Preparation method of graphite composite negative electrode material of lithium ion battery

Abstract

The invention discloses a lithium ion battery graphite composite negative electrode material preparation method, which comprises: 1) synthesizing a porous crystal material ZIF-8: using a certain amount of dimethylimidazole and zinc nitrate hexahydrate as raw materials, and preparing the ZIF-8 through a hydrothermal method; (2) heating and premixing: heating and fully premixing the ZIF-8 obtained in the step (1) with a certain amount of asphalt and lithium carbonate to obtain a premixed coating material; 3) graphite coating: stirring a certain amount of graphite and the premixed coating material at a high temperature to obtain pretreated graphite; and 4) carbonizing and pore-forming: putting the pretreated graphite into a tubular furnace, sealing, introducing hydrogen phosphide gas, heating, and naturally cooling to room temperature to obtain the graphite composite negative electrode material. According to the preparation method of the lithium ion battery graphite composite negative electrode material provided by the invention, the energy storage performance and the rate capability of the graphite composite material are improved, and meanwhile, the initial coulombic efficiency of the graphite material and the energy density of the lithium ion battery are also improved.

Description

Technical Field

[0001] The invention relates to the technical field of battery negative electrode material preparation, and in particular to a method for preparing a lithium ion battery graphite composite negative electrode material. Background Art

[0002] At present, the energy density of commercial lithium-ion batteries is approaching its theoretical limit. In order to further improve the energy density of lithium-ion batteries, the development of new electrode materials with high specific capacity is extremely important. Although many new electrode materials have high specific capacity, their low first coulombic efficiency limits their practical application.

[0003] Lithium phosphide is a lithium-supplementing material with high specific capacity (1550mAh / g) and high lithium source content, and can also improve the first coulombic efficiency of electrode negative materials. However, the application of lithium phosphide is still subject to several limitations. On the one hand, the current synthesis method of lithium phosphide is mainly to prepare lithium phosphide materials with lower purity through solid-phase chemical reaction between metallic lithium and red phosphorus. On the other hand, blocky and large-sized lithium phosphide is not conducive to good contact with the conductive agent, resulting in poor electronic conductivity of the lithium phosphide material. On the third hand, lithium phosphide easily reacts with water vapor in the air, resulting in more stringent requirements for the optimization methods (such as reducing the scale, carbon coating, etc.) and applications of lithium phosphide materials.

[0004] Patent CN111039269 discloses a method for preparing lithium phosphide powder by high-temperature calcination. In this method, metallic lithium and red phosphorus powder are directly combined by high-temperature calcination under an inert environment. However, this method requires long-term calcination at high temperature, which consumes a lot of energy. Since highly active metallic lithium is used for calcination, there are also high safety hazards. Therefore, it is necessary to seek a method with simple process to improve the performance of lithium phosphide materials and promote its application in electrode negative materials. At the same time, the conventional coating method is to form a carbon coating layer on the graphite surface after carbonization of the adhesive asphalt, which has the problems of poor conductivity and low lithium ion transmission rate. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a graphite composite negative electrode material for a lithium ion battery, which improves the energy storage performance and rate performance of the graphite composite material, while also improving the first coulomb efficiency of the graphite material and the energy density of the lithium ion battery.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a graphite composite negative electrode material for a lithium ion battery, the preparation method comprising the following steps:

[0007] Step 1), synthesizing the porous crystalline material ZIF-8: using a certain amount of dimethylimidazole and zinc nitrate hexahydrate as raw materials, ZIF-8 is prepared by a hydrothermal method;

[0008] Step 2), premixing by heating: the ZIF-8 obtained in step 1) is fully premixed with a certain amount of asphalt and lithium carbonate by heating to obtain a premixed coating material;

[0009] Step 3), graphite coating: stirring a certain amount of graphite and a premixed coating material at high temperature to obtain pretreated graphite;

[0010] Step 4), carbonization and pore formation: the pretreated graphite is placed in a tubular furnace, sealed, phosphine gas is introduced, the temperature is increased, and naturally cooled to room temperature to obtain a graphite composite negative electrode material.

[0011] Furthermore, the ZIF-8 material prepared in step 1) is a new metal organic framework material with adjustable pore size, high porosity, good biocompatibility and high stability, and the specific surface area is 1000-1500m 2 / g.

