A high-capacity, high-cycle negative electrode material and its preparation method and application

Abstract

The present invention provides a high-capacity, high-cycle negative electrode material, and its preparation method and application, which belong to the field of negative electrode materials. The present invention forms a porous skeleton by utilizing the coordination effect of metal ions and 2-methylimidazole, and generates nitrogen-rich carbon nitride through heat treatment and introduction of melamine for nitrogen doping, providing a high specific surface area and active sites to optimize lithium ion storage and diffusion performance; further compounding graphene quantum dots, utilizing their conductivity and surface functional groups to enhance interface stability and electron transport network, while providing more active sites. Porous phenolic resin carbon spheres are carbonized to form a high specific surface area and porous structure to enhance mechanical stability; one-dimensional transition metal oxide nanofibers prepared by electrospinning provide high conductivity and ion diffusion channels, and enhance interface bonding and buffer volume expansion through a polydopamine coating. The composite material exhibits excellent performance under the synergistic effect of each component.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and relates to a high-capacity and high-cycle negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of electric vehicles and renewable energy storage systems, improving the performance of lithium-ion batteries, the primary energy storage device, has become increasingly important. The choice of anode material in lithium-ion batteries directly impacts the battery's energy density, cycle life, and safety. Currently, widely used anode materials include graphite and silicon.

[0003] Graphite anodes are widely used due to their excellent stability and commercial maturity, but their low theoretical capacity limits the battery's energy output. Although their performance has been improved to some extent through methods such as doping or modification, the problem of limited room for capacity improvement remains. In addition, graphite's insufficient conductivity and lithium ion diffusion rate under high-rate discharge conditions lead to poor battery performance in high-power applications.

[0004] Silicon negative electrodes have attracted widespread attention due to their extremely high theoretical capacity. However, silicon undergoes significant volume changes during the charge and discharge process. This volume expansion and contraction can lead to destruction of the electrode structure and consumption of the electrolyte, resulting in rapid capacity decay and poor cycle stability.

[0005] In recent years, porous carbon materials have attracted attention due to their excellent electrical conductivity and large specific surface area. However, in practical applications, their electrochemical activity and ion conductivity remain insufficient. The combination of metal oxides and conductive polymers is considered an effective strategy to enhance the performance of anode materials, but how to improve cycling stability while maintaining high capacity remains an urgent challenge. Summary of the Invention

[0006] In response to the above problems, the purpose of the present invention is to provide a high-capacity and high-cycle negative electrode material and a preparation method thereof. The present invention forms a three-dimensional porous framework by utilizing the coordination effect of metal ions and 2-methylimidazole, introduces melamine as a nitrogen source through heat treatment, and prepares nitrogen-rich carbon nitride, which provides a high specific surface area and active sites to optimize lithium ion storage and diffusion performance; further, by composite graphene quantum dots, its high conductivity and surface functional groups are utilized to enhance interface stability and electron transport network, while giving the material more active sites. Porous phenolic resin carbon spheres are formed into a porous structure by high-temperature carbonization, providing excellent mechanical stability, high compaction density and abundant lithium ion storage sites. The one-dimensional transition metal oxide nanofibers prepared by electrospinning improve the electron transport and ion diffusion channels, and are compounded with a polydopamine coating to enhance interface bonding and buffer volume expansion. The composite material exhibits excellent performance under the synergistic effect of each component.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a high-capacity, high-cycle negative electrode material, the method comprising:

[0009] S1: Metal salts are reacted with 2-methylimidazole to obtain multi-metallic MOF precursor powder, which is then heat-treated with melamine under an inert atmosphere to obtain porous carbon nitride nanosheets;

[0010] S2: hydrothermally treating a graphene oxide dispersion to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, and adding porous carbon nitride nanosheets to react to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0011] S3: mixing phenol and formaldehyde solution to obtain a phenolic resin sphere precursor, and heat-treating it under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0012] S4: adding an inorganic salt to a solution of polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a precursor solution, and obtaining transition metal oxide nanofibers by electrospinning and calcining;

[0013] S5: adding porous phenolic resin carbon spheres and dopamine hydrochloride to a tris(hydroxymethylaminomethane) buffer solution for reaction, followed by adding transition metal oxide nanofibers to obtain a ternary composite porous phenolic resin carbon sphere;

[0014] S6: Add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black into an aqueous binder solution and evenly disperse them to obtain a high-capacity and high-cycle negative electrode material.

[0015] Specifically, S1: dispersing a metal salt in deionized water, adding 2-methylimidazole and stirring the mixture, filtering, washing, and drying to obtain a multi-metallic MOF precursor powder; placing the precursor powder in a porcelain boat, adding melamine, and heat-treating the mixture under an inert atmosphere to obtain porous carbon nitride nanosheets;

[0016] S2: preparing a graphene oxide dispersion, hydrothermally treating it to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, adding porous carbon nitride nanosheets, stirring and adsorbing it, and then spray drying it to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0017] S3: Phenol and formaldehyde solutions are mixed, the pH is adjusted with ammonia water to obtain reaction solution A, the mixture is reacted at a constant temperature, centrifuged, washed, and dried to obtain a phenolic resin sphere precursor, and then heat-treated under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0018] S4: preparing a polyvinyl pyrrolidone-N,N-dimethylformamide solution, adding an inorganic salt and stirring to form a uniform precursor solution, obtaining a pretreated fiber membrane by electrospinning, and calcining to obtain transition metal oxide nanofibers;

[0019] S5: The porous phenolic resin carbon spheres are dispersed in tris (hydroxymethylaminomethane) buffer and the pH is maintained, dopamine hydrochloride is added, and after stirring, transition metal oxide nanofibers are added and the reaction is continued, followed by centrifugation, washing, and drying to obtain the ternary composite porous phenolic resin carbon spheres;

[0020] S6: Prepare an aqueous binder solution, add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black in sequence, and evenly disperse them to obtain a high-capacity and high-cycle negative electrode material.

