Heteroatom-doped hard carbon negative electrode material, preparation method and application

Abstract

The invention provides a heteroatom-doped hard carbon negative electrode material, a preparation method and application, and belongs to the technical field of electrode materials. The preparation method of the heteroatom-doped hard carbon negative electrode material comprises the following steps: (1) uniformly mixing and dissolving a hard carbon material and a heteroatom reagent in a solvent, and then sequentially carrying out ultrasonic dispersion and stirring to obtain a dispersion solution; and (2) placing the dispersion solution in a microwave reactor, carrying out a heating reaction, and drying to obtain the heteroatom-doped hard carbon negative electrode material. According to the method, the heteroatom doping of the hard carbon material is quickly and efficiently realized by utilizing microwaves, the reaction speed is high, the process is simple, the reaction temperature is low, the equipment investment is small, the cost is low, and large-scale industrial production can be met. Compared with commercial hard carbon, the hard carbon material subjected to microwave doping treatment has higher specific capacity and rate capability, and the sodium ion battery assembled by adopting the hard carbon material has better first charge specific capacity, first discharge specific capacity and first effect.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and particularly relates to a heteroatom-doped hard carbon anode material, a preparation method and an application thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high capacity and long cycle life, and have a large application market in the fields of large-scale energy storage and power batteries. However, lithium resources have problems such as limited reserves, uneven distribution and high production costs. Sodium resources have rich reserves, uniform distribution and low development prices, and the two elements of sodium and lithium have similar physical and chemical properties and electrochemical behaviors. Therefore, sodium-ion batteries have better development prospects in various types of energy storage scenarios.

[0003] With the in-depth development of the anode materials for sodium-ion batteries, it has been found that hard carbon has advantages such as rich raw materials, low cost and relatively stable structure, which makes it the primary anode material in the field of sodium-ion batteries. However, commercially available hard carbon produced on a large scale at present is difficult to meet the electrochemical performance requirements of the anode materials for sodium-ion batteries, showing low specific capacity and poor rate performance. Therefore, there is an urgent need for a rapid and efficient process method to improve the specific capacity and rate performance of commercially available hard carbon, which will further promote the large-scale commercial application of hard carbon materials.

[0004] Using heteroatom doping (such as N, P, S, etc.) can change the defects and interlayer spacing of hard carbon to provide more active sites, promote electron conductivity and diffusion kinetics, and finally obtain more excellent electrochemical performance.

[0005] The prior art records that N, S-doped carbon was synthesized by a simple one-step high-temperature pyrolysis method using walnut shell as raw material (Li Q, Zhang Y N, Feng S, et al. N,S self-doped porous carbon with enlarged interlayer distance as anode for high-performance Sodium ion batteries. Int J Energy Res, 2021, 45(5): 7082.), and the reversible specific capacity was only 182 mAh / g after 1500 charge-discharge cycles at a current density of 1000 mA / g, but its rate performance was poor.

[0006] The hard carbon spherical structure prepared by the emulsion method and high-temperature pyrolysis with (NH4)2HPO4 as the nitrogen dopant (J Zhang, J Duan, Y Zhang, et al. Facile Synthesis of N,P-codoped Hard Carbon Nanoporous Microspheres from Lignin for High-Performance Anodes of Sodium-Ion Batteries. ChemElectroChem, 2021, 8(18): 3544-3552.) has an extremely low nitrogen content. The interplanar spacing of the (002) crystal plane is only 0.375 nm, and the charge-discharge specific capacity is only 100 mAh / g at a current density of 800 mA / g. The charge-discharge cycle stability is poor because the insertion and extraction of sodium ions with a large ionic radius damage the internal microstructure of the hard carbon, resulting in a loss of reversible capacity.

[0007] The patent with the application number 202311615951.5 uses saccharide substances as precursors to construct a porous carbon nanosheet structure by igniting the carbon source, heteroatom dopant, and structure regulator, and utilizes the high temperature of the flame to generate a large number of active sites to form N, S, O heteroatom-doped hard carbon.

[0008] The patent with the application number 202310301037.7 mixes rosin, nitrogen source, metal salt, alkali metal hydroxide, and solvent and carbonizes them at a high temperature of 600-900 °C to obtain a rosin-based nitrogen-doped porous hard carbon material.

