High specific power lithium ion battery negative electrode material and preparation and application thereof

Abstract

The application discloses a high specific power lithium ion battery negative electrode material and a preparation method thereof. The material is prepared by pre-carbonizing, removing impurities, soaking in salt, coating pitch and carbonizing a biomass raw material, and forms a core-shell structure with a larger internal disorder interlayer spacing and a graphite-like characteristic on the outside. The negative electrode material can meet the requirements of storing more lithium ions in the electrode and fast charging and discharging, realizes the high capacity and high rate performance of the negative electrode material, and reduces the irreversible capacity loss caused by the formation of too much solid electrolyte interface film, and has a higher first cycle coulombic efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a negative electrode material for high specific power lithium ion batteries and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries, as the mainstream secondary battery technology, are widely used in consumer electronics, electric vehicles and large-scale energy storage industries, greatly improving human life. With the change of application environment, lithium ion batteries are increasingly required to have fast charging and discharging capacity, such as start-stop batteries for cars, high-speed rails and subways, and unmanned aerial vehicle model batteries.

[0003] Fast charging and discharging performance requires lithium ion batteries to complete electrochemical reactions in a very short time. Therefore, high requirements are placed on electron and ion transmission, especially the transmission speed of lithium ions in the negative electrode and its vicinity is a key factor restricting the high specific power of lithium ions. Currently, the negative electrode materials on the market include graphite, amorphous carbon material and lithium titanate. The specific capacity of graphite can reach more than 300 mA·h / g, and the first cycle coulombic efficiency can reach more than 90%, but graphite material has the problems of poor structural stability and poor compatibility with electrolyte. In the process of charging and discharging, it is easy to have a co-embedding reaction with propylene carbonate organic solvent in the electrolyte, resulting in structural damage, thereby affecting the cycle stability and charging and discharging efficiency of the battery. Moreover, due to the anisotropic structure characteristics of graphite, the free diffusion of lithium ions in the graphite structure is limited, and the interlayer spacing is small, which affects the rate performance of the graphite negative electrode material. Amorphous carbon materials mainly include hard carbon and soft carbon. Compared with graphite, they have low crystallinity, exist micropores, and the sheet structure is not as regular and ordered as graphite, and the repeated graphite sheet structure is generally less than 2-3 layers. This interlaced layered structure allows Li+ to be embedded and extracted from various angles of the material, and the interlayer spacing is large, which is beneficial to the rapid diffusion of lithium ions, thereby realizing the rapid charging and discharging of the material. Hard carbon and soft carbon materials have the advantage of good cycle performance because they do not have the solvent co-embedding and significant lattice expansion and contraction phenomena that graphite materials are prone to. In addition, as the processing process does not require graphitization treatment, the cost of hard carbon and soft carbon materials is significantly lower than that of graphite negative electrode materials. However, the first cycle efficiency of this type of material is low (40-60%), and the specific capacity is low (about 300 mAh / g), which limits their commercial application. SUMMARY

[0004] In order to solve the problems of low first cycle coulombic efficiency and low specific capacity of the existing biomass-based hard carbon material, the application provides a kind of powder-like carbon material with core-shell structure for high specific power lithium ion battery negative electrode material, the particle size of core is 3-8 μm, contains a large number of micropores with pore size of 0.001-0.5 nm, accounts for 60-90% of total pore volume of core, the rest is micropore with pore size of greater than 0.5 nm-50 nm, the interlayer spacing of 002 crystal face is 0.39-0.41 nm;The thickness of shell is 10-1000 nm, preferably 10-200 nm, the interlayer spacing of 002 crystal face is 0.34-0.36 nm;The specific surface area of the material is 2-4 m 2 / g. Both can meet the requirements of a large number of lithium storage space inside the electrode and fast charging and discharging, and can realize the dense solid electrolyte interface film outside the negative electrode.

