A preparation method and application for improving the fast-charging performance of graphite composite materials

Abstract

This invention discloses a preparation method and application for improving the fast-charging performance of graphite composite materials. The preparation method involves mixing a graphite precursor with a catalyst and a conductive liquid, ball milling the mixture, followed by pre-carbonization, low-temperature graphitization, and acid washing to obtain a graphite precursor material. Then, the graphite precursor is mixed with a heteroatom polymer, a phosphorus compound, and an organotitanium compound, and heat-treated to obtain the graphite composite material. The graphite composite material prepared by this invention utilizes a catalyst to enhance the anisotropy of carbon during graphitization, and improves electronic conductivity through the conductive agent doped into the core. The titanium dioxide coating on the composite material's outer shell has the characteristics of large interlayer spacing, low expansion rate, and structural stability, which improves the lithium-ion insertion / extraction rate and rate performance. Since phosphorus itself has high specific capacity and a high voltage plateau, phosphorus doping improves the specific capacity and voltage plateau of the composite material, thus enhancing its fast-charging performance.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material preparation, specifically relating to a preparation method and application for improving the fast-charging performance of graphite composite materials. Background Technology

[0002] With the increasing market demand for fast-charging graphite, graphite needs to balance high fast-charging performance with low energy density and high-temperature performance. Currently, methods to improve the fast-charging performance of graphite mainly involve reducing aggregate particle size, increasing coating, doping, and selecting isotropic coke raw materials to improve the electronic and ionic conductivity of the material, thereby improving rate performance. Although some researchers have improved the fast-charging performance of materials by coating the surface with conductive agents or doping the core with conductive agents, and coating the outer layer with lithium titanate, these methods have limited effectiveness in improving fast-charging performance and may even reduce the material's energy density.

[0003] Therefore, it is essential to develop an anode material that can balance fast charging performance and energy density. To improve the fast charging performance of graphite while maintaining energy density, this invention enhances the electronic conductivity and interlayer spacing of the material by doping conductive agents into the graphite core and coating the outer shell with heteroatoms and titanium oxide, thereby increasing the lithium-ion insertion / extraction rate and improving rate performance. Summary of the Invention

[0004] The purpose of this invention is to provide a preparation method for improving the fast-charging performance of graphite composite materials.

[0005] Another objective of this invention is to provide an application of fast-charging graphite composite material.

[0006] This invention is achieved through the following technical solution: The preparation method of the present invention includes the following steps: Step S1: The graphite precursor is mixed with the catalyst and conductive liquid and ball-milled at 500-1000 rpm for 24-72 h. The resulting material is pre-carbonized at 500-800℃ for 1-6 h, then graphitized at 2200-2600℃ for 48-96 h. After that, it is cooled to room temperature in an inert atmosphere and acid-washed with a mixed acid to obtain the graphite precursor material. Step S2: Heteroatomic polymers, organotitanium compounds, and phosphorus compounds are added to an organic solvent and dispersed evenly. Then, graphite precursor materials are added and mixed evenly. The mixture is filtered, and the resulting material is then mixed evenly in a rotary kiln. The mixture is then heated to 1100-1300℃ for 6-24 hours and then cooled to 500-700℃. A reducing gas is introduced and held at a flow rate of 100-500 mL / min for 30-300 minutes to obtain the graphite composite material.

[0007] The mass ratio of graphite precursor, catalyst, and conductive liquid in step S1 of this invention is 100:1-5:100-500.

[0008] The graphite precursor mentioned in step S1 of this invention is one of petroleum coke, needle coke, pitch coke, and coal-based coke. The catalyst is one of ferric chloride, nickel chloride, copper chloride, and cobalt chloride; The phosphorus compound is one of ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid; The conductive liquid is one of carbon nanotube conductive liquid, graphene conductive liquid, or carbon black conductive liquid, with a concentration of 1-5 wt% and N-methylpyrrolidone as the solvent.

[0009] The mixed acid in step S1 of this invention is a mixed solution of concentrated hydrochloric acid (37wt%) and concentrated sulfuric acid (98wt%) in a volume ratio of 1:1.

[0010] The heteroatom polymer mentioned in step S2 of this invention is one of polythiophene, polypyrrole, polyaniline, polybenzimidazole, polyamide, polyurethane, and polyphenylene sulfide; The organotitanium compound is one of the following: tetrabutyl titanate, tetrabutyl titanate, tetrabutyl titanate, tetrapropyl titanate, titanium trichloride ethoxy, tetraisopropoxy, tetraisopropyl titanate, and tetraisopropyl titanate. The phosphorus compound is one of ammonium dihydrogen phosphate or diammonium hydrogen phosphate; The organic solvent is one of diethyl ether, benzene, chloroform, and isopropanol.

