Preparation method of a graphite composite negative electrode material for a lithium-ion battery

Abstract

The present invention discloses a preparation method of a graphite composite anode material for a lithium-ion battery, comprising the following steps: Step 1), synthesizing porous crystal material ZIF-8: using a certain amount of dimethylimidazole and zinc nitrate hexahydrate as raw materials, preparing ZIF-8 by a hydrothermal method; Step 2), heating and 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 the premixed coating material at a high temperature to obtain pretreated graphite; Step 4), carbonization and pore formation: placing the pretreated graphite in a tubular furnace, sealing it, introducing phosphine gas, heating up, and naturally cooling to room temperature to obtain the graphite composite anode material. The preparation method of the graphite composite anode material for a lithium-ion battery provided by the present invention improves the energy storage performance and rate performance of the graphite composite material, and at the same time also improves the first Coulomb efficiency of the graphite material and the energy density of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of battery anode materials, and particularly to a method for preparing a graphite composite anode material for a lithium-ion battery. 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 initial Coulomb efficiency limits their practical applications.

[0003] Lithium phosphide is a lithium supplement material with a high specific capacity (1550 mAh / g) and a high lithium source content, and can also improve the initial Coulomb efficiency of the anode material of the electrode. However, the application of lithium phosphide is still limited in several aspects. First, at present, the synthesis method of lithium phosphide is mainly to prepare lithium phosphide materials with low purity through the solid-phase chemical reaction between metallic lithium and red phosphorus. Second, massive and relatively large-sized lithium phosphide is not conducive to good contact with the conductive agent, resulting in poor electronic conductivity of the lithium phosphide material. Third, lithium phosphide is extremely easy to react 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 the lithium phosphide material.

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

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a graphite composite anode material for a lithium-ion battery, which improves the energy storage performance and rate performance of the graphite composite material, and at the same time also improves the initial 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 problems is: a method for preparing a graphite composite anode material for a lithium-ion battery, the preparation method comprising the following steps:

[0007] Step 1): Synthesize porous crystalline material ZIF-8: Using a certain amount of dimethylimidazole and zinc nitrate hexahydrate as raw materials, prepare ZIF-8 by a hydrothermal method;

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

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

[0010] Step 4), carbonization and pore formation: Place the pretreated graphite in a tube furnace, seal it, introduce phosphine gas, heat it up, and naturally cool it to room temperature to obtain a graphite composite negative electrode material.

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

[0012] Furthermore, in Step 1), in terms of molar ratio, dimethylimidazole: zinc nitrate hexahydrate = 2 - 6:1.

[0013] Furthermore, in Step 1), add zinc nitrate hexahydrate, dimethylimidazole, and methanol to a reaction vessel, stir at 100 - 400 r / min at room temperature for 0.5 - 1 h, then transfer it to an oven at 110 - 130 °C for reaction for 3 - 5 h. After the reaction, naturally cool it to room temperature, centrifuge it, and wash it with methanol 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; the temperature for heating and premixing is 110 - 130 °C.

[0015] Furthermore, in Step 3), the mass ratio of graphite and the premixed coating material is 100:13 - 22; heat it at 550 - 650 °C for 3 - 5 h, and stir it at a rotation speed of 30 - 70 Hz during the heating process to obtain pretreated graphite. During the coating process, CO2 generated by the decomposition of lithium carbonate and metal Zn vapor can form a mesoporous structure. The derived mesoporous nanocarbon 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 electron and ion conduction channels. Moreover, the pore structure of the porous carbon material determines the capacitance energy storage performance of the material, and the microporous structure is beneficial to the energy storage of the porous carbon.

[0016] When the micropore volume increases, the conduction resistance of ions into the pores of the porous carbon increases, resulting in a decrease in specific capacitance during charge and discharge at high current densities. When a certain proportion of mesopores exists, multiple micropores can be connected through the mesopores, effectively improving the transfer efficiency of lithium ions, accelerating the speed of electrolyte ions transmitted from the electrode surface to the graphite composite material, thereby improving the energy storage performance and rate performance of the graphite composite material.

