Lithium battery modified graphite negative electrode material, preparation method thereof and lithium battery

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a lithium battery modified graphite negative electrode material, a preparation method thereof and a lithium battery, and the preparation method comprises the following steps: slowly adding water into an alcohol dispersion liquid of niobium pentoxide, stirring, and preheating for a set time to obtain a niobium pentoxide mixed solution; mixing the porous graphite precursor with the niobium pentoxide mixed solution, heating and stirring to volatilize the solvent to obtain solid powder; and carrying out heat treatment on the solid powder in an inert atmosphere at the temperature of 700-900 DEG C for 2-3 hours, thereby obtaining the product. A three-dimensional interconnected porous network is constructed in graphite particles, and a coating layer is constructed on the surface of graphite, so that an internal and external synergistic effect is realized, the wettability of graphite to an electrolyte is remarkably improved, and meanwhile, the fast charging capacity of a battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and specifically relates to a modified graphite anode material for lithium batteries, its preparation method, and lithium batteries thereof. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries, with their advantages of high energy density, high operating voltage, low self-discharge rate, no memory effect, long cycle life, environmental friendliness, and support for fast charging and discharging, have been widely used in consumer electronics, new energy power batteries, and energy storage power stations. Among various anode materials, graphite stands out due to its suitable lithium intercalation potential, good conductivity, high theoretical specific capacity, long cycle life, low cost, and good processing performance. It achieves a good balance between performance, safety, lifespan, and cost, making it the mainstream choice for lithium-ion battery anode materials.

[0004] However, the surface of graphite anode materials is an inert carbon structure with low surface energy, resulting in weak affinity and insufficient wettability with the electrolyte. This issue directly affects the actual reversible capacity, cycle life, fast charging performance, and safety of lithium-ion batteries, especially fast charging capability, becoming one of the key factors restricting further improvements in battery performance. Therefore, improving the wettability of graphite anode materials is of great significance for promoting the development of lithium-ion battery technology.

[0005] Currently, the technical approaches to improving the wettability of lithium-ion batteries mainly cover three aspects: modification of graphite anode materials, optimization of electrolytes, and improvement of battery manufacturing processes. Among them, in terms of modification of graphite anode materials, existing technologies adopt surface coating methods, that is, constructing an amorphous carbon layer on the graphite surface, utilizing its hydrophilicity to improve compatibility with the electrolyte. However, the following technical problems exist: 1) Limited improvement in wettability: Surface coating can only improve the hydrophilicity of the outer surface of graphite particles, but has limited improvement on the wettability of the electrolyte liquid phase in the micropores inside the electrode. 1) The electrolyte is difficult to penetrate quickly and fully into the depth of the thick electrode, resulting in a long injection and formation time, and uneven utilization of active materials inside the electrode, which restricts the actual capacity of the battery; 2) Poor rate performance: Existing surface coating technology has inherent performance bottlenecks. The coating layer, especially the dense amorphous carbon layer, adds an extra lithium ion migration barrier to the outside of the graphite particles. This significantly increases the internal resistance of the battery, causing severe polarization and a sharp drop in capacity during high-rate (fast charging) charging and discharging, which makes it difficult to meet the needs of current fast-charging batteries. Summary of the Invention

[0006] To address the limitations of existing technologies that chemically coat graphite surfaces to improve the wettability of anode materials, resulting in limited improvement in wettability and poor rate performance, this invention aims to provide a modified graphite anode material for lithium-ion batteries, its preparation method, and a lithium-ion battery. This invention achieves a synergistic effect of internal and external coatings by constructing a three-dimensional interconnected porous network within graphite particles and building a coating layer on the graphite surface. This significantly improves the wettability of graphite to the electrolyte while enhancing the battery's fast-charging capability.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a modified graphite anode material for lithium batteries, comprising the following steps: Water was slowly added to the niobium pentoxide alcohol dispersion, stirred, and preheated for a set time to obtain a niobium pentoxide mixture. The porous graphite precursor was mixed with a niobium pentoxide mixture, and the mixture was heated and stirred to evaporate the solvent, resulting in a solid powder. The solid powder is heat-treated in an inert atmosphere at a temperature of 700-900℃ for 2-3 hours to obtain the product.

[0008] Secondly, the present invention provides a modified graphite anode material for lithium batteries, which is prepared by the aforementioned preparation method.

[0009] Thirdly, the present invention provides a lithium battery, wherein the negative electrode is made of the modified graphite negative electrode material.

