S-doped g-C3N4 coated modified graphite material, preparation method thereof and lithium ion battery negative electrode

Abstract

The invention relates to an S-doped g-C3N4 coated modified graphite material, a preparation method thereof and a lithium ion battery negative electrode. The method comprises the following steps: mixing a g-C3N4 precursor with a sulfur source, and then carrying out heat treatment under the condition of shielding gas to obtain sulfur-doped graphite phase carbon nitride S-g-C3N4; carrying out plasma modification treatment on the surface of the graphite material by adopting plasma reaction gas to obtain modified graphite; mixing S-g-C3N4 with the modified graphite to obtain a mixed material; and calcining the mixed material in a protective gas environment to obtain the S-doped g-C3N4 coated modified graphite material. The invention also provides the graphite material prepared by the method and a lithium ion battery negative electrode prepared from the graphite material. The graphite material has relatively high conductivity, interface compatibility and structural stability.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing technology, specifically relating to an S-doped g-C3N4 coated modified graphite material, its preparation method, and a lithium-ion battery anode. Background Technology

[0002] Currently, graphite-based materials still dominate the field of lithium-ion battery anodes, with natural graphite attracting widespread attention due to its abundant sources and low cost. However, natural graphite anodes still face significant challenges in practical applications: the anisotropy of its layered structure leads to uneven volume expansion and contraction during lithium-ion insertion / extraction, causing particle pulverization, electrode structure damage, and contact failure between the active material and the current collector; simultaneously, the intrinsic conductivity and lithium-ion diffusion rate of natural graphite are limited, resulting in high charge transfer impedance of the electrode. These problems severely limit the application of natural graphite in high-performance batteries.

[0003] Coating is considered one of the most common and effective strategies for improving the properties of natural graphite. This method aims to buffer volume changes, reduce the exposure of active surfaces to suppress electrolyte side reactions, and improve interfacial properties by constructing a protective coating layer on the surface of graphite particles. However, existing coating technologies have core defects that urgently need to be addressed: First, the intrinsic conductivity of coating layers such as amorphous carbon or polymers is insufficient, with low electronic / ionic conductivity, which may not only fail to improve but also exacerbate the overall charge transfer impedance. Second, the interaction between the coating layer and the graphite substrate is mostly physical adhesion or weak interaction, lacking strong chemical bonding. First, under long-term charge-discharge stress, the traditional coating layer is prone to interface peeling or contact failure, thus losing its protective function. Second, the traditional coating layer lacks mechanical strength and flexibility, making it difficult to effectively constrain the anisotropic expansion of graphite particles. Furthermore, the coating layer itself may crack or pulverize during cycling, failing to maintain the integrity of the electrode structure in the long term. Third, conventional coating materials lack polar functional groups that can significantly improve the compatibility of the electrode / electrolyte interface, resulting in limited improvement on lithium-ion interfacial transport dynamics. These defects make it difficult for traditional coating strategies to synergistically improve conductivity, interfacial bonding force, and structural stability, thus limiting the potential for performance improvement.

[0004] Therefore, developing an innovative modification technology that can simultaneously and significantly reduce the charge transfer impedance of graphite anodes, effectively suppress volume expansion and particle agglomeration during cycling, and ensure strong interfacial bonding between the coating layer and the substrate is crucial for improving the overall performance of natural graphite anodes. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide an S-doped g-C3N4-coated modified graphite material and its preparation method. Through the synergistic effect of S-doped g-C3N4 coating and plasma-modified graphite, the conductivity, interfacial compatibility, and structural stability of graphite can be significantly improved, thereby enhancing its electrochemical performance.

[0006] Another objective of this invention is to provide a lithium-ion battery negative electrode, which is prepared from the above-mentioned materials.

[0007] To achieve the above objectives, the present invention provides a method for preparing S-doped g-C3N4 coated modified graphite material, wherein the method includes:

[0008] S1. Mix g-C3N4 (graphitic carbon nitride) precursor with sulfur source at a molar ratio of (1-20):1, and then heat treat at 400-800℃ under protective gas to obtain Sg-C3N4 with specific sulfur doping content.

[0009] S2. The surface of the graphite material is subjected to plasma modification treatment using plasma reactive gas to obtain modified graphite.

