Preparation method of carbon-coated graphite composite material, carbon-coated graphite composite material and battery negative electrode

Abstract

The present application belongs to the technical field of carbon materials and batteries, and particularly relates to a method for preparing a carbon-coated graphite composite material, a carbon-coated graphite composite material, and a battery negative electrode. A method for preparing a carbon-coated graphite composite material comprises the following steps: mixing an alkaline mixed liquid containing a graphite material, a main carbon source for coating, a synergistic carbon source for coating, and an auxiliary agent to obtain a dispersion; drying and coking the dispersion under preset conditions to form a carbon-coated graphite precursor; carbonizing the carbon-coated graphite precursor under protective gas environment conditions to obtain a carbon-coated graphite composite material; the main carbon source for coating comprises a carbohydrate; the synergistic carbon source for coating comprises a compound containing non-carbon heteroatoms; the auxiliary agent comprises a surfactant, which can synergistically act with the synergistic carbon source for coating to fully disperse the alkaline mixed liquid to obtain a uniformly distributed dispersion.

Description

Technical Field

[0001] The present application belongs to the technical field of carbon materials and batteries, and in particular relates to a method for preparing a carbon-coated graphite composite material, a carbon-coated graphite composite material and a battery negative electrode. Background Art

[0002] Lithium-ion batteries are now widely used in various electrical devices, and related technologies and industries have achieved rapid development. Applications such as electric vehicles and electrochemical energy storage are placing increasingly high demands on the performance of lithium-ion batteries, especially in terms of high safety, high power, and long life.

[0003] Graphite is widely used as the negative electrode material for lithium-ion batteries, offering advantages such as low operating potential, long cycle life, and relatively low cost. However, graphite's layered structure is unstable and prone to collapse after prolonged charge-discharge cycles, resulting in a significant decrease in battery specific capacity and a significantly shortened energy storage life. Furthermore, graphite negative electrodes have poor rate performance and cannot handle high currents, making them unsuitable for the development of power batteries and frequency-modulated energy storage. Therefore, effective modification of graphite materials is required to ensure their suitability as negative electrode materials for high-performance power and energy storage batteries.

[0004] Surface modification by coating with an ultra-thin carbon layer is an effective way to improve the electrochemical performance of graphite. It can modify defects such as pores, grooves, and cracks in the graphite material, optimize the solid electrolyte layer formed at the interface, prevent the co-embedding of the electrolyte, and effectively prevent the peeling and pulverization of the graphite layer during the charge and discharge process, thereby improving the electrochemical reversible capacity and cycle performance of the material. Currently, the most commonly used coating methods are mainly solid-phase or liquid-phase coating of asphalt, which have the disadvantages of uneven coating and poor coating effect. Summary of the Invention

[0005] The embodiments of the present application provide a method for preparing a carbon-coated graphite composite material, a carbon-coated graphite composite material, and a battery negative electrode, which can uniformly and completely coat a graphite material with carbon.

[0006] In a first aspect, an embodiment of the present application provides a method for preparing a carbon-coated graphite composite material, comprising:

[0007] Mixing an alkaline mixed solution containing a graphite material, a main carbon source for coating, a co-carbon source for coating and an additive to obtain a dispersion;

[0008] The dispersion is dried and coked under preset conditions to form a carbon-coated graphite precursor;

[0009] Carbonizing the carbon-coated graphite precursor under protective gas environment to obtain a carbon-coated graphite composite material;

[0010] The main carbon source for coating includes sugars;

[0011] The co-carbon source for coating includes a compound containing non-carbon heteroatoms;

[0012] The auxiliary agent includes a surfactant, which can cooperate with the synergistic carbon source for coating and can fully disperse the alkaline mixed liquid to obtain a uniformly distributed dispersion.

[0013] In any embodiment of the present application, in the step of obtaining the dispersion, the auxiliary agent includes at least one of polyacrylate, chitosan, chitosan derivatives, alginate, polyethylene diamine, polyvinyl alcohol, acetylene glycol polyether and polyethylene glycol octylphenyl ether.

