Carbon-based negative electrode material surface modification method for lithium ion battery and carbon-based negative electrode material

Abstract

The invention relates to the field of energy storage batteries, in particular to a surface modification method of a carbon-based negative electrode material for a lithium ion battery and the carbon-based negative electrode material.The surface modification method comprises the following steps that S1, the carbon-based material, soluble saccharides, a lithium source and a solvent are mixed; s2, carrying out ball milling treatment on the slurry to obtain a precursor mixture; s3, calcining the precursor mixture to obtain a primary modified carbon material; s4, treating the primary modified carbon material in ozone to obtain an oxidation modified carbon material; and S5, dispersing the oxidation modified carbon material in a solution containing a conductive monomer and an oxidizing agent for chemical polymerization reaction, and depositing on the surface of the carbon material to form a polymer coating layer, thereby obtaining the surface modified carbon-based negative electrode material. By constructing a pre-lithiated carbon coated inner core and an ozone activation interface and preparing a modification layer of a conductive polymer, the core problems that a traditional carbon negative electrode is low in first efficiency, short in cycle life and poor in rate capability and is difficult to consider at the same time are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage batteries, in particular to a carbon-based negative electrode material surface modification method for lithium ion batteries and a carbon-based negative electrode material. BACKGROUND

[0002] The carbon-based negative electrode material for lithium ion batteries still faces a series of key challenges in practical application. First, during the first charge and discharge process of the battery, the electrolyte will irreversibly decompose on the surface of the negative electrode to form a solid electrolyte interface film (SEI film), which will permanently consume lithium ions, resulting in low first coulomb efficiency and capacity loss of the battery. Secondly, during long-term cycling, the carbon material will produce volume expansion and contraction when lithium ions are repeatedly inserted and extracted, which will easily cause electrode structure pulverization and destruction, and the continuous reconstruction of the unstable SEI film will continuously consume active materials, resulting in accelerated capacity decay and shortened cycle life. In addition, the inherent electronic conductivity and ion migration rate of carbon materials are limited, and the interface compatibility with the electrolyte is poor, which seriously restricts the high-rate charge and discharge performance (fast charging ability) of the battery. These interrelated problems jointly limit the further improvement of the energy density, life and power performance of lithium ion batteries. Therefore, it has become an urgent need in the field to develop a carbon-based negative electrode material surface modification technology that can simultaneously improve the first efficiency, cycle stability and rate performance.

[0003] CN105633407B discloses a modification method for carbon-based negative electrode material surface coated with Li2B4O7 for lithium ion batteries, comprising the following steps: pretreating the surface pores of the carbon-based negative electrode material by infiltrating a lithium salt solution, then performing in-situ reaction, drying and calcining to obtain the carbon-based negative electrode material coated with Li2B4O7 on the surface; by adjusting the infiltration process sequence, first infiltrate the non-glassy lithium salt solution which is easy to infiltrate into the surface pores of the carbon negative electrode material into the surface pores of the carbon negative electrode material, then add an appropriate amount of non-glassy borate-containing compound, through the reaction of Li+ and BO33- in the surface pores of the carbon negative electrode material, without the need to prolong the infiltration time and enhance the stirring intensity, the purpose of infiltrating the glassy Li2B4O7 aqueous solution into the surface pores of the carbon negative electrode material is easily achieved, the infiltration effect is improved, and the carbon negative electrode material modified by the glassy Li2B4O7 has improved overall electrochemical performance. However, it cannot solve the problems of low first coulomb efficiency and capacity loss, or electrode structure pulverization and destruction caused by expansion and contraction. SUMMARY

[0004] In order to solve the above problems, the present application provides a surface modification method of carbon-based negative electrode material for lithium ion battery and carbon-based negative electrode material, by constructing a pre-lithiation carbon coated core, further by ozone activation interface, and preparing a multiple synergistic modification layer of conductive polymer outer sheath, which effectively compensates for the first lithium loss, significantly enhances the structural stability of carbon material and the interface ion / electron transport dynamics, thereby overcoming the core problem of low first efficiency, short cycle life and poor rate performance of traditional carbon negative electrode.

[0005] To achieve the above purpose, the technical scheme of the present application is: A surface modification method of carbon-based negative electrode material for lithium ion battery, comprising the following steps: S1. 8-10 parts of carbon-based material, 0.5-0.8 parts of soluble sugar, 0.1-0.2 parts of lithium source and 20-30 parts of solvent are mixed according to the mass fraction, and stirred to form a uniform slurry; S2. The slurry is subjected to ball milling treatment to obtain a precursor mixture; S3. The precursor mixture is subjected to calcination treatment under vacuum or inert atmosphere, with a heating rate of 1-3 ℃ / min to 600-750 ℃, and isothermal for 3-5 h, and after natural cooling, a primary modified carbon material is obtained; S4. The primary modified carbon material is subjected to ozone treatment to obtain an oxidized modified carbon material; S5. The oxidized modified carbon material is dispersed in a solution containing a conductive monomer and an oxidizing agent to perform a chemical polymerization reaction, the reaction temperature is 0-40 ℃, the reaction time is 3-8 h, and a polymer coating layer is deposited on the surface of the carbon material; after the reaction is completed, the product is filtered, washed and dried to obtain a surface modified carbon-based negative electrode material; Wherein, the increase rate of the mass of the product after drying in step S5 relative to the mass of the oxidized modified carbon material obtained in step S4 is calculated to control the polymer coating amount, and the mass increase rate is controlled to be 5%-10%.

