Preparation method of porous graphite and silicon-carbon composite material and application thereof
By depositing nano-silicon and coating it with a double lithium compound on a porous graphite matrix, a silicon-carbon composite material with high conductivity and uniform pore distribution was prepared, which solved the problem of poor rate performance of silicon-carbon materials in the prior art and improved the electrochemical performance of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI HUIYANG NEW ENERGY MATERIALS CO LTD
- Filing Date
- 2026-03-05
- Publication Date
- 2026-05-29
Smart Images
Figure CN121778725B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery materials technology, specifically a method for preparing porous graphite and silicon-carbon composite materials and their applications. Background Technology
[0002] Currently, commercially available silicon-carbon materials mainly consist of porous carbon and nano-silicon deposited within the pores. The porous carbon provides the matrix to reduce expansion, while the nano-silicon provides specific capacity. Although the resulting materials exhibit high specific capacity and excellent cycling performance, the poor electronic conductivity of the porous carbon itself leads to deviations in rate performance. Therefore, to improve the rate performance of silicon-carbon materials, improvements need to be made to the carbon matrix, increasing electronic conductivity and reducing interfacial impedance. Porous graphite, on the other hand, is a porous structure prepared from artificial graphite through activation and pore creation. Due to the high anisotropy of the carbon matrix, it possesses high electronic conductivity, and high-temperature graphitization reduces defects, thus improving initial efficiency. Although some researchers have prepared silicon-carbon composite materials by mixing porous graphite with nano-silicon, for example, patent application number CN202211083375.X discloses a method and application for preparing silicon-carbon composite anode materials using porous graphite. The preparation method is as follows: first, porous graphite is prepared and then mixed with a certain proportion of nano-silicon and ball-milled to embed the nano-silicon into the crater structure on the surface of the graphite powder; finally, the mixed material is carbon-coated. However, there are problems such as poor mixing uniformity and large expansion of nano-silicon, which causes deviations in the cycle performance of the composite material. Summary of the Invention
[0003] To improve the power performance of silicon-carbon materials, this invention prepares porous graphite as a matrix, deposits nano-silicon, and coats its surface with organic lithium salt (lithium sulfonate) and inorganic lithium salt (lithium molybdate) to obtain a silicon-carbon composite material coated with a double lithium compound; at the same time, a method for preparing porous graphite-silicon-carbon composite material is proposed.
[0004] A method for preparing modified porous graphite includes the following steps:
[0005] According to the mass ratio of metal:petroleum coke:dopant = 1-5:100:0.5-2, the metal, petroleum coke and dopant are mixed evenly and pre-carbonized at 600-900℃ for 1-6 hours. Then, the temperature is raised to 2800℃-3200℃ for graphitization for 12-48 hours, and then cooled to room temperature under a nitrogen atmosphere to obtain graphite material. Finally, it is etched to create pores by plasma technology, and then activated by water vapor at 900-1200℃ for 0.5-2 hours to obtain porous graphite.
[0006] Preferably, the metal is one of nano-iron, cobalt, nickel, and zinc, with a particle size of 0.5-5 μm; the dopant is one of zinc chloride, zinc bromide, and zinc sulfide.
[0007] Preferably, the parameters of the plasma etching are a vacuum degree of 1-10×10⁻⁶. -6 Pa, power 1000W, etching gas is oxygen, temperature 300-600℃, speed 10-100 ml / s, time 10-120 min.
[0008] A method for preparing a silicon-carbon composite material includes the following steps:
[0009] Step S1:
[0010] Porous graphite is transferred to a rotary furnace. First, an inert gas is introduced to purge the air from the tube. After heating to 450-600℃, a silane mixed gas (volume ratio: silane:nitrogen = 1-5:10) is introduced at a flow rate of 100-500 ml / min, maintaining the pressure in the chamber at 1.01-1.1 MPa for 30-300 min. Then, the temperature is raised to 650-750℃, and acetylene gas is introduced at a flow rate of 10-50 ml / min for 30-300 min to obtain silicon-carbon precursor material.