[0010] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are mixed at a mass ratio of 1:(1-50) to obtain a mixture; the mixture is calcined at 500-1200℃ under a protective atmosphere to obtain S-doped g-C3N4 coated modified graphite material.

[0011] According to a specific embodiment of the present invention, preferably, the preparation method of the S-doped g-C3N4 coated modified graphite material provided by the present invention includes the following specific steps:

[0012] S1. The g-C3N4 precursor and sulfur source are ground and mixed at a molar ratio of (1-20):1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated at 400-800℃ under continuous protective gas to obtain specific sulfur-doped graphitic carbon nitride Sg-C3N4. The sulfur doping content is 5wt%-30wt%, with the sum of the mass of sulfur and g-C3N4 being 100%.

[0013] S2. Place the graphite material in a plasma cleaner, introduce plasma reaction gas, and perform plasma modification treatment on the surface of the graphite material to obtain modified graphite; wherein, the power of the plasma modification treatment is 50-300W, and the time is 5-30min.

[0014] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled and mixed at a mass ratio of 1:(1-50) to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 500-1200℃ under a protective gas environment. After calcination, S-doped g-C3N4 coated modified graphite material is obtained.

[0015] According to a specific embodiment of the present invention, preferably, the molar ratio of the g-C3N4 precursor to the sulfur source is (1-10):1, more preferably (1-4):1.

[0016] According to a specific embodiment of the present invention, the sulfur doping amount can be controlled by adjusting the molar ratio of the g-C3N4 precursor to the sulfur source. The present invention controls the sulfur doping amount to 5wt%-30wt%, which provides a sufficient number of active sites without adversely affecting the material itself. If the sulfur doping amount is too low, there will be insufficient active sites, making performance improvement impossible; if the sulfur doping amount is too high, it will damage the material's structure and inhibit performance improvement.

[0017] According to a specific embodiment of the present invention, preferably, the g-C3N4 precursor includes one or more of melamine, urea, and cyanamide.

[0018] According to a specific embodiment of the present invention, preferably, the sulfur source includes one or a combination of two or more of thiourea, trithiocyanate, and elemental sulfur.

[0019] According to a specific embodiment of the present invention, preferably, the heat treatment time in step S1 is 1-10 hours; more preferably, the heat treatment temperature is 400-600°C and the heat treatment time is 3-8 hours; and even more preferably, the heat treatment temperature is 450-600°C and the heat treatment time is 4-6 hours.

[0020] According to a specific embodiment of the present invention, preferably, the protective gas in step S1 includes one or more combinations of Ar, N2, and Ne.

[0021] According to a specific embodiment of the present invention, preferably, the sulfur doping content in step S1 is 5%-20%, more preferably 8%-12%.

[0022] According to a specific embodiment of the present invention, preferably, the graphite material is natural spherical graphite, and the purity of the graphite material is >99%.

[0023] According to a specific embodiment of the present invention, preferably, the plasma reaction gas includes one or more of O2, Ar, H2, N2, Ar / H2, and Ar / O2.

[0024] According to a specific embodiment of the present invention, preferably, the power of the plasma modification treatment is 50-150W and the time is 5-15min.

[0025] According to a specific embodiment of the present invention, preferably, the mass ratio of Sg-C3N4 to modified graphite is 1:(1-25), more preferably 1:(5-15).

[0026] According to a specific embodiment of the present invention, preferably, the mixing process of S3 is carried out by ball milling, wherein the ball milling speed is 100-200 r / min and the ball milling time is 5-30 min, more preferably the ball milling speed is 150-200 r / min and the ball milling time is 10-25 min.

[0027] According to a specific embodiment of the present invention, preferably, the protective gas in step S3 includes one or more combinations of Ar, N2, and Ne.

[0028] According to a specific embodiment of the present invention, preferably, the calcination temperature in step S3 is 600-1000℃ and the calcination time is 3-10h; more preferably, the calcination temperature is 650-850℃ and the calcination time is 3-6h.

[0029] The method provided by this invention imparts more defects and active sites to g-C3N4 through sulfur doping, enhancing its conductivity and lithium-ion adsorption and migration capabilities to reduce charge transfer impedance. Simultaneously, plasma modification introduces functional groups into the graphite surface to improve its interfacial compatibility and bonding with Sg-C3N4, reduce interfacial impedance, and optimize the surface structure for uniform coating. The Sg-C3N4 coating layer on the graphite surface effectively suppresses volume expansion and particle agglomeration during graphite charging and discharging, maintaining electrode structural stability, reducing capacity decay, and ultimately improving the battery's cycle performance and rate performance.