[0009] The patent with the application number 202211676320.X selects biomass materials and organic carbon sources as raw materials. Through two high-temperature calcinations, the iron, cobalt, and nickel elements further catalyze the biomass precursor materials to form a composite biomass hard carbon material with organic hard carbon coated on biomass hard carbon. The biomass hard carbon inhibits the side reaction between biomass carbon and electrolyte by coating organic carbon on the surface, removes the residual metal on the surface by acid treatment, and further dopes boron, sulfur, phosphorus, and nitrogen elements on the surface through microwave treatment to improve its conductivity.

[0010] The above methods are all preparation methods of heteroatom-doped hard carbon materials, but there are also some deficiencies. For example, the reaction temperature required for the synthesis of element-doped hard carbon materials is high, there are many additives used, the process conditions are complex, and the required equipment is relatively expensive. In addition to the above patents, there are also many preparation methods of doped hard carbon materials. These methods are time-consuming and costly in the actual doping process, and the electrochemical performance of the finally obtained electrode materials tested is not ideal, and the preparation yield is low. Summary of the Invention

[0011] In view of this, the present invention provides a heteroatom-doped hard carbon negative electrode material and a preparation method thereof, and a sodium ion battery is prepared by using the same. The hard carbon material prepared by the present invention has greatly improved specific capacity and rate performance, and the preparation method is simple and can be mass-produced.

[0012] To achieve the above object, the present invention adopts the following technical solutions.

[0013] A preparation method of a heteroatom-doped hard carbon negative electrode material includes the following steps:

[0014] (1) Mix the hard carbon material and the heteroatom reagent evenly, dissolve them in a solvent, and then perform ultrasonic dispersion and stirring in sequence to obtain a dispersion solution;

[0015] (2) Place the dispersion solution in a microwave reactor, carry out a heating reaction, and obtain a heteroatom-doped hard carbon negative electrode material after drying;

[0016] The heteroatom reagent is at least one of a nitrogen source, a sulfur source, a phosphorus source, a boron source, an oxygen source, and a fluorine source; the mass ratio of the hard carbon material to the heteroatom reagent is 0.1-1:0.1-7.

[0017] Preferably, the nitrogen source is one or more of thiourea, nitric acid, melamine, and ammonium hydrogen phosphate; the sulfur source is one or more of thiourea, dimethyl sulfoxide (DMSO), nano sulfur powder, and urea; the phosphorus source is one or more of phytic acid and phosphoric acid; the boron source is one or more of boric acid and ammonium pentaborate tetrahydrate; the oxygen source is one or more of sodium carbonate, sodium bicarbonate, hydrogen peroxide, and sodium perchlorate; the fluorine source is one or more of 2,3,5,6-tetrafluoro-4-benzoic acid, hydrofluoric acid, sodium fluoride, and tetrafluoro terephthalic acid.

[0018] The heteroatom in the present invention can also be a metal element, and the metal element includes one or more of Sn, Ni, Sb, Zn, and Zr; when the heteroatom is a metal, the heteroatom reagent is one or more of oxides (SnO2, NiO, Sb2O3, Sb2O5, ZnO, ZrO2), hydrochlorides (SnCl2, SnCl4, NiCl2·6H2O, SbCl3, ZnCl2, ZrOCl2·8H2O), sulfates (NiSO4·6H2O, ZnSO4·7H2O, Zr(SO4)2·4H2O), and nitrates (Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, Zr(NO3)4·5H2O) of the metal.

[0019] Preferably, the solvent in step (1) is ethanol or water; the ratio of the solvent to the hard carbon material is 20-30 mL:0.1-2 g.

[0020] Preferably, the power of the ultrasonic dispersion in step (1) is 500-2000 W, and the time is 5-30 min.

[0021] Preferably, the rotation speed of the stirring in step (1) is 100-500 r / min, and the time is 10-30 min.

[0022] Preferably, the frequency of the microwave reactor in step (2) is 1000-4000 MHz, and the output power is 500-2000 w.

[0023] Preferably, the heating rate of the heating reaction in step (2) is 2-50 °C / min, the heating temperature is 100-400 °C, and the heating time is 5-50 min.

[0024] Preferably, the temperature of the drying in step (2) is 60-150 °C, and the time is 1-3 h.

