Nano transition metal nitride / nitrogen-doped graphene composite material for negative electrode of lithium ion battery and preparation method of nano transition metal nitride / nitrogen-doped graphene composite material

Abstract

The invention discloses a nano transition metal nitride / nitrogen-doped graphene composite material for a negative electrode of a lithium ion battery and a preparation method of the nano transition metal nitride / nitrogen-doped graphene composite material. Nano transition metal nitride is packaged in multi-layer graphene with a specific thickness to form the nano transition metal nitride / nitrogen-doped graphene composite material with a layered structure characteristic. According to the nano transition metal nitride packaged in the graphene sheet layer, the particle size is controlled to be 3-15 nm through the space confinement effect of the graphene sheet layer, and the thickness of the multi-layer graphene is controlled to be 2-12 nm. The nano transition metal nitride / nitrogen-doped graphene composite material shows high lithium storage activity, high electronic conductivity, high lithium ion diffusivity and good structural stability, further obtains excellent lithium storage capacity, rate capability and cycling stability in application of a negative electrode material, and the preparation method is relatively low in raw material cost, simple in process and suitable for industrial production. And the large-scale application and production requirements of the lithium ion battery can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery negative electrode materials, and in particular to a nano transition metal nitride / nitrogen-doped graphene composite material for lithium ion battery negative electrodes with a novel structure and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of industries such as portable electronic products and electric vehicles, the development of lithium-ion batteries with high energy density, high power density and long cycle life has become a research hotspot in the field of energy storage. Generally, the electrochemical performance of lithium-ion batteries depends largely on the characteristics of the electrode materials [1]. At present, the mainstream commercial negative electrode material of lithium-ion batteries is graphite, which is mainly attributed to its high cost-effectiveness, moderate theoretical specific capacity, excellent cycle stability and low lithium insertion potential (0.1V vs.Li + / Li) and many other advantages, but the energy density of lithium-ion batteries based on graphite negative electrode materials has approached the theoretical limit (372mAh g -1 ), which is difficult to meet the high performance requirements of today's power lithium-ion batteries for practical applications [2]. In order to pursue lithium-ion batteries with higher energy density, a series of conversion anode materials (such as metal oxides, sulfides, nitrides, phosphides and their composite materials) with theoretical specific capacity higher than that of graphite have attracted close attention from researchers [3]. Among them, transition metal nitrides are the most popular among the above-mentioned conversion anode materials due to their high element abundance, high theoretical capacity (for example, iron nitride has a capacity of ~900 mAh g - 1 vs. 372mAh g of graphite -1 ), high theoretical density (e.g., 7.3 g cm for iron nitride -3 vs. 2.2 g cm for graphite -3 ) is considered to be a very promising new negative electrode material to replace traditional graphite[4]. In particular, transition metal nitrides have partially filled d orbitals and vacancy-rich crystal structures, present multiple valence states, and have high electron and ion transport properties, making them have good application prospects in fields such as efficient lithium storage. However, transition metal nitrides usually undergo large volume expansion and contraction effects (~200%) during repeated charge and discharge processes, and unfavorable phenomena such as irreversible interfacial side reactions and severe electrode crushing during lithiation and delithiation processes, resulting in low coulombic efficiency and rapid capacity decline[5]. Therefore, pure phase transition metal nitrides are still a challenge in practical applications, and further innovations are needed in material composites, structural design, and morphology control.

[0003] The latest research shows that the composite of transition metal nitride and carbon matrix can minimize its particle size, inhibit side reactions and stabilize lithiation / delithiation behavior, maintain the integrity of the electrode, and is one of the effective ways to obtain high-performance negative electrode materials [6]. In the past two decades, graphene, as one of the typical carbon materials, is a carbon atom with sp 2 The carbon atoms are tightly packed into a single-layer two-dimensional honeycomb lattice structure with a thickness of only 0.334 nm, which has excellent conductivity, large specific surface area and high theoretical capacity (744 mAh g -1 ), has attracted more and more attention in the application of lithium-ion battery negative electrodes [7]. Transition metal nitrides are embedded and encapsulated in graphene sheets, and the spatial confinement effect of graphene sheets is used to control the particle size of transition metal nitrides to a smaller nanometer size, and they are not easily oxidized and inactivated in the air. At the same time, it can effectively alleviate the structural pulverization during the charge and discharge process, and show high lithium storage activity and cycle stability. In addition, combined with the high electron transport and lithium ion diffusion of the graphene sheet structure itself, this type of composite material can further improve the battery's lithium storage capacity, rate performance and coulombic efficiency in negative electrode applications. In addition, the particle size of transition metal nitrides and the thickness of graphene are key factors affecting electron transport, ion diffusion, lithium storage and release performance and structural stability, and need to be controllably prepared in the composite material. Therefore, how to construct a transition metal nitride / graphene composite material with controllable morphology and structure is crucial to obtaining high-performance lithium-ion battery negative electrode materials.

