Fast-charging graphite composite material, preparation method thereof and lithium ion battery

Abstract

The invention discloses a fast-charging graphite composite material, a preparation method thereof and a lithium ion battery, and relates to the technical field of battery preparation, the preparation method of the fast-charging graphite composite material comprises the following steps: S1, mixing artificial graphite, an intercalator, an oxidant and water, and carrying out a hydrothermal reaction to obtain modified graphite; s2, in the atmosphere of sulfur source gas, performing sulfur doping reaction on the modified graphite to obtain sulfur-doped modified graphite; s3, providing a coating liquid, wherein the coating liquid comprises resin, an inorganic carbon conductive agent and an organic solvent; and S4, mixing the coating liquid with the sulfur-doped modified graphite, and sequentially performing first carbonization treatment and second carbonization treatment in an inert atmosphere to obtain the fast-charging graphite composite material. The fast-charging graphite composite material prepared by the method disclosed by the invention has relatively good fast-charging performance and cycle performance.

Description

A fast-charging graphite composite material, its preparation method, and a lithium-ion battery Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a fast-charging graphite composite material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Graphite is widely used as the negative electrode active material in lithium-ion batteries. However, with the increasing demand for high-rate fast charging performance in the fields of electric vehicles and consumer electronics, traditional graphite negative electrodes have exposed problems such as slow lithium-ion diffusion kinetics, easy lithium deposition, and significant volume expansion under high-current charge and discharge conditions, making it difficult to balance fast charging capability and long-cycle stability.

[0003] Currently, the main strategies for improving the fast charging performance of graphite anodes include surface coating and bulk doping, which enhance the fast charging performance by increasing the diffusion rate of lithium ions during charging and discharging.

[0004] However, although coating the surface of graphite anode active material with solid electrolyte material can improve ionic conductivity, it does not improve the electronic or ionic conductivity of the material core. Therefore, although coating the surface of solid electrolyte material improves the fast-charging performance of graphite anode active material, the improvement is not significant and does not improve cycle performance. Summary of the Invention

[0005] The main objective of this invention is to propose a fast-charging graphite composite material, its preparation method, and a lithium-ion battery, aiming to solve the problem that existing lithium-ion battery anode materials are difficult to simultaneously possess good fast-charging performance and cycle performance.

[0006] To achieve the above objectives, the present invention provides a method for preparing a fast-charging graphite composite material, the method comprising the following steps:

[0007] S1. Artificial graphite, intercalating agent, oxidant and water are mixed and subjected to a hydrothermal reaction to obtain modified graphite; S2. Under the atmosphere of sulfur source gas, the modified graphite is subjected to a sulfur doping reaction to obtain sulfur-doped modified graphite; S3. A coating liquid is provided, the coating liquid comprising resin, inorganic carbon conductive agent and organic solvent; S4. The coating liquid and the sulfur-doped modified graphite are mixed and subjected to a first carbonization treatment and a second carbonization treatment in sequence under an inert atmosphere to obtain the fast-charging graphite composite material.

[0008] In one embodiment, in step S3, the coating solution further includes a lithium sulfonate derivative.

[0009] In one embodiment, in step S3, the coating solution further includes a molybdate compound.

[0010] In one embodiment, in step S1, the intercalating agent includes at least one of formic acid, acetic acid, and propionic acid; and / or, in step S1, the oxidizing agent includes at least one of hydrogen peroxide, potassium permanganate, and perchloric acid; and / or, in step S1, the mass ratio of the artificial graphite, the intercalating agent, and the oxidizing agent is 100:30-60:30-60; and / or, in step S1, the temperature of the hydrothermal reaction is 100-200℃; and / or, in step S1, the time of the hydrothermal reaction is 1-6h; and / or, in step S2, the sulfur source gas includes at least one of thiol, benzene disulfide, and dipropanol trisulfide; and / or, in step S2, the gas input flow rate of the sulfur source gas is 10-100mL / min; and / or, in step S2, the temperature of the sulfur doping reaction is 500-800℃; and / or, in step S2, the time of the sulfur doping reaction is 30-300min.

[0011] In one embodiment, the coating solution further includes a lithium sulfonate derivative and a molybdate compound: in step S3, the mass ratio of the resin, the molybdate compound, the lithium sulfonate derivative, and the inorganic carbon conductive agent is 100:5-15:1-5:1-3; and / or, in step S3, the mass concentration of the coating solution is 1-5 wt%; and / or, in step S3, the resin includes at least one of hydroxyl acrylic resin, alkyd resin, and unsaturated polyester resin; and / or, in step S3, the molybdate compound includes at least one of ammonium molybdate, sodium molybdate, diammonium molybdate, tetrathioammonium molybdate, tetraammonium molybdate, phosphomolybdic acid, calcium molybdate, and zinc molybdate; and / or Alternatively, in step S3, the lithium sulfonate derivative includes at least one of lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, lithium perfluorohexane sulfonate, lithium 4-methylbenzenesulfonate, and lithium dioxane sulfonate; and / or, in step S4, the mass ratio of the coating solution to the sulfur-doped modified graphite is 100-200:100; and / or, in step S4, the temperature of the first carbonization treatment is 400-600℃; and / or, in step S4, the time of the first carbonization treatment is 1-6h; and / or, in step S4, the temperature of the second carbonization treatment is 1000-1300℃; and / or, in step S4, the time of the second carbonization treatment is 1-6h.

