Surface-modified carbon negative electrode material and preparation method thereof, battery

Abstract

The application provides a surface-modified carbon negative electrode material, a preparation method thereof and a battery. The preparation method comprises the following steps: mixing a graphite carbon source and a pore-forming agent, and then performing graphitization treatment on the obtained mixture to form porous graphite; performing oxidation treatment on the porous graphite to prepare porous oxidized graphite particles; placing the porous oxidized graphite particles in a tin source solution containing tin cations, so that the tin source solution adheres to the pore surface of the porous oxidized graphite particles, and tin oxide adhering to the pore surface of the porous oxidized graphite particles is formed based on the tin source solution; and placing the porous oxidized graphite particles in a carbon-containing reducing gas environment for calcination treatment, to prepare carbon-coated tin nanowires based on the tin oxide. The preparation method uses carbon-coated tin nanowires to modify the surface and pores of the carbon negative electrode material, which can effectively improve the discharge performance of the battery at a high rate.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a surface-modified carbon anode material, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are currently widely used as energy sources for electric vehicles, drones, and other electric devices. With the rapid development of electric vehicles and drones, the requirements for the charge / discharge rate performance of lithium-ion batteries are becoming increasingly stringent. A lithium-ion battery typically consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The materials of the positive and negative electrodes have a significant impact on the charge / discharge specific capacity, cycle performance, and charge / discharge power of the lithium-ion battery.

[0003] Currently, commercially available lithium-ion batteries typically use graphite as the negative electrode material. During charging and discharging, lithium ions repeatedly insert into and extract from the graphite lattice. However, due to the inherent properties of graphite, the insertion and extraction rates of lithium ions in the graphite lattice are relatively slow. This results in a significantly lower specific capacity of graphite at higher charge / discharge rates, thus highlighting the need to improve the high-rate performance of batteries. Summary of the Invention

[0004] Therefore, it is necessary to provide a method for preparing surface-modified carbon anode materials. This method uses carbon-coated tin nanowires to modify the surface and pores of the carbon anode material, which can effectively improve the discharge performance of the battery at higher rates.

[0005] Some embodiments of this application provide a method for preparing a surface-modified carbon anode material, which includes the following steps:

[0006] A graphite carbon source and a pore-forming agent are mixed, and then the resulting mixture is graphitized to form porous graphite.

[0007] The porous graphite is subjected to oxidation and crushing treatment to form porous graphite oxide particles;

[0008] The porous graphene oxide particles are placed in a tin source solution containing tin cations, so that the tin source solution adheres to the pore surface of the porous graphene oxide particles, and tin oxide is formed on the pore surface of the porous graphene oxide particles based on the tin source solution; and the porous graphene oxide particles are calcined in a carbon-containing reducing gas environment to prepare carbon-coated tin nanowires based on the tin oxide.

[0009] In some embodiments of this application, the solvent of the tin source solution includes one or more of water, methanol, and ethanol; and / or, the solute of the tin source solution includes one or more of stannous chloride, stannous oxalate, stannous acetate, and stannous nitrate.

[0010] In some embodiments of this application, the concentration of tin cations in the tin source solution is 0.001 mol / L to 0.01 mol / L.

[0011] In some embodiments of this application, the step of forming tin oxide adhering to the pore surface of the porous graphite oxide particles based on the tin source solution includes: adjusting the pH value of the tin source solution to 1.5~2.5, so that the tin subions form a precipitate on the pore surface of the porous graphite oxide particles, and then performing a drying treatment to form the tin oxide.

[0012] In some embodiments of this application, the gas in the carbon-containing reducing gas environment includes hydrocarbons and a protective gas, wherein the hydrocarbons are selected from one or more of ethylene, acetylene, and propylene, and the protective gas is selected from argon or nitrogen.

[0013] During calcination, the calcination temperature is 500℃~1000℃ and the calcination time is 20min~60min.

[0014] In some embodiments of this application, the steps of oxidizing and crushing the porous graphite include:

[0015] The porous graphite is oxidized using an electrochemical oxidation method to form porous graphite oxide; and the porous graphite oxide is crushed to form porous graphite oxide particles.