[0004] In situ growth of graphene around transition metal nitrides is an ideal method for constructing transition metal nitride / nitrogen-doped graphene composite electrode materials with efficient electron and ion transport channels and good lithium storage structural properties. This method can avoid the aggregation of graphene and metal nitrides, improve the dispersion of the two, and increase the interface contact area. However, the traditional method of preparing graphene using the Hummers method of H2 reduction of graphite oxide and subsequent mechanical exfoliation of expanded graphite is cumbersome and has low yields[8]. Large-area graphene can also be prepared by high-temperature graphitization of SiC at 1300℃, but this graphene film is not easy to be exfoliated from the matrix material, and the synthesis route has high energy consumption[9]. In addition, large-area, high-quality graphene can be grown by chemical vapor deposition (CVD) at relatively low temperatures below 1000°C using transition metal (such as Ni, Fe, Cu) substrates to catalytically decompose hydrocarbons such as methane and ethylene. This synthesis strategy is controllable and low-cost, and is one of the effective ways to achieve in-situ growth of graphene around transition metal carbides and then construct nano-transition metal nitride / graphene composite materials through nitridation post-treatment

[10] .

[0005] Therefore, exploring a class of effective solid hydrocarbons as a new carbon source, establishing an effective synthesis strategy, and then preparing transition metal nitride / graphene composite materials with controllable morphology and structure, and realizing controllable modulation of important structural parameters such as transition metal nitride particle size and number of graphene layers in the composite, to obtain high lithium storage and release activity, high electronic conductivity, high ion transport properties, and further obtain good discharge specific capacity, rate performance, and charge and discharge cycle stability, is an urgent need for the large-scale application of high-performance lithium-ion battery negative electrode materials.

[0006] References

[0007] [1] Zhu, ZX; Jiang, TL; Ali, M.; Meng, YH; Jin, Y.; Cui, Y.; Chen, W. Rechargeable Batteries for Grid Scale Energy Storage. Chem. Rev. 2022, 122, 16610-16751.

[0008] [2]Chen, M.; Zhao, MY; Liu, FM; Li, MT; Zhang, ML; Qian, X.; Yuan, ZY; Li, CS; Wan, R. 2024,40,4852-4859.

[0009] [3]Chen, M.; Liu, FM; Zhao, MY; Qian, X.; Yuan, ZY; Wan, R.; Li, CS; Zhang, 2024,230,119579.

[0010] [4]Dong,Y.F.;Li,Y.;Shi,H.D.;Qin,J.Q.;Zheng,S.H.;He,R.H.;Wu,Z.S.Graphene Encapsulated Iron Nitrides Confined in 3D Carbon NanosheetFrameworks for High-Rate Lithium Ion Batteries.Carbon 2020,159,213-220.

[0011] [5]Wang,G.;Yu,M.H.;Feng,X.L.Carbon Materials for Ion-IntercalationInvolved Rechargeable Battery Technologies.Chem.Soc.Rev.2021,50,2388-2443.

[0012] [6]Sun,Z.X.;Fang,S.Y.;Hu,Y.H.3D Graphene Meresaterials:fromUnderstanding to Design and Synthesis Control.Chem.Rev.2020,120,10336-10453.

[0013] [7]Raccichini,R.;Varzi,A.;Passerini,S.;Scrosati,B.The Role ofGraphene for Electrochemical Energy Storage.Nat.Mater.2015,14,271-279.

[0014] [8]Allen,M.J.;Tung,V.C.;Kaner,R.B.Honeycomb Carbon:A Review ofGraphene.Chem.Rev.2010,110,132-145.