[0005] The application also provides a preparation method of the above-mentioned negative electrode material, comprising the following steps:

[0006] 1) after drying and crushing the biomass raw material, pre-carbonization treatment is carried out at 400-600 DEG C for 1-3h in inert atmosphere, to obtain product A;

[0007] 2) product A is immersed and stirred in NaOH solution and acid solution in sequence, and then cleaned (the purpose of cleaning is to remove impurities (including silicon, metal elements, etc.) other than carbon in the raw material), and then filtered, washed to neutral, dried, and crushed by airflow crusher to obtain carbon powder B with particle size of 3-8 μm;

[0008] 3) carbon powder B is immersed and stirred in NaCl or Na2CO3 solution, and then filtered and dried to obtain carbon powder C, and the molar ratio of carbon to NaCl or Na2CO3 is 10 / 1-100 / 1;

[0009] 4) carbon powder C is subjected to pitch coating treatment, and the specific steps are as follows: carbon powder C and pitch are put into an internal mixer, heated to 200-260 DEG C, and mixed by internal mixing for 20-30 min;Then carbonization treatment is carried out at 1100-1300 DEG C for 1-3h in inert atmosphere, to obtain the negative electrode material.

[0010] Among them,

[0011] The biomass raw material is one or more of coconut shell, peach shell, apricot shell and walnut shell.

[0012] The inert atmosphere in steps 1) and 4) is nitrogen atmosphere and / or argon atmosphere respectively;

[0013] The concentration of the NaOH solution in step 2) is 1-5 mol / L, the acid solution is hydrochloric acid solution, sulfuric acid solution or nitric acid solution, and the concentration is 1-5 mol / L; the impregnation stirring time is 1-100 h, preferably 25-50 h; and the temperature during stirring is 25-70℃, preferably 50-70℃.

[0014] The concentration of the NaCl or Na2CO3 solution in step 3) is 1-5 mol / L; the impregnation stirring time is 1-100 h, preferably 25-50 h; and the temperature during stirring is 25-50℃.

[0015] The asphalt is petroleum asphalt, and the softening point is 200-250℃.

[0016] The mass ratio of the carbon powder C to the asphalt is 7 / 3-9 / 1.

[0017] The present application has the following advantages:

[0018] (1) The negative electrode material provided by the present application has a hard carbon structure inside, a large interlayer spacing, and is beneficial to the diffusion of lithium ions therein, and can meet the fast charge and discharge of the electrode, and realize the high rate performance of the negative electrode material.

[0019] (2) The negative electrode material provided by the present application has a large number of micropores inside, a large lithium storage space, and can obtain a higher specific capacity.

[0020] (3) The negative electrode material provided by the present application has a graphite-like feature on the outer surface, has good conductivity, can reduce the resistance of the negative electrode, and is beneficial to realizing the high rate performance of the negative electrode material.

[0021] (4) The negative electrode material provided by the present application has a lower specific surface area than the hard carbon material, can reduce the irreversible capacity loss caused by the formation of too much solid electrolyte interface film, and has a higher first cycle coulombic efficiency. DETAILED DESCRIPTION

[0022] The present application will be described in detail below through specific examples.

[0023] The prepared negative electrode material is used for testing in button cells, and the battery testing methods in the examples and comparative examples are the same, and are as follows: the prepared negative electrode material, conductive agent (Super-P), and polyvinylidene fluoride are mixed in a mass ratio of 90:2:8, uniformly dispersed in N-methyl pyrrolidone, coated on the surface of a copper foil to form an electrode sheet containing 3±0.3 mg of negative electrode material per square centimeter of copper foil. After the electrode sheet is punched into a round sheet, a battery structure with a sandwich structure of the round sheet, a separator (Celgard), and metal lithium is formed, and an electrolyte (lithium hexafluorophosphate concentration of 1 mol / L, solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (volume ratio of 1:1:1), and containing 2% of vinylene carbonate by mass) is added. The battery performance test uses the CCCV charging and discharging method, that is, charging to 0 V at a current of 0.1 C, then constant voltage charging to 0.02 C to terminate, then discharging to 1.5 V at a current of 0.1 C as one cycle, and the first cycle coulomb efficiency of the negative electrode material is recorded in Table 1 by using the discharge capacity to charge capacity. Then, charging and discharging at a current of 1 C, 2 C, and 5 C are carried out, and the cut-off voltage is 0 V-1.5 V. Each current is operated for 5 cycles, and the average value is recorded in Table 1.