[0014] In any embodiment of the present application, in the step of obtaining a dispersion, the mass percentage ratio of the graphite material, the main carbon source for coating, the synergistic carbon source for coating and the additive in the dispersion is (2-8):1:(0.1-1):(0.03-0.1).

[0015] In any embodiment of the present application, in the step of obtaining the dispersion, the graphite material includes at least one of artificial graphite and natural graphite.

[0016] In any embodiment of the present application, in the step of obtaining the dispersion, the sugar includes at least one of glucose, sucrose, fructose, cellulose and starch.

[0017] In any embodiment of the present application, in the step of obtaining the dispersion, the non-carbon heteroatom-containing compound includes at least one of dopamine, aniline, o-toluidine, pyridine, amino acid, polyvinylpyrrolidone, tannic acid, and citric acid.

[0018] In any embodiment of the present application, in the step of obtaining the dispersion, the pH value of the alkaline mixed solution is 8-9.

[0019] In any embodiment of the present application, in the preparation of the carbon-coated graphite precursor, the drying treatment time is 1 hour to 48 hours, the drying treatment temperature is 60°C to 100°C, the coking treatment time is 1 hour to 48 hours, and the coking treatment temperature is 100°C to 200°C.

[0020] In any embodiment of the present application, in the preparation of the carbon-coated graphite composite material, the carbonization treatment time is 60 min-240 min, and the carbonization treatment temperature is 600° C.-3500° C.

[0021] In any embodiment of the present application, the carbonization step includes a first carbonization sub-step and a second carbonization sub-step;

[0022] The first carbonization treatment temperature is 600℃-1500℃, and the time is 60min-240min;

[0023] The second carbonization treatment temperature is 1500° C.-3500° C., and the time is 60 min-240 min.

[0024] In any embodiment of the present application, in the preparation of the carbon-coated graphite composite material, the heating rate of carbonization is 2° C. / min-20° C. / min.

[0025] In a second aspect, an embodiment of the present application provides a carbon-coated graphite composite material.

[0026] A carbon-coated graphite composite material is obtained by the above-mentioned preparation method, wherein the carbon-coated graphite composite material comprises a carbon coating layer and a graphite layer, wherein the carbon coating layer is continuously and uniformly coated on the graphite layer;

[0027] The thickness of the carbon coating layer is 1 nm to 15 nm.

[0028] In a third aspect, an embodiment of the present application provides a battery negative electrode.

[0029] A battery negative electrode comprises the carbon-coated graphite composite material as described above.

[0030] The preparation method of the carbon-coated graphite composite material, the carbon-coated graphite composite material and the battery negative electrode of the embodiment of the present application effectively prevent the merging and agglomeration of graphite particles by synergizing the carbon source and the auxiliary agent to enhance dispersion and adsorption, so that the carbon source is evenly distributed on the graphite surface, achieving uniform and complete coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] Figure 1 This is a scanning electron microscope photo of commercially available artificial graphite.

[0033] Figure 2 This is a transmission electron microscope photo of commercially available artificial graphite.

[0034] Figure 3 This is a scanning electron microscope photograph of the carbon-coated graphite composite material prepared in Example 1.

[0035] Figure 4 This is a transmission electron microscope photograph of the carbon-coated graphite composite material prepared in Example 1.

[0036] Figure 5 The cycle performance of soft-pack lithium-ion batteries assembled with the carbon-coated graphite composite material prepared in Example 1 and the graphite material of Comparative Example 1 as negative electrode materials respectively. DETAILED DESCRIPTION

[0037] In order to more clearly understand the above-mentioned objectives, features and advantages of the present application, the scheme of the present application will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present application may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present application, rather than all of the embodiments.

