon microspheres, then uses nickel nitrate hexahydrate and cobalt acetate tetrahydrate as metal ions, which can load nickel and cobalt double metal oxides into the micropores and surface of the pore expanded hard carbon microspheres after calcination, and obtains supported hard carbon microspheres, finally, the supported hard carbon microspheres are treated with sodium alginate and aniline, the sodium alginate can occur complexation under the action of calcium chloride, the crosslinking degree is improved, and a large amount of calcium ions are introduced, the calcium ions can effectively improve the conductivity after dissociation, then the amino group in aniline and the active groups such as hydroxyl group and carboxyl group in sodium alginate interact through hydrogen bond, so that aniline is adsorbed on the surface of sodium alginate, then under the action of ammonium persulfate initiator, aniline is directly polymerized on the surface of sodium alginate to generate polyaniline, so that polyaniline and crosslinked sodium alginate can intertwine and form a three-dimensional network composite gel structure with high mechanical strength, which is coated on the surface of the supported hard carbon microspheres, and the hard carbon negative electrode material for fast-charging sodium ion battery is obtained.

[0024] The hard carbon negative electrode material for fast-charging sodium ion battery of the present application can improve the conductivity and reaction kinetics of the material by doping nickel-cobalt metal oxide into the nitrogen-containing hard carbon microspheres, thereby improving the theoretical capacity of the material, significantly improving the charge and discharge rate of the sodium ion battery, enhancing the electrochemical performance of the battery, and effectively improving the structural stability of the material after being coated with the composite gel structure, reducing the volume change of the material during the cycle process, thereby improving the cycle stability of the material and reducing the heat accumulation of the sodium ion battery during fast charging, which can significantly improve the cycle stability of the sodium ion battery, realize fast charging while maintaining a long cycle life and high capacity retention rate, and prolong the service life of the battery.

[0025] In summary, the hard carbon negative electrode material for fast-charging sodium ion batteries can greatly improve the comprehensive performance of sodium ion batteries when used in sodium ion batteries, thereby providing key material support for high-energy efficiency and faster-charging sodium ion batteries, meeting the urgent needs of modern portable electronic devices and electric vehicles for fast-charging and high-energy density batteries, and the preparation method is simple and easy to implement, has low cost, and is suitable for large-scale production. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] Embodiment 1

[0028] The present embodiment is a preparation method of a hard carbon negative electrode material for fast-charging sodium ion batteries, comprising the following steps:

[0029] Step one: 10g melamine and 50mL 37% mass fraction formaldehyde solution are added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, nitrogen is introduced for protection, stirring is carried out at a temperature of 20℃ and a stirring rate of 300r / min for 20min, then the temperature is raised to 60℃ and stirring is continued for 2h, then 2g polyvinyl alcohol, 100mL deionized water and 6mL anhydrous acetic acid are added and stirring is continued for 1h, after the reaction is completed, the reaction product is cooled to room temperature, then centrifugation is carried out, the precipitate is washed with distilled water and anhydrous ethanol for 2 times respectively, then it is placed in a vacuum drying oven and dried at a temperature of 50℃ for 2h, thereby obtaining melamine formaldehyde resin;

[0030] Step two: 10g melamine formaldehyde resin and 0.3g urea are uniformly mixed and placed in a tube furnace, nitrogen is introduced for protection, and the temperature is raised to 700℃ at a temperature raising rate of 1℃ / min and calcined for 5h, then the furnace is cooled, thereby obtaining high-nitrogen hard carbon microspheres;

[0031] Step three: 5g high-nitrogen hard carbon microspheres and 80mL 5% mass fraction hydrochloric acid solution are added to a three-necked flask equipped with a stirrer and a thermometer, ultrasonic treatment is carried out at an ultrasonic power of 200W for 30min, then stirring is carried out at a temperature of 40℃ and a stirring rate of 300r / min for 2h, after the reaction is completed, the reaction product is cooled to room temperature, then it is left to stand for 2h, then centrifugation is carried out, the precipitate is washed with distilled water for 2 times, then it is placed in a vacuum drying oven and dried at a temperature of 70℃ for 4h, thereby obtaining expanded hard carbon microspheres;

