Graphite composite material, method for preparing the same and use thereof in lithium-ion batteries

Abstract

The application relates to the technical field of lithium ion battery electrode materials, and discloses a graphite composite material, a preparation method thereof and application of the graphite composite material in lithium ion batteries. The preparation method of the graphite composite material comprises the following steps: S1, mixing amino-graphite, carboxyl-graphite, a conductive agent, a coupling agent and a solvent, performing solvent thermal treatment, taking filter residues, drying, and performing first carbonization to obtain modified graphite; S2, mixing the modified graphite, a transition metal precursor and a carbon source, drying, and performing second carbonization to obtain graphite@transition metal doped hard carbon material; and S3, in-situ growing carbon nanotubes on the surface of the graphite@transition metal doped hard carbon material to obtain the graphite composite material. Through the technical scheme, the problem of poor kinetic performance of the graphite electrode material in the related art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery electrode materials, in particular to a graphite composite material, a preparation method thereof and application thereof in a lithium ion battery. BACKGROUND

[0002] With the increasing demand for fast-charging performance of negative electrode materials in the market, it is required that the negative electrode used in lithium ion batteries has excellent fast-charging performance. The negative electrode currently on the market is mainly composed of graphite and soft carbon or hard carbon coated on the surface of the graphite, and is subjected to secondary granulation. Since the material is granulated, the binding force between the materials is poor and the impedance is large. At the same time, the electronic conductivity of the soft carbon or hard carbon coated on the outer layer is poor, which limits the improvement of the fast-charging performance. The current graphite material is subjected to high-temperature graphitization, and the surface of the material has no chemical groups, and the kinetic performance is poor. At the same time, the specific surface area of the current graphite material is low, which affects the kinetic performance of the material.

[0003] In view of the problem of unsatisfactory kinetic performance of the graphite material, some improvement schemes exist in the prior art. For example, a fast-charging lithium battery is disclosed in Chinese Patent No. CN114361410A, which includes a porous copper foil, and a slurry layer provided on both sides of the porous copper foil, the slurry layer including a first negative electrode layer, a second negative electrode layer and a third negative electrode layer. The coating method of the slurry layer is as follows: S1, graphite particles, polyaniline-carbon nanotube particles, a binder, a conductive agent and a solvent are mixed to form a first slurry, the first slurry is coated on both sides of the porous copper foil, and the first slurry is dried and compacted to obtain the first negative electrode layer; S2, graphite-hard carbon particles, a binder, a conductive agent and a solvent are mixed to form a second slurry, the second slurry is coated on the outer side of the first negative electrode layer to form the second negative electrode layer; S3, graphite-hard carbon-carbon nanotube particles, a binder, a conductive agent and a solvent are mixed to obtain a third slurry, and the third slurry is coated on the outer side of the second negative electrode layer to obtain the third negative electrode layer.

[0004] For another example, a multi-element carbon-based fast-charging negative electrode composite material is disclosed in Chinese Patent Document No. CN114447305A, which has a core-shell structure, the inner core being a graphite particle and hard carbon composite body doped with nitrogen elements and tin elements, and the outer shell being a carbon nanotube and amorphous carbon composite layer.

[0005] In summary, although some improvement means exist in the prior art, the kinetic performance such as the electronic conductivity and the rate performance of the graphite negative electrode material still needs to be further improved. SUMMARY

[0006] The present application provides a graphite composite material, a preparation method thereof and application thereof in a lithium ion battery, which solves the problem of poor kinetic performance of the graphite electrode material in the related art.

[0007] The technical scheme of the present application is as follows:

[0008] The application provides a preparation method of a graphite composite material, which comprises the following steps:

[0009] S1, mixing amino-graphite, carboxylated graphite, a conductive agent, a coupling agent and a solvent, performing a solvothermal treatment, taking filter residues, drying, and performing first carbonization to obtain modified graphite;

[0010] S2, mixing the modified graphite, a transition metal precursor and a carbon source, drying, and performing second carbonization to obtain a graphite-transition metal doped hard carbon material;

[0011] S3, growing carbon nanotubes on the surface of the graphite-transition metal doped hard carbon material in situ to obtain a graphite composite material.

