Modified graphite negative electrode material, preparation method thereof, and secondary battery

Abstract

The application provides a modified graphite negative material, a preparation method thereof, and a secondary battery. The preparation method comprises the following steps: etching a MAX phase powder by using a fluorine-containing etchant to obtain an accordion-shaped multilayer Nb2CT x MXene, and performing hydrothermal reaction and dialysis on the suspension to obtain Nb2CT x MXene quantum dot solution; performing amino treatment on artificial graphite to obtain an amino-graphite aqueous solution; mixing the Nb2CT x MXene quantum dot solution and the amino-graphite aqueous solution, and performing solid-liquid separation and drying treatment. The preparation method can inhibit the chaotic growth of lithium dendrites, and construct high-speed ion channels to improve the fast-charging capacity, and is beneficial to the improvement of the low-temperature and fast-charging performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of new energy material preparation technology, and in particular to modified graphite anode materials, their preparation methods, and secondary batteries. Background Technology

[0002] In recent years, industries such as new energy vehicles, portable consumer electronics, and large-scale energy storage power stations have experienced explosive growth, leading to more stringent market requirements for lithium-ion batteries in terms of fast charging capabilities, low-temperature adaptability, cycle stability, and safety performance. With its advantages of high energy density, long cycle life, and stable operating voltage, lithium-ion batteries have become the core power source for various energy storage and power supply devices, and their overall performance directly determines the user experience and operational safety of end products.

[0003] The anode material is a key component of lithium-ion batteries, directly affecting the battery's ion transport efficiency and electrochemical stability. Currently, commercially available lithium-ion batteries commonly use natural graphite and artificial graphite as the mainstream anode materials. These materials possess advantages such as good conductivity, stable lithium intercalation capacity, and low cost, making them suitable for applications requiring normal room temperature and low-rate charging / discharging. However, under extreme and complex conditions such as low-temperature environments and high-rate fast charging, traditional graphite anodes exhibit significant kinetic hysteresis. At low temperatures, the ion activity of the electrolyte decreases significantly, while the lithium intercalation barrier of the graphite lattice increases significantly. This makes it difficult for lithium ions to quickly and uniformly intercalate into the internal lattice structure of graphite. Consequently, a large number of free lithium ions are reduced and precipitated on the anode surface, continuously generating irregular lithium dendrites.

[0004] The continuous growth of lithium dendrites can lead to multiple technical drawbacks. On the one hand, it can cause irreversible loss of active lithium, resulting in a continuous decline in the effective capacity of the battery and a significant reduction in cycle life. On the other hand, sharp lithium dendrites can easily pierce the battery separator, causing micro-short circuits or even thermal runaway inside the battery, leading to safety accidents such as fires and explosions. This greatly limits the large-scale application of lithium-ion batteries in high-altitude and cold regions, high-power fast charging equipment, and high-frequency energy storage equipment.

[0005] To address these issues, existing technologies primarily improve graphite anode performance through conductivity modification, structural optimization, and interface modification, aiming to reduce electrochemical polarization and suppress lithium dendrite growth. An ideal high-performance graphite anode needs to possess both a low lithium-ion intercalation barrier and a low bulk transport barrier. This can be achieved by improving conductivity, shortening ion diffusion paths, and optimizing interface characteristics, thus enabling efficient fast charging and safe operation. However, existing modification technologies can only improve battery performance under normal operating conditions at room temperature and cannot effectively solve the core challenges of ion transport lag and dendrite growth under low-temperature and high-rate conditions. The industry still lacks high-performance graphite anode modification solutions suitable for extreme operating conditions. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a modified graphite anode material, its preparation method, and a secondary battery. The preparation method of this invention can suppress the disordered growth of lithium dendrites and construct high-speed ion channels to improve fast charging capability, which is beneficial to improving the low-temperature and fast-charging performance of lithium-ion batteries.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a modified graphite anode material, comprising the steps of: (I) Accordion-shaped multilayer Nb2CT was obtained by etching MAX phase powder with a fluorine-containing etchant. x -MXene, after lamellar exfoliation, yields a suspension. This suspension is then subjected to a hydrothermal reaction followed by dialysis to obtain Nb2CT. x -MXene quantum dot solution; (II) The artificial graphite is subjected to amination treatment to obtain an amination graphite ink solution; (III) The Nb2CT x The MXene quantum dot solution and the amino fossil ink solution are mixed, then subjected to solid-liquid separation and drying.

[0008] In the preparation method of this invention, accordion-shaped multilayer Nb2CT can be obtained by etching the MAX phase powder with a fluorine-containing etchant. x -MXene, accordion-shaped multilayer Nb2CT x MXene, after intercalation and layered exfoliation, yields a suspension. Through intercalation and hydrothermal reaction, zero-dimensional nanoparticles are obtained. These extremely small nanoparticles possess abundant surface active sites. As a coating material, they can be strongly adsorbed onto the graphite surface via electrostatic interactions with positively charged amino groups grafted onto the graphite surface, thus reconstructing the surface properties of the artificial graphite. The surface of MXene is rich in functional groups, exhibiting a strong adsorption capacity for lithium ions. This is equivalent to creating numerous uniform "anchor points" on the graphite surface, significantly reducing the nucleation difficulty of lithium ion deposition. This allows for easier and more uniform nucleation, rather than random dendrite growth. Furthermore, utilizing the size effect of MXene quantum dots provides more reaction sites and shortens ion transport paths, essentially building an efficient "highway network" for lithium ions. Therefore, this is beneficial for improving the low-temperature and fast-charging performance of lithium-ion batteries.

