Method for improving fast charging performance of silicon-carbon composite material

Abstract

The application discloses a method for improving the fast charging performance of silicon-carbon composite materials, which comprises the following steps: first, preparing a heteroatom-doped MOF material; then, through a silane cracking method, introducing silane gas and heteroatom gas, and performing low-temperature passivation to obtain a silicon-carbon precursor material; configuring an organic solvent of resin, then adding graphene oxide solution and uniformly dispersing, and then adding the silicon-carbon precursor, and performing spray drying; and finally, introducing hydrogen gas to reduce the obtained material at a temperature of 700-1000 DEG C, and the method is completed.The material obtained by the method can improve the rate performance and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material preparation, specifically a method for improving the fast-charging performance of silicon-carbon composite materials. Background Technology

[0002] Silicon-carbon materials are composed of porous carbon and nano-silicon deposited in the pores. Due to the high specific surface area and poor electronic conductivity of porous carbon, the initial efficiency and fast-charging performance of the material are reduced. Furthermore, the expansion of nano-silicon during charging and discharging causes deviations in the material's cycle performance. Therefore, it is necessary to dope the porous carbon to improve its electronic conductivity and to coat it to improve both electronic and ionic conductivity, thereby improving the material's rate capability and cycle performance. For example, Chinese patent application number 202410056002.6 discloses a method for preparing a rare-earth-doped amorphous carbon-coated silicon-carbon composite material. First, lithium-doped porous carbon is prepared, then lithium metal is deposited through lithium hydride pyrolysis, followed by the deposition of nano-silicon through the introduction of silane gas to obtain a lithium-doped silicon-carbon precursor material; then, rare-earth-doped amorphous carbon is coated on the surface to obtain the silicon-carbon composite material. However, due to the uneven pore size distribution and small pore volume of the core, and the limited improvement in electronic conductivity of the outer rare-earth-doped amorphous carbon, the improvement in the fast-charging performance and cycle performance of this composite material is limited. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a method for improving the fast charging performance of silicon-carbon composite materials, which can improve rate performance and cycle performance.

[0004] The present invention provides a method for improving the fast-charging performance of silicon-carbon composite materials, comprising the following steps:

[0005] Step S1: According to the mass ratio of imidazole derivative: chloride salt: heteroatom compound: DMF (N,N-dimethylformamide) = (100-200): 100: 1-5: 500-1500, add imidazole derivative, chloride salt and heteroatom compound to DMF solution, transfer to high pressure reactor, react at 50-120℃ and 1-2 MPa for 1-6 h, filter, wash 3 times with acetone, then soak in methanol for 24 h, filter, freeze dry the obtained filter residue at -40℃ for 24 h to obtain heteroatom-doped MOF material;

[0006] Step S2: Transfer the heteroatom-doped MOF material to a fluidized bed, heat it to 450-550℃, and introduce silane gas at a flow rate of 50-200 SCCM for 30-300 min. Then, raise the temperature to 850-1000℃ and introduce heteroatom gas at a flow rate of 10-100 SCCM for 30-300 min. Then, cool it down to 300-450℃, evacuate it to a vacuum degree of 0.1-0.5 MPa, and introduce oxygen passivation gas at a flow rate of 50-200 SCCM for 30-300 min. Finally, cool it down to room temperature to obtain the silicon-carbon precursor material.

[0007] Step S3: According to the mass ratio of resin: 1-5wt% graphene oxide solution: silicon carbon precursor: dispersant = 5-15: 100: 100: 1-5, the resin is added to an organic solvent to prepare a 1-10wt% solution. Then, 1-5wt% graphene oxide solution, silicon carbon precursor, and dispersant are added and dispersed evenly. Spray drying is performed (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h, 2h). The resulting material is then transferred to a tube furnace and heated to 700-1000℃. Hydrogen gas is introduced at a flow rate of 10-100SCCM for 60-600min to obtain the silicon carbon composite material.

[0008] The imidazole derivative mentioned in step S1 is one of 2-mercaptoimidazoline, 4-formylimidazolium, N-butylimidazolium, 2-propylimidazolium, methimidazolium, or 2-hydroxybenzimidazole; the chloride salt is one of ferric chloride hexahydrate, aluminum chloride hexahydrate, tin tetrachloride pentahydrate, or zirconium chloride hydrate; and the heteroatom compound is one of melamine, urea, phosphoric acid, boric acid, or ammonia.

[0009] The heteroatom gas mentioned in step S2 is one of ammonia, hydrogen sulfide, or boron trichloride.

[0010] The resin mentioned in step S3 is one of phenolic resin, epoxy resin or furfural resin; the organic solvent is one of benzene, xylene, methanol, ethanol, 1,4-butanediol or acetone; and the dispersant is one of lithium carboxymethyl cellulose, lithium polyacrylate or lithium polyvinyl alcohol.