[0010] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: The modified graphite anode material of the present invention significantly shortens the solid-phase diffusion path of lithium ions inside the active material particles by constructing a three-dimensional interconnected porous structure inside the graphite particles, effectively reducing the lithium ion transport impedance, so that the composite material can still maintain excellent rate performance and voltage plateau stability under high rate charge and discharge conditions.

[0011] The internal porous structure of the modified graphite anode material significantly enhances the penetration rate and retention of electrolyte into the particle interior through capillary effect, achieving uniform distribution of electrolyte from the macroscopic surface of the electrode to the microscopic pores of the active material, and significantly improving the wettability of the anode material.

[0012] The porous structure and surface coating of the modified graphite anode material produce a significant synergistic effect. The internal porous network provides efficient ion transport channels, effectively solving the problem of rate performance degradation caused by the presence of the coating. Meanwhile, the external continuous coating constructs a stable electrode-electrolyte interface, effectively suppressing the side reactions aggravated by the increased specific surface area of ​​the porous structure, and maintaining good stability over long-term cycling. Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0014] Figure 1 This is an SEM image of the porous graphite material with surface coating provided in Embodiment 1 of the present invention; Figure 2 This refers to the preparation steps of surface-coated porous graphite in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the surface-coated porous graphite and the lithium battery anode prepared therefrom in Embodiment 1 of the present invention.

[0015] Among them, 1. copper foil current collector, 2. negative electrode material coating layer, 3. surface-coated porous graphite material, 31. niobium pentoxide chemical coating layer, 32. porous graphite, 33. pores. Detailed Implementation

[0016] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0017] To address the limitations of existing technologies that use chemical coating on graphite surfaces to improve the wettability of anode materials and result in poor rate performance, this invention provides a method for preparing a modified graphite anode material for lithium-ion batteries, comprising the following steps: Water was slowly added to the niobium pentoxide alcohol dispersion, stirred, and preheated for a set time to obtain a niobium pentoxide mixture. The porous graphite precursor was mixed with a niobium pentoxide mixture, and the mixture was heated and stirred to evaporate the solvent, resulting in a solid powder. The solid powder is heat-treated in an inert atmosphere at a temperature of 700-900℃ for 2-3 hours to obtain the product.

[0018] Niobium pentoxide, as an oxide, can form a stable sol in an alcohol-water mixed solvent by adjusting its polarity. After heat treatment, it transforms into a crystalline nano-coating layer that can be uniformly deposited on the graphite surface and within its pores. Niobium chloride, on the other hand, is a halide that readily hydrolyzes to generate HCl gas. This can not only corrode equipment but also cause precursor agglomeration or coating defects, preventing the formation of a continuous and uniform coating layer. Furthermore, residual Cl may remain after heat treatment of niobium chloride. - Impurity ions can exacerbate electrolyte decomposition, leading to decreased cycle stability. Furthermore, niobium chloride hydrolysis products may disrupt interfacial compatibility, weakening the electrolyte wetting effect.

[0019] Uniform dispersion of niobium pentoxide precursor is achieved using an alcohol-water mixed solvent. Anhydrous ethanol serves as the initial solvent for dispersing niobium pentoxide, while the slow addition of water adjusts the solution polarity, promoting the formation of a stable sol or suspension of the precursor and preventing aggregation due to excessively high local concentrations. Stirring further ensures thorough mixing of the water and alcohol solution, resulting in a uniform distribution of the niobium pentoxide precursor throughout the system, laying the foundation for uniform coating in subsequent processes.

[0020] Although anhydrous ethanol can initially disperse niobium pentoxide, the lack of water to adjust the solution polarity prevents the formation of a stable sol or suspension. The precursor is prone to agglomeration due to excessively high local concentrations. When the precursor that has not formed a stable sol is subsequently mixed with porous graphite, it is difficult to uniformly adsorb onto the graphite surface and pores through solvent evaporation. This may result in local agglomeration or coating blind areas, leading to coating layer defects, which in turn reduces ion transport capacity and fails to effectively construct a stable electrode-electrolyte interface. Consequently, the improvement in wettability is limited, the rate performance decreases, and the cycle stability deteriorates.

[0021] Preheating accelerates the solvation reaction of the niobium pentoxide precursor, forming more readily depositable active species. Simultaneously, preheating adjusts the solution viscosity, placing the precursor in a metastable state, facilitating spontaneous adsorption on the graphite surface via solvent evaporation during subsequent mixing with porous graphite. The homogeneous mixture prepared in this step, after mixing with the porous graphite precursor, allows for uniform deposition of the niobium pentoxide precursor on the graphite surface and within the pores through solvent evaporation via heating. Uneven dispersion or instability of the precursor can easily lead to defects in the coating layer, consequently affecting the electrochemical stability and ion transport performance of the coating layer after subsequent heat treatment.