[0012] The present invention also provides a fast-charging graphite composite material, which is prepared by the aforementioned method for preparing fast-charging graphite composite materials; the fast-charging graphite composite material includes a core material and a shell material; the core material includes modified graphite and sulfur atoms doped in the modified graphite, the modified graphite has a multilayer structure, and the interlayer of the modified graphite is modified with oxygen-containing functional groups; the shell material at least partially covers the core material, and the shell material includes amorphous carbon and an inorganic carbon conductive agent.

[0013] In one embodiment, the housing material further includes LiMo. X P Y Q Z Where 0 < X ​​< 2, Y > 0, Z > 0, P represents sulfur, and Q represents oxygen.

[0014] In one embodiment, the shell material further includes molybdenum oxide.

[0015] In one embodiment, the oxygen-containing functional group includes at least one of carboxyl and hydroxyl groups; and / or, the inorganic carbon conductive agent includes at least one of carbon nanotubes, carbon fibers, graphene, and hollow carbon spheres.

[0016] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery comprises a fast-charging graphite composite material prepared by the aforementioned fast-charging graphite composite material preparation method or the aforementioned fast-charging graphite composite material.

[0017] In the technical solution of this invention, artificial graphite is oxidized and expanded using oxidants and dopants to increase the interlayer spacing and surface reactive sites, thereby improving the lithium-ion insertion / extraction rate during charging and discharging and thus enhancing the material's fast-charging performance. Subsequently, sulfur source gas doping is used to improve the material's electronic conductivity, improve rate performance, reduce expansion, and enhance cycle performance. The fast-charging graphite composite material provided in this application possesses both good fast-charging and cycle performance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 is a scanning electron microscope image of the fast-charging graphite composite material prepared in Example 1 of the present invention.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Graphite is widely used as the negative electrode active material in lithium-ion batteries. However, with the increasing demand for high-rate fast charging performance in the fields of electric vehicles and consumer electronics, traditional graphite negative electrodes have exposed problems such as slow lithium-ion diffusion kinetics, easy lithium deposition, and significant volume expansion under high-current charge and discharge conditions, making it difficult to balance fast charging capability and long-cycle stability.

[0023] Currently, the main strategies for improving the fast-charging performance of graphite anodes include surface coating and bulk doping, which improve fast-charging performance by increasing the diffusion rate of lithium ions during charging and discharging.

[0024] However, although coating the surface of graphite anode active material with solid electrolyte material can improve ionic conductivity, it does not improve the electronic or ionic conductivity of the material core. Therefore, although coating the surface of solid electrolyte material improves the fast-charging performance of graphite anode active material, the improvement is not significant and does not improve cycle performance.

[0025] In view of this, the present invention provides a method for preparing a fast-charging graphite composite material, the method comprising the following steps: Step S1, mixing artificial graphite, intercalating agent, oxidant and water, and performing a hydrothermal reaction to obtain modified graphite; Step S2, performing a sulfur doping reaction on the modified graphite under a sulfur source gas atmosphere to obtain sulfur-doped modified graphite; Step S3, providing a coating liquid, the coating liquid comprising resin, inorganic carbon conductive agent and organic solvent; Step S4, mixing the coating liquid and the sulfur-doped modified graphite, and performing a first carbonization treatment and a second carbonization treatment sequentially under an inert atmosphere to obtain the fast-charging graphite composite material.

