Porous carbon coated graphite composite material for energy storage battery and preparation method of porous carbon coated graphite composite material

Abstract

The invention discloses a porous carbon-coated graphite composite material for an energy storage battery and a preparation method of the porous carbon-coated graphite composite material. The porous carbon-coated graphite composite material consists of inner core graphite and lithium heteroatom-doped porous carbon coated on the surface of the inner core graphite, the preparation method comprises the following steps: preparing an organic template agent solution, adding resin and an amino organic lithium compound, uniformly mixing, adding a hydrogen peroxide oxidizing agent, reacting, filtering, and activating at high temperature to obtain lithium-doped porous carbon; the preparation method comprises the following steps: adding lithium-doped porous carbon into an organic solvent, then adding graphite and an organic aluminum-based compound, uniformly dispersing, dropwise adding an amino solution, carrying out chemical reaction at the temperature of 50-120 DEG C, filtering, and carrying out vacuum drying and high-temperature carbonization on obtained filter residues to obtain the lithium-doped porous carbon composite material. The cycle performance and the storage performance of the graphite can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of lithium-ion battery materials, specifically a porous carbon-coated graphite composite material for energy storage batteries, and also relates to a preparation method of the porous carbon-coated graphite composite material for energy storage batteries. Background Art

[0002] At present, the negative electrode materials for energy storage batteries on the market are mainly single-particle artificial graphite, which has the advantages of small specific surface area, few surface defects, and high isotropy. However, due to poor liquid absorption performance and high swelling at full charge, the cycle performance of the material is reduced. To this end, doping heteroatoms into amorphous carbon on the material surface is used to reduce the defects of the material, improve the first efficiency and cycle performance of the material. For example, patent application number CN202211634265.8 discloses a long-cycle lithium battery negative electrode material, its preparation method, a negative electrode sheet and a lithium battery. The negative electrode material includes a core, an intermediate layer coating the core, and an outer layer coating the intermediate layer; the core includes a carbon-based negative electrode active material, the intermediate layer includes fluorine-doped amorphous carbon, and the outer layer includes a film-forming auxiliary agent. Coating a fluorine-doped amorphous carbon layer on the surface of the carbon-based negative electrode active material can effectively inhibit the co-insertion of solvated lithium ions and prevent the structural damage of the active material during the cycle. The effect of the fluorine-doped amorphous carbon layer formed by the chemical vapor deposition coating process is the best; and uniformly loading a film-forming auxiliary agent layer on the outer layer surface is beneficial to forming a uniform and stable SEI film on the negative electrode surface, ensuring the cycle performance, stability and service life of the assembled battery. However, the swelling of the negative electrode material during the cycle causes the reaction recombination of SEI to consume lithium ions, reducing the cycle performance and resulting in a limited improvement in the cycle performance of the negative electrode material. Summary of the Invention

[0003] The purpose of the present invention is to provide a porous carbon-coated graphite composite material for energy storage batteries that can improve the cycle performance and storage performance of graphite, overcoming the above-mentioned drawbacks.

[0004] Another purpose of the present invention is to provide a preparation method of the porous carbon-coated graphite composite material for energy storage batteries.

[0005] A porous carbon-coated graphite composite material for energy storage batteries of the present invention is composed of a core graphite and lithium heteroatom-doped porous carbon coated on the surface; calculated according to the mass ratio of the composite material of 100%, the mass ratio of the outer shell is 5-10 wt%; the outer shell is composed of 1-5 wt% of lithium oxide, 1-5 wt% of aluminum oxide, 0.5-2% of heteroatoms, 5-10 wt% of porous carbon, and the rest is amorphous carbon.

[0006] In the above-mentioned porous carbon-coated graphite composite material for energy storage batteries, the heteroatom is a nitrogen atom.

[0007] A preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to the present invention comprises the following steps: Step S1: According to the mass ratio of metal-organic framework: resin: lithium amino-organic compound: hydrogen peroxide = 5 - 15: 100: 1 - 5: 1 - 5, add the metal-organic framework to an organic solvent to prepare an organic template agent solution with a mass concentration of 1 - 10%. Then add the resin and the lithium amino-organic compound, mix them evenly, add hydrogen peroxide, and react at a temperature of 50 - 120°C for 6 - 24 h. Filter, and activate the filter residue at a high temperature of 900 - 1300°C for 1 - 6 h to obtain lithium-doped porous carbon; Step S2: According to the mass ratio of lithium-doped porous carbon: organic solvent: graphite: aluminum organic compound: organic base = 5 - 15: 500: 100: 5 - 10: 5 - 10, add the lithium-doped porous carbon to the organic solvent, then add graphite and the aluminum organic compound, disperse them evenly, dropwise add the organic base, and carry out a chemical reaction at a temperature of 50 - 120°C. Filter, and vacuum-dry the obtained filter residue at 80°C for 24 h, and carbonize it at a high temperature of 1000 - 1300°C for 1 - 6 h to obtain the product.