[0012] As a further technical scheme, the mass ratio of the amino-graphite, the carboxylated graphite, the conductive agent and the coupling agent is 100:50-150:1-5:1-10.

[0013] As a further technical scheme, the mass ratio of the total mass of the amino-graphite and the carboxylated graphite to the solvent is 1-3:10.

[0014] As a further technical scheme, the mass ratio of the carbon source, the transition metal precursor and the modified graphite is 10-30:1-5:100.

[0015] As a further technical scheme, the solvent comprises water and / or an organic solvent, the organic solvent is a water-soluble organic solvent, and the organic solvent comprises one or more of C1-C6 alcohols and acetone.

[0016] As a further technical scheme, the preparation method of the amino-graphite comprises the following steps:

[0017] mixing an amine compound and graphite as raw materials, taking filter residues for ammoniation roasting to obtain amino-graphite;

[0018] The amine compound comprises a binary amine compound or a polyamine compound, preferably, the amine compound comprises a C2-C8 binary amine compound;

[0019] The mass ratio of the amine compound to the graphite is 10-50:100;

[0020] The mixing reaction further adds an organic solvent, the mixing reaction is performed for 1-6 hours at a temperature of 50-100 DEG C;

[0021] The ammoniation roasting is performed in an ammonia atmosphere;

[0022] The ammoniation roasting is performed for 1-3 hours.

[0023] As a further technical solution, the preparation method of the carboxylated graphite comprises the following steps:

[0024] The graphite and the oxidizing acid liquid are mixed to perform a carboxylating reaction to obtain the carboxylated graphite;

[0025] The carboxylating reaction is followed by filtration, washing and drying treatment in sequence;

[0026] The components of the oxidizing acid liquid include hydrogen peroxide, permanganate and concentrated sulfuric acid;

[0027] The mass ratio of the hydrogen peroxide, the permanganate and the concentrated sulfuric acid is 1-5:5-10:100-200;

[0028] The temperature of the carboxylating reaction is 50-80℃, and the time is 6-24h.

[0029] As a further technical solution, the conductive agent includes one or more of carbon nanotubes, graphene, carbon black and carbon fibers;

[0030] The coupling agent includes an aluminum-based coupling agent, and the aluminum-based coupling agent includes one or more of distearyl oxyisopropylaluminum, isopropyl distearyloxyaluminum, trimethylaluminum and triisopropylaluminum;

[0031] The transition metal precursor includes a water-soluble salt containing a transition metal element, and the transition metal element includes one or more of iron, cobalt and nickel;

[0032] The carbon source includes a water-soluble resin;

[0033] The water-soluble resin includes one or more of diallyl isophthalate resin, malic acid resin, acrylic acid resin and fumaric acid resin.

[0034] As a further technical solution, the temperature of the solvothermal treatment is above 100℃, the time is 6-18h, and the pressure is 1-5MPa; preferably, the temperature of the solvothermal treatment is 100-200℃;

[0035] The temperature of the first carbonization and the second carbonization is each independently 1000-1400℃;

[0036] The holding time of the first carbonization and the second carbonization is each independently 1-6h.

[0037] As a further technical solution, the in-situ growth of the carbon nanotubes is performed in an atmosphere containing a gas-phase carbon source;

[0038] The gas-phase carbon source comprises a gaseous carbon-containing raw material with carbon number less than 12, preferably, the gas-phase carbon source comprises one or more of alkane, alkene, alkyne and benzene with carbon number less than 8;

[0039] The gas-phase carbon source comprises a gaseous carbon-containing raw material with carbon number less than 12, preferably, the gas-phase carbon source comprises one or more of alkane, alkene, alkyne and benzene with carbon number less than 8;

[0040] The flow rate of the gas-phase carbon source-containing atmosphere is 10-50sccm;

[0041] The temperature for in-situ growth of carbon nanotubes is 700-1000℃, and the time is 60-600min;

[0042] After the in-situ growth of carbon nanotubes, the washing treatment and the drying treatment are sequentially performed.