[0015] [9] de Heera, WA; Bergera, C.; Wu, XS; First, PN; Conrad, EH; Li, XB; Li, TB; Sprinkle, M.;

[0016]

[10] Zhang, Y.; Zhang, LY; Zhou, CWReview of Chemical Vapor Depositionof Graphene and Related Applications. Acc. Chem. Res. 2013, 46, 2329-2339. Summary of the Invention

[0017] In order to explore a class of effective solid hydrocarbons as a new carbon source, establish an effective synthesis strategy, and then prepare transition metal nitride / graphene composite materials with controllable morphology and structure, and realize controllable modulation of important structural parameters such as transition metal nitride particle size and number of graphene layers in the composite, thereby obtaining high lithium storage and release activity, high electronic conductivity, and high ion transport properties, and further obtaining good discharge specific capacity, rate performance, and charge and discharge cycle stability, the present invention provides a nano transition metal nitride / nitrogen-doped graphene composite material for lithium ion battery negative electrode and a preparation method thereof.

[0018] The object of the present invention is achieved like this:

[0019] A nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrodes is characterized in that the nano transition metal nitride is encapsulated in multilayer graphene of a specific thickness to form a nano transition metal nitride and nitrogen-doped graphene composite material with layered structural characteristics.

[0020] In the above-mentioned nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, the particle diameter of the nano transition metal nitride is between 3 and 15 nm, and the thickness of the multilayer graphene is between 2 and 12 nm.

[0021] In the above-mentioned nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, the nano transition metal nitride is one of iron nitride, cobalt nitride, and nickel nitride, and the mass fraction of the nano transition metal nitride in the material is between 55 and 80 wt%.

[0022] The electronic conductivity of the nano transition metal nitride / nitrogen-doped graphene composite material for the negative electrode of the lithium ion battery is 2.0-2.5S cm -1 The lithium ion diffusion rate is between 2.0×10 -12 ~3×10 -12 cm 2 s -1 between.

[0023] The nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode is prepared by using polycyclic aromatic hydrocarbons and transition metal salts, wherein the polycyclic aromatic hydrocarbons are preferably polyphenyl aromatic hydrocarbons formed by two or more benzene rings fused together in a manner of sharing two adjacent carbon atoms.

[0024] In the above-mentioned nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, the nano transition metal nitride encapsulated in the graphene sheet utilizes the spatial confinement effect of the graphene sheet to control the particle size to a smaller nanometer size, and is not easily oxidized and inactivated in an air atmosphere, exhibiting high lithium storage activity and high structural cycle stability; multilayer graphene and its hierarchical structure exhibit high electron transport and lithium ion diffusion properties; and the lithium storage capacity, rate performance and cycle stability are further improved in the application of negative electrode materials.

[0025] The method for preparing the nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode comprises the following steps:

[0026] 1) using polycyclic aromatic hydrocarbons as a carbon source and transition metal salts as a metal source, uniformly mixing and drying in a solution of water and ethanol, and performing high-temperature pyrolysis under an inert atmosphere to obtain a transition metal carbide / graphene composite material;

[0027] 2) placing the transition metal carbide / graphene composite material obtained in step 1) and a nitrogen source precursor under an inert atmosphere for high-temperature nitriding treatment to obtain a transition metal nitride / nitrogen-doped graphene composite material.

[0028] In the above-mentioned preparation method, step 1) comprises the following steps: dissolving 1 to 5 g of polycyclic aromatic hydrocarbons in a water and ethanol solution, then adding 1 to 3 g of a transition metal salt, vigorously stirring to form a brown colloid, drying, and then pyrolyzing the mixture at 700 to 1000° C. for 2 to 5 hours in an inert atmosphere of argon to obtain a transition metal carbide / graphene composite material;

[0029] In the above preparation method, step 2) includes the following steps: placing 1 to 3 g of the transition metal carbide / graphene composite material obtained in step 1) and 5 to 15 g of a nitrogen source precursor under an inert atmosphere of argon, and performing a high-temperature nitriding treatment at 400 to 500°C for 0.5 to 2 hours to obtain a transition metal nitride / nitrogen-doped graphene composite material.

[0030] In the above preparation method, the polycyclic aromatic hydrocarbons in step 1) are one or more combinations of naphthalene, acenaphthene, anthracene, phenanthrene, fluorene, pyrene, fluoranthene, perylene, and anthranthene; the transition metal salt is one or more combinations of carbonates, nitrates, and chlorides of transition metals such as iron, cobalt, and nickel; and the nitrogen source precursor in step 2) is urea.