[0008] The metal-organic framework described in Step S1 is one of ZIF-8, MOF-74, MOF-525, ZIF-67, UIO-66 or PFC-1; the organic solvent is one of N-methylpyrrolidone, acetone, dimethylformamide or dimethylacetamide.

[0009] The resin described in Step S1 is one of urea-formaldehyde resin, polyimide resin, benzoxazine resin or polyarylacetylene resin.

[0010] The lithium amino-organic compound described in Step S1 is one of lithium amide, lithium (dimethylamino) trihydroborate, lithium diisopropylamide, lithium hexamethyldisilazide or lithium amide.

[0011] The aluminum organic compound described in Step S2 is one of aluminum acetate, aluminum distearate, aluminum citrate, aluminum isooctoate, aluminum abietate, aluminum stearate, aluminum lactate or aluminum diacetate; the organic base is one of pyridine, imidazole, indole or pyrrole; the organic solvent is one of methanol, ethanol, propanol, ethylene glycol, glycerol or propylene glycol.

[0012] Compared with the prior art, the present invention has obvious beneficial effects. From the above technical solutions, it can be seen that in the present invention, resin, amino organolithium compound, and metal-organic framework are carbonized and activated to obtain nitrogen and lithium-doped porous carbon. The lithium-doped porous carbon itself has a high pore structure, which can reduce swelling and improve the liquid retention performance, thereby improving the cycling performance. The amino organolithium compound is polymerized under the condition of hydrogen peroxide oxidant to obtain a polyamino lithium compound to improve the structural stability and electronic conductivity of the material; the high porosity of the metal-organic framework is used to improve the pore strength of the porous carbon, and to improve the lithium storage function of the material and reduce swelling; the organoaluminum compound reacts with the organic base at a temperature of 50-120 °C to generate aluminum hydroxide, which is carbonized to obtain porous alumina and coated on the surface of graphite to reduce defects and improve the initial efficiency. Description of the Drawings

[0013] Figure 1 SEM diagram of Example 1. Detailed Description of the Invention

[0014] Example 1 A preparation method of a porous carbon-coated graphite composite material for energy storage batteries, comprising the following steps: Step S1: Add 10 g of ZIF-8 to 200 g of N-methylpyrrolidone to prepare an organic template agent solution with a mass concentration of 5 wt%, add 100 g of urea-formaldehyde resin and 3 g of amino lithium and mix evenly, then add 3 g of hydrogen peroxide, react at a temperature of 80 °C for 12 h, filter, and activate the obtained filter residue at a high temperature of 1100 °C for 3 h to obtain lithium-doped porous carbon; Step S2: Add 10 g of lithium-doped porous carbon to 500 g of N-methylpyrrolidone, then add 100 g of artificial graphite and 8 g of aluminum acetate and disperse evenly, dropwise add 8 g of pyridine solution, and carry out a chemical reaction at a temperature of 80 °C for 3 h, filter, and vacuum-dry the obtained filter residue at 80 °C for 24 h and carbonize it at a high temperature of 1200 °C for 3 h to obtain the product.

[0015] Example 2 A preparation method of a porous carbon-coated graphite composite material for energy storage batteries, comprising the following steps: Step S1: Add 5 g of MOF-74 to 500 g of acetone solvent to prepare an organic template agent solution with a mass concentration of 1 wt%, add 100 g of polyimide resin and 1 g of diisopropylamino lithium and mix evenly, then add 1 g of hydrogen peroxide oxidant, react at a temperature of 50 °C for 24 h, filter, and activate the obtained filter residue at a high temperature of 900 °C for 6 h to obtain lithium-doped porous carbon; Step S2: Add 5 g of lithium-doped porous carbon to 500 g of N-methylpyrrolidone organic solvent, then add 100 g of artificial graphite and 5 g of aluminum distearate, disperse them evenly, dropwise add 5 g of imidazole solution, and carry out a chemical reaction at 50 °C for 6 h. Filter, and vacuum dry the obtained filter residue at 80 °C for 24 h, and then perform high-temperature carbonization at 1000 °C for 6 h to obtain the product.