[0024] Example 1

[0025] After 1 kg of coconut shell is dried in a vacuum drying oven at an environment of 110°C for 8 h, it is crushed by a crusher, and pre-carbonization treatment is carried out in an argon atmosphere, the heat treatment temperature is 500°C, and the time is 2 h. Then, it is ultrasonically cleaned in a 1M NaOH solution for 2 h, and then ultrasonically cleaned in a 2M hydrochloric acid solution for 2 h. After filtration, it is washed with deionized water until the pH value is 7, dried at 110°C, and then crushed by an airflow crusher to obtain carbon powder with a particle size of 3-8 μm. 100 g of the carbon powder is added to a 2M NaCl solution and immersed at room temperature for 25 h, the molar ratio of the carbon powder to NaCl is 10 / 1, and after filtration and drying, it is mixed with petroleum pitch with a softening point of 200°C in a ratio of 8 / 2 in a banbury mixer, the banbury mixer temperature is 220°C, and the banbury mixing time is 25 min. After uniform mixing, it is carbonized at 1100°C in an argon atmosphere for 1 h, cooled to room temperature, crushed and sieved to obtain the negative electrode material with a core-shell structure, wherein the particle size of the core is 3-8 μm, contains a large number of micropores with a pore size of 0.001-0.5 nm, accounting for 75% of the total pore volume of the core, the rest are micropores with a pore size of greater than 0.5 nm-50 nm, the interlayer spacing of the 002 crystal face is 0.39 nm, the thickness of the shell is 50-200 nm, the interlayer spacing of the 002 crystal face is 0.35 nm, and the specific surface area is 3.5 m 2 / g.

[0026] The negative electrode material is made into a button cell, and the button cell is subjected to battery performance detection. The charge-discharge reversible specific capacity of the battery is 430 mAh / g, the first cycle coulombic efficiency is 82.2%, and the rate performance reversible capacity at 5C / 0.1C is 72.3%.

[0027] Example 2

[0028] After 1 kg of coconut shell is dried at 110°C in a vacuum drying oven for 8 h, it is crushed by a crusher, and is subjected to pre-carbonization treatment in an argon atmosphere. The heat treatment temperature is 600°C, and the time is 2 h. Then, it is placed in a 1M NaOH solution for ultrasonic cleaning for 2 h, and is placed in a 2M hydrochloric acid solution for ultrasonic cleaning for 2 h. After filtration, it is washed with deionized water until the pH value is 7, is dried at 110°C, and is subjected to crushing treatment by an air flow crusher to obtain carbon powder with a particle size of 3-8 μm. 100 g of the carbon powder is added to a 2M NaCl solution for immersion at room temperature for 25 h. The molar ratio of the carbon powder to NaCl is 20 / 1. After filtration and drying, it is added to a Banbury mixer with petroleum pitch with a softening point of 200°C in a ratio of 8 / 2 for mixing. The Banbury mixer temperature is 220°C, and the mixing time is 25 min. After uniform mixing, it is taken out, is subjected to carbonization treatment at 1100°C in an argon atmosphere for 2 h, is crushed and sieved after cooling to room temperature, and the negative electrode material with a core-shell structure is obtained. The particle size of the core is 3-8 μm, contains a large number of micropores with a pore size of 0.001-0.5 nm, which accounts for 72% of the total pore volume of the core, and the rest are micropores with a pore size of greater than 0.5 nm-50 nm. The 002 crystal face interlayer spacing is 0.4 nm, the thickness of the shell is 100-500 nm, the 002 crystal face interlayer spacing is 0.35 nm, and the specific surface area is 3.8 m 2 / g. The negative electrode material is made into a button cell, and the performance of the button cell is shown in Table 1.

[0029] Example 3

[0030] The 1 kg of coconut shell was dried in a vacuum drying oven at 110°C for 8 h, then crushed by a crusher, and pre-carbonized at 500°C for 2 h under argon atmosphere. Then, the coconut shell was ultrasonically cleaned in 1 M NaOH solution for 2 h, and then in 2 M HCl solution for 2 h. After filtration, the coconut shell was washed with deionized water until the pH value was 7, dried at 110°C, and then crushed by a jet mill to obtain carbon powder with a particle size of 3-8 μm. 100 g of the carbon powder was immersed in 2 M NaCl solution at room temperature for 25 h, and the molar ratio of carbon powder to NaCl was 50 / 1. After filtration and drying, the carbon powder was mixed with petroleum pitch with a softening point of 200°C at a ratio of 8 / 2 in an internal mixer at a temperature of 220°C for 25 min. After mixing, the mixture was taken out, carbonized at 1200°C for 1 h under argon atmosphere, and then crushed and sieved after cooling to room temperature to obtain the negative electrode material with core-shell structure, wherein the particle size of the core was 3-8 μm, contained a large number of micropores with a pore size of 0.001-0.5 nm, which accounted for 70% of the total pore volume of the core, and the rest were micropores with a pore size of greater than 0.5 nm-50 nm, the interlayer spacing of the 002 crystal face was 0.39 nm, the thickness of the shell was 100-500 nm, the interlayer spacing of the 002 crystal face was 0.35 nm, and the specific surface area was 2.3 m 2 / g. The negative electrode material was made into a button cell, and the performance was as shown in Table 1.