[0011] Step S2:
[0012] Lithium molybdate:lithium sulfonate:silicon-carbon precursor material = 5-15:1-5:100 was dissolved in an organic solvent to prepare a solution with a mass concentration of 1-10 wt%. Then, lithium sulfonate was added and dispersed evenly. After that, silicon-carbon precursor material was added and spray-dried to obtain a silicon-carbon composite material coated with a double lithium compound.
[0013] Preferably, the organic solvent in step S2 is one of methanol, ethanol, 1,3-butanediol or ethylene glycol.
[0014] Preferably, the lithium sulfonate in step S2 is one of lithium trifluoromethanesulfonate, lithium p-toluenesulfinate, lithium 4-styrenesulfonate, and lithium 1,3-trifluoromethanesulfonate.
[0015] The silicon-carbon composite material prepared by the above method is used in lithium-ion batteries.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0017] 1. Using porous graphite as the matrix, compared with porous carbon, it has higher electronic conductivity, fewer defects, and larger pore size, which improves the fast charging performance and specific capacity of the material. At the same time, plasma etching is used to create pores, which has the advantages of high consistency and controllable process. Meanwhile, the dopants leave micron-sized pores after low-temperature carbonization and volatilization, which interact with the nanopores created by plasma etching to generate a suitable pore distribution structure.
[0018] 2. Coating lithium sulfonate / lithium molybdate onto the surface of silicon-carbon precursor materials forms a structure similar to an artificial SEI film, which improves the ionic conductivity and diffusion coefficient of the material, thereby improving the initial efficiency and rate performance. Furthermore, both lithium sulfonate and lithium molybdate have strong solvation capabilities, which enhance the lithium ion insertion / extraction rate during charging and discharging, thus improving rate performance. Attached Figure Description
[0019] Figure 1 The image shows a SEM image of the silicon-carbon composite material prepared in Example 1. Detailed Implementation
[0020] Example 1
[0021] Preparation of porous graphite:
[0022] 3g of nano-nickel, 100g of petroleum coke, and 1g of zinc chloride were mixed evenly and pre-carbonized at 800℃ for 3 hours. Then, the temperature was increased to 3000℃ for graphitization for 24 hours, followed by cooling to room temperature under a nitrogen atmosphere to obtain graphite material. This material was then processed using plasma technology (vacuum degree 5×10⁻⁶). -6 The graphite was etched at 1000W power, with oxygen as the etching gas, at 500℃ and a speed of 50 ml / s for 60 min. Then, the temperature was raised to 1100℃ and water vapor was introduced for activation for 1 h to obtain porous graphite.
[0023] A method for preparing a silicon-carbon composite material includes the following steps:
[0024] Step S1:
[0025] Porous graphite was transferred to a rotary furnace. First, argon inert gas was introduced to purge the air from the tube. After heating to 550°C, a silane mixed gas (volume ratio: silane:nitrogen = 3:10) was introduced at a flow rate of 300 ml / min, maintaining the pressure in the chamber at 1.08 MPa for 150 min. Then, the temperature was raised to 700°C, and acetylene gas was introduced at a flow rate of 30 ml / min for 150 min to obtain silicon-carbon precursor material.
[0026] Step S2:
[0027] 10g of lithium molybdate was dissolved in 200g of methanol organic solvent to prepare a solution with a mass concentration of about 5wt%. Then, 3g of lithium trifluoromethanesulfonate was added and dispersed evenly. Then, 100g of silicon-carbon precursor material was added and spray-dried to obtain a silicon-carbon composite material coated with a double lithium compound (hereinafter referred to as: silicon-carbon composite material).