[0032] Step four: 10 mmol of nickel nitrate hexahydrate, 10 mmol of cobalt acetate tetrahydrate and 150 mL of deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a reflux condenser, protected by nitrogen, stirred at a temperature of 20 DEG C and a stirring rate of 300 r / min for 25 min, then 8 g of the hard carbon microspheres, 0.1 g of polyvinylpyrrolidone and 0.2 mL of ethylenediamine were added and the stirring was continued for 5 min, then the temperature was raised to 150 DEG C and the stirring was continued for 5 h, after the reaction was completed, the reaction product was cooled to room temperature, then centrifuged, the precipitate was washed with distilled water for 2 times, then placed in a vacuum drying oven and dried at a temperature of 80 DEG C for 6 h, then placed in a tube furnace and calcined at a temperature of 450 DEG C with a temperature rising rate of 1 DEG C / min for 3 h, then cooled with the furnace, to obtain the supported hard carbon microspheres;

[0033] Step five: 0.25 g of sodium alginate and 45 mL of deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a constant pressure dropping funnel, protected by nitrogen, stirred at a temperature of -5 DEG C and a stirring rate of 300 r / min for 1 h, then 20 mL of a 0.2 mol / L calcium chloride solution was added and the stirring was continued for 20 min, then 10 g of the supported hard carbon microspheres, 0.42 g of aniline and 0.02 g of sodium dodecyl sulfate were added and the stirring was continued for 40 min, then 10 mL of a 1.5% ammonium persulfate solution was added dropwise while stirring, the dropping rate was controlled at 1 drop / s, after the dropping was completed, the stirring was continued for 6 h, then freeze-dried, to obtain the hard carbon anode material for fast-charging sodium ion batteries.

[0034] Example 2:

[0035] The present embodiment is a preparation method of a hard carbon anode material for fast-charging sodium ion batteries, comprising the following steps:

[0036] Step one: 11 g of melamine and 52 mL of a 39% formaldehyde solution were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, protected by nitrogen, stirred at a temperature of 22 DEG C and a stirring rate of 350 r / min for 22 min, then the temperature was raised to 62 DEG C and the stirring was continued for 2.5 h, then 4 g of polyvinyl alcohol, 110 mL of deionized water and 7 mL of anhydrous acetic acid were added and the stirring was continued for 1.2 h, after the reaction was completed, the reaction product was cooled to room temperature, then centrifuged, the precipitate was washed with distilled water and anhydrous ethanol for 2 times, respectively, then placed in a vacuum drying oven and dried at a temperature of 52 DEG C for 2.5 h, to obtain the melamine formaldehyde resin;

[0037] Step two: 10 g melamine formaldehyde resin and 1.1 g urea were mixed uniformly and placed in a tube furnace, nitrogen was introduced for protection, and the temperature was raised to 750℃ at a rate of 1.5℃ / min for calcination for 5.5 h, and then the furnace was cooled down to obtain high-nitrogen hard carbon microspheres;

[0038] Step three: 5 g high-nitrogen hard carbon microspheres and 90 mL 10% hydrochloric acid solution were added to a three-necked flask equipped with a stirrer and a thermometer, and ultrasonic treatment was carried out at an ultrasonic power of 225 W for 35 min, then stirring was carried out at a temperature of 42℃ and a stirring rate of 350 r / min for 2.5 h, after the reaction was completed, the reaction product was cooled to room temperature, then it was left to stand for 2.5 h, then it was centrifuged, the precipitate was washed with distilled water for 2 times, then it was placed in a vacuum drying oven and dried at a temperature of 72℃ for 4.5 h to obtain hard carbon microspheres with pore expansion;