[0011] Compared with existing technologies, this invention has significant advantages. As can be seen from the above technical solution: This invention first prepares a heteroatom-doped MOF material, deposits nano-silicon in its pores, and coats it with graphene-doped amorphous carbon. The heteroatom-doped MOF material, utilizing its tunable chemical structure, high specific surface area, and large pore size and volume of metal-organic frameworks (MOFs), can reduce the expansion of nano-silicon during charging and discharging, thereby improving the material's electronic conductivity and rate performance. Coating the silicon-carbon precursor surface with graphene and amorphous carbon improves the material's electronic conductivity and confines the expansion of nano-silicon during charging and discharging; simultaneously, the coating solution contains a lithium dispersant, and after carbonization, lithium-doped amorphous carbon is obtained, improving the material's electronic and ionic conductivity and enhancing rate performance. Attached Figure Description

[0012] Figure 1 The image shows a SEM image of the silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0013] Example 1:

[0014] A method for improving the fast-charging performance of silicon-carbon composite materials includes the following steps:

[0015] Step S1: Add 150g of 4-formylimidazole, 100g of ferric chloride hexahydrate and 3g of melamine to 1000g of DMF solution, and transfer to a high-pressure reactor. React at 80℃ and 1.5MPa for 3h. Filter, wash three times with acetone, then soak in methanol for 24h, filter, and freeze-dry the obtained material at -40℃ for 24h to obtain heteroatom-doped MOF material.

[0016] Step S2: The heteroatom-doped MOF material is transferred to a fluidized bed and heated to 500°C. Then, silane gas (SiH4) is introduced through silane pyrolysis at a flow rate of 100 SCCM for 150 min. After that, the temperature is raised to 950°C and ammonia gas is introduced at a flow rate of 50 SCCM for 150 min. Then, the temperature is lowered to 400°C and a vacuum is drawn to a vacuum degree of 0.3 MPa. Oxygen passivation gas is introduced at a flow rate of 100 SCCM for 150 min. After that, the temperature is lowered to room temperature to obtain the silicon-carbon precursor material.

[0017] Step S3: Add 10g of phenolic resin to 200g of xylene organic solvent to prepare a 5wt% solution. Then add 100g of 3wt% graphene oxide solution, 3g of lithium carboxymethyl cellulose, and 100g of silicon-carbon precursor and disperse evenly. Spray dry (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h, 2h). Then transfer the obtained material to a tube furnace, heat to 850℃, and introduce hydrogen gas at a flow rate of 50SCCM for 150min to obtain silicon-carbon composite material.

[0018] Example 2:

[0019] A method for improving the fast-charging performance of silicon-carbon composite materials includes the following steps:

[0020] Step S1: Add 100g of 2-propylimidazolium, 100g of aluminum chloride hexahydrate and 1g of urea to 500g of DMF solution, and transfer to a high-pressure reactor. Then react at 50℃ and 2MPa for 6h. After filtration, wash with acetone 3 times, soak in methanol for 24h, filter, and freeze-dry the obtained material at -40℃ for 24h to obtain heteroatom-doped MOF material.

[0021] Step S2: The heteroatom-doped MOF material is transferred to a fluidized bed and heated to 450°C. Then, silane (SiH4) gas is introduced by silane pyrolysis at a flow rate of 50 SCCM for 300 min. After that, the temperature is raised to 850°C and hydrogen sulfide gas is introduced at a flow rate of 10 SCCM for 300 min. Then, the temperature is lowered to 300°C and a vacuum is drawn to a vacuum degree of 0.1 MPa. Oxygen passivation gas is introduced at a flow rate of 50 SCCM for 300 min. After that, the temperature is lowered to room temperature to obtain the silicon-carbon precursor material.

[0022] Step S3: Add 5g of epoxy resin to 500g of methanol organic solvent to prepare a 1wt% solution, then add 100g of 1wt% graphene oxide solution, 1g of lithium polyacrylate, and 100g of silicon-carbon precursor and disperse evenly. Spray dry (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h, 2h). Then transfer the obtained material to a tube furnace, heat to 700℃, and introduce hydrogen gas at a flow rate of 10SCCM for 600min to obtain silicon-carbon composite material.

[0023] Example 3:

[0024] A method for improving the fast-charging performance of silicon-carbon composite materials includes the following steps:

[0025] Step S1: Add 200g of methimazole, 100g of tin tetrachloride pentahydrate and 5g of phosphoric acid to 1500g of DMF solution, and transfer to a high-pressure reactor. Then react at 120℃ and 1MPa for 1h, filter, wash three times with acetone, soak in methanol for 24h, and freeze dry at -40℃ for 24h to obtain heteroatom-doped MOF material.

