A hard carbon negative electrode material and preparation method thereof

Abstract

The present invention discloses a hard carbon negative electrode material and a preparation method thereof, which belongs to the technical field of sodium ion batteries. The synthesis step adopts a two-step plasma method, step 1: using biomass carbon, anthracite and metal salt as reactants, the mixture is ball-milled by a plasma ball milling process. Step 2: The precursor obtained in step 1 is subjected to plasma ball milling, and the temperature in the plasma ball ink chamber is in situ heated to 200-400°C. The particle size of the anthracite after ball milling is 2-15μm; step 3: high-temperature sintering is performed under an inert atmosphere, and the obtained product is soaked in hydrochloric acid to remove impurities in the ash, and then washed with water to neutrality, and finally a hard carbon negative electrode material is obtained. The hard carbon negative electrode material prepared by the present invention exhibits high coulombic efficiency and specific capacity, good cycle stability and excellent rate performance.

Description

Technical Field

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

[0002] Hard carbon is widely used as anode material for sodium-ion and lithium-ion batteries. However, in practical use, hard carbon materials suffer from low specific capacity, initial coulombic efficiency, and rate performance. Currently, methods for modifying hard carbon anode materials primarily include controlling the type of precursor and carbonization temperature, doping with heteroatoms, and introducing defect sites. Heteroatom doping is an effective method for improving the specific capacity of hard carbon. Heteroatom doping can effectively enhance the electrical conductivity of hard carbon anode materials while also introducing surface, interface, and bulk defects to provide more sodium storage sites, thereby effectively improving the rate performance and specific capacity of hard carbon materials. Currently, impurity atoms doped include nitrogen, phosphorus, fluorine, and transition metals (copper, manganese, nickel, and cobalt). Currently, heteroatom doping is typically achieved through high-temperature solid-phase synthesis, chemical deposition, spray drying, and sol-gel methods. These methods can lead to poor separation of impurity atoms and instability in hard carbon materials. To address these issues, the present invention uses plasma ball milling to introduce impurity atoms and defect vacancies. Summary of the Invention

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

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

[0005] A method for preparing a hard carbon negative electrode material comprises the following steps:

[0006] (1) Biomass carbon, anthracite and substance A are mixed in proportion, placed in a plasma ball mill chamber, evacuated to 0.1-10 Pa, and then filled with a mixture of inert gas and reactive gas to 10-500 Pa for plasma ball milling;

[0007] (2) Plasma ball milling discharge is performed on the product of step (1) and the ball mill chamber is heated in situ at a heating temperature of 200-400°C, a reaction time of 0.5-3 h, and a heating rate of 5-20°C / min;

[0008] (3) Sintering at high temperature in an inert atmosphere at a sintering temperature of 600-1500°C, a heating rate of 5-20°C / min, and a holding time of 1-5 h. The obtained product is acid-washed and washed with water until neutral, and finally a hard carbon negative electrode material is obtained.

[0009] In the above technical solution, the raw material of the biomass carbon is selected from at least one of coconut shells, cotton shells, bean stalks, sugarcane stalks, and corn cobs.

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

[0011] In the above technical solution, the substance A is one or more 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 step (1) and step (2) is 0.5-3 h, and the ball-to-powder ratio is 100:1-10:1. In the above technical solution, the gas in the plasma ball milling process in step (1) and step (2) is a mixed gas of an inert gas and a reactive gas, wherein the inert gas is at least one of nitrogen, argon, helium, and neon; and the reactive gas is at least one of carbon tetrafluoride, ammonia, phosphine, and hydrogen sulfide, wherein the volume ratio of the inert gas to the reactive gas is 100:1 to 1:100.

[0013] In the above technical solution, the plasma discharge power in the plasma ball milling process in step (1) and step (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 the plasma ball milling treatment in step (2) is 2-15 μm.

[0015] In the above technical solution, the pickling in step (3) uses 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 used for high-temperature sintering in step (3) is one of nitrogen and argon, or a mixture of the two.

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

[0018] Beneficial effects:

[0019] 1. Collaborative optimization of defects and doping: A two-step plasma method (plasma ball milling + in-situ heating) is used to achieve in-situ doping of bulk defects in hard carbon materials with elements such as nitrogen, phosphorus, and fluorine, thereby increasing defect density and sodium storage active sites.

[0020] 2. Performance improvement: Its specific capacity is ≥300mA / g (conventional hard carbon materials ≤300mAh / g) at a current density of 10 mA / g, and the capacity retention rate is ≥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 This is the SEM morphology of the hard carbon prepared in Example 1.

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

[0024] Figure 3 Performance characterization of the hard carbon prepared in Example 1, a: cycle test performance at a current density of 10 mA / g, b: rate performance at different current densities. DETAILED DESCRIPTION