[0025] A heteroatom-doped hard carbon negative electrode material is prepared by the above method.

[0026] An application of a heteroatom-doped hard carbon negative electrode material, wherein the negative electrode material is used to prepare a sodium ion battery.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention uses a heteroatom reagent and a hard carbon material as raw materials, and uses microwave to quickly and efficiently realize the heteroatom doping of the hard carbon material. This method has a fast reaction speed, a simple process, a low reaction temperature, a small equipment investment, and a low cost, and can meet large-scale industrial production. Compared with commercial hard carbon, the hard carbon material doped by microwave in the present invention is assembled into a sodium ion battery. It is found that after testing in the voltage range of 0.01-3 V, it still has a discharge specific capacity of 431.67 mAh / g after cycling 50 times at a current density of 30 mA / g, and has reversible sodium storage capacities of 423.59, 409.6, 391.83, 376.87, 360.91, 326.53, and 261.63 at current densities of 0.03, 0.06, 0.15, 0.3, 0.6, 1.5, and 3 A / g, respectively. The present invention can obtain a heteroatom-doped hard carbon material at a low reaction temperature in a short time, with a simple process and no special reaction equipment. The specific capacity and rate performance of the hard carbon material doped in the present invention have been greatly improved, which can effectively improve the performance of the sodium ion battery and has broad application prospects. Description of the Drawings

[0029] Figure 1 Graphs for performance detection of the hard carbon materials in Example 1 and Comparative Example 2;

[0030] Figure 2Cycling curves of the hard carbon materials of Example 1 and Comparative Example 2 at a current density of 30 mA / g;

[0031] Figure 3 Cycling curves of the hard carbon materials of Example 1 and Comparative Example 2 at a current density of 1500 mA / g;

[0032] Figure 4 Rate performance graphs of the hard carbon prepared in Example 1 and Comparative Example 2 at different current densities;

[0033] Figure 5 Electrochemical impedance diagrams of the hard carbon materials prepared in Example 1 and Comparative Example 2 at a test frequency of 0.01 - 10000 Hz. Detailed implementation mode

[0034] The present invention provides a preparation method for a heteroatom - doped hard carbon negative electrode material, and the steps are as follows:

[0035] (1) Mix the hard carbon material and the heteroatom reagent evenly according to a mass ratio of 0.1 - 1:0.1 - 7, dissolve them in ethanol or water, and ultrasonically disperse them at 500 - 2000 W for 5 - 30 min to ensure that the hard carbon material and the heteroatom reagent are evenly dispersed in the mixed solution. Then, set the rotation speed to 100 - 500 r / min and magnetically stir for 10 - 30 min to promote more heteroatom reagents to adsorb on the hard carbon material, obtaining a dispersed solution; the ratio of the solvent to the hard carbon material is 20 - 30 mL:0.1 - 2 g;

[0036] (2) Place the dispersed solution in a microwave reactor with a frequency of 1000 - 4000 MHz and an output power of 500 - 2000 w, heat it at a heating rate of 2 - 50 °C / min to 100 - 400 °C, keep it warm for 5 - 50 min, and then dry it at 60 - 150 °C for 1 - 3 h to obtain the heteroatom - doped hard carbon negative electrode material.

[0037] Preferably, a preparation method for a heteroatom - doped hard carbon negative electrode material, and the steps are as follows:

[0038] (1) Mix the hard carbon material and the heteroatom reagent evenly according to a mass ratio of 0.1 - 1:0.1 - 7, dissolve them in ethanol or water, and ultrasonically disperse them at 700 - 900 W for 5 - 30 min to ensure that the hard carbon material and the heteroatom reagent are evenly dispersed in the mixed solution. Then, set the rotation speed to 250 - 350 r / min and magnetically stir for 10 - 30 min to promote more heteroatom reagents to adsorb on the hard carbon material, obtaining a dispersed solution; the ratio of the solvent to the hard carbon material is 20 - 30 mL:0.1 - 2 g;

[0039] (2) Place the dispersion solution in a microwave reactor with a frequency of 2400 - 2500 MHz and an output power of 500 - 900 W, heat it up to 110 - 120 °C at a heating rate of 10 - 20 °C / min, keep it warm for 10 - 20 min, and then dry it at 60 - 80 °C for 1 - 3 h to obtain the heteroatom-doped hard carbon anode material.