[0017] Further, in step 4), the time for introducing phosphine gas is 20 - 40 min to remove internal gases, and the temperature is raised to 1100 °C and kept warm for 1 - 3 h. The Li2O and PH3 produced by pyrolysis react to produce lithium phosphide, and lithium phosphide materials with higher purity and smaller size can be obtained. At the same time, under the bonding and coating effects of asphalt, it can effectively prevent the lithium phosphide material from contacting with water vapor in the air. Such a technical design can improve the initial Coulomb efficiency of the graphite material and the energy density of the lithium-ion battery.

[0018] Further, the specific surface area of the prepared graphite composite anode material for lithium-ion batteries reaches 7 - 9.5 m 2 / g; the ionic conductivity reaches 9.0 - 9.9×10 4 S / m; the battery capacity reaches 356 - 359 mAh / g; the initial efficiency of the battery reaches 92 - 95%.

[0019] The beneficial effects of the present invention are as follows: Compared with the prior art, the preparation method of the graphite composite anode material for lithium-ion batteries provided by the present invention has the following advantages:

[0020] 1) Using ZIF-8 materials with adjustable pore size, high porosity, good biocompatibility, and high stability, after mixing with asphalt and lithium carbonate, the graphite material is coated at high temperature. During the coating process, CO2 generated by the decomposition of lithium carbonate and metal Zn vapor can form a mesoporous structure. The derived mesoporous nanocarbon from the pyrolysis of ZIF-8 is uniformly dispersed on the outer surface of the 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, providing more electron and ion conduction channels, and improving the energy storage performance and rate performance of the graphite composite material;

[0021] 2) During the carbonization and pore formation process, the Li2O produced by pyrolysis reacts with PH3 to produce lithium phosphide, and lithium phosphide materials with higher purity and smaller size can be obtained. At the same time, under the bonding and coating effects of asphalt, it can effectively prevent the lithium phosphide material from contacting with water vapor in the air, 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 graphite composite anode material for lithium-ion batteries modified by the present invention can reach 7 - 9.5 m 2The / g ionic conductivity can reach 9.0 - 9.9 * 10 4 S / m, the battery capacity can reach 356 - 359 mAh / g, and the initial efficiency of the battery can reach 92 - 95%. Description of the Drawings

[0023] Figure 1 It is a flowchart of the preparation method provided by the present invention. Detailed Embodiments

[0024] The present invention will be further described below through specific examples. However, these examples are only used to illustrate the present invention and not to limit the scope of the present invention.

[0025] Example 1

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

[0027] S2. Heat and premix 5.0 g of ZIF-8, 2.0 g of lithium carbonate, and 11.0 g of pitch 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, with stirring at a rotation speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0029] S4. Put the pretreated graphite into a tubular furnace, seal it, introduce phosphine gas for 30 min to remove the internal gas, heat to 1100 °C and hold for 2 h, and naturally cool to room temperature to obtain a graphite composite negative electrode material.

[0030] Example 2

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

[0032] S2. Heat and premix 3.5 g of ZIF-8, 2.0 g of lithium carbonate, and 11.0 g of pitch 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, with stirring at a rotation speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0034] S4. Place the pretreated graphite into a tube furnace, seal it, introduce phosphine gas for 30 min to remove the internal gas, heat it to 1100 °C and hold for 2 h, and then naturally cool it to room temperature to obtain a graphite composite anode material.

[0035] Example 3

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

[0037] S2. Heat and premix 6.5 g of ZIF-8, 2.0 g of lithium carbonate, and 11.0 g of pitch 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, with stirring at a rotation speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0039] S4. Place the pretreated graphite into a tube furnace, seal it, introduce phosphine gas for 30 min to remove the internal gas, heat it to 1100 °C and hold for 2 h, and then naturally cool it to room temperature to obtain a graphite composite anode material.