[0009] As a technical solution of the present invention, the MAX phase powder is selected from at least one of Ti3AlC2, V2AlC, Nb2AlC, Nb4AlC3 and Mo2AlC.

[0010] As one technical solution of the present invention, the fluorinated etchant contains hydrofluoric acid, or the fluorinated etchant is a mixed solution of fluoride and inorganic acid, the ratio of the amount of fluoride to the amount of inorganic acid is 1g:10~20mL, the fluoride is selected from at least one of lithium fluoride, sodium fluoride, potassium fluoride, zinc fluoride, aluminum fluoride and calcium fluoride, the concentration of the inorganic acid is 10~14mol / L, and the inorganic acid is selected from hydrochloric acid.

[0011] As one technical solution of the present invention, the hydrothermal reaction involves placing the suspension in a high-pressure reactor and reacting it at 80~120℃ for 4~8 hours.

[0012] As one technical solution of the present invention, the dialysis is performed in deionized water, and the dialysis time is 5 to 10 days, with a rotation speed of 30 to 50 rpm.

[0013] As a technical solution of the present invention, the Nb2CT x The solubility of MXene quantum dot solutions is 0.2~2.0 mg / mL.

[0014] As a technical solution of the present invention, the mixing is to mix the Nb2CT x -MXene quantum dot solution is added dropwise to the amino fossil ink solution and stirred for 1 to 3 hours at a speed of 400 to 600 rpm.

[0015] As one technical solution of the present invention, the solid-liquid separation is high-speed centrifugation, the high-speed centrifugation speed is 4000~8000 rpm, and the time is 20~40 min.

[0016] As one technical solution of the present invention, the drying process is to dry at 50~80℃ under vacuum for 8~20 hours.

[0017] As a technical solution of the present invention, the etching includes the following steps: stirring and mixing the fluorine-containing etchant and the MAX phase powder, followed by solid-liquid separation, washing, and drying.

[0018] As a technical solution of the present invention, the stirring includes stirring at room temperature first and then stirring continuously at 30~40°C for 20~28h; the solid-liquid separation is centrifugal separation; the washing is repeated washing with deionized water and anhydrous ethanol until the supernatant is neutral; and the drying is drying under vacuum at 50~80°C for 8~20h.

[0019] As a technical solution of the present invention, the layered ablation includes removing the accordion-shaped multilayer Nb2CT x -MXene is swollen, then the lower solid layer is collected by high-speed centrifugation and then ultrasonically dispersed.

[0020] As a technical solution of the present invention, the swelling treatment is to swell the accordion-shaped multilayer Nb2CT x -MXene was dispersed in an aqueous solution of tetramethylammonium hydroxide and stirred continuously at room temperature for 12-36 h, wherein the concentration of the aqueous solution of tetramethylammonium hydroxide was 15-40 wt.%.

[0021] As one technical solution of the present invention, the high-speed centrifuge speed is 6000~10000 rpm and the centrifugation time is 20~40 min.

[0022] As a technical solution of the present invention, the ultrasonic dispersion is to ultrasonically disperse the lower solid in deionized water under a nitrogen atmosphere, wherein the ultrasonic dispersion is performed 2 to 4 times and the duration of each dispersion is 10 to 20 minutes.

[0023] As one technical solution of the present invention, the amination treatment involves mixing artificial graphite with an aqueous solution of an aminosilane coupling agent, followed by filtration, washing, and volume adjustment to obtain an amination graphite ink solution with a graphite content of 10-200 mg / mL.

[0024] As one technical solution of the present invention, the artificial graphite has a Dv50 of 5~15μm, a specific capacity of 320~360mAh / g, and a specific surface area of ​​0.5~3.0m². 2 / g, tap density is 0.5~1.5g / cm³ 3 .

[0025] As a technical solution of the present invention, the concentration of the aminosilane coupling agent aqueous solution is 0.1~1.0 mg / mL, and the aminosilane coupling agent in the aminosilane coupling agent aqueous solution is selected from one or more of γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, β-aminoethyltrimethoxysilane, N-cyclohexyl-γ-aminopropylmethyldimethoxysilane, and bis(triethoxysilylpropyl)amine.

[0026] The second aspect of this invention provides a modified graphite anode material prepared by the aforementioned method for preparing modified graphite anode materials, comprising a graphite matrix and Nb2CT coating the graphite matrix. x -MXene quantum dots, the Nb2CT x -MXene quantum dots account for 0.5 to 2.0% of the mass of the graphite matrix. The modified graphite anode material of the present invention is tested using Nb2CT. x- MXene quantum dots' "interface engineering" reconstructs the surface properties of artificial graphite, which can not only suppress lithium dendrite growth, but also build an efficient "highway network" for lithium ions, which is beneficial to improving the low-temperature and fast-charging performance of lithium-ion batteries.