[0006] The core technology mechanism lies in constructing a multi-layered, functionalized composite structure layer on the surface of carbon-based materials through a series of rigorous and coordinated process steps, thereby achieving synergistic optimization of the material's bulk phase and interface. Firstly, in steps S1 and S3, the key is to achieve in-situ doping and carbon coating through precise matching of component ratios and calcination processes. The carbon-based material, soluble sugars, and lithium source are blended and then ball-milled to achieve uniform mixing at the molecular level. The milling intensity and time must be sufficient to ensure that the sugars and lithium source fully adhere to the surface and defects of the carbon-based material; however, excessive milling may damage the structure of the carbon material itself. Subsequently, temperature-controlled calcination under an inert atmosphere is crucial: the sugars, acting as the carbon source, pyrolyze at high temperatures to form an amorphous carbon coating layer. This coating layer physically isolates the direct erosion of the carbon core by the electrolyte and provides a more active surface for subsequent processing; while the lithium source decomposes at high temperatures, some lithium ions may embed into the carbon layer or react with surface functional groups, achieving pre-lithiation to compensate for the irreversible lithium consumption during the subsequent formation of the SEI film. The heating rate at this stage is crucial. Too rapid a heating rate leads to rapid carbonization of the sugars, resulting in numerous pores or uneven coating, while too slow a rate results in low efficiency. The calcination temperature directly determines the graphitization degree and conductivity of the amorphous carbon. Too low a temperature results in poor conductivity of the carbon layer, while too high a temperature may lead to an overly dense coating or unnecessary side reactions with the lithium source. Next, the strong oxidizing power of ozone in step S4 aims to introduce oxygen-containing functional groups (such as carboxyl and carbonyl groups) onto the carbon material surface. These functional groups not only improve the material's hydrophilicity but also serve as active sites, providing anchoring points for the in-situ chemical polymerization in step S5. Insufficient ozone treatment results in insufficient active sites, while excessive oxidation destroys the sp² conjugated structure on the carbon material surface, introducing too many defects and impairing its intrinsic conductivity and structural stability. Finally, step S5 is key to forming the outermost functional coating, and its essence lies in precisely controlling the thickness and continuity of the polymer coating by controlling the rate of mass gain. As described above, the ozone treatment in step S4 does not uniformly modify the entire carbon material in bulk, but rather selectively introduces oxygen-containing functional groups onto the surface of the carbon material (especially the primary modified carbon material formed after calcination in S3). These functional groups act as chemical anchoring sites, confining the chemical polymerization reactions in step S5 (such as the oxidative polymerization of pyrrole) primarily to the surface of the carbon material, making it a typical surface-initiated polymerization. This means that the formation and deposition of conductive polymers (such as polypyrrole) do not occur randomly in the bulk solution, but preferentially and selectively nucleate and grow on the surface of carbon particles. Therefore, the increase in the final product mass largely comes from the polymer coating layer attached to the carbon core surface, rather than from free polymer particles. The mild reaction conditions in step S5 are designed to control the rate of polymerization, preventing it from becoming too vigorous. If the reaction is too fast, monomers may self-polymerize in the solution before reaching the carbon surface, forming independent polymer particles, resulting in uneven coating and a poor correlation between the rate of mass increase and the coating thickness.The slow, controllable polymerization process facilitates the full diffusion of monomer molecules to the active sites on the carbon material surface, enabling ordered chain growth and forming a continuous, dense, and uniformly thick coating film. Utilizing the active sites created in step S4, conductive monomers (such as pyrrole) undergo directional polymerization on the carbon material surface under the action of an oxidant, forming a highly conductive and flexible polymer network (such as polypyrrole). This layer serves a dual function: firstly, its excellent electronic conductivity constructs a highly efficient conductive network between carbon particles, greatly improving the rate performance of the electrode; secondly, the flexibility of its polymer chains can buffer the volume changes of the carbon core during charging and discharging, improving cycle stability. However, the polymer coating amount must be strictly controlled. If the mass gain rate is too low, the coating layer will be discontinuous, resulting in poor protection and conductivity; if it is too high, an excessively thick insulating polymer layer will hinder lithium-ion migration, leading to increased internal resistance and decreased rate performance. The choice of solvent, monomer concentration, reaction temperature, and time collectively determine the rate and uniformity of the polymerization reaction. Low-temperature, slow reactions are beneficial for forming a denser and more uniform coating layer. In summary, the successful implementation of this scheme highly depends on the precise positioning of the functions of each component and the precise coordination between various process parameters. Each step creates conditions for the next step, ultimately improving the electrochemical performance of the carbon-based anode material.