[0011] The mass ratio of the graphite precursor material, heteroatom polymer, phosphorus compound, and organotitanium compound in step S2 of this invention is 100:5-10:1-5:1-5.

[0012] The amount of organic solvent used in step S2 of this invention is 1000g.

[0013] The reducing gas in step S2 of this invention is carbon monoxide or hydrogen.

[0014] The graphite composite material with improved fast-charging performance is prepared by the preparation method described in this invention.

[0015] The application of the graphite composite material described in this invention as a negative electrode material for lithium-ion batteries.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention improves the electronic conductivity of a graphite precursor (coke raw material) by adding a conductive agent, changes the orientation of carbon through a catalyst to improve the isotropy of the material, reduces the OI value, and improves the kinetic performance of the core. The material is coated with heteroatom polymers, phosphorus compounds, and organotitanium compounds, and carbonized to obtain heteroatom / titanium dioxide / phosphorus-doped amorphous carbon. The heteroatoms improve the electronic conductivity of the material, while the large interlayer spacing, low expansion rate, and stable structure of titanium dioxide improve the lithium-ion insertion / extraction rate and rate performance. In addition, phosphorus has high specific capacity and high voltage plateau. Therefore, phosphorus doping improves the specific capacity and voltage plateau of the composite material, thereby improving fast charging performance.

[0017] 2. The soft-pack battery test shows that the capacity retention rate of the graphite composite material prepared by this invention is above 93% after 500 cycles, and the charging DCR impedance at different SOCs is significantly lower than that of the comparative example. The coin cell battery test shows that the prepared material has higher discharge specific capacity, first efficiency and diffusion coefficient than the comparative example, and has excellent performance. Attached Figure Description

[0018] Figure 1 SEM image of the graphite composite material prepared in Example 1. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0020] Example 1

[0021] Step S1: 100g of petroleum coke was mixed with 3g of ferric chloride and 300g of carbon nanotube conductive liquid with a mass concentration of 3wt%. The mixture was ball-milled at 800rpm for 48h. The resulting material was pre-carbonized at 650℃ for 3h, and then graphitized at 2400℃ for 72h. After that, it was cooled to room temperature under a nitrogen atmosphere and acid-washed with a mixed acid (volume ratio: concentrated hydrochloric acid: concentrated sulfuric acid = 1:1). The mixture was then washed with water to obtain the graphite precursor material. Step S2: 8g of polythiophene, 3g of tetrabutyl titanate, and 3g of ammonium dihydrogen phosphate were added to 1000g of diethyl ether organic solvent and dispersed evenly. Then, 100g of graphite precursor material was added and mixed evenly. The mixture was filtered, and then the resulting material was mixed evenly in a rotary kiln. The temperature was raised to 1200℃ and heat-treated for 12h. After that, the temperature was lowered to 600℃ and carbon monoxide reducing gas was introduced. The temperature was maintained at 300mL / min for 150min to obtain the graphite composite material.

[0022] Example 2

[0023] Step S1: 100g of needle coke was mixed with 1g of nickel chloride and 100g of 1wt% graphene conductive liquid. The mixture was ball-milled at 500rpm for 72h. The resulting material was pre-carbonized at 500℃ for 6h, then graphitized at 2200℃ for 96h. After that, it was cooled to room temperature under a nitrogen inert atmosphere and acid-washed with a mixed acid (volume ratio: concentrated hydrochloric acid: concentrated sulfuric acid = 1:1). The mixture was then washed with water to obtain the graphite precursor material. Step S2: 5g of polypyrrole, 1g of tetrabutyl titanate, and 1g of diammonium hydrogen phosphate were added to 1000g of chloroform organic solvent and dispersed evenly. Then, 100g of graphite precursor material was added and mixed evenly. The mixture was filtered, and then the resulting material was mixed evenly in a rotary kiln. The temperature was raised to 1100℃ and heat-treated for 24h. After that, the temperature was lowered to 500℃ and hydrogen gas was introduced. The mixture was kept at a flow rate of 100mL / min for 300min to obtain the graphite composite material.