[0012] Furthermore, in step 1), the molar ratio of dimethylimidazole to zinc nitrate hexahydrate is 2 to 6:1.

[0013] Further, in step 1), zinc nitrate hexahydrate, dimethylimidazole and methanol are added to a reaction container, stirred at 100-400 r / min at room temperature for 0.5-1 h, then transferred to an oven at 110-130° C. for reaction for 3-5 h, and naturally cooled to room temperature after the reaction, centrifuged and washed with methanol for multiple times to collect the white solid product ZIF-8.

[0014] Furthermore, in step 2), the mass ratio of ZIF-8, lithium carbonate and asphalt is 3.5-6.5:2:8-14; and the temperature of the premixing is 110-130°C.

[0015] Furthermore, in step 3), the mass ratio of graphite to premixed coating material is 100:13-22; heating is performed at 550-650°C for 3-5h, and stirring is performed at a speed of 30-70Hz during the heating process to obtain pretreated graphite. During the coating process, CO2 and metal Zn vapor generated by the decomposition of lithium carbonate can form a mesoporous structure, and the mesoporous nanocarbon derived from the pyrolysis of ZIF-8 is uniformly dispersed on the outer surface of graphite to form a conductive network, which can reduce the contact resistance between graphite particles, thereby reducing the internal resistance of the graphite composite material, and can also provide more conductive electron and ion channels. In addition, the pore structure of the porous carbon material determines the material's capacitance energy storage performance, and the microporous structure is conducive to porous carbon energy storage.

[0016] When the pore volume of micropores increases, the resistance to ion conduction into the porous carbon channels will increase, resulting in a decrease in specific capacitance during high current density charging and discharging. When a certain proportion of mesopores exists, multiple micropores can be connected through the mesopores, effectively improving the transfer efficiency of lithium ions and accelerating the speed at which electrolyte ions are transferred from the electrode surface to the graphite composite material, thereby improving the energy storage performance and rate performance of the graphite composite material.

[0017] Furthermore, in step 4), the time of introducing phosphine gas is 20 to 40 minutes to remove the internal gas, and the temperature is raised to 1100°C and kept at this temperature for 1 to 3 hours. The Li2O produced by pyrolysis reacts with PH3 to produce lithium phosphide, and a lithium phosphide material with high purity and small size can be obtained. At the same time, under the bonding and coating effect of asphalt, the lithium phosphide material can be effectively prevented from contacting with water vapor in the air. Such a technical design can improve the first coulomb efficiency of graphite materials and improve the energy density of lithium-ion batteries.

[0018] Furthermore, the specific surface area of ​​the prepared lithium-ion battery graphite composite negative electrode material is 7 to 9.5 m 2 / g; ionic conductivity reaches 9.0~9.9*10 4 S / m; battery capacity reaches 356-359 mAh / g; battery initial efficiency reaches 92-95%.

[0019] The beneficial effects of the present invention are as follows: compared with the prior art, the method for preparing the graphite composite negative electrode material for lithium ion batteries provided by the present invention has the following advantages:

[0020] 1) ZIF-8 material with adjustable pore size, high porosity, good biocompatibility and high stability is used, and the graphite material is coated at high temperature after being mixed with asphalt and lithium carbonate. During the coating process, CO2 and metal Zn vapor generated by the decomposition of lithium carbonate can form a mesoporous structure, and the mesoporous nanocarbon derived from the pyrolysis of ZIF-8 is evenly dispersed on the outer surface of the graphite to form a conductive network, which can reduce the contact resistance between the graphite particles, thereby reducing the internal resistance of the graphite composite material, providing more electron and ion channels, and improving the energy storage performance and rate performance of the graphite composite material;

[0021] 2) During the carbonization pore-forming process, Li2O produced by pyrolysis reacts with PH3 to produce lithium phosphide, which can obtain lithium phosphide materials with higher purity and smaller size. At the same time, under the bonding and coating effects of asphalt, the lithium phosphide materials can be effectively prevented from contacting with water vapor in the air, thereby improving the initial coulomb efficiency of the graphite material and the energy density of the lithium-ion battery.

