A preparation method of a hard carbon negative electrode material

Abstract

The present invention relates to a method for preparing a hard carbon negative electrode, belonging to the field of secondary battery materials. The preparation method includes the following steps: First, the carbon source is crushed to a certain fineness to obtain precursor 1, which is dispersed in water dissolved with a sulfur-containing surfactant; then a mixed acid is added for purification and impurity removal, and it is washed and filtered with pure water multiple times until the filtrate is close to neutral, and then dried to obtain precursor 2; finally, under the protection of an inert atmosphere, precursor 2 is carbonized at a high temperature and post-treated to obtain the hard carbon negative electrode material. The present invention uses a sulfonate-type anionic surfactant as an additive in the pickling process, which not only improves the wetting and dispersion efficiency of the precursor powder in water, but also significantly improves the effect of purification and impurity removal; further, S atom doping is realized on the surface of the hard carbon material, obtaining better rate performance, and promoting the components of SEI to tend to be mainly inorganic salts during the first charge and discharge of the battery, thereby improving the Coulomb efficiency and reversible specific capacity of the first cycle of the material.

Description

Technical Field

[0001] The present invention belongs to the field of secondary battery materials, and particularly relates to a method for preparing a hard carbon negative electrode material. Background Art

[0002] Lithium-ion batteries have excellent electrical performance and are one of the most commercially successful secondary batteries, with a very wide range of applications, from mobile phones and watches to cars and energy storage. However, the low reserves of lithium elements in the earth's crust limit the further wide application of lithium-ion batteries. Sodium-ion and potassium-ion batteries have become a research hotspot today due to their rich resources and low cost. The diameters of sodium ions and potassium ions are relatively large, and graphite used as the negative electrode in lithium-ion batteries is not suitable for sodium / potassium-ion batteries. The negative electrode materials for sodium / potassium-ion batteries are mainly hard carbon materials, which are widely sourced and easy to prepare, making them the first choice for sodium / potassium-ion battery negative electrode materials. However, their research is not yet mature, especially the low specific capacity and first efficiency, which seriously affect the battery energy density and urgently need to be further improved.

[0003] Patent CN109301246B selects high-sulfur coal as the carbon source to prepare the hard carbon material for potassium-ion batteries. Sulfur atom doping can obtain a larger interlayer spacing, and the uniformly distributed pore structure is suitable for the insertion / extraction of potassium ions. However, the specific surface area of this hard carbon material is very large, and it shows only about 40% first Coulomb efficiency in the coin cell performance test, and it does not have industrial application value. CN116281939B improved it by using organotin, cerium nitrate, and lanthanum nitrate. However, these substances are relatively expensive, increasing the preparation cost.

[0004] Patent CN115881919A dopes boron, sulfur, phosphorus, and nitrogen elements on the surface of hard carbon to improve the conductivity of the material itself, making the prepared biomass composite hard carbon negative electrode material have a higher first efficiency, superior rate performance, and cycling performance. The sulfur source used is magnesium sulfate, and the sulfate radical basically does not change after high-temperature treatment and remains in the product in the form of ash, reducing the product performance.

[0005] Patent CN109911878A provides a method for preparing a high-capacity asphalt / epoxy resin-based modified hard carbon negative electrode material, which uses a sulfonic acid derivative. This substance provides an acidic medium to play a catalytic role, without being consumed or converted into reaction products. Patent CN115849337A introduces sulfur elements with a surfactant-based doping source. The surfactant has two main functions. One is to enhance the wetting of the carbonaceous surface and pores, expand the range of element doping and deposition amount, and the other is to increase the interlayer spacing to provide more active sites, that is, to increase the positions for storing lithium ions. In this method, the surfactant is added after pickling, without precipitation or stratification, and cannot be separated by solid-liquid separation in an efficient pressure filtration manner, and can only remove water by evaporation. Summary of the Invention

[0006] To overcome the above disadvantages, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing a hard carbon negative electrode material. First, a carbon source is crushed to a certain fineness to obtain a precursor 1, which is dispersed in water dissolved with a sulfur-containing surfactant; then a mixed acid is added for purification and impurity removal, and the mixture is washed and filtered with pure water multiple times until the filtrate is close to neutral, and then dried to obtain a precursor 2; finally, under the protection of an inert atmosphere, the precursor 2 is carbonized at a high temperature and subjected to post-treatment to obtain a high-performance hard carbon negative electrode material.