[0040] The hard carbon material in the present invention is a raw material purchased conventionally in the market. In a specific embodiment of the present invention, the hard carbon material is Kuraray hard carbon material (KURANODE TM Type2(5μm)) from Japan.

[0041] The heteroatom reagent is at least one of a nitrogen source, a sulfur source, a phosphorus source, a boron source, an oxygen source, and a fluorine source.

[0042] Preferably, the nitrogen source is one or more of thiourea, nitric acid, melamine, and ammonium hydrogen phosphate; the sulfur source is one or more of thiourea, dimethyl sulfoxide (DMSO), nano sulfur powder, and urea; the phosphorus source is one or more of phytic acid and phosphoric acid; the boron source is one or more of boric acid and ammonium pentaborate tetrahydrate; the oxygen source is one or more of sodium carbonate, sodium bicarbonate, hydrogen peroxide, and sodium perchlorate; the fluorine source is one or more of 2,3,5,6-tetrafluoro-4-benzoic acid, hydrofluoric acid, sodium fluoride, and tetrafluoroterephthalic acid.

[0043] The above-mentioned heteroatom reagents are in two forms, solid and liquid (such as dimethyl sulfoxide, hydrofluoric acid, etc.). Among them, the solid heteroatom reagent can be added in the form of a solution (heteroatom reagent solution). The concentration of the solution is an analytical pure commercial heteroatom reagent, and the mass ratio of the hard carbon material to the heteroatom reagent solution is 1:5 - 7.

[0044] The mass ratio of the hard carbon material to the solid heteroatom reagent is 1:0.1 - 1; the mass ratio of the hard carbon material to the liquid heteroatom reagent is 0.2:5 - 7.

[0045] The heteroatom-doped hard carbon anode material prepared by the above method can be used to prepare sodium-ion batteries.

[0046] The preparation method of the battery is as follows: Mix the heteroatom-doped hard carbon anode material prepared in the present invention, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, then add an appropriate amount of N-methylpyrrolidone (NMP), mix evenly, coat it on a copper foil with a diameter of 13 mm, and the total coating amount is 1.0 - 2.0 mg. Dry it in a vacuum oven at 80 °C. Use a Na sheet as the anode, the electrolyte is 1 M NaPF6 / DME (NP-035), and the separator is a glass fiber separator with a diameter of 19 mm (Whatman, GF / D circular (1823)). Assemble it into a CR2032 button cell in a glove box with the water and oxygen content both less than 0.01 ppm and filled with argon. The used spring washer is 15.4 * 1.1 mm, and the gasket is 15.8 * 1 mm.

[0047] The present invention will be further described below in conjunction with embodiments.

[0048] Example 1

[0049] A preparation method of a heteroatom-doped hard carbon anode material is as follows:

[0050] (1) Mix 1.0 g of hard carbon material and 0.2 g of thiourea evenly, dissolve them in 20 ml of ethanol, ultrasonically disperse them at 800 W for 20 min, then set the rotation speed to 300 r / min and magnetically stir for 20 min to obtain a dispersion solution;

[0051] (2) Place the dispersion solution in a microwave reactor with a frequency of 2450 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 10 °C / min and keep it warm for 15 min, then dry it at 120 °C for 2 h. Obtain a nitrogen and sulfur-doped hard carbon anode material.

[0052] Use the hard carbon anode material to prepare a CR2032 button cell.

[0053] Example 2

[0054] A preparation method of a heteroatom-doped hard carbon anode material is as follows:

[0055] (1) Mix 1.0 g of hard carbon material and 0.15 g of thiourea evenly, dissolve them in 30 ml of ethanol, ultrasonically disperse them at 800 W for 10 min, then set the rotation speed to 400 r / min and magnetically stir for 20 min to obtain a dispersion solution;

[0056] (2) Place the dispersion solution in a microwave reactor with a frequency of 3000 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 10 °C / min and keep it warm for 10 min, then dry it at 80 °C for 2 h. Obtain a nitrogen and sulfur-doped hard carbon anode material.

[0057] Prepare a CR2032 button cell using the hard carbon negative electrode material described above.