[0016] In some embodiments of this application, during the oxidation treatment of the porous graphite using an electrochemical oxidation method, the pH value of the electrolyte is ≤3; and / or, the D50 particle size of the porous oxidized graphite particles is 3μm~20μm.

[0017] In some embodiments of this application, the pore-forming agent is capable of decomposing and generating gas during the graphitization process;

[0018] The graphitization process includes heating the mixture to above 2500°C to convert the mixture of the graphite carbon source and the pore-forming agent into porous graphite.

[0019] Some embodiments of this application provide a surface-modified carbon anode material, which is prepared by the preparation method described in any of the above embodiments;

[0020] The carbon anode material comprises porous graphite oxide particles and carbon-coated tin nanowires, with at least a portion of the carbon-coated tin nanowires attached to the pore walls of the porous graphite oxide particles.

[0021] Some embodiments of this application provide a battery including a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is located between the positive electrode and the negative electrode, and the negative electrode includes the surface-modified carbon negative electrode material described in any of the above embodiments.

[0022] In the preparation method of surface-modified carbon anode material in at least one embodiment of this application, porous graphite is first prepared using a pore-forming agent. Due to the effect of the pore-forming agent, the porous graphite has a rich pore structure inside, which can shorten the diffusion path of lithium ions and provide a certain volume change space for rapid charging and discharging. Then, the porous graphite is oxidized. On the one hand, the surface of the pore wall of the porous graphite becomes hydrophilic, which is conducive to the subsequent wetting of the tin source solution. On the other hand, the oxygen-containing functional groups (mainly carboxyl and hydroxyl groups) formed after oxidation are negatively charged after ionization, which is conducive to the enrichment of tin cations on the pore wall surface. The tin cations enriched on the pore wall surface are further converted into tin oxides attached to the pore wall surface, thereby forming carbon-coated tin nanowires grown on the pore wall surface during the subsequent calcination process. At least one embodiment of this application also provides a carbon material with carbon-coated tin nanowires modified on the pore surface. As a surface modification structure, carbon-coated tin nanowires can support the pores in the graphite particles, thereby inhibiting the collapse and breakage of the pore structure and improving the cycle performance of the battery. On the other hand, carbon-coated tin nanowires can also act as fast ion conductors to attract and promote the migration of lithium ions into the pores of graphite particles, thereby effectively improving the discharge performance of the battery in high-rate charge and discharge scenarios. Detailed Implementation

[0023] To facilitate understanding of this application, a more complete description will be provided below. Preferred embodiments of this application are shown below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0026] Some related technologies propose adding pore-forming agents in situ during graphite manufacturing to increase the interlayer spacing of graphite, widen the lithium-ion transport channels, and thus improve the speed of lithium-ion insertion and extraction. However, on the one hand, the electrolyte does not easily wet the interior of the graphite pores, and the process of lithium-ion diffusion and migration from the outside to the graphite pores is still relatively slow, which actually limits the further improvement of battery rate performance. On the other hand, the structural stability of graphite after pore-forming by pore-forming agents is poor, and it is prone to structural damage and pulverization during long-term cycling.

[0027] The method for preparing surface-modified carbon anode materials provided in this application embodiment enables the modification of the porous graphite pore surface with carbon-coated tin nanowires. The preparation method includes the following steps S1 to S4.

[0028] Step S1: Mix the graphite carbon source and the pore-forming agent, and then graphitize the resulting mixture to form porous graphite.

[0029] The graphite carbon source should be selected from carbon materials capable of being converted into graphite. In some embodiments of this application, the graphite carbon source includes coke, which may be selected from one or more of petroleum coke, needle coke, and pitch coke. In some embodiments of this application, the graphite carbon source also includes phenolic resin. Phenolic resin has a binding effect and can fill the gaps between coke particles, which is beneficial for obtaining uniform and highly crystalline artificial graphite. It is understood that other carbon materials capable of being converted into graphite may also be used as the graphite carbon source.

[0030] In the embodiments of this application, the mass ratio of coke to phenolic resin is (5~10):1.