[0008] The carbon source can be coal or biomass carbonized material. The preparation method of the biomass carbonized material is as follows: the biomass raw material is broken into granular or flaky shapes and carbonized in a carbonization furnace at 400-750°C for 1-4 hours.

[0009] The carbon source is crushed, and the crushing fineness is D 50 of 5-10 μm, and the crushing method is mechanical crushing or air flow crushing.

[0010] The sulfur-containing surfactant is a sulfonate-type anionic surfactant, selected from at least one of alkylbenzene sulfonate, α-olefin sulfonate, α-sulfo monocarboxylic acid ester, fatty acid sulfalkyl ester, sulfosuccinate, alkyl naphthalene sulfonate, petroleum sulfonate, lignin sulfonate, and alkyl glycerol ether sulfonate, and the dosage is 0.2-2% of the weight of the carbon source powder.

[0011] For the purification and impurity removal, the acids used are any combination of hydrochloric acid, nitric acid or hydrofluoric acid, and the reaction conditions are: acid concentration of 1-20%, reaction temperature of 25-100°C, solid-liquid ratio of 1:2-10, and stirring time of 1-10 hours.

[0012] The inert atmosphere is protected by nitrogen, or it can also be argon, helium or xenon.

[0013] The high-temperature carbonization is carried out by heating to 1000-1600°C at a rate of 0.5-10°C / min and holding for 2-10 hours.

[0014] The post-treatment includes crushing, sieving, demagnetization, packaging, etc.

[0015] In the present invention, the sulfonate-type anionic surfactant can significantly enhance the wetting effect of the raw carbon powder, greatly shorten the dispersion time of the powder in water, effectively improve the efficiency of purification and impurity removal, and also obtain a precursor with lower ash content. The surfactant selected in the present invention is uniformly mixed with precursor 1 in the liquid phase to form a slurry. After adding the acid solution, the surfactant becomes ineffective and precipitates and layers with the carbon powder. Through pressure filtration, solid-liquid separation can be quickly achieved, and finally a mixture precursor 2 of carbon powder and sulfur-containing organic matter is obtained. During the high-temperature carbonization process, the sulfur-containing organic matter loses H and O, and C-S chemical bonds are formed on the surface of the carbon powder to obtain a sulfur-doped hard carbon negative electrode material.

[0016] The sulfur atom has a larger radius than the carbon atom, which can increase the interlayer spacing of the hard carbon material, provide a fast channel for lithium, sodium, and potassium ions, and is beneficial to the high-rate performance; in the C-S bond on the material surface, S has a stronger electronegativity, which acts on Li + / Na + / K + to generate inorganic compounds similar to Li2S / Na2S / K2S. During the first charge and discharge of the battery, it promotes the SEI component to mainly consist of inorganic salts LiF / NaF / KF, reducing the irreversible capacity loss caused by the formation of SEI to a certain extent, improving the first Coulombic efficiency of the hard carbon material, and the coin cell test results also prove this point.

[0017] The beneficial effects of the present invention are as follows: The present invention uses a sulfonate-type anionic surfactant as an additive in the pickling process, which not only improves the wetting and dispersion efficiency of the precursor powder in water, but also significantly improves the purification and impurity removal effect, that is, reduces the ash content of the product; further, the formation of C-S bonds on the surface of the hard carbon material realizes S atom doping, increases the interlayer spacing of graphite microcrystals, obtains better rate performance, and promotes the SEI component to mainly consist of inorganic salts during the first charge and discharge of the battery, thereby improving the first cycle charge and discharge Coulombic efficiency and the reversible specific capacity of the material. Description of the Drawings

[0018] Figure 1 is the first charge and discharge curve of the hard carbon negative electrode material prepared in Example 1;

[0019] Figure 2 is the first charge and discharge curve of the hard carbon negative electrode material prepared in Example 2;

[0020] Figure 3 is the first charge and discharge curve of the hard carbon negative electrode material prepared in Example 3;

[0021] Figure 4 is the first charge and discharge curve of the hard carbon negative electrode material prepared in Comparative Example 1;

[0022] Figure 5 is the first charge and discharge curve of the hard carbon negative electrode material prepared in Comparative Example 2;

[0023] Figure 6 The first charge-discharge curve of the hard carbon negative electrode material prepared in Comparative Example 3. Specific embodiments

[0024] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. In the embodiments and comparative examples: atom% is the surface atom ratio, measured by XPS. The charge-discharge voltage range of the sodium battery is 0 - 2.0V, the charge-discharge voltage range of the lithium battery is 0.005 - 2V, and the charge-discharge voltage range of the potassium battery is 0.005 - 2.0V.