[0007] Preferably, in step S1, the carbon-based material is one or more of graphene, artificial graphite, natural graphite, hard carbon, or soft carbon; the soluble sugar is glucose or sucrose; the lithium source is lithium nitrate; and the solvent is deionized water or ethanol.

[0008] Soluble sugars are limited to glucose or sucrose, with the key being their solubility in solvents and their pyrolysis behavior: these sugar molecules contain a large number of hydroxyl groups, which can form a uniform slurry in water or ethanol solvents, ensuring uniform coating on the carbon material surface during ball milling and subsequent drying; during the calcination process in step S3, they act as a carbon source, undergoing dehydration, coking, and carbonization, ultimately forming an amorphous carbon layer with abundant defects and micropores. This layer is not only conductive but also effectively conducts lithium ions. Its amorphous structure is more conducive to the rapid insertion / extraction of lithium than graphitized carbon and acts as a physical barrier to improve interface stability. Lithium nitrate was chosen after comprehensively considering its thermal decomposition characteristics and residues: it can completely or partially decompose at a calcination temperature of 600-750℃. Part of the lithium oxide produced by decomposition can achieve pre-lithiation of the carbon matrix through solid-phase diffusion or surface reaction, directly compensating for the initial irreversible capacity loss; another part may be doped into the amorphous carbon coating layer, changing its electron cloud density and further enhancing lithium ion affinity and transport kinetics.

[0009] Preferably, in step S1, 0.05-0.15 parts of boric acid or borate are added as a dopant.

[0010] The role of boron is as follows: 1) Enhancing electronic conductivity: As an electron acceptor, boron atoms can capture electrons from the valence band of carbon, creating more holes in the valence band, thereby significantly improving the electronic conductivity of the material. This lays the physical foundation for improving the rate performance of batteries. 2) Optimizing lithium-ion adsorption and migration: The local electron-deficient environment created by boron atoms gives it a stronger electrostatic attraction to lithium ions. This not only lowers the energy barrier for lithium ions to embed on the surface of carbon materials, promoting the formation of the initial SEI film, but may also provide more preferential adsorption sites and diffusion paths for lithium ions. In addition, the introduction of boron may also inhibit excessive graphitization of carbon materials at high temperatures, which is beneficial to maintaining a moderately disordered structure in the coating layer, thereby retaining more lithium-ion storage sites and fast diffusion channels. If the amount added is too low, the doping concentration is insufficient to form a continuous modification effect on a macroscopic scale, and the improvement on electronic structure and interface properties is negligible, like a drop in the ocean. However, adding too much boron can lead to serious side effects: excessive boron may not be able to fully integrate into the carbon lattice, but instead accumulates at the grain boundaries or surface in the form of insulating phases such as amorphous boride or boron carbide. These impurity phases will hinder the transport of lithium ions and electrons, significantly increase the interface impedance, and thus degrade the rate performance and cycle life of the battery.

[0011] Preferably, in step S2, the ball milling speed is 200-500 r / min, the ball milling time is 2-4 h, and then the mixture is dried at 80-120℃ for 2-4 h to obtain a precursor mixture with an average particle size ≤0.8 μm.

[0012] Ball milling is used to achieve nanoscale uniform mixing and tight composite of sugars, lithium sources, dopants and carbon-based material particles, and also to achieve an average particle size of ≤0.8μm.

[0013] Preferably, in step S4, the ozone treatment process involves: an ozone concentration of 30-50 mg / L, and treatment at room temperature to 60-80°C for 20-40 minutes.

[0014] Ozone's strong oxidizing properties create a maximum number of stable oxygen-containing functional groups on the surface of carbon materials. These functional groups play a dual role in step S5: first, they act as anchoring points, ensuring a strong bond in the coating layer through chemical bonding; second, they enhance surface hydrophilicity and improve electrolyte wettability. If the ozone concentration is too high, or the reaction time or temperature is too long, the oxidation reaction will no longer be limited to the surface but will extend into the bulk phase. This will lead to two serious consequences: first, the sp2 conjugated structure of the carbon material itself will be largely destroyed, and the intrinsic electronic conductivity will drop sharply, as if an insulating layer is wrapped around the conductive carbon core, completely violating the original intention of improving rate performance; second, excessive oxidation will erode the carbon surface, creating structural defects and even causing particle pulverization, weakening its mechanical stability and thus being detrimental to cycle life. Conversely, insufficient oxidation kinetics and a slow reaction rate will prevent the generation of a sufficient number of oxygen-containing functional groups as active sites on the carbon surface within a reasonable time, resulting in ineffective subsequent polymer grafting and a discontinuous and weak coating layer.