[0030] The present invention also provides an S-doped g-C3N4 coated modified graphite anode material, wherein the anode material is prepared by the above method.

[0031] According to a specific embodiment of the present invention, preferably, the thickness of the S-doped g-C3N4 coating layer is 5-20 nm, more preferably 8-15 nm.

[0032] According to a specific embodiment of the present invention, preferably, the S doping content in the S-doped g-C3N4 coated modified graphite material is 0.1%-10%, more preferably 0.1%-5%, and even more preferably 0.5%-2.5%.

[0033] The present invention also provides a lithium-ion battery anode, wherein the lithium-ion battery anode is prepared from the above-mentioned S-doped g-C3N4 coated modified graphite anode material.

[0034] The present invention also provides a lithium-ion battery having the negative electrode of the lithium-ion battery provided by the present invention.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The present invention utilizes g-C3N4 with nitrogen-rich properties as a coating layer. With the help of its abundant nitrogen-containing polar functional groups (such as -NH2, -NH-, etc.), the interaction between the coating layer and the electrolyte can be significantly enhanced, thereby improving the wettability of the electrode / electrolyte interface and promoting lithium-ion transport efficiency, which is ultimately beneficial to the improvement of battery performance.

[0037] (2) By modifying g-C3N4 with S doping, the present invention effectively regulates its electronic structure, significantly enhances its conductivity, thereby promoting the transport of lithium ions in the electrode material, reducing the overall impedance of the battery, and improving electrochemical performance.

[0038] (3) By performing plasma modification on graphite materials, active functional groups are introduced on their surface. When combined with the Sg-C3N4 coating layer, the interfacial bonding ability is significantly enhanced, the interfacial impedance is reduced, and the charge transport efficiency of the material is further optimized. At the same time, the coating layer can be prevented from falling off during charging and discharging, thus improving the overall structural stability of the material. Attached Figure Description

[0039] Figure 1 Cycle performance graphs of batteries made from the negative electrode materials provided in Examples 1-6 and Comparative Examples 1-8.

[0040] Figure 2 The first charge-discharge curves of batteries made from the negative electrode materials provided in Examples 1-6.

[0041] Figure 3 AC impedance spectra of batteries made from the negative electrode materials provided in Examples 1-6 and Comparative Examples 1-8.

[0042] Figure 4 Rate performance diagrams of batteries made from the negative electrode materials provided in Examples 1-6 and Comparative Examples 1-8. Detailed Implementation

[0043] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0044] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0046] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0047] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0048] Example 1:

[0049] This embodiment provides a method for preparing S-doped g-C3N4 coated modified graphite material, including the following steps:

[0050] S1. Melamine and thiourea are ground and mixed at a molar ratio of 2:1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated under continuous Ar protective gas. The heat treatment temperature is 500℃ and the heat treatment time is 5h. Through the above operation, Sg-C3N4 with a theoretical sulfur doping content of 9.76% is obtained.

[0051] S2. Place the graphite material in a plasma cleaner and use O2 as the cleaning gas to perform plasma modification treatment on the surface of the graphite material. The treatment power is 100W and the treatment time is 10min to obtain modified graphite.

[0052] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled at a mass ratio of 1:9. The ball milling speed is set to 180 r / min and the milling time is 20 min to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 700℃ under Ar atmosphere for 4 h. After calcination, S-doped g-C3N4-coated modified graphite material is obtained, wherein the sulfur content of the material is 0.98% and the coating thickness is 10 nm.

[0053] Example 2:

[0054] This embodiment provides a method for preparing S-doped g-C3N4 coated modified graphite material, including the following steps:

[0055] S1. Melamine and thiourea are ground and mixed at a molar ratio of 2:1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated under continuous Ar protective gas. The heat treatment temperature is 500℃ and the heat treatment time is 5 hours. Through the above operation, Sg-C3N4 with a theoretical sulfur doping content of 9.76% is obtained.

[0056] S2. Place the graphite material in a plasma cleaner and use O2 as the cleaning gas to perform plasma modification treatment on the surface of the graphite material. The treatment power is 100W and the treatment time is 15min to obtain modified graphite.