[0026] In the technical solution of this invention, in step S1, during the hydrothermal reaction, the oxidant and the intercalating agent work simultaneously. On the one hand, the oxidant generates highly active ·OH free radicals under hydrothermal reaction conditions. These free radicals attack the edge and defect sites of the artificial graphite. Furthermore, these free radicals can enhance the dissociation of ions (such as H+) generated by the intercalating agent. + HCOO - The intercalating agent's ability to diffuse into the graphite interlayer allows ions to be inserted into the graphite interlayer with the assistance of the oxidant, thereby introducing oxygen-containing functional groups into the graphite interlayer and even its surface, slightly widening the interlayer spacing to obtain modified graphite. This method can retain the main structure of graphite, and the defective and edge parts, after being attacked by free radicals generated by the oxidant, form surface active sites, which facilitate subsequent sulfur doping. In step S2, at the sulfur doping reaction temperature, the sulfur source will pyrolyze to generate active sulfur species (·S, H2S), which then react with the modified graphite, and sulfur atoms are incorporated into the modified graphite in the form of sulfides (-CSC-). Since sulfur is an electron donor, the lattice or edge of graphite can increase the charge carrier capacity of the material. In addition, the atomic radius of sulfur is larger than that of carbon, which can slightly increase the interlayer spacing of graphite, thus obtaining sulfur-doped modified graphite. In step S3, an organic solvent is used as a solvent, and resin and inorganic carbon conductive agent are used as solutes to prepare a coating solution. In step S4, the coating solution and sulfur-doped modified graphite are mixed and subjected to two-step carbonization. The temperature of the first carbonization treatment is lower than that of the second carbonization treatment. During the two-step carbonization process, the resin and organic solvent form amorphous carbon, which together with the inorganic carbon conductive agent constitutes a coating layer, forming a dense, conductive, and stable shell material.

[0027] It should be noted that the present invention uses oxidants and dopants to oxidize and expand the artificial graphite, thereby increasing the interlayer spacing of the artificial graphite and increasing the reactive sites on its surface, thus improving the lithium ion insertion and extraction rate during charging and discharging, thereby improving the fast charging performance of the material; subsequently, sulfur source gas is used to dope the material to improve the electronic conductivity, improve the rate performance and reduce its expansion, thereby improving the cycle performance.

[0028] In some embodiments, in step S3, the coating solution further includes a lithium sulfonate derivative. In this case, in step S4, the lithium sulfonate derivative reacts with the molybdate compound during a two-step carbonization process to generate a lithium molybdate derivative, ultimately forming the lithium molybdate compound LiMo. X P Y Q Z In this composition, 0 < X ​​< 2, Y > 0, Z > 0, P represents sulfur, and Q represents oxygen. This composition has a high ionic conductivity.

[0029] In some embodiments, in step S3, the coating solution further includes a molybdate compound. In this case, in step S4, part of the molybdate compound reacts with a lithium sulfonate derivative during the two-step carbonization process to form a lithium molybdate compound to improve ionic conductivity; the other part decomposes into molybdenum oxide.

[0030] In some embodiments, in step S3, the coating liquid may also include lithium sulfonate derivatives and molybdate compounds. After two-step carbonization treatment, the two can be converted into lithium molybdate compounds with high ionic conductivity to improve ionic conductivity and structural stability of the composite material. At the same time, excess molybdenum compounds form molybdenum oxide after carbonization, which improves the ion diffusion coefficient and solvation ability of the material. In addition, inorganic carbon conductive agents have good electronic conductivity. The three, together with amorphous carbon, constitute the shell material and synergistically improve the fast charging performance of the material.

[0031] In some embodiments, in step S1, the intercalating agent includes at least one of formic acid, acetic acid, and propionic acid. That is, the intercalating agent can be any one of formic acid, acetic acid, and propionic acid, or two or more of these acids, all within the scope of this invention. The above-mentioned intercalating agent can be pre-mixed with water to form an aqueous solution of the intercalating agent, the concentration of which is 10-30 wt%. Under hydrothermal reaction conditions, the above-mentioned intercalating agent can rapidly dissociate to generate intercalated ions (such as H+). + HCOO - ).

[0032] In some embodiments, in step S1, the oxidant includes at least one of hydrogen peroxide, potassium permanganate, and perchloric acid. That is, the oxidant can be any one of hydrogen peroxide, potassium permanganate, and perchloric acid, or two or more of these three substances, all within the scope of this invention. The above-mentioned oxidants have strong oxidizing properties and can rapidly generate highly active ·OH free radicals under hydrothermal reaction conditions. The above-mentioned oxidants can be pre-mixed with water to form an aqueous oxidant solution, wherein the concentration of the oxidant in the aqueous oxidant solution is 10-30 wt%.

[0033] In some embodiments, in step S1, the mass ratio of the artificial graphite, the intercalating agent, and the oxidizing agent is 100:30-60:30-60. The mass ratio of the aqueous solution of the artificial graphite, the intercalating agent, and the oxidizing agent can be 100:50:50, 100:30:60, or 100:60:30. A mass ratio within the above range can ensure that the interlayer spacing of the artificial graphite is moderately increased, the orientation index is reduced, and more oxygen-containing functional groups such as hydroxyl or carboxyl groups are inserted into the interlayer.

[0034] In some embodiments, in step S1, the temperature of the hydrothermal reaction is 100-200°C; and / or, in step S1, the time of the hydrothermal reaction is 1-6 hours. It is understood that the temperature of the hydrothermal reaction can be 100°C, 150°C, or 200°C, and the time of the hydrothermal reaction can be 1 hour, 3 hours, or 6 hours. Controlling the temperature and time of the hydrothermal reaction within the above ranges can ensure a better intercalation effect, and moderately increase the interlayer spacing of the artificial graphite while reducing the orientation index.