[0031] Example 4

[0032] The 1 kg of coconut shell was dried in a vacuum drying oven at 110°C for 8 h, then crushed by a crusher, and pre-carbonized at 500°C for 2 h under argon atmosphere. Then, the coconut shell was ultrasonically cleaned in 1 M NaOH solution for 2 h, and then in 2 M HCl solution for 2 h. After filtration, the coconut shell was washed with deionized water until the pH value was 7, dried at 110°C, and then crushed by a jet mill to obtain carbon powder with a particle size of 3-8 μm. 100 g of the carbon powder was immersed in 2 M NaCl solution at room temperature for 25 h, and the molar ratio of carbon powder to NaCl was 50 / 1. After filtration and drying, the carbon powder was mixed with petroleum pitch with a softening point of 200°C at a ratio of 8 / 2 in an internal mixer at a temperature of 220°C for 25 min. After mixing, the mixture was taken out, carbonized at 1200°C for 1 h under argon atmosphere, and then crushed and sieved after cooling to room temperature to obtain the negative electrode material with core-shell structure, wherein the particle size of the core was 3-8 μm, contained a large number of micropores with a pore size of 0.001-0.5 nm, which accounted for 70% of the total pore volume of the core, and the rest were micropores with a pore size of greater than 0.5 nm-50 nm, the interlayer spacing of the 002 crystal face was 0.39 nm, the thickness of the shell was 100-500 nm, the interlayer spacing of the 002 crystal face was 0.35 nm, and the specific surface area was 2.3 m 2 / g. The negative electrode material was made into button cells, and the performance is shown in Table 1.

[0033] Example 5

[0034] After 1 kg of coconut shell was dried in a vacuum drying oven at 110°C for 8 h, it was crushed by a crusher, and pre-carbonization treatment was carried out under an argon atmosphere, the temperature of heat treatment was 500°C, and the time was 2 h; then it was put into a 1M NaOH solution for ultrasonic cleaning for 2 h, and then into a 2M hydrochloric acid solution for ultrasonic cleaning for 2 h, after filtration, it was washed with deionized water until the pH value was 7, and after drying at 110°C, it was crushed by an air flow crusher to obtain carbon powder with a particle size of 3-8 μm; 100 g of the carbon powder was added to a 2M NaCl solution for immersion at room temperature for 50 h, the molar ratio of carbon powder to NaCl was 10 / 1, after filtration and drying, it was added to a Banbury mixer with petroleum pitch with a softening point of 200°C at a ratio of 9 / 1, the temperature of the Banbury mixer was 220°C, the mixing time was 25 min, after uniform mixing, it was taken out, carbonization treatment was carried out at 1100°C under an argon atmosphere for 1 h, after cooling to room temperature, it was crushed and sieved to obtain the negative electrode material with a core-shell structure, wherein the particle size of the core was 3-8 μm, the micropores with a pore size of 0.001-0.5 nm accounted for 80% of the total pore volume of the core, the rest were micropores with a pore size of greater than 0.5 nm-50 nm, the interlayer spacing of the 002 crystal face was 0.4 nm, the thickness of the shell was 100-500 nm, the interlayer spacing of the 002 crystal face was 0.35 nm, and the specific surface area was 2.5 m 2 / g. The negative electrode material was made into button cells, and the performance is shown in Table 1.