[0031] The main function of the pore-forming agent is to introduce pores into the prepared graphite material. In some embodiments of this application, the pore-forming agent can decompose and generate gas during the graphitization process.

[0032] In some embodiments of this application, the graphitization process includes heating the mixture to above 2500°C to convert the mixture of graphite carbon source and pore-forming agent into porous graphite. Further, the graphitization process includes heating at a first temperature for 0.5-3 hours, then at a second temperature for 0.5-3 hours, and then at a third temperature for 0.5-3 hours, wherein the first temperature is 1300-1600°C, the second temperature is 2200-2500°C, and the third temperature is 2500-3000°C. Using a gradient temperature heating method is beneficial for promoting the complete pyrolysis of the phenolic resin, the complete decomposition of the pore-forming agent, and the complete graphitization of the carbon material, thereby maximizing the improvement of the properties of the porous graphite.

[0033] In some embodiments of this application, the pore-forming agent includes an alkali metal nitrate. For example, the pore-forming agent includes lithium nitrate, which can decompose to generate gas during the high-temperature graphitization process, and the lithium element therein can also pre-lithiate the graphite.

[0034] Step S2: Oxidize the porous graphite to prepare porous graphite oxide particles.

[0035] The porous graphite, after oxidation treatment, exhibits hydroxyl and carboxyl groups on both its outer and inner pore surfaces. These hydroxyl and carboxyl groups ionize in solution to generate anions. One effect of the oxidation treatment is to improve the hydrophilicity of the porous graphite surface, promoting the diffusion of the subsequent tin source solution into the pores. Another effect is that the Coulombic force exerted by the negatively charged hydroxyl and carboxyl groups on the tin cations after ionization allows the tin cations to accumulate inside the pores of the porous graphite, thus enabling carbon-coated tin nanowires to grow directly from within the pores of the porous graphite.

[0036] In some embodiments of this application, the step of oxidizing porous graphite includes: oxidizing the porous graphite using an electrochemical oxidation method to form porous graphite oxide; and crushing the porous graphite oxide to form porous graphite oxide particles. The electrochemical oxidation method refers to using porous graphite as the anode material and applying a voltage to the porous graphite, causing oxidation of its surface. Oxidation using an electrochemical oxidation method has the following advantages: due to the "sharpness effect," the more rugged inner surface of the porous graphite pores is preferentially oxidized during electrochemical oxidation, resulting in a relatively higher number of oxygen-containing functional groups on the inner surface of the porous graphite pores, which is more conducive to the subsequent enrichment of tin cations. In other embodiments, gas-phase oxidation or liquid-phase oxidation can also be used to oxidize the porous graphite, but compared to gas-phase oxidation and liquid-phase oxidation, electrochemical oxidation can preferentially oxidize the inner surface of the porous graphite pores. Furthermore, the porous graphite oxide particles are first oxidized using an electrochemical oxidation method and then crushed. The outer surface of the crushed particles is not actually in contact with the electrolyte and is therefore not oxidized. This allows the inner surface of the pores to adsorb more tin cations than the outer surface of the particles.

[0037] In some embodiments of this application, during the oxidation treatment of porous graphite using an electrochemical oxidation method, the pH value of the electrolyte is ≤3. Using an electrolyte with a pH value ≤3 is beneficial for forming more acidic groups on the surface of porous graphite, thereby generating more anions in the solution.

[0038] It is understood that in this application, the progress of the electrochemical oxidation process can be controlled by controlling the voltage and the energizing time during the electrochemical treatment. In some embodiments of this application, during the electrochemical oxidation process, the voltage applied to the porous graphite is controlled to be 1.5V~3V, and the electrochemical treatment duration is 60s~600s.

[0039] In the embodiments of this application, the crushing process can be carried out by mechanical grinding.

[0040] In some embodiments of this application, after crushing, the D50 particle size of the porous graphite oxide particles is 3μm~20μm.

[0041] Step S3: The porous graphene oxide particles are placed in a tin source solution containing tin cations, so that the tin source solution adheres to the pore surface of the porous graphene oxide particles, and tin oxide is formed on the pore surface of the porous graphene oxide particles based on the tin source solution.