[0022] 3) The specific surface area of ​​the modified lithium-ion battery graphite composite negative electrode material can reach 7 to 9.5 m 2 / g ion conductivity can reach 9.0~9.9*10 4 S / m, the battery capacity can reach 356-359 mAh / g, and the battery initial efficiency can reach 92-95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention provides a flow chart of the preparation method. DETAILED DESCRIPTION

[0024] The present invention is further described below by specific examples, but these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0025] Example 1

[0026] S1. Add 5.12 g zinc nitrate hexahydrate, 6.16 g dimethylimidazole and 150 mL methanol into a reaction vessel, stir at 200 r / min for 0.5 h at room temperature, then transfer to a 120 °C oven for reaction for 4 h. After the reaction is completed, naturally cool to room temperature, centrifuge and wash with methanol for multiple times to collect the white solid product ZIF-8.

[0027] S2. 5.0 g ZIF-8, 2.0 g lithium carbonate and 11.0 g asphalt are premixed by heating at 120° C. to obtain a premixed coating material.

[0028] S3. Heat 100 g of graphite and the premixed coating material at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0029] S4. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0030] Example 2

[0031] S1. Add 5.12 g zinc nitrate hexahydrate, 6.16 g dimethylimidazole and 150 mL methanol into a reaction vessel, stir at 200 r / min for 0.5 h at room temperature, then transfer to a 120 °C oven for reaction for 4 h. After the reaction is completed, naturally cool to room temperature, centrifuge and wash with methanol for multiple times to collect the white solid product ZIF-8.

[0032] S2. 3.5 g ZIF-8, 2.0 g lithium carbonate and 11.0 g asphalt are premixed by heating at 120° C. to obtain a premixed coating material.

[0033] S3. Heat 100 g of graphite and the premixed coating material at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0034] S4. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0035] Example 3

[0036] S1. Add 5.12 g zinc nitrate hexahydrate, 6.16 g dimethylimidazole and 150 mL methanol into a reaction vessel, stir at 200 r / min for 0.5 h at room temperature, then transfer to a 120 °C oven for reaction for 4 h. After the reaction is completed, naturally cool to room temperature, centrifuge and wash with methanol for multiple times to collect the white solid product ZIF-8.

[0037] S2. Premix 6.5 g ZIF-8, 2.0 g lithium carbonate and 11.0 g asphalt under heating at 120° C. to obtain a premixed coating material.

[0038] S3. Heat 100 g of graphite and the premixed coating material at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0039] S4. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0040] Example 4

[0041] S1. Add 5.12 g zinc nitrate hexahydrate, 6.16 g dimethylimidazole and 150 mL methanol into a reaction vessel and stir at 200 r / min for 0.5 h at room temperature.

[0042] The mixture was transferred to an oven at 120° C. for reaction for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged and washed with methanol for multiple times to collect the white solid product P-ZIF-8.

[0043] S2. 5.0 g ZIF-8, 2.0 g lithium carbonate and 8.0 g asphalt are premixed by heating at 120° C. to obtain a premixed coating material.

[0044] S3. Heat 100 g of graphite and the premixed coating material at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0045] S4. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0046] Example 5

[0047] S1. Add 5.12 g zinc nitrate hexahydrate, 6.16 g dimethylimidazole and 150 mL methanol into a reaction vessel, stir at 200 r / min for 0.5 h at room temperature, then transfer to a 120 °C oven for reaction for 4 h. After the reaction is completed, naturally cool to room temperature, centrifuge and wash with methanol for multiple times to collect the white solid product ZIF-8.

[0048] S2. 5.0 g ZIF-8, 2.0 g lithium carbonate and 14.0 g asphalt are premixed by heating at 120° C. to obtain a premixed coating material.

[0049] S3. Heat 100 g of graphite and the premixed coating material at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0050] S4. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0051] Comparative Example 1

[0052] S1. Add 5.12 g zinc nitrate hexahydrate, 6.16 g dimethylimidazole and 150 mL methanol into a reaction vessel, stir at 200 r / min for 0.5 h at room temperature, then transfer to a 120 °C oven for reaction for 4 h. After the reaction is completed, naturally cool to room temperature, centrifuge and wash with methanol for multiple times to collect the white solid product ZIF-8.

[0053] S2. 5.0 g ZIF-8 and 11.0 g asphalt are premixed by heating at 120° C. to obtain a premixed coating material.

[0054] S3. Heat 100 g of graphite and the premixed coating material at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0055] S4. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0056] Comparative Example 2

[0057] S1, 2.0 g of lithium carbonate and 11.0 g of asphalt were premixed by heating at 120°C to obtain a premixed coating material.