[0057] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled at a mass ratio of 1:9. The ball milling speed is set to 180 r / min and the milling time is 20 min to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 700℃ under Ar atmosphere for 4 h. After calcination, S-doped g-C3N4-coated modified graphite material is obtained, wherein the sulfur content of the material is 0.98% and the coating thickness is 15 nm.

[0058] Example 3:

[0059] This embodiment provides a method for preparing S-doped g-C3N4 coated modified graphite material, including the following steps:

[0060] S1. Melamine and thiourea are ground and mixed at a molar ratio of 1:1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated under continuous Ar protective gas. The heat treatment temperature is 500℃ and the heat treatment time is 5 hours. Through the above operation, Sg-C3N4 with a theoretical sulfur doping content of 15.84% is obtained.

[0061] S2. Place the graphite material in a plasma cleaner and use O2 as the cleaning gas to perform plasma modification treatment on the surface of the graphite material. The treatment power is 100W and the treatment time is 10min to obtain modified graphite.

[0062] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled at a mass ratio of 1:9. The ball milling speed is set to 180 r / min and the milling time is 20 min to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 700℃ under Ar atmosphere for 4 h. After calcination, S-doped g-C3N4-coated modified graphite material is obtained, wherein the sulfur content of the material is 1.58% and the coating thickness is 15 nm.

[0063] Example 4:

[0064] This embodiment provides a method for preparing S-doped g-C3N4 coated modified graphite material, including the following steps:

[0065] S1. Melamine and thiourea are ground and mixed at a molar ratio of 2:1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated under continuous Ar protective gas. The heat treatment temperature is 450℃ and the heat treatment time is 6 hours. Through the above operation, Sg-C3N4 with a theoretical sulfur doping content of 9.76% is obtained.

[0066] S2. Place the graphite material in a plasma cleaner and use O2 as the cleaning gas to perform plasma modification treatment on the surface of the graphite material. The treatment power is 100W and the treatment time is 10min to obtain modified graphite.

[0067] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled at a mass ratio of 1:9. The ball milling speed is set to 180 r / min and the milling time is 20 min to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 800℃ under Ar atmosphere for 5 h. After calcination, S-doped g-C3N4-coated modified graphite material is obtained, wherein the sulfur content of the material is 0.98% and the coating thickness is 8 nm.

[0068] Example 5:

[0069] This embodiment provides a method for preparing S-doped g-C3N4 coated modified graphite material, including the following steps:

[0070] S1. Urea and thiourea are ground and mixed at a molar ratio of 4:1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated under continuous Ar protective gas. The heat treatment temperature is 500℃ and the heat treatment time is 5 hours. Through the above operation, Sg-C3N4 with a theoretical sulfur doping content of 10.13% is obtained.

[0071] S2. Place the graphite material in a plasma cleaner and use H2 as the cleaning gas to perform plasma modification treatment on the surface of the graphite material. The treatment power is 100W and the treatment time is 10min to obtain modified graphite.

[0072] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled at a mass ratio of 1:9. The ball milling speed is set to 180 r / min and the milling time is 20 min to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 700℃ under Ar atmosphere for 4 h. After calcination, S-doped g-C3N4-coated modified graphite material is obtained, wherein the sulfur content of the material is 1.01% and the coating thickness is 10 nm.

[0073] Example 6:

[0074] This embodiment provides a method for preparing S-doped g-C3N4 coated modified graphite material, including the following steps:

[0075] S1. Melamine and thiourea are ground and mixed at a molar ratio of 2:1. After uniform mixing, the mixture is transferred to a tube furnace and heat-treated under continuous Ar protective gas. The heat treatment temperature is 500℃ and the heat treatment time is 5 hours. Through the above operation, Sg-C3N4 with a theoretical sulfur doping content of 9.76% is obtained.

[0076] S2. Place the graphite material in a plasma cleaner and use H2 as the cleaning gas to perform plasma modification treatment on the surface of the graphite material. The treatment power is 100W and the treatment time is 10min to obtain modified graphite.

[0077] S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are ball-milled at a mass ratio of 1:9. The ball milling speed is set to 180 r / min and the milling time is 20 min to obtain a mixture. The mixture is then transferred to a tube furnace and calcined at 700℃ under Ar atmosphere for 4 h. After calcination, S-doped g-C3N4-coated modified graphite material is obtained, wherein the sulfur content of the material is 0.98% and the coating thickness is 10 nm.