[0042] Tin cations refer to positively charged ions containing the element tin, such as tin ions (Sn). 4+ ) and tin ions (Sn2+ One or more of the following.

[0043] In some embodiments of this application, the solvent for the tin source solution includes one or more of water, methanol, and ethanol.

[0044] In some embodiments of this application, the solute in the tin source solution includes one or more of stannous chloride, stannous oxalate, stannous acetate, and stannous nitrate.

[0045] In some embodiments of this application, the concentration of tin cations in the tin source solution is 0.001 mol / L to 0.01 mol / L. Controlling the concentration of tin cations aims to enrich sufficient tin elements in the graphite pores while preventing excessive tin elements from adhering to the outer surface of the graphite particles. The concentration of tin cations should not be too high or too low. If it is too high, more tin elements will adhere to the outer surface of the graphite particles, affecting the charge-discharge performance of the graphite particles. If it is too low, it will be difficult to enrich sufficient tin ions in the pores of the graphite particles, thus making it difficult to form sufficiently long carbon-coated tin nanowires.

[0046] In some embodiments of this application, the step of forming tin oxide adhering to the pore surface of porous graphite oxide particles based on a tin source solution includes: adjusting the pH value of the tin source solution to 1.5-2.5, causing tin cations to precipitate on the pore surface of the porous graphite oxide particles, followed by drying to form tin oxide. It is understood that during the precipitation of tin cations, corresponding hydroxides are first formed, and then the hydroxides are further converted into tin oxides during the drying process.

[0047] Step S4: Porous graphene oxide particles are placed in a carbon-containing reducing gas environment for calcination treatment to prepare carbon-coated tin nanowires based on tin oxide.

[0048] In this process, when porous graphene oxide particles are calcined in a carbon-reducing gas environment, tin oxide can be reduced and directionally grown into tin nanowires. Simultaneously, carbon atoms are in situ coated onto the surface of the tin nanowires, forming carbon-coated tin nanowires. Furthermore, since the tin nanowires grow based on tin oxide, for tin oxide adhering to the pore walls, the tin nanowires can grow directly in situ on the pore walls during calcination.

[0049] In some embodiments of this application, the gas in the carbon-containing reducing gas environment includes hydrocarbons and a protective gas. The hydrocarbons are selected from one or more of ethylene, acetylene, and propylene, and the protective gas is selected from argon or nitrogen. Further, the flow rate ratio of hydrocarbons to protective gas is 1:(1~10).

[0050] In some embodiments of this application, the calcination temperature is 500℃~1000℃ and the calcination time is 20min~60min.

[0051] It is understood that the surface-modified carbon anode material of this application can be prepared through the above steps S1 to S4. An embodiment of this application provides a surface-modified carbon anode material, which includes porous graphite oxide particles and carbon-coated tin nanowires modified on the surface of the porous graphite oxide particles, wherein at least some of the carbon-coated tin nanowires are attached to the pore walls of the porous graphite oxide particles.

[0052] In the preparation method of surface-modified carbon anode material in at least one embodiment of this application, porous graphite is first prepared using a pore-forming agent. Due to the effect of the pore-forming agent, the porous graphite has a rich pore structure inside, which can shorten the diffusion path of lithium ions and provide a certain volume change space for rapid charging and discharging. Then, the porous graphite is oxidized. On the one hand, the surface of the pore wall of the porous graphite becomes hydrophilic, which is conducive to the subsequent wetting of the tin source solution. On the other hand, the oxygen-containing functional groups (mainly carboxyl and hydroxyl groups) formed after oxidation are negatively charged after ionization, which is conducive to the enrichment of tin cations on the pore wall surface. The tin cations enriched on the pore wall surface are further converted into tin oxides attached to the pore wall surface, thereby forming carbon-coated tin nanowires grown on the pore wall surface during the subsequent calcination process. At least one embodiment of this application also provides a carbon material with carbon-coated tin nanowires modified on the pore surface. As a surface modification structure, carbon-coated tin nanowires can support the pores in the graphite particles, thereby inhibiting the collapse and breakage of the pore structure and improving the cycle performance of the battery. On the other hand, carbon-coated tin nanowires can also act as fast ion conductors to attract and promote the migration of lithium ions into the pores of graphite particles, thereby effectively improving the discharge performance of the battery in high-rate charge and discharge scenarios.