[0035] In some embodiments, in step S2, the sulfur source gas includes at least one of thiols, ammonium persulfate, benzene disulfide, and dipropanol trisulfide; and / or, in step S2, the gas input flow rate of the sulfur source gas is 10-100 mL / min; and / or, in step S2, the temperature of the sulfur doping reaction is 500-800 °C; and / or, in step S2, the time of the sulfur doping reaction is 30-300 min. That is, the sulfur source gas may include any one of thiols, benzene disulfide, and dipropanol trisulfide, or two or more of these substances, all within the scope of this invention. The aforementioned thiols can rapidly generate active sulfur species under sulfur doping reaction conditions. Simultaneously controlling the gas input flow rate of the sulfur source gas, the temperature of the sulfur doping reaction, and the time of the sulfur doping reaction can ensure relatively uniform sulfur doping in the modified graphite.

[0036] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: In step S3, the mass ratio of the resin, the molybdate compound, the lithium sulfonate derivative, and the inorganic carbon conductive agent is 100:5-15:1-5:1-3. The mass ratio of the resin, molybdate compound, lithium sulfonate derivative, and inorganic carbon conductive agent can be 100:5:1:1, 100:10:3:2, or 100:15:5:3. Excess molybdate compound can be converted into lithium molybdate compound and molybdenum oxide during the reaction. At the same time, the mass ratio within the above range can ensure that the proportion of amorphous carbon, molybdenum oxide, lithium molybdate compound, and inorganic carbon conductive agent in the final shell material is appropriate, which can synergistically improve the electronic conductivity, ionic conductivity, and fast charging performance of the material.

[0037] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: in step S3, the mass concentration of the coating solution is 1-5 wt%. The mass concentration of the coating solution can be 1 wt%, 3 wt%, or 5 wt%, and a mass ratio within the above range can ensure a good improvement in the electronic conductivity and ionic conductivity of the shell material.

[0038] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: In step S3, the resin includes at least one of hydroxyl acrylic resin, alkyd resin, and unsaturated polyester resin. That is, the resin can be any one of hydroxyl acrylic resin, alkyd resin, and unsaturated polyester resin, or two or more of hydroxyl acrylic resin, alkyd resin, and unsaturated polyester resin, all of which are within the scope of protection of this invention. The above-mentioned resin can form amorphous carbon in the two-step carbonization process, protecting the core material.

[0039] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: In step S3, the molybdate compound includes at least one of ammonium molybdate, sodium molybdate, diammonium molybdate, tetrathioammonium molybdate, tetraammonium molybdate, phosphomolybdic acid, calcium molybdate, and zinc molybdate. That is, the molybdate compound can be any one of ammonium molybdate, sodium molybdate, diammonium molybdate, tetrathioammonium molybdate, tetraammonium molybdate, phosphomolybdic acid, calcium molybdate, and zinc molybdate, or two or more of these compounds, all within the scope of this invention. All of the above molybdate compounds can react with lithium sulfonate derivatives to form lithium molybdate compounds or can form molybdenum oxide during the two-step carbonization process.

[0040] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: In step S3, the lithium sulfonate derivative includes at least one of lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, lithium perfluorohexane sulfonate, lithium 4-methylbenzenesulfonate, and lithium dioxane sulfonate. That is, the lithium sulfonate derivative can be any one of lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, lithium perfluorohexane sulfonate, lithium 4-methylbenzenesulfonate, and lithium dioxane sulfonate, or two or more of these compounds, all within the scope of this invention. The above-mentioned lithium sulfonate derivatives readily react with molybdate compounds to form lithium molybdate compounds, thereby improving the ion diffusion coefficient and structural stability.

[0041] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: In step S4, the mass ratio of the coating solution to the sulfur-doped modified graphite is 100-200:100. The mass ratio of the coating solution to the sulfur-doped modified graphite can be 100:100, 100:150, or 100:200. A mass ratio within the above range ensures that the proportion of the shell material is not too high, thereby affecting the proportion of the active material.

[0042] In some embodiments, the coating solution further includes lithium sulfonate derivatives and molybdate compounds: in step S4, the temperature of the first carbonization treatment is 400-600°C; and / or, in step S4, the time of the first carbonization treatment is 1-6 hours; and / or, in step S4, the temperature of the second carbonization treatment is 1000-1300°C; and / or, in step S4, the time of the second carbonization treatment is 1-6 hours. That is, the temperature of the first carbonization treatment can be 400°C, 500°C, or 600°C, and the time of the first carbonization treatment can be 1 hour, 4 hours, or 6 hours; the temperature of the second carbonization treatment can be 1000°C, 1200°C, or 1300°C, and the time of the second carbonization treatment can be 1 hour, 4 hours, or 6 hours. Controlling the conditions of the first and second carbonization treatments within the above ranges ensures that the substances in the coating solution are well carbonized.