[0058] Example 3

[0059] A method for preparing a heteroatom-doped hard carbon negative electrode material is as follows:

[0060] (1) Mix 1.0 g of hard carbon material with 1.0 g of thiourea evenly, dissolve it in 30 ml of ethanol, and ultrasonically disperse it for 15 min at 700 W, then set the rotation speed to 300 r / min and stir magnetically for 15 min to obtain a dispersed solution;

[0061] (2) Place the dispersed solution in a microwave reactor with a frequency of 4000 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 10 °C / min and keep it warm for 10 min, then dry it at 100 °C for 2 h. Obtain a nitrogen and sulfur-doped hard carbon negative electrode material.

[0062] Prepare a CR2032 button cell using the hard carbon negative electrode material described above.

[0063] Example 4

[0064] A method for preparing a heteroatom-doped hard carbon negative electrode material is as follows:

[0065] (1) Mix 1.0 g of hard carbon material with 4.0 g of thiourea evenly, dissolve it in 30 ml of ethanol, and ultrasonically disperse it for 15 min at 600 W, then set the rotation speed to 300 r / min and stir magnetically for 15 min to obtain a dispersed solution;

[0066] (2) Place the dispersed solution in a microwave reactor with a frequency of 24000 MHz and an output power of 850 w, heat it to 120 °C at a heating rate of 20 °C / min and keep it warm for 15 min, then dry it at 120 °C for 3 h. Obtain a nitrogen and sulfur-doped hard carbon negative electrode material.

[0067] Prepare a CR2032 button cell using the hard carbon negative electrode material described above.

[0068] Example 5

[0069] A method for preparing a heteroatom-doped hard carbon negative electrode material is as follows:

[0070] (1) Mix 0.2 g of hard carbon material with 5.5 g of dimethyl sulfoxide evenly, dissolve it in 30 ml of ethanol, and ultrasonically disperse it for 20 min at 800 W, then set the rotation speed to 300 r / min and stir magnetically for 20 min to obtain a dispersed solution;

[0071] (2) Place the dispersion solution in a microwave reactor with a frequency of 2450 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 10 °C / min and keep it warm for 15 min, and then dry it at 120 °C for 3 h. A sulfur-doped hard carbon negative electrode material is obtained.

[0072] Use the obtained hard carbon negative electrode material to prepare a CR2032 button cell.

[0073] Example 6

[0074] A preparation method of a heteroatom-doped hard carbon negative electrode material is as follows:

[0075] (1) Mix 0.2 g of hard carbon material evenly with 7 g of dimethyl sulfoxide, dissolve it in 30 ml of ethanol, ultrasonically disperse it at 1000 W for 15 min, and then set the magnetic stirring speed at 500 r / min for 15 min to obtain a dispersion solution;

[0076] (2) Place the dispersion solution in a microwave reactor with a frequency of 3000 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 25 °C / min and keep it warm for 20 min, and then dry it at 120 °C for 3 h. A sulfur-doped hard carbon negative electrode material is obtained.

[0077] Use the obtained hard carbon negative electrode material to prepare a CR2032 button cell.

[0078] Example 7

[0079] A preparation method of a heteroatom-doped hard carbon negative electrode material is as follows:

[0080] (1) Mix 1 g of hard carbon material evenly with 0.2 g of nano sulfur powder, dissolve it in 30 ml of ethanol, ultrasonically disperse it at 800 W for 15 min, and then set the magnetic stirring speed at 400 r / min for 30 min to obtain a dispersion solution;

[0081] (2) Place the dispersion solution in a microwave reactor with a frequency of 2400 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 10 °C / min and keep it warm for 15 min, and then dry it at 120 °C for 3 h. A sulfur-doped hard carbon negative electrode material is obtained.

[0082] Use the obtained hard carbon negative electrode material to prepare a CR2032 button cell.

[0083] Example 8

[0084] A preparation method of a heteroatom-doped hard carbon negative electrode material is as follows:

[0085] (1) Mix 1.0 g of hard carbon material with 0.15 g of nano sulfur powder evenly, dissolve them in 30 ml of ethanol, and ultrasonically disperse for 20 min at 800 W. Then set the rotation speed to 300 r / min and magnetically stir for 20 min to obtain a dispersed solution;

[0086] (2) Place the dispersed solution in a microwave reactor with a frequency of 3500 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 15 °C / min and keep it warm for 20 min, and then dry it at 120 °C for 3 h. Obtain a sulfur-doped hard carbon negative electrode material.