[0053] This application also provides a battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive and negative electrodes are arranged facing each other, the electrolyte is located between the positive and negative electrodes, and the negative electrode comprises a surface-modified carbon negative electrode material prepared by the preparation method of any of the above embodiments.

[0054] In some embodiments of this application, the positive electrode includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. The positive electrode active material may include one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate. The positive electrode may also include a positive electrode binder and a positive electrode conductive agent.

[0055] In some embodiments of this application, the negative electrode includes a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector. The negative electrode active material may include a surface-modified carbon negative electrode material prepared by the preparation method of any of the above embodiments. The negative electrode may also include a negative electrode binder and a negative electrode conductive agent.

[0056] This application also provides the following embodiments and comparative examples to further illustrate the implementation and advantages of this application.

[0057] Example 1

[0058] (1) Lithium nitrate is dissolved in ethanol to form a saturated solution of lithium nitrate, and needle coke powder and phenolic resin are added to the saturated solution. The resulting mixture is then kneaded, and the solvent ethanol is basically evaporated during this process. The mass ratio of needle coke powder to phenolic resin is 10:1.

[0059] (2) Under a nitrogen atmosphere, the kneaded mixture is heated to 1500℃ and calcined for 1 hour, then heated to 2400℃ and calcined for 1 hour, and finally calcined at 2800℃ for 1 hour to complete the graphitization process; during the calcination process, lithium nitrate decomposes to generate gas that creates pores in the graphite material, thereby forming porous graphite.

[0060] (3) Using the porous graphite obtained in step (2) as the working electrode, a platinum electrode as the counter electrode, sulfuric acid as the electrolyte, and a calomel electrode as the reference electrode, electrochemical oxidation was performed using a constant potential method. The voltage applied to the working electrode was 2V, and the electrode was removed after 120s as porous graphite oxide. The porous graphite oxide was then crushed to form porous graphite oxide particles with a D50 particle size of approximately 10μm.

[0061] (4) Dissolve stannous chloride in water to form a tin source solution with a stannous ion concentration of 0.005 mol / L. Then, place porous graphite oxide particles in the tin source solution to fully impregnate them and sonicate them. Then, add ammonia water at a uniform rate until the pH value of the tin source solution is maintained at about 2.0, so that the stannous ions precipitate. Then, take out the porous graphite oxide particles and transfer them to a vacuum drying oven to dry them at 60°C, so that the stannous ions are converted into stannous oxide.

[0062] (5) Place porous graphite oxide particles in a tube furnace and continuously introduce a mixed gas flow of acetylene and argon into the tube furnace. Then gradually heat the furnace to 700°C for 2 hours to form carbon-coated tin nanowires based on tin oxide. Then remove the nanowires after they have cooled down naturally.

[0063] Example 2

[0064] The main difference between Example 2 and Example 1 is step (4). In step (4) of Example 2, stannous oxalate is used instead of stannous chloride.

[0065] Example 3

[0066] The main difference between Example 3 and Example 1 is step (4). In step (4) of Example 3, the concentration of stannous ions is 0.02 mol / L.

[0067] Comparative Example 1

[0068] The main difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not perform the electrochemical oxidation treatment in step (3), but directly crushes the porous graphite into particles with a D50 particle size of about 10 μm, and the subsequent processing steps are the same.

[0069] Comparative Example 2

[0070] The main difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not perform the steps (4) and (5) of preparing carbon-coated tin nanowires.

[0071] Comparative Example 3

[0072] The main difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not perform the electrochemical oxidation treatment in step (3), nor does it perform steps (4) and (5), and directly crushes the porous graphite into particles with a D50 particle size of about 10 μm.

