Atomic layer deposition silicon-carbon composite material, preparation method and application thereof

Abstract

The application discloses a kind of atomic layer deposition silicon-carbon composite material, preparation method and application thereof, adopt by core and shell composition core-shell coating structure, wherein, the core is multi-element doped silicon-carbon material, the shell is solid electrolyte composite layer;The mass ratio of the core and shell is 80-95:5-20;The application is deposited solid electrolyte on its specific silicon-carbon material surface by atomic vapor deposition method, reduces its expansion, and improves the cycle performance of application battery.

Description

Technical Field

[0001] This invention belongs to the field of silicon-carbon composite materials for batteries, specifically relating to an atomic layer deposition silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] As the market demands higher energy density for lithium-ion batteries, the amount of silicon-carbon composite material added to the negative electrode of lithium-ion batteries is gradually increasing. However, this approach increases the full-charge expansion of the negative electrode sheet and reduces cycle performance. Therefore, it is necessary to reduce the expansion of the silicon-carbon composite material itself, which requires improving the pore volume of the silicon-carbon composite material and optimizing its coating layer to reduce expansion.

[0003] However, current silicon-carbon composite materials typically use vapor deposition to deposit carbon coatings onto the silicon-carbon material, resulting in low coating strength, poor compressive strength, and difficulty in reducing silicon-carbon expansion. Furthermore, the low pore volume of the porous carbon core hinders the improvement of nano-silicon expansion during charge and discharge. Therefore, it is necessary to optimize the porous carbon core and modify its surface in silicon-carbon composite materials to reduce material expansion while also considering rate performance. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an atomic layer deposition silicon-carbon composite material, a preparation method thereof, and its application, wherein a solid electrolyte is deposited on the surface of a specific silicon-carbon material by atomic vapor deposition, thereby reducing its expansion and improving the cycle performance of the battery.

[0005] The technical solution adopted in this invention is as follows: An atomic layer deposition silicon-carbon composite material adopts a core-shell encapsulation structure consisting of a core and an outer shell, wherein the core is a multi-element doped silicon-carbon material and the outer shell is a solid electrolyte composite layer; the mass ratio of the core to the outer shell is 80-95:5-20.

[0006] Preferably, a method for preparing a silicon-carbon composite material according to the above-described atomic layer deposition includes the following steps: S1: According to the mass ratio of porous carbon precursor: catalyst: activator = 100:10-30:5-10, the porous carbon precursor and catalyst solution are mixed evenly and reacted at a temperature not lower than 70℃ for at least 2.5 hours. After filtration, the mixture is carbonized at a low temperature of 300-500℃ for 1-3 hours. Then, the material obtained from the low temperature carbonization is mixed with the activator and carbonized at a medium temperature of 1000-1300℃ for 1-3 hours. The material obtained from the medium temperature carbonization is then acid-washed to obtain the porous carbon material. S2: Transfer the porous carbon material obtained in step S1 into a tube furnace, introduce inert gas to purge the air inside the tube, evacuate to 1-10 Pa, and heat to 500-900℃. Then, at a total flow rate of 1-10 ml / min, simultaneously introduce lithium source gas, phosphorus source gas, and their crosslinking gas to modify the pores in the porous carbon material for 10-60 minutes. After that, raise the temperature to 1000-1300℃ and introduce carbon dioxide gas at a flow rate of 10-50 ml / min to expand the pores for 30-300 minutes to obtain modified porous carbon. S3: The modified porous carbon obtained in step S2 is fed into a fluidized bed and heated to 450-550℃ under an inert gas atmosphere. A silane mixed gas is introduced at a flow rate of 100-300 ml / min for 60-600 minutes to obtain silicon-carbon material. S4: Transfer the silicon-carbon material obtained in step S3 to the atomic vapor deposition reaction chamber, evacuate to 1-10 Torr, heat to 200-400°C, introduce an inert carrier gas, and deposit the solid electrolyte composite vapor on its surface for 30-300 minutes; then, introduce fluorinated carbon derivative gas at a flow rate of 10-60 ml / min for pyrolysis deposition for 60-600 minutes to obtain the atomic layer deposition silicon-carbon composite material.

[0007] Preferably, in step S1, the porous carbon precursor is any one of glucose, asphalt, epoxy resin, phenolic resin, furfural resin, polyethylene glycol, polyamide resin, and cellulose; the catalyst is any one of ferric chloride, nickel chloride, cobalt chloride, ferric nitrate, nickel nitrate, and cobalt nitrate, with a concentration of 1-5 wt% in the catalyst solution; and the activator is any one of potassium carbonate, potassium hydroxide, sodium carbonate, and sodium hydroxide.

[0008] Preferably, in step S1, the pickling process includes: pickling the material obtained by medium-temperature carbonization with a 0.1 mol / L mixed acid, wherein the mixed acid is hydrochloric acid and hydrofluoric acid in a volume ratio of 1:1.

[0009] Preferably, in step S2, the lithium source gas is any one of lithium acetate, lithium citrate, lithium formate, and lithium isobutyrate; the phosphorus source gas is any one of tetramethylfluorourea hexafluorophosphate, tripolyphosphate, 2,3-dibromo-1-propanol phosphate, 2-ethylhexyl phosphate, ethyl dichlorophosphate, vinyl phosphate, and 2-butoxyethanol phosphate; and the crosslinking gas is any one of di-tert-butane peroxide, di-tert-butane peroxide, isononanoyl peroxide, tert-amyl peroxide, tert-butyl hydroperoxide, tert-butanol peroxide, hydroxyisopropylbenzene peroxide, diisopropylbenzene peroxide, benzoyl peroxide, and dibenzoyl peroxide.