[0043] The washing treatment comprises acid washing and water washing sequentially.

[0044] The application further provides application of the graphite composite prepared by the preparation method in a lithium ion battery.

[0045] The working principle and beneficial effects of the application are as follows:

[0046] In the application, the amino graphite and the carboxylated graphite are hydrothermally condensed and carbonized with the aid of a coupling agent, a first-stage carbonization treatment is performed, the modified graphite with special physical and chemical characteristics is prepared, the transition metal element-doped hard carbon is compounded on the surface of the modified graphite as a substrate, and the surface is subjected to a gas-phase deposition treatment, so that the carbon nanotubes are induced to grow in-situ on the surface of the hard carbon, and the graphite composite is prepared; the carboxylated graphite and the amino graphite are hydrothermally condensed and carbonized, the graphite is connected by chemical bonds, the tap density is improved, the impedance is reduced, the surface activity is improved, the embedding and extraction rate of lithium ions in the charging and discharging process is improved, and in addition, the hard carbon and the carbon nanotubes are compounded on the modified graphite as a substrate, so that the performance of the material can be further synergistically improved, the electronic conductivity of the material is improved, and the rate performance is improved.

[0047] The preparation method of the graphite composite can regulate the physical and chemical characteristics of the material, can improve the electronic conductivity of the graphite material, can improve the ion transmission channel, and can improve the fast charging, stability and other performances of the material, and significantly improves the kinetic performance of the graphite electrode material by grafting chemical groups on the surface of the material. BRIEF DESCRIPTION OF DRAWINGS

[0048] The application will be further described in detail below with reference to the drawings and specific embodiments.

[0049] Figure 1 The SEM image of the graphite composite prepared in Example 1 of the application. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0051] Embodiment 1

[0052] The preparation method of the graphite composite material comprises the following steps:

[0053] S1, preparation of amino graphite: 30 g of hexanediamine is uniformly dispersed in 500 g of N,N dimethylformamide, 100 g of artificial graphite is added and uniformly dispersed, and then reacted at a temperature of 80℃ for 3 h, filtered, and the filter residue is transferred to a tube furnace, ammonia gas is introduced at a temperature of 550℃ for 2 h to obtain amino graphite;

[0054] S2, preparation of carboxylated graphite: 3 g of hydrogen peroxide, 8 g of potassium permanganate and 150 g of concentrated sulfuric acid are added to 100 g of artificial graphite, and reacted at a temperature of 60℃ for 12 h, filtered, washed with deionized water, and vacuum dried at 80℃ for 24 h to obtain carboxylated graphite;

[0055] S3, 100 g of amino graphite and 100 g of carboxylated graphite are added to 1000 g of deionized water to prepare a 20 wt% solution, then 5 wt% of a carbon nanotube conductive agent solution 80 g and diisostearyl oxyisopropylaluminumate 5 g are uniformly dispersed, and then transferred to a high-pressure reaction kettle, reacted at a temperature of 100℃ and a pressure of 3 MPa for 12 h, filtered, and the filter residue is vacuum dried at 80℃ for 24 h, and then carbonized at a temperature of 1200℃ for 3 h to obtain modified graphite;

[0056] S4, 20 g of diallyl phthalate resin is dissolved in 2000 g of deionized water to prepare a 1 wt% solution, 3 g of cobalt chloride catalyst is uniformly dispersed, 100 g of modified graphite is uniformly dispersed, and then spray dried, and then placed in a rotary furnace and carbonized at a temperature of 1200℃ for 3 h to obtain graphite@transition metal doped hard carbon material;

[0057] S5, the graphite@transition metal doped hard carbon material is transferred to a rotary furnace, argon inert gas is introduced to discharge the air in the tube, and then heated to 800℃, and then acetylene / hydrogen mixed gas (volume ratio of acetylene to hydrogen is 10:1) is introduced at a flow rate of 30 sccm for 300 min, then cooled to room temperature, and then washed with 0.1 mol / L hydrochloric acid and deionized water to obtain the graphite composite material.

