Multi-element doped graphite composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrode materials of lithium ion batteries, and provides a preparation method of a multi-element doped graphite composite material, which comprises the following steps: S1, carrying out first-stage gas-solid treatment on porous graphite in an atmosphere A, and carrying out second-stage gas-solid treatment in an atmosphere B to obtain modified graphite; s2, the modified graphite, ionic liquid and a reducing agent are subjected to a reaction, and a multi-element doped graphite composite material is obtained; the atmosphere A comprises a tin-based atmosphere and a phosphorus-based atmosphere; and the atmosphere B comprises a carbon-based atmosphere and a halogen atmosphere. By means of the technical scheme, the problems that in the prior art, graphite composite materials are poor in fast charging performance and low in first-time efficiency are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials for lithium ion batteries, and in particular to a multi-element doped graphite composite material and a preparation method and application thereof. Background Art

[0002] As the market demand for fast-charging negative electrode materials for lithium-ion batteries increases, graphite materials are required to have fast-charging performance while also taking into account the energy density, high-temperature performance and processing performance of the materials. Currently, the negative electrode materials used in the market are mainly artificial graphite, and the fast-charging performance is mainly improved by reducing the particle size, increasing the carbon coating amount, and silicon composite.

[0003] For example, a Chinese invention patent application with publication number CN116283292A discloses a method for preparing a fast-charging graphite negative electrode material, comprising the following steps: (1) mixing graphite and cationic emulsified asphalt to obtain premixed graphite; (2) heating the obtained premixed graphite and stirring it to obtain pretreated graphite; (3) mixing the pretreated graphite with a conductive carbon source dispersed in water, the conductive carbon source having a negative charge, to obtain modified graphite; (4) calcining the obtained modified graphite to obtain a fast-charging graphite negative electrode material; the mass of asphalt in the cationic emulsified asphalt in step (1) is 0.6wt%~15wt% of the graphite. The Chinese invention patent application with publication number CN117577798A discloses a preparation process of a silane coupling agent composite modified graphite lithium ion battery negative electrode material. The negative electrode material uses a silane coupling agent as a molecular bridge to tightly combine graphite with a polymerized functional monomer, dope silicon on the graphite surface, and use a cross-linking agent to cause a cross-linking reaction in the polymerized functional monomer to firmly coat the graphite doped silicon structure, thereby preparing a composite graphite negative electrode material with high capacity and high rate cycle performance. In addition, the invention patent application with publication number CN114156458A discloses a graphite / silicon gradient electrode material, its preparation method and fast charging application, which makes full use of the excellent conductivity of the graphite negative electrode to compensate for the low conductivity of the silicon negative electrode, and uses the high capacity, excellent lithium affinity and concentration gradient design of the silicon negative electrode to compensate for the low capacity and easy generation of lithium dendrites of the graphite negative electrode, thereby achieving the excellent fast charging performance of the graphite / silicon gradient electrode.

[0004] In summary, although there are many ways to improve graphite fast charging in the prior art, there are still problems with low energy density and initial efficiency. Although silicon-based materials have high specific capacity, their initial efficiency is low and their full-charge expansion is large, which can easily cause the battery cycle performance and high-temperature storage performance to deteriorate. Therefore, there is a need for a composite material that can not only improve the fast-charging performance of graphite composite materials, but also take into account energy density, initial efficiency and full-charge expansion, and be used in lithium-ion batteries. Summary of the invention

[0005] The present invention provides a multi-element doped graphite composite material and a preparation method and application thereof, which solve the problems of poor fast charging performance and low initial efficiency of the graphite composite material in the related art.

[0006] The technical solution of the present invention is as follows: The present invention provides a method for preparing a multi-element doped graphite composite material, comprising the following steps: S1, subjecting porous graphite to a first gas-solid treatment in atmosphere A and a second gas-solid treatment in atmosphere B to obtain modified graphite; S2, reacting the modified graphite, ionic liquid and reducing agent to obtain a multi-element doped graphite composite material; The composition of the atmosphere A includes a tin-based atmosphere and a phosphorus-based atmosphere; Components of the atmosphere B include carbon-based atmosphere and halogen atmosphere.

[0007] As a further technical solution, in step S2, filtering and drying are further performed after the reaction; The drying is vacuum drying, the drying temperature is 80° C., and the drying time is 24 hours.

[0008] As a further technical solution, the volume ratio of the tin-based atmosphere to the phosphorus-based atmosphere is 1:1-3; The volume ratio of the carbon-based atmosphere to the halogen atmosphere is 10:1-3.

