Preparation method of high-energy-density fast-charging negative electrode material

Abstract

The application relates to the technical field of lithium ion battery materials, and discloses a preparation method of a high-energy-density fast-charging negative electrode material, which comprises the following steps: S1, mixing pitch, an organic solvent, a metal catalyst and an organic metal compound to obtain a coating liquid; S2, mixing oxidized natural graphite and the coating liquid, and then introducing sulfur dioxide gas to obtain a pitch / catalyst / metal oxide coated natural graphite material after reaction; and S3, carbonizing the pitch / catalyst / metal oxide coated natural graphite material in a mixed gas to obtain phosphorus-doped amorphous carbon coated natural graphite; the mixed gas in the step S3 is phosphine and argon. Through the technical scheme, the problems of low first discharge specific capacity and poor cycle performance of the graphite negative electrode material in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a method for preparing a high-energy-density fast-charging negative electrode material. Background Technology

[0002] Currently, commercially available lithium-ion battery anode materials are mainly modified natural graphite and artificial graphite. The market demands that anode materials not only have high energy density but also improved fast-charging performance. Developing high-energy, fast-charging artificial graphite requires design considerations such as raw material selection and material surface coating. For example, patent CN 201910987301.0 mixes single-particle graphitized materials with secondary-particle graphitized materials to obtain a high-energy-density graphite anode material with a mixture of single and secondary particles, but its capacity is less than 358 mAh / g, which cannot meet the requirements for high-rate charging and discharging. For example, patent CN202210609143.7 discloses a method for preparing high-energy-density graphite anode materials for lithium batteries that also facilitate fast charging. By uniformly distributing modified graphene in the graphite phase, the conductivity of the graphite material and its coating layer is greatly enhanced, and the amount of conductive agent added is reduced, thereby increasing the energy density. Catalytic graphitization can increase the capacity of graphite to over 360 mAh / g, further improving the energy density of the battery. However, it has defects such as power performance deviation and low-temperature performance deviation, and the process of removing residual catalyst is complex, which affects its industrialization and promotion. Summary of the Invention

[0003] This invention proposes a method for preparing a high-energy-density fast-charging anode material, which solves the problems of low initial discharge specific capacity and poor cycle performance of graphite anode materials in related technologies.

[0004] The technical solution of the present invention is as follows:

[0005] A method for preparing a high-energy-density fast-charging anode material includes the following steps:

[0006] S1. Mix asphalt, organic solvent, metal catalyst, and organometallic compound to obtain a coating solution;

[0007] S2. After mixing oxidized natural graphite and coating liquid, sulfur dioxide gas is introduced, and after reaction, asphalt / catalyst / metal oxide coated natural graphite material is obtained.

[0008] S3. Carbonize the asphalt / catalyst / metal oxide coated natural graphite material in a mixed gas to obtain phosphorus-doped amorphous carbon coated natural graphite.

[0009] The mixed gas in S3 is phosphine and argon.

[0010] As a further technical solution, the volume ratio of phosphine to argon is 1-5:10.

[0011] As a further technical solution, the softening point of the asphalt in S1 is 40-80℃.

[0012] As a further technical solution, the mass ratio of the metal catalyst, asphalt and organometallic compound in S1 is 1-5:5-20:1-5.

[0013] As a further technical solution, the concentration of the coating liquid in S1 is 1-10 wt%.

[0014] As a further technical solution, the metal catalyst in S1 includes one or more of ferric chloride, cobalt chloride, and nickel chloride; the organometallic compound includes one or more of 1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride, bismuth isooctanoate, cobalt isooctanoate, copper isooctanoate, zinc isooctanoate, zirconium isooctanoate, zinc formate, magnesium formate, calcium acetate, and aluminum acetate.

[0015] As a further technical solution, the method for preparing oxidized natural graphite in S2 includes the following steps:

[0016] A1. After mixing spherical natural graphite with an oxidizing agent, a mixture is obtained;

[0017] A2. After filtration and drying, the mixture is oxidized at 200-400℃ for 1-6 hours to obtain oxidized natural graphite.

[0018] As a further technical solution, the mass ratio of oxidized natural graphite to coating liquid in S2 is 100:100-500.

[0019] As a further technical solution, S2 involves mixing oxidized natural graphite and coating liquid, evacuating to -0.1 MPa, introducing sulfur dioxide gas to 0.5-0.9 MPa, stirring at 50-100℃ for 30-300 minutes, filtering, and drying to obtain asphalt / catalyst / metal oxide coated natural graphite material.