[0021] As a preferred technical solution of the present invention, in step S1, the mass ratio of zinc nitrate, cobalt nitrate and ferric nitrate is 1:0.8-1.2:1, for example, it can be 1:0.80:1, 1:0.84:1, 1:0.88:1, 1:0.92:1, 1:0.96:1, 1:1.00:1, 1:1.04:1, 1:1.08:1, 1:1.12:1, 1:1.16:1 or 1:1.20:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional embodiments, the total concentration of the metal salt dispersed in deionized water is 0.1-0.3M, for example, it can be 0.10M, 0.12M, 0.14M, 0.16M, 0.18M, ​​0.20M, 0.22M, 0.24M, 0.26M, 0.28M or 0.30M, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional embodiments, the total molar ratio of the 2-methylimidazole to the metal salt is 2-3:1, for example, it can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0024] In some optional embodiments, the temperature of the stirring reaction is 30-40°C, for example, it can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] In some optional embodiments, the stirring reaction time is 4-6h, for example, it can be 4.0h, 4.2h, 4.4h, 4.6h, 4.8h, 5.0h, 5.2h, 5.4h, 5.6h, 5.8h or 6.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional embodiments, the mass ratio of melamine to multi-metal MOF precursor powder is 0.1-0.2:1, for example, it can be 0.10:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1 or 0.20:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0027] In some optional embodiments, the first temperature of the heat treatment is 300-400°C, for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In some optional embodiments, the first time of the heat treatment is 0.5-1h, for example, it can be 0.50h, 0.55h, 0.60h, 0.65h, 0.70h, 0.75h, 0.80h, 0.85h, 0.90h, 0.95h or 1.00h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional embodiments, the second temperature of the heat treatment is 700-800°C, for example, it can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some optional embodiments, the second time of the heat treatment is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] As a preferred technical solution of the present invention, in step S2, the mass fraction of the graphene oxide dispersion is 0.1-0.3wt.%, for example, it can be 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, 0.26%, 0.28% or 0.30%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0032] In some optional embodiments, the temperature of the hydrothermal treatment is 180-200°C, for example, it can be 180°C, 182°C, 184°C, 186°C, 188°C, 190°C, 192°C, 194°C, 196°C, 198°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] In some optional embodiments, the hydrothermal treatment time is 15-20h, for example, it can be 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h or 20h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional embodiments, the mass ratio of the porous carbon nitride nanosheets to the graphene quantum dots is 5-10:1, for example, it can be 5.0:1, 5.5:1, 6.0:1, 6.5:1, 7.0:1, 7.5:1, 8.0:1, 8.5:1, 9.0:1, 9.5:1 or 10.0:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0035] In some optional embodiments, the stirring adsorption time is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] As a preferred technical solution of the present invention, in step S3, the mass fraction of the formaldehyde solution is 35-40wt.%, for example, it can be 35.0%, 35.5%, 36.0%, 36.5%, 37.0%, 37.5%, 38.0%, 38.5%, 39.0%, 39.5% or 40.0%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0037] In some optional embodiments, the molar ratio of phenol to formaldehyde is 1:1.5-2, for example, it can be 1:1.50, 1:1.60, 1:1.70, 1:1.80, 1:1.90 or 1:2.00, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional embodiments, the pH is adjusted to 8-9 with aqueous ammonia, for example, 8.0, 8.2, 8.4, 8.6, 8.8 or 9.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional embodiments, the temperature of the constant temperature reaction of the reaction liquid A is 40-60°C, for example, it can be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0040] In some optional embodiments, the constant temperature reaction time of the reaction liquid A is 2-4 hours, for example, it can be 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional embodiments, the heat treatment temperature of the phenolic resin ball precursor is 800-1000°C, for example, it can be 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C or 1000°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0042] In some optional embodiments, the heat treatment time of the phenolic resin ball precursor is 1-2 hours, for example, it can be 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2.0 hours, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] As a preferred technical solution of the present invention, in step S4, the mass fraction of the N,N-dimethylformamide solution of polyvinyl pyrrolidone is 8-12wt.%, for example, it can be 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5% or 12.0%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0044] In some optional embodiments, the mass ratio of the inorganic salt to polyvinylpyrrolidone is 0.5-1:1, for example, it can be 0.50:1, 0.60:1, 0.70:1, 0.80:1, 0.90:1, 1.00:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0045] In some optional embodiments, the first temperature for calcining the pretreated fiber membrane is 300-400°C, for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0046] In some optional embodiments, the first calcination time of the pretreated fiber membrane is 1-2h, for example, it can be 1.0h, 1.2h, 1.4h, 1.6h, 1.8h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some optional embodiments, the second temperature for calcining the pretreated fiber membrane is 500-700°C, for example, it can be 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C or 700°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0048] In some optional embodiments, the second time for calcining the pretreated fiber membrane is 1-2h, for example, it can be 1.0h, 1.2h, 1.4h, 1.6h, 1.8h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] As a preferred technical solution of the present invention, in step S5, the mass fraction of the porous phenolic resin carbon spheres dispersed in the tris(hydroxymethyl)aminomethane buffer solution is 1-3wt.%, for example, it can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8% or 3.0%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0050] In some optional embodiments, the pH is maintained at 8-9, for example, 8.0, 8.2, 8.4, 8.6, 8.8 or 9.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In some optional embodiments, the mass ratio of dopamine hydrochloride to porous phenolic resin carbon balls is 0.2-0.4:1, for example, it can be 0.20:1, 0.24:1, 0.28:1, 0.32:1, 0.36:1 or 0.40:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0052] In some optional embodiments, the stirring time is 1-2 hours, for example, it can be 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2.0 hours, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] In some optional embodiments, the feeding amount of the transition metal oxide nanofibers is 3-5% of the mass of the porous phenolic resin carbon balls, for example, it can be 3.0%, 3.4%, 3.8%, 4.2%, 4.6% or 5.0%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0054] As a preferred technical solution of the present invention, in step S6, the mass fraction of the aqueous adhesive solution is 6-10wt.%, for example, it can be 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5% or 10.0%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0055] In some optional embodiments, the mass ratio of polyacrylic acid to sodium alginate in the aqueous adhesive is 7:3-8:2, for example, it can be 7.0:3.0, 7.2:2.8, 7.4:2.6, 7.6:2.4, 7.8:2.2 or 8.0:2.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0056] As a preferred technical solution of the present invention, the mass ratio of the nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is: (15-20): (30-35): (20-25): (15-20): (5-10).

[0057] In a second aspect, the present invention provides a high-capacity and high-cycle negative electrode material.

[0058] This invention successfully constructs a polymetallic MOF precursor with a high specific surface area and adjustable pore structure by mixing polymetallic salts with the organic ligand 2-methylimidazole in solution and leveraging the coordination interaction and self-assembly between metal ions and imidazole groups. In this process, the metal ions act as nodes connected to the 2-methylimidazole molecules via coordination bonds, forming a highly regular three-dimensional porous framework. The porosity and high degree of order of the MOF material provide an ideal skeletal template for subsequent heat treatment, ensuring the material's structural stability and enabling further manipulation of its microstructure and chemical composition.

[0059] It is worth noting that the synergistic effect between different metal ions plays a key role in optimizing material properties. By selectively introducing multiple metal ions, a variety of nano-dispersed phases of metal oxides or metal nitrides can be produced during subsequent heat treatment. These nano-dispersed phases are uniformly embedded in the carbon-based framework, providing the material with abundant defect sites and introducing a large number of potential active centers through the metal / metal oxide interface effect. These defect sites and active centers have a significant promoting effect on the storage and transport of lithium ions and can effectively enhance the electrochemical properties of the material.

[0060] During the heat treatment of the multi-metallic MOF under an inert atmosphere, the present invention introduces melamine as a nitrogen source. Melamine decomposes at high temperatures, gradually releasing ammonia and nitride intermediates. These nitrogen elements are effectively doped into the carbon-based skeleton during the carbonization process, ultimately forming nitrogen-rich carbon nitride. The ordered skeleton structure of the multi-metallic MOF during the heat treatment process acts as a "self-template", allowing the generated carbon nitride material to retain the porous characteristics and high specific surface area of ​​the MOF. This "template-induced" strategy ensures the microstructural stability of the material while providing excellent conditions for the adsorption, storage, and diffusion of lithium ions.