[0016] Example 3 A preparation method of a porous carbon-coated graphite composite material for energy storage batteries, comprising the following steps: Step S1: Add 15 g of MOF-525 to 150 g of dimethylformamide solvent to prepare an organic template agent solution with a mass concentration of 10 wt%, then add 100 g of benzoxazine resin and 5 g of lithium hexamethyldisilazide, mix them evenly, add 5 g of hydrogen peroxide oxidant, and react at 120 °C for 6 h. Filter, and perform high-temperature activation of the obtained material at 1300 °C for 1 h to obtain lithium-doped porous carbon; Step S2: Add 15 g of lithium-doped porous carbon to 500 g of N-methylpyrrolidone organic solvent, then add 100 g of artificial graphite and 10 g of aluminum citrate, disperse them evenly, then dropwise add 10 g of indole solution, and carry out a chemical reaction at 120 °C for 1 h. Filter, and vacuum dry the obtained filter residue at 80 °C for 24 h, and then perform high-temperature carbonization at 1300 °C for 1 h to obtain the product.

[0017] Comparative Example 1: A preparation method of a graphite composite material for energy storage batteries, comprising: Different from Example 1, ZIF-8 metal organic framework is not added in Step S1, and the others are the same as in Example 1.

[0018] Comparative Example 2: A preparation method of a graphite composite material for energy storage batteries, comprising: Different from Example 1, lithium amide is not added in Step S1, and the others are the same as in Example 1.

[0019] Comparative Example 3: A preparation method of a graphite composite material for energy storage batteries, comprising: Different from Example 1, aluminum acetate and pyridine are not added in Step S2, and the others are the same as in Example 1.

[0020] Test Example 1: SEM test Perform SEM test on the porous carbon-coated graphite composite material prepared in Example 1, and the results are as Figure 1 shown. It can be seen from Figure 1 that the material presents a single-particle structure, with some materials coated on the surface, low smoothness, and the particle size is between 10 - 15 μm.

[0021] Experimental Example 2: Physicochemical Property Test The specific surface area of the graphite composite anode materials in Examples 1-3 and Comparative Examples 1-3 was tested according to the test method in the standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-Ion Batteries". And the diffusion coefficient of its powder material was tested by GITT; the powder resistivity was tested by a four-probe tester; the OI value of its powder was also tested by XRD; the test results are shown in Table 1.

[0022] Table 1 As can be seen from Table 1, the diffusion coefficient and resistivity of the porous carbon-coated graphite composite materials prepared in Examples 1-3 are significantly better than those in Comparative Examples 1-3. The reason is that doping lithium ions in the material improves the ionic conductivity of the material, and coating porous alumina improves the lithium ion transport rate of the material, improves the diffusion coefficient of the material and reduces the powder resistivity.

[0023] Experimental Example 3: Coin Cell Test The porous carbon-coated graphite composite materials prepared in Examples 1-3 and the graphite composite materials in Comparative Examples 1-3 were assembled into coin cells respectively according to the following method: the graphite composite anode materials prepared in Examples 1-3 and Comparative Examples 1-3 were used as the anode (the dosage ratio of the composite anode material, SP, PVDF, and NMP was 90g:4g:6g:250mL), and a coin cell was assembled with a lithium sheet, electrolyte and separator in a glove box where the argon and water content were both lower than 0.1 ppm. Among them, the separator was celegard 2400; the electrolyte was a solution of LiPF6, and in the electrolyte, the concentration of LiPF6 was 1 mol / L, and the solvent was a mixed solution obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DMC) according to a weight ratio of 1:1.

[0024] The performance of the prepared coin cells was tested by a blue battery tester respectively. The test conditions were: charge and discharge at a rate of 0.1C, the voltage range was 0.005-2V, and the test was stopped after 3 cycles, and then the discharge specific capacity under the condition of 1C was tested, and the rate performance of 1C / 0.1C and the cycle performance (25±3°C, 0.2C / 0.2C, 100 cycles) were calculated. The test results are shown in Table 2.

[0025] Table 2 As can be seen from Table 2, for the coin cells using the porous carbon-coated graphite composite materials of Examples 1-3, their discharge specific capacity and initial efficiency are significantly higher than those of Comparative Examples 1-3. The experimental results show that the reason is that coating lithium on the material surface improves the diffusion rate of lithium ions during the charge and discharge process, improves the rate and cycle performance, and porous alumina reduces its irreversible capacity and improves the initial efficiency.

[0026] Test Example 4: Performance Test of Soft Pack Battery Using the porous carbon-coated graphite composites of Examples 1-3 and Comparative Examples 1-3 as the negative electrode active material, a 5 Ah soft pack battery was assembled with the positive electrode active material lithium iron phosphate, the electrolyte, and the separator.