[0058] S2. 100 g of graphite and the premixed coating material were heated at 600° C. for 4 h, accompanied by stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0059] S3. Put the pretreated graphite into a tubular furnace, seal it, pass phosphine gas for 30 minutes to expel the internal gas, heat it to 1100° C. and keep it warm for 2 hours, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0060] The performance test results of Examples 1-5 and Comparative Examples 1-2 are as follows.

[0061] batch number <![CDATA[Specific surface area (m 2 / g)]]> Ionic conductivity (S / m) Gram capacity (mAh / g) First discharge efficiency (%) Example 1 8.415 <![CDATA[9.901*10 4 ]]> 359.01 94.96 Example 2 7.568 <![CDATA[9.314*10 4 ]]> 356.26 92.68 Example 3 9.412 <![CDATA[9.623*10 4 ]]> 357.56 93.56 Example 4 8.215 <![CDATA[9.512*10 4 ]]> 357.23 93.42 Example 5 8.566 <![CDATA[9.794*10 4 ]]> 358.73 94.21 Comparative Example 1 7.012 <![CDATA[9.215*10 4 ]]> 352.11 90.12 Comparative Example 2 7.127 <![CDATA[9.027*10 4 ]]> 351.69 89.78

[0062] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing a graphite composite negative electrode material for a lithium ion battery, characterized in that: The preparation method comprises the following steps: Step 1), synthesizing the porous crystalline material ZIF-8: using a certain amount of dimethylimidazole and zinc nitrate hexahydrate as raw materials, ZIF-8 is prepared by a hydrothermal method; Step 2), heating premixing: heating and fully premixing the ZIF-8 obtained in step 1) with a certain amount of asphalt and lithium carbonate to obtain a premixed coating material; Step 3), graphite coating: stirring a certain amount of graphite and a premixed coating material at high temperature to obtain pretreated graphite; Step 4), carbonization and pore formation: the pretreated graphite is placed in a tubular furnace, sealed, phosphine gas is introduced, the temperature is increased, and the furnace is naturally cooled to room temperature to obtain a graphite composite negative electrode material.

2. The method for preparing a graphite composite negative electrode material for a lithium ion battery according to claim 1, characterized in that: The specific surface area of ​​the ZIF-8 material prepared in step 1) is 1000-1500 m 2 / g.

3. The method for preparing a graphite composite negative electrode material for a lithium ion battery according to claim 1, characterized in that: In step 1), the molar ratio of dimethylimidazole to zinc nitrate hexahydrate is 2 to 6:

1.

4. The method for preparing a lithium-ion battery graphite composite negative electrode material according to claim 1, characterized in that: In step 1), zinc nitrate hexahydrate, dimethylimidazole and methanol are added to a reaction vessel, stirred at 100-400 r / min at room temperature for 0.5-1 h, then transferred to an oven at 110-130° C. for reaction for 3-5 h. After the reaction is completed, it is naturally cooled to room temperature, centrifuged and washed with methanol for multiple times to collect the white solid product ZIF-8.

5. The method for preparing a lithium-ion battery graphite composite negative electrode material according to claim 1, characterized in that: In step 2), the mass ratio of ZIF-8, lithium carbonate and asphalt is 3.5-6.5:2:8-14; the temperature of heating premix is ​​110-130°C.

6. The method for preparing a lithium-ion battery graphite composite negative electrode material according to claim 1, characterized in that: In step 3), the mass ratio of graphite to premixed coating material is 100:13-22; heating is performed at 550-650° C. for 3-5 hours, accompanied by stirring at a speed of 30-70 Hz during the heating process, to obtain pretreated graphite.

7. The method for preparing a graphite composite negative electrode material for a lithium ion battery according to claim 1, characterized in that: In step 4), the phosphine gas is introduced for 20 to 40 minutes to remove the internal gas, and the temperature is raised to 1100° C. and maintained for 1 to 3 hours.

8. The method for preparing a graphite composite negative electrode material for a lithium ion battery according to claim 1, characterized in that: The specific surface area of ​​the prepared graphite composite negative electrode material for lithium-ion batteries is 7 to 9.5 m 2 / g; ionic conductivity reaches 9.0~9.9*10 4 S / m; battery capacity reaches 356-359 mAh / g; battery initial efficiency reaches 92-95%.

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