[0061] The chemical composition and structural properties of carbon nitride further optimize the material's performance. In carbon nitride, nitrogen atoms primarily exist in the form of pyridinic, pyrrolic, and graphitic nitrogen. Pyridinic nitrogen, as an electron acceptor, can induce chemical adsorption of lithium ions on the material's surface; pyrrolic nitrogen imparts higher conductivity and improves the electron transport efficiency during lithium ion insertion and extraction; and graphitic nitrogen modulates conductivity by altering the electron density of the carbon skeleton and promoting the rapid diffusion of lithium ions across the material's surface.

[0062] Furthermore, the porous structure of carbon nitride plays a crucial role in its electrochemical performance. These pores provide more active sites for lithium-ion storage and create low-impedance channels for lithium-ion diffusion, significantly shortening the lithium-ion diffusion path. This not only increases the material's lithium storage capacity but also improves the kinetics of the electrochemical reaction, effectively alleviating the limitations of lithium-ion transport at high rates.

[0063] In the present invention, in order to further optimize the electrochemical properties of the material, graphene quantum dots are compounded with porous carbon nitride. Graphene quantum dots are prepared by hydrothermal treatment of graphene oxide. Graphene quantum dots have extremely small sheet sizes, excellent electronic conductivity, and abundant surface chemical functional groups. In particular, the hydroxyl and carboxyl groups on their surfaces can bind to the defect sites of porous carbon nitride through hydrogen bonds or coordination bonds in the composite system, thereby greatly enhancing the structural stability of the composite material. In addition, the high specific surface area and high dispersibility of graphene quantum dots enable them to be evenly attached to the skeleton surface and pores of porous carbon nitride, providing the composite material with more effective electron transmission channels and abundant active sites.

[0064] During the composite process, the porous skeleton structure of porous carbon nitride provides an ideal support platform for the adsorption and distribution of graphene quantum dots. At the same time, the active sites such as pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen in its nitrogen-rich structure can form stable chemical bonds with the carboxyl groups on the surface of graphene quantum dots. This close interfacial interaction not only improves the structural integrity of the composite material, but also optimizes the stability of the material interface reaction during the insertion and deinsertion of lithium ions. In addition, the distribution of graphene quantum dots in the pores of porous carbon nitride forms a highly interconnected conductive network, which significantly reduces the electron transfer impedance of the composite material and provides an efficient path for the rapid storage and transmission of lithium ions. Thanks to the nanoscale characteristics of graphene quantum dots, their quantum size effect further improves the electronic structure of the composite material. The widening of the band gap enhances the material's chemical adsorption capacity for lithium ions and improves the storage capacity of lithium ions in the composite material.

[0065] The introduction of graphene quantum dots not only improves conductivity but also provides more active sites within the composite material. These sites effectively enhance the reversible storage capacity of lithium ions, significantly increasing the specific capacity of the composite material. Furthermore, the high surface energy and chemical activity of graphene quantum dots further promote the rapid diffusion of lithium ions, shortening the transport path of lithium ions from the electrolyte into the material, and improving the kinetic properties of the composite material.

[0066] In the present invention, phenol and formaldehyde undergo hydroxymethylation and condensation reaction under alkaline conditions to form a three-dimensional cross-linked phenolic resin. The phenolic resin generated in this process has a highly uniform size distribution and a dense internal structure. Subsequently, the phenolic resin carbon spheres are placed in an inert atmosphere and subjected to high-temperature pyrolysis, where the resin decomposes into carbon material accompanied by the release of small molecular gases. These gases expand and escape inside the porous phenolic resin carbon spheres, inducing the formation of pores, thereby giving the porous phenolic resin carbon spheres porous properties. The resulting porous phenolic resin carbon spheres not only retain the superiority of the spherical structure, but also have a high specific surface area and rich pore structure, providing multiple advantages for the lithium storage performance of lithium-ion battery negative electrode materials.

[0067] Porous phenolic resin carbon spheres have high mechanical stability and packing density, which is particularly critical for the overall structural design of negative electrode materials. The spherical particles can be densely packed, thereby increasing the compaction density of the electrode and, in turn, the volumetric capacity of the lithium-ion battery. In addition, the stability of the spherical particles enables them to effectively resist deformation during long-term charge and discharge cycles, reducing the material's pulverization and structural collapse problems. The introduction of a porous structure further enhances the lithium storage capacity and kinetic performance of the porous phenolic resin carbon spheres. The presence of pores provides more active sites for the storage of lithium ions, while shortening the diffusion path of lithium ions, thereby significantly improving the kinetic behavior of the electrochemical reaction. This porous spherical carbon material can also alleviate the stress concentration effect caused by the volume expansion of silicon-based materials or metal oxides during the lithium storage process, providing a good buffering effect for the composite electrode. In addition, the high specific surface area of ​​the porous phenolic resin carbon spheres provides an ideal platform for subsequent surface functionalization or the loading of other active materials, further improving the overall performance of the negative electrode material.

[0068] In order to further optimize the performance of the negative electrode material, the present invention adopts electrostatic spinning technology to prepare transition metal oxide nanofibers. Electrostatic spinning is a technology that stretches a solution or melt into ultrafine fibers through a high-voltage electric field. In this process, polyvinyl pyrrolidone is used as a spinning template and mixed with a transition metal salt to form a uniform spinning solution. After applying a high electric field, the spinning solution is stretched by electrostatic force and solidified into a nanofiber membrane. The fiber membrane is then placed in a high-temperature environment and calcined. The polyvinyl pyrrolidone decomposes into gas at high temperature and escapes, while the metal salt is oxidized to form transition metal oxide nanofibers. These nanofibers have a typical one-dimensional structure. The fibrous morphology not only provides excellent mechanical support capabilities, but also provides a directional channel for the diffusion of lithium ions, significantly improving the lithium storage kinetics of the material.

[0069] Transition metal oxide nanofibers play an important role in negative electrode materials. On the one hand, their one-dimensional nanostructure significantly shortens the diffusion path of lithium ions, provides a fast channel for electrochemical reactions, and greatly improves the kinetic performance. On the other hand, the flexibility and high aspect ratio of nanofibers enable them to alleviate the volume expansion problem of metal oxides during lithium ion insertion / deintercalation to a certain extent, thereby improving the cycle stability. However, the conductivity of transition metal oxides themselves is poor, which may limit their rate performance and the efficiency of electrochemical reactions. Therefore, it is necessary to compensate for their shortcomings by compounding with a conductive matrix. In addition, transition metal oxides have a high theoretical specific capacity, which makes them a very promising energy storage material.