[0015] Preferably, in step S5, the conductive monomer is one or more of pyrrole, aniline, or 3,4-ethylenedioxythiophene; the oxidant is one of ammonium persulfate, ferric chloride, or hydrogen peroxide, and the molar ratio of the oxidant to the conductive monomer is 1-3:1. The chemical polymerization reaction is carried out in the liquid phase, and the solvent is one or more of water, ethanol, or acetonitrile. The concentration of the conductive monomer in the solvent is 0.1-0.5 mol / L; The mass-to-volume ratio of the oxidized modified carbon material to the solvent is 1 g / (20-30) mL.

[0016] Preferably, in step S5, after drying, a heat treatment step is also included: the surface-modified carbon-based anode material is heated to 300-450°C in a vacuum or inert atmosphere at a heating rate of 1-5°C / min, and held at that temperature for 1-3 hours.

[0017] The role of heat treatment is to induce partial carbonization and structural rearrangement in conductive polymers. When the temperature rises to a specific window of 300-450℃, the molecular chains of conductive polymers such as polypyrrole and polyaniline begin to undergo pyrolysis and recombination. This process does not completely transform them into pure carbon similar to graphite, but rather forms a nitrogen-doped glassy carbon-like structure or a highly conjugated polymer structure. This transformation brings several crucial optimization effects: significantly enhanced electronic conductivity of the coating layer: partial carbonization eliminates disordered structures and defects in the polymer chains, enhancing the continuity of the π-π conjugated system, thereby qualitatively improving the intrinsic conductivity of the coating layer and enabling it to more efficiently perform its function of constructing a conductive network. Greatly improved chemical and electrochemical stability of the coating layer: the original conductive polymer may partially degrade or undergo unnecessary side reactions under long-term cycling or high voltage. After heat treatment, the formed carbon-like structure has a wider electrochemical window and higher inertness, which can more effectively resist the erosion of electrolytes and provide more durable and stable protection for the internal carbon core. Strengthening the bond between the coating layer and the carbon core: During the heat treatment process, the polymer coating layer and the surface of the underlying ozone-activated carbon material may undergo further chemical bonding or physical embedding, making the interface between the two more robust and effectively preventing the coating layer from peeling off due to volume changes during battery cycling.

[0018] This solution also discloses a carbon-based anode material for lithium-ion batteries prepared by the above-mentioned surface modification method.

[0019] This solution also discloses a negative electrode for a lithium-ion battery prepared from a carbon-based negative electrode material for lithium-ion batteries, which is modified using the above-mentioned surface modification method.

[0020] Compared to existing technologies, the technical advantages of this solution are: 1. This scheme constructs a multi-level functionalized system through the synergistic combination of various functional components. Soluble sugars are used as a carbon source to form an amorphous carbon coating layer at high temperatures, providing basic physical protection for the carbon core. The introduction of lithium nitrate not only serves as a lithium source but, more importantly, enables pre-lithiation, directly compensating for irreversible lithium loss during the first charge and discharge cycle. The addition of trace amounts of boric acid (or borate) allows for electron doping of the carbon layer at the atomic scale, effectively improving the intrinsic conductivity of the material and enhancing its adsorption capacity for lithium ions. The selected conductive monomers (such as pyrrole) ultimately polymerize to form a highly conductive and flexible outer coating.

[0021] 2. In terms of process, by constructing a pre-lithiated carbon-coated core, further activating the interface with ozone, and preparing a multi-layer synergistic modification of the conductive polymer outer sheath, the structural stability of the carbon material and the interfacial ion / electron transport dynamics are significantly enhanced while effectively compensating for the first lithium loss. This overcomes the core problem of traditional carbon anodes, which suffer from low first-cycle efficiency, short cycle life, and poor rate performance. Attached Figure Description

[0022] Figure 1 SEM image of the modified carbon-based anode material for lithium-ion batteries in Example 1; Figure 2 The image shows a SEM image of the precursor mixture during the modification process in Example 1. Detailed Implementation

[0023] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 A surface modification method for carbon-based anode materials for lithium-ion batteries is disclosed. SEM images of the modified carbon-based anode material for lithium-ion batteries are shown below. Figure 1 As shown, the particles are uniformly coated on the surface and have a relatively uniform size. The modification process includes the following steps: S1. By weight, mix 9 parts artificial graphite, 0.65 parts glucose, 0.15 parts lithium nitrate and 25 parts deionized water, and add 0.1 parts boric acid, and stir to form a uniform slurry; S2. The slurry is ball-milled at a speed of 350 r / min for 3 h, and then dried at 100 °C for 3 h to obtain a precursor mixture with an average particle size of 0.75 μm. Figure 2 The image shown is an SEM image of the precursor mixture. It can be seen that the surface edges of the particles are distinct, and the particles have good uniformity after ball milling. S3. The precursor mixture is calcined in an argon atmosphere, heated to 670°C at a heating rate of 2°C / min, held at that temperature for 4 hours, and then naturally cooled to obtain a primary modified carbon material. S4. The primary modified carbon material is subjected to ozone treatment at a concentration of 40 mg / L at 70°C for 30 min to obtain an oxidized modified carbon material. S5. The oxidized carbon material is dispersed in an aqueous solution containing pyrrole and ammonium persulfate for chemical polymerization. The molar ratio of ammonium persulfate to pyrrole is 2:1; the concentration of pyrrole in water is 0.3 mol / L; the mass-to-volume ratio of oxidized carbon material to water is 1 g / 25 mL; the reaction temperature is 20 °C, and the reaction time is 5.5 h. A polymer coating layer is deposited on the surface of the carbon material. After the reaction, the material is filtered, washed, and dried. The surface-modified carbon-based anode material is heated to 380 °C under vacuum at a heating rate of 3 °C / min and held at that temperature for 2 h to obtain the surface-modified carbon-based anode material. The mass increase rate of the polymer coating is controlled at 7.5%.