[0058] Example 2

[0059] A method for preparing a graphite composite material, comprising the following steps:

[0060] S1, preparation of amino graphite: 10 g of hexanediamine is uniformly dispersed in 500 g of N,N dimethylformamide, 100 g of artificial graphite is added and uniformly dispersed, reacted at a temperature of 50°C for 6 h, filtered, and the residue is transferred to a tube furnace, ammonia gas is introduced at a temperature of 500°C for 3 h to obtain amino graphite;

[0061] S2, preparation of carboxylated graphite: 1 g of hydrogen peroxide, 5 g of potassium permanganate, and 100 g of concentrated sulfuric acid are added to 100 g of artificial graphite and reacted at a temperature of 50°C for 24 h, filtered, washed with deionized water, and vacuum dried at 80°C for 24 h to obtain carboxylated graphite;

[0062] S3, 100 g of amino graphite and 50 g of carboxylated graphite are added to 1500 g of deionized water to prepare a 10 wt% solution, then 5 wt% graphene conductive agent solution 50 g, isopropyl bis-stearyl oxy aluminate 1 g are uniformly dispersed, and transferred to a high-pressure reaction kettle, reacted at a temperature of 80°C and a pressure of 1 MPa for 18 h, filtered, and the residue is vacuum dried at 80°C for 24 h, and then carbonized at a temperature of 1000°C for 6 h to obtain modified graphite;

[0063] S4, 10 g of malic acid resin is dissolved in 100 g of deionized water to prepare a 1 wt% solution, 1 g of nickel chloride catalyst is uniformly dispersed, 100 g of modified graphite is uniformly dispersed, and after spray drying, it is placed in a rotary furnace and carbonized at a temperature of 1000°C for 6 h to obtain graphite@transition metal doped hard carbon material;

[0064] S5, the graphite@transition metal doped hard carbon material is transferred to a rotary furnace, argon inert gas is introduced to discharge the air in the tube, and the temperature is raised to 700°C, acetylene / hydrogen mixed gas (volume ratio of acetylene to hydrogen is 15:1) is introduced, the flow rate is 10 sccm, and the temperature is kept for 600 min, then the temperature is lowered to room temperature, and 0.1 mol / L hydrochloric acid is used for acid washing, deionized water is used for washing, and graphite composite material is obtained.

[0065] Example 3

[0066] A method for preparing a graphite composite material, comprising the following steps:

[0067] S1, preparation of amino graphite: 10 g of hexanediamine is uniformly dispersed in 500 g of N,N dimethylformamide, 100 g of artificial graphite is added and uniformly dispersed, reacted at a temperature of 50°C for 6 h, filtered, and the residue is transferred to a tube furnace, ammonia gas is introduced at a temperature of 500°C for 3 h to obtain amino graphite;

[0068] S2, Preparation of carboxylated graphite: 5 g of hydrogen peroxide, 10 g of potassium permanganate, 200 g of concentrated sulfuric acid were added to 100 g of artificial graphite and reacted at a temperature of 80°C for 6 h, filtered, washed with deionized water, and vacuum dried at 80°C for 24 h to obtain carboxylated graphite;

[0069] S3, 100 g of aminated graphite and 150 g of carboxylated graphite were added to 830 g of deionized water to prepare a 30 wt% solution, then 5 wt% of a carbon black conductive agent solution 100 g, trimethylaluminum 10 g were uniformly dispersed, and transferred to a high-pressure reaction kettle, reacted at a temperature of 150°C and a pressure of 5 MPa for 6 h, filtered, and the residue was taken out and vacuum dried at 80°C for 24 h, then carbonized at a temperature of 1400°C for 1 h to obtain modified graphite;

[0070] S4, 30 g of fumaric acid resin was dissolved in 3000 g of deionized water to prepare a 1 wt% solution, and 5 g of cobalt chloride catalyst was uniformly dispersed, and 100 g of modified graphite was uniformly dispersed, and after spray drying, it was placed in a rotary furnace and carbonized at a temperature of 1400°C for 1 h to obtain graphite@transition metal doped hard carbon material;