[0039] Below, the preparation method of the carbon-coated graphite composite material, the carbon-coated graphite composite material and the battery negative electrode embodiment of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0040] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0043] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0044] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0045] Unless otherwise specified, this application adopts conventional test methods or test methods recommended by the instrument.

[0046] In the prior art, when coating an ultra-thin carbon layer for surface modification, the merging and agglomeration of graphite particles results in uneven coating and poor coating effect.

[0047] The present application can effectively prevent the merging and agglomeration of graphite particles by synergizing the carbon source and the additive to enhance dispersion and adsorption, so that the carbon source is evenly distributed on the graphite surface, achieving low-cost, ultra-thin, uniform and complete coating.

[0048]

Preparation method

[0049] A method for preparing a carbon-coated graphite composite material comprises the following steps:

[0050] Mixing an alkaline mixed solution containing a graphite material, a main carbon source for coating, a co-carbon source for coating and an additive to obtain a dispersion;

[0051] The dispersion is dried and coked under preset conditions to form a carbon-coated graphite precursor;

[0052] Carbonizing the carbon-coated graphite precursor under protective gas environment to obtain a carbon-coated graphite composite material;

[0053] The main carbon source for coating includes sugars;

[0054] The co-carbon source for coating includes a compound containing non-carbon heteroatoms;

[0055] The auxiliary agent includes a surfactant, which can cooperate with the synergistic carbon source for coating and can fully disperse the alkaline mixed liquid to obtain a uniformly distributed dispersion.

[0056] In carbon-coated graphite, the enhanced dispersion and adsorption effects of the synergistic carbon source and additives effectively prevent the merging and agglomeration of graphite particles, ensuring a uniform distribution of the carbon source across the graphite surface. Furthermore, the primary and synergistic carbon sources differ from graphite-based materials, effectively regulating the doping and short-range structure of the carbon coating. Furthermore, the primary and synergistic carbon sources contain heteroatoms, the introduction of which can optimize electronic and ion pathways at the electrode interface.

[0057] In the step of obtaining the dispersion, vigorous stirring is required to achieve uniform mixing of the graphite material, the main carbon source for coating, the synergistic carbon source for coating and the additive. The stirring speed may be 200 rpm-1600 rpm.

[0058] In the preparation of the carbon-coated graphite precursor, the drying method can be spray drying, freeze drying, vacuum drying or rotary evaporation drying.

[0059] In the preparation of carbon-coated graphite composite materials, the carbonization equipment is a tubular furnace, a rotary kiln or a box furnace.

[0060] In some embodiments, in the step of obtaining a dispersion, the mass percentage ratio of the graphite material, the main carbon source for coating, the synergistic carbon source for coating and the additive in the dispersion is (2-8):1:(0.1-1):(0.03-0.1).

[0061] Optionally, the mass percentage ratio of the graphite material, the main carbon source for coating, the synergistic carbon source for coating and the additive in the dispersion is (3-7):1:(0.3-0.8):(0.05-0.08).

[0062] Optionally, the mass percentage ratio of the graphite material, the main carbon source for coating, the synergistic carbon source for coating and the additive in the dispersion is (4-6):1:(0.4-0.6):(0.06-0.08).

[0063] The ratio of the main carbon source for coating and the synergistic carbon source for coating can be adjusted within the above range. Without affecting the uniformity and integrity of the coating, the amount of the synergistic carbon source for coating can be reduced to save costs.

[0064] In some embodiments, the compound containing non-carbon heteroatoms includes at least one of dopamine, aniline, o-toluidine, pyridine, amino acids, polyvinylpyrrolidone, tannic acid, and citric acid. The compound containing non-carbon heteroatoms contains carbon and non-carbon heteroatoms.

[0065] In some embodiments, the graphite material includes at least one of artificial graphite and natural graphite. Artificial graphite refers to a blocky solid material made from low-impurity carbonaceous raw materials (such as petroleum coke and pitch coke) as aggregate and coal tar as binder, through processes such as batching, kneading, molding, carbonization, and graphitization. Natural graphite refers to dense crystalline graphite, flake graphite, and cryptocrystalline graphite formed by the long-term transformation of carbon-rich organic matter under high-temperature and high-pressure geological conditions.