[0025] Example 1

[0026] A method for preparing a hard carbon negative electrode material, comprising the following steps: crushing semi-coke by roller crushing and jet milling to a precursor 1 with a D 50 of 8 μm; adding 150 g of sodium lignosulfonate in batches to stir and dissolve under the conditions of 50 kg of pure water, stirring, and heating, and maintaining a constant temperature of 80°C; continuously adding 15 kg of precursor 1 within 3 min, and continuing to stir for 5 min until completely dispersed to obtain a uniform slurry; adding 8 kg of hydrochloric acid with a concentration of 30 wt% and 2.5 kg of hydrofluoric acid with a concentration of 40 wt% in sequence, and stirring at a constant temperature of 80°C for 4 h; stopping stirring, filtering the slurry multiple times and washing with pure water until the filtrate is close to neutral, and drying the filter cake in an oven at 105°C to obtain precursor 2; carbonizing at high temperature under a nitrogen atmosphere with an oxygen content of less than 50 ppm, heating at a rate of 4°C / min to 1600°C, maintaining the temperature for 2 h, and cooling with the furnace to below 60°C for discharging; crushing and sieving through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 0.85%, and the surface S content is 1.05 atom%. A button half-cell is prepared with metallic sodium as the counter electrode, and the test data are as Figure 1 shown, the reversible capacity is 266.70 mAh / g, and the first-cycle Coulombic efficiency is 86.39%.

[0027] Example 2

[0028] A method for preparing a hard carbon negative electrode material, comprising the following steps: crushing coconut shells into flakes within 20 mm, and pre-carbonizing at 500°C in a carbonization furnace for 4 h to obtain coconut shell carbonized material; crushing the coconut shell carbonized material by jaw crushing, roller crushing, and jet milling to a D 50Precursor 1 with a size of 5 μm; Under the conditions of stirring and heating in 50 kg of pure water, 300 g of sodium succinate sulfonate was added in batches until dissolved by stirring, and the temperature was kept constant at 100 °C; 15 kg of precursor 1 was continuously added within 3 min, and stirring was continued for 8 min until complete dispersion. The smaller the particle size, the slower the dispersion; 3 kg of hydrochloric acid with a concentration of 30 wt% and 1 kg of hydrofluoric acid with a concentration of 40 wt% were added in sequence, and stirring was carried out at a constant temperature of 100 °C for 3 h; Stirring was stopped, and the slurry was filtered and washed with pure water multiple times until the filtrate was close to neutral. The filter cake was dried in an oven at 105 °C to obtain precursor 2; High-temperature carbonization was carried out under a nitrogen atmosphere with an oxygen content of less than 50 ppm. The temperature was raised to 1200 °C at a rate of 4 °C / min, and the holding time was 8 h. It was cooled in the furnace to below 60 °C before discharging; After crushing and passing through a 400-mesh sieve, the hard carbon negative electrode material was obtained. Among them, the ash content was 0.22%, and the surface S content was 0.55 atom%. A button half-cell was prepared with metallic sodium as the counter electrode, and the test data was as Figure 2 shown, the reversible capacity was 288.04 mAh / g, and the first-cycle Coulombic efficiency was 85.52%.