[0078] Comparative Example 1:

[0079] This comparative example provides a method for preparing a negative electrode material, which is carried out in accordance with the steps of Example 1, except that thiourea is not added in step S1, while the other steps and proportions remain unchanged, to obtain a negative electrode material, wherein the coating layer thickness is 4 nm.

[0080] Comparative Example 2:

[0081] This comparative example provides a method for preparing a negative electrode material, which is carried out in accordance with the steps of Example 1, except that: in step S2, the graphite is not subjected to plasma treatment, while the other steps and proportions remain unchanged, and a negative electrode material is obtained, wherein the coating layer thickness is 4 nm.

[0082] Comparative Example 3:

[0083] This comparative example provides a method for preparing a negative electrode material, which is carried out in accordance with the steps of Example 1, except that: in step S3, high-temperature calcination is not performed, only ball milling is performed, and the remaining steps and proportions remain unchanged to obtain a negative electrode material, wherein the coating layer thickness is 2 nm.

[0084] Comparative Example 4:

[0085] This comparative example provides a method for preparing a negative electrode material, which is carried out according to the steps of Example 1, except that: in step S2, the plasma treatment power is 150W and the treatment time is 1h, while the other steps and proportions remain unchanged, and a negative electrode material is obtained, wherein the coating layer thickness is 25 nm.

[0086] Comparative Example 5:

[0087] This comparative example provides a method for preparing a negative electrode material, which is carried out in accordance with the steps of Example 1, except that: in step S1, melamine and thiourea are in a molar ratio of 1:2.44, while the remaining steps and ratios remain unchanged, to obtain a negative electrode material, wherein the coating layer thickness is 22 nm.

[0088] Comparative Example 6:

[0089] This comparative example provides a method for preparing a negative electrode material, which is carried out in accordance with the steps of Example 1, except that: in step S1, the heat treatment temperature is 850℃ and the heat treatment time is 12 h, while the other steps and proportions remain unchanged, and a negative electrode material is obtained, wherein the coating layer thickness is 3 nm.

[0090] Comparative Example 7:

[0091] This comparative example provides a method for preparing a negative electrode material, which is carried out according to the steps of Example 1, except that: in step S3, the ball milling speed is 220 r / min and the ball milling time is 1 h, while the other steps and proportions remain unchanged, and a negative electrode material is obtained, wherein the coating layer thickness is 15 nm.

[0092] Comparative Example 8:

[0093] This comparative example provides a method for preparing a negative electrode material, which is carried out in accordance with the steps of Example 1, except that: in step S3, the high-temperature calcination temperature is 400°C and the calcination time is 20h, while the other steps and proportions remain unchanged, and a negative electrode material is obtained, wherein the coating layer thickness is 4nm.

[0094] The performance of the anode materials prepared in Examples 1-6 and Comparative Examples 1-8 was tested in the following details:

[0095] The negative electrode materials of Examples 1-6 and Comparative Examples 1-8 were used to fabricate electrodes, and 2032 coin cells were assembled for electrochemical testing. The electrochemical testing was carried out according to the following steps:

[0096] The test material was mixed evenly according to the mass ratio of negative electrode material: conductive agent (Super P): binder (LA133) = 94 : 3 : 3. Water was used as solvent to form a slurry, which was coated on copper foil with a coating thickness of 200 μm and dried in a vacuum oven at 80°C for 12 h to obtain the negative electrode sheet.

[0097] CR2032 button cells were assembled in a glove box (water and oxygen concentrations were both less than 0.01 ppm, manufactured by Shanghai MICARONA Electromechanical Technology Co., Ltd.). Lithium foil was used as the counter electrode, and the electrolyte was a mixed solution of LiPF6 dissolved in DMC (dimethyl carbonate), DEC (diethyl carbonate), and EC (ethylene carbonate) (DMC:DEC:EC volume ratio of 1:1:1), with a concentration of 1 mol / L.

[0098] The coin cells assembled using the negative electrode materials from Examples 1-6 and Comparative Examples 1-8 were subjected to charge-discharge cycle tests and rate tests at 0.1C / 0.3C / 0.5C / 1C / 3C / 5C on a Landian system (manufacturer: Wuhan Landian Electronics Co., Ltd., model CT3002A). The results of the charge-discharge cycle tests are as follows: Figure 1 As shown, the initial charge-discharge curves are as follows: Figure 2 As shown, the relevant data is recorded in Table 1; the results of the magnification test are as follows. Figure 4 As shown.