[0071] S5, the graphite@transition metal doped hard carbon material was transferred to a rotary furnace, first argon inert gas was introduced to discharge the air in the pipe, and then the temperature was raised to 1000°C, and acetylene / hydrogen mixed gas (volume ratio of acetylene to hydrogen is 5:1) was introduced at a flow rate of 50 sccm for 60 min, then the temperature was lowered to room temperature, and 0.1 mol / L hydrochloric acid was used for acid washing, and deionized water was used for washing to obtain a graphite composite material.

[0072] Comparative Example 1

[0073] The preparation method of the graphite composite material comprises the following steps:

[0074] S1, 200 g of artificial graphite was added to 1000 g of deionized water to prepare a 20 wt% solution, then 5 wt% of a carbon nanotube conductive agent solution 80 g was uniformly dispersed, and transferred to a high-pressure reaction kettle, reacted at a temperature of 100°C and a pressure of 3 MPa for 12 h, filtered, and the residue was taken out and vacuum dried at 80°C for 24 h, then carbonized at a temperature of 1200°C for 3 h to obtain modified graphite;

[0075] S2, 20 g of isophthalic acid diallyl ester resin was dissolved in 2000 g of deionized water to prepare a 1 wt% solution, and 3 g of cobalt chloride catalyst was uniformly dispersed, and 100 g of modified graphite was uniformly dispersed, and after spray drying, it was placed in a rotary furnace and carbonized at a temperature of 1200°C for 3 h to obtain graphite@transition metal doped hard carbon material;

[0076] S3, the graphite@transition metal doped hard carbon material is transferred to a rotary furnace, argon gas is first introduced into the pipe to discharge the air, and the temperature is raised to 800 DEG C, acetylene / hydrogen mixed gas (volume ratio of acetylene and hydrogen is 10:1) is introduced, the flow rate is 30 sccm, and the temperature is kept for 300 min, then the temperature is lowered to room temperature, and 0.1 mol / L hydrochloric acid is used for acid washing, deionized water is used for washing, and the graphite composite material is obtained.

[0077] Comparative Example 2

[0078] The difference between the present comparative example and Example 1 is that no cobalt chloride catalyst is added in step S4.

[0079] Comparative Example 3

[0080] The difference between the present comparative example and Example 1 is that step S1 is not included and 100g of carboxylated graphite is replaced by 100g of aminated graphite in step S3.

[0081] Comparative Example 4

[0082] The difference between the present comparative example and Example 1 is that step S2 is not included and 100g of aminated graphite is replaced by 100g of carboxylated graphite in step S3.

[0083] Comparative Example 5

[0084] The difference between the present comparative example and Example 1 is that no distearyl oxyisopropylaluminumate is added in step S3.

[0085] Comparative Example 6

[0086] The preparation method of the graphite composite material comprises the following steps:

[0087] S1, preparation of aminated graphite: 30g of hexanediamine is uniformly dispersed in 500g of N,N dimethylformamide, 100g of artificial graphite is added and uniformly dispersed, and the reaction is carried out at a temperature of 80 DEG C for 3h, filtration is carried out, the filter residue is transferred to a tube furnace, ammonia gas is introduced at a temperature of 550 DEG C for 2h, and aminated graphite is obtained;

[0088] S2, preparation of carboxylated graphite: 3g of hydrogen peroxide, 8g of potassium permanganate and 150g of concentrated sulfuric acid are added to 100g of artificial graphite, the reaction is carried out at a temperature of 60 DEG C for 12h, filtration is carried out, deionized water is used for washing, and vacuum drying is carried out at a temperature of 80 DEG C for 24h, and carboxylated graphite is obtained;