[0031] Positive and beneficial effects: The nano-transition metal nitride / nitrogen-doped graphene composite material prepared by the present invention has a unique morphology and structure, wherein the nano-transition metal nitride is encapsulated in multilayer graphene of a specific thickness, forming a nano-transition metal nitride and nitrogen-doped graphene composite material with layered structural characteristics. Among them, the nano-transition metal nitride encapsulated in the graphene sheet utilizes the spatial confinement effect of the graphene sheet to control the particle size between 3 and 15 nm, and the thickness of the multilayer graphene is controlled between 2 and 12 nm, so that the nano-transition metal nitride / nitrogen-doped graphene composite material exhibits high lithium storage activity and high electronic conductivity (2.0 to 2.5 S cm -1 ), high lithium ion diffusivity (2.0×10 -12 ~3×10 - 12 cm 2 s -1 ) and good cycle stability, and further obtains better lithium storage capacity, rate performance and cycle stability in the application of negative electrode materials; the present invention uses polycyclic aromatic hydrocarbons as a specific type of solid carbon source, especially preferably polyphenyl aromatic hydrocarbons composed of two or more benzene rings fused to each other in a manner of sharing two adjacent carbon atoms, and forms small molecular carbon C by pyrolysis of polycyclic aromatic hydrocarbons catalyzed by transition metals at 700-1000 ° C. 6n (1≤n≤3), and simultaneously carbon thermal reduction to form carburized transition metals, thereby obtaining transition metal carbides, and in situ catalytic growth of graphene to obtain a transition metal carbide / graphene composite material. Subsequent high-temperature nitridation treatment successfully produced a nano-transition metal nitride / nitrogen-doped graphene composite material with small particle size and controllable thickness, exhibiting hierarchical structural characteristics. This composite material exhibits significant structural advantages in lithium-ion battery anode material applications. Furthermore, the entire process has low preparation cost and energy consumption, is simple, and easily implements industrial production of nano-transition metal nitride / nitrogen-doped graphene composite anode materials, meeting the requirements for large-scale application of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the synthesis of the nano-iron nitride / nitrogen-doped graphene composite material prepared in Example 1 of the present invention;

[0033] Figure 2 Scanning electron microscopy, energy dispersive X-ray elemental mapping, transmission electron microscopy, and atomic force microscopy images of the nano-iron nitride / nitrogen-doped graphene composite material prepared in Example 1 of the present invention;

[0034] Figure 3 This is a graph showing the constant current charge and discharge performance of the nano-iron nitride / nitrogen-doped graphene composite material prepared in Example 1 of the present invention;

[0035] Figure 4 This is a rate performance diagram of the nano-iron nitride / nitrogen-doped graphene composite material prepared in Example 1 of the present invention;

[0036] Figure 5 This is the 600-cycle charge-discharge cycle stability of the nano-iron nitride / nitrogen-doped graphene composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to specific embodiments:

[0038] Example 1

[0039] (1) 3 g of phenanthrene was dissolved in 20 ml of a mixed solution of water and ethanol, and then 1.5 g of FeCl3·6H2O was added. After vigorous stirring, a brown colloid was formed and dried at 60°C. Then, the colloid was pyrolyzed at 900°C for 3 h in an inert atmosphere of argon to obtain an iron carbide / graphene composite material (Fe3C / mG).

[0040] (2) 2 g of the iron carbide / graphene composite material obtained in step (1) and 10 g of urea were placed in an inert atmosphere of argon and subjected to high-temperature nitriding treatment at 450 ° C for 1 h to obtain an iron nitride / nitrogen-doped graphene composite material (Fe3N / N-mG).

[0041] The prepared Fe3N / N-mG was mixed with polyvinylidene fluoride in a mass ratio of 9:1, and N-methylpyrrolidone (NMP) was used as a solvent and stirred for 24 hours to prepare a slurry. The prepared slurry was coated on the surface of copper foil (diameter 13 mm, thickness 0.3 mm) with a coating density of 1.0 mg / cm2 and vacuum dried at 80°C for 24 hours to prepare a working electrode sheet. Lithium foil was used as the reference electrode and counter electrode (diameter 13 mm, thickness 0.5 mm), the electrolyte was 1.0M LiPF6 / EC (ethylene carbonate): DMC (dimethyl carbonate) = 1:1 (V / V), the diaphragm was Celgard 2300 membrane (25μm thick polyethylene), and the battery was assembled into a button cell (CR2032) in a high-purity argon glove box. Constant current charge and discharge tests were carried out using the Wuhan Blue Electric charge and discharge test system to study the charge and discharge specific capacity and cycle performance of the Fe3N / N-mG material. Voltage test range: 0.01-3.0V (vs Li / Li + ).