[0039] Step four: 10 mmol nickel nitrate hexahydrate, 10 mmol cobalt acetate tetrahydrate and 165 mL deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a reflux condenser, nitrogen was introduced for protection, stirring was carried out at a temperature of 22℃ and a stirring rate of 350 r / min for 28 min, then 9 g hard carbon microspheres with pore expansion, 0.12 g polyvinylpyrrolidone and 0.4 mL ethylenediamine were added and stirring was continued for 9 min, then the temperature was raised to 155℃ and stirring was continued for 5.5 h, after the reaction was completed, the reaction product was cooled to room temperature, then it was centrifuged, the precipitate was washed with distilled water for 2 times, then it was placed in a vacuum drying oven and dried at a temperature of 82℃ for 7 h, then it was placed in a tube furnace and calcined at a rate of 1.5℃ / min to 500℃ for 3.5 h, and then the furnace was cooled down to obtain supported hard carbon microspheres;

[0040] Step five: 0.5 g sodium alginate and 48 mL deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a constant pressure dropping funnel, nitrogen was introduced for protection, stirring was carried out at a temperature of -3℃ and a stirring rate of 350 r / min for 1.5 h, then 25 mL calcium chloride solution with a molar concentration of 0.4 mol / L was added and stirring was continued for 25 min, then 10 g supported hard carbon microspheres, 0.65 g aniline and 0.03 g sodium dodecyl sulfate were added and stirring was continued for 45 min, then 12 mL 2% ammonium persulfate solution was added dropwise while stirring, the dropping rate was controlled at 1 drop / s, after the addition was completed, stirring was continued for 7 h, and then freeze-drying was carried out to obtain hard carbon negative electrode material for fast-charging sodium ion batteries.

[0041] Example 3:

[0042] The embodiment is a preparation method of a hard carbon negative material for a fast-charging sodium ion battery, including the following steps.

[0043] Step one: 12g melamine and 55mL formaldehyde solution with a mass fraction of 40% are added into a three-necked flask equipped with a stirrer, a thermometer and a gas inlet pipe, nitrogen is introduced for protection, stirring is carried out at a temperature of 25℃ and a stirring speed of 400r / min for 25min, then the temperature is increased to 65℃, and the stirring is continued for 3h, then 5g polyvinyl alcohol, 120mL deionized water and 8mL anhydrous acetic acid are added, and the stirring is continued for 1.5h, after the reaction is completed, the reaction product is cooled to room temperature, then centrifugation is carried out, the precipitate is washed with distilled water and anhydrous ethanol for three times, then it is placed in a vacuum drying box, dried at a temperature of 55℃ for 3h, and melamine formaldehyde resin is obtained;

[0044] Step two: 10g melamine formaldehyde resin and 1.9g urea are uniformly mixed and placed in a tube furnace, nitrogen is introduced for protection, and the temperature is increased to 800℃ at a temperature increasing rate of 2℃ / min for calcination for 6h, then the furnace is cooled, and high-nitrogen hard carbon microspheres are obtained;

[0045] Step three: 5g high-nitrogen hard carbon microspheres and 100mL hydrochloric acid solution with a mass fraction of 15% are added into a three-necked flask equipped with a stirrer and a thermometer, ultrasonic treatment is carried out at an ultrasonic power of 250W for 40min, then stirring is carried out at a temperature of 45℃ and a stirring speed of 400r / min for 3h, after the reaction is completed, the reaction product is cooled to room temperature, then it is placed for 3h, then centrifugation is carried out, the precipitate is washed with distilled water for three times, then it is placed in a vacuum drying box, dried at a temperature of 75℃ for 5h, and hole-expanding hard carbon microspheres are obtained;

[0046] Step four: 10mmol nickel nitrate hexahydrate, 10mmol cobalt acetate tetrahydrate and 180mL deionized water are added into a three-necked flask equipped with a stirrer, a thermometer, a gas inlet pipe and a reflux condenser, nitrogen is introduced for protection, stirring is carried out at a temperature of 25℃ and a stirring speed of 400r / min for 30min, then 10g hole-expanding hard carbon microspheres, 0.15g polyvinylpyrrolidone and 0.6mL ethylenediamine are added, and the stirring is continued for 10min, then the temperature is increased to 160℃, and the stirring is continued for 6h, after the reaction is completed, the reaction product is cooled to room temperature, then centrifugation is carried out, the precipitate is washed with distilled water for three times, then it is placed in a vacuum drying box, dried at a temperature of 85℃ for 8h, then it is placed in a tube furnace, the temperature is increased to 550℃ at a temperature increasing rate of 2℃ / min for calcination for 4h, then the furnace is cooled, and supported hard carbon microspheres are obtained;