[0022] After mixing porous graphite precursor with a niobium pentoxide mixture, the solvent (ethanol-water mixture) is evaporated by heating and stirring. The concentration gradient and surface tension changes during solvent evaporation drive the niobium pentoxide precursor to be uniformly adsorbed and deposited on the outer surface and internal pore walls of the porous graphite. This process ensures the uniform dispersion of the precursor in the graphite matrix, avoiding the localized agglomeration or coating blind spots that are prone to occur in traditional coating processes.

[0023] Heat treatment at 700-900℃ in an inert atmosphere (such as argon) promotes the dehydration, decomposition, and crystallization of the deposited niobium pentoxide precursor, transforming it into a crystalline niobium pentoxide (Nb₂O₅) nanocoating. This coating exhibits high electrochemical stability and ion conductivity, constructing a stable electrode-electrolyte interface and suppressing side reactions exacerbated by the increased specific surface area of ​​the porous structure. Synergistically with the internal three-dimensional porous network, it retains short-path channels for ion transport (due to the porous structure) and reduces interfacial impedance through the coating, thus addressing the rate performance degradation problem caused by traditional coatings. The inert atmosphere prevents graphite oxidation at high temperatures, ensuring the integrity of the porous structure and the graphite matrix.

[0024] By employing a porous graphite precursor, the permeation rate and retention of electrolyte into the particle interior are significantly enhanced through capillary effect, achieving a uniform distribution of electrolyte from the macroscopic surface of the electrode to the microscopic pores of the active material. This avoids the problem of electrolyte difficulty in penetrating the interior in traditional dense graphite. The crystalline niobium pentoxide nanocoating layer possesses hydrophilic properties, ensuring continuous wetting capability of the electrolyte during cycling. Together, these two components address the issue that traditional surface coatings only improve the wetting of the outer surface.

[0025] In some embodiments, the solvent in the niobium pentoxide alcohol dispersion is anhydrous ethanol.

[0026] Preferably, the ratio of niobium pentoxide to ethanol is 1:10-20, g:mL.

[0027] In some embodiments, the volume ratio of ethanol to water is 3-4:1, and the water is added over a period of 20-40 minutes.

[0028] In some embodiments, the preheating temperature is 40-60°C, the preheating time is 0.5-1h, and the mixture is stirred continuously during the preheating process.

[0029] If the preheating temperature is too low (below 40℃), the solvation reaction rate of the niobium pentoxide precursor will be insufficient, making it difficult to form easily depositable active species. The solution viscosity adjustment effect will be poor, and the precursor will not be able to remain in a stable metastable state. When mixed with porous graphite, uneven dispersion or agglomeration will easily occur, resulting in coating defects. If the preheating temperature is too high (above 60℃), the solvent may evaporate too quickly, the stability of the solution system will decrease, and the niobium pentoxide precursor will easily agglomerate due to excessively high local concentrations. It will be impossible to achieve uniform dispersion by stirring, which will also cause uneven distribution of the coating layer on the graphite surface and in the pores, affecting the continuity of ion transport channels.

[0030] In some embodiments, niobium pentoxide accounts for 10%-30% of the total mass of niobium pentoxide and graphite.

[0031] In some embodiments, the temperature at which the solvent evaporates by heating and stirring is 60-80°C.

[0032] In some embodiments, the heating rate during the heat treatment process is 2-5 °C / min.

[0033] In some embodiments, the step of washing and drying the heat-treated product with water is also included.

[0034] In some embodiments, the preparation method of the porous graphite precursor is as follows: after mixing graphite and silica nanospheres in a certain proportion, the mixture is heated to 700-900℃ under an inert atmosphere and kept at that temperature for 2-3 hours for heat treatment. The heat-treated mixed powder was etched with hydrofluoric acid solution to create pores, thus obtaining a porous graphite precursor.

[0035] This invention employs a template method to construct a three-dimensional porous structure: silica nanospheres of a specific particle size are uniformly dispersed in a graphite matrix as pore-forming templates. After heat treatment to fix the spatial structure, the templates are selectively etched away with hydrofluoric acid to form a uniformly sized, interconnected mesoporous network. This porous structure provides short-path diffusion channels for lithium-ion transport, significantly improving ion transport kinetics.