[0024] Example 3

[0025] Step S1: 100g of graphite precursor was mixed with 5g of cobalt chloride and 500g of 5wt% carbon black conductive liquid and ball-milled at 1000rpm for 24h. The resulting material was pre-carbonized at 800℃ for 1h, then graphitized at 2600℃ for 48h. After that, it was cooled to room temperature under a nitrogen inert atmosphere and acid-washed with a mixed acid (volume ratio: concentrated hydrochloric acid: concentrated sulfuric acid = 1:1). The mixture was then washed with water to obtain the graphite precursor material. Step S2: 10g of polyaniline, 5g of tetrabutyl titanate, and 5g of ammonium phosphate were added to 1000g of isopropanol organic solvent and dispersed evenly. Then, 100g of graphite precursor material was added and mixed evenly. The mixture was filtered, and then the resulting material was mixed evenly in a rotary kiln. The temperature was raised to 1300℃ and heat-treated for 6 hours. After that, the temperature was lowered to 700℃ and hydrogen reducing gas was introduced. The mixture was kept at a flow rate of 500mL / min for 30 minutes to obtain the graphite composite material.

[0026] Comparative Example 1 Unlike Example 1, ferric chloride and carbon nanotube conductive liquid are not added in step S1, but everything else is the same as in Example 1.

[0027] Comparative Example 2 Unlike Example 1, tetrabutyl titanate and ammonium dihydrogen phosphate are not added in step S2, but otherwise the same as in Example 1.

[0028] To verify the effectiveness of the invention, the inventive team conducted a series of experiments, as follows: (1) SEM test The graphite composite material prepared in Example 1 was subjected to SEM testing, and the results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the obtained composite material exhibits a secondary granular structure with a particle size between 10-15 μm and a uniform size distribution.

[0029] (2) Button cell battery test The graphite composite materials obtained in Examples 1-3 and the graphite composite materials in Comparative Examples 1-2 were assembled into coin cells according to the following methods: A binder, conductive agent, and solvent are added to the negative electrode material and stirred until homogeneous to form a negative electrode slurry. This slurry is then coated onto copper foil, dried, rolled, and cut to obtain the negative electrode sheet. The binder is LA132, the conductive agent is SP, and the solvent is double-distilled water. The weight ratio of the negative electrode material, SP conductive agent, LA132 binder, and double-distilled water is 95:1:4:220. A lithium metal sheet is used as the counter electrode, and polyethylene propylene (PEP) is used as the separator. ( The electrolyte was prepared by using a solution with a concentration of 1.1 mol / L and a volume ratio of EC to DEC of 1:1. The battery was assembled in an argon-filled glove box.

[0030] The fabricated button cells were installed on a Wuhan 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 its rate performance (2C / 0.1C) and cycle performance (0.2C / 0.2C, 100 cycles) were calculated. The diffusion coefficient of the material was tested by GITT, and the OI value of the powder material was tested by XRD. The test results are shown in Table 1.

[0031] As shown in Table 1, the graphite composite materials prepared in Examples 1-3 exhibit higher discharge specific capacity, first-time efficiency, and diffusion coefficient than those in Comparative Examples 1-2. This may be because the doping of conductive agents in the examples increases the electronic conductivity, and the doping of catalysts alters the orientation of carbon, improving isotropy, reducing OI value, decreasing polarization, and thus increasing first-time efficiency and diffusion coefficient. Compared to Example 1, Comparative Example 1, lacking the addition of ferric chloride catalyst and carbon nanotube conductive liquid, shows increased resistivity, a higher OI value, increased polarization, and reduced specific capacity and first-time efficiency. Simultaneously, the increased electronic conductivity results in a higher rate performance, and the higher OI value indicates greater material expansion, reducing cycle performance. Compared to Example 1, Comparative Example 2, lacking the addition of tetrabutyl titanate and ammonium dihydrogen phosphate to the coating layer, has a lower diffusion coefficient. The absence of phosphorus doping also reduces the specific capacity of the composite material, thereby decreasing its rate performance and cycle performance.

[0032] (3) Soft-pack battery test The graphite composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were used as negative electrodes, respectively, and ternary materials ( ) as the positive pole, with A 2Ah soft-pack battery was prepared using EC+DEC (1:1 volume ratio, 1.1 mol / L concentration) as the electrolyte and Celegard 2400 as the separator.

[0033] In the preparation of the negative electrode, a binder, a conductive agent, and a solvent are added to the negative electrode material and stirred to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto copper foil, dried, rolled, and cut to obtain the negative electrode sheet. The binder is LA136D binder, the conductive agent is SP conductive agent, and the solvent is double-distilled water. The weight ratio of the negative electrode material, SP conductive agent, LA136D binder, and double-distilled water is 95:1:4:200.

[0034] 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.