[0025] Example 2 A method for surface modification of carbon-based anode materials for lithium-ion batteries, comprising the following steps: S1. By weight, mix 8 parts of natural graphite, 0.5 parts of sucrose, 0.1 parts of lithium nitrate and 20 parts of anhydrous ethanol, and add 0.05 parts of sodium borate, and stir to form a uniform slurry; S2. The slurry is ball-milled at a speed of 200 r / min for 4 h, and then dried at 80 °C for 4 h to obtain a precursor mixture with an average particle size of 0.7 μm. S3. The precursor mixture is calcined under vacuum, heated to 600°C at a heating rate of 1°C / min, held at that temperature for 5 hours, and then naturally cooled to obtain the primary modified carbon material. S4. The primary modified carbon material is placed in ozone treatment at a concentration of 30 mg / L for 40 min at room temperature to obtain an oxidized modified carbon material. S5. The oxidized carbon material is dispersed in an aqueous hydrochloric acid solution containing aniline and ferric chloride for chemical polymerization. The molar ratio of ferric chloride to aniline is 1:1; the concentration of aniline in the aqueous hydrochloric acid solution is 0.1 mol / L; the mass-to-volume ratio of the oxidized carbon material to the solution is 1 g / 30 mL; the reaction temperature is 0 °C, and the reaction time is 8 h. A polymer coating layer is deposited on the surface of the carbon material. After the reaction, the material is filtered, washed, and dried. The surface-modified carbon-based anode material is heated to 300 °C at a heating rate of 1 °C / min under an argon atmosphere and held at that temperature for 3 h to obtain the surface-modified carbon-based anode material. The mass increase rate of the polymer coating is controlled at 5%.

[0026] Example 3 A method for surface modification of carbon-based anode materials for lithium-ion batteries, comprising the following steps: S1. By mass, mix 10 parts hard carbon, 0.8 parts glucose, 0.2 parts lithium nitrate and 30 parts deionized water, and add 0.15 parts boric acid, and stir to form a uniform slurry; S2. The slurry is ball-milled at a speed of 500 r / min for 2 h, and then dried at 120 °C for 2 h to obtain a precursor mixture with an average particle size of 0.8 μm. S3. The precursor mixture is calcined in an argon atmosphere, heated to 750°C at a heating rate of 3°C / min, held at that temperature for 3 hours, and then naturally cooled to obtain a primary modified carbon material. S4. The primary modified carbon material is subjected to ozone treatment at a concentration of 50 mg / L at 80°C for 20 min to obtain an oxidized modified carbon material. S5. The oxidized carbon material is dispersed in an ethanol-water solution containing 3,4-ethylenedioxythiophene and ammonium persulfate for chemical polymerization. The molar ratio of ammonium persulfate to 3,4-ethylenedioxythiophene is 3:1; the concentration of 3,4-ethylenedioxythiophene in the solution is 0.5 mol / L; the mass-to-volume ratio of the oxidized carbon material to the solution is 1 g / 20 mL; the reaction temperature is 40 °C, and the reaction time is 3 h. A polymer coating layer is deposited on the surface of the carbon material. After the reaction, the material is filtered, washed, and dried. The surface-modified carbon-based anode material is heated to 450 °C under vacuum at a heating rate of 5 °C / min and held at that temperature for 1 h to obtain the surface-modified carbon-based anode material. The mass increase rate of the polymer coating is controlled at 10%.