[0027] A third aspect of the present invention provides a secondary battery comprising a positive electrode material, a negative electrode material and an electrolyte, characterized in that the negative electrode material comprises the aforementioned modified graphite negative electrode material. Attached Figure Description

[0028] Figure 1 Nb2CT is used in the preparation method of the modified graphite anode material of the present invention. x -Schematic diagram of the synthesis process of MXene quantum dots.

[0029] Figure 2 Accordion-shaped multilayer Nb2CT in Example 1 x - SEM image of MXene.

[0030] Figure 3 Nb2CT after lamellar dissection in Example 1 x - SEM image of MXene.

[0031] Figure 4 Nb2CT in Example 1 x -TEM image of MXene quantum dots at 20 nm.

[0032] Figure 5 Nb2CT in Example 1 x -TEM image of MXene quantum dots at 5nm.

[0033] Figure 6 This is a SEM image of the modified graphite anode material of Example 1.

[0034] Figure 7 This is a TEM image of the modified graphite anode material of Example 1 at 20 nm.

[0035] Figure 8 This is a TEM image of the modified graphite anode material of Example 1 at 5 nm. Detailed Implementation

[0036] The modified graphite anode material of this invention can be used alone or in combination with other anode active materials (such as natural graphite, silicon-oxygen materials, silicon-carbon materials, hard carbon, soft carbon, etc.). The modified graphite anode material can be applied to secondary batteries, such as lithium-ion batteries or sodium-ion batteries. Secondary batteries include a cathode material, an electrolyte, and a cathode material.

[0037] The modified graphite anode material of the present invention includes a graphite matrix and Nb2CT coated on the graphite matrix. x -MXene quantum dots. Nb2CT x -MXene quantum dots comprise 0.5–2.0% of the graphite matrix by mass. As a technical solution, Nb2CT... x -MXene quantum dots comprise 1.0~2.0% of the graphite matrix by mass. As a technical solution, Nb2CT... x -MXene quantum dots account for 1.0~1.5% of the mass of the graphite matrix.

[0038] The preparation method of the modified graphite anode material of the present invention may include the following steps.

[0039] (I) Accordion-shaped multilayer Nb2CT was obtained by etching MAX phase powder with a fluorine-containing etchant. x -MXene, after lamellar exfoliation, yields a suspension. This suspension is then subjected to a hydrothermal reaction followed by dialysis to obtain Nb2CT. x -MXene quantum dot solution.

[0040] (II) The artificial graphite is amination treatment to obtain an amination graphite ink solution.

[0041] (III) Nb2CT x The MXene quantum dot solution and the amino fossil ink solution are mixed, then subjected to solid-liquid separation and drying.

[0042] Nb2CT x The synthesis process of MXene quantum dots is as follows: Figure 1 As shown, MAX phase powder was etched to obtain accordion-shaped multilayer Nb2CT. x -MXene, obtained by laminar exfoliation, yields few-layered Nb2CT x -MXene, followed by hydrothermal reaction and dialysis, yields Nb2CT. x -MXene quantum dot solution. Nb2CT x The solubility of MXene quantum dot solutions is 0.2~2.0 mg / mL.

[0043] The fluorinated etchant may contain hydrofluoric acid, which can be used as an aqueous solution or as a mixture of hydrofluoric acid and hydrochloric acid. When using a mixture of hydrofluoric acid and hydrochloric acid, the mass ratio of hydrofluoric acid to hydrochloric acid is 1:10~40. Alternatively, the fluorinated etchant may be a mixture of fluoride and inorganic acid. The ratio of fluoride to inorganic acid is 1g:10~20mL. The fluoride is selected from at least one of lithium fluoride, sodium fluoride, potassium fluoride, zinc fluoride, aluminum fluoride, and calcium fluoride. The concentration of the inorganic acid is 10~14mol / L, and the inorganic acid is selected from hydrochloric acid. The MAX phase powder is selected from at least one of Ti3AlC2, V2AlC, Nb2AlC, Nb4AlC3, and Mo2AlC. The etching process includes the following steps: mixing the fluorinated etchant and the MAX phase powder, followed by solid-liquid separation, washing, and drying. The stirring process includes stirring at room temperature followed by continuous stirring at 30-40°C for 20-28 hours. Solid-liquid separation is performed by centrifugation. Washing involves repeated washing with deionized water and anhydrous ethanol until the supernatant is neutral. Drying is performed under vacuum at 50-80°C for 8-20 hours. Etching transforms the MAX phase powder into a loose, multi-layered structure, similar to an accordion. After etching, it is sandwiched within Nb2CT. x Al atoms between layers were successfully eliminated, resulting in a characteristic MXene morphology with an average size of approximately 10–15 μm.