[0035] Comparative Example 1

[0036] After 1 kg of coconut shell was dried in a vacuum drying oven at 110°C for 8 h, it was crushed by a crusher, and pre-carbonization treatment was carried out under an argon atmosphere, the temperature of heat treatment was 500°C, and the time was 2 h; then it was put into a 1M NaOH solution for ultrasonic cleaning for 2 h, and then into a 2M hydrochloric acid solution for ultrasonic cleaning for 2 h, after filtration, it was washed with deionized water until the pH value was 7, and after drying at 110°C, it was crushed by an air flow crusher to obtain carbon powder with a particle size of 3-8 μm; 100 g of the carbon powder was added to a 2M NaCl solution for immersion at room temperature for 50 h, the molar ratio of carbon powder to NaCl was 10 / 1, after filtration and drying, it was added to a Banbury mixer with petroleum pitch with a softening point of 200°C at a ratio of 9 / 1, the temperature of the Banbury mixer was 220°C, the mixing time was 25 min, after uniform mixing, it was taken out, carbonization treatment was carried out at 1100°C under an argon atmosphere for 1 h, after cooling to room temperature, it was crushed and sieved to obtain the negative electrode material with a core-shell structure, wherein the particle size of the core was 3-8 μm, the micropores with a pore size of 0.001-0.5 nm accounted for 80% of the total pore volume of the core, the rest were micropores with a pore size of greater than 0.5 nm-50 nm, the interlayer spacing of the 002 crystal face was 0.4 nm, the thickness of the shell was 100-500 nm, the interlayer spacing of the 002 crystal face was 0.35 nm, and the specific surface area was 2.5 m

[0037] Comparative Example 2

[0038] 1 kg of petroleum pitch with softening point of 200 °C was dried in a vacuum drying oven at 110 °C for 8 h, and then pre-carbonized at 500 °C for 2 h under argon atmosphere. The carbon powder with particle size of 3-8 μm was obtained by using a jet mill. Then the carbon powder was carbonized at 1100 °C for 2 h under argon atmosphere. After cooling to room temperature, the powder was crushed and sieved to obtain the negative electrode material with particle size of 3-8 μm and interlayer spacing of 0.35 nm in 002 crystal plane. The performance of the button cell made therefrom is shown in Table 1.

[0039] Comparative Example 3

[0040] 1 kg of coconut shell was dried in a vacuum drying oven at 110 °C for 8 h, and then crushed by a crusher. The crushed coconut shell was pre-carbonized at 500 °C for 2 h under argon atmosphere. The pre-carbonized coconut shell was ultrasonically cleaned in 1 M NaOH solution for 2 h, and then in 2 M HCl solution for 2 h. After filtration, the pre-carbonized coconut shell was washed with deionized water until the pH value was 7. The pre-carbonized coconut shell was dried at 110 °C, and then crushed by a jet mill to obtain the carbon powder with particle size of 3-8 μm. The carbon powder was coated with petroleum pitch with softening point of 200 °C and xylene at a mass ratio of 80:20:50 in a reaction kettle at 220 °C for 2 h. The coated carbon powder was carbonized at 1100 °C for 2 h under argon atmosphere. After cooling to room temperature, the powder was crushed and sieved to obtain the negative electrode material with core-shell structure, wherein the particle size of the core was 3-8 μm, the micropores with pore size of 0.001-0.5 nm in the core accounted for 60% of the total pore volume of the core, the interlayer spacing of 002 crystal plane was 0.38 nm, the thickness of the shell was 100-500 nm, and the interlayer spacing of 002 crystal plane was 0.35 nm. The performance of the button cell made therefrom is shown in Table 1.

[0041] Comparative Example 4

[0042] Different from Example 1, 100 g of the carbon powder was immersed in 5 M NaCl solution at room temperature for 25 h, and the molar ratio of the carbon powder to NaCl was 2 / 1. The negative electrode material with core-shell structure was obtained, wherein the particle size of the core was 3-8 μm, the micropores with pore size of 0.001-0.5 nm in the core accounted for 30% of the total pore volume of the core, the interlayer spacing of 002 crystal plane was 0.39 nm, the thickness of the shell was 100-500 nm, and the interlayer spacing of 002 crystal plane was 0.35 nm. The performance of the button cell made therefrom is shown in Table 1.

[0043] Comparative Example 5

[0044] The difference from Example 1 is that 100 g of carbon powder is added to a 2M NaCl solution and immersed at room temperature for 25 h, and the molar ratio of carbon powder to NaCl is 200 / 1. A negative electrode material with a core-shell structure is obtained, wherein the particle size of the core is 3-8 μm, the micropores with a pore size of 0.001-0.5 nm in the core account for 65% of the total pore volume of the core, the interlayer spacing of the 002 crystal face is 0.38 nm, the thickness of the shell is 100-500 nm, and the interlayer spacing of the 002 crystal face is 0.35 nm. It is made into a button cell, and its performance is shown in Table 1.