[0027] Among them, when preparing the negative electrode, a binder, a conductive agent, and a solvent were added to the negative electrode material, and stirred and mixed evenly to make a negative electrode slurry. The negative electrode slurry was coated on the copper foil, dried, rolled, and cut to obtain a negative electrode sheet. The binder was LA132 binder, the conductive agent was SP conductive agent, the solvent was secondary distilled water, and the weight ratio of the negative electrode material, SP conductive agent, LA132 binder to secondary distilled water was 95 g: 1 g: 4 g: 220 mL.

[0028] Among them, the separator was celegard 2400, and the electrolyte was a LiPF6 solution (the solvent was a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 was 1.1 mol / L). The cycle and rate performance of the prepared soft pack battery were tested, and the test results are shown in Table 3.

[0029] 1) Room temperature cycle performance: The 500-week cycle performance of the battery was tested at a charge-discharge rate of 1C / 1C and a voltage range of 2.5V-3.65V at a temperature of 25±3°C; 2) Rate performance: At a rate of 2C, the battery was charged to 100% SOC using a constant current + constant voltage mode (2C constant current charging + 0.1C constant voltage charging), and then the constant current ratio = constant current capacity / (constant current capacity + constant voltage capacity) was calculated.

[0030] Table 3

[0031] The cycle performance and rate performance of the soft pack battery prepared from the porous carbon-coated graphite composite material obtained in Table 3. It can be seen from the table that the cycle performance of the batteries of Examples 1-3 is significantly better than that of Comparative Examples 1-3. The reason is that the lithium salt coated on the surface of the graphite composite material in the examples reduces the consumption of lithium ions during the charge-discharge process and has high liquid retention performance, improving its cycle performance; at the same time, the materials in the examples have high diffusion coefficients and low resistivity, improving the rate performance.

[0032] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. For those skilled in the art, the present invention can have various modifications and changes, and any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention.

Claims

1. A porous carbon-coated graphite composite material for energy storage batteries, characterized in that: It consists of core graphite and lithium heteroatom-doped porous carbon coated on the surface; calculated according to the mass ratio of the composite material being 100%, the mass ratio of the outer shell is 5-10 wt%; the outer shell is composed of 1-5 wt% lithium oxide, 1-5 wt% aluminum oxide, 0.5-2% heteroatoms, 5-10 wt% porous carbon, and the rest is amorphous carbon.

2. A porous carbon-coated graphite composite material for an energy storage battery as described in claim 1, wherein the heteroatom is a nitrogen atom.

3. A preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery, comprising the following steps: Step S1: According to the mass ratio of metal-organic framework: resin: amino organolithium compound: hydrogen peroxide = 5-15: 100: 1-5: 1-5, add the metal-organic framework to an organic solvent to prepare an organic template agent solution with a mass concentration of 1-10%, then add the resin and the amino organolithium compound and mix evenly, then add hydrogen peroxide, react at a temperature of 50-120 °C for 6-24 h, filter, and activate the filter residue at a high temperature of 900-1300 °C for 1-6 h to obtain lithium-doped porous carbon; Step S2: According to the mass ratio of lithium-doped porous carbon: organic solvent: graphite: organoaluminum compound: organic base = 5-15: 500: 100: 5-10: 5-10, add the lithium-doped porous carbon to the organic solvent, then add graphite and the organoaluminum-based compound and disperse evenly, then dropwise add the organic base, carry out a chemical reaction at a temperature of 50-120 °C, filter, and vacuum-dry the obtained filter residue at 80 °C for 24 h and carbonize it at a high temperature of 1000-1300 °C for 1-6 h to obtain the product.

4. The preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to claim 3, wherein: The metal-organic framework described in Step S1 is one of ZIF-8, MOF-74, MOF-525, ZIF-67, UIO-66 or PFC-1; the organic solvent is one of N-methylpyrrolidone, acetone, dimethylformamide or dimethylacetamide.

5. The preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to claim 3, wherein: The resin described in Step S1 is one of urea-formaldehyde resin, polyimide resin, benzoxazine resin or polyarylacetylene resin.

6. The preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to claim 3, wherein: The amino organolithium compound described in Step S1 is one of lithium amide, lithium (dimethylamino) trihydroborate, lithium diisopropylamide, lithium hexamethyldisilazide or lithium amide.

7. The preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to claim 3, wherein: The organoaluminum compound described in Step S2 is one of aluminum acetate, aluminum distearate, aluminum citrate, aluminum isooctoate, aluminum abietate, aluminum octadecanoate, aluminum lactate or aluminum diacetate.

8. The preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to claim 3, wherein: The organic base described in Step S2 is one of pyridine, imidazole, indole or pyrrole.

9. The preparation method of a hetero-porous carbon-coated graphite composite material for an energy storage battery according to claim 3, wherein: The organic solvent described in Step S2 is one of methanol, ethanol, propanol, ethylene glycol, glycerol or propylene glycol.

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