[0020] As a further technical solution, the flow rate of the mixed gas in S3 is 10-100 mL / min, and the introduction time is 1-6 h.

[0021] The working principle and beneficial effects of this invention are as follows:

[0022] 1. In the preparation process, the present invention relies on the action of metal catalysts to accelerate the reaction process and improve the graphitization degree of the material, and uses the coating material obtained after carbonization of organometallic compounds to improve the electronic conductivity of the material. The resulting material has the characteristics of high energy density, good power performance and excellent cycle performance when applied to lithium-ion batteries.

[0023] 2. The composite material of the present invention modifies its surface by means of a phosphine mixed gas, which improves the energy density by means of the high specific capacity of phosphorus itself, and removes defects on the surface of natural graphite by phosphine, reduces side reactions, and improves high-temperature performance.

[0024] 3. Under negative pressure conditions, the present invention utilizes the good fluidity of the coating liquid to fill the pores of natural graphite with metal catalysts and organometallic compounds, and then performs carbonization to obtain amorphous carbon and metal-doped natural graphite, thereby reducing impedance and material defects, reducing side reactions, and improving cycle performance and storage performance. Attached Figure Description

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] Figure 1 This is a SEM image of natural graphite coated with phosphorus-doped amorphous carbon obtained in Example 1. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] The preparation methods of oxidized natural graphite in the following examples and comparative examples are as follows: 100g of spherical natural graphite and 500g of potassium permanganate mixed solution are thoroughly stirred and mixed, filtered, vacuum dried at 80℃ for 24h, and then oxidized at 300℃ for 3h under argon inert atmosphere to obtain oxidized natural graphite.

[0029] Example 1

[0030] A method for preparing high-energy-density fast-charging anode materials includes the following steps:

[0031] S1. Add 10g of low softening point asphalt to 320g of carbon tetrachloride organic solvent and mix evenly. Then add 3g of ferric chloride and 3g of bismuth isooctanoate and disperse evenly to obtain a coating solution with a mass concentration of 5wt%. The softening point of the low softening point asphalt is 60℃.

[0032] S2. Add 100g of oxidized natural graphite to 300g of coating liquid, mix evenly, and transfer to a vacuum reactor. After the reactor is evacuated to -0.1Mpa, sulfur dioxide gas is introduced until the pressure inside the chamber is 0.75Mpa. After stirring continuously at 80℃ for 90min, filter and vacuum dry at 80℃ for 24h to obtain asphalt / catalyst / metal oxide coated natural graphite material.

[0033] S3. The above-mentioned asphalt / catalyst / metal oxide coated natural graphite material is transferred to a tube furnace, and argon inert gas is introduced to remove air from the tube. Then, a mixed gas (gas flow rate of 50 mL / min) is introduced, and the temperature is raised to 900℃. After carbonization for 3 hours, the temperature is lowered to room temperature under an argon inert atmosphere to obtain phosphorus-doped amorphous carbon coated natural graphite. The mixed gas is phosphine and argon, and the volume ratio of phosphine to argon is 3:10.

[0034] Example 2

[0035] A method for preparing high-energy-density fast-charging anode materials includes the following steps:

[0036] S1. Add 5g of low softening point asphalt to 700g of cyclohexane organic solvent and mix evenly. Then add 1g of nickel chloride and 1g of cobalt isooctanoate and disperse evenly to obtain a coating solution with a mass concentration of 1wt%. The softening point of the low softening point asphalt is 40℃.

[0037] S2. Add 100g of oxidized natural graphite to 100g of coating liquid, mix evenly, and transfer to a vacuum reactor. After the reactor is evacuated to -0.1Mpa, sulfur dioxide gas is introduced until the pressure inside the chamber is 0.5Mpa. After stirring continuously at 50℃ for 30min, filter and vacuum dry at 80℃ for 24h to obtain asphalt / catalyst / metal oxide coated natural graphite material.

[0038] S3. The above-mentioned asphalt / catalyst / metal oxide coated natural graphite material is transferred to a tube furnace, and argon inert gas is introduced to remove air from the tube. Then, a mixed gas (gas flow rate of 10 mL / min) is introduced, and the temperature is raised to 800°C. After carbonization for 6 hours, the temperature is lowered to room temperature under an argon inert atmosphere to obtain phosphorus-doped amorphous carbon coated natural graphite. The mixed gas is phosphine and argon, and the volume ratio of phosphine to argon is 1:10.