[0047] Step five: 0.75 g of sodium alginate, 50 mL of deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a constant pressure dropping funnel, protected by nitrogen, stirred at a temperature of 0 ℃ and a stirring rate of 400 r / min for 2 h, then 30 mL of 0.6 mol / L calcium chloride solution was added and stirred for 30 min, then 10 g of supported hard carbon microspheres, 0.88 g of aniline and 0.04 g of sodium dodecyl sulfate were added and stirred for 50 min, then 15 mL of 2.5% ammonium persulfate solution was added dropwise while stirring, the dropping rate was controlled at 2 drops / s, after the addition was completed, the reaction was continued for 8 h, then freeze-drying was carried out to obtain the hard carbon anode material for fast-charging sodium ion batteries.

[0048] Comparative example 1:

[0049] The present comparative example is a preparation method of a hard carbon anode material for fast-charging sodium ion batteries, comprising the following steps:

[0050] Step one: 12 g of melamine and 55 mL of 40% formaldehyde solution were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, protected by nitrogen, stirred at a temperature of 25 ℃ and a stirring rate of 400 r / min for 25 min, then heated to a temperature of 65 ℃ and stirred for 3 h, then 5 g of polyvinyl alcohol, 120 mL of deionized water and 8 mL of anhydrous acetic acid were added and stirred for 1.5 h, after the reaction was completed, the reaction product was cooled to room temperature, then centrifuged, the precipitate was washed with distilled water and anhydrous ethanol for 3 times, then placed in a vacuum drying oven and dried at a temperature of 55 ℃ for 3 h to obtain melamine formaldehyde resin.

[0051] Step two: 10 g of melamine formaldehyde resin was uniformly mixed and placed in a tube furnace, protected by nitrogen, and heated to 800 ℃ at a heating rate of 2 ℃ / min for 6 h, then cooled in the furnace to obtain the hard carbon anode material for fast-charging sodium ion batteries.

[0052] Comparative example 2:

[0053] The present comparative example is a preparation method of a hard carbon anode material for fast-charging sodium ion batteries, comprising the following steps:

[0054] Step one: 12 g of melamine and 55 mL of formaldehyde solution with a mass fraction of 40% were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube, and then stirred at a temperature of 25°C and a stirring rate of 400 r / min for 25 min under the protection of nitrogen, and then stirred at a temperature of 65°C for 3 h, and then 5 g of polyvinyl alcohol, 120 mL of deionized water, and 8 mL of anhydrous acetic acid were added and stirred for 1.5 h, and then the reaction product was cooled to room temperature, and then centrifuged, and the precipitate was washed with distilled water and anhydrous ethanol for three times, and then placed in a vacuum drying oven and dried at a temperature of 55°C for 3 h, to obtain melamine formaldehyde resin;

[0055] Step two: 10 g of melamine formaldehyde resin and 1.9 g of urea were uniformly mixed and placed in a tube furnace, and then calcined at a temperature of 800°C for 6 h under the protection of nitrogen and at a temperature increasing rate of 2°C / min, and then cooled with the furnace, to obtain the hard carbon negative electrode material for fast-charging sodium ion batteries.

[0056] Comparative Example 3

[0057] The present comparative example is a preparation method of a hard carbon negative electrode material for fast-charging sodium ion batteries, comprising the following steps:

[0058] Step one: 12 g of melamine and 55 mL of formaldehyde solution with a mass fraction of 40% were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas inlet tube, and then stirred at a temperature of 25°C and a stirring rate of 400 r / min for 25 min under the protection of nitrogen, and then stirred at a temperature of 65°C for 3 h, and then 5 g of polyvinyl alcohol, 120 mL of deionized water, and 8 mL of anhydrous acetic acid were added and stirred for 1.5 h, and then the reaction product was cooled to room temperature, and then centrifuged, and the precipitate was washed with distilled water and anhydrous ethanol for three times, and then placed in a vacuum drying oven and dried at a temperature of 55°C for 3 h, to obtain melamine formaldehyde resin;

[0059] Step two: 10 g of melamine formaldehyde resin and 1.9 g of urea were uniformly mixed and placed in a tube furnace, and then calcined at a temperature of 800°C for 6 h under the protection of nitrogen and at a temperature increasing rate of 2°C / min, and then cooled with the furnace, to obtain the hard carbon negative electrode material for fast-charging sodium ion batteries.