[0028] Example 2:
[0029] Preparation of porous graphite:
[0030] 1g of nano-iron, 100g of petroleum coke, and 0.5g of zinc bromide were mixed evenly and pre-carbonized at 600℃ for 6h, then graphitized at 2800℃ for 48h, and finally cooled to room temperature under a nitrogen atmosphere to obtain graphite material; subsequently, it was processed using plasma technology (vacuum degree 1×10⁻⁶). -6 The graphite was etched and pores were created for 10 minutes at a set temperature of 1000W, with oxygen as the etching gas, a temperature of 300℃, and a speed of 100 ml / s. Then, the temperature was raised to 900℃ and water vapor was introduced for activation for 2 hours to obtain porous graphite.
[0031] A method for preparing a silicon-carbon composite material includes the following steps:
[0032] Step S1:
[0033] Porous graphite was transferred to a rotary furnace. First, argon inert gas was introduced to purge the air from the tube. After heating to 450°C, a silane mixed gas (volume ratio: silane:nitrogen = 1:10) was introduced at a flow rate of 100 ml / min, maintaining the pressure in the chamber at 1.01 MPa for 300 min. Then, the temperature was raised to 650°C, and acetylene gas was introduced at a flow rate of 10 ml / min for 300 min to obtain silicon-carbon precursor material.
[0034] Step S2:
[0035] 5g of lithium molybdate was dissolved in 500g of ethanol organic solvent to prepare a solution with a mass concentration of about 1wt%. Then, 1g of lithium p-toluenesulfinate was added and dispersed evenly. Then, 100g of silicon-carbon precursor material was added and spray-dried to obtain a silicon-carbon composite material coated with a double lithium compound (hereinafter referred to as: silicon-carbon composite material).
[0036] Example 3
[0037] Preparation of porous graphite:
[0038] 5g of nano-cobalt, 100g of petroleum coke, and 2g of zinc sulfide were mixed evenly and pre-carbonized at 900℃ for 1 hour. Then, the temperature was increased to 3200℃ for graphitization for 12 hours, followed by cooling to room temperature under a nitrogen atmosphere to obtain graphite material. This material was then processed using plasma technology (vacuum degree 10×10⁻⁶). -6The graphite was etched at 1000W power, with oxygen as the etching gas, at 600℃ and a speed of 10 ml / s for 120 min to create pores. Then, the temperature was raised to 1200℃ and water vapor was introduced for activation for 0.5 h to obtain porous graphite.
[0039] A method for preparing a silicon-carbon composite material includes the following steps:
[0040] Step S1:
[0041] Porous graphite was transferred to a rotary furnace. First, argon inert gas was introduced to purge the air from the tube. After heating to 600°C, a silane mixed gas (volume ratio: silane:nitrogen = 5:10) was introduced at a flow rate of 500 ml / min, maintaining the pressure in the chamber at 1.1 MPa for 30 min. Then, the temperature was raised to 750°C, and acetylene gas was introduced at a flow rate of 50 ml / min for 30 min to obtain silicon-carbon precursor material.
[0042] Step S2:
[0043] 15g of lithium molybdate was dissolved in 150g of 1,3-butanediol organic solvent to prepare a solution with a mass concentration of approximately 10wt%. Then, 5g of lithium 4-styrene sulfonate was added and dispersed evenly. After that, 100g of silicon-carbon precursor material was added and spray-dried to obtain a silicon-carbon composite material coated with a double lithium compound (hereinafter referred to as: silicon-carbon composite material).
[0044] Comparative Example 1:
[0045] The difference from Example 1 is that porous carbon (manufacturer: Kuraray Co., Ltd., Japan; model: YP-80F) was used instead of porous graphite, otherwise it was the same as Example 1.
[0046] Comparative Example 2:
[0047] Unlike Example 1, lithium trifluoromethanesulfonate is not added in step S2; otherwise, it is the same as in Example 1.
[0048] Comparative Example 3:
[0049] Unlike Example 1, lithium molybdate is not added in step S2. The detailed preparation process is as follows: 10g of lithium trifluoromethanesulfonate is dissolved in 200g of methanol organic solvent to prepare a solution with a mass concentration of about 5wt%, and then 100g of silicon-carbon precursor material is added and spray-dried to obtain a silicon-carbon composite material coated with a double lithium compound (hereinafter referred to as: silicon-carbon composite material).