[0073] Preparation of the negative electrode sheet: The surface-modified carbon material prepared in the above embodiments and comparative examples is mixed evenly with the negative electrode conductive agent and the negative electrode binder at a mass ratio of 90:7:3 and dispersed in a solvent. After stirring evenly, the mixture is coated onto the surface of copper foil, then dried and stamped to form the negative electrode sheet. The negative electrode conductive agent is conductive carbon black, the negative electrode binder is a 1:1 mixture of carboxymethyl cellulose and styrene-butadiene rubber, and the solvent is deionized water.

[0074] Preparation of the full cell: The positive electrode of the battery uses lithium nickel cobalt manganese oxide (NCM111), a positive electrode conductive agent, and a positive electrode binder. These three components are mixed evenly in a solvent at a mass ratio of 94:3:3, stirred evenly, and then coated onto the surface of aluminum foil. After drying, the mixture is stamped into a positive electrode sheet. The positive electrode conductive agent is conductive carbon black, the positive electrode binder is polyvinylidene fluoride, and the solvent is N-methylpyrrolidone. The negative and positive electrode sheets are then assembled into a full cell. The electrolyte is a 1.0 mol / L LiPF6 solution, and the solvent for the electrolyte is a mixed solvent prepared by EC, EMC, and DMC in a volume ratio of 1:1:1.

[0075] Testing: After the full battery was left to stand for 24 hours, charge-discharge cycle tests were conducted on a constant current charge-discharge tester. The test voltage range was 2.5V~4.2V, and the first cycle was activated at a current density of 0.05C. For rate performance testing, a fixed charging rate of 1C was used, and the discharge specific capacity of the battery was tested at discharge rates of 1C, 2C, 5C, and 10C. Separate batteries were used to test cycle performance, using a charging rate of 1C and a discharging rate of 5C, and the capacity retention rate was tested after 100 and 800 cycles. The test results are shown in Table 1 below.

[0076] Table 1

[0077]

[0078] Referring to Table 1, Comparative Example 3 directly used the porous graphite particles prepared in step (2) as the negative electrode active material, serving as a pure control group. The battery prepared in Comparative Example 3 had a discharge specific capacity of only 295 mAh / g at an extremely high discharge rate of 10C, and only 78.5% of its capacity was retained after 800 cycles at a discharge rate of 5C. The batteries corresponding to Examples 1 to 3 all exhibited a discharge specific capacity of over 347 mAh / g at an extremely high discharge rate of 10C, and maintained a cycle capacity retention rate of over 90.8% after 800 cycles at a discharge rate of 5C. It can be seen that Examples 1 to 3 significantly improved the discharge specific capacity and cycle capacity retention rate of the batteries at high discharge rates compared to Comparative Example 3. This is mainly due to the following: First, the porous graphite is oxidized to impart oxygen-containing functional groups such as carboxyl and hydroxyl groups to its surface. These carboxyl and hydroxyl groups ionize in solution and become negatively charged, attracting positively charged tin cations from the tin source solution, thus enriching the tin cations on the surface of the graphite particles. In the subsequent calcination process, tin oxide can directly grow in situ on the surface of the graphite particles to form carbon-coated tin nanowires. These tin nanowires can act as fast ion transport channels, promoting the migration of lithium ions into the interior of the graphite particles, thereby further improving the discharge performance of this graphite material at extremely high rates.

[0079] Referring to Table 1, compared with Example 1, the discharge specific capacity of Example 3 at each discharge rate was lower overall. This is mainly because the concentration of tin cations in the tin source solution is higher, resulting in more carbon-coated tin metal nanowires formed subsequently, which in turn hinders the normal discharge of some graphite, resulting in a lower discharge specific capacity.

[0080] Referring to Table 1, compared to Comparative Example 3, Comparative Example 1, which prepared carbon-coated tin nanowires without electrochemical oxidation, showed a slight improvement in the overall rate performance and cycle performance of the battery. This is mainly due to the inherent conductivity and ion-conductivity of the carbon-coated tin nanowires. However, because the graphite material was not electrochemically oxidized, the tin source solution could not easily penetrate into the pores of the graphite material, making it virtually impossible for carbon-coated tin nanowires to grow on the surface of the pores. Therefore, only the ion-conductivity of the outer surface of the graphite material was improved, while the ion-conductivity inside the pores remained unimproved. Furthermore, compared to Comparative Example 3, Comparative Example 2, which only underwent electrochemical oxidation without preparing carbon-coated tin nanowires, actually showed a certain decrease in the overall rate performance and cycle performance of the battery. This is mainly because the surface conductivity of the graphite material is significantly reduced after oxidation, which is detrimental to the full charge and discharge of the graphite material.