[0042] like Figure 1 As shown, the present invention uses solid polycyclic aromatic hydrocarbons (such as phenanthrene) as a specific type of solid carbon source and transition metal salts (such as ferric chloride) as a transition metal source. After uniform mixing and drying, the polycyclic aromatic hydrocarbons (such as phenanthrene) are pyrolyzed at 700-1000°C by transition metal catalysis to form small molecular carbon C 6n (1≤n≤3), and simultaneously carbon thermal reduction to form transition metal carbides (such as Fe3C), and in situ catalytic growth of graphene to obtain transition metal carbide / graphene composite materials (such as Fe3C / mG). Subsequently, through high-temperature nitridation treatment, nano-iron nitride / nitrogen-doped graphene composite materials with small particle size and controllable thickness and hierarchical structural characteristics (such as Fe3N / N-mG) were successfully prepared and used as negative electrode materials in lithium-ion battery devices.

[0043] Figure 2 (a, f) are scanning electron micrographs of Fe3N / N-mG, in which graphene nanosheets show an ordered interlayer stacking structure, forming a layered morphology. Energy dispersive X-ray elemental map ( Figure 2 be) confirmed that Fe3N nanocrystals are uniformly encapsulated in nitrogen-doped graphene nanosheets. In addition, the thickness of graphene sheets in Fe3N / N-mG was measured by atomic force microscopy and transmission electron microscopy. The atomic force microscopy image of Fe3N / N-mG shows ( Figure 2 g), the thickness of 5 randomly selected graphene layers is about 2.0nm, corresponding to a single layer thickness of 0.4nm. Transmission electron microscopy image ( Figure 2 h) shows that the thickness of single-layer graphene is about 0.39nm, which is basically consistent with the thickness results tested by atomic force microscopy. Figure 2i is the scanning electron micrograph of Fe3N / N-mG, from which we can see that the actual edge thickness of the graphene nanosheet is 3.5nm, indicating that the layered graphene in the Fe3N / N-mG sample is formed by stacking about 9 layers of graphene sheets. In addition, the transmission electron micrograph of Fe3N / N-mG ( Figure 2 j) shows that many dark nanoparticles with a crystal size of 5-10nm are encapsulated and embedded on the surface of graphene nanosheets. High-resolution transmission electron microscopy ( Figure 2 k) further shows that the lattice spacing of the dark nanoparticles is 0.22, 0.24 and 0.29 nm, corresponding to the (002), (110) and (101) planes of Fe3N. The above results confirm that Fe3N nanocrystals with an average size of 5-10 nm are encapsulated in nitrogen-doped multilayer graphene nanosheets. The controllable morphology and structural properties make the nano-iron nitride / nitrogen-doped graphene composite material have good electronic conductivity (2.1S cm -1 ), ion diffusivity (2.39×10 -12 cm 2 s -1 ), structural stability and mechanical strength, so that it can show excellent charge and discharge performance, rate performance and cycle stability in lithium-ion battery applications.

[0044] from Figure 3 It can be seen that with 0.1Ag -1 The constant current charge and discharge test was carried out, and the initial discharge / charge capacity of Fe3N / N-mG was 1018 / 601mAh g -1 , which is higher than the pure phase Fe3N prepared in Comparative Example 1-2 (1072 / 502mAh g -1 ), graphene (513 / 435mAh g -1 ) initial discharge / charge capacity. Furthermore, the Coulombic efficiency of Fe3N / N-mG is 59%, higher than that of pure Fe3N (47%). This is mainly due to the fact that the Fe3N encapsulation and embedding in graphene sheets can reduce direct contact with the electrolyte, thereby reducing side reactions and stabilizing the phase change structure characteristics of lithium storage and release.

[0045] from Figure 4 It can be seen that 0.1-5Ag -1 The rate performance test was carried out at different current densities (corresponding to different rates of 0.1-5C). The specific capacities of Fe3N / N-mG after 30 cycles at different rates of 0.1-5C were 590, 544, 503, 455, and 412 mAh g -1 Its rate performance is better than that of Fe3N in comparative example 1-2 (485, 412, 370, 324, 282 mAh g -1), graphene (409, 312, 282, 255, 220 mAh g -1 )’s corresponding performance.