[0043] The present invention also provides a fast-charging graphite composite material, the fast-charging graphite composite material comprising a core material and a shell material; the core material comprising modified graphite and sulfur atoms doped in the modified graphite, the modified graphite having a multilayer structure, and the interlayer of the modified graphite being modified with oxygen-containing functional groups; the shell material at least partially covers the core material, the shell material comprising amorphous carbon and an inorganic carbon conductive agent.

[0044] In the technical solution of this invention, the oxygen-containing functional group-modified graphite has a larger interlayer spacing and lower powder orientation, which facilitates the insertion and extraction of lithium ions during charging and discharging, improves the lithium ion diffusion rate in the core material, and thus improves the fast-charging performance of the material. Furthermore, sulfur-doped modified graphite further improves the electronic conductivity of the material, enhances its rate performance, and reduces the expansion rate during multiple cycles. Therefore, the fast-charging graphite composite material provided in this application possesses both good fast-charging performance and good cycle performance.

[0045] It is understandable that modified graphite can be modified with oxygen-containing functional groups in the interlayer, or it can be modified with oxygen-containing functional groups in both the interlayer and its surface. Oxygen-containing functional groups include hydroxyl groups, carboxyl groups, etc. Compared with artificial graphite, modified graphite has a lower powder orientation index and a smaller expansion rate during cycling.

[0046] In some embodiments, the housing material further includes LiMo. X P Y Q Z Where 0 < X ​​< 2, Y > 0, Z > 0. LiMo X P Y Q ZP represents sulfur and Q represents oxygen. Its high ionic conductivity can further improve the lithium-ion diffusion coefficient of fast-charging graphite composite materials, thereby improving the fast-charging performance of fast-charging graphite composite materials. At the same time, it can reduce the full-charge expansion of fast-charging graphite composite materials, thereby improving the cycle performance of fast-charging graphite composite materials.

[0047] In some embodiments, the shell material further includes molybdenum oxide. Molybdenum oxide (MoO3) has strong Lewis acid sites on its surface, which can adsorb and weaken Li. + - Solvent interaction, accelerating Li + Desolvation promotes the interfacial desolvation process, thereby significantly improving the fast-charging performance of the material.

[0048] In some embodiments, the housing material may also include LiMo. X P Y Q Z Improving the lithium-ion diffusion rate of materials can also synergistically reduce the material's full-charge expansion and powder orientation index.

[0049] In some embodiments, the inorganic carbon conductive agent includes at least one of carbon nanotubes, carbon fibers, graphene, and hollow carbon spheres. That is, the inorganic carbon conductive agent can be any one of carbon nanotubes, carbon fibers, graphene, and hollow carbon spheres, or two or more of these materials, all within the scope of this invention. The aforementioned inorganic carbon conductive agents have high conductivity.

[0050] This invention also provides a lithium-ion battery comprising the aforementioned fast-charging graphite composite material or the fast-charging graphite composite material prepared by the aforementioned method. Therefore, it possesses all the beneficial effects of the aforementioned fast-charging graphite composite material or its preparation method, which will not be elaborated upon here.

[0051] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0052] Example 1: A fast-charging graphite composite material, comprising the following steps: Step S1: 100g of artificial graphite is added to 300g of an aqueous solution of 20wt% formic acid and 300g of an aqueous solution of 20wt% hydrogen peroxide, and transferred to a high-pressure reactor at 150℃ for 3h. After filtration, washing with water, and vacuum drying at 80℃ for 48h, modified graphite is obtained; Step S2: The modified graphite is transferred to a tube furnace and thiol gas is introduced at 650℃ and a flow rate of 50mL / min for 150min to obtain heteroatom-doped modified graphite; Step S3: 100g of hydroxyl acrylic resin is dissolved in 3000g of chloroform organic... A 3wt% solution was prepared in a solvent, and then 10g of ammonium molybdate, 3g of lithium trifluoromethanesulfonate, and 3g of carbon nanotubes were added and dispersed evenly to obtain a coating solution. Step S4: 150g of the coating solution and 100g of heteroatom-doped modified graphite were added to a mixer, heated to 500℃ and held for 3h under an argon inert atmosphere, then heated to 1200℃ and held for 3h, and then cooled to room temperature under an argon inert atmosphere to obtain a fast-charging graphite composite material.