[0040] Example 4

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

[0042] Transfer it to an oven at 120 °C and react for 4 h. After the reaction, naturally cool it to room temperature, centrifuge it, and wash it with methanol multiple times to collect the white solid product P-ZIF-8.

[0043] S2. Heat and premix 5.0 g of ZIF-8, 2.0 g of lithium carbonate, and 8.0 g of pitch 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, with stirring at a rotation speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0045] S4. Place the pretreated graphite into a tube furnace, seal it, introduce phosphine gas for 30 min to remove the internal gas, heat it to 1100 °C and hold for 2 h, then naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0046] Example 5

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

[0048] S2. Heat and premix 5.0 g of ZIF-8, 2.0 g of lithium carbonate and 14.0 g of pitch 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, with stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0050] S4. Place the pretreated graphite into a tube furnace, seal it, introduce phosphine gas for 30 min to remove the internal gas, heat it to 1100 °C and hold for 2 h, then naturally cool it to room temperature to obtain a graphite composite negative electrode material.

[0051] Comparative Example 1

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

[0053] S2. Heat and premix 5.0 g of ZIF-8 and 11.0 g of pitch 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, with stirring at a speed of 50 Hz during the heating process, to obtain pretreated graphite.

[0055] S4. Place the pretreated graphite into a tube furnace, seal it, introduce phosphine gas for 30 min to remove the internal gas, heat it to 1100 °C and hold for 2 h, then 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 are heated and premixed at 120 °C to obtain a premixed coating material.

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

[0059] S3. The pretreated graphite is placed in a tubular furnace, sealed, and phosphine gas is introduced for 30 min to remove the internal gas. Then it is heated to 1100 °C and kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain a graphite composite anode material.

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

[0061] Lot number <![CDATA[Specific surface area (m 2 / g)]]> Ionic conductivity (S / m) Specific capacity (mAh / g) Initial 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 embodiments are only used to illustrate the present invention, rather than to limit the present invention. Those of ordinary skill 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 shall be defined by the claims.

Claims

1. A preparation method of a graphite composite negative electrode material for a lithium-ion battery, characterized in that: The preparation method includes the following steps: Step 1), synthesize porous crystal material ZIF-8: Using a certain amount of dimethylimidazole and zinc nitrate hexahydrate as raw materials, prepare ZIF-8 by hydrothermal method; Step 2), heat and premix: Heat and premix 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: Stir a certain amount of graphite and the premixed coating material at high temperature to obtain pretreated graphite; Step 4), carbonize and form pores: Place the pretreated graphite in a tubular furnace, seal it, introduce phosphine gas, raise the temperature, and naturally cool to room temperature to obtain a graphite composite negative electrode material.

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

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

1.

4. The preparation method of a graphite composite anode material for a lithium-ion battery according to claim 1, characterized in that: In step 1), add zinc nitrate hexahydrate, dimethylimidazole and methanol into a reaction vessel, stir at 100-400 r / min at room temperature for 0.5-1 h, then transfer it to an oven at 110-130 °C for reaction for 3-5 h. After the reaction, naturally cool to room temperature, centrifuge and wash with methanol multiple times to collect the white solid product ZIF-8.

5. The preparation method of a graphite composite anode material for a lithium-ion battery 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 for heat and premix is 110-130 °C.

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

7. The preparation method of a graphite composite negative electrode material for a lithium-ion battery according to claim 1, characterized in that: In step 4), the time for introducing phosphine gas is 20-40 min to remove internal gas, and raise the temperature to 1100 °C and keep it warm for 1-3 h.

8. The preparation method of 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 anode material for lithium-ion batteries reaches 7-9.5 m 2 / g; the ionic conductivity reaches 9.0-9.9*10 4 S / m; the battery capacity reaches 356-359 mAh / g; the initial efficiency of the battery reaches 92-95%.

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