[0036] High-temperature heat treatment (700-900℃) causes localized sintering or bonding of graphite particles on their surface, forming a stable framework structure. Simultaneously, silica nanospheres act as rigid templates, fixed at specific locations within the graphite matrix. This prevents the graphite matrix from collapsing due to loss of support during subsequent etching, ensuring precise replication of the spatial distribution of the silica template after etching, resulting in a three-dimensional interconnected porous network structure. Without heat treatment, the mixing of graphite and silica nanospheres is merely physical contact. During etching, after the silica nanospheres are removed, graphite particles are prone to agglomeration or structural deformation, failing to maintain the pre-designed porous channels.

[0037] Preferably, the graphite is artificial graphite with a D50 of 8-16 μm and a compacted density of 1.6-1.8 g / cm³. 3 .

[0038] More preferably, the mass ratio of graphite to silica nanospheres is 6-8:1.

[0039] More preferably, the particle size of the silica nanospheres is 20-40 nm.

[0040] If the particle size of silica nanospheres is too large, it will result in excessively large pore size, weakening the physical support of the graphite matrix and making the structure prone to collapse during cycling, leading to a decrease in capacity retention. If the particle size is too small, it may cause pore blockage or reduce electrolyte wetting efficiency.

[0041] Preferably, the dry mixing time of graphite and silica nanospheres is 3-6 hours.

[0042] Preferably, the concentration of the hydrofluoric acid solution is 4-6 wt%.

[0043] Further preferably, the etching time is 18-24 hours, and the process is continuously stirred.

[0044] Preferably, the method further includes a step of washing and drying the obtained porous graphite precursor.

[0045] Secondly, the present invention provides a modified graphite anode material for lithium batteries, which is prepared by the aforementioned preparation method.

[0046] Thirdly, the present invention provides a lithium battery, wherein the negative electrode is made of the modified graphite negative electrode material.

[0047] The present invention will be further described below with reference to the embodiments.

[0048] Example 1 A method for preparing a modified graphite anode material for lithium batteries, such as Figure 2 As shown, it includes the following steps: Step a (Preparation of porous graphite precursor): 1. Mechanical mixing: Mix artificial graphite powder (D50=12μm, compacted density 1.7g / cm³) 3 ), silica nanospheres (30nm) were placed in a high-speed mixer at a mass ratio of 7:1 and dry-mixed for 5 hours under argon protection.

[0049] 2. Heat treatment: Place the powder mixed in step 1 in a tube furnace, and heat it to 800°C at a rate of 3°C / min under an argon atmosphere, and then hold it at that temperature for 2.5 hours.

[0050] 3. Etching and hole creation: Immerse the cooled material from step 2 in a 5wt% hydrofluoric acid solution and stir magnetically for 20 hours.

[0051] 4. Washing and drying: The product from step 3 was washed with deionized water by vacuum filtration and centrifugation and then dried to obtain a porous graphite precursor.

[0052] Step b (Constructing a niobium pentoxide coating): 1. Pretreatment: Niobium pentoxide was dispersed in anhydrous ethanol (the mass ratio of niobium pentoxide to the volume ratio of ethanol was 1 g: 15 mL), and deionized water was added dropwise over 30 min (the volume ratio of ethanol to deionized water was 3.5: 1). The mixture was preheated to 50 °C and stirred for 1 hour to obtain a niobium pentoxide mixture.

[0053] 2. Chemical coating: The porous graphite precursor obtained in step a is added to the niobium pentoxide mixture in step 1 (the mass of niobium pentoxide accounts for 20% of the total mass of niobium pentoxide and porous graphite precursor), the temperature is raised to 70°C, and the mixture is stirred until the liquid solvent is evaporated. After drying, a solid powder is obtained. 3. Heat treatment: The solid powder obtained in step 2 is placed in a tube furnace and heated to a set temperature of 800℃ at a rate of 3℃ / min under an argon atmosphere, and then held at that temperature for 2.5 hours.

[0054] 4. Washing and drying: The product from step 3 is washed with deionized water by vacuum filtration and centrifugation and then dried to obtain porous graphite with a surface coating.

[0055] Example 2 The difference between Example 2 and Example 1 is that in step a,1, the mass ratio of artificial graphite to silicon dioxide is 6:1, while all other aspects are the same as in Example 1.

[0056] Example 3 The difference between Example 3 and Example 1 is that in step a,1, the mass ratio of artificial graphite to silicon dioxide is 8:1.