[0087] Prepare a CR2032 button cell using the said hard carbon negative electrode material.

[0088] Example 9

[0089] A preparation method of a heteroatom-doped hard carbon negative electrode material is as follows:

[0090] (1) Mix 1.0 g of hard carbon material with 6.65 g of phytic acid solution (aqueous phytic acid solution with a mass concentration of 70%) evenly, dissolve them in 20 ml of ethanol, and ultrasonically disperse for 20 min at 800 W. Then set the rotation speed to 300 r / min and magnetically stir for 25 min to obtain a dispersed solution;

[0091] (2) Place the dispersed solution in a microwave reactor with a frequency of 2400 MHz and an output power of 900 w, heat it to 120 °C at a heating rate of 10 °C / min and keep it warm for 20 min, and then dry it at 120 °C for 3 h. Obtain a phosphorus-doped hard carbon negative electrode material.

[0092] Example 10

[0093] A preparation method of a heteroatom-doped hard carbon negative electrode material is as follows:

[0094] (1) Mix 1.0 g of hard carbon material with 4 g of phytic acid solution (aqueous phytic acid solution with a mass concentration of 70%) evenly, dissolve them in 30 ml of ethanol, and ultrasonically disperse for 30 min at 900 W. Then set the rotation speed to 300 r / min and magnetically stir for 10 min to obtain a dispersed solution;

[0095] (2) Place the dispersed solution in a microwave reactor with a frequency of 2500 MHz and an output power of 1500 w, heat it to 120 °C at a heating rate of 20 °C / min and keep it warm for 25 min, and then dry it at 120 °C for 5 h. Obtain a phosphorus-doped hard carbon negative electrode material.

[0096] Example 11

[0097] A preparation method of a heteroatom-doped hard carbon negative electrode material is as follows:

[0098] (1) Mix 1.0 g of hard carbon material evenly with 0.2 g of sodium carbonate, dissolve them in 30 ml of ethanol, and ultrasonically disperse for 15 min at 800 W. Then set the rotation speed to 300 r / min and magnetically stir for 20 min to obtain a dispersed solution;

[0099] (2) Place the dispersed solution in a microwave reactor with a frequency of 2450 MHz and an output power of 900 w, heat it up to 120 °C at a heating rate of 10 °C / min and keep it warm for 15 min, and then dry it at 80 °C for 2 h. An oxygen-doped hard carbon anode material is obtained.

[0100] Use the obtained hard carbon anode material to prepare a CR2032 button cell.

[0101] Example 12

[0102] A preparation method of a heteroatom-doped hard carbon anode material is as follows:

[0103] (1) Mix 1.0 g of hard carbon material evenly with 2.0 g of sodium carbonate, dissolve them in 50 ml of ethanol, and ultrasonically disperse for 20 min at 1000 W. Then set the rotation speed to 500 r / min and magnetically stir for 25 min to obtain a dispersed solution;

[0104] (2) Place the dispersed solution in a microwave reactor with a frequency of 3000 MHz and an output power of 1500 w, heat it up to 150 °C at a heating rate of 30 °C / min and keep it warm for 15 min, and then dry it at 110 °C for 3 h. An oxygen-doped hard carbon anode material is obtained.

[0105] Use the obtained hard carbon anode material to prepare a CR2032 button cell.

[0106] Example 13

[0107] A preparation method of a heteroatom-doped hard carbon anode material is as follows:

[0108] (1) Mix 1.0 g of hard carbon material evenly with 0.15 g of sodium fluoride, dissolve them in 20 ml of ethanol, and ultrasonically disperse for 15 min at 800 W. Then set the rotation speed to 300 r / min and magnetically stir for 20 min to obtain a dispersed solution;

[0109] (2) Place the dispersed solution in a microwave reactor with a frequency of 2400 MHz and an output power of 900 w, heat it up to 120 °C at a heating rate of 10 °C / min and keep it warm for 15 min, and then dry it at 80 °C for 2 h. A fluorine-doped hard carbon anode material is obtained.

[0110] Use the obtained hard carbon anode material to prepare a CR2032 button cell.