[0060] Step three: 5 g high-nitrogen hard carbon microspheres, 100 mL 15% hydrochloric acid solution were added to a three-necked flask equipped with a stirrer, a thermometer, and an ultrasonic generator, and then ultrasonic treatment was carried out at an ultrasonic power of 250 W for 40 min. After that, the reaction was stirred at a temperature of 45 ℃ and a stirring rate of 400 r / min for 3 h. After the reaction was completed, the reaction product was cooled to room temperature, and then was left to stand for 3 h. After that, the precipitate was washed with distilled water for 3 times, and then was placed in a vacuum drying oven and dried at a temperature of 75 ℃ for 5 h to obtain the expanded hard carbon microspheres;

[0061] Step four: 10 mmol of nickel nitrate hexahydrate and 180 mL of deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a reflux condenser, and then nitrogen protection was carried out. The reaction was stirred at a temperature of 25 ℃ and a stirring rate of 400 r / min for 30 min. After that, 10 g of the expanded hard carbon microspheres, 0.15 g of polyvinylpyrrolidone and 0.6 mL of ethylenediamine were added and the reaction was continued to be stirred for 10 min. After that, the temperature was increased to 160 ℃ and the reaction was continued to be stirred for 6 h. After the reaction was completed, the reaction product was cooled to room temperature, and then was centrifuged. The precipitate was washed with distilled water for 3 times, and then was placed in a vacuum drying oven and dried at a temperature of 85 ℃ for 8 h. After that, it was placed in a tube furnace and calcined at 550 ℃ for 4 h at a temperature increasing rate of 2 ℃ / min. After that, it was cooled with the furnace to obtain the supported hard carbon microspheres, thereby obtaining the hard carbon negative electrode material for fast-charging sodium ion batteries.

[0062] Comparative example 4:

[0063] The present comparative example is a preparation method of a hard carbon negative electrode material for fast-charging sodium ion batteries, which comprises the following steps:

[0064] Step one: 12 g of melamine and 55 mL of 40% formaldehyde solution were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, and then nitrogen protection was carried out. The reaction was stirred at a temperature of 25 ℃ and a stirring rate of 400 r / min for 25 min. After that, the temperature was increased to 65 ℃ and the reaction was continued to be stirred for 3 h. After that, 5 g of polyvinyl alcohol, 120 mL of deionized water and 8 mL of anhydrous acetic acid were added and the reaction was continued to be stirred for 1.5 h. After the reaction was completed, the reaction product was cooled to room temperature, and then was centrifuged. The precipitate was washed with distilled water and anhydrous ethanol for 3 times, respectively, and then was placed in a vacuum drying oven and dried at a temperature of 55 ℃ for 3 h to obtain the melamine formaldehyde resin;

[0065] Step two: 10 g of the melamine formaldehyde resin and 1.9 g of urea were uniformly mixed and then were placed in a tube furnace. Nitrogen protection was carried out, and the temperature was increased to 800 ℃ at a temperature increasing rate of 2 ℃ / min and then was calcined for 6 h. After that, it was cooled with the furnace to obtain the high-nitrogen hard carbon microspheres.

[0066] Step three: 5 g high-nitrogen hard carbon microspheres, 100 mL of 15% hydrochloric acid solution were added to a three-necked flask equipped with a stirrer, a thermometer, and an ultrasonic power of 250 W was treated for 40 min, then stirred at a temperature of 45 ℃ and a stirring rate of 400 r / min for 3 h, after the reaction was completed, the reaction product was cooled to room temperature, then stood for 3 h, then centrifuged, the precipitate was washed with distilled water for 3 times, then placed in a vacuum drying oven, dried at a temperature of 75 ℃ for 5 h, to obtain the reamed hard carbon microspheres;