[0044] Layered ablation includes accordion-shaped multilayer Nb2CT x -MXene is swollen, then the lower solid layer is collected by high-speed centrifugation and then ultrasonically dispersed. The swelling treatment involves accordion-shaped multilayer Nb2CT. x MXene was dispersed in a tetramethylammonium hydroxide aqueous solution and stirred continuously at room temperature for 12–36 h. The concentration of the tetramethylammonium hydroxide aqueous solution was 15–40 wt.%. High-speed centrifugation was performed at 6000–10000 rpm for 20–40 min. Ultrasonic dispersion involved ultrasonically dispersing the lower solid layer in deionized water under a nitrogen atmosphere, with 2–4 ultrasonic dispersions performed, each lasting 10–20 min. Less layered Nb2CT was obtained by intercalation with the tetramethylammonium hydroxide aqueous solution via layered exfoliation. x The morphology of the nanosheets shows an average size of approximately 2–3 μm.

[0045] The hydrothermal reaction involves placing the suspension in an autoclave and reacting at 80-120°C for 4-8 hours. Dialysis is performed in deionized water for 5-10 days at a rotation speed of 30-50 rpm. Through hydrothermal reaction and dialysis, few-layer Nb2CT can be removed. x Nanosheets converted into Nb2CT x -MXene quantum dots.

[0046] Amination treatment involves mixing artificial graphite with an aqueous solution of an aminosilane coupling agent, followed by filtration, washing, and volume adjustment to obtain an amination-treated graphite ink solution with a graphite content of 10–200 mg / mL. The artificial graphite has a Dv50 of 5–15 μm, a specific capacity of 320–360 mAh / g, and a specific surface area of ​​0.5–3.0 m². 2 / g, tap density is 0.5~1.5g / cm³ 3 The concentration of the aminosilane coupling agent aqueous solution is 0.1~1.0 mg / mL. The aminosilane coupling agent in the aqueous solution is selected from one or more of γ-aminopropyltriethoxysilane (KH-550), 3-aminopropyltrimethoxysilane (APS), N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH-792), γγ-aminopropylmethyldiethoxysilane (Si-902), β-aminoethyltrimethoxysilane (KH560), N-cyclohexyl-γ-aminopropylmethyldimethoxysilane (KH612), and bis(triethoxysilylpropyl)amine (GX-552). Amination treatment grafts positively charged amino groups onto the graphite surface, thereby enabling the strong adsorption of negatively charged Nb₂CT via electrostatic interactions. x -MXene quantum dots, thereby reconstructing the surface properties of artificial graphite.

[0047] Nb2CT x -MXene quantum dot solution and amino fossil ink solution are mixed to obtain Nb2CT x MXene quantum dot solution was added dropwise to an amino fossil ink solution and stirred. Stirring time was 1–3 hours at a speed of 400–600 rpm. Solid-liquid separation was performed by high-speed centrifugation at 4000–8000 rpm for 20–40 minutes. Drying was carried out under vacuum at 50–80°C for 8–20 hours. The uniformity of coating was controlled by dropwise mixing, followed by stirring and dispersion. The solution was then passed through a negatively charged Nb₂CT... x The electrostatic interaction between MXene quantum dots and amino-modified graphite causes the quantum dots to coat the graphite surface. Modified graphite anode material can be obtained by solid-liquid separation and drying.

[0048] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0049] Example 1 This embodiment describes a method for preparing a modified graphite anode material, comprising the following steps.

[0050] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT x MXene powder was added to 20 mL of tetramethylammonium hydroxide aqueous solution (25 wt.%) and stirred continuously at room temperature for 24 h. The supernatant was then removed by centrifugation at 8000 rpm for 30 min. Deionized water was added and centrifuged three times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated three times (15 min each time) under a nitrogen atmosphere at 15 °C. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 150 sccm for 15 min to purge air. The reaction was then carried out at 100 °C for 6 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 40 rpm for 7 days to obtain Nb2CT with a concentration of 0.2 mg / mL. x -MXene quantum dot solution.

[0051] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0052] (III) Add 25 mL of Nb2CT x -MXene quantum dot solution (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, the mixture was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0053] During the preparation process, an accordion-shaped multilayer Nb2CT was used. x -MXene was used for SEM detection, and the results are as follows Figure 2 As shown, it displays multi-slice Nb2CT xIt exhibits a loose, layered structure, similar to an accordion, thus verifying that after the etching process, it is sandwiched within Nb2CT. x Al atoms between layers were successfully eliminated, resulting in a characteristic MXene morphology. This was observed in Nb2CT after layered exfoliation. x -MXene was used for SEM detection, and the results are as follows Figure 3 As shown, this illustrates the multilayered Nb2CT after intercalation with tetramethylammonium hydroxide. x -MXene detaches into less layered Nb2CT x -MXene ultrathin nanosheets. For the fabricated Nb2CT x -MXene quantum dots were subjected to TEM detection at 20nm and 5nm, respectively, and the results are as follows: Figure 4 and Figure 5 As shown, it has become a 0-dimensional Nb2CT x -MXene quantum dot nanoparticles.

[0054] The prepared modified graphite anode material was analyzed by SEM and TEM, and the results are as follows: Figures 6-8 As shown in the figure, Nb2CT is clearly displayed. x -MXene quantum dots are tightly adhered to the surface of artificial graphite.

