Hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a hard carbon negative electrode material and a preparation method thereof, and belongs to the technical field of sodium ion batteries, the synthesis steps adopt a two-step plasma method, and the method comprises the following steps: step 1, taking biomass carbon, anthracite and metal salt as reactants, and carrying out ball milling on the mixture by adopting a plasma ball milling process; 2, the precursor obtained in the step 1 is subjected to plasma ball milling, the temperature in a plasma ball-milling cavity is heated to 200-400 DEG C in situ, and the particle size of the anthracite after ball milling is 2-15 microns; and step 3, performing high-temperature sintering in an inert atmosphere, soaking the obtained product in hydrochloric acid to remove impurities in ash, and then washing to be neutral to finally obtain the hard carbon negative electrode material. The hard carbon negative electrode material prepared by the invention shows high coulombic efficiency and specific capacity, good cycling stability and excellent rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] Hard carbon is widely used as a negative electrode material for sodium-ion batteries and lithium-ion batteries. However, in actual use, there are problems such as low specific capacity, first Coulombic efficiency, and rate performance in hard carbon materials. At present, the modification methods for hard carbon negative electrode materials mainly include: controlling the types of precursors and carbonization temperature, heteroatom doping, introducing defect sites, etc. Among them, heteroatom doping is an effective method to improve the specific capacity of hard carbon. The doping of heteroatoms can effectively improve the conductivity of hard carbon negative electrode materials, and at the same time can introduce surface and bulk defects to provide more sodium storage sites, thereby effectively improving the rate performance and specific capacity of hard carbon materials. Currently, the doped impurity atoms include nitrogen, phosphorus, fluorine, and transition metal elements (copper, manganese, nickel, cobalt), etc. At present, the doping of heteroelements usually adopts high-temperature solid-phase synthesis method, chemical deposition method, spray drying method, and sol-gel method, etc. By using the above methods to prepare doped hard carbon materials, it is easy to cause the separation failure of impurity atoms and there is a problem of insufficient stability. To solve the above problems, in the present invention, plasma ball milling is used to introduce impurity atoms and defect vacancies. Summary of the Invention

[0003] In order to solve the problems in the background art, the present invention proposes a hard carbon negative electrode material and a preparation method thereof.

[0004] The technical solution of the present invention is as follows:

[0005] A preparation method of a hard carbon negative electrode material, comprising the following steps:

[0006] (1) Mix biomass carbon, anthracite, and metal salt in proportion, place them in a plasma ball milling cavity, evacuate to 0.1 - 10 Pa, and then fill with a mixed gas of inert gas and reactive gas to 10 - 500 Pa, and perform plasma ball milling treatment;

[0007] (2) Perform plasma ball milling discharge on the product of step (1) and in-situ heat the ball milling cavity, the heating temperature is 200 - 400 °C, the reaction time is 0.5 - 3 h, and the heating rate is 5 - 20 °C / min;

[0008] (3) High-temperature sintering is carried out under an inert atmosphere, the sintering temperature is 600 - 1500 °C, the heating rate is 5 - 20 °C / min, and the heat preservation time is 1 - 5 h. The obtained product is washed with acid and water until neutral, and finally a hard carbon negative electrode material is obtained.

[0009] In the above technical solution, the biomass carbon is selected from at least one of coconut shell, cotton shell, soybean stalk, sugarcane stalk, fruit shell carbon, and corn cob.

[0010] In the above technical solution, the mass ratio of the biomass carbon, anthracite, and metal salt is 50:1:0.1 - 1:10:0.5.

[0011] In the above technical solution, the metal salt is one or several of sodium chloride, sodium dihydrogen phosphate, urea, and thiourea.

[0012] In the above technical solution, the ball milling time in the plasma ball milling process in steps (1) and (2) is 0.5 - 3 h, and the ball - powder ratio is 100:1 - 10:1. In the above technical solution, the gas in the plasma ball milling process in steps (1) and (2) is a mixed gas of an inert gas and a reactive gas. The inert gas is at least one of nitrogen, argon, helium, and neon; the reactive gas is at least one of carbon tetrafluoride, ammonia, phosphine, and hydrogen sulfide. Among them, the volume ratio of the inert gas to the reactive gas is 100:1~1:100.

[0013] In the above technical solution, the plasma discharge power in the plasma ball milling process in steps (1) and (2) is 100 - 1000 W, and the discharge time is 0.5 h - 3 h.