[0070] In the present invention, a composite material with a surface-coated polydopamine layer was successfully prepared by introducing dopamine hydrochloride as a precursor and utilizing its self-polymerization behavior under alkaline conditions. Dopamine is a typical biomimetic molecule, and its chemical structure contains both phenolic hydroxyl groups and amine groups, which give it excellent chemical reactivity and adhesion ability. Under weakly alkaline conditions, dopamine forms a polydopamine film through oxidative polymerization. Polydopamine is a "bionic coating" whose excellent adhesion properties enable it to form a stable bond with the surfaces of various materials, significantly enhancing the interfacial stability of the composite material.

[0071] The polydopamine layer not only acts as an adhesive in the composite material, but also provides a variety of functional advantages. First, the phenolic hydroxyl groups and amine groups rich in the surface of polydopamine can chemically bond with the carbon atoms on the surface of the porous phenolic resin carbon spheres and the metal oxides in the transition metal oxide nanofibers through hydrogen bonds or coordination bonds. This strong bond significantly enhances the interfacial interaction between the components in the composite material, prevents the separation or shedding of the material during the charge and discharge process, thereby effectively improving the cycle stability. Secondly, polydopamine, as a "soft" polymer layer, has certain elasticity and flexibility. During the charge and discharge process of lithium-ion batteries, the active material expands or contracts in volume due to lithium insertion / delithiation. The polydopamine layer can act as an elastic buffer, absorbing and dispersing the stress caused by the volume change, thereby protecting the overall structure of the material and extending the service life of the electrode.

[0072] In the design of composite materials, the introduction of transition metal oxide nanofibers makes an important contribution to the specific capacity of active materials. The one-dimensional transition metal oxide nanofibers prepared by electrospinning technology have a high aspect ratio and a highly ordered fiber network structure. On the one hand, these nanofibers are evenly attached to the surface of porous phenolic resin carbon spheres through electrostatic interaction and physical adsorption, and together with the polydopamine layer, they construct a stable composite interface; on the other hand, the transition metal oxide itself has a high theoretical specific capacity, and its fibrous morphology provides excellent electron transport and ion diffusion channels, effectively improving the lithium storage performance of the composite material. The introduction of one-dimensional nanofibers also provides the composite material with a "hard" porous skeleton to support it. This rigid skeleton can further alleviate the mechanical deformation problem of carbon-based materials and metal oxides during the cycle process and improve the overall structural stability of the material.

[0073] As the core carrier of the composite material, the porous phenolic resin carbon spheres perform multiple functions. Their porous structure provides a high specific surface area, creating more active sites for lithium ion storage and diffusion; their spherical morphology and mechanical stability provide the basis for the high compaction density and stable conductive network of the composite material; at the same time, the excellent conductivity of the porous phenolic resin carbon spheres enables them to effectively reduce the overall resistance of the composite material and improve the rate performance of the electrode. The porous phenolic resin carbon spheres not only serve as a supporting material for the transition metal oxide and polydopamine, but their porosity and conductivity also work synergistically with other components to make the composite material more efficient in electron conduction and lithium ion migration during the lithium storage process.

[0074] The present invention also has a synergistic enhancement effect. There is a significant synergistic enhancement effect between polydopamine and porous phenolic resin carbon spheres. The porous phenolic resin carbon spheres provide a high specific surface area and a porous skeleton, providing an ideal support platform for the uniform deposition of polydopamine. Polydopamine strongly bonds to the surface of the porous phenolic resin carbon spheres through its abundant phenolic hydroxyl and amino groups, forming an adhesive interface. This combination significantly enhances the structural stability of the composite material and prevents particle separation during the charge and discharge process. In addition, the spherical structure and porous properties of the porous phenolic resin carbon spheres have good mechanical stability and can buffer volume expansion, and the introduction of the polydopamine flexible layer further optimizes this buffering effect. The elastic characteristics of polydopamine enable it to absorb and disperse the stress generated during lithium ion insertion / deinsertion, thereby avoiding the fracture and collapse of the porous phenolic resin carbon sphere skeleton. This synergistic effect improves the stability and long-term service life of the composite material during the cycle process.

[0075] The synergistic effect between polydopamine and transition metal oxide nanofibers is mainly reflected in two aspects: enhanced interfacial adhesion and alleviated volume expansion. First, the phenolic hydroxyl and amino groups on the surface of polydopamine can chemically bond with the surface of the metal oxide, significantly enhancing the interfacial bonding between the metal oxide and other components in the composite material. This combination improves the dispersion uniformity and stability of the metal oxide nanofibers in the composite material, and reduces the particle shedding phenomenon caused by the volume expansion of the metal oxide during the charge and discharge process. Secondly, metal oxide nanofibers usually undergo a large volume expansion during the lithium insertion process, and the flexible properties of polydopamine provide an elastic buffer for this process. The polydopamine layer can absorb the stress caused by the expansion of the metal oxide, thereby effectively delaying the mechanical failure of the fiber structure. In addition, the adhesive layer of polydopamine can also inhibit the agglomeration of metal oxide particles, further improving the cyclic stability of the material.

[0076] The synergistic effect between the porous phenolic resin carbon spheres and transition metal oxide nanofibers is primarily manifested in enhanced conductivity and optimized kinetic performance. The porous phenolic resin carbon spheres, serving as the core skeleton of the composite, possess excellent conductivity and porosity. Their porous structure supports the distribution of the transition metal oxide nanofibers and provides more active sites for lithium ion storage. The metal oxide nanofibers, through their one-dimensional structure, provide channels for rapid electron conduction and ion diffusion. The combination of the two forms an efficient electron transport network and lithium ion migration pathway, significantly enhancing the kinetic performance of the composite. Furthermore, the porous skeleton of the porous phenolic resin carbon spheres mitigates stress concentration caused by volume expansion of the metal oxide nanofibers during charge and discharge. The mechanical stability of the porous phenolic resin carbon spheres combined with the high aspect ratio of the metal oxide fibers create a structural optimization of "rigid support + flexible buffering" within the composite. This synergistic effect not only enhances the material's cycling stability but also significantly improves its rate capability.

[0077] There is a ternary synergistic effect between polydopamine, porous phenolic resin carbon spheres, and transition metal oxide nanofibers: polydopamine acts as an adhesion layer, firmly bonding the porous phenolic resin carbon spheres and metal oxide nanofibers together to form a stable interface structure. This adhesive interface can effectively alleviate the delamination or separation problems caused by volume changes of the components during charging and discharging, thereby improving the long-term stability of the composite material; secondly, the porous phenolic resin carbon spheres provide a highly conductive skeleton structure, while the metal oxide nanofibers further optimize the electron transfer path through their one-dimensional structure. The introduction of polydopamine not only enhances interfacial bonding, but also provides additional electron transfer pathways through its rich functional groups, ultimately forming a multi-level interconnected conductive network. This network structure can significantly reduce the charge transfer impedance and improve the rate performance of the material. In addition, the high capacity characteristics of metal oxide nanofibers make them prone to significant volume expansion during the lithium insertion process, and the mechanical stability of the porous phenolic resin carbon spheres and the flexible buffering effect of polydopamine work together to effectively absorb and disperse the stress caused by the expansion, thereby protecting the overall structure of the composite material. At the same time, the porous phenolic resin carbon spheres provide abundant lithium ion storage sites and fast ion diffusion channels. Metal oxide nanofibers, as high-capacity active ingredients, significantly improve the specific capacity of the composite material. The introduction of polydopamine provides additional active centers through its surface functional groups, thereby further enhancing the lithium storage capacity of the material.