[0099] AC impedance spectroscopy was performed on the negative electrode materials provided in Examples 1-6 and Comparative Examples 1-8 using a CHI660E electrochemical workstation (manufactured by Shanghai Chenhua Instrument Co., Ltd.) under standard testing conditions. The obtained AC impedance spectra are shown below. Figure 3 As shown.

[0100] The contact angles between the negative electrode materials and the LiPF6 electrolyte provided in Examples 1-6 and Comparative Examples 1-8 were tested. The specific test steps are as follows:

[0101] A suitable amount of negative electrode material sample was weighed and placed in a mold, and then pressed to form a tablet sample. Next, 10 μL of electrolyte was dropped onto the surface of the tablet sample. Simultaneously, a contact angle measuring instrument (manufactured by Kunshan Beidou Precision Instruments Co., Ltd., model CA200) was used to photograph the profile of the droplet side and automatically record the values. To ensure the reliability of the test results, each tablet sample was measured five times at different locations, and the average value was calculated. The data are summarized in Table 1.

[0102] Table 1. Comparison of electrochemical performance and contact angle test results between Examples 1-6 and Comparative Examples 1-8

[0103] As shown in Table 1, the electrochemical test results show that, compared with Comparative Examples 1-8, the S-doped g-C3N4-coated modified graphite materials prepared in Examples 1-6 have improved first-cycle charge specific capacity and first-cycle coulombic efficiency, and their capacity retention after 100 cycles has been significantly improved. As shown in Table 1, the contact angle test results show that, compared with Comparative Examples 1-8, the S-doped g-C3N4-coated modified graphite materials prepared in Examples 1-6 have a lower contact angle with the electrolyte, indicating that the electrolyte has a better wetting effect on them, which is beneficial to the rapid charge transport.

[0104] Depend on Figure 1 It can be seen that the cycle performance of the modified samples in Examples 1-6 was significantly improved;

[0105] Depend on Figure 2 It can be seen that Examples 1-6 all exhibit a clear voltage plateau at around 0.2 V. This plateau corresponds to the lithium ion insertion-extraction movement, indicating that the modified samples retain the characteristics of graphite's low lithium insertion potential and good voltage plateau.

[0106] The significant improvement in cycle performance is attributed to the Sg-C3N4 coating layer's effective suppression of volume expansion and particle agglomeration of graphite materials during charge and discharge, thus maintaining the integrity of the electrode structure. Specifically, this coating layer effectively buffers the anisotropic expansion stress caused by lithium-ion insertion / extraction between graphite layers, preventing excessive expansion of graphite particles that could lead to cracking and pulverization. Furthermore, its excellent mechanical flexibility and enhanced interfacial bonding strength with plasma-modified graphite allow it to tightly encapsulate graphite particles, effectively suppressing the migration and agglomeration of active material particles during cycling. This maintains the continuity of the conductive network and the stability of the electrode structure, thereby significantly suppressing capacity decay during cycling.

[0107] Depend on Figure 3 It can be seen that, compared with Comparative Examples 1-8, the charge transfer impedance of Examples 1-6 is significantly reduced. This is due to the result of multi-factor synergistic optimization in the technical solution of this invention:

[0108] 1) Sulfur doping effectively enhances the electronic conductivity of the g-C3N4 coating layer and optimizes its adsorption and migration ability for lithium ions, thereby significantly promoting charge transport in the bulk phase of the material.

[0109] 2) The active functional groups introduced on the graphite surface by plasma treatment significantly enhance the interfacial compatibility and bonding force between the graphite and the Sg-C3N4 coating layer, and effectively reduce the interfacial impedance.

[0110] 3) The inherent nitrogen-rich properties and polar functional groups of g-C3N4 significantly improve the wettability of the electrode / electrolyte interface, promote the full wetting of the electrolyte, and provide a more uniform and low-resistance interfacial transport channel for lithium ions.