[0039] Example 3

[0040] A method for preparing high-energy-density fast-charging anode materials includes the following steps:

[0041] S1. Add 20g of low softening point asphalt to 300g of butanediol and mix evenly. Then add 5g of cobalt chloride and 5g of copper isooctanoate and disperse evenly to obtain a coating solution with a mass concentration of 10wt%. The softening point of the low softening point asphalt is 80℃.

[0042] S2. Add 100g of oxidized natural graphite to 500g of coating liquid, mix evenly, and then transfer to a vacuum reactor. After the reactor is evacuated to -0.1Mpa, sulfur dioxide gas is introduced until the pressure inside the chamber is 0.9Mpa. After stirring continuously at 100℃ for 300min, filter and vacuum dry at 80℃ for 24h to obtain asphalt / catalyst / metal oxide coated natural graphite material.

[0043] S3. The above-mentioned asphalt / catalyst / metal oxide coated natural graphite material is transferred to a tube furnace, and argon inert gas is introduced to remove air from the tube. Then, a mixed gas (gas flow rate of 100 mL / min) is introduced, and the temperature is raised to 1100℃. After carbonization for 1 hour, the temperature is lowered to room temperature under an argon inert atmosphere to obtain phosphorus-doped amorphous carbon coated natural graphite. The mixed gas is phosphine and argon, and the volume ratio of phosphine to argon is 5:10.

[0044] Comparative Example 1

[0045] S1. Add 10g of low softening point asphalt to 200g of carbon tetrachloride organic solvent and mix evenly to obtain a coating solution with a mass concentration of 5wt%; wherein the softening point of the low softening point asphalt is 60℃.

[0046] S2. Add 100g of oxidized natural graphite to 300g of coating liquid and mix evenly. Stir continuously at 80℃ for 90min, then filter and vacuum dry at 80℃ for 24h to obtain asphalt / coated natural graphite material.

[0047] S3. Transfer the above-mentioned asphalt / coated natural graphite material to a tube furnace, first introduce argon inert gas to remove air from the tube, and heat to 900°C. After carbonization for 3 hours, cool to room temperature to obtain amorphous carbon-coated natural graphite.

[0048] Comparative Example 2

[0049] S1. Add 10g of low softening point asphalt to 320g of carbon tetrachloride organic solvent and mix evenly. Then add 3g of ferric chloride and 3g of bismuth isooctanoate and disperse evenly to obtain a coating solution with a mass concentration of 5wt%. The softening point of the low softening point asphalt is 60℃.

[0050] S2. Add 100g of oxidized natural graphite to 300g of coating liquid and mix evenly. Stir continuously at 80℃ for 90min, filter, and vacuum dry at 80℃ for 24h to obtain asphalt / catalyst / metal oxide coated natural graphite material; wherein the preparation method of oxidized natural graphite is the same as in Example 1.

[0051] S3. The above-mentioned asphalt / catalyst / metal oxide coated natural graphite material is transferred to a tube furnace. First, the air inside the tube is removed by argon inert gas, and the temperature is raised to 900°C. After carbonization for 3 hours, the temperature is lowered to room temperature in an argon inert atmosphere to obtain metal oxide amorphous carbon coated natural graphite.

[0052] Comparative Example 3

[0053] Compared with Example 1, the difference in Comparative Example 3 is in S2. In Comparative Example 3, S2 involves adding 100g of oxidized natural graphite to 300g of coating liquid, mixing evenly, stirring continuously at 80°C for 90min, filtering, and vacuum drying at 80°C for 24h to obtain asphalt / catalyst / metal oxide coated natural graphite material.

[0054] Comparative Example 4

[0055] Compared with Example 1, the difference in Comparative Example 4 is in S3. In Comparative Example 4, S3 involves transferring the above-mentioned asphalt / catalyst / metal oxide coated natural graphite material into a tube furnace, introducing argon inert gas to remove air from the tube, heating to 900°C, carbonizing for 3 hours, and then cooling to room temperature in an argon inert atmosphere to obtain amorphous carbon coated natural graphite.

[0056] Experimental Example 1

[0057] The amorphous carbon-coated natural graphite prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown.

[0058] Depend on Figure 1 It can be seen that the material particles have a reasonable spherical structure, with a particle size between 10-15μm, and the material surface cross-section has a small amount of porous structure.