[0057] Example 4 The difference between Example 4 and Example 1 is that in step b, 2, the mass of niobium pentoxide accounts for 10% of the total mass of niobium pentoxide and porous graphite precursor.

[0058] Example 5 The difference between Example 5 and Example 1 is that in step b, 2, the mass of niobium pentoxide accounts for 30% of the total mass of niobium pentoxide and porous graphite precursor.

[0059] Comparative Example 1 The comparative negative electrode material uses artificial graphite powder (D50=12μm, compaction density 1.7g / cm3) without any modification.

[0060] Comparative Example 2 The difference from Example 1 is that the "2. Heat treatment" step in step a is omitted, while everything else is the same as in Example 1.

[0061] Comparative Example 3 The difference from Example 1 is that in step a, "2. Heat treatment", the heat treatment temperature is 600°C, while all other steps are the same as in Example 1.

[0062] Comparative Example 4 The difference from Example 1 is that the step of "adding deionized water drop by drop" in step b "1. Pretreatment" is omitted, while the rest is the same as in Example 1.

[0063] Comparative Example 5 The difference from Example 1 is that in step b, “1. Pretreatment”, niobium pentoxide is dispersed in a mixture of anhydrous ethanol and water, while the rest is the same as in Example 1.

[0064] Comparative Example 6 The difference from Example 1 is that in step b, “1. Pretreatment”, the step of preheating to 50°C is omitted and replaced with stirring at room temperature for 1 hour. Everything else is the same as in Example 1.

[0065] Comparative Example 7 The difference from Example 1 is that in step b, “1. Pretreatment”, niobium pentoxide is replaced with niobium pentachloride, the molar amount of niobium is the same as in Example 1, and everything else is the same as in Example 1.

[0066] Comparative Example 8 The difference from Example 1 is that step a is omitted, and the porous graphite precursor in step b is replaced with artificial graphite powder (D50=12μm, compacted density 1.7g / cm³). 3 Everything else is the same as in Example 1.

[0067] Table 1 shows the electrical performance data of the pouch cells made from the graphite anode materials of Examples 1-5 and Comparative Examples 1-8.

[0068] The porous graphite anode material prepared in Example 1 was coated onto a copper foil current collector, resulting in a corresponding anode sheet for a lithium battery. (See reference...) Figure 3 The cross-section of the negative electrode was characterized by SEM, see [see image]. Figure 1 It was observed that the prepared graphite negative electrode had a large number of pores.

[0069] Electrolyte wettability: The contact angles of dimethyl carbonate (DMC) with Examples 1-5 and Comparative Example 1 were tested. The contact angle data showed that the surface-coated porous graphite anode had a significantly reduced contact angle compared to the original artificial graphite, and its wettability with DMC was significantly enhanced.

[0070] The negative electrode materials of Examples 1-5 and Comparative Examples 1-8 were used to make pouch cells with other main materials, and their electrical performance was compared. The results are as follows: Ratio performance: 1) The 4C discharge capacity retention rates of Examples 1-5 are all greater than 90%, which is higher than that of the comparative example (76.78%), indicating that the corresponding coating and porosimetry improve the rate performance of the anode material. 2) Among Examples 1-5, Example 4 has the lowest 4C discharge capacity retention rate of 93.74%. Example 4 uses a relatively small amount of niobium pentoxide material for coating. It can be seen that the content of niobium pentoxide has a significant impact on the rate performance of the battery. Within a certain range, increasing the proportion of niobium pentoxide can improve the rate performance of the battery. 3) In Examples 1-5, the 4C discharge capacity retention rate of Example 1 is higher than that of Examples 2 and 3. It can be seen that appropriate silica particle size can optimize the ion transport path and thus improve the rate performance.

[0071] 4) The 4C discharge capacity retention rate of Examples 1-5 is significantly higher than that of Comparative Examples 2-3, indicating that the heat treatment in step a of the catalyst preparation is used for the curing of silica. If there is no heat treatment or the heat treatment temperature is insufficient, the pore formation of the material will be insufficient, resulting in a decrease in the rate performance of the material. 5) The 4C discharge capacity retention rate of Examples 1-5 was significantly higher than that of Comparative Examples 4-5. In Comparative Examples 4-5, water was added too quickly or niobium pentoxide was directly added to the ethanol-water mixture when preparing a suitable niobium pentoxide colloidal solution for coating, which caused niobium pentoxide to agglomerate and precipitate, seriously affecting the uniform coating effect of niobium pentoxide and resulting in a significant decrease in the rate performance of the material. At the same time, the 4C discharge capacity retention rate of Comparative Example 6 decreased to a certain extent, indicating that stirring at a lower temperature would result in insufficient dispersion. 6) The rate performance of Comparative Example 7 (75.13%) was significantly lower than that of Examples 1-5 and lower than that of Comparative Example 1 (76.78%). Niobium pentachloride itself does not have a lithium storage structure, and coating it with graphite will increase the surface resistance of the graphite and reduce the rate performance. 8) The rate performance of Comparative Example 8 is lower than that of Examples 1-5, indicating that the porosity of graphite can improve its rate performance.