[0067] Step four: 10 mmol of nickel nitrate hexahydrate, 10 mmol of cobalt acetate tetrahydrate and 180 mL of deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a reflux condenser, and protected by nitrogen, stirred at a temperature of 25 ℃ and a stirring rate of 400 r / min for 30 min, then 10 g of reamed hard carbon microspheres, 0.15 g of polyvinylpyrrolidone and 0.6 mL of ethylenediamine were added and continued to stir for 10 min, then heated to 160 ℃ and continued to stir for 6 h, after the reaction was completed, the reaction product was cooled to room temperature, then centrifuged, the precipitate was washed with distilled water for 3 times, then placed in a vacuum drying oven, dried at a temperature of 85 ℃ for 8 h, then placed in a tube furnace, heated to 550 ℃ at a heating rate of 2 ℃ / min and calcined for 4 h, then cooled with the furnace, to obtain the fast-charging sodium-ion battery hard carbon negative electrode material.

[0068] Comparative example 5:

[0069] The present comparative example is a preparation method of a fast-charging sodium-ion battery hard carbon negative electrode material, comprising the following steps:

[0070] Step one: 12 g of melamine and 55 mL of 40% formaldehyde solution were added to a three-necked flask equipped with a stirrer, a thermometer and a gas inlet tube, protected by nitrogen, stirred at a temperature of 25 ℃ and a stirring rate of 400 r / min for 25 min, then heated to a temperature of 65 ℃ and continued to stir for 3 h, then 5 g of polyvinyl alcohol, 120 mL of deionized water and 8 mL of anhydrous acetic acid were added and continued to stir for 1.5 h, after the reaction was completed, the reaction product was cooled to room temperature, then centrifuged, the precipitate was washed with distilled water and anhydrous ethanol for 3 times, then placed in a vacuum drying oven, dried at a temperature of 55 ℃ for 3 h, to obtain the melamine formaldehyde resin;

[0071] Step two: 10 g melamine formaldehyde resin and 1.9 g urea were mixed uniformly and placed in a tube furnace, nitrogen was introduced for protection, and the temperature was raised to 800℃ at a rate of 2℃ / min for calcination of 6 h, and then the furnace was cooled down to obtain high-nitrogen hard carbon microspheres;

[0072] Step three: 5 g high-nitrogen hard carbon microspheres and 100 mL 15% hydrochloric acid solution were added to a three-necked flask equipped with a stirrer and a thermometer, and then ultrasonic treatment was performed at an ultrasonic power of 250 W for 40 min, and then stirring was performed at a temperature of 45℃ and a stirring rate of 400 r / min for 3 h, and then the reaction product was cooled to room temperature, and then was left to stand for 3 h, and then was centrifuged, and then the precipitate was washed with distilled water for 3 times, and then was placed in a vacuum drying oven and dried at a temperature of 75℃ for 5 h to obtain hard carbon microspheres with pore expansion;

[0073] Step four: 10 mmol nickel nitrate hexahydrate, 10 mmol cobalt acetate tetrahydrate and 180 mL deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a reflux condenser, and then nitrogen was introduced for protection, and then stirring was performed at a temperature of 25℃ and a stirring rate of 400 r / min for 30 min, and then 10 g hard carbon microspheres with pore expansion, 0.15 g polyvinylpyrrolidone and 0.6 mL ethylenediamine were added and stirring was continued for 10 min, and then the temperature was raised to 160℃ and stirring was continued for 6 h, and then the reaction product was cooled to room temperature, and then was centrifuged, and then the precipitate was washed with distilled water for 3 times, and then was placed in a vacuum drying oven and dried at a temperature of 85℃ for 8 h, and then was placed in a tube furnace and calcined at a rate of 2℃ / min to 550℃ for 4 h, and then the furnace was cooled down to obtain supported hard carbon microspheres;

[0074] Step five: 0.75 g sodium alginate and 50 mL deionized water were added to a three-necked flask equipped with a stirrer, a thermometer, a gas inlet tube and a constant pressure dropping funnel, and then nitrogen was introduced for protection, and then stirring was performed at a temperature of 0℃ and a stirring rate of 400 r / min for 2 h, and then 10 g supported hard carbon microspheres, 0.88 g aniline and 0.04 g sodium dodecyl sulfate were added and stirring was continued for 50 min, and then 15 mL 2.5% ammonium persulfate solution was added dropwise while stirring, and the dropping rate was controlled at 2 drops / s, and after the addition was completed, stirring was continued for 8 h, and then freeze-drying was performed to obtain a hard carbon negative electrode material for fast-charging sodium ion batteries.