[0014] In the above technical solution, the particle size of the anthracite after plasma ball milling treatment in step (2) is 2 - 15 μm.

[0015] In the above technical solution, in step (3), the pickling is carried out with a hydrochloric acid solution with a concentration of 1 - 5 mol / L, and the soaking time is 2 - 6 h.

[0016] In the above technical solution, the inert gas for high - temperature sintering in step (3) is one or a mixed gas of nitrogen and argon.

[0017] A hard carbon material is prepared by the above method. At a current density of 10 mA / g, its specific capacity ≥ 300 mAh / g, and the capacity retention rate ≥ 90% after 300 cycles.

[0018] Beneficial effects:

[0019] 1. Synergistic optimization of defects and doping: Through a two - step plasma method (plasma ball milling + in - situ heating), in - situ doping of bulk - phase defects and elements such as nitrogen / phosphorus / fluorine in the hard carbon material is achieved, the defect density is increased, and the sodium - storage active sites are increased.

[0020] 2. Performance improvement: At a current density of 10 mA / g, its specific capacity ≥ 300 mA / g (conventional hard carbon materials ≤ 300 mAh / g), and the capacity retention rate ≥ 90% after 300 cycles;

[0021] 3. Enhanced impurity binding force: Element doping is embedded in the carbon skeleton in the form of chemical bonds (proven by EDS-mapping), avoiding the problem of surface coating shedding. Brief Description of the Drawings

[0022] Figure 1 It is the SEM morphology of the hard carbon prepared in Example 1.

[0023] Figure 2 It is the EDS-mapping of the hard carbon prepared in Example 1.

[0024] Figure 3 It is the performance characterization of the hard carbon prepared in Example 1. a: Cycling test performance at a current density of 10 mA / g, b: Rate performance at different current densities. Detailed Description of the Invention

[0025] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the protection scope of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0026] Example 1

[0027] Using 0.5 kg of coconut shell, 1 kg of anthracite, and 0.1 kg of urea as reactants, and 15 kg of steel balls were put into the plasma ball milling cavity for ball milling. After evacuating, when the pressure in the cavity reached 1 Pa, a mixed gas of argon and ammonia was introduced, and the gas volume ratio was 50:1. When the pressure in the cavity reached 15 Pa, plasma discharge was carried out with a discharge power of 100 W for 1 h. Subsequently, in-situ heating was carried out on the plasma ball milling cavity, plasma discharge was carried out with a discharge power of 500 W, and the quartz cavity was heated to 300 °C for 2 h. Then, the obtained product was soaked in hydrochloric acid to remove impurities in the ash, and then washed with water until neutral. The product obtained in the above steps was sintered at 1000 °C in a nitrogen atmosphere with a heating rate of 5 °C / min and a calcination time of 4 h, finally obtaining a nitrogen-doped hard carbon anode material. The hard carbon prepared in the above example was tested by scanning electron microscopy (SEM) and elemental distribution test (EDS-mapping). The SEM morphology of the hard carbon prepared in Example 1 is as Figure 1 shown, and the EDS-mapping of the hard carbon prepared in Example 1 is as Figure 2As shown in the figure. The prepared hard carbon material shows a block structure with a size of 2 - 5 μm and uniform distribution. EDS-mapping elemental analysis shows that nitrogen elements exist in the prepared hard carbon, confirming that plasma doping effectively realizes the bulk embedding of heteroatoms.

[0028] The cyclic test performance of the hard carbon prepared in the above example was carried out at a current density of 10 mA / g, and the rate performance was tested at different current densities. The results are as Figure 3 shown in a and b of. The results show that at a current density of 10 mA / g, its specific capacity is 310 mA / g, and the capacity retention rate is 91% after 300 cycles; as Figure 3 shown in b of, at current densities of 0.08C, 2C, and 10C, its specific capacities are 310 mA / g, 250 mA / g, and 125 mA / g respectively.