[0026] Step S2: The heteroatom-doped MOF material is transferred to a fluidized bed and heated to 550°C. Then, silane (SiH4) gas is introduced by silane pyrolysis at a flow rate of 200 SCCM for 30 min. After that, the temperature is raised to 1000°C and boron trichloride gas is introduced at a flow rate of 100 SCCM for 30 min. Then, the temperature is lowered to 450°C and a vacuum is drawn to a vacuum degree of 0.5 MPa. Oxygen passivation gas is introduced at a flow rate of 200 SCCM for 30 min. After that, the temperature is lowered to room temperature to obtain the silicon-carbon precursor material.

[0027] Step S3: Add 15g of furfural resin to 150g of ethanol organic solvent to prepare a 10wt% solution. Then add 100g of 5wt% graphene oxide solution, 5g of lithium polyvinyl alcohol, and 100g of silicon-carbon precursor and disperse evenly. Spray dry (inlet temperature 200℃, outlet temperature 80℃, flow rate 0.1kg / h, 2h). Then transfer the obtained material to a tube furnace, heat to 1000℃, and introduce hydrogen gas at a flow rate of 100SCCM for 60min to obtain silicon-carbon composite material.

[0028] Comparative Example 1:

[0029] A method for preparing a silicon-carbon composite material, comprising:

[0030] The difference from Example 1 is that the heteroatom-doped MOF material in step S1 is replaced with porous carbon (Kuraray Co., Ltd., Japan, YP-50F), while the rest is the same as in Example 1.

[0031] Comparative Example 2:

[0032] A method for preparing a silicon-carbon composite material, comprising:

[0033] Unlike Example 1, step S3 does not involve the addition of graphene oxide solution and lithium carboxymethyl cellulose; otherwise, it is the same as Example 1.

[0034] Experimental Example 1:

[0035] The silicon-carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the data, the composite material prepared in Example 1 has a porous structure with a particle size between 5 and 10 μm.

[0036] Experimental Example 2: Physical and Chemical Properties Test

[0037] The tap density and specific surface area of ​​the silicon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested according to the method of national standard GBT-38823-2020 "Silicon Carbon". At the same time, the powder resistivity of the materials was tested using a four-probe tester. The test results are shown in Table 1.

[0038] Table 1

[0039]

[0040] Test Example 3: Button Cell Test

[0041] The silicon composite materials from Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries to assemble coin cells. The specific method for preparing the negative electrode material was as follows: a binder, conductive agent, and solvent were added to the composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled. The binder used was LA132, the conductive agent was SP, and the solvent was double-distilled water. The negative electrode sheet was prepared according to the ratio of composite material: SP:LA132:double-distilled water = 90g:4g:6g:250mL. A lithium metal sheet was used as the positive electrode. The electrolyte was LiPF6 / EC+DEC, where LiPF6 was the electrolyte, and a 1:1 volume ratio mixture of EC and DEC was used as the solvent, with an electrolyte concentration of 1.3 mol / L. The separator was a composite membrane of polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP). The coin cells were assembled in an argon-filled glove box. Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The initial discharge capacity and initial efficiency of the coin cell were tested, along with the charge DCR (50% SOC) and cycle performance (0.2C / 0.2C, 100 cycles). The negative electrode expansion rate was also tested by dissecting the coin cell at 100% SOC after full charge. Simultaneously, the liquid absorption capacity of the negative electrode was tested (1 mL of electrolyte was added to the negative electrode and the time t was recorded until the electrolyte was completely absorbed). The test results are shown in Table 2.

[0042] Table 2

[0043]

[0044] As can be seen from Tables 1 and 2, the embodiments are superior to the comparative examples in terms of specific capacity, DCR, expansion, and cycle performance. This is because the MOF material has low full-charge expansion and high specific surface area, which improves cycle performance. At the same time, the doping of graphene and lithium salt improves the electronic and ionic conductivity of the material, thereby improving the first-pass efficiency and reducing the DCR.

[0045] Test Example 4: Pouch Battery Test

[0046] The silicon-carbon composite materials in Examples 1-3 and Comparative Examples 1-2 were mixed with 90% artificial graphite as negative electrodes, and negative electrode sheets were prepared by slurry mixing and coating. Ternary materials (LiNi) were used. 1 / 3 Co 1 / 3 Mn 1 / 3 A 2Ah pouch cell was prepared using O2 as the positive electrode, LiPF6 (solvent EC+DEC, volume ratio 1:1, electrolyte concentration 1.3mol / L) as the electrolyte, and Ce L Gard 2400 membrane as the separator.