[0053] Example 2: A method for preparing a fast-charging graphite composite material, comprising the following steps: Step S1: Add 100g of artificial graphite to 100g of an aqueous solution of 30wt% acetic acid and 100g of an aqueous solution of 30wt% potassium permanganate, and transfer to a high-pressure reactor to react at 100℃ for 6h. Filter, wash with water, and vacuum dry at 80℃ for 48h to obtain modified graphite; Step S2: Transfer the modified graphite to a tube furnace and introduce benzene disulfide gas at 500℃ and a flow rate of 10mL / min for 300min to obtain heteroatom-doped modified graphite; Step S3: Dissolve 100g of alkyd resin in 10000g of chloroform. A 1 wt% solution was prepared in an organic solvent, and then 5 g of ammonium dimolybdate, 1 g of lithium perfluorobutyl sulfonate, and 1 g of carbon fiber were added and dispersed evenly to obtain a coating solution. Step S4: 100 g of coating solution and 100 g of heteroatom-doped modified graphite were added to a mixer, heated to 400 °C and held for 6 h under an argon inert atmosphere, then heated to 1000 °C and held for 6 h, and then cooled to room temperature under an argon inert atmosphere to obtain a fast-charging graphite composite material.

[0054] Example 3: A method for preparing a fast-charging graphite composite material, comprising the following steps: Step S1: Add 100g of artificial graphite to 500g of an aqueous solution of 10wt% propionic acid and 500g of an aqueous solution of 10wt% perchloric acid, and transfer to a high-pressure reactor to react at 200℃ for 1h. Filter, wash with water, and vacuum dry at 80℃ for 48h to obtain modified graphite; Step S2: Transfer the modified graphite to a tube furnace and introduce dipropanol trisulfide gas at 800℃ and a flow rate of 100mL / min for 30min to obtain heteroatom-doped modified graphite; Step S3: Dissolve 100g of unsaturated polyester resin in 2000g of chloroform organic... A 5 wt% solution was prepared in a solvent, and then 15 g of ammonium tetrathiomolybdate, 5 g of lithium perfluorohexanesulfonate, and 3 g of graphene conductive agent were added and dispersed evenly to obtain a coating solution. Step S4: 100 g of coating solution and 100 g of heteroatom-doped modified graphite were added to a mixer, heated to 600 °C and held for 1 h under an argon inert atmosphere, then heated to 1300 °C and held for 1 h, and then cooled to room temperature under an argon inert atmosphere to obtain a fast-charging graphite composite material.

[0055] Example 4 differs from Example 1 in that ammonium molybdate and lithium trifluoromethanesulfonate are not added in step S3.

[0056] Example 5 differs from Example 1 in that ammonium molybdate is not added in step S3, while the rest is the same as in Example 1.

[0057] Example 6 differs from Example 1 in that lithium trifluoromethanesulfonate is not added in step S3, while the rest is the same as in Example 1.

[0058] Comparative Example 1 differs from Example 4 in that step S1 is omitted, and the modified graphite in step S2 is replaced with artificial graphite; otherwise, it is the same as Example 4.

[0059] Performance Test 1. Scanning Electron Microscopy (SEM) The fast-charging graphite composite material prepared in Example 1 was subjected to scanning electron microscopy (SEM) testing, and the results are shown in Figure 1.

[0060] As can be seen from Figure 1, the obtained composite material exhibits a secondary granular structure with a particle size between 8 and 12 μm and a uniform size distribution.

[0061] II. Physicochemical Properties and Button Cell Testing Following the methods specified in GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries", the specific surface area and tap density of the graphite composite materials prepared in Examples 1-6 and Comparative Example 1 were tested; the powder OI value of the graphite composite materials prepared in Examples 1-6 and Comparative Example 1 was tested using an XRD diffractometer. The test results are shown in Table 1.

[0062] Table 1. Performance characterization of the graphite composite materials prepared in Examples 1-6 and Comparative Example 1.

[0063] The fast-charging graphite composite materials prepared in each embodiment and comparative example were assembled into coin cells, including: adding a binder, a conductive agent, and a solvent to the fast-charging graphite composite material, stirring and mixing evenly to prepare a negative electrode slurry, coating the negative electrode slurry onto copper foil, drying, rolling, and cutting to obtain a negative electrode sheet. The binder was LA133 binder, the conductive agent was SP conductive agent, and the solvent was double-distilled water, with a weight ratio of fast-charging graphite composite material, SP conductive agent, LA133 binder, and double-distilled water of 95:1:4:220. Using a lithium metal sheet as the counter electrode, polyethylene propylene (PEP) as the separator, and LiPF6 (LiPF6 concentration of 1.1 mol / L) and solvent (EC+DEC, with a volume ratio of EC to DEC of 1:1, EC referring to ethylene carbonate and DEC referring to diethyl carbonate) as the electrolyte, the battery assembly was carried out in an argon-filled glove box.