[0066] In some embodiments, the protective gas environment condition can be achieved by filling at least one gas selected from argon, nitrogen, and neon.

[0067] In some embodiments, during the preparation of the carbon-coated graphite composite material, carbonization can be performed in stages: first, maintaining the temperature at 600-1500° C. for 60-240 minutes; then raising the temperature to 1500-3500° C. for 60-240 minutes.

[0068]

Carbon-coated graphite composite materials

[0069] A carbon-coated graphite composite material is obtained by the above-mentioned preparation method, wherein the carbon-coated graphite composite material comprises a carbon coating layer and a graphite layer, wherein the carbon coating layer is continuously and uniformly coated on the graphite layer;

[0070] The thickness of the carbon coating layer is 1 nm to 15 nm.

[0071] The carbon-coated graphite composite material has a complete and uniform coating layer. The coating layer is composed of two or more carbon materials different from graphite, which can effectively control the doping and short-range structure of the coating layer. The introduction of heteroatoms into the coating layer can optimize the electronic and ion pathways at the electrode interface.

[0072]

Battery

[0073] A battery negative electrode comprises the carbon-coated graphite composite material as described above.

[0074] Carbon-coated graphite composites avoid direct contact between the graphite negative electrode and the electrolyte to inhibit side reactions, significantly improving the rate performance and cycle life of the graphite negative electrode and the entire battery.

[0075] The carbon-coated graphite composite material can be used as the active material of the negative electrode material of lithium-ion batteries, and is mixed evenly with carboxymethyl cellulose CMC and styrene-butadiene rubber SBR in a certain proportion to make a slurry and coat it on copper foil. After drying, it is rolled and die-cut to make negative electrode sheets.

[0076] Conventional methods can be used to assemble button half-cells and soft-pack batteries.

[0077] [Example]

[0078] Example 1

[0079] Dissolve 5g of glucose and 2.5g of dopamine in 80ml of deionized water, stir until fully dissolved, and adjust the pH to 8.5. Weigh 20g of artificial graphite and add it to the above solution. Then, add 3% of the total weight of glucose, dopamine, and artificial graphite as an additive, polyethylenediamine. Rapidly stir mechanically for 4 hours to obtain a dispersion. After evaporating the dispersion to dryness, coke it at 150°C for 3 hours. Transfer the coked sample to a tube furnace and carbonize it under an argon atmosphere. The gas flow rate is 100ml / min. The carbonization conditions are: increase the temperature to 600°C at a rate of 2°C / min and hold it at this temperature for 2 hours; then increase the temperature to 2000°C at a rate of 5°C / min and hold it at this temperature for 1 hour. This results in a carbon-coated graphite composite material.

[0080] Example 2

[0081] Dissolve 5g of sucrose and 1.5g of tannic acid in 100ml of deionized water, stir until fully dissolved, and adjust the pH to 8. Weigh 40g of artificial graphite and add it to the solution. Add polyethylenediamine (5% by weight, based on the total weight of sucrose, tannic acid, and artificial graphite) as an additive. Rapid mechanical stirring is performed for 6 hours to obtain a dispersion. After vacuum drying, the dispersion is coked at 140°C for 6 hours. The coked sample is transferred to a box furnace and carbonized under a nitrogen atmosphere at a gas flow rate of 100ml / min. Carbonization conditions are: increase the temperature to 1000°C at a rate of 3°C / min and hold for 3 hours; then increase the temperature to 2500°C at a rate of 10°C / min and hold for 1 hour. This results in a carbon-coated graphite composite material.