[0047] 4.1 HPPC Ratio Performance Test:

[0048] The rate performance of the pouch battery was tested under a charge / discharge voltage range of 2.5–4.2V and a temperature of 25±3.0℃. The resistance was measured under different SOC conditions (90%, 70%, 50%, 30%, 10%, 5%) by charging at 3C and discharging at 4.0C. The test results are shown in Table 3.

[0049] Table 3

[0050]

[0051] As shown in Table 3, the impedance of the soft-pack battery made of silicon composite material prepared by the materials of Examples 1-3 is significantly lower than that of Comparative Examples 1-2, that is, the charging time is shorter. The reason for this is that lithium ions need to migrate during the battery charging process. The materials of the examples have low powder resistivity and their porous metal framework MOF material has the characteristics of strong liquid absorption capacity and high lithium ion conductivity, which reduces impedance and DCR.

[0052] 4.2 Cyclic Performance Test:

[0053] The obtained soft-pack batteries were subjected to cycle performance testing under the following conditions: charge / discharge current 1C / 1C, voltage range 2.5-4.2V, number of cycles 500, and the charge DCR (50% SOC) of 500 cycles was tested. The test results are shown in Table 4.

[0054] Table 4

[0055] project Retention rate (%) after 500 cycles Charging DCR (mΩ) Example 1 94.76 19.34 Example 2 93.03 21.05 Example 3 95.51 18.53 Comparative Example 1 88.36 24.63 Comparative Example 2 90.91 28.12

[0056] As shown in Table 4, the lithium-ion batteries prepared using the composite materials obtained in Examples 1-3 exhibit significantly better cycle performance than those in Comparative Examples 1-2. The experimental results indicate that this is because the materials in these examples have low expansion and low powder resistivity, reducing the lithium ions consumed by repeated SE I repair during charging and discharging, thus improving cycle performance.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments without departing from the technical essence of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for improving the fast-charging performance of silicon-carbon composite materials, comprising the following steps: Step S1: According to the mass ratio of imidazole derivative: chloride salt: heteroatom compound: DMF = (100-200): 100: 1-5: 500-1500, add imidazole derivative, chloride salt and heteroatom compound to DMF solution, transfer to high pressure reactor, react at 50-120℃ and 1-2MPa for 1-6h, filter, wash 3 times with acetone, then soak in methanol for 24h, filter, freeze dry the obtained filter residue at -40℃ for 24h to obtain heteroatom-doped MOF material; Step S2: Transfer the heteroatom-doped MOF material to a fluidized bed, heat it to 450-550℃, and introduce silane gas at a flow rate of 50-200 SCCM for 30-300 min. Then raise the temperature to 850-1000℃ and introduce heteroatom gas at a flow rate of 10-100 SCCM for 30-300 min. Then cool it down to 300-450℃, evacuate it to a vacuum degree of 0.1-0.5 MPa, and introduce oxygen passivation gas at a flow rate of 50-200 SCCM for 30-300 min. Then cool it down to room temperature to obtain the silicon-carbon precursor material. Step S3: According to the mass ratio of resin: 1-5wt% graphene oxide solution: silicon carbon precursor: dispersant = 5-15: 100: 100: 1-5, the resin is added to an organic solvent to prepare a 1-10wt% solution. Then, 1-5wt% graphene oxide solution, silicon carbon precursor, and dispersant are added and dispersed evenly. The inlet temperature is 200℃, the outlet temperature is 80℃, the flow rate is 0.1kg / h, and spray drying is carried out for 2h. After that, the obtained material is transferred to a tube furnace and heated to 700-1000℃. Hydrogen gas is introduced at a flow rate of 10-100SCCM for 60-600min to obtain silicon carbon composite material.

2. The method for improving the fast-charging performance of silicon-carbon composite materials as described in claim 1, wherein the imidazole derivative in step S1 is one of 2-mercaptoimidazoline, 4-formylimidazolium, N-butylimidazolium, 2-propylimidazolium, methimidazolium, or 2-hydroxybenzimidazole; the chloride salt is one of ferric chloride hexahydrate, aluminum chloride hexahydrate, tin tetrachloride pentahydrate, or zirconium chloride hydrate; and the heteroatom compound is one of melamine, urea, phosphoric acid, boric acid, or ammonia.

3. The method for improving the fast charging performance of silicon-carbon composite materials as described in claim 1, wherein the heteroatom gas in step S2 is one of ammonia, hydrogen sulfide, or boron trichloride.

4. The method for improving the fast-charging performance of silicon-carbon composite materials as described in claim 1, wherein the resin in step S3 is one of phenolic resin, epoxy resin or furfural resin; the organic solvent is one of benzene, xylene, methanol, ethanol, 1,4-butanediol or acetone; and the dispersant is one of lithium carboxymethyl cellulose, lithium polyacrylate or lithium polyvinyl alcohol.

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