[0089] S3, 100 g of amino graphite and 100 g of carboxylated graphite were added to 1000 g of deionized water to configure a 20 wt% solution, then 5 wt% of a carbon nanotube conductive agent solution 80 g, bis-stearyl oxy isopropyl aluminate 5 g was uniformly dispersed, and was transferred to a high-pressure reaction kettle, reacted at a temperature of 100 ℃ and a pressure of 3 MPa for 12 h, filtered, the filter residue was taken, vacuum dried at 80 ℃ for 24 h, then carbonized at a temperature of 1200 ℃ for 3 h to obtain modified graphite;

[0090] S4, 20 g of isophthalic acid diallyl ester resin was dissolved in 2000 g of deionized water to configure a 1 wt% solution, and 3 g of cobalt chloride catalyst was uniformly dispersed, 100 g of modified graphite was uniformly dispersed, after spray drying, it was placed in a rotary furnace and carbonized at a temperature of 1200 ℃ for 3 h to obtain a graphite composite material.

[0091] Comparative Example 7

[0092] The preparation method of the graphite composite material comprises the following steps:

[0093] S1, preparation of amino graphite: 30 g of hexanediamine was uniformly dispersed in 500 g of N,N dimethylformamide, 100 g of artificial graphite was added and uniformly dispersed, reacted at a temperature of 80 ℃ for 3 h, filtered, the filter residue was taken and transferred to a tube furnace, reacted at a temperature of 550 ℃ by passing in ammonia gas for 2 h to obtain amino graphite;

[0094] S2, preparation of carboxylated graphite: 3 g of hydrogen peroxide, 8 g of potassium permanganate, and 150 g of concentrated sulfuric acid were added to 100 g of artificial graphite and reacted at a temperature of 60 ℃ for 12 h, filtered, washed with deionized water, and vacuum dried at 80 ℃ for 24 h to obtain carboxylated graphite;

[0095] S3, 100 g of amino graphite and 100 g of carboxylated graphite were added to 1000 g of deionized water to configure a 20 wt% solution, then 5 wt% of a carbon nanotube conductive agent solution 80 g, bis-stearyl oxy isopropyl aluminate 5 g was uniformly dispersed, and was transferred to a high-pressure reaction kettle, reacted at a temperature of 100 ℃ and a pressure of 3 MPa for 12 h, filtered, the filter residue was taken, vacuum dried at 80 ℃ for 24 h, then carbonized at a temperature of 1200 ℃ for 3 h to obtain modified graphite;

[0096] S4, the modified graphite was transferred to a rotary furnace, argon inert gas was first introduced to discharge the air in the tube, and then the temperature was raised to 800 ℃, acetylene / hydrogen mixed gas (volume ratio of acetylene to hydrogen was 10:1) was introduced, the flow rate was 30 sccm, and the temperature was kept for 300 min, then the temperature was lowered to room temperature, and 0.1 mol / L hydrochloric acid was used for acid washing, deionized water was used for washing, and a graphite composite material was obtained.

[0097] The performance of the graphite composite materials prepared in Examples 1-3 and Comparative Examples 1-7 were tested respectively:

[0098] 1. SEM testing

[0099] The graphite composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the results, the graphite composite material prepared in Example 1 is granular with a uniform size distribution and a particle size between 10 and 15 μm.

[0100] 2. Physical and chemical performance testing

[0101] The electrical conductivity, compacted density, specific surface area, and OI value of the graphite composite materials prepared in each embodiment and comparative example were tested.

[0102] Testing of powder conductivity: The composite materials prepared in each case were pressed into block structures, and then the conductivity of the powder was tested using a four-probe tester.

[0103] Test of powder compaction density: The graphite composite powder prepared in the examples and comparative examples were weighed and placed into the mold, and pressed with a pressure of 2T (using a powder compaction density meter, 1g of powder was placed in a fixed container and then pressed with a pressure of 2T, left to stand for 10 seconds, and then the volume under compression was calculated and the compaction density was calculated).

[0104] Specific surface area test: Tested according to the method of national standard GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0105] Powder OI value: tested using XRD.

[0106] The results are shown in Table 1.