[0055] Example 2 This embodiment describes a method for preparing a modified graphite anode material, comprising the following steps.

[0056] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT xMXene powder was added to 20 mL of tetramethylammonium hydroxide aqueous solution (25 wt.%) and stirred continuously at room temperature for 24 h. The supernatant was then removed by centrifugation at 8000 rpm for 30 min. Deionized water was added and centrifuged three times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated three times (15 min each time) under a nitrogen atmosphere at 15 °C. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 150 sccm for 15 min to purge air. The reaction was then carried out at 100 °C for 6 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 40 rpm for 7 days to obtain Nb2CT with a concentration of 0.2 mg / mL. x -MXene quantum dot solution.

[0057] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0058] (III) Add 50 mL of Nb2CT x -MXene quantum dot solution (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, the mixture was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0059] Example 3 This embodiment describes a method for preparing a modified graphite anode material, comprising the following steps.

[0060] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT xMXene powder was added to 20 mL of tetramethylammonium hydroxide aqueous solution (25 wt.%) and stirred continuously at room temperature for 24 h. The supernatant was then removed by centrifugation at 8000 rpm for 30 min. Deionized water was added and centrifuged three times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated three times (15 min each time) under a nitrogen atmosphere at 15 °C. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 150 sccm for 15 min to purge air. The reaction was then carried out at 100 °C for 6 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 40 rpm for 7 days to obtain Nb2CT with a concentration of 0.2 mg / mL. x -MXene quantum dot solution.

[0061] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0062] (III) Add 75 mL of Nb2CT x -MXene quantum dot solution (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, the mixture was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0063] Example 4 This embodiment describes a method for preparing a modified graphite anode material, comprising the following steps.

[0064] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT xMXene powder was added to 20 mL of tetramethylammonium hydroxide aqueous solution (25 wt.%) and stirred continuously at room temperature for 24 h. The supernatant was then removed by centrifugation at 8000 rpm for 30 min. Deionized water was added and centrifuged three times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated three times (15 min each time) under a nitrogen atmosphere at 15 °C. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 150 sccm for 15 min to purge air. The reaction was then carried out at 100 °C for 6 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 40 rpm for 7 days to obtain Nb2CT with a concentration of 0.2 mg / mL. x -MXene quantum dot solution.

[0065] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0066] (III) Add 100 mL of Nb2CT x -MXene quantum dot solution (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, the mixture was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0067] Example 5 This embodiment describes a method for preparing a modified graphite anode material, comprising the following steps.

[0068] (I) 6.0 g of Nb2AlC powder was slowly immersed in hydrofluoric acid solution (49 wt.%) in batches. The mixture was first stirred at room temperature and then stirred continuously at 60 °C for 12 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 75 °C for 8 h. After grinding in a quartz mortar, an accordion-shaped multilayer Nb2CT was obtained. x -MXene powder. Weigh out 150mg Nb2CT xMXene powder was added to 30 mL of tetramethylammonium hydroxide aqueous solution (40 wt.%) and stirred continuously at room temperature for 30 h. The supernatant was then removed by centrifugation at 8500 rpm for 25 min. Deionized water was added and centrifuged four times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated four times (10 min each time) at 13 °C under a N2 atmosphere. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 140 sccm for 20 min to purge air. The reaction was then carried out at 120 °C for 4 h. Finally, the precipitate was filtered through a 0.20 μm membrane, and the suspension was dialyzed against deionized water at 25 rpm for 10 days to obtain Nb2CT with a concentration of 1.0 mg / mL. x -MXene quantum dot solution.

[0069] (II) 1.5g of artificial graphite (Dv50 is 12μm, specific capacity is 350mAh / g, specific surface area is 1.8m²) 2 / g, tap density is 1.0g / cm³ 3 Disperse the solution in 100 mL of APS aqueous solution (0.5 mg / mL), then stir at 75 °C for 10 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0070] (III) Add 40 mL of Nb2CT x -MXene quantum dot solution (1.0 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (50 mg / mL) and stirred at 600 rpm for 1 h. Then, the mixture was centrifuged (7500 rpm for 15 min). Finally, the obtained solid product was placed in an 80 °C vacuum drying oven and dried for 8 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0071] Example 6 This embodiment describes a method for preparing a modified graphite anode material, comprising the following steps.

[0072] (I) 4.5 g of Nb4AlC3 powder was slowly immersed in a mixed solution of hydrofluoric acid and HCl (1 mL of hydrofluoric acid (49 wt.%) solution was added dropwise to 30 mL of 10 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 40 °C for 15 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until its pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 80 °C for 7 h. After grinding in a quartz mortar, an accordion-shaped multilayer Nb2CT was obtained. x -MXene powder. Weigh out 160mg Nb2CT xMXene powder was added to 30 mL of tetramethylammonium hydroxide aqueous solution (35 wt.%) and stirred continuously at room temperature for 32 h. The supernatant was then removed by centrifugation at 6500 rpm for 40 min. Deionized water was added and centrifuged four times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated three times (20 min each time) at 15 °C under a N2 atmosphere. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 130 sccm for 20 min to purge air. The reaction was then carried out at 100 °C for 5 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 45 rpm for 9 days to obtain Nb2CT with a concentration of 0.5 mg / mL. x -MXene quantum dot solution.