[0029] Example 3

[0030] A preparation method of a hard carbon negative electrode material includes the following steps: Crushing walnut shells into particles within 10 mm, and obtaining walnut shell carbonized material by pre-carbonization at 750 °C in a carbonization furnace for 1 h; Crushing the walnut shell carbonized material by roll crushing and airflow milling to D 50 Precursor 1 with a size of 5 μm; Under the conditions of stirring and heating in 50 kg of pure water, 100 g of potassium lignosulfonate was added until dissolved by stirring, and the temperature was kept constant at 60 °C; 15 kg of precursor 1 was continuously added within 3 min, and stirring was continued for 5 min until complete dispersion; 2 kg of hydrochloric acid with a concentration of 30 wt% and 0.5 kg of hydrofluoric acid with a concentration of 40 wt% were added in sequence, and stirring was carried out at a constant temperature of 60 °C for 6 h; Stirring was stopped, and the slurry was filtered and washed with pure water multiple times until the filtrate was close to neutral. The filter cake was dried in an oven at 105 °C to obtain precursor 2; High-temperature carbonization was carried out under an argon atmosphere with an oxygen content of less than 50 ppm. The temperature was raised to 1300 °C at a rate of 2 °C / min, and the holding time was 4 h. It was cooled in the furnace to below 60 °C before discharging; After crushing and passing through a 400-mesh sieve, the hard carbon negative electrode material was obtained. Among them, the ash content was 0.28%, and the surface S content was 0.46 atom%. A button half-cell was prepared with metallic sodium as the counter electrode, and the test data was as Figure 3 shown, the reversible capacity was 324.04 mAh / g, and the first-cycle Coulombic efficiency was 87.85%.

[0031] Example 4

[0032] A preparation method of a hard carbon negative electrode material, comprising the following steps: crushing walnut shells into particles within 10 mm, and obtaining walnut shell carbonized material by pre-carbonizing in a carbonization furnace at 550 °C for 3 h; subjecting the walnut shell carbonized material to roll crushing and jet milling to grind it into a precursor 1 with D 50 of 7 μm; adding 80 g of sodium petroleum sulfonate to 20 kg of pure water under the conditions of stirring and heating until it is stirred and dissolved, and maintaining a constant temperature of 30 °C; continuously adding 15 kg of the precursor 1 within 3 min, and continuing to stir for 3 min until it is completely dispersed; successively adding 3 kg of hydrochloric acid with a concentration of 30 wt% and 7 kg of nitric acid with a concentration of 68 wt%, and stirring at a constant temperature of 30 °C for 8 h; stopping stirring, filtering the slurry multiple times and washing it with pure water until the filtrate is close to neutral, drying the filter cake in an oven at 105 °C to obtain a precursor 2; performing high-temperature carbonization under a nitrogen atmosphere with an oxygen content of less than 50 ppm, heating at a rate of 2 °C / min to 1300 °C, maintaining the temperature for 4 h, and cooling with the furnace to below 60 °C for discharging; performing crushing and sieving through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 0.15%, and the surface S content is 0.59 atom%. Preparing a button half-cell with metallic sodium as the counter electrode, and the test data is as Figure 4 shown, the reversible capacity is 336.14 mAh / g, and the first-cycle Coulombic efficiency is 88.81%.

[0033] Example 5

[0034] A preparation method of a hard carbon negative electrode material, comprising the following steps: crushing apricot shells into particles within 6 mm, and obtaining apricot shell carbonized material by pre-carbonizing in a carbonization furnace at 650 °C for 2 h; subjecting the apricot shell carbonized material to roll crushing and jet milling to grind it into a precursor 1 with D 50 of 9 μm; adding 200 g of diisopropylnaphthalenesulfonic acid sodium in batches to 100 kg of pure water under the condition of stirring until it is stirred and dissolved, and heating to a constant temperature of 60 °C; continuously adding 15 kg of the precursor 1 within 3 min, and continuing to stir for 4 min until it is completely dispersed; successively adding 3 kg of hydrochloric acid with a concentration of 30 wt% and 1 kg of hydrofluoric acid with a concentration of 40 wt%, and stirring at a constant temperature of 60 °C for 1 h; stopping stirring, filtering the slurry multiple times and washing it with pure water until the filtrate is close to neutral, drying the filter cake in an oven at 105 °C to obtain a precursor 2; performing high-temperature carbonization under a nitrogen atmosphere with an oxygen content of less than 50 ppm, heating at a rate of 2 °C / min to 1400 °C, maintaining the temperature for 4 h, and cooling with the furnace to below 60 °C for discharging; performing crushing and sieving through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 0.23%, and the surface S content is 0.34 atom%. Preparing a button half-cell with metallic lithium as the counter electrode, and the test data is as Figure 5 shown, the reversible capacity is 315.95 mAh / g, and the first-cycle Coulombic efficiency is 87.92%.