[0064] The fabricated button cells were installed on a Landian CT2001A battery tester and charged and discharged at a rate of 0.1C, with a charging and discharging voltage range of 0.005V to 2.0V. The initial discharge capacity and initial discharge efficiency were measured. The 2C rate discharge capacity was tested, and the rate performance (2C / 0.1C) was calculated. The diffusion coefficient of the fast-charging graphite composite material was tested using GITT (giant current intermittent titration), and the OI value of its electrodes was measured using X-ray diffraction (XRD). 004 / I 002 , where I 004 and I 002 These represent the diffraction intensities of the corresponding crystal planes.

[0065] Full charge expansion test method: First, test the thickness of the electrode sheet after rolling and measure it as D1. Then, fully charge the button cell to 100% SOC. After that, dissect and test the thickness of the negative electrode sheet in the fully charged state as D2, and calculate the full charge expansion = (D2-D1) / D1×100%.

[0066] The test results are shown in Table 2.

[0067] Table 2 Performance characterization of coin cells corresponding to Examples 1-6 and Comparative Example 1

[0068] As can be seen from Table 2, the discharge specific capacity, initial efficiency, full charge expansion and rate performance of the electrode composite materials prepared in each embodiment of the present invention are significantly better than those of the comparative example.

[0069] Compared with Comparative Example 1, in Example 4, replacing artificial graphite with modified graphite increased the diffusion coefficient of the material and reduced the full-charge expansion.

[0070] A comparison of Examples 1, 4, 5, and 6 revealed the following: In Example 4, without the addition of ammonium molybdate and lithium trifluoromethanesulfonate to the coating solution, the battery prepared from the graphite composite material exhibited a high expansion rate and a low ion diffusion rate. In Example 6, adding ammonium molybdate alone or lithium trifluoromethanesulfonate alone to the coating solution (Example 5) did not significantly change the expansion rate of the graphite composite material, but the ion diffusion rate improved. In Example 1, the simultaneous addition of ammonium molybdate and lithium trifluoromethanesulfonate synergistically improved the expansion performance and ion diffusion rate of the graphite composite material. This may be due to the presence of LiMo in the final fast-charging graphite composite material. X P Y Q Z As a fast ion conductor, it can improve the ion diffusion coefficient, and molybdenum oxide has a high solvation ability, which can improve the ion diffusion rate, ultimately improving the charge and discharge efficiency and rate performance of the material.

[0071] III. Soft-pack battery testing: Negative electrode sheets were prepared using the fast-charging graphite composite materials prepared in each embodiment and comparative example, with ternary materials (LiMn) as the basis. 1 / 3 Co 1 / 3 Ni 1 / 3 A 2Ah soft-pack battery was fabricated using O2 as the positive electrode, LiPF6 (solvent: EC+DEC, volume ratio 1:1, concentration 1.1mol / L) as the electrolyte, and Celegard 2400 as the separator. For the negative electrode preparation, a binder, conductive agent, and solvent were added to the negative electrode material and stirred until homogeneous to form a negative electrode slurry. The negative electrode slurry was coated onto copper foil, dried, rolled, and cut to obtain the negative electrode sheet. The binder was LA136D binder, the conductive agent was SP conductive agent, and the solvent was double-distilled water. The weight ratio of the negative electrode material, SP conductive agent, LA136D binder, and double-distilled water was 95:1:4:250. In the preparation of the positive electrode, a binder solution is prepared, followed by the addition of a conductive agent and the positive electrode material. The mixture is stirred and stirred until homogeneous to form a positive electrode slurry. This slurry is then coated onto aluminum foil, dried, rolled, and cut to obtain the positive electrode sheet. The binder is PVDF, the conductive agent is SP, and the solvent is N-methylpyrrolidone. The weight ratio of the positive electrode material, conductive agent, binder, and solvent is 97:1:2:140.

[0072] 1. Cyclic performance test: The battery's cycle performance was tested at a charge / discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, 500 cycles, and a temperature of 25±3℃.

[0073] 2. HPPC Performance Test: Using the HPPC method, a 4C discharge pulse (lasting 10 seconds) and a 3C charging pulse (lasting 10 seconds) are applied at SOCs of 10%, 30%, 50%, 70%, and 90%, respectively, and the charging DC internal resistance (DCR) at each SOC is calculated.

[0074] The test results for the pouch batteries are shown in Table 3.

[0075] Table 3 Performance characterization of the pouch cells corresponding to Examples 1-6 and Comparative Example 1

[0076] As shown in Table 3, the cycle performance and rate performance of the soft-pack batteries obtained from the fast-charging composite materials in the various embodiments of the present invention are significantly better than those of the comparative examples.

[0077] Compared with Comparative Example 1, in Example 4, replacing artificial graphite with modified graphite resulted in a lower charge DCR and improved cycle performance.

[0078] A comparison of Examples 1, 4, 5, and 6 revealed that the simultaneous addition of ammonium molybdate and lithium trifluoromethanesulfonate synergistically improved the fast-charging and cycle performance of the pouch battery.