[0046] from Figure 5 It can be seen that at 0.1A g -1 The long-term cycling stability of Fe3N / N-mG was evaluated at a current density of 0.1C. After 600 cycles of charge and discharge, the specific capacity of Fe3N / N-mG at 0.1C remained at 530 mAh g -1 Compared with the initial capacity, there is no obvious attenuation, and it is significantly better than Fe3N (283mAh g -1 ) and graphene (165mAh g -1 The results show that Fe3N / N-mG has good electrochemical structural stability and exhibits excellent charge-discharge cycle stability.

[0047] The above results show that the nano-Fe3N encapsulated in the graphene sheet uses the spatial confinement effect of the graphene sheet to control the particle size between 5-10nm, and the thickness of the multilayer graphene is controlled at 3.5nm, so that the nano-iron nitride / nitrogen-doped graphene composite material exhibits high lithium storage activity, high electronic conductivity, high lithium ion diffusivity and good cycle stability, and further obtains better lithium storage capacity, rate performance and cycle stability in the application of negative electrode materials.

[0048] Example 2

[0049] The steps are basically the same as the preparation process of Example 1.

[0050] (1) 4 g of anthracene was dissolved in 20 ml of a mixed solution of water and ethanol, and then 1.5 g of Ni(NO3)2·6H2O was added. After vigorous stirring to form a colloid, the colloid was dried at 60°C and then pyrolyzed at 900°C for 3 h in an inert atmosphere of argon to obtain a nickel carbide / graphene composite material (Ni3C / mG).

[0051] (2) 2 g of the nickel carbide / graphene composite material obtained in step (1) and 10 g of urea were placed in an inert atmosphere of argon and subjected to high-temperature nitridation treatment at 450°C for 1 h to obtain a nickel nitride / nitrogen-doped graphene composite material (Ni3N / N-mG). The electrochemical properties of the Ni3N / N-mG negative electrode material are shown in Table 2.

[0052] Example 3

[0053] The steps are basically the same as the preparation process of Example 1.

[0054] (1) 3 g of naphthalene was dissolved in 20 ml of a mixed solution of water and ethanol, followed by the addition of 1.5 g of Co(CO3)2·6H2O. The mixture was stirred vigorously to form a colloid, dried at 60°C, and then pyrolyzed at 900°C for 3 h in an inert atmosphere of argon to obtain a cobalt carbide / graphene composite material (Co3C / mG).

[0055] (2) 2 g of the cobalt carbide / graphene composite material obtained in step (1) and 10 g of urea were placed in an inert atmosphere of argon and subjected to high-temperature nitridation treatment at 450°C for 1 h to obtain a cobalt nitride / nitrogen-doped graphene composite material (Co3N / N-mG). The electrochemical properties of the Co3N / N-mG negative electrode material are shown in Table 2.

[0056] Comparative Example 1

[0057] 3g of phenanthrene was dissolved in 20ml of a mixture of water and ethanol, followed by the addition of 1.5g of FeCl3·6H2O. After vigorous stirring, a brown colloid formed. After drying at 60°C, the mixture was pyrolyzed at 900°C for 3h in an inert atmosphere of argon to obtain an iron carbide / graphene composite (Fe3C / mG). The resulting Fe3C / mG was placed in a Teflon-lined stainless steel autoclave containing 40ml of concentrated nitric acid and hydrothermally treated at 80°C for 12h. The residual solid was filtered and annealed at 500°C for 3h to obtain pure graphene.

[0058] Comparative Example 2

[0059] 3 g of phenanthrene was dissolved in a 20 ml mixture of water and ethanol. 1.5 g of FeCl₃·6H₂O was then added and stirred vigorously to form a brown colloid, which was then dried at 60°C. The resulting material was transferred to a muffle furnace and heated at 700°C for 1 h to obtain Fe₂O₃ powder. Subsequently, 1 g of Fe₂O₃ and 5 g of urea were added to two separate quartz boats, each of which was then transferred to a tube furnace under an Ar flow. The urea-filled quartz boat was placed in the upper Ar flow, while the Fe₂O₃-filled boat was placed in the lower Ar flow. Nitridation was performed at 450°C for 1 h to convert the Fe₂O₃ into Fe₃N. The electrochemical properties of the Fe₃N anode material are shown in Table 2.