[0045] Table 1 Key parameters for preparation of negative electrode materials in each example and comparative example

[0046]

[0047] Table 2 Performance of negative electrode material batteries prepared in each example and comparative example

[0048]

[0049] The results show that compared with Comparative Example 1, the first cycle coulombic efficiency of the battery using the negative electrode material of Example 1 of the application is increased by more than 30%, which is mainly due to the large reduction in specific surface area after coating with pitch. Compared with Comparative Example 2, the charge-discharge reversible capacity is increased by about 180 mAh / g, which is because the pitch-based carbon material is mostly soft carbon and does not have suitable micropores for storing lithium, so the charge-discharge capacity is much lower than that of hard carbon. Compared with Comparative Example 3, the introduction of Na salt in Example 1 creates more micropores in the particle interior during the subsequent high-temperature carbonization process using the pore-forming ability of Na ions, providing space for the storage of lithium ions, thereby increasing the charge-discharge reversible specific capacity by 48 mAh / g. Further research has found that the amount of Na salt and the immersion time have a greater impact on the proportion of micropores in the core structure and the specific surface area of the carbon material. As can be seen from Examples 4 and 5 and Comparative Example 5, when too much Na salt is introduced, the proportion of micropores with a pore size of 0.001-0.5 nm in the total pore volume of the core decreases, the space suitable for storing lithium decreases, and the discharge capacity decreases. If too little Na salt is introduced, the pore structure of the obtained carbon material does not change much from that of Comparative Example 1, and the specific capacity does not increase significantly. Therefore, the appropriate amount of sodium salt and the immersion time are key factors for obtaining the technical effects of the application. In summary, the use of the negative electrode material of the application can achieve high reversible capacity and high first cycle coulombic efficiency.

Claims

1. A high specific power lithium-ion battery anode material, characterized in that: The negative electrode material is prepared from asphalt and biomass raw materials. This material is a powdered carbon material with a core-shell structure. The core has a particle size of 3-8 μm and contains a large number of micropores with a diameter of 0.001-0.5 nm, accounting for 60-90% of the total core pore volume. The remainder consists of micropores with a diameter greater than 0.5 nm and less than or equal to 50 nm. The interlayer spacing of the 002 crystal planes is 0.39-0.41 nm. The shell thickness is 10-1000 nm, and the interlayer spacing of the 002 crystal planes is 0.34-0.36 nm. The specific surface area of ​​this material is 2-4 m². 2 / g.

2. The negative electrode material according to claim 1, characterized in that: The shell thickness is 10-200nm.

3. A method for preparing the negative electrode material according to claim 1 or 2, characterized in that: The preparation method of the negative electrode material is as follows. 1) After drying and pulverizing the biomass raw material, pre-carbonize it at 400~600℃ for 1-3 hours in an inert atmosphere to obtain product A; 2) Product A was successively immersed and stirred in NaOH solution and acid solution for washing, then filtered, washed until neutral, dried, and then pulverized by air jet mill to obtain carbon powder B with a particle size of 3~8μm; 3) Immerse carbon powder B in NaCl or Na2CO3 solution and stir, then filter and dry to obtain carbon powder C. The molar ratio of carbon to NaCl or Na2CO3 is 10 / 1 to 100 / 1. 4) The carbon powder C is coated with asphalt. The specific steps are as follows: put the carbon powder C and asphalt into a mixer, heat to 200~260℃, and mix them in an internal mixer for 20-30 minutes; then carbonize in an inert atmosphere at 1100~1300℃ for 1-3 hours to obtain the negative electrode material.

4. The preparation method according to claim 3, characterized in that: The biomass raw material is one or more of the following: coconut shell, peach shell, apricot shell, and walnut shell.

5. The preparation method according to claim 3, characterized in that: The inert atmospheres mentioned in steps 1) and 4) are nitrogen atmosphere and / or argon atmosphere, respectively; In step 2), the concentration of the NaOH solution is 1-5 mol / L, and the acid solution is hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 1-5 mol / L; the soaking and stirring time is 1-100 h; and the temperature range during stirring is 25-70 °C. In step 3), the concentration of the NaCl or Na2CO3 solution is 1-5 mol / L; the impregnation and stirring time is 1-100 hh; and the temperature range during stirring is 25-50 °C.

6. The preparation method according to claim 3, characterized in that: The asphalt is petroleum asphalt with a softening point of 200-250℃.

7. The preparation method according to claim 3, characterized in that: The mass ratio of carbon powder C to asphalt is 7 / 3 to 9 / 1.

8. The application of the negative electrode material according to claim 1 or 2 as a negative electrode material in a lithium-ion battery.

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