[0111] Example 14

[0112] A preparation method of a heteroatom-doped hard carbon anode material is as follows:

[0113] (1) Mix 1.0 g of hard carbon material with 1.0 g of sodium fluoride evenly, dissolve it in 30 ml of ethanol, and ultrasonically disperse it for 10 min at 900 W, then set the rotation speed to 300 r / min and stir magnetically for 15 min to obtain a dispersion solution;

[0114] (2) Place the dispersion solution in a microwave reactor with a frequency of 3000 MHz and an output power of 1200 w, heat it up to 130 °C at a heating rate of 15 °C / min and keep it warm for 20 min, then dry it at 115 °C for 3 h. Obtain a fluorine-doped hard carbon anode material.

[0115] Use the obtained hard carbon anode material to prepare a CR2032 button cell.

[0116] Comparative Example 1

[0117] A preparation method of a hard carbon anode material is as follows:

[0118] (1) Dissolve 1.0 g of hard carbon material evenly in 20 ml of ethanol, and ultrasonically disperse it for 20 min at a power of 800 W to obtain a dispersion solution;

[0119] (3) Transfer the obtained dispersion solution to a microwave chemical reactor with a frequency of 2450 MHz and an output power of 900 W, heat it up to 120 °C at a rate of 10 °C / min and keep it warm for 15 min, then dry it at 120 °C for 2 h to obtain a microwave-treated hard carbon material.

[0120] Use the obtained hard carbon anode material to prepare a CR2032 button cell.

[0121] Comparative Example 2

[0122] Use a commercially available hard carbon material purchased directly to prepare a CR2032 button cell.

[0123] Use the hard carbon anode materials prepared in Examples 1-13 and Comparative Examples 1-2 to prepare sodium ion batteries for performance testing, and the electrochemical performance of the sodium ion batteries is shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] As can be seen from Table 1, the hard carbon materials prepared in Example 1 all have relatively high initial discharge specific capacity, initial charge specific capacity, and initial efficiency; while the initial charge specific capacity and initial efficiency of the materials in Comparative Examples 1 and 2 are lower than those in the examples. This is because the hard carbon materials prepared in Comparative Examples 1 and 2 do not undergo heteroatom doping, resulting in a smaller interlayer spacing, which leads to a decrease in their initial charge-discharge specific capacity and initial efficiency. This indicates that heteroatom-doped hard carbon prepared by the microwave method can have a larger interlayer spacing, thereby rapidly and efficiently improving the rate performance and cycle stability of hard carbon.

[0128] Perform performance tests on the hard carbon materials in Example 1, Example 5, Example 9, Comparative Example 1, and Comparative Example 2, and obtain the XRD patterns of the hard carbon materials in Example 1, Example 5, Example 9, Comparative Example 1, and Comparative Example 2 as Figure 1 . From Figure 1 it can be seen that the hard carbon prepared in Example 1 has a lattice spacing of 0.398 nm, while the hard carbon prepared in Comparative Example 2 only has a lattice spacing of 0.384 nm, and the lattice spacing of Example 1 is wider.

[0129] The cyclic voltammetry curves of the hard carbon materials in Example 1 and Comparative Example 2 at a current density of 30 mA / g (voltage range 0.01 - 3 V) are as Figure 2 . From Figure 2 it can be seen that the hard carbons prepared in Example 1, Example 5, Example 7, and Example 9 have discharge specific capacities of 431.67, 521.07, 355.33, and 391.66 mAh / g respectively after 50 cycles, while the hard carbons prepared in Comparative Example 1 and Comparative Example 2 only have reversible specific capacities of 316.3 and 325.71 mAh / g respectively.

[0130] The cyclic voltammetry curves of the hard carbon materials in Example 1 and Comparative Example 2 at a current density of 1500 mA / g are as Figure 3 . From Figure 3 it can be seen that the hard carbons prepared in Example 1, Example 5, and Example 9 have reversible specific capacities of 303.24, 325.80, and 275.05 mAh / g respectively after cycling 1000 times at a high current density of 1500 mA / g, while the hard carbon prepared in Comparative Example 2 only has a sodium storage capacity of 209.52 mAh / g.