[0029] Example 2

[0030] Using 1 kg of cotton hulls, 3 kg of anthracite, and 0.2 kg of sodium dihydrogen phosphate as reactants, and 18 kg of steel balls were put into the plasma ball milling cavity for ball milling. After evacuating, when the pressure in the cavity reached 2 Pa, argon, nitrogen, and hydrogen sulfide gases were introduced, and their volume ratio was 80:10:10. When the pressure in the cavity reached 20 Pa, plasma discharge was carried out with a discharge power of 200 W for 2 h. Subsequently, in-situ heating of the plasma ball milling cavity was carried out, plasma discharge was carried out with a discharge power of 700 W, and the quartz cavity was heated to 350 °C for 3 h; then the obtained product was soaked in hydrochloric acid to remove impurities in the ash, and then washed with water until neutral; the product obtained in the above steps was sintered at 1200 °C in a nitrogen atmosphere with a heating rate of 10 °C / min and a calcination time of 3 h, and finally a hard carbon anode material was obtained.

[0031] Example 3

[0032] Using 3 kg of corncob, 0.8 kg of anthracite, and 0.1 kg of urea as reactants, along with 20 kg of steel balls, they are placed in a plasma ball-milling cavity for ball milling. After evacuating to a vacuum, when the pressure in the cavity reaches 5 Pa, helium and carbon tetrafluoride are introduced, with a gas volume ratio of 90:10. When the pressure in the cavity reaches 25 Pa, plasma discharge is carried out with a discharge power of 500 W for 3 h of ball milling. Subsequently, in-situ heating of the plasma ball-milling cavity is carried out, plasma discharge is performed with a discharge power of 800 W, and the quartz cavity is heated to 400 °C with a heating time of 3.5 h. Then, the obtained product is soaked in hydrochloric acid to remove impurities in the ash, and then washed with water until neutral. The product obtained from the above steps is subjected to high-temperature sintering at 1500 °C in a nitrogen atmosphere with a heating rate of 20 °C / min and a calcination time of 5 h, finally obtaining a hard carbon anode material.

[0033] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A preparation method of a hard carbon negative electrode material, characterized in that, It includes the following steps: (1) Mix biomass carbon, anthracite, and metal salt in a certain proportion, place them in a plasma ball-milling cavity, evacuate to 0.1 - 10 Pa, and then fill with a mixed gas of inert gas and reactive gas to 10 - 500 Pa, and carry out plasma ball-milling process treatment; (2) Carry out plasma ball-milling process treatment on the product of step (1) and in-situ heat the ball-milling cavity, with the heating temperature being 200 - 400 °C, the reaction time being 0.5 - 3 h, and the heating rate being 5 - 20 °C / min; (3) High-temperature sinter in an inert atmosphere, with the sintering temperature being 600 - 1500 °C, the heating rate being 5 - 20 °C / min, and the heat preservation time being 1 - 5 h. Wash the obtained product with acid and water until neutral to finally obtain a hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: The biomass carbon is selected from at least one of coconut shell, cotton shell, soybean stalk, sugarcane stalk, fruit shell carbon, and corn cob.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the biomass carbon, anthracite, and metal salt is 50:1:0.1 - 1:10:0.

5.

4. The preparation method according to claim 1, characterized in that: The metal salt is one or several of sodium chloride, sodium dihydrogen phosphate, urea, and thiourea.

5. The preparation method according to claim 1, characterized in that: In the plasma ball-milling process in steps (1) and (2), the ball-milling time is 0.5 - 3 h, and the ball-to-powder ratio is 100:1 - 10:

1.

6. The preparation method according to claim 1, characterized in that: In the plasma ball-milling process in steps (1) and (2), the gas is a mixed gas of inert gas and reactive gas. The inert gas is at least one of nitrogen, argon, helium, and neon; the reactive gas is at least one of carbon tetrafluoride, ammonia, phosphine, and hydrogen sulfide. Among them, the volume ratio of the inert gas to the reactive gas is 100:1 ~ 1:

100.

7. The preparation method according to claim 1, characterized in that: In the plasma ball-milling process in steps (1) and (2), the plasma discharge power is 100 - 1000 W, and the discharge time is 0.5 - 3 h.

8. The preparation method according to claim 1, characterized in that: The particle size of the anthracite after plasma ball-milling treatment in step (2) is 2 - 15 μm.

9. The preparation method according to claim 1, characterized in that: In step (3), the acid washing uses a hydrochloric acid solution with a concentration of 1 - 5 mol / L, and the soaking time is 2 - 6 h; the inert gas for high-temperature sintering is one or a mixture of nitrogen and argon.

10. A hard carbon material, characterized in that, Prepared by the method according to any one of claims 1 - 9, with a specific capacity ≥ 300 mAh / g at a current density of 10 mA / g, and a capacity retention rate ≥ 90% after 300 cycles.

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