[0050] 1) SEM testing:
[0051] Figure 1The SEM image of the silicon-carbon composite material coated with the double lithium compound prepared in Example 1 shows that the material has a spherical structure with slight adhesion, and the particle size is between 1-5 μm with uniform size distribution.
[0052] 2) Physicochemical and button cell tests:
[0053] The specific surface area and tap density of the silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-3 were tested according to the methods in the national standard GB / T38823-2020 "Silicon-Carbon". The powder resistivity of the powder material was tested using a powder resistance tester. The gas production of the powder material was also tested (45℃, 48h). The test results are shown in Table 1 below.
[0054] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-3 were used as the active materials for the negative electrode sheets of the batteries to prepare and assemble five coin cells respectively; the specific preparation process of each coin cell is as follows:
[0055] Preparation of battery negative electrode sheets: A binder, conductive agent, and solvent were added to the silicon-carbon composite materials (as the active material of the battery negative electrode sheets) corresponding to Examples 1-3 and Comparative Examples 1-3, respectively. The mixture was stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the respective battery negative electrode sheets. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The ratio was: silicon-carbon composite material: SP: LA132: NMP = 95g: 1g: 4g: 220mL. Preparation of coin cells: The electrolyte was a LiPF6 solution, wherein Li... The concentration of PF6 was 1 mol / L, and the solvent used was a 1:1 weight ratio mixture of ethylene carbonate (EC) and diethyl carbonate (DMC). A lithium metal sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator. The simulated battery assembly was conducted in an argon-filled glove box. Electrochemical performance was performed using a Wuhan Landian CT2001A battery tester under the following conditions: charge / discharge voltage range of 0.005V to 2.0V, and charge / discharge rate of 0.1C. The discharge specific capacity and initial efficiency of the coin cell were tested, as well as its rate performance (1C / 0.1C). A full-charge expansion test was also performed: the thickness D1 of the negative electrode sheet of the rolled coin cell was measured. Then, the coin cell was fully charged to 100% SOC, and the negative electrode sheet was dissected to measure its thickness D2. The full-charge expansion rate was then calculated as (D2-D1) / D1*100%. The test results are shown in Table 1 below.
[0056]
[0057] As shown in Table 1 above, the coin cells made using the novel silicon-carbon composite materials provided in Examples 1-3 of this application have significantly better first-discharge specific capacity and first-discharge efficiency than those of Comparative Examples 1-3. The reason for this is that the materials in this application use porous graphite as a matrix and deposit nano-silicon in its pores. The porous graphite itself has high isotropy of carbon material and low powder resistivity. The double lithium compound coated on its surface has high ion transport rate, which reduces its irreversible capacity, improves its first-discharge efficiency and specific surface area, and the double-layer coating improves the coating integrity of silicon-carbon material and reduces gas production.
[0058] 3) Pouch battery test:
[0059] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-3 were doped with 90% artificial graphite as negative electrode materials (i.e., negative electrode sheets). Ternary material LiNi1 / 3Co1 / 3Mn1 / 3O2 was used as the positive electrode material, along with the electrolyte and separator, to assemble 5Ah pouch batteries. The separator for the pouch batteries was Shanghai Enjiepu Kong 9+2+2, and the electrolyte was a LiPF6 solution. The LiPF6 solution was a 1:1 volume ratio mixture of EC and DEC, with a LiPF6 concentration of 1.3 mol / L. The following performance tests were performed on each pouch battery:
[0060] a. Liquid absorption capacity test: Using a 1mL burette, 1mL of electrolyte was drawn and a drop was added to the surface of the negative electrode. The time was recorded until the electrolyte was completely absorbed, and the liquid absorption time t (unit: S) was recorded. The test results are shown in Table 2.
[0061] b. Electrode surface resistance test: Using an electrode surface resistance tester, place the electrode (100cm2) on the test stage and test its resistance under a pressure of 500kg.