[0082] Example 3

[0083] Dissolve 10g of fructose and 4g of citric acid in 400ml of deionized water, stir until fully dissolved, and adjust the pH to 9. Weigh 50g of artificial graphite and add it to the above solution. Then, add 8% of the total weight of fructose, citric acid, and polyacrylate to the artificial graphite as an additive. Rapidly stir mechanically for 4 hours to obtain a dispersion. After spray drying, the dispersion is coked at 160°C for 6 hours. Transfer the coked sample to a rotary kiln and carbonize it under a nitrogen atmosphere. The gas flow rate is 100ml / min. The carbonization conditions are: increase the temperature to 1200°C at a rate of 5°C / min and hold at this temperature for 4 hours; then increase the temperature to 3000°C at a rate of 20°C / min and hold at this temperature for 2 hours. This results in a carbon-coated graphite composite material.

[0084] Example 4

[0085] Dissolve 5g of glucose and 0.5g of citric acid in 80ml of deionized water, stir until fully dissolved, and adjust the pH to 8. Weigh 30g of artificial graphite and add it to the above solution. Then, add 10% of the total mass of glucose, citric acid, and artificial graphite in polyvinyl alcohol as an additive. Rapidly stir mechanically for 3 hours to obtain a dispersion. After the dispersion is freeze-dried, coke it at 140°C for 3 hours. Transfer the coked sample to a tube furnace and carbonize it under an argon atmosphere. The gas flow rate is 80ml / min. The carbonization conditions are: increase the temperature to 1100°C at a rate of 3°C / min and hold it at this temperature for 3 hours; then increase the temperature to 2800°C at a rate of 15°C / min and hold it at this temperature for 2 hours. This results in a carbon-coated graphite composite material.

[0086] Example 5

[0087] Dissolve 10g of cellulose and 2g of polyvinylpyrrolidone in 100ml of deionized water, stir until fully dissolved, and adjust the pH to 8.5. Weigh 40g of artificial graphite and add it to the solution. Add chitosan (3% of the total weight of the cellulose, polyvinylpyrrolidone, and artificial graphite) as an additive. Rapid mechanical stirring is performed for 4 hours to obtain a dispersion. After spray drying, the dispersion is coked at 150°C for 4 hours. The coked sample is transferred to a box furnace and carbonized under a nitrogen atmosphere at a gas flow rate of 90ml / min. Carbonization conditions are as follows: increase the temperature to 1500°C at a rate of 5°C / min and hold for 2 hours; then increase the temperature to 2500°C at a rate of 10°C / min and hold for 1 hour. This results in a carbon-coated graphite composite material.

[0088] Example 6

[0089] Dissolve 10g of starch and 2g of tannic acid in 200ml of deionized water, stir until fully dissolved, and adjust the pH to 8. Weigh 50g of artificial graphite and add it to the solution. Add 4% of the total weight of starch, tannic acid, and artificial graphite in an acetylene glycol polyether as an additive. Rapid mechanical stirring is performed for 3 hours to obtain a dispersion. After spray drying, the dispersion is coked at 150°C for 6 hours. The coked sample is transferred to a rotary kiln and carbonized under a nitrogen atmosphere at a gas flow rate of 80ml / min. Carbonization conditions are: heating at a rate of 2°C / min to 900°C and holding for 4 hours; then heating at a rate of 20°C / min to 3500°C and holding for 1 hour. This results in a carbon-coated graphite composite material.

[0090] Example 7

[0091] Dissolve 8g of fructose and 1g of dopamine in 300ml of deionized water, stir until fully dissolved, and adjust the pH to 9. Weigh 40g of artificial graphite and add it to the above solution. Then, add 10% of the total mass of fructose, dopamine, and artificial graphite in alginate as an additive. Rapidly stir mechanically for 4 hours to obtain a dispersion. After freeze-drying, the dispersion was coked at 150°C for 4 hours. The coked sample was transferred to a box furnace and carbonized under a nitrogen atmosphere. The gas flow rate was 150ml / min. The carbonization conditions were: increase the temperature to 1300°C at a rate of 4°C / min and hold the temperature for 2 hours; then increase the temperature to 2800°C at a rate of 15°C / min and hold the temperature for 2 hours. This resulted in a carbon-coated graphite composite material.