[0035] Cyclic performance and rate testing: Cycle performance and rate testing were performed on the pouch cells of each embodiment and comparative example.

[0036] Cyclic performance test: charge / discharge voltage range of 2.8~4.2V, temperature of 25±3.0℃, charge / discharge rate of 0.5C / 1.0C, and number of cycles of 500.

[0037] Rate performance test: Charged at a 3C rate, the charging DCR impedance was tested at different SOCs (10%, 30%, 50%, 70%, 90%).

[0038] The test results for cycle performance and rate capability are shown in Table 2.

[0039] As shown in Table 2, the soft-pack lithium-ion batteries prepared using the composite electrode materials of the various embodiments of the present invention exhibit better cycle performance and rate performance than the comparative examples. This is because the composite electrode materials of the present invention have lower OI values ​​and higher specific surface areas, which improve the liquid retention performance and cycle performance. Simultaneously, the composite electrode materials of the embodiments have lower powder resistivity, which improves their kinetic performance, thereby increasing the constant current ratio during charge and discharge, i.e., improving their power performance. Compared to Comparative Example 1, Example 1 shows improved cycle performance and reduced DCR due to the increased electronic conductivity and restraint of material expansion during charge and discharge caused by the doping of conductive agents. Compared to Example 1, Comparative Example 2 shows reduced diffusion coefficient and smaller interlayer spacing due to the absence of titanium dioxide and phosphorus coating in the coating layer, leading to increased DCR and greater expansion, thus reducing cycle performance.

[0040] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing graphite composite materials with improved fast-charging performance, characterized in that, The preparation method includes the following steps: Step S1: The graphite precursor is mixed with the catalyst and conductive liquid and ball-milled at 500-1000 rpm for 24-72 h. The resulting material is pre-carbonized at 500-800℃ for 1-6 h, then graphitized at 2200-2600℃ for 48-96 h. After that, it is cooled to room temperature in an inert atmosphere and acid-washed with a mixed acid to obtain the graphite precursor material. Step S2: Heteroatomic polymers, organotitanium compounds, and phosphorus compounds are added to an organic solvent and dispersed evenly. Then, graphite precursor materials are added and mixed evenly. The mixture is filtered, and the resulting material is then mixed evenly in a rotary kiln. The mixture is then heated to 1100-1300℃ for 6-24 hours and then cooled to 500-700℃. A reducing gas is introduced and held at a flow rate of 100-500 mL / min for 30-300 minutes to obtain the graphite composite material.

2. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The mass ratio of the graphite precursor, catalyst, and conductive liquid in step S1 is 100:1-5:100-500.

3. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The graphite precursor mentioned in step S1 is one of petroleum coke, needle coke, pitch coke, and coal-associated coke. The catalyst is one of ferric chloride, nickel chloride, copper chloride, and cobalt chloride; The phosphorus compound is one of ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid; The conductive liquid is one of carbon nanotube conductive liquid, graphene conductive liquid, or carbon black conductive liquid, with a concentration of 1-5 wt% and N-methylpyrrolidone as the solvent.

4. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The mixed acid in step S1 is a mixed solution of 37wt% concentrated hydrochloric acid and 98wt% concentrated sulfuric acid in a volume ratio of 1:

1.

5. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The mass ratio of the graphite precursor material, heteroatom polymer, phosphorus compound, and organotitanium compound in step S2 is 100:5-10:1-5:1-5.

6. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The heteroatom polymer mentioned in step S2 is one of polythiophene, polypyrrole, polyaniline, polybenzimidazole, polyamide, polyurethane, and polyphenylene sulfide; The organotitanium compound is one of the following: tetrabutyl titanate, tetrabutyl titanate, tetrabutyl titanate, tetrapropyl titanate, titanium trichloride ethoxy, tetraisopropoxy, tetraisopropyl titanate, and tetraisopropyl titanate. The phosphorus compound is one of ammonium dihydrogen phosphate or diammonium hydrogen phosphate; The organic solvent is one of diethyl ether, benzene, chloroform, and isopropanol.

7. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The amount of organic solvent used in step S2 is 1000g.

8. The preparation method for improving the fast-charging performance of graphite composite materials according to claim 1, characterized in that, The reducing gas mentioned in step S2 is carbon monoxide or hydrogen.

9. A graphite composite material prepared by the preparation method for improving the fast-charging performance of graphite composite materials as described in claims 1-8.

10. The graphite composite material prepared by the method for improving the fast-charging performance of graphite composite materials as described in claims 1-8 is used as a negative electrode material for lithium-ion batteries.

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