[0062] The test results are shown in Table 2 below.
[0063]
[0064] As can be seen from Table 2 above, the liquid absorption time and electrode surface resistance of the novel silicon-carbon composite materials provided in Examples 1-3 of this application are significantly better than those in Comparative Examples 1-3. The reason is that the materials in Examples 1-3 have a high specific surface area, which improves the liquid absorption capacity of the materials, and a low powder resistivity, which reduces the electrode surface resistance.
[0065] c. Rate and cycle performance: Cycle performance and rate tests were conducted on each pouch cell.
[0066] The test conditions for the cycle performance test are as follows: charge / discharge voltage range of 2.5 to 4.2V, temperature of 25±3.0℃, charge / discharge rate of 1.0C / 1.0C, and 500 cycles; see Table 3 for details.
[0067] The test conditions for the rate test are as follows: the constant current ratio of the charge is tested at different charging rates (0.5C / 1C / 2C / 3C); the test results are shown in Table 3 below.
[0068]
[0069] As shown in Table 3 above, the rate performance and cycle performance of the soft-pack lithium-ion batteries prepared using the silicon-carbon composite materials provided in Examples 1-3 of this application are better than those of Comparative Examples 1-3. This is because the silicon-carbon composite materials provided in the examples of this application have low powder resistivity and low electrode surface resistance, which improves the rate performance of the material; at the same time, the low full-charge expansion and high specific surface area improve the liquid retention performance and improve the cycle performance.
[0070] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: Step S1: According to the mass ratio of metal:petroleum coke:dopant = 1-5:100:0.5-2, the metal, petroleum coke and dopant are mixed evenly and pre-carbonized at 600-900℃ for 1-6 hours, then graphitized at 2800℃-3200℃ for 12-48 hours, and then cooled to room temperature under a nitrogen atmosphere to obtain porous graphite material; then, pores are formed by etching using plasma technology, and then activated by heating to 900-1200℃ and introducing water vapor for 0.5-2 hours to obtain modified porous graphite. The metal is one of nano-iron, cobalt, nickel, or zinc, with a particle size of 0.5-5 μm; the dopant is one of zinc chloride, zinc bromide, or zinc sulfide. The parameters for the plasma etching are a vacuum level of 1-10×10⁻⁶. -6 Pa, power 1000W, etching gas is oxygen, temperature 300-600℃, speed 10-100 ml / s, time 10-120 min; Step S2: The modified porous graphite prepared in step S1 is transferred to a rotary kiln. First, an inert gas is introduced to purge the air from the tube. After heating to 450-600℃, a silane mixed gas is introduced. The volume ratio of the silane mixed gas to silane to nitrogen is 1-5:10, and the flow rate is 100-500 ml / min. The pressure of the chamber is maintained at 1.01-1.1 MPa. The gas is introduced for 30-300 min. Then, the temperature is raised to 650-750℃, and acetylene gas is introduced at a flow rate of 10-50 ml / min for 30-300 min to obtain the silicon-carbon precursor material. Step S3: Lithium molybdate:lithium sulfonate:silicon-carbon precursor material = 5-15:1-5:100 was dissolved in an organic solvent to prepare a solution with a mass concentration of 1-10 wt%. Then, lithium sulfonate was added and dispersed evenly. After that, silicon-carbon precursor material was added and spray-dried to obtain a silicon-carbon composite material coated with a double lithium compound.
2. The method for preparing a silicon-carbon composite material according to claim 1, characterized in that, The organic solvent in step S3 is one of methanol, ethanol, 1,3-butanediol or ethylene glycol.
3. The method for preparing a silicon-carbon composite material according to claim 1, characterized in that, In step S3, the lithium sulfonate is one of lithium trifluoromethanesulfonate, lithium p-toluenesulfinate, and lithium 4-styrenesulfonate.
4. An application of a silicon-carbon composite material, characterized in that, The silicon-carbon composite material is prepared by the preparation method described in claim 1, and the silicon-carbon composite material is used in lithium-ion batteries.