[0027] Example 4 A method for surface modification of carbon-based anode materials for lithium-ion batteries, comprising the following steps: S1. By mass, mix 8.5 parts of a mixture of artificial graphite and soft carbon, 0.6 parts of sucrose, 0.12 parts of lithium nitrate and 22 parts of anhydrous ethanol, and add 0.08 parts of boric acid, and stir to form a uniform slurry; S2. The slurry is ball-milled at a speed of 280 r / min for 3.5 h, and then dried at 90 °C for 3.5 h to obtain a precursor mixture with an average particle size of 0.72 μm. S3. The precursor mixture is calcined in an argon atmosphere, heated to 680°C at a heating rate of 1.5°C / min, and held at that temperature for 4.5 hours. After natural cooling, a primary modified carbon material is obtained. S4. The primary modified carbon material is subjected to ozone treatment at a concentration of 35 mg / L at 50°C for 35 min to obtain an oxidized modified carbon material. S5. The oxidized carbon material is dispersed in an aqueous solution containing pyrrole and hydrogen peroxide for chemical polymerization. The molar ratio of hydrogen peroxide to pyrrole is 1.5:1; the concentration of pyrrole in water is 0.2 mol / L; the mass-to-volume ratio of oxidized carbon material to water is 1 g / 28 mL; the reaction temperature is 10 °C, and the reaction time is 6 h. A polymer coating layer is deposited on the surface of the carbon material. After the reaction, the material is filtered, washed, and dried. The surface-modified carbon-based anode material is heated to 350 °C at a heating rate of 2 °C / min under an argon atmosphere and held at that temperature for 2.5 h to obtain the surface-modified carbon-based anode material. The mass increase rate of the polymer coating is controlled at 6%.

[0028] Example 5 A method for surface modification of carbon-based anode materials for lithium-ion batteries, comprising the following steps: S1. By weight, mix 9.5 parts of natural graphite, 0.75 parts of glucose, 0.18 parts of lithium nitrate and 28 parts of deionized water, and add 0.12 parts of sodium borate, and stir to form a uniform slurry; S2. The slurry is ball-milled at a speed of 420 r / min for 2.5 h, and then dried at 110 °C for 2.5 h to obtain a precursor mixture with an average particle size of 0.78 μm. S3. The precursor mixture is calcined under vacuum, heated to 700°C at a heating rate of 2.5°C / min, and held at that temperature for 3.5 hours. After natural cooling, a primary modified carbon material is obtained. S4. The primary modified carbon material is subjected to ozone treatment at a concentration of 45 mg / L at 60°C for 25 min to obtain an oxidized modified carbon material. S5. The oxidized carbon material is dispersed in an aqueous solution containing aniline and ammonium persulfate for chemical polymerization. The molar ratio of ammonium persulfate to aniline is 2.5:1; the concentration of aniline in water is 0.4 mol / L; the mass-to-volume ratio of oxidized carbon material to water is 1 g / 22 mL; the reaction temperature is 30 °C, and the reaction time is 4 h. A polymer coating layer is deposited on the surface of the carbon material. After the reaction, the material is filtered, washed, and dried. The surface-modified carbon-based anode material is heated to 400 °C under vacuum at a heating rate of 4 °C / min and held at that temperature for 1.5 h to obtain the surface-modified carbon-based anode material. The mass increase rate of the polymer coating is controlled at 8.5%.

[0029] Comparative Example 1 The only difference from Example 1 is that lithium nitrate was not added.

[0030] Comparative Example 2 The only difference from Example 1 is that no soluble sugars were added.

[0031] Comparative Example 3 The only difference from Example 1 is that no dopant was added.

[0032] Comparative Example 4 The only difference from Example 1 is that the dopant was added in excess, at 0.2 parts.

[0033] Comparative Example 5 The only difference from Example 1 is that the amount of soluble sugar added is 1 part and the amount of lithium nitrate added is 0.3 parts.

[0034] Comparative Example 6 The only difference from Example 1 is that the S1 slurry was not ball-milled, but was stirred at 600 rpm for 5 hours.

[0035] Comparative Example 7 The only difference from Example 1 is that the calcination temperature is too high, at 760°C.

[0036] Comparative Example 8 The only difference from Example 1 is that the calcination temperature is too low, at 580°C.

[0037] Comparative Example 9 The only difference from Example 1 is that it was not treated with ozone.

[0038] Comparative Example 10 The only difference from Example 1 is that the ozone concentration is too high, at 60 mg / L.

[0039] Comparative Example 11 The only difference from Example 1 is that the polymer coating amount is 11%.

[0040] Comparative Example 12 The only difference from Example 1 is that the polymer coating amount is 4%.

[0041] Comparative Example 13 The only difference from Example 1 is that step S5 does not involve heat treatment.

[0042] Comparative Example 14 The only difference from Example 1 is that the heat treatment temperature in step S5 is too high, at 470°C.