[0073] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 80 mL of KH-560 aqueous solution (0.8 mg / mL), then stir at 70 °C for 10 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0074] (III) Add 25 mL of Nb2CT x -MXene quantum dot solution (0.5 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 650 rpm for 1 h. Then, the mixture was centrifuged (7000 rpm for 15 min). Finally, the obtained solid product was placed in a vacuum drying oven at 75 °C and dried for 10 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0075] Comparative Example 1 This comparative example illustrates a method for preparing a modified graphite anode material, comprising the following steps.

[0076] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 0.2g of Nb2CT. x -MXene powder was dispersed in 100 mL of deionized water to obtain Nb2CT. x-MXene dispersion.

[0077] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0078] (III) Add 25 mL of Nb2CT x -MXene dispersion (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, it was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0079] Comparative Example 2 This comparative example illustrates a method for preparing a modified graphite anode material, comprising the following steps.

[0080] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT x MXene powder was added to 20 mL of tetramethylammonium hydroxide aqueous solution (25 wt.%) and stirred continuously at room temperature for 24 h. The supernatant was then removed by centrifugation at 8000 rpm for 30 min. Deionized water was added and centrifuged three times to remove the solvent. The bottom precipitate was then dispersed in deionized water. The mixture was sonicated three times (15 min each time) under a N2 atmosphere at 15 °C. The suspension was then filtered through a 0.22 μm membrane and brought to a final volume to obtain a few-layered Nb2CT concentration of 0.2 mg / mL. x -MXene solution.

[0081] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0082] (III) Add 25 mL of Nb2CT x -MXene quantum dot solution (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, the mixture was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0083] Comparative Example 3 This comparative example illustrates a method for preparing a modified graphite anode material, comprising the following steps.

[0084] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT x MXene powder was added to 20 mL of deionized water to obtain a suspension. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 150 sccm for 15 min to purge air. The reaction was then carried out at 100 °C for 6 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 40 rpm for 7 days to obtain Nb2CT with a concentration of 0.2 mg / mL. x -MXene quantum dot solution.

[0085] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3 Disperse the solution in 100 mL of KH-550 aqueous solution (0.2 mg / mL), then stir at 60 °C for 12 h, and finally wash repeatedly with deionized water to obtain an amino fossil ink solution.

[0086] (III) Add 25 mL of Nb2CTx -MXene quantum dot solution (0.2 mg / mL) was added dropwise to 100 mL of amino graphite ink solution (10 mg / mL) and stirred at 500 rpm for 2 h. Then, the mixture was centrifuged (6000 rpm for 25 min). Finally, the obtained solid product was placed in a vacuum drying oven at 60 °C and dried for 12 h. After grinding in a quartz mortar, the modified graphite anode material was obtained.

[0087] Comparative Example 4 This comparative example illustrates a method for preparing a modified graphite anode material, comprising the following steps.

[0088] (I) 5.0 g of Nb₂AlC powder was slowly immersed in a mixed solution of LiF and HCl (3.2 g of LiF dissolved in 40 mL of 12 mol / L hydrochloric acid). The mixture was first stirred at room temperature and then stirred continuously at 35 °C for 24 h. The reaction product was repeatedly washed with deionized water and anhydrous ethanol until the pH value was greater than 6.5. Finally, the obtained solid product was dried in a vacuum drying oven at 60 °C for 10 h, and then ground in a quartz mortar to obtain an accordion-shaped multilayer Nb₂CT. x -MXene powder. Weigh out 160mg Nb2CT x MXene powder was added to 20 mL of tetramethylammonium hydroxide aqueous solution (25 wt.%) and stirred continuously at room temperature for 24 h. The supernatant was then removed by centrifugation at 8000 rpm for 30 min. Deionized water was added and centrifuged three times to remove the solvent. The bottom precipitate was then dispersed in deionized water, and the mixture was sonicated three times (15 min each time) under a nitrogen atmosphere at 15 °C. The suspension was then transferred to a PTFE-lined stainless steel autoclave, and nitrogen gas was introduced at a flow rate of 150 sccm for 15 min to purge air. The reaction was then carried out at 100 °C for 6 h. Finally, the precipitate was filtered through a 0.22 μm membrane, and the suspension was dialyzed against deionized water at 40 rpm for 7 days to obtain Nb2CT with a concentration of 0.2 mg / mL. x -MXene quantum dot solution, Nb2CT x -MXene quantum dot solution was freeze-dried to obtain Nb2CT x -MXene quantum dot powder.

[0089] (II) 1g of artificial graphite (Dv50 is 10μm, specific capacity is 340mAh / g, specific surface area is 1.33m²) 2 / g, tap density is 1.2g / cm³ 3The solution was dispersed in 100 mL of KH-550 aqueous solution (0.2 mg / mL), stirred at 60 °C for 12 h, and finally washed repeatedly with deionized water to obtain an amino graphite ink solution. The amino graphite ink solution was then filtered and dried to obtain amino graphite powder.