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

[0026] Example 1

[0027] 0.5 kg coconut shell, 1 kg anthracite and 0.1 kg urea were used as reactants, and 15 kg steel balls were placed in the plasma ball milling chamber for ball milling. The chamber was vacuumed and the pressure in the chamber reached 1 Pa, a mixed gas of argon and ammonia is introduced with a gas volume ratio of 50:1. When the pressure of the cavity reaches 15 Pa, plasma discharge is performed with a discharge power of 100 W and ball milling is performed for 1 hour. Subsequently, the plasma ball milling cavity is in-situ heated and plasma discharge is performed with a discharge power of 500 W. The quartz cavity is added to 300°C and the heating time is 2 hours. The obtained product is then soaked in hydrochloric acid to remove impurities in the ash, and then washed with water to neutrality. The product obtained in the above steps is sintered at a high temperature of 1000°C under a nitrogen atmosphere with a heating rate of 5°C / min and a calcination time of 4 hours to finally obtain a nitrogen-doped hard carbon negative electrode material. The hard carbon prepared in the above embodiment is subjected to scanning electron microscopy (SEM) and element distribution test (EDS-mapping) tests. The scanning electron microscopy (SEM) morphology of the hard carbon prepared in Example 1 is as shown in FIG. Figure 1 As shown, the EDS-mapping of the hard carbon prepared in Example 1 is as follows Figure 2The figure shows that the prepared hard carbon material has a block structure with a size of 2-5μm and is evenly distributed. EDS-mapping elemental analysis shows that nitrogen is present in the prepared hard carbon, confirming that plasma doping effectively achieves bulk embedding of heteroatoms.

[0028] The hard carbon prepared in the above embodiment was subjected to cycle performance test at a current density of 10 mA / g, and rate performance test at different current densities. The results are as follows: Figure 3 As shown in a and b in the figure, 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; Figure 3 As shown in b, the specific capacities at current densities of 0.08C, 2C, and 10C are 310 mA / g, 250 mA / g, and 125 mA / g, respectively.

[0029] Example 2

[0030] Cotton shells (1 kg), anthracite (3 kg), sodium dihydrogen phosphate (0.2 kg) and steel balls (18 kg) were used as reactants and placed in a plasma ball milling chamber for ball milling. The chamber was evacuated and, when the pressure in the chamber reached 2 Pa, argon, nitrogen and hydrogen sulfide gases were introduced with a gas volume ratio of 80:10:10. When the pressure in the chamber reached 20 Pa, plasma discharge was performed with a discharge power of 200 W and ball milling was performed for 2 hours. The plasma ball milling chamber was then in-situ heated with plasma discharge at a discharge power of 700 W, and the quartz chamber was heated to 350°C for 3 hours. The product was then 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 hours to finally obtain a hard carbon negative electrode material.

[0031] Example 3

[0032] Corn cobs, anthracite, and urea (3 kg in mass, 0.8 kg in mass, and 0.1 kg in mass) were used as reactants, and 20 kg in mass of steel balls were placed in a plasma ball milling chamber for ball milling. The chamber was evacuated and, when the pressure in the chamber reached 5 Pa, helium and carbon tetrafluoride were introduced with a gas volume ratio of 90:10. When the pressure in the chamber reached 25 Pa, plasma discharge was performed with a discharge power of 500 W, and the milling was carried out for 3 hours. Subsequently, the plasma ball milling chamber was in situ heated with plasma discharge at a discharge power of 800 W, and the quartz chamber was heated to 400°C for 3.5 hours. The obtained product was then 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 1500°C in a nitrogen atmosphere with a heating rate of 20°C / min and a calcination time of 5 hours to finally obtain a hard carbon negative electrode material.

[0033] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized in that: The following steps are involved: (1) Biomass carbon, anthracite and substance A are mixed in a certain proportion, wherein substance A is one or more of sodium chloride, sodium dihydrogen phosphate, urea and thiourea, and placed in a plasma ball milling chamber. After vacuuming to 0.1-10 Pa, a mixed gas of inert gas and reactive gas is filled to 10-500 Pa, and a plasma ball milling process is performed; (2) subjecting the product of step (1) to a plasma ball milling process, in-situ heating of the ball mill cavity, and plasma discharge thereof, with a heating temperature of 200-400°C, a reaction time of 0.5-3 h, and a heating rate of 5-20°C / min; (3) Sintering at high temperature in an inert atmosphere at a sintering temperature of 600-1500°C, a heating rate of 5-20°C / min, and a holding time of 1-5h. The obtained product is acid-washed and washed with water until neutral, thereby obtaining a hard carbon negative electrode material. The gas used in the plasma ball milling process in step (1) and step (2) is a mixed gas of an inert gas and a reactive gas, wherein the inert gas is at least one of nitrogen, argon, helium, and neon; and the reactive gas is at least one of carbon tetrafluoride, ammonia, phosphine, and hydrogen sulfide, wherein the volume ratio of the inert gas to the reactive gas is 100:1 to 1:

100.

2. The preparation method according to claim 1, wherein: The raw material of the biomass carbon is selected from at least one of coconut shells, cotton shells, soybean stalks, sugarcane stalks, and corn cobs.

3. The preparation method according to claim 1, wherein: The mass ratio of the biomass carbon, anthracite and substance A is 50:1:0.1-1:10:0.

5.

4. The preparation method according to claim 1, wherein: The ball milling time in the plasma ball milling process in step (1) and step (2) is 0.5-3 h, and the ball-to-powder ratio is 100:1-10:

1.

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

6. The preparation method according to claim 1, wherein: The anthracite particles after the plasma ball milling treatment in step (2) have a particle size of 2-15 μm.

7. The preparation method according to claim 1, wherein: In step (3), the pickling is performed using 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 of nitrogen and argon or a mixture of the two.

8. A hard carbon material, characterized in that Prepared by the method according to any one of claims 1 to 7, the specific capacity is ≥300 mAh / g at a current density of 10 mA / g, and the capacity retention rate is ≥90% after 300 cycles.

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