[0107] Table 1. Results of physicochemical performance tests

[0108]

[0109] 3. Button cell battery test

[0110] The graphite composite prepared in Examples 1-3 and Comparative Examples 1-7 was assembled into a button cell as a lithium ion battery negative electrode material. The negative electrode material was prepared by adding a binder, a conductive agent and a solvent to the graphite composite, stirring to form a slurry, coating on a copper foil, and drying and rolling to obtain. The binder used was LA132 binder, the conductive agent was SP, and the solvent was double-distilled water. The negative electrode sheet was prepared according to the composite material: SP: LA132: double-distilled water = 95g: 1g: 4g: 220mL. Lithium metal was used as the counter electrode. The electrolyte used LiPF6 / EC+DEC, LiPF6 as the electrolyte, and a mixture of EC and DEC in a volume ratio of 1:1 as the solvent, with an electrolyte concentration of 1.2mol / L. The separator used was a polyethylene (PE), polypropylene (PP) or polyethylene propylene (PEP) composite film. The button cell was assembled in an argon-filled glove box. The electrochemical performance was tested on a Wuhan Lan Electric CT2001A battery tester, with a charge and discharge voltage range of 0.005V to 2.0V, a charge and discharge rate of 0.1C, and the first discharge capacity and first efficiency of the button cell and its rate performance (1C / 0.1C) were tested. The test results are shown in Table 2.

[0111] Table 2 Button cell test

[0112]

[0113] As can be seen from Table 2, the lithium ion battery using the graphite composite obtained in Examples 1-3 as the negative electrode material has better first discharge specific capacity and rate performance than the lithium ion batteries of Comparative Examples 1-7.

[0114] Compared with Comparative Examples 3-4, the lithium ion battery using the graphite composite prepared in Example 1 as the negative electrode material has better first discharge specific capacity and rate performance, indicating that the graphite composite prepared by jointly using aminated graphite and carboxylated graphite has better kinetic performance as a negative electrode material for a lithium ion battery.

[0115] Compared with Comparative Examples 6-7, the lithium ion battery using the graphite composite prepared in Example 1 as the negative electrode material has better first discharge specific capacity and rate performance, indicating that the graphite composite prepared by sequentially preparing transition metal-doped hard carbon and in-situ grown carbon nanotubes on the surface of graphite as the core has better kinetic performance as a negative electrode material for a lithium ion battery.

[0116] 4. Soft package battery test

[0117] The graphite composite material was prepared into slurry, coated to prepare a negative electrode sheet (the preparation method is the same as above), lithium iron phosphate was used as a positive electrode (the positive electrode material includes lithium iron phosphate, PVDF and conductive carbon black in a weight ratio of 9:0.5:0.5), LiPF6 (a solvent is EC+DEC, a volume ratio is 1:1, and an electrolyte concentration is 1.3 mol / L) was used as an electrolyte, and Celgard2400 film was used as a separator to prepare a 5 Ah soft package battery, and the cycle performance and rate performance of the soft package battery were tested. The rate performance test conditions were as follows: charging DCR according to different charging SOCs (90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10% and 5%).

[0118] Table 3: Test of soft package battery

[0119]

[0120] As can be seen from Table 3, compared with Comparative Examples 1-7, the soft package battery prepared from the graphite composite material prepared in Inventive Examples 1-3 has a lower DCR.

[0121] Compared with Comparative Examples 3-4, the soft package battery using the graphite composite material prepared in Inventive Example 1 as a negative electrode material has a lower DCR at different SOCs, indicating that the graphite composite material prepared by jointly using aminated graphite and carboxylated graphite as a negative electrode material has more excellent kinetic performance.

[0122] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a graphite composite material, characterized by, The method comprises the following steps: S1, mixing amino-graphite, carboxylated graphite, conductive agent, coupling agent and solvent, and then performing solvent thermal treatment, taking the filter residue, drying, first carbonization, and obtaining modified graphite; S2, mixing the modified graphite, transition metal precursor and carbon source, drying, second carbonization, and obtaining graphite@transition metal doped hard carbon material; S3, in-situ growing carbon nanotubes on the surface of the graphite@transition metal doped hard carbon material, and obtaining graphite composite material.