[0059] Experimental Example 2

[0060] Button cell battery test

[0061] The amorphous carbon-coated natural graphite obtained in Examples 1-3 and Comparative Examples 1-4 was used as the negative electrode material for lithium-ion batteries and assembled into coin cells.

[0062] The specific preparation method is as follows: A binder, conductive agent, and solvent are added to the negative electrode material of a lithium-ion battery, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the negative electrode sheet. The binder used is PVDF, the conductive agent is conductive carbon black (SP), and the solvent is N-methylpyrrolidone (NMP). The ratio of negative electrode material, SP, PVDF, and NMP is 95g:1g:4g:220mL. LiPF6 is used as the electrolyte, and a 1:1 mixture of EC and DEC (by volume) is used as the solvent. A lithium metal sheet is used as the counter electrode, and a polypropylene (PP) membrane is used as the separator. The button cell assembly is performed in an argon-filled glove box. Electrochemical performance is tested using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V-2.0V and a charge / discharge rate of 0.1C. The results of the tests on its rate capability (2C / 0.1C) and cycle performance (0.2C / 0.2C, 100 cycles) are shown in Table 1.

[0063] Table 1 Performance test results of different anode materials

[0064]

[0065] As can be seen from the data in Table 1, the initial discharge specific capacity and initial efficiency of the phosphorus-doped amorphous carbon-coated natural graphite prepared in Examples 1-3 of this invention are superior to those of the comparative examples. This is because the examples used a chemical deposition method to uniformly coat the graphite surface with phosphorus-doped amorphous carbon, resulting in a high specific surface area that increases the material's specific surface area; the doped phosphorus increases the material's specific capacity; and simultaneously, filling the pores of natural graphite with amorphous carbon reduces impedance, thus improving rate capability and cycle performance. Comparative Example 1 did not add any metal catalyst or organometallic compound, and neither vacuum was evacuated to negative pressure nor was a mixed gas containing phosphine and argon introduced. Comparative Example 2 did not vacuum be evacuated to negative pressure nor was a mixed gas containing phosphine and argon introduced. Comparative Example 3 mixed natural graphite oxide with coating liquid without vacuuming to negative pressure and then introducing sulfur dioxide. Comparative Example 4 did not introduce a mixed gas containing phosphine and argon during carbonization. As a result, the performance of the amorphous carbon-coated natural graphite prepared in Comparative Examples 1-4 as a negative electrode material was lower than that of the Examples.

[0066] Experimental Example 3

[0067] Anode sheets were prepared by coating natural graphite with multiphosphorus-doped amorphous carbon as the anode material in Examples 1-3 and Comparative Examples 1-4, using ternary materials (Li(Ni) 0.6 Co 0.2 Mn 0.2LiPF6 was used as the positive electrode material; a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used as the electrolyte; and a 5Ah soft-pack battery was prepared using a Celgard 2400 membrane as the separator, labeled as C1, C2, C3 and D1, D2, D3, D4.

[0068] 3.1 Liquid absorption capacity and liquid retention rate test

[0069] (1) Liquid absorption capacity test

[0070] Using a 1 mL burette, a volume of electrolyte (V mL) was drawn and a drop was added to the electrode surface. Timing was maintained until the electrolyte was completely absorbed, and the time (t) was recorded. The absorption rate of the electrode (V / t) was then calculated. The test results are shown in Table 2.

[0071] (2) Liquid retention rate test

[0072] The theoretical liquid absorption capacity m1 of the electrode was calculated based on the electrode parameters, and the weight m2 of the electrode was measured. The electrode was then immersed in the electrolyte for 24 hours, and its weight m3 was measured. The liquid absorption capacity m3-m2 was calculated, and the liquid retention rate was calculated using the following formula: Liquid retention rate = (m3-m2)*100% / m1. The test results are shown in Table 2.

[0073] 3.2 Cyclic Performance Test

[0074] The battery's cycle performance was tested at a charge / discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, and a temperature of 25±3℃. The test results are shown in Table 3.

[0075] 3.3 High-Temperature Storage Performance Test

[0076] The battery was charged to 100% SOC and its capacity was measured as M1. It was then placed in an oven at 55℃ for 7 days, and its capacity was measured as M2. The battery was then charged to 100% SOC and its capacity was measured as M3. Finally, the battery's charge retention was calculated as M2 / M1*100%, and the capacity recovery was calculated as M3 / M1*100%. The test results are shown in Table 3.