[0009] As a further technical solution, the precursor of the tin-based atmosphere includes one or more of tin tetrachloride, tin dichloride, dimethyltin dichloride, and trimethyltin chloride; The precursor of the phosphorus-based atmosphere includes one or more of phosphine, phosphorus pentachloride, and phosphorus trichloride; The carbon-based atmosphere includes hydrocarbon compounds with a carbon number of less than 8; preferably, the hydrocarbon compounds include one or more of methane, ethane, acetylene, ethylene, and propyne; The halogen atmosphere includes one or more of carbon tetrafluoride, carbon difluoride, carbon trichloride and carbon dichloride.

[0010] As a further technical solution, the mass ratio of the modified graphite, the ionic liquid and the reducing agent is 100:5~15:5~15.

[0011] As a further technical solution, the temperature of the first stage of gas-solid treatment is 500-800°C and the time is 30-300min; The temperature of the second gas-solid treatment is 800-1200°C and the time is 30-300 minutes; The reaction temperature is 50-150° C., the pressure is 1-5 MPa, and the reaction time is 1-6 h.

[0012] As a further technical solution, the ionic liquid includes an imidazolyl ionic liquid; preferably, the imidazolyl ionic liquid includes one or more of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium tetrafluoroborate; The reducing agent includes one or more of sodium borohydride, potassium borohydride, and cysteine.

[0013] As a further technical solution, the method for preparing the porous graphite comprises the following steps: The coke raw material, catalyst and pore-enlarging agent are mixed and graphitized to obtain porous graphite.

[0014] As a further technical solution, the temperature of the graphitization treatment is 2800-3200° C., and the time is more than 5 hours. Preferably, the time of the graphitization treatment is 6-30 hours.

[0015] As a further technical solution, the mass ratio of the coke raw material, the catalyst, and the pore-enlarging agent is 100:1~5:50~150; The coke raw material includes one or more of petroleum coke, needle coke, asphalt coke, and mesophase asphalt; The catalyst is a compound containing a transition metal element; preferably, the compound containing a transition metal element includes one or more of chloride, sulfate, and nitrate; preferably, the transition metal element in the compound containing a transition metal element includes one or more of iron, cobalt, and nickel; The pore expanding agent includes one or more of hydrogen peroxide solution, oxalic acid solution, and potassium permanganate solution; The mass concentration of the pore expanding agent is 5% to 30%.

[0016] The invention also provides a multi-element doped graphite composite material, which is prepared by the preparation method.

[0017] The present invention also proposes the application of the multi-element doped graphite composite material prepared by the preparation method of the multi-element doped graphite composite material in lithium ion batteries.

[0018] As a further technical solution, the application in lithium-ion batteries may be used as negative electrode active materials of lithium-ion batteries.

[0019] The working principle and beneficial effects of the present invention are: In the present invention, the porous graphite is innovatively subjected to a first gas-solid treatment in atmosphere A in advance, and tin phosphide is chemically vapor deposited in the pore structure and skeleton of the graphite, thereby achieving the doping of tin and phosphorus in high-capacity materials, improving the specific capacity of the graphite and reducing the resistance of the graphite; then a second gas-solid treatment is carried out in atmosphere B to reduce the defects of the graphite material and improve the electronic conductivity, and then the subsequent ionic liquid and reducing agent are reacted to form a protective film on the surface of the modified graphite, so that the graphite material not only has the characteristics of high electronic and ionic conductivity, but also can avoid direct contact between the tin phosphorus in the inner core and the electrolyte, reduce the occurrence of side reactions, and has excellent compatibility with organic electrolytes. The first gas-solid treatment and the second gas-solid treatment cooperate with each other to improve the electronic conductivity of the material, restrain the expansion of tin phosphide, and improve the cycle performance and fast charging performance.