[0035] Example 6

[0036] A preparation method of a hard carbon negative electrode material, comprising the following steps: crushing jujube husks into particles within 5 mm, and obtaining walnut shell carbonized material by pre-carbonizing at 550 °C in a carbonization furnace for 3 h; crushing the walnut shell carbonized material by roll crushing and airflow milling to obtain a precursor 1 with a D 50 of 7 μm; under the conditions of stirring and heating in 50 kg of pure water, adding 30 g of sodium dodecylbenzenesulfonate and stirring until dissolved, and maintaining a constant temperature of 25 °C; continuously adding 15 kg of the precursor 1 within 3 min, and continuing to stir for 5 min until completely dispersed; successively adding 4 kg of nitric acid with a concentration of 68 wt% and 0.5 kg of hydrofluoric acid with a concentration of 40 wt%, and stirring at a constant temperature of 25 °C for 10 h; stopping stirring, filtering the slurry multiple times and washing with pure water until the filtrate is close to neutral, drying the filter cake in an oven at 105 °C to obtain a precursor 2; performing high-temperature carbonization under a nitrogen atmosphere, with an oxygen content of less than 50 ppm, heating at a rate of 2 °C / min to 1000 °C, holding for 10 h, and cooling with the furnace to below 60 °C for discharging; crushing and passing through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 0.35%, and the surface S content is 0.25 atom%. Preparing a button half-cell with metallic potassium as the counter electrode, and the test data is as Figure 6 shown, the reversible capacity is 315.26 mAh / g, and the first-cycle Coulombic efficiency is 86.93%.

[0037] Comparative Example 1

[0038] A preparation method of a hard carbon negative electrode material, comprising the following steps: crushing semi-coke by roll crushing and airflow milling to obtain a precursor 1 with a D 50 of 8 μm; stirring and heating 50 kg of pure water to 80 °C; continuously adding 15 kg of the precursor 1 within 3 min, and continuing to stir for 60 min until completely dispersed to obtain a uniform slurry. Since a large amount of the material floats on the liquid surface, manual auxiliary stirring is required; successively adding 8 kg of hydrochloric acid with a concentration of 30 wt% and 2.5 kg of hydrofluoric acid with a concentration of 40 wt%, and stirring at a constant temperature of 80 °C for 4 h; stopping stirring, filtering the slurry multiple times and washing with pure water until the filtrate is close to neutral, drying the filter cake in an oven at 105 °C to obtain a precursor 2; performing high-temperature carbonization under a nitrogen atmosphere, with an oxygen content of less than 50 ppm, heating at a rate of 4 °C / min to 1600 °C, holding for 2 h, and cooling with the furnace to below 60 °C for discharging; crushing and passing through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 1.45%, and the surface S content is 0.68 atom%. Preparing a button half-cell with metallic sodium as the counter electrode, and the test data is as Figure 4 shown, the reversible capacity is 239.02 mAh / g, and the first-cycle Coulombic efficiency is 82.23%.

[0039] Comparative Example 2

[0040] A preparation method of a hard carbon negative electrode material, comprising the following steps: crushing coconut shells into flakes with a size within 20 mm, and pre-carbonizing in a carbonization furnace at 500 °C for 3 h to obtain coconut shell carbonized material; crushing the coconut shell carbonized material through jaw crusher, roll crusher, and airflow mill to a precursor 1 with D 50 of 5 μm; stirring 50 kg of pure water and heating it to 100 °C; adding 15 kg of precursor 1 in 3 portions, continuously adding 5 kg within 5 min, continuing to stir for 20 min until completely dispersed, and repeating twice to obtain a uniform slurry; successively adding 3 kg of hydrochloric acid with a concentration of 30 wt% and 1 kg of hydrofluoric acid with a concentration of 40 wt%, and stirring at a constant temperature of 100 °C for 3 h; stopping stirring, filtering the slurry multiple times and washing with pure water until the filtrate is close to neutral, drying the filter cake in an oven at 105 °C to obtain precursor 2; performing high-temperature carbonization in a nitrogen atmosphere with an oxygen content less than 50 ppm, heating to 1200 °C at a rate of 4 °C / min, holding for 8 h, and cooling with the furnace to below 60 °C for discharging; crushing and passing through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 0.38%, and the surface S content is not detected. Using metallic sodium as the counter electrode to prepare a button half-cell, the test data is as Figure 5 shown, the reversible capacity is 279.42 mAh / g, and the first-cycle Coulombic efficiency is 82.91%.