[0092] Comparative Example 1

[0093] Weigh an appropriate amount of artificial graphite without any treatment.

[0094] Comparative Example 2

[0095] Dissolve 5g of glucose in 80ml of deionized water, stir until fully dissolved, and adjust the pH to 8.5. Weigh 20g of artificial graphite and add it to the above solution. Then, add 3% of the total mass of glucose and artificial graphite, polyethylenediamine, as an additive. Rapidly stir mechanically for 4 hours to obtain a dispersion. After the dispersion is dried by rotary evaporation, it is coked at 150°C for 3 hours. The coked sample is transferred to a tube furnace and carbonized under an argon atmosphere. The gas flow rate is: 100ml / min. The carbonization conditions are: increase the temperature to 600°C at a rate of 2°C / min and hold the temperature for 2 hours; then increase the temperature to 2000°C at a rate of 5°C / min and hold the temperature for 1 hour. A carbon-coated graphite composite material is obtained.

[0096] Comparative Example 3

[0097] Dissolve 2.5g of dopamine in 80ml of deionized water, stir until fully dissolved, and adjust the pH to 8.5. Weigh 20g of artificial graphite and add it to the above solution. Then, add 3% of the total mass of dopamine and artificial graphite, polyethylenediamine, as an additive. Rapidly stir mechanically for 4 hours to obtain a dispersion. After the dispersion is dried by rotary evaporation, it is coked at 150°C for 3 hours. The coked sample is transferred to a tube furnace and carbonized under an argon atmosphere. The gas flow rate is: 100ml / min. The carbonization conditions are: increase the temperature to 600°C at a rate of 2°C / min and hold the temperature for 2 hours; then increase the temperature to 2000°C at a rate of 5°C / min and hold the temperature for 1 hour. A carbon-coated graphite composite material is obtained.

[0098] Comparative Example 4

[0099] Dissolve 5g of glucose and 2.5g of dopamine in 80ml of deionized water, stir until fully dissolved, and adjust the pH to 8.5. Weigh 20g of artificial graphite and add it to the above solution. Rapid mechanical stirring is performed for 4h to obtain a dispersion. After the dispersion is dried by rotary evaporation, it is coked at 150°C for 3h. The coked sample is transferred to a tube furnace and carbonized under an argon atmosphere. The gas flow rate is 100ml / min, and the carbonization conditions are as follows: heat up to 600°C at a rate of 2°C / min and hold at this temperature for 2h; then heat up to 2000°C at a rate of 5°C / min and hold at this temperature for 1h. A carbon-coated graphite composite material is obtained.

[0100] The materials obtained in the above examples and comparative examples were used as active materials for the negative electrode materials of lithium-ion batteries, and were evenly mixed with carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a ratio of 9:0.5:0.5 to prepare a slurry, which was then coated on copper foil. The prepared electrode was vacuum-dried at 90°C for 12 hours, and then rolled and die-cut after drying.

[0101] The button half-cell was assembled using conventional methods to test its initial coulombic efficiency and capacity; a soft-pack battery was assembled using NCM811 as the positive electrode to test its cycle performance.

[0102] Button cell battery test: Under normal temperature conditions, charge and discharge were performed at a constant current of 0.1C in the voltage range of 0.001V-1.5V. The initial charge and discharge capacity and efficiency were tested and recorded. The test results are shown in Table 1.

[0103] Soft pack battery test: Under normal temperature conditions, first use 0.1C to make 2 cycles, then 0.5C charge and discharge cycle to test its cycle performance. The test results are as follows Figure 1-Figure 5 shown.