[0090] (III) 2mg Nb2CT x Modified graphite anode material was obtained by grinding MXene quantum dot powder and 200 mg of amino graphite powder in a quartz mortar.

[0091] The modified graphite anode materials of Examples 1-6 and Comparative Examples 1-4, as well as artificial graphite (Dv50 of 10 μm, specific capacity of 340 mAh / g, specific surface area of ​​1.33 m²), were compared. 2 / g, tap density is 1.2g / cm³ 3 Electrochemical performance tests were conducted, and the test methods are shown below. The test results are shown in Table 1.

[0092] The specific surface area of ​​the modified graphite anode materials and artificial graphite in Examples 1-6 and Comparative Examples 1-4 was tested. The modified graphite anode materials and artificial graphite in Examples 1-6 and Comparative Examples 1-4 were used as anode active materials, mixed with conductive agent SP and binder PVDF at a weight ratio of 91:2:7, and NMP was used as a solvent to prepare a slurry. The slurry was then coated, dried, and rolled to prepare anode sheets. A lithium metal sheet was used as the counter electrode, and a polypropylene microporous membrane was used as the separator. An electrolyte (1 mol / L LiPF6, and a 1:1:1 volume ratio mixture of EC, DMC, and EMC) was added, and button half-cells were assembled and allowed to stand for 2 hours. The first charge-discharge curves of the half-cells were tested using a Blue Electric testing system manufactured by Blue Electric Electronics Co., Ltd. The constant current rate was controlled at 0.1C, and the charge-discharge voltage was controlled between 0.005V and 2.0V to obtain the specific capacity and initial coulombic efficiency of the materials. Using the aforementioned button cell battery, with the charge / discharge voltage limited to 0.005V to 2.0V, under normal temperature conditions, it is cycled for 5 cycles at a current of 0.1C, then sequentially cycled for 5 cycles at a current of 1C, 1.5C, 2C, and 3C, and finally cycled for 5 cycles at a current of 0.1C. The discharge capacity retention rate at 3C is then calculated.

[0093] 3C discharge capacity retention rate = (Lithium-depleted specific capacity after 5 cycles at 3C / Lithium-depleted specific capacity after 5 cycles at 0.1C) × 100% In addition, the modified graphite anode materials of Examples 1-6 and Comparative Examples 1-4, as well as artificial graphite, were used as anode active materials and mixed with CMC, SBR, and SP at a mass ratio of 95.8:1.2:2:1. A slurry was prepared using NMP as a solvent, and then coated, dried, and rolled to prepare the anode sheet. Lithium iron phosphate was used as the cathode active material and mixed with PVDF and conductive SP at a mass ratio of 96:2:2. A slurry was prepared using NMP as a solvent, and then coated, dried, and rolled to prepare the cathode sheet. The electrolyte was a 1 mol / L LiPF6 solution (the solvent was a mixture of EC, DMC, and EMC at a volume ratio of 1:1:1), and the separator was a polypropylene microporous membrane. The cathode sheet, separator, and anode sheet were wound to form a soft-pack battery cell, packaged in aluminum-plastic film, filled with electrolyte, and after formation and capacity testing, a 1.2 Ah lithium-ion battery was produced. First, the battery was subjected to a 0.33C capacity test at room temperature, and the calibrated capacity was recorded. Then, it was charged to 100% SOC at room temperature using a 0.33C charge. Next, the battery was discharged at -20°C using a 0.33C charge, and the capacity was recorded. The low-temperature discharge capacity retention rate is the ratio of the discharge capacity at low temperature to the calibrated capacity. Additionally, the battery was cycled at 25°C with a 1C rate between 2.50 and 3.65V, and the capacity retention rate after 1000 cycles was calculated.

[0094] Capacity retention rate after 1000 cycles = (Capacity on cycle 1000 / Capacity on cycle 1) × 100% Table 1. Performance results of Examples 1-6, Comparative Examples 1-4, and artificial graphite.

[0095] As shown in Table 1, the modified graphite anode materials of Examples 1-6 exhibit better electrochemical performance. This is due to the accordion-shaped multilayer Nb2CT... x -MXene, after being exfoliated in layers, can be used to obtain zero-dimensional nanoparticles Nb2CT through intercalation and hydrothermal reaction. x -MXene quantum dots, when loaded onto the surface of graphite, can reconstruct the surface properties of artificial graphite, improve the electronic and ionic conductivity of the material, reduce its irreversible capacity, improve the first efficiency and specific capacity, and at the same time, increase more active sites, improve the lithium ion insertion and extraction channels during charging and discharging, thus improving rate performance.