[0078] The introduction of graphene quantum dots provides additional synergistic effects for the composite material. Graphene quantum dots have excellent conductivity and abundant surface chemical functional groups, which can bind to defect sites on the surfaces of porous phenolic resin carbon spheres and metal oxides, providing additional lithium ion adsorption sites, thereby enhancing the lithium storage capacity of the composite material.

[0079] In a third aspect, the present invention provides an application of a high-capacity and high-cycle negative electrode material in a lithium-ion battery.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] The present invention prepares a multi-metallic MOF precursor by self-assembly of multi-metal salts and 2-methylimidazole, and introduces melamine for heat treatment under an inert atmosphere to form a nitrogen-rich porous carbon nitride material. The multi-metallic MOF provides an ordered skeleton template, and the metal oxide or nitride dispersed phase generated by heat treatment is embedded in the carbon-based skeleton, forming abundant defect sites and active centers. Nitrogen doping enhances lithium ion adsorption, conductivity, and diffusion properties, while the porous structure shortens the diffusion path and reduces impedance, thereby significantly improving the material's lithium storage capacity, kinetic performance, and cycle stability.

[0082] This invention enhances the electrochemical performance of the material by combining graphene quantum dots with porous carbon nitride. The graphene quantum dots, with their high conductivity and surface functional groups, combine with the active sites of the porous carbon nitride to enhance structural stability, form a conductive network, and reduce electron transfer resistance. Their quantum size effect and high dispersion promote rapid diffusion and efficient storage of lithium ions, while optimizing interfacial reactions and kinetics, significantly increasing the material's specific capacity.

[0083] The present invention prepares phenolic resin carbon spheres by hydroxymethylation and condensation reaction of phenol and formaldehyde under alkaline conditions, and generates a carbon material with a porous structure through high-temperature pyrolysis. The release of small molecular gases during the pyrolysis process induces pore formation, so that the phenolic resin carbon spheres have a high specific surface area and abundant pores, while retaining the mechanical stability and high packing density of the spherical structure. The porous structure provides more active sites for the storage of lithium ions, shortens the diffusion path, improves the kinetic performance, and alleviates the stress concentration caused by volume expansion. In addition, the high specific surface area provides an ideal platform for subsequent surface functionalization and active material loading, thereby significantly enhancing the lithium storage performance and cycle stability of the electrode material;

[0084] The present invention prepares transition metal oxide nanofibers through electrospinning technology and composites them with porous phenolic resin carbon spheres and polydopamine, significantly optimizing the performance of lithium-ion battery negative electrode materials. The one-dimensional nanofibers generated by electrospinning have a high aspect ratio and a conductive network, providing efficient channels for lithium ion diffusion, while alleviating the volume expansion problem and improving cycle stability and specific capacity. Dopamine forms a polydopamine coating through self-polymerization behavior, which enhances the interfacial bonding of the composite material and provides elastic buffering to protect the material structure. The porous phenolic resin carbon spheres provide high specific surface area, porosity and conductivity, forming a synergistic effect with other components to optimize electron conduction and ion migration paths, effectively improving lithium storage performance and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 Flow chart of the preparation method of the high-capacity and high-cycle negative electrode material provided in Example 1 of the present invention; DETAILED DESCRIPTION

[0086] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0087] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without further purification or treatment.

[0088] Example 1

[0089] This embodiment provides a high-capacity and high-cycle negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0090] S1: Metal salts are reacted with 2-methylimidazole to obtain multi-metallic MOF precursor powder, which is then heat-treated with melamine under an inert atmosphere to obtain porous carbon nitride nanosheets;

[0091] Specifically, S1: Dispersing metal salts of zinc nitrate, cobalt nitrate, and iron nitrate in deionized water at a mass ratio of 1:1:1, wherein the concentration of the metal salt solution is 0.2M, adding 2-methylimidazole at a total molar ratio of 2.4:1 to the metal salt, stirring and reacting at 35°C for 4 hours, filtering, washing, and drying to obtain a multi-metallic MOF precursor powder; placing it in a porcelain boat, and adding melamine, wherein the mass ratio of melamine to the multi-metallic MOF precursor powder is 0.15:1, and heat treating under an inert atmosphere to obtain porous carbon nitride nanosheets, wherein the first heat treatment temperature is 300°C, the first time is 0.8h, the second temperature is 800°C, and the second time is 1h;

[0092] S2: hydrothermally treating a graphene oxide dispersion to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, and adding porous carbon nitride nanosheets to react to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0093] Specifically, S2: preparing a graphene oxide dispersion with a mass fraction of 0.2 wt.%, hydrothermally treating it at 190°C for 18 hours to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, adding porous carbon nitride nanosheets, wherein the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is 8:1, stirring and adsorbing for 40 minutes, and then spray drying to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0094] S3: mixing phenol and formaldehyde solution to obtain a phenolic resin sphere precursor, and heat-treating it under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0095] Specifically, S3: mixing phenol with a 35 wt.% formaldehyde solution, wherein the molar ratio of phenol to formaldehyde is 1:1.7, adjusting the pH to 8 with aqueous ammonia to obtain a reaction solution A, reacting at a constant temperature of 40°C for 3 hours, centrifuging, washing, and drying to obtain a phenolic resin sphere precursor, and heat-treating at 800°C for 1 hour under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0096] S4: adding an inorganic salt to a solution of polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a precursor solution, and obtaining transition metal oxide nanofibers by electrospinning and calcining;

[0097] Specifically, S4: preparing a 10 wt.% polyvinyl pyrrolidone N,N-dimethylformamide solution, adding inorganic nickel nitrate and stirring to form a uniform precursor solution, wherein the mass ratio of inorganic nickel nitrate to polyvinyl pyrrolidone is 0.8:1, obtaining a pretreated fiber membrane by electrospinning, and calcining to obtain transition metal oxide nanofibers, wherein the first calcination temperature is 350°C and the first time is 1 hour; the second temperature is 500°C and the second time is 1 hour;

[0098] S5: adding porous phenolic resin carbon spheres and dopamine hydrochloride to a tris(hydroxymethylaminomethane) buffer solution for reaction, followed by adding transition metal oxide nanofibers to obtain a ternary composite porous phenolic resin carbon sphere;

[0099] Specifically, S5: dispersing porous phenolic resin carbon spheres in tris(hydroxymethylaminomethane) buffer and maintaining the pH at 8.5, wherein the mass fraction of the porous phenolic resin carbon spheres dispersed in the tris(hydroxymethylaminomethane) buffer is 2 wt.%, adding dopamine hydrochloride, wherein the mass ratio of dopamine to the porous phenolic resin carbon spheres is 0.3:1, stirring for 1 hour, adding transition metal oxide nanofibers in an amount of 4% of the mass of the porous phenolic resin carbon spheres and continuing the reaction, and then centrifuging, washing, and drying to obtain a ternary composite porous phenolic resin carbon spheres;

[0100] S6: Add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black into an aqueous binder solution and evenly disperse them to obtain a high-capacity and high-cycle negative electrode material.