[0104] Table 1. Performance of button-type half-cells corresponding to the negative electrodes prepared in each group of examples and comparative examples

[0105]

[0106]

[0107] Figure 2 and Figure 4 Comparison shows that the carbon-coated graphite composite material forms a uniform core-shell structure, and the coated carbon layer is about 6nm. Figure 5 The battery test performance shows that this application improves the first coulombic efficiency and cycle performance by constructing an ultra-thin carbon layer that tightly wraps the graphite negative electrode, avoiding direct contact between the graphite negative electrode and the electrolyte, thereby inhibiting side reactions.

Claims

1. A method for preparing a carbon-coated graphite composite material, characterized in that: include: Mixing an alkaline mixed solution containing a graphite material, a main carbon source for coating, a co-carbon source for coating and an additive to obtain a dispersion; Drying and coking the dispersion under preset conditions to form a carbon-coated graphite precursor; Carbonizing the carbon-coated graphite precursor under protective gas environment to obtain a carbon-coated graphite composite material; The main carbon source for coating includes sugars; The synergistic carbon source for coating includes a compound containing non-carbon heteroatoms; The auxiliary agent includes a surfactant, which can cooperate with the synergistic carbon source for coating and can fully disperse the alkaline mixed liquid to obtain a uniformly distributed dispersion.

2. The preparation method according to claim 1, characterized in that In the step of obtaining the dispersion, the auxiliary agent includes at least one of polyacrylate, chitosan, chitosan derivatives, alginate, polyethylene diamine, polyvinyl alcohol, acetylene glycol polyether and polyethylene glycol octylphenyl ether.

3. The preparation method according to claim 1, characterized in that In the step of obtaining the dispersion, the mass percentage ratio of the graphite material, the main carbon source for coating, the synergistic carbon source for coating and the auxiliary agent in the dispersion is (2-8):1:(0.1-1):(0.03-0.1).

4. The preparation method according to any one of claims 1 to 3, characterized in that In the step of obtaining the dispersion, the graphite material includes at least one of artificial graphite and natural graphite.

5. The preparation method according to any one of claims 1 to 3, characterized in that In the step of obtaining the dispersion, the sugar includes at least one of glucose, sucrose, fructose, cellulose and starch.

6. The preparation method according to any one of claims 1 to 3, characterized in that In the step of obtaining the dispersion, the compound containing non-carbon heteroatoms includes at least one of dopamine, aniline, o-toluidine, pyridine, amino acid, polyvinylpyrrolidone, tannic acid, and citric acid.

7. The preparation method according to claim 1, characterized in that In the step of obtaining the dispersion, the pH value of the alkaline mixed solution is 8-9.

8. The preparation method according to claim 1, characterized in that In the step of forming a carbon-coated graphite precursor, The drying time is 1h-48h, the drying temperature is 60℃-100℃, the coking time is 1h-48h, and the coking temperature is 100℃-200℃; And / or, in the step of obtaining the carbon-coated graphite composite material, the carbonization treatment time is 60 min-240 min, and the carbonization treatment temperature is 600° C.-3500° C.; And / or, in the obtained carbon-coated graphite composite material, the heating rate of the carbonization treatment is 2° C. / min-20° C. / min.

9. The preparation method according to claim 1, characterized in that The carbonization step includes a first carbonization sub-step and a second carbonization sub-step; The first carbonization treatment temperature is 600°C-1500°C, and the time is 60min-240min; The second carbonization treatment temperature is 1500° C.-3500° C., and the time is 60 min-240 min.

10. A carbon-coated graphite composite material, characterized in that: The carbon-coated graphite composite material is obtained by the preparation method according to any one of claims 1 to 9, characterized in that the carbon-coated graphite composite material comprises a carbon coating layer and a graphite layer, and the carbon coating layer is continuously and uniformly coated on the graphite layer; The thickness of the carbon coating layer is 1 nm to 15 nm.

11. A battery negative electrode, characterized in that: The carbon-coated graphite composite material comprises the carbon-coated graphite composite material as claimed in claim 10.

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