[0043] Performance testing: 1. Examples 1-5, Comparative Examples 1-14 and untreated artificial graphite were assembled into R2032 coin cells, and the initial coulombic efficiency, initial charge-discharge capacity, rate performance and cycle life were tested. 2. Electrode Volume Expansion Rate Detection: By testing the change in electrode thickness before and after cycles, the volume expansion rate is calculated (thickness change rate ≈ volume change rate, since the electrode area remains essentially unchanged), directly quantifying the degree of volume expansion. Preparation of current collector-free electrode sheet: Coat the negative electrode sheet with polytetrafluoroethylene plate according to the negative electrode sheet formula (avoid interference from copper foil thickness), dry and cut into 10mm×10mm samples, weigh (m) and measure the thickness (d0, take the average value at 5 different positions with a micrometer). Assemble a simulated battery: Assemble the electrode sheet, lithium sheet, separator, and electrolyte in a transparent plastic shell and cycle them 50 times at 0.5C. Post-cycle treatment: Disassemble the battery, clean the electrolyte on the electrode surface with DMC, vacuum dry for 8 hours, and measure the thickness after cycling (d1, also averaged at 5 points). Volume expansion rate = (d1-d0) / d0 × 100%; 3. Conductivity Testing: The volumetric conductivity of the material was tested using the four-probe method. The modified carbon-based material was pressed into a disc with a diameter of 10 mm and a thickness of 2 mm (pressure 10 MPa, holding pressure for 5 min). The thickness (d) and area (S) were measured. The four-probe probe was pressed vertically onto the surface of the disc, a current (I) was passed through it, and the voltage (V) was measured. The conductivity σ was calculated as σ = (I × d) / (V × S). Target: Conductivity of the example ≥ 100 S / m.

[0044] The test results are shown in Table 1.

[0045] Table 1. Performance test results of the examples and comparative examples. During the first charge and discharge cycle, the electrolyte decomposes to form an SEI film, which consumes lithium ions, resulting in a low initial coulombic efficiency and capacity loss. In long-term cycling, the repeated insertion and extraction of lithium ions causes the carbon material to expand and contract in volume, which can easily lead to the pulverization and damage of the electrode structure. At the same time, the unstable SEI film continuously reconstructs, which consumes active materials and shortens the cycle life. The inherent electronic conductivity and ion migration rate of carbon materials are limited, and their interfacial compatibility with the electrolyte is poor, which seriously restricts the high-rate charge and discharge performance of the battery.

[0046] This invention uses soluble sugars as a carbon source to form an amorphous carbon coating layer through calcination. This layer physically isolates the electrolyte and buffers volume expansion. High-temperature decomposition of lithium nitrate achieves pre-lithiation to compensate for the initial lithium loss. Trace amounts of boric acid / borate doping enhance electronic conductivity and optimize lithium-ion adsorption and migration. Ball milling ensures uniform mixing of all components at the molecular level. Calcination at specific temperatures and times guarantees the conductivity and structural stability of the carbon coating layer. Ozone oxidation introduces oxygen-containing functional groups to provide anchoring points for polymer coating and improves interfacial compatibility. Directional polymerization of conductive polymers forms a flexible, highly conductive outer layer, which strengthens the electron transport network and further buffers volume changes. Optimization of polymer coating amount and subsequent heat treatment parameters ensures a balance between function and transport efficiency. Overall, when parameters are within the optimal range, each step synergistically complements the others, resulting in superior performance.

[0047] Compared to Example 1, the reasons for the performance differences in each comparative example are clear: Comparative Example 1 did not add lithium nitrate, lacking pre-lithiation, and could not compensate for the lithium ions consumed in the formation of the SEI film, resulting in a significant decrease in the initial coulombic efficiency; Comparative Example 2 did not add soluble sugars, and could not form an amorphous carbon coating layer. The carbon-based material lacked basic physical protection, leading to increased volume expansion and easy damage to the electrode structure, resulting in a significant shortening of cycle life; Comparative Example 3 did not add dopants, and the electronic structure of the carbon layer was not optimized, resulting in insufficient electronic conductivity, a high lithium-ion transport barrier, and a significant deterioration in rate performance; Comparative Example 4 added excessive dopants, exceeding the carbon lattice's capacity limit. The excess boron elements formed amorphous borides or boron carbide and other insulating phases, hindering electron and lithium-ion transport, which not only deteriorated the rate performance but also shortened the cycle life. Cyclic stability was also affected; in Comparative Example 5, the amount of soluble sugar and lithium nitrate added exceeded the preferred range. Excessive sugar could lead to an excessively thick carbon coating layer, affecting ion migration, while excessive lithium source could trigger unnecessary side reactions, damaging the integrity of the carbon coating layer and causing a decrease in both rate and cycle performance; in Comparative Example 6, no ball milling was performed, and the components were only mixed by stirring, which could not achieve nanoscale uniform composite. Subsequent carbon coating, lithium source distribution, and polymer coating all showed unevenness, resulting in local lack of protection for the carbon-based material, poor volume expansion control, and impaired cycle and rate performance; in Comparative Example 7, the calcination temperature was too high, exceeding the preferred range of 600-750℃, which could easily lead to an excessively dense amorphous carbon coating layer, hindering lithium ion insertion and extraction, and could also cause lithium nitrate decomposition products to react with the carbon layer. Side reactions occur, reducing the conductivity of the carbon layer and inhibiting both cycle and rate performance. Comparative Example 8 has an excessively low calcination temperature, below the lower limit of the preferred range. The amorphous carbon coating layer is insufficiently graphitized, resulting in poor conductivity and a loose structure, failing to effectively perform physical protection and ion transport functions, leading to poor rate and cycle performance. Comparative Example 9, lacking ozone treatment, has a carbon material surface lacking oxygen-containing functional groups. This fails to provide effective anchoring points for conductive polymer polymerization, resulting in a weak and easily detached polymer coating layer. It also makes it difficult to guide the uniform formation of the SEI film, deteriorating initial efficiency, cycle stability, and volume expansion control. Comparative Example 10 has an excessively high ozone concentration, exceeding the preferred range of 30-50 mg / L. The strong oxidation effect destroys the conjugated structure on the carbon material surface, introducing side reactions. Excessive structural defects reduce the intrinsic electronic conductivity of carbon materials, significantly deteriorating rate performance. In Comparative Example 11, the polymer coating amount exceeds the preferred upper limit of 5%-10%. The excessively thick polymer layer hinders the migration of lithium ions on and inside the carbon-based material, increasing ion transport impedance and drastically reducing rate performance. In Comparative Example 12, the polymer coating amount is below the preferred lower limit. The discontinuous coating layer cannot form a complete protective and conductive network, failing to effectively buffer volume expansion or enhance electron transport, resulting in poor cycle stability and volume expansion control. In Comparative Example 13, no heat treatment was performed, and the conductive polymer coating layer did not undergo structural rearrangement or partial carbonization. Its chemical stability and bonding force with the carbon-based material are insufficient, making it prone to degradation or peeling during long-term cycling, shortening cycle life.Comparative Example 14's heat treatment temperature was too high, exceeding the preferred range of 300-450℃, leading to excessive carbonization and embrittlement of the conductive polymer. The coating layer lost its flexibility and became prone to cracking, failing to buffer volume expansion and resulting in poor cycle stability and volume expansion control. The blank group, without any modification treatment, failed to address the three core problems of low initial efficiency, short cycle life, and poor rate performance of the carbon-based anode, resulting in the worst overall performance.