[0060] Table 1. Structural parameters of lithium-ion battery negative electrode materials in Examples and Comparative Examples

[0061]

[0062] As can be seen from Table 1, compared with pure phase graphene and iron nitride, the nano transition metal nitride / nitrogen-doped graphene composite material in the present invention has higher electronic conductivity and lithium ion diffusion performance, as well as a high content of transition metal nitride lithium storage active components, and is expected to exhibit excellent lithium storage capacity, rate performance and cycle stability during the charge and discharge process of lithium-ion batteries.

[0063] Table 2. Charge and discharge performance of lithium-ion battery negative electrode materials in examples and comparative examples

[0064]

[0065]

[0066] As can be seen from Table 2, compared with pure Fe3N and graphene, the nano transition metal nitride / nitrogen-doped graphene composite material of the present invention has a higher discharge specific capacity and excellent cycle stability. The capacity retention rate is above 90% after 600 cycles, which can meet the application requirements of high-performance and high-stability lithium-ion batteries.

[0067] The preparation method of the present invention discloses a method of using polycyclic aromatic hydrocarbons as a specific type of solid carbon source, particularly preferably polyphenyl aromatic hydrocarbons composed of two or more benzene rings fused in a manner of sharing two adjacent carbon atoms, and thermally decomposing the polycyclic aromatic hydrocarbons at 700-1000°C by transition metal catalysis to form small molecular carbon C 6n (1≤n≤3), and simultaneously carbon thermal reduction to form transition metals, thereby obtaining transition metal carbides, and in situ catalytic growth of graphene to obtain a transition metal carbide / graphene composite material. Subsequent high-temperature nitridation treatment successfully produced a nano-transition metal nitride / nitrogen-doped graphene composite material with small particle size, controllable thickness, and hierarchical structure. This composite material exhibits significant structural advantages in lithium-ion battery anode material applications. Furthermore, the entire process has low preparation cost and energy consumption, is simple, and easily implements industrial production of nano-transition metal nitride / nitrogen-doped graphene composite anode materials, meeting the requirements for large-scale application of lithium-ion batteries.

[0068] The nano-transition metal nitride / nitrogen-doped graphene composite prepared in the present invention can be characterized by the following method: the prepared nano-transition metal nitride / nitrogen-doped graphene composite is mixed with polyvinylidene fluoride in a mass ratio of 9:1, stirred in N-methylpyrrolidone (NMP) as a solvent, and prepared into a slurry for 24 hours. The prepared slurry is then coated onto a copper foil surface (13 mm diameter, 0.3 mm thickness) at a coating density of 1.0 mg / cm² and vacuum-dried at 80°C for 24 hours to form a working electrode sheet. Lithium foil (13 mm diameter, 0.5 mm thickness) is used as the reference electrode and counter electrode. The electrolyte is 1.0 M LiPF6 / EC (ethylene carbonate): DMC (dimethyl carbonate) in a 1:1 (V / V) ratio. A Celgard 2300 membrane (25 μm thick polyethylene) is used as the separator. The cells are assembled into button-type cells (CR2032) in a high-purity argon glove box. The constant current charge and discharge test was carried out using the Wuhan Blue Electric charge and discharge test system to study the charge and discharge specific capacity, rate performance and cycle performance of the nano transition metal nitride / nitrogen-doped graphene composite material. The voltage test range was 0.01-3.0V (vs Li / Li + ).

[0069] The nano-transition metal nitride / nitrogen-doped graphene composite material produced by the present invention has a unique morphology and structure, wherein the nano-transition metal nitride is encapsulated in multilayer graphene of a specific thickness, forming a nano-transition metal nitride and nitrogen-doped graphene composite material with a layered structure. The nano-transition metal nitride encapsulated in the graphene sheets utilizes the spatial confinement effect of the graphene sheets to control the particle size between 3 and 15 nm, and the thickness of the multilayer graphene is controlled between 2 and 12 nm. This enables the nano-transition metal nitride / nitrogen-doped graphene composite material to achieve excellent lithium storage capacity, rate performance, and cycle stability in negative electrode material applications.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, characterized in that: Nano-transition metal nitrides are encapsulated in multi-layer graphene of a specific thickness to form a nano-transition metal nitride and nitrogen-doped graphene composite material with layered structural characteristics.