[0101] Specifically, S6: prepare an aqueous binder solution, wherein the mass ratio of polyacrylic acid to sodium alginate in the aqueous binder is 7:3, and the total mass fraction of the aqueous binder solution is 8wt.%, and sequentially add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black, wherein the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 18:32:24:17:6, and uniformly disperse to obtain a high-capacity and high-cycle negative electrode material.

[0102] Example 2

[0103] This embodiment provides a high-capacity and high-cycle negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0104] S1: Metal salts are reacted with 2-methylimidazole to obtain multi-metallic MOF precursor powder, which is then heat-treated with melamine under an inert atmosphere to obtain porous carbon nitride nanosheets;

[0105] Specifically, S1: Dispersing metal salts of zinc nitrate, cobalt nitrate, and iron nitrate in deionized water at a mass ratio of 0.8:1, wherein the concentration of the metal salt solution is 0.23M, adding 2-methylimidazole at a total molar ratio of 2 to the metal salt, stirring and reacting at 38°C for 5 hours, filtering, washing, and drying to obtain a multi-metallic MOF precursor powder; placing it in a porcelain boat, and adding melamine, wherein the mass ratio of melamine to the multi-metallic MOF precursor powder is 0.18:1, and heat treating under an inert atmosphere to obtain porous carbon nitride nanosheets, wherein the first heat treatment temperature is 380°C, the first time is 0.5h, the second temperature is 720°C, and the second time is 2h;

[0106] S2: hydrothermally treating a graphene oxide dispersion to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, and adding porous carbon nitride nanosheets to react to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0107] Specifically, S2: preparing a graphene oxide dispersion with a mass fraction of 0.1 wt.%, hydrothermally treating it at 195°C for 16 hours to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, adding porous carbon nitride nanosheets, wherein the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is 7.5:1, stirring and adsorbing for 60 minutes, and then spray drying to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0108] S3: mixing phenol and formaldehyde solution to obtain a phenolic resin sphere precursor, and heat-treating it under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0109] Specifically, S3: mixing phenol with a 38 wt.% formaldehyde solution, wherein the molar ratio of phenol to formaldehyde is 1:1.8, adjusting the pH to 8.5 with aqueous ammonia to obtain a reaction solution A, reacting at a constant temperature of 50°C for 3.5 hours, centrifuging, washing, and drying to obtain a phenolic resin sphere precursor, and heat treating at 900°C for 1.8 hours under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0110] S4: adding an inorganic salt to a solution of polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a precursor solution, and obtaining transition metal oxide nanofibers by electrospinning and calcining;

[0111] Specifically, S4: preparing an N,N-dimethylformamide solution of polyvinyl pyrrolidone with a mass fraction of 11 wt.%, adding inorganic salt manganese nitrate and stirring to form a uniform precursor solution, wherein the mass ratio of inorganic salt manganese nitrate to polyvinyl pyrrolidone is 0.5:1, obtaining a pretreated fiber membrane by electrospinning, and calcining to obtain transition metal oxide nanofibers, wherein the first calcination temperature is 300° C. and the first time is 1.6 hours; the second temperature is 600° C. and the second time is 2 hours;

[0112] S5: adding porous phenolic resin carbon spheres and dopamine hydrochloride to a tris(hydroxymethylaminomethane) buffer solution for reaction, followed by adding transition metal oxide nanofibers to obtain a ternary composite porous phenolic resin carbon sphere;

[0113] Specifically, S5: dispersing porous phenolic resin carbon spheres in tris(hydroxymethylaminomethane) buffer and maintaining the pH at 8, wherein the mass fraction of the porous phenolic resin carbon spheres dispersed in the tris(hydroxymethylaminomethane) buffer is 1.5 wt.%, adding dopamine hydrochloride, wherein the mass ratio of dopamine to the porous phenolic resin carbon spheres is 0.35:1, stirring for 1.7 hours, adding transition metal oxide nanofibers in an amount of 3% of the mass of the porous phenolic resin carbon spheres and continuing the reaction, and then centrifuging, washing, and drying to obtain a ternary composite porous phenolic resin carbon spheres;

[0114] S6: Add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black into an aqueous binder solution and evenly disperse them to obtain a high-capacity and high-cycle negative electrode material.

[0115] Specifically, S6: prepare an aqueous binder solution, wherein the mass ratio of polyacrylic acid to sodium alginate in the aqueous binder is 7.5:2.5, and the total mass fraction of the aqueous binder solution is 6wt.%, and nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black are added in sequence, wherein the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 15:34:22:20:8, and they are evenly dispersed to obtain a high-capacity and high-cycle negative electrode material.

[0116] Example 3

[0117] This embodiment provides a high-capacity and high-cycle negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0118] S1: Metal salts are reacted with 2-methylimidazole to obtain multi-metallic MOF precursor powder, which is then heat-treated with melamine under an inert atmosphere to obtain porous carbon nitride nanosheets;

[0119] Specifically, S1: Dispersing metal salts of zinc nitrate, cobalt nitrate, and iron nitrate in deionized water at a mass ratio of 1.1, wherein the concentration of the metal salt solution is 0.1M, adding 2-methylimidazole at a total molar ratio of 2.7 to the metal salt, stirring and reacting at 30°C for 5.5h, filtering, washing, and drying to obtain a multi-metallic MOF precursor powder; placing it in a porcelain boat, and adding melamine, wherein the mass ratio of melamine to the multi-metallic MOF precursor powder is 0.1:1, and heat treating under an inert atmosphere to obtain porous carbon nitride nanosheets, wherein the first heat treatment temperature is 350°C, the first time is 0.7h, the second temperature is 700°C, and the second time is 1.6h;

[0120] S2: hydrothermally treating a graphene oxide dispersion to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, and adding porous carbon nitride nanosheets to react to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0121] Specifically, S2: preparing a graphene oxide dispersion with a mass fraction of 0.25 wt.%, hydrothermally treating it at 200 ° C for 15 hours to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, adding porous carbon nitride nanosheets, wherein the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is 5:1, stirring and adsorbing for 50 minutes, and then spray drying to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0122] S3: mixing phenol and formaldehyde solution to obtain a phenolic resin sphere precursor, and heat-treating it under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0123] Specifically, S3: mixing phenol with a 37 wt.% formaldehyde solution, wherein the molar ratio of phenol to formaldehyde is 1:1.5, adjusting the pH to 8.8 with aqueous ammonia to obtain a reaction solution A, reacting at a constant temperature of 53°C for 2 hours, centrifuging, washing, and drying to obtain a phenolic resin sphere precursor, and heat treating at 950°C for 1.5 hours under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0124] S4: adding an inorganic salt to a solution of polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a precursor solution, and obtaining transition metal oxide nanofibers by electrospinning and calcining;