[0079] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for preparing a fast-charging graphite composite material, characterized in that, The preparation method of the fast-charging graphite composite material includes the following steps: S1, mixing artificial graphite, intercalating agent, oxidant and water, and carrying out a hydrothermal reaction to obtain modified graphite; S2, carrying out a sulfur doping reaction on the modified graphite in an atmosphere of sulfur source gas to obtain sulfur-doped modified graphite; S3, providing a coating liquid, the coating liquid including resin, inorganic carbon conductive agent and organic solvent; S4, mixing the coating liquid and the sulfur-doped modified graphite, and carrying out a first carbonization treatment and a second carbonization treatment in sequence under an inert atmosphere to obtain the fast-charging graphite composite material.

2. The preparation method of the fast-charging graphite composite material as described in claim 1, characterized in that, In step S3, the coating solution also includes a lithium sulfonate derivative.

3. The preparation method of the fast-charging graphite composite material as described in claim 1, characterized in that, In step S3, the coating solution also includes a molybdate compound.

4. The preparation method of the fast-charging graphite composite material as described in claim 1, characterized in that, In step S1, the intercalating agent includes at least one of formic acid, acetic acid, and propionic acid; and / or, in step S1, the oxidizing agent includes at least one of hydrogen peroxide, potassium permanganate, and perchloric acid; and / or, in step S1, the mass ratio of the artificial graphite, the intercalating agent, and the oxidizing agent is 100:30-60:30-60; and / or, in step S1, the temperature of the hydrothermal reaction is 100-200℃; and / or, in step S1, the time of the hydrothermal reaction is 1-6h; and / or, in step S2, the sulfur source gas includes at least one of thiol, benzene disulfide, and dipropanol trisulfide; and / or, in step S2, the gas input flow rate of the sulfur source gas is 10-100mL / min; and / or, in step S2, the temperature of the sulfur doping reaction is 500-800℃; and / or, in step S2, the time of the sulfur doping reaction is 30-300min.

5. The preparation method of the fast-charging graphite composite material as described in claim 1, characterized in that, The coating solution further includes lithium sulfonate derivatives and molybdate compounds: in step S3, the mass ratio of the resin, the molybdate compound, the lithium sulfonate derivative, and the inorganic carbon conductive agent is 100:5-15:1-5:1-3; and / or, in step S3, the mass concentration of the coating solution is 1-5 wt%; and / or, in step S3, the resin includes at least one of hydroxyl acrylic resin, alkyd resin, and unsaturated polyester resin; and / or, in step S3, the molybdate compound includes at least one of ammonium molybdate, sodium molybdate, diammonium molybdate, tetrathioammonium molybdate, tetraammonium molybdate, phosphomolybdic acid, calcium molybdate, and zinc molybdate; and / or, in step S3... In step S3, the lithium sulfonate derivative includes at least one of lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, lithium perfluorohexane sulfonate, lithium 4-methylbenzenesulfonate, and lithium dioxane sulfonate; and / or, in step S4, the mass ratio of the coating solution to the sulfur-doped modified graphite is 100-200:100; and / or, in step S4, the temperature of the first carbonization treatment is 400-600℃; and / or, in step S4, the time of the first carbonization treatment is 1-6h; and / or, in step S4, the temperature of the second carbonization treatment is 1000-1300℃; and / or, in step S4, the time of the second carbonization treatment is 1-6h.

6. A fast-charging graphite composite material, characterized in that, The fast-charging graphite composite material is prepared by the preparation method of the fast-charging graphite composite material according to any one of claims 1 to 5; the fast-charging graphite composite material includes a core material and a shell material; the core material includes modified graphite and sulfur atoms doped in the modified graphite, the modified graphite has a multilayer structure, and the interlayer of the modified graphite is modified with oxygen-containing functional groups; the shell material at least partially covers the core material, and the shell material includes amorphous carbon and inorganic carbon conductive agent.

7. The fast-charging graphite composite material as described in claim 6, characterized in that, The shell material also includes LiMo. X P Y Q Z Where 0 < X ​​< 2, Y > 0, Z > 0, P represents sulfur, and Q represents oxygen.

8. The fast-charging graphite composite material as described in claim 7, characterized in that, The shell material also includes molybdenum oxide.

9. The fast-charging graphite composite material as described in claim 8, characterized in that, The oxygen-containing functional group includes at least one of carboxyl and hydroxyl groups; and / or, the inorganic carbon conductive agent includes at least one of carbon nanotubes, carbon fibers, graphene, and hollow carbon spheres.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a fast-charging graphite composite material prepared by the method for preparing fast-charging graphite composite material as described in any one of claims 1 to 5, or a fast-charging graphite composite material as described in any one of claims 6 to 9.

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