[0075] The hard carbon negative electrode material of the fast-charging sodium ion battery of examples 1-3 and comparative examples 1-5, conductive carbon black and PVDF binder were mixed in a mass ratio of 7:2:1, then added into N-methyl pyrrolidone to form a slurry, then the obtained slurry was scraped on the surface of a copper foil, and then dried, cut, pressed and vacuum dried to obtain a negative electrode sheet, and a CR2016 button cell was assembled in a glove box with a metal sodium sheet as a positive electrode sheet, 1M NaPF6-EC / DMC (v / v, 1:1) as an electrolyte, and Celgard 2400 as a separator, and the electrochemical performance test was carried out at 0.1A / g after the battery was placed for 24h, and the test results are shown in the following table:

[0076]

[0077] Referring to the data in the above table, it can be seen that the hard carbon negative electrode material of the fast-charging sodium ion battery of the application has excellent capacity and excellent cycle stability;

[0078] According to the comparison between comparative example 1 and comparative example 2, it can be seen that the addition of urea can further dope N elements, thereby improving the capacity of the hard carbon negative electrode material of the fast-charging sodium ion battery;

[0079] According to the comparison between comparative example 2 and comparative example 3, it can be seen that after using hydrochloric acid solution to expand the high-nitrogen hard carbon microspheres, doping nickel-based metal oxides into them can further improve the capacity of the hard carbon negative electrode material of the fast-charging sodium ion battery; but the doping of nickel-based metal oxides is prone to volume expansion, resulting in poor cycle stability;

[0080] According to the comparison between comparative example 3 and comparative example 4, it can be seen that after using hydrochloric acid solution to expand the high-nitrogen hard carbon microspheres, doping nickel, cobalt-based bimetallic oxides into them can further improve the capacity of the hard carbon negative electrode material of the fast-charging sodium ion battery; but the doping of nickel-based metal oxides is prone to volume expansion, resulting in poor cycle stability;

[0081] According to the comparison between comparative example 4 and comparative example 5, it can be seen that after being wrapped with a sodium alginate, polyaniline cross-linked network composite gel formed by sodium alginate and aniline, the volume expansion of the metal oxide is inhibited, which can greatly improve the cycle stability of the hard carbon negative electrode material of the fast-charging sodium ion battery;

[0082] According to the comparison between example 3 and comparative example 5, it can be seen that the use of calcium chloride solution can improve the conductivity of the composite gel, thereby further improving the capacity of the hard carbon negative electrode material of the fast-charging sodium ion battery.

[0083] In the description of the specification, reference to terms "one embodiment", "an example", "a specific example" and so on is intended to indicate that a particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. Descriptive expressions of the above terms in the specification do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0084] The above is only an example and illustration of the application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways, as long as they do not deviate from the application or exceed the scope defined by the claims.