[0111] The synergistic effect of the above three aspects effectively reduces charge transfer impedance, thereby promoting the migration kinetics of lithium ions at the electrode / electrolyte interface. Therefore, the S-doped g-C3N4-coated modified graphite anode material provided by this invention exhibits significantly improved rate performance, such as... Figure 4 As shown.

[0112] In summary, this invention, through an optimized strategy combining a sulfur-doped g-C3N4 coating layer with plasma-modified graphite substrate, effectively improves the electronic conductivity and lithium-ion migration capability of the material, significantly enhances the compatibility and adhesion of the graphite / coating layer interface, and strengthens the wettability of the electrode / electrolyte interface. Simultaneously, the coating layer effectively suppresses the volume expansion and particle agglomeration of graphite during cycling. These synergistic effects significantly reduce the charge transfer impedance of the electrode system, markedly enhance the structural stability of the electrode, and thus effectively improve the electrochemical performance of the lithium-ion battery.

Claims

1. A method for preparing an S-doped g-C3N4 coated modified graphite material, characterized in that, The method includes: S1. The g-C3N4 precursor and the sulfur source are mixed at a molar ratio of (1-20):1, and then heat-treated at 400-800℃ under a protective atmosphere to obtain sulfur-doped graphitic carbon nitride Sg-C3N4, wherein the sulfur doping amount is 5wt%-30wt% based on the sum of the mass of sulfur and g-C3N4 as 100%. S2. The surface of the graphite material is subjected to plasma modification treatment using plasma reactive gas to obtain modified graphite, wherein the power of the plasma modification treatment is 50-300W and the time is 5-30min. S3. The Sg-C3N4 prepared in step S1 and the modified graphite obtained in step S2 are mixed at a mass ratio of 1:(1-50) to obtain a mixture; the mixture is calcined at 500-1200℃ under a protective atmosphere to obtain S-doped g-C3N4 coated modified graphite material.

2. The method according to claim 1, characterized in that, The molar ratio of the g-C3N4 precursor to the sulfur source is (1-10):

1.

3. The method according to claim 1, characterized in that, The g-C3N4 precursor includes one or more of melamine, urea, and cyanamide.

4. The method according to claim 1, characterized in that, The sulfur source includes one or more of thiourea, trithiocyanate, and elemental sulfur.

5. The method according to claim 1, characterized in that, The heat treatment time in step S1 is 1-10 hours.

6. The method according to claim 5, characterized in that, The heat treatment temperature in step S1 is 400-600℃, and the heat treatment time is 3-8h.

7. The method according to claim 1, characterized in that, The sulfur doping amount in step S1 is 5%-20%.

8. The method according to claim 1, characterized in that, The graphite material is natural spherical graphite, and the purity of the graphite material is >99%.

9. The method according to claim 1, characterized in that, The plasma reaction gas includes one or more of O2, Ar, H2, N2, Ar / H2, and Ar / O2.

10. The method according to claim 1, characterized in that, The mixing process of S3 is carried out by ball milling, with a ball milling speed of 100-200 r / min and a ball milling time of 5-30 min.

11. The method according to claim 1, characterized in that, The mass ratio of Sg-C3N4 to modified graphite is 1:(1-25).

12. The method according to claim 1, characterized in that, The calcination time in step S3 is 1-15 hours.

13. The method according to claim 12, characterized in that, The calcination temperature in step S3 is 600-1000℃, and the time is 3-10h.

14. An S-doped g-C3N4-coated modified graphite anode material, characterized in that, The negative electrode material is prepared by the method described in any one of claims 1-13.

15. The S-doped g-C3N4-coated modified graphite anode material according to claim 14, characterized in that, The thickness of the S-doped g-C3N4 coating layer is 5-20 nm.

16. The S-doped g-C3N4-coated modified graphite anode material according to claim 15, characterized in that, The thickness of the S-doped g-C3N4 coating layer is 8-15 nm.

17. The S-doped g-C3N4-coated modified graphite anode material according to claim 1, characterized in that, The S-doping content in the S-doped g-C3N4 coated modified graphite material is 0.1%-10%.

18. The S-doped g-C3N4-coated modified graphite anode material according to claim 17, characterized in that, The S-doping content in the S-doped g-C3N4 coated modified graphite material is 0.1%-5%.

19. A lithium-ion battery negative electrode, characterized in that, The lithium-ion battery anode is prepared from the S-doped g-C3N4 coated modified graphite anode material as described in any one of claims 14-18.

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