[0020] In the present invention, by optimizing the composition and physicochemical structure of the material, improving the hierarchical adaptability, and reducing the impedance, the ionic and electronic conductivity of the graphite composite material can be improved, and the graphite composite material can have excellent initial efficiency, fast charging and other properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] Figure 1 This is a SEM image of the multi-element doped graphite composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1 The preparation method of the multi-element doped graphite composite material comprises the following steps: S0, add 100g petroleum coke, 3g ferric chloride, and 100g oxalic acid solution (concentration 10wt%) into a ball mill and mix well, then transfer to a graphitization furnace and graphitize at 3000℃ for 12h to obtain porous graphite; S1, placing porous graphite in a vacuum tube furnace, heating it to 650°C, introducing tin tetrachloride gas and phosphine gas for the first gas-solid treatment (the volume ratio of tin tetrachloride gas to phosphine gas is 1:2, the introduction flow rate is 50SCCM, and the introduction time is 150min), then introducing a mixed gas of methane and carbon tetrafluoride and heating it to 950°C for the second gas-solid treatment (the volume ratio of methane to carbon tetrafluoride is 10:2, the introduction flow rate is 50SCCM, and the introduction time is 150min), to obtain modified graphite; S2. Add 100 g of modified graphite into 200 g of 1-butyl-3-methylimidazolium chloride solution (the mass concentration of 1-butyl-3-methylimidazolium chloride solution is 5%, and the solvent in the 1-butyl-3-methylimidazolium chloride solution is acetone), mix well, add 10 g of sodium borohydride to react (reaction temperature 80°C, reaction pressure 3 MPa, reaction time 3 h), filter, and vacuum dry at 80°C for 24 h to obtain a multi-element doped graphite composite material.

[0025] Example 2 The preparation method of the multi-element doped graphite composite material comprises the following steps: S0, 100g of needle coke, 1g of nickel chloride, and 50g of hydrogen peroxide solution (concentration 30wt%) were added to a ball mill and mixed evenly, and then transferred to a graphitization furnace and graphitized at 2800°C for 24h to obtain porous graphite; S1, placing porous graphite in a vacuum tube furnace, heating it to 500°C, introducing tin dichloride gas and phosphorus pentachloride gas for the first gas-solid treatment (the volume ratio of tin dichloride gas to phosphorus pentachloride gas is 1:1, the introduction flow rate is 10SCCM, and the introduction time is 300min), then introducing a mixed gas of ethylene and carbon difluoride and heating it to 800°C for the second gas-solid treatment (the volume ratio of ethylene to carbon difluoride is 10:1, the introduction flow rate is 10SCCM, and the introduction time is 300min), to obtain modified graphite; S2. Add 100 g of modified graphite into 500 g of 1-ethyl-3-methylimidazolium chloride solution (the mass concentration of 1-ethyl-3-methylimidazolium chloride solution is 1%, and the solvent in the 1-ethyl-3-methylimidazolium chloride solution is acetone), mix well, add 5 g of potassium borohydride to react (reaction temperature 50°C, reaction pressure 5 MPa, reaction time 6 h), filter, and vacuum dry at 80°C for 24 h to obtain a multi-element doped graphite composite material.

[0026] Example 3 The preparation method of the multi-element doped graphite composite material comprises the following steps: S0, add 100g of pitch coke, 5g of cobalt chloride, and 150g of potassium permanganate solution (concentration 5wt%) into a ball mill and mix well, then transfer to a graphitization furnace and graphitize at 3200°C for 8h to obtain porous graphite; S1. The porous graphite is placed in a vacuum tube furnace, heated to 800°C, and dimethyltin dichloride gas and phosphorus trichloride gas are introduced to perform a first gas-solid treatment (the volume ratio of dimethyltin dichloride gas to phosphorus trichloride gas is 1:3, the introduction flow rate is 100 SCCM, and the introduction time is 30 min), and then a mixed gas of acetylene and carbon dichloride is introduced and heated to 1200°C for a second gas-solid treatment (the volume ratio of acetylene to carbon dichloride is 10:3, the introduction flow rate is 100 SCCM, and the introduction time is 30 min) to obtain modified graphite; S2. Add 100 g of modified graphite into 150 g of 1-butyl-2,3-dimethylimidazolium chloride solution (the mass concentration of 1-butyl-2,3-dimethylimidazolium chloride solution is 10%, and the solvent in the 1-butyl-2,3-dimethylimidazolium chloride solution is acetone) and mix well, add 15 g of cysteine ​​to react (reaction temperature 150°C, reaction pressure 1 MPa, reaction time 1 h), filter, and vacuum dry at 80°C for 24 h to obtain a multi-element doped graphite composite material.

[0027] Comparative Example 1 The difference between this comparative example and Example 1 is that the preparation method of the multi-element doped graphite composite material does not include step S1, and the modified graphite in step S2 is replaced by the porous graphite prepared in step S0.

[0028] Comparative Example 2 The only difference between this comparative example and Example 1 is that the preparation method of the multi-element doped graphite composite material does not include step S2.

[0029] Comparative Example 3 The difference between this comparative example and Example 1 is that the tin tetrachloride gas in step S1 is replaced by silicon tetrachloride gas.

[0030] Comparative Example 4 The only difference between this comparative example and Example 1 is that sodium borohydride is not added in step S2.

[0031] SEM Testing The multi-element doped graphite composite material prepared in Example 1 was subjected to SEM testing. The results are as follows: Figure 1 shown.