[0096] Furthermore, a comparison of Examples 1-4 shows that the electrochemical performance of the material first increases and then decreases with increasing loading. This is because the increased loading of Nb2CT... x -MXene quantum dots exhibit aggregation, therefore, considering Nb2CT... x The performance of MXene quantum dots is optimal when the loading ratio on graphite is 1.0%.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a modified graphite anode material, characterized in that, Including the following steps: (I) Accordion-shaped multilayer Nb2CT was obtained by etching MAX phase powder with a fluorine-containing etchant. x -MXene, after lamellar exfoliation, yields a suspension. This suspension is then subjected to a hydrothermal reaction followed by dialysis to obtain Nb2CT. x -MXene quantum dot solution; (II) The artificial graphite is subjected to amination treatment to obtain an amination graphite ink solution; (III) The Nb2CT x The MXene quantum dot solution and the amino fossil ink solution are mixed, then subjected to solid-liquid separation and drying.

2. The method for preparing the modified graphite anode material according to claim 1, characterized in that, Includes at least one of the following features (1) to (8): (1) The MAX phase powder is selected from at least one of Ti3AlC2, V2AlC, Nb2AlC, Nb4AlC3 and Mo2AlC; (2) The fluorinated etchant contains hydrofluoric acid, or the fluorinated etchant is a mixed solution of fluoride and inorganic acid, the ratio of the amount of fluoride to the amount of inorganic acid is 1g:10~20mL, the fluoride is selected from at least one of lithium fluoride, sodium fluoride, potassium fluoride, zinc fluoride, aluminum fluoride and calcium fluoride, the concentration of the inorganic acid is 10~14mol / L, and the inorganic acid is selected from hydrochloric acid; (3) The hydrothermal reaction is to place the suspension in a high-pressure reactor and react it at 80~120℃ for 4~8h; (4) The dialysis is performed in deionized water for 5 to 10 days and the rotation speed is 30 to 50 rpm; (5) The Nb2CT x The solubility of MXene quantum dot solutions is 0.2~2.0 mg / mL; (6) The mixing is to mix the Nb2CT x -MXene quantum dot solution is added dropwise to the amino fossil ink solution and stirred for 1-3 hours at a speed of 400-600 rpm; (7) The solid-liquid separation is carried out by high-speed centrifugation, the speed of which is 4000~8000 rpm and the time is 20~40 min; (8) The drying process is to dry at 50~80℃ under vacuum for 8~20h.

3. The method for preparing the modified graphite anode material according to claim 1, characterized in that, The etching process includes the following steps: mixing the fluorine-containing etchant and the MAX phase powder, followed by solid-liquid separation, washing, and drying.

4. The method for preparing the modified graphite anode material according to claim 3, characterized in that, The stirring includes stirring at room temperature first and then stirring continuously at 30-40°C for 20-28 hours. The solid-liquid separation is centrifugal separation. The washing is repeated with deionized water and anhydrous ethanol until the supernatant is neutral. The drying is vacuum drying at 50-80°C for 8-20 hours.

5. The method for preparing the modified graphite anode material according to claim 1, characterized in that, The layered ablation includes dissecting the accordion-shaped multilayer Nb2CT. x -MXene is swollen, then the lower solid layer is collected by high-speed centrifugation and then ultrasonically dispersed.

6. The method for preparing the modified graphite anode material according to claim 5, characterized in that, Includes at least one of the following features (i) to (iii): (i) The swelling treatment is to swell the accordion-shaped multilayer Nb2CT x -MXene was dispersed in an aqueous solution of tetramethylammonium hydroxide and stirred continuously at room temperature for 12-36 h, wherein the concentration of the aqueous solution of tetramethylammonium hydroxide was 15-40 wt.%. (ii) The speed of the high-speed centrifuge is 6000~10000 rpm, and the centrifugation time is 20~40 min; (iii) The ultrasonic dispersion is to ultrasonically disperse the lower solid in deionized water under a nitrogen atmosphere, wherein the ultrasonic dispersion is performed 2 to 4 times and the time for each time is 10 to 20 minutes.

7. The method for preparing the modified graphite anode material according to claim 1, characterized in that, The amination treatment involves mixing artificial graphite with an aqueous solution of an aminosilane coupling agent, followed by filtration, washing, and volume adjustment to obtain an amination graphite ink solution with a graphite content of 10-200 mg / mL.

8. The method for preparing the modified graphite anode material according to claim 7, characterized in that, Includes at least one of the following features (i) to (ii): (i) The artificial graphite has a Dv50 of 5~15μm, a specific capacity of 320~360mAh / g, and a specific surface area of ​​0.5~3.0m². 2 / g, tap density is 0.5~1.5g / cm³ 3 ; (ii) The concentration of the aqueous solution of the aminosilane coupling agent is 0.1~1.0 mg / mL, and the aminosilane coupling agent in the aqueous solution of the aminosilane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, β-aminoethyltrimethoxysilane, N-cyclohexyl-γ-aminopropylmethyldimethoxysilane and bis(triethoxysilylpropyl)amine.

9. The modified graphite anode material prepared by the method for preparing the modified graphite anode material according to any one of claims 1 to 8, characterized in that, Includes a graphite matrix and Nb2CT coating the graphite matrix. x -MXene quantum dots, the Nb2CT x -MXene quantum dots account for 0.5 to 2.0% of the mass of the graphite matrix.

10. A secondary battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, The negative electrode material includes the modified graphite negative electrode material as described in claim 9.

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