[0077] Table 2. Test results of liquid absorption and retention capacity of electrodes made from different negative electrode materials.

[0078]

[0079]

[0080] As shown in Table 2, the liquid absorption and retention capacity of phosphorus-doped amorphous carbon-coated natural graphite obtained in Examples 1-3 is significantly higher than that of the comparative examples. Comparative Example 1 did not add any metal catalyst or organometallic compound, and neither vacuum pressure nor a mixed gas containing phosphine and argon was introduced. Comparative Example 2 did not vacuum pressure nor a mixed gas containing phosphine and argon was introduced. Comparative Example 3 mixed oxidized natural graphite with the coating liquid without vacuum pressure or introducing sulfur dioxide. Comparative Example 4 did not introduce a mixed gas containing phosphine and argon during carbonization. As a result, the liquid absorption and retention capacity of Comparative Examples 1-4 was lower than that of the examples. The experimental results show that the phosphorus-doped amorphous carbon-coated natural graphite provided by this invention has a high liquid absorption and retention capacity. This is mainly because the graphite composite anode material provided by this invention has a high specific surface area, which enhances the liquid absorption and retention capacity of the material.

[0081] Table 3. Test results of cycling performance and high-temperature storage performance

[0082]

[0083] As shown in Table 3, the battery prepared by phosphorus-doped amorphous carbon-coated natural graphite provided by this invention exhibits significantly better cycle performance than the comparative examples. Comparative Example 1 did not add any metal catalyst or organometallic compound, and neither vacuum pressure nor a mixed gas containing phosphine and argon was introduced. Comparative Example 2 did not vacuum pressure nor a mixed gas containing phosphine and argon was introduced. Comparative Example 3 mixed oxidized natural graphite with the coating liquid without vacuum pressure or introducing sulfur dioxide. Comparative Example 4 did not introduce a mixed gas containing phosphine and argon during carbonization. As a result, the cycle performance and high-temperature storage performance of Comparative Examples 1-4 were all lower than those of the examples. This is because the composite material provided by this invention has advantages such as high density, structural stability, and low impedance, which improves its cycle performance. While a larger specific surface area may reduce high-temperature storage performance, the low contact impedance and low expansion between the core and shell of the materials in the examples can improve the high-temperature storage performance.

[0084] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-energy-density fast-charging negative electrode material, characterized in that, Includes the following steps: S1. Mix asphalt, organic solvent, metal catalyst, and organometallic compound to obtain a coating solution; S2. After mixing oxidized natural graphite and coating liquid, sulfur dioxide gas is introduced, and after reaction, asphalt / catalyst / metal oxide coated natural graphite material is obtained. S3. Carbonize the asphalt / catalyst / metal oxide coated natural graphite material in a mixed gas to obtain phosphorus-doped amorphous carbon coated natural graphite. S2 involves mixing oxidized natural graphite and a coating solution, evacuating to -0.1 MPa, introducing sulfur dioxide gas to 0.5-0.9 MPa, stirring at 50-100°C for 30-300 minutes, filtering, and drying to obtain asphalt / catalyst / metal oxide coated natural graphite material. The mixed gas in S3 is phosphine and argon.

2. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The volume ratio of phosphine to argon is 1-5:

10.

3. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The softening point of the asphalt in S1 is 40-80℃.

4. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The mass ratio of the metal catalyst, pitch and organometallic compound in S1 is 1-5:5-20:1-5.

5. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The concentration of the coating solution in S1 is 1-10 wt%.

6. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The metal catalyst in S1 includes one or more of ferric chloride, cobalt chloride, and nickel chloride; the organometallic compound includes one or more of [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride, bismuth isooctanoate, cobalt isooctanoate, copper isooctanoate, zinc isooctanoate, zirconium isooctanoate, zinc formate, magnesium formate, calcium acetate, and aluminum acetate.

7. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The method for preparing oxidized natural graphite in S2 includes the following steps: A1. After mixing spherical natural graphite with an oxidizing agent, a mixture is obtained; A2. After filtration and drying, the mixture is oxidized at 200-400℃ for 1-6 hours to obtain oxidized natural graphite.

8. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The mass ratio of oxidized natural graphite to coating liquid in S2 is 100:100-500.

9. The method for preparing a high energy density fast-charging negative electrode material according to claim 1, characterized in that, The flow rate of the mixed gas in S3 is 10-100 mL / min, and the introduction time is 1-6 h.

Images