[0032] Depend on Figure 1 It can be seen that the prepared multi-element doped graphite composite material presents a granular structure with slight bonding, a particle size between 10 and 15 μm, and a uniform size distribution.

[0033] Button Cell Battery Test The multi-element doped graphite composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were respectively used as negative electrode materials and assembled into button cells according to the following method for performance testing: Adding a binder, a conductive agent, and a solvent to the negative electrode material, stirring and mixing to form a negative electrode slurry, coating the negative electrode slurry on a copper foil, drying, rolling, and cutting to form a negative electrode sheet; Wherein, the binder is polyvinylidene fluoride, the conductive agent is SP conductive agent, and the solvent is NMP; The mass ratio of negative electrode material, SP conductive agent, polyvinylidene fluoride and NMP (N-methylpyrrolidone) is 95:1:4:220; The button cell was assembled in an argon-filled glove box using a lithium metal sheet as the counter electrode, a polypropylene (PP) membrane as the separator, and LiPF6 / EC+DEC (the concentration of LiPF6 was 1.3 mol / L, and the volume ratio of EC to DEC was 1:1) as the electrolyte. The button cells were installed on the Wuhan Blue Electric CT2001A battery tester, and charged and discharged at a rate of 0.1C. The charge and discharge voltage range was 0.005V to 2.0V, and the first discharge capacity and first discharge efficiency were measured. The 2C rate discharge capacity was tested, and the rate performance (2C / 0.1C), cycle performance (0.1C / 0.1C, 100 weeks) and initial charge DCR (50% SOC) were calculated. According to the national standard GB / T 24533-2019 "Graphite Anode Materials for Lithium Ion Batteries", the specific surface areas of the multi-element doped graphite composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested respectively; the powder conductivity of the multi-element doped graphite composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was tested respectively by four-probe; the powder OI values ​​of the multi-element doped graphite composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested respectively by XRD; The test results are shown in Table 1.

[0034] Table 1 Performance test results of multi-element doped graphite composites

[0035] It can be seen from Table 1 that compared with Comparative Examples 1 to 4, the discharge specific capacity, initial efficiency and powder conductivity of the multi-element doped graphite composite materials prepared in Examples 1 to 3 are all higher, indicating that the porous graphite is first subjected to the first stage of chemical vapor deposition in atmosphere A, and the second stage of vapor deposition is carried out in atmosphere B, and the subsequent reaction of ionic liquid and reducing agent is coordinated, which significantly improves the initial efficiency and discharge specific capacity of the graphite composite material.

[0036] Soft pack battery test The multi-element doped graphite composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were used as negative electrode materials to prepare negative electrodes, NCM111 was used as positive electrode material to prepare positive electrodes, 1.3 mol / L LiPF6 solution (the solvent was EC and DEC, and the volume ratio of EC to DEC was 1:1) was used as electrolyte, and Celegard2400 was used as a separator to prepare 2Ah soft-pack batteries; When preparing the negative electrode, a binder, a conductive agent, and a solvent are added to the negative electrode material, stirred and mixed to form a negative electrode slurry, and the negative electrode slurry is coated on a copper foil, dried, rolled, and cut to form a negative electrode sheet. The binder is LA132 binder, the conductive agent is SP conductive agent, and the solvent is double distilled water; The mass ratio of negative electrode material, SP conductive agent, LA132 binder and double distilled water is 95:1:4:220; When preparing the positive electrode, a binder, a conductive agent, and a solvent are added to the positive electrode material, and the mixture is stirred and mixed to form a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil, dried, rolled, and cut to form a positive electrode sheet. The binder is PVDF, the conductive agent is SP, and the solvent is N-methylpyrrolidone; The mass ratio of the positive electrode material, the conductive agent, the binder and the solvent is 93:3:4:140.

[0037] The 2Ah soft-pack batteries prepared in the above embodiments and comparative examples were subjected to rate performance tests: the charge and discharge voltage range was 2.8~4.35V, the test temperature was 25±3.0℃, and they were charged at 1.0C, 2.0C, 3.0C, and 5.0C, and discharged at 1.0C. The constant current ratio and temperature of the battery under different charging modes were tested, and the results are shown in Table 2.

[0038] Table 2 Soft pack battery rate performance test results

[0039] It can be seen from Table 2 that compared with Comparative Examples 1 to 4, the multi-element doped graphite composite materials prepared in Examples 1 to 3 have a higher and better constant current ratio after being made into soft-pack batteries, and the charging time is shorter, indicating that the multi-element doped graphite composite materials prepared in the present invention have excellent fast charging performance.