[0041] Comparative Example 3

[0042] A preparation method of a hard carbon negative electrode material, comprising the following steps: crushing walnut shells into particles with a size within 10 mm, and pre-carbonizing in a carbonization furnace at 750 °C for 1 h to obtain walnut shell carbonized material; crushing the walnut shell carbonized material through roll crusher and airflow mill to a precursor 1 with D 50 of 5 μm; stirring 50 kg of pure water and heating it to 60 °C; adding 15 kg of precursor 1 in 3 portions, continuously adding 5 kg within 5 min, continuing to stir for 16 min until completely dispersed, and repeating twice to obtain a uniform slurry; successively adding 2 kg of hydrochloric acid with a concentration of 30 wt% and 0.5 kg of hydrofluoric acid with a concentration of 40 wt%, and stirring at a constant temperature of 60 °C for 6 h; stopping stirring, filtering the slurry multiple times and washing with pure water until the filtrate is close to neutral, drying the filter cake in an oven at 105 °C to obtain precursor 2; performing high-temperature carbonization in an argon atmosphere with an oxygen content less than 50 ppm, heating at a rate of 2 °C / min to 1300 °C, holding for 4 h, and cooling with the furnace to below 60 °C for discharging; crushing and passing through a 400-mesh sieve to obtain the hard carbon negative electrode material. Among them, the ash content is 0.35%, and the surface S content is not detected. Using metallic sodium as the counter electrode to prepare a button half-cell, the test data is as Figure 6 shown, the reversible capacity is 317.90 mAh / g, and the first-cycle Coulombic efficiency is 85.38%.

Claims

1. A method for preparing a hard carbon negative electrode, characterized in that, First, the carbon source is crushed to a certain fineness to obtain precursor 1, which is dispersed in water dissolved with a sulfur-containing surfactant; then a mixed acid is added for purification and impurity removal, and it is washed and filtered with pure water multiple times until the filtrate is close to neutral, and then dried to obtain precursor 2; finally, under the protection of an inert atmosphere, precursor 2 is carbonized at a high temperature and is post-treated to obtain the hard carbon anode material.

2. The method for preparing a hard carbon negative electrode according to claim 1, characterized in that, The carbon source is coal or biomass carbonized material.

3. The method for preparing a hard carbon negative electrode according to claim 2, characterized in that, The preparation method of the biomass carbonized material is: crushing the biomass raw material into granular or flaky shape, and carbonizing it in a carbonization furnace at 400 - 750 °C for 1 - 4 h.

4. The method for preparing the hard carbon negative electrode according to claim 1, characterized in that, The carbon source is crushed, and the crushing fineness is that D50 is 5 - 10 μm, and the crushing method is mechanical crushing or air flow crushing.

5. The method for preparing a hard carbon negative electrode according to claim 1, wherein The sulfur-containing surfactant is a sulfonate-type anionic surfactant, selected from at least one of alkylbenzene sulfonate, α-olefin sulfonate, α-sulfomonocarboxylate, fatty acid sulfalkyl ester, sulfosuccinate, alkylnaphthalene sulfonate, petroleum sulfonate, lignin sulfonate, alkyl glycerol ether sulfonate.

6. The method for preparing the hard carbon negative electrode according to claim 5, wherein, The dosage of the sulfur-containing surfactant is 0.2 - 2% of the weight of the carbon source powder.

7. The method for preparing a hard carbon negative electrode according to claim 1, characterized in that, For the purification and impurity removal, the acid used is any combination of hydrochloric acid, nitric acid or hydrofluoric acid, and the reaction conditions are: acid concentration is 1 - 20%, reaction temperature is 25 - 100 °C, solid-liquid ratio is 1:2 - 10, and stirring time is 1 - 10 h.

8. The method for preparing a hard carbon negative electrode according to claim 1, wherein, The high-temperature carbonization is to heat up to 1000 - 1600 °C at a rate of 0.5 - 10 °C / min and keep the temperature for 2 - 10 h.

9. The method for preparing a hard carbon negative electrode according to claim 1, wherein The inert atmosphere is protected by nitrogen, argon, helium or xenon.

10. The method for preparing the hard carbon negative electrode according to claim 1, characterized in that, The post-treatment includes crushing, sieving, demagnetization and packaging.

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