2. The method of claim 1, wherein the graphite composite is prepared by a process comprising: The mass ratio of the amino-graphite, carboxylated graphite, conductive agent and coupling agent is 100:50-150:1-5:1-10.

3. The method of claim 1, wherein the graphite composite is prepared by a process comprising: The mass ratio of the total mass of the amino-graphite and carboxylated graphite to the solvent is 1-3:

10. ​ 4. The method of claim 1, wherein the graphite composite is prepared by a process comprising: The mass ratio of the carbon source, transition metal precursor and modified graphite is 10-30:1-5:

100.

5. The method for preparing graphite composite material according to claim 1, characterized in that, The preparation method of the amino-graphite comprises the following steps: mixing amine compounds and graphite as raw materials to perform a mixing reaction, taking the filter residue to perform ammoniation roasting, and obtaining amino-graphite; The amine compounds comprise polyamine compounds. The mass ratio of the amine compounds to graphite is 10-50:

100. The mixing reaction is performed at a temperature of 50-100℃ for 1-6h. The ammoniation roasting is performed for 1-3h.

6. The method of claim 5, wherein the graphite composite is prepared by a process comprising: The amine compounds comprise C2-C8 binary amine compounds.

7. The method for preparing graphite composite material according to claim 1, characterized in that, The preparation method of the carboxylated graphite comprises the following steps: mixing graphite and oxidizing acid liquid to perform carboxylation reaction, and obtaining carboxylated graphite; The components of the oxidizing acid liquid comprise hydrogen peroxide, permanganate and concentrated sulfuric acid. The mass ratio of the hydrogen peroxide, permanganate and concentrated sulfuric acid is 1-5:5-10:100-200. The carboxylation reaction is performed at a temperature of 50-80℃ for 6-24h.

8. The method of claim 1, wherein the graphite composite is prepared by a process comprising: a) providing a mixture of graphite particles and a binder; b) forming a graphite composite by extruding the mixture; and c) sintering the graphite composite. The conductive agent comprises one or more of carbon nanotubes, graphene, carbon black and carbon fiber. The coupling agent comprises an aluminum-based coupling agent, and the aluminum-based coupling agent comprises one or more of distearyl oxyisopropylaluminumate, trimethyl aluminumate and triisopropyl aluminumate. The transition metal precursor comprises a water-soluble salt containing a transition metal element, and the transition metal element comprises one or more of iron, cobalt and nickel. The carbon source comprises a water-soluble resin. The water-soluble resin comprises one or more of diallyl phthalate resin, malic acid resin, acrylic acid resin and fumaric acid resin.

9. The method for preparing the graphite composite material according to claim 1, characterized in that, The solvent thermal treatment is performed at a temperature of 100℃ or above for 6-18h under a pressure of 1-5MPa. The temperature of the first carbonization and the second carbonization is independently 1000-1400℃. The holding time of the first carbonization and the second carbonization is independently 1-6h.

10. The method of claim 9, wherein the graphite composite is prepared by a process comprising: The temperature of the solvent thermal treatment is 100-200℃. ​ 11. The method for preparing the graphite composite material according to claim 1, characterized in that, The in-situ growing of carbon nanotubes is performed in an atmosphere containing a gas-phase carbon source. The gas-phase carbon source comprises a gaseous carbon-containing raw material with a carbon number of 12 or less. The atmosphere containing the gas-phase carbon source further comprises hydrogen, and the volume ratio of the gas-phase carbon source to the hydrogen is 5-15:

1. The flow rate of the atmosphere containing the gas-phase carbon source is 10-50sccm. The temperature for growing the carbon nanotubes in situ is 700-1000 ℃, and the time is 60-600 min.

12. The method of claim 11, wherein the graphite composite is prepared by a process comprising: The gas-phase carbon source includes one or more of alkanes, alkenes, alkynes, and benzene with carbon number less than 8.

13. Use of the graphite composite prepared by the method according to any one of claims 1-12 in a lithium ion battery.

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