[0040] The 2Ah soft-pack batteries prepared in the above embodiments and comparative examples were subjected to cycle performance tests: at a charge and discharge rate of 2C / 2C and a voltage range of 2.8-4.35V, 100, 300, and 500 charge and discharge cycles were performed in sequence to test their capacity retention rates. The results are shown in Table 3.

[0041] Table 3 Soft pack battery cycle performance test results

[0042] It can be seen from Table 3 that compared with Comparative Examples 1 to 4, the multi-element doped graphite composite materials prepared in Examples 1 to 3 are made into soft-pack batteries and have higher retention rates after 100, 300 and 500 cycles, indicating that the multi-element doped graphite composite materials prepared in the present invention can improve the cycle performance of lithium-ion batteries as negative electrode materials of lithium-ion batteries. Thanks to the high specific surface area and low powder OI value of the multi-element doped graphite composite materials, the liquid retention performance of the negative electrode material can be improved, the expansion can be reduced, and the cycle performance of the lithium-ion battery can be improved.

[0043] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a multi-element doped graphite composite material, characterized in that: The following steps are involved: S1, subjecting porous graphite to a first gas-solid treatment in atmosphere A and a second gas-solid treatment in atmosphere B to obtain modified graphite; S2, reacting the modified graphite, ionic liquid and reducing agent to obtain a multi-element doped graphite composite material; The composition of the atmosphere A includes a tin-based atmosphere and a phosphorus-based atmosphere; Components of the atmosphere B include carbon-based atmosphere and halogen atmosphere.

2. The method for preparing a multi-element doped graphite composite material according to claim 1, characterized in that: The volume ratio of the tin-based atmosphere to the phosphorus-based atmosphere is 1:1-3; The volume ratio of the carbon-based atmosphere to the halogen atmosphere is 10:1-3.

3. The method for preparing a multi-element doped graphite composite material according to claim 1, characterized in that: The precursor of the tin-based atmosphere includes one or more of tin tetrachloride, tin dichloride, dimethyltin dichloride, and trimethyltin chloride; The precursor of the phosphorus-based atmosphere includes one or more of phosphine, phosphorus pentachloride, and phosphorus trichloride; The carbon-based atmosphere includes hydrocarbon compounds with a carbon number of less than 8; preferably, the hydrocarbon compounds include one or more of methane, ethane, acetylene, ethylene, and propyne; The halogen atmosphere includes one or more of carbon tetrafluoride, carbon difluoride, carbon trichloride and carbon dichloride.

4. The method for preparing a multi-element doped graphite composite material according to claim 1, characterized in that: The mass ratio of the modified graphite, the ionic liquid and the reducing agent is 100:5-15:5-15.

5. The method for preparing a multi-element doped graphite composite material according to claim 1, characterized in that: The temperature of the first gas-solid treatment is 500-800°C and the time is 30-300 minutes; The temperature of the second gas-solid treatment is 800-1200°C and the time is 30-300 minutes; The reaction temperature is 50-150° C., the pressure is 1-5 MPa, and the reaction time is 1-6 h.

6. The method for preparing a multi-element doped graphite composite material according to claim 1, characterized in that: The ionic liquid includes an imidazolyl ionic liquid; preferably, the imidazolyl ionic liquid includes one or more of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium tetrafluoroborate; The reducing agent includes one or more of sodium borohydride, potassium borohydride, and cysteine.

7. The method for preparing a multi-element doped graphite composite material according to claim 1, characterized in that: The method for preparing the porous graphite comprises the following steps: The coke raw material, catalyst and pore-enlarging agent are mixed and graphitized to obtain porous graphite.

8. The method for preparing a multi-element doped graphite composite material according to claim 7, characterized in that: The mass ratio of the coke raw material, the catalyst and the pore expanding agent is 100:1~5:50~150; The coke raw material includes one or more of petroleum coke, needle coke, asphalt coke, and mesophase asphalt; The catalyst is a compound containing a transition metal element; preferably, the compound containing a transition metal element includes one or more of chloride, sulfate, and nitrate; preferably, the transition metal element in the compound containing a transition metal element includes one or more of iron, cobalt, and nickel; The pore expanding agent includes one or more of hydrogen peroxide solution, oxalic acid solution, and potassium permanganate solution; The mass concentration of the pore expanding agent is 5% to 30%.

9. A multi-element doped graphite composite material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the multi-element doped graphite composite material obtained by the preparation method according to any one of claims 1 to 8 or the multi-element doped graphite composite material according to claim 9 in lithium ion batteries.

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