Claims

1. A method for surface modification of a carbon-based negative electrode material for lithium-ion batteries, characterized by, Comprising the following steps: S1. 8-10 parts by mass of carbon-based material, 0.5-0.8 parts of soluble sugar, 0.1-0.2 parts of lithium source and 20-30 parts of solvent are mixed to form a uniform slurry by stirring; S2. The slurry is subjected to ball milling treatment to obtain a precursor mixture; S3. The precursor mixture is subjected to calcination treatment under vacuum or inert atmosphere, the temperature is raised to 600-750℃ at a rate of 1-3℃ / min, and the temperature is maintained for 3-5h, and the primary modified carbon material is obtained after natural cooling; S4. The primary modified carbon material is subjected to ozone treatment to obtain an oxidized modified carbon material; S5. The oxidized modified carbon material is dispersed in a solution containing a conductive monomer and an oxidizing agent to undergo a chemical polymerization reaction, and a polymer coating layer is deposited on the surface of the carbon material; after the reaction, the surface modified carbon-based anode material is obtained after filtration, washing and drying; Wherein, the mass increase rate of the product after step S5 drying relative to the mass of the oxidized modified carbon material obtained in step S4 is 5%-10%.

2. The surface modification method according to claim 1, wherein, In step S1, the carbon-based material is one or more of graphene, artificial graphite, natural graphite, hard carbon or soft carbon; the soluble sugar is glucose or sucrose; the lithium source is lithium nitrate; and the solvent is deionized water or ethanol.

3. The surface modification method according to claim 1, wherein In step S1, 0.05-0.15 parts of boric acid or borate is also added as a dopant.

4. The surface modification method of claim 1, wherein In step S2, the ball milling speed is 200-500r / min, the ball milling time is 2-4h, and then the precursor mixture with an average particle size of ≤0.8μm is obtained after drying at 80-120℃ for 2-4h.

5. The surface modification method of claim 1, wherein In step S4, during the ozone treatment: the ozone concentration is 30-50mg / L, and the treatment is carried out at room temperature to 60-80℃ for 20-40min.

6. The surface modification method of claim 1, wherein, In step S5, the conductive monomer is one or more of pyrrole, aniline or 3,4-ethylenedioxythiophene; the oxidizing agent is one of ammonium persulfate, ferric chloride or hydrogen peroxide, and the molar ratio of oxidizing agent to conductive monomer is 1-3:1; The chemical polymerization reaction is carried out in liquid phase, and the solvent is one or more of water, ethanol or acetonitrile; The concentration of the conductive monomer in the solvent is 0.1-0.5mol / L; The mass-volume ratio of the oxidized modified carbon material to the solvent is 1g / (20-30)mL.

7. The surface modification method of claim 1, wherein In step S5, after drying, a heat treatment step is also included: the surface modified carbon-based anode material is heated to 300-450℃ at a rate of 1-5℃ / min under vacuum or inert atmosphere, and the temperature is maintained for 1-3h.

8. A lithium ion battery carbon-based anode material modified by the surface modification method of any one of claims 1-7.

9. A lithium ion battery anode prepared by the surface modified carbon-based anode material of any one of claims 1-7.

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