Claims

1. A method for preparing a hard carbon anode material for a fast-charging sodium-ion battery, characterized in that, Includes the following steps: Step 1: Add melamine and formaldehyde solution to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and stir at 20-25℃ and 300-400 r / min for 20-25 min. Then raise the temperature to 60-65℃ and continue stirring for 2-3 h. Add polyvinyl alcohol, deionized water, and anhydrous acetic acid and continue stirring for 1-1.5 h. After the reaction is complete, cool the reaction product to room temperature and centrifuge. Wash the precipitate 2-3 times with distilled water and anhydrous ethanol. Then place it in a vacuum drying oven and dry at 50-55℃ for 2-3 h to obtain melamine-formaldehyde resin. Step 2: After the melamine-formaldehyde resin and urea are mixed evenly, they are placed in a tube furnace, nitrogen gas is introduced for protection, and the temperature is raised to 700-800℃ for 5-6 hours at a heating rate of 1-2℃ / min. After that, the furnace is cooled to obtain high nitrogen hard carbon microspheres. Step 3: Add high-nitrogen hard carbon microspheres and hydrochloric acid solution to a three-necked flask equipped with a stirrer and thermometer. Sonicate the mixture for 30-40 minutes at an ultrasonic power of 200-250W. Then stir the mixture at a temperature of 40-45℃ and a stirring rate of 300-400r / min for 2-3 hours. After the reaction is complete, cool the reaction product to room temperature and let it stand for 2-3 hours. Then centrifuge the product and wash the precipitate 2-3 times with distilled water. Then place the product in a vacuum drying oven and dry it at a temperature of 70-75℃ for 4-5 hours to obtain expanded pore hard carbon microspheres. Step 4: Add nickel nitrate hexahydrate, cobalt acetate tetrahydrate, and deionized water to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and reflux condenser. Purge with nitrogen for protection and stir for 25-30 minutes at 20-25℃ and a stirring rate of 300-400 r / min. Then add expanded pore hard carbon microspheres, polyvinylpyrrolidone, and ethylenediamine and continue stirring for 5-10 minutes. Then raise the temperature to 150-160℃ and continue stirring for 5-6 hours. After the reaction is complete, cool the reaction product to room temperature, centrifuge, wash the precipitate 2-3 times with distilled water, and then place it in a vacuum drying oven at 80-85℃ for 6-8 hours. Then place it in a tube furnace and calcine at 450-550℃ at a heating rate of 1-2℃ / min for 3-4 hours. Then cool with the furnace to obtain supported hard carbon microspheres. Step 5: Add sodium alginate and deionized water to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and constant pressure dropping funnel. Purge with nitrogen for protection and stir for 1-2 hours at a temperature of -5 to 0℃ and a stirring rate of 300-400 r / min. Then add calcium chloride solution and continue stirring for 20-30 minutes. Next, add supported hard carbon microspheres, aniline, and sodium dodecyl sulfate and continue stirring for 40-50 minutes. Then, add ammonium persulfate solution dropwise while stirring, controlling the dropping rate to 1-2 drops / s. After the addition is complete, continue stirring for 6-8 hours. Finally, freeze-dry to obtain the hard carbon anode material for fast-charging sodium-ion batteries.

2. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, The ratio of melamine, formaldehyde solution, polyvinyl alcohol, deionized water and anhydrous acetic acid used in step one is 10-12g: 50-55mL: 2-5g: 100-120mL: 6-8mL.

3. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, The formaldehyde solution in step one has a mass fraction of 37-40%.

4. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, In step two, the ratio of melamine-formaldehyde resin to urea is 10g:0.3-1.9g.

5. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, In step three, the ratio of the high-nitrogen hard carbon microspheres to the hydrochloric acid solution is 5g:80-100mL.

6. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, The hydrochloric acid solution in step three has a mass fraction of 5-15%.

7. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, In step four, the ratio of nickel nitrate hexahydrate, cobalt acetate tetrahydrate, deionized water, expanded pore hard carbon microspheres, polyvinylpyrrolidone, and ethylenediamine is 10 mmol: 10 mmol: 150-180 mL: 8-10 g: 0.1-0.15 g: 0.2-0.6 mL.

8. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, In step five, the ratio of sodium alginate, deionized water, calcium chloride solution, supported hard carbon microspheres, aniline, sodium dodecyl sulfate, and ammonium persulfate solution is 0.25-0.75g: 45-50mL: 20-30mL: 10g: 0.42-0.88g: 0.02-0.04g: 10-15mL.

9. The method for preparing a hard carbon anode material for a fast-charging sodium-ion battery according to claim 1, characterized in that, The molar concentration of the calcium chloride solution in step five is 0.2-0.6 mol / L; the mass fraction of the ammonium persulfate solution is 1.5-2.5%.

10. A hard carbon anode material for fast-charging sodium-ion batteries, characterized in that, The fast-charging sodium-ion battery hard carbon anode material is prepared by the method described in any one of claims 1-9.

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