2. The nano transition metal nitride / nitrogen-doped graphene composite material for a lithium-ion battery negative electrode according to claim 1, characterized in that: In the above-mentioned nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, the particle diameter of the nano transition metal nitride is between 3 and 15 nm, and the thickness of the multilayer graphene is between 2 and 12 nm.

3. The nano transition metal nitride / nitrogen-doped graphene composite material for a lithium ion battery negative electrode according to claim 1, characterized in that: In the above-mentioned nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, the nano transition metal nitride is one of iron nitride, cobalt nitride, and nickel nitride, and the mass fraction of the nano transition metal nitride in the material is between 55 and 80 wt%.

4. The nano transition metal nitride / nitrogen-doped graphene composite material for a lithium-ion battery negative electrode according to claim 1, characterized in that: The electronic conductivity of nano-transition metal nitride / nitrogen-doped graphene composite materials for lithium-ion battery negative electrodes is 2.0-2.5 S cm -1 The lithium ion diffusion rate is between 2.0×10 -12 ~3×10 -12 cm 2 s -1 between.

5. The nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode according to claim 1, characterized in that: The nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode is prepared by using polycyclic aromatic hydrocarbons and transition metal salts, wherein the polycyclic aromatic hydrocarbons are preferably fused aromatic hydrocarbons in which two or more benzene rings are fused to each other in a manner of sharing two adjacent carbon atoms.

6. The nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode according to claim 1, characterized in that: In the above-mentioned nano transition metal nitride / nitrogen-doped graphene composite material for lithium-ion battery negative electrode, the nano transition metal nitride encapsulated in the graphene sheet utilizes the spatial confinement effect of the graphene sheet to control the particle size to a smaller nanometer size, and is not easily oxidized and inactivated in an air atmosphere, exhibiting high lithium storage activity and high structural cycle stability; multilayer graphene and its hierarchical structure exhibit high electron transport and lithium ion diffusion properties; and the lithium storage capacity, rate performance and cycle stability are further improved in the application of negative electrode materials.

7. A method for preparing a nano transition metal nitride / nitrogen-doped graphene composite material for a lithium ion battery negative electrode according to any one of claims 1 to 6, comprising the following steps: 1) using polycyclic aromatic hydrocarbons as a carbon source and transition metal salts as a metal source, uniformly mixing and drying in a solution of water and ethanol, and performing high-temperature pyrolysis under an inert atmosphere to obtain a transition metal carbide / graphene composite material; 2) placing the transition metal carbide / graphene composite material obtained in step 1) and a nitrogen source precursor under an inert atmosphere for high-temperature nitriding treatment to obtain a transition metal nitride / nitrogen-doped graphene composite material.

8. The method for preparing the nano transition metal nitride / nitrogen-doped graphene composite material for lithium ion battery negative electrode according to claim 7, characterized in that: In the above-mentioned preparation method, step 1) comprises the following steps: dissolving 1 to 5 g of polycyclic aromatic hydrocarbons in a water and ethanol solution, then adding 1 to 3 g of a transition metal salt, vigorously stirring to form a brown colloid, and drying it, and then pyrolyzing it at 700 to 1000° C. for 2 to 5 hours in an inert atmosphere of argon to obtain a transition metal carbide / graphene composite material.

9. The method for preparing the nano transition metal nitride / nitrogen-doped graphene composite material for lithium ion battery negative electrode according to claim 7, characterized in that: In the above preparation method, step 2) comprises the following steps: placing 1-3 g of the transition metal carbide / graphene composite material obtained in step 1) and 5-15 g of a nitrogen source precursor under an inert atmosphere of argon, and performing a high-temperature nitriding treatment at 400-500°C for 0.5-2 h to obtain a transition metal nitride / nitrogen-doped graphene composite material.

10. The method for preparing the nano transition metal nitride / nitrogen-doped graphene composite material for lithium ion battery negative electrode according to claim 7, characterized in that: In the above preparation method, the polycyclic aromatic hydrocarbons in step 1) are one or more combinations of naphthalene, acenaphthene, anthracene, phenanthrene, fluorene, pyrene, fluoranthene, perylene, and anthranthene; the transition metal salt is one or more combinations of carbonates, nitrates, and chlorides of transition metals such as iron, cobalt, and nickel; and the nitrogen source precursor in step 2) is urea.

Images