[0131] The rate performance diagrams of the hard carbons prepared in Example 1 and Comparative Example 2 at different current densities are as Figure 4 . Figure 4The hard carbon prepared in Example 1 shows reversible sodium storage capacities of 423.59, 409.6, 391.83, 376.87, 360.91, 326.53, 261.63 mAh / g at current densities of 0.03, 0.06, 0.15, 0.3, 0.6, 1.5, 3 A / g respectively. While the hard carbon prepared in Comparative Example 2 shows reversible sodium storage capacities of 318.51, 303.19, 289.1, 284.88, 257.12, 218.75, 156.59 mAh / g at current densities of 0.03, 0.06, 0.15, 0.3, 0.6, 1.5, 3 A / g respectively. In addition, the hard carbon prepared in Example 5 has the best rate performance, with reversible sodium storage capacities of 502.88, 496.19, 489.34, 477.23, 466.27, 444.44, 394.84 mAh / g at current densities of 0.03, 0.06, 0.15, 0.3, 0.6, 1.5, 3 A / g respectively

[0132] The electrochemical impedance diagrams of the hard carbon materials prepared in Example 1 and Comparative Example 2 at a test frequency of 0.01 - 10,000 Hz are as follows Figure 5 . From Figure 5 it can be seen that the hard carbon material prepared in Example 1 has a smaller electrochemical impedance and better kinetic performance

[0133] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention

Claims

1. A preparation method of a heteroatom-doped hard carbon anode material, characterized in that, It includes the following steps: (1) Mix the hard carbon material and the heteroatom reagent evenly, dissolve them in a solvent, and then perform ultrasonic dispersion and stirring in sequence to obtain a dispersion solution; (2) Place the dispersion solution in a microwave reactor for heating reaction, and obtain a heteroatom-doped hard carbon negative electrode material after drying; The heteroatom reagent is at least one of a nitrogen source, a sulfur source, a phosphorus source, a boron source, an oxygen source, and a fluorine source; the mass ratio of the hard carbon material to the heteroatom reagent is 0.1-1:0.1-7.

2. The preparation method of the heteroatom-doped hard carbon negative electrode material according to claim 1, wherein, The nitrogen source is one or more of thiourea, nitric acid, melamine, and ammonium hydrogen phosphate; the sulfur source is one or more of thiourea, dimethyl sulfoxide, nano sulfur powder, and urea; the phosphorus source is one or more of phytic acid and phosphoric acid; the boron source is one or more of boric acid and tetraammonium pentaborate tetrahydrate; the oxygen source is one or more of sodium carbonate, sodium bicarbonate, hydrogen peroxide, and sodium perchlorate; the fluorine source is one or more of 2,3,5,6-tetrafluoro-4-benzoic acid, hydrofluoric acid, sodium fluoride, and tetrafluoroterephthalic acid.

3. The preparation method of the heteroatom-doped hard carbon negative electrode material according to claim 1, characterized in that, The solvent in step (1) is ethanol or water; the ratio of the solvent to the hard carbon material is 20-30 mL:0.1-2 g.

4. The preparation method of the heteroatom-doped hard carbon negative electrode material according to claim 1, characterized in that, The power of the ultrasonic dispersion in step (1) is 500-2000 W, and the time is 5-30 min.

5. The preparation method of the heteroatom-doped hard carbon negative electrode material according to claim 1, characterized in that, The rotation speed of the stirring in step (1) is 100-500 r / min, and the time is 10-30 min.

6. The preparation method of the heteroatom-doped hard carbon anode material according to claim 1, characterized in that, The frequency of the microwave reactor in step (2) is 1000-4000 MHz, and the output power is 500-2000 w.

7. The preparation method of the heteroatom-doped hard carbon negative electrode material according to claim 1, characterized in that, The heating rate of the heating reaction in step (2) is 2-50 °C / min, the heating temperature is 100-400 °C, and the heating time is 5-50 min.

8. The preparation method of the heteroatom-doped hard carbon negative electrode material according to claim 1, characterized in that, The drying temperature in step (2) is 60-150 °C, and the time is 1-3 h.

9. A heteroatom-doped hard carbon negative electrode material, characterized in that, It is prepared by using any one of the preparation methods of claims 1-8.

10. Use of the heteroatom-doped hard carbon negative electrode material according to claim 9, characterized in that, The heteroatom-doped hard carbon negative electrode material is used to prepare a sodium ion battery.

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