[0072] Cyclic performance: 1) The 500-cycle capacity retention rate of Example 1 is close to that of Comparative Example 1, indicating that appropriate modification does not affect the rate performance of the cell. 2) Among Examples 1-5, Example 5 has the lowest capacity retention rate. Example 5 is coated with a thicker niobium pentoxide layer. It can be seen that an excessively thick niobium pentoxide layer will affect the capacity retention rate of the cell. An excessively thick coating layer may crack during cycling. 3) Among Examples 1-5, the capacity retention rate of Example 3 is relatively low. The silica particles used in Example 3 have a larger particle size and larger pore size, which has a certain impact on the structural physical stability of graphite, resulting in a decrease in the cycle capacity retention rate.

[0073] 4) The cycling performance of Comparative Example 7 decreased significantly. After 500 cycles, the capacity retention rate was less than 80%, indicating that niobium pentachloride coating seriously affects the stability of the anode material.

[0074] In summary, constructing porous graphite with appropriate pore size and coating it with a niobium pentoxide coating of appropriate thickness is beneficial for improving the wettability of the negative electrode material, enhancing the rate performance of the battery cell, and maintaining cycle stability.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium battery modified graphite negative electrode material, characterized by: The method comprises the following steps: Slowly adding water to an alcohol dispersion of niobium pentoxide, stirring, and preheating for a set time to obtain a niobium pentoxide mixture; Mixing the porous graphite precursor with the niobium pentoxide mixture, heating and stirring to volatilize the solvent, and obtaining a solid powder; Heat-treating the solid powder in an inert atmosphere at a temperature of 700-900℃ for 2-3h.

2. The method for preparing a lithium battery modified graphite negative electrode material according to claim 1, characterized in that: The solvent in the alcohol dispersion of niobium pentoxide is anhydrous ethanol. Preferably, the ratio of the amount of niobium pentoxide to the amount of ethanol is 1:10-20, g:mL. Preferably, the volume ratio of ethanol to water is 3-4:

1.

3. The method for preparing the modified graphite anode material for lithium batteries according to claim 1, characterized in that: The preheating temperature is 40-60℃, the preheating time is 0.5-1h, and the stirring is continuous during the preheating process.

4. The method for preparing the modified graphite anode material for lithium batteries according to claim 1, characterized in that: The mass percentage of niobium pentoxide in the total mass of niobium pentoxide and graphite is 10%-30%. Preferably, the volatilization temperature of the solvent by heating and stirring is 60-80℃. Preferably, the heating rate during the heat-treating process is 2-5℃ / min.

5. The method for preparing the modified graphite anode material for lithium batteries according to claim 1, characterized in that: The preparation method of the porous graphite precursor is as follows: mixing graphite and silica nanospheres in a certain proportion, heating to 700-900℃ in an inert atmosphere, and heat-treating for 2-3h. Etching the mixed powder after heat-treating with a hydrofluoric acid solution to obtain the porous graphite precursor.

6. The method for preparing the lithium battery modified graphite anode material according to claim 5, characterized in that: The graphite is artificial graphite, D50 is 8-16 μm, compacted density is 1.6-1.8 g / cm 3 ; Preferably, the mass ratio of graphite to silica nanospheres is 6-8:

1. Preferably, the particle size of the silica nanospheres is 20-40nm.

7. The method for preparing the modified graphite anode material for lithium batteries according to claim 5, characterized in that: The dry mixing time of graphite and silica nanospheres is 3-6h.

8. The method for preparing the lithium battery modified graphite anode material according to claim 5, characterized in that: The concentration of the hydrofluoric acid solution is 4-6wt%. Preferably, the etching time is 18-24h, and the stirring is continuous during the etching process.

9. A lithium battery modified graphite negative electrode material, characterized by: Prepared by the preparation method of any one of claims 1-8.

10. A lithium battery, characterized by: The negative electrode is prepared from the modified graphite negative electrode material of claim 9.

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