[0081] The above detailed description is a specific description of the feasible embodiments of this application. These embodiments are not intended to limit the patent scope of this application. All equivalent implementations or modifications that do not depart from the scope of this application should be included in the patent scope of this application.

Claims

1. A method for preparing a surface-modified carbon anode material, characterized in that, Includes the following steps: A graphite carbon source and a pore-forming agent are mixed, and then the resulting mixture is graphitized to form porous graphite. The porous graphite is subjected to oxidation treatment to prepare porous graphite oxide particles; The steps of oxidizing the porous graphite include: The porous graphite is oxidized using an electrochemical oxidation method to form porous graphite oxide; and the porous graphite oxide is crushed to form porous graphite oxide particles. The porous graphite oxide particles are placed in a tin source solution containing tin cations, so that the tin source solution adheres to the pore surface of the porous graphite oxide particles, and tin oxide is formed on the pore surface of the porous graphite oxide particles based on the tin source solution. The step of forming tin oxide on the pore surface of the porous graphite oxide particles based on the tin source solution includes: adjusting the pH value of the tin source solution to 1.5~2.5, so that the tin cations precipitate on the pore surface of the porous graphite oxide particles, and then performing a drying treatment to form the tin oxide; Furthermore, the porous graphene oxide particles are calcined in a carbon-containing reducing gas environment to prepare carbon-coated tin nanowires based on the tin oxide.

2. The method for preparing surface-modified carbon anode material according to claim 1, characterized in that, Tin cations include one or more of tin ions and stannous ions.

3. The method for preparing surface-modified carbon anode material according to claim 1, characterized in that, The solvent of the tin source solution includes one or more of water, methanol, and ethanol; and / or, the solute of the tin source solution includes one or more of stannous chloride, stannous oxalate, stannous acetate, and stannous nitrate.

4. The method for preparing surface-modified carbon anode material according to claim 3, characterized in that, The concentration of tin cations in the tin source solution is 0.001 mol / L to 0.01 mol / L.

5. The method for preparing the surface-modified carbon anode material according to any one of claims 1 to 4, characterized in that, The gases in the carbon-containing reducing gas environment include hydrocarbons and protective gases, wherein the hydrocarbons are selected from one or more of ethylene, acetylene, and propylene, and the protective gases are selected from argon or nitrogen. During calcination, the calcination temperature is 500℃~1000℃ and the calcination time is 20min~60min.

6. The method for preparing the surface-modified carbon anode material according to any one of claims 1 to 4, characterized in that, During the electrochemical oxidation process, the voltage applied to the porous graphite is controlled to be 1.5V~3V, and the electrochemical treatment time is 60s~600s.

7. The method for preparing the surface-modified carbon anode material according to any one of claims 1 to 4, characterized in that, During the oxidation treatment of the porous graphite using electrochemical oxidation, the pH value of the electrolyte is ≤3; and / or the D50 particle size of the porous oxidized graphite particles is 3μm~20μm.

8. The method for preparing the surface-modified carbon anode material according to any one of claims 1 to 4, characterized in that, The pore-forming agent can decompose and generate gas during the graphitization process. The graphitization process includes heating the mixture to above 2500°C to convert the mixture of the graphite carbon source and the pore-forming agent into porous graphite.

9. A surface-modified carbon anode material, characterized in that, Prepared by the preparation method according to any one of claims 1 to 8; The carbon anode material includes porous graphite oxide particles and carbon-coated tin nanowires modified on the surface of the porous graphite oxide particles, and at least a portion of the carbon-coated tin nanowires are attached to the pore walls of the porous graphite oxide particles.

10. A battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is located between the positive electrode and the negative electrode, and the negative electrode includes the surface-modified carbon negative electrode material as described in claim 9.

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