[0125] Specifically, S4: preparing an 8 wt.% N,N-dimethylformamide solution of polyvinyl pyrrolidone, adding inorganic salt cobalt nitrate and stirring to form a uniform precursor solution, wherein the mass ratio of inorganic salt cobalt nitrate to polyvinyl pyrrolidone is 0.7:1, obtaining a pretreated fiber membrane by electrospinning, and calcining to obtain transition metal oxide nanofibers, wherein the first calcination temperature is 400°C and the first time is 2 hours; the second temperature is 630°C and the second time is 1.6 hours;

[0126] S5: adding porous phenolic resin carbon spheres and dopamine hydrochloride to a tris(hydroxymethylaminomethane) buffer solution for reaction, followed by adding transition metal oxide nanofibers to obtain a ternary composite porous phenolic resin carbon sphere;

[0127] Specifically, S5: dispersing porous phenolic resin carbon spheres in tris(hydroxymethyl)aminomethane buffer and maintaining the pH at 9, wherein the mass fraction of the porous phenolic resin carbon spheres dispersed in the tris(hydroxymethyl)aminomethane buffer is 2.6 wt.%, adding dopamine hydrochloride, wherein the mass ratio of dopamine to the porous phenolic resin carbon spheres is 0.2:1, stirring for 1.5 hours, adding transition metal oxide nanofibers in an amount of 4.7% of the mass of the porous phenolic resin carbon spheres and continuing the reaction, and then centrifuging, washing, and drying to obtain a ternary composite porous phenolic resin carbon spheres;

[0128] S6: Add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black into an aqueous binder solution and evenly disperse them to obtain a high-capacity and high-cycle negative electrode material.

[0129] Specifically, S6: prepare an aqueous binder solution, wherein the mass ratio of polyacrylic acid to sodium alginate in the aqueous binder is 7.8:2.2, and the total mass fraction of the aqueous binder solution is 8.7wt.%, and sequentially add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black, wherein the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 17:30:25:15:5, and uniformly disperse to obtain a high-capacity and high-cycle negative electrode material.

[0130] Example 4

[0131] This embodiment provides a high-capacity and high-cycle negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0132] S1: Metal salts are reacted with 2-methylimidazole to obtain multi-metallic MOF precursor powder, which is then heat-treated with melamine under an inert atmosphere to obtain porous carbon nitride nanosheets;

[0133] Specifically, S1: Dispersing metal salts of zinc nitrate, cobalt nitrate, and iron nitrate in deionized water at a mass ratio of 1.2:1, wherein the concentration of the metal salt solution is 0.3M, adding 2-methylimidazole at a total molar ratio of 3:1 to the metal salt, stirring and reacting at 40°C for 6 hours, filtering, washing, and drying to obtain a multi-metallic MOF precursor powder; placing it in a porcelain boat, and adding melamine, wherein the mass ratio of melamine to the multi-metallic MOF precursor powder is 0.2:1, and heat treating under an inert atmosphere to obtain porous carbon nitride nanosheets, wherein the first heat treatment temperature is 400°C, the first time is 1 hour, the second temperature is 780°C, and the second time is 1.8 hours;

[0134] S2: hydrothermally treating a graphene oxide dispersion to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, and adding porous carbon nitride nanosheets to react to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0135] Specifically, S2: preparing a graphene oxide dispersion with a mass fraction of 0.3 wt.%, hydrothermally treating it at 180°C for 20 h to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, adding porous carbon nitride nanosheets, wherein the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is 10:1, stirring and adsorbing for 30 min, and then spray drying to obtain a porous carbon nitride-graphene quantum dot composite powder;

[0136] S3: mixing phenol and formaldehyde solution to obtain a phenolic resin sphere precursor, and heat-treating it under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0137] Specifically, S3: mixing phenol with a 40 wt.% formaldehyde solution, wherein the molar ratio of phenol to formaldehyde is 1:2, adjusting the pH to 9 with aqueous ammonia to obtain a reaction solution A, reacting at a constant temperature of 60°C for 4 hours, centrifuging, washing, and drying to obtain a phenolic resin sphere precursor, and heat treating at 1000°C for 2 hours under an inert atmosphere to obtain porous phenolic resin carbon spheres;

[0138] S4: adding an inorganic salt to a solution of polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a precursor solution, and obtaining transition metal oxide nanofibers by electrospinning and calcining;

[0139] Specifically, S4: preparing a 12 wt.% polyvinyl pyrrolidone N,N-dimethylformamide solution, adding an inorganic salt nickel nitrate and stirring to form a uniform precursor solution, wherein the mass ratio of the inorganic salt nickel nitrate to the polyvinyl pyrrolidone is 1:1, obtaining a pretreated fiber membrane by electrospinning, and calcining to obtain transition metal oxide nanofibers, wherein the first calcination temperature is 380°C and the first time is 1.8 hours; the second temperature is 700°C and the second time is 1.8 hours;

[0140] S5: adding porous phenolic resin carbon spheres and dopamine hydrochloride to a tris(hydroxymethylaminomethane) buffer solution for reaction, followed by adding transition metal oxide nanofibers to obtain a ternary composite porous phenolic resin carbon sphere;

[0141] Specifically, S5: dispersing porous phenolic resin carbon spheres in tris(hydroxymethylaminomethane) buffer and maintaining the pH at 8.7, wherein the mass fraction of the porous phenolic resin carbon spheres dispersed in the tris(hydroxymethylaminomethane) buffer is 3 wt.%, adding dopamine hydrochloride, wherein the mass ratio of dopamine to the porous phenolic resin carbon spheres is 0.4:1, stirring for 2 hours, adding transition metal oxide nanofibers in an amount of 5% of the mass of the porous phenolic resin carbon spheres and continuing the reaction, and then centrifuging, washing, and drying to obtain a ternary composite porous phenolic resin carbon spheres;

[0142] S6: Add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black into an aqueous binder solution and evenly disperse them to obtain a high-capacity and high-cycle negative electrode material.

[0143] Specifically, S6: prepare an aqueous binder solution, wherein the mass ratio of polyacrylic acid to sodium alginate in the aqueous binder is 8:2, and the total mass fraction of the aqueous binder solution is 10wt.%, and sequentially add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black, wherein the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 20:35:20:16:10, and uniformly disperse to obtain a high-capacity and high-cycle negative electrode material.

[0144] Comparative Example 1

[0145] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S2, the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is 15:1, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0146] Comparative Example 2

[0147] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S2, the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is 2:1, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0148] Comparative Example 3

[0149] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S5, the feeding amount of transition metal oxide nanofibers is 8% of the mass of porous phenolic resin carbon balls, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0150] Comparative Example 4

[0151] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S5, the feeding amount of transition metal oxide nanofibers is 1% of the mass of porous phenolic resin carbon balls, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0152] Comparative Example 5

[0153] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S6, the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 18:32:30:17:6, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0154] Comparative Example 6

[0155] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S6, the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 18:32:12:17:6, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0156] Comparative Example 7

[0157] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S6, the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 18:32:24:25:6, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0158] Comparative Example 8

[0159] This comparative example provides a high-capacity and high-cycle negative electrode material. The difference from Example 1 is that in S6, the mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is 18:32:24:10:6, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0160] The performance test of the high-capacity and high-cycle negative electrode materials of Examples 1-4 and Comparative Examples 1-8 was conducted, and the specific process is as follows:

[0161] The prepared negative electrode material was evenly coated on copper foil and vacuum dried as the working electrode, metallic lithium was used as the counter electrode, polypropylene microporous membrane was used as the separator, and 1M LiPF6 / DMC:EC:DEC=1:1:1 solution was used as the electrolyte to assemble into a simulated battery.

[0162] At 25°C, the simulated battery is first charged at a constant current of 1C to 4.3V, then further charged at a constant voltage of 4.3V to a current of 0.025C, and then discharged at a constant current of 1C to 3.0V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. Repeat the above-mentioned charge and discharge test for multiple times to obtain the discharge capacity of the 300th cycle;

[0163] The capacity retention rate (%) of the battery after 300 cycles = [discharge capacity at the 300th cycle / discharge capacity at the 1st cycle] × 100%. The test results are shown in Table 1.

[0164] Table 1: Performance test results of high capacity and high cycle negative electrode materials of Examples 1-4 and Comparative Examples 1-8

[0165]

[0166]

[0167] From the test results of Example 1 and Comparative Examples 1 and 2, it can be seen that when the mass ratio of porous carbon nitride nanosheets to graphene quantum dots is too high, due to insufficient content of graphene quantum dots, the conductive network is discontinuous and the interface electron transport is blocked, causing the initial discharge capacity to drop to 892.3 mAh / g, and the capacity decays to 673.5 mAh / g after 300 cycles; when the mass ratio is too low, the excess graphene quantum dots agglomerate, hindering the ion transport channel. Although the initial discharge capacity can reach 1186.7 mAh / g, due to the interface instability caused by agglomeration, the capacity rapidly decays to 782.4 mAh / g after 300 cycles;

[0168] The test results of Example 1 and Comparative Examples 3 and 4 show that when the feed rate of transition metal oxide nanofibers is too high, the excess metal oxide fibers occupy too much electrode space and cause blockage of the ion transmission channel, resulting in the initial discharge capacity dropping to 956.8 mAh / g, and the capacity after 300 cycles is only 698.5 mAh / g; when the feed rate is too low, due to the incomplete conductive skeleton and insufficient structural support, although the initial discharge capacity reaches 1198.4 mAh / g, the structure gradually collapses during the cycle, and the capacity rapidly decays to 745.2 mAh / g after 300 cycles;

[0169] From the test results of Example 1 and Comparative Examples 5 and 6, it can be seen that when the content of the porous carbon nitride-graphene quantum dot composite powder is too high, the excess conductive phase occupies too much electrode space, significantly reducing the content of the active material silicon, resulting in the initial discharge capacity dropping to 867.4 mAh / g and 756.8 mAh / g after 300 cycles; when the composite powder content is too low, due to the lack of sufficient conductive network and volume expansion buffer space, although the initial discharge capacity can reach 1167.3 mAh / g, the electrode structure is gradually destroyed during the cycle, the interface impedance continues to increase, and the capacity rapidly decays to 682.3 mAh / g after 300 cycles;

[0170] From the test results of Example 1 and Comparative Examples 7 and 8, it can be seen that when the content of the ternary composite porous phenolic resin carbon ball is too high, too many inactive components occupy the electrode space, reducing the overall specific capacity. The first discharge capacity is only 923.5 mAh / g, and it is 834.6 mAh / g after 300 cycles; when the carbon ball content is too low, due to the lack of sufficient structural support and interfacial stabilizer, the electrode structure is unstable during the cycle, and the SEI film is repeatedly broken and formed. Although the first discharge capacity reaches 1186.4 mAh / g, the capacity drops sharply to 654.8 mAh / g after 300 cycles.

[0171] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high-capacity and high-cycle negative electrode material, characterized in that: The preparation method comprises: S1: reacting a metal salt with 2-methylimidazole at a molar ratio of 1:(2-3) to obtain a multi-metallic MOF precursor powder, wherein the metal salt is zinc nitrate, cobalt nitrate, and iron nitrate in a mass ratio of 1:(0.8-1.2):1, and then heat-treating with melamine under an inert atmosphere to obtain porous carbon nitride nanosheets, wherein the mass ratio of melamine to the multi-metallic MOF precursor powder is (0.1-0.2):1; S2: hydrothermally treating a graphene oxide dispersion to obtain graphene quantum dots, preparing a graphene quantum dot dispersion, adding porous carbon nitride nanosheets to react to obtain a porous carbon nitride-graphene quantum dot composite powder, wherein the mass ratio of the porous carbon nitride nanosheets to the graphene quantum dots is (5-10):1; S3: mixing phenol and formaldehyde solution to react to obtain a phenolic resin sphere precursor, wherein the molar ratio of phenol to formaldehyde is 1:(1.5-2), and heat treating under an inert atmosphere to obtain porous phenolic resin carbon spheres; S4: adding an inorganic salt to an 8-12 wt.% solution of polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a precursor solution, wherein the inorganic salt is any one of nickel nitrate, cobalt nitrate, and manganese nitrate; the mass ratio of the inorganic salt to polyvinyl pyrrolidone is (0.5-1):1, and obtaining transition metal oxide nanofibers by electrospinning and calcining; S5: adding porous phenolic resin carbon spheres and dopamine hydrochloride in a mass ratio of (0.2-0.4):1 to a tris(hydroxymethylaminomethane) buffer solution for reaction, and then adding transition metal oxide nanofibers in an amount of 3-5% of the mass of the porous phenolic resin carbon spheres to react to obtain a ternary composite porous phenolic resin carbon sphere; S6: Add nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black to an aqueous binder solution with a mass fraction of 6-10wt.%, wherein the aqueous binder is polyacrylic acid and sodium alginate with a mass ratio of 7:3-8:2, and uniformly disperse to obtain a high-capacity and high-cycle negative electrode material. The mass ratio of nano-silicon, hard carbon, porous carbon nitride-graphene quantum dot composite powder, ternary composite porous phenolic resin carbon balls and conductive carbon black is: (15-20): (30-35): (20-25): (15-20): (5-10).

2. A high-capacity and high-cycle negative electrode material prepared by the preparation method according to claim 1.

3. Use of a high-capacity and high-cycle negative electrode material prepared by the preparation method according to claim 1 in a lithium-ion battery.

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