[0010] Preferably, in step S3, the silane mixed gas is any one of silane, silane, monochlorosilane, dichlorosilane, and monochlorosilane mixed with nitrogen, and the volume ratio of the two is 1-5:10.

[0011] Preferably, in step S4, the inert carrier gas includes any one or a mixture of helium, argon, or xenon; the solid electrolyte complex vapor is formed by mixing any one of the solid electrolytes, namely lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium germanium aluminum phosphate, or lithium titanium aluminum phosphate, with MOF material, and the mass ratio of the two is 0.5-2:1; and the fluorinated carbon derivative gas is any one of carbon tetrafluoride, hexafluoroethane, and trichlorofluoromethane.

[0012] Preferably, the MOF material is any one of ZIF-8 (2-methylimidazolium-zinc nitrate), ZIF-67 (2-methylimidazolium-cobalt nitrate), MIL-101 (iron-terephthalic acid), and MIL-53 (aluminum-terephthalic acid).

[0013] Preferably, in step S4, the volume ratio of the solid electrolyte complex vapor to the inert carrier gas is 1-5:1, and the total flow rate is 10-60 ml / min.

[0014] Preferably, in an application of the atomic layer deposition silicon-carbon composite material described above, the atomic layer deposition silicon-carbon composite material is used as an active material raw material for preparing battery electrodes, and more preferably as an active material raw material for lithium-ion battery negative electrode electrodes.

[0015] On the one hand, this application deposits a solid electrolyte composite on the surface of silicon-carbon material by atomic vapor deposition, which has the advantages of dense deposition thickness, high lithium-ion conductivity, and good liquid retention performance. At the same time, the solid electrolyte coating on the silicon-carbon surface restricts the expansion of silicon during charge and discharge, thereby improving cycle performance. Furthermore, the doped MOF material has the characteristics of good liquid retention and low expansion, which further reduces the expansion of the silicon-carbon composite material. On the other hand, fluorinated carbon derivatives are introduced into its surface and carbonized to obtain fluorine-doped amorphous carbon, which improves the compatibility between the material and the electrolyte, reduces side reactions, and improves storage performance. In another aspect, this application adds a catalyst to the porous carbon precursor to change the orientation of carbon and improve the electronic conductivity of the material. The resulting material is then mixed with an activator for activation, which creates pores to increase pore volume and pore size, providing a buffer space for the expansion of nano-silicon and reducing the expansion of the silicon-carbon composite material. The higher pore volume allows for the deposition of more nano-silicon, thus increasing the specific capacity. Simultaneously, lithium source gas, phosphorus source gas, and their crosslinking gas are introduced into the porous carbon material obtained in step S1, and lithium is deposited on the inner wall and outer shell of the porous carbon to improve ionic conductivity. Phosphorus is used to improve electronic conductivity, and the crosslinking agent forms a crosslinked structure between phosphorus and lithium, which significantly improves the structural stability of the deposited layer. Attached Figure Description

[0016] Figure 1 This is a SEM image of the atomic layer deposited silicon-carbon composite material obtained in Example 1 of this application. Detailed Implementation

[0017] This embodiment proposes an atomic layer deposition silicon-carbon composite material, which adopts a core-shell encapsulation structure consisting of a core and an outer shell. The core is a multi-element doped silicon-carbon material, and the outer shell is a solid electrolyte composite layer. The mass ratio of the core to the outer shell is 80-95:5-20.

[0018] Preferably, a method for preparing a silicon-carbon composite material according to the above-described atomic layer deposition includes the following steps: S1: The porous carbon precursor, catalyst, and activator are mixed uniformly according to a mass ratio of 100:10-30:5-10. The mixture is then reacted at a temperature not lower than 70°C (preferably 78-85°C) for at least 2.5 hours. After filtration, the mixture is subjected to low-temperature carbonization at 300-500°C for 1-3 hours. The resulting material is then mixed with the activator and subjected to medium-temperature carbonization at 1000-1300°C for 1-3 hours. The medium-temperature carbonized material is then acid-washed to obtain the porous carbon material. Preferably, in step S1, the porous carbon… The precursor is any one of glucose, asphalt, epoxy resin, phenolic resin, furfural resin, polyethylene glycol, polyamide resin, and cellulose; the catalyst is any one of ferric chloride, nickel chloride, cobalt chloride, ferric nitrate, nickel nitrate, and cobalt nitrate, with a concentration of 1-5 wt% in the catalyst solution, and acetone can be used as the catalyst solution; the activator is any one of potassium carbonate, potassium hydroxide, sodium carbonate, and sodium hydroxide; preferably, in step S1, the acid washing process includes: acid washing the material obtained by medium-temperature carbonization with a 0.1 mol / L mixed acid, wherein the mixed acid is hydrochloric acid and hydrofluoric acid with a volume ratio of 1:1; S2: Transfer the porous carbon material obtained in step S1 to a tube furnace, introduce inert gas to purge the air inside the tube, evacuate to 1-10 Pa, and heat to 500-900℃. Then, at a total flow rate of 1-10 ml / min, simultaneously introduce lithium source gas, phosphorus source gas, and their crosslinking gas to modify the pores of the porous carbon material for 10-60 minutes. Afterward, raise the temperature to 1000-1300℃ and introduce carbon dioxide gas at a flow rate of 10-50 ml / min to expand the pores for 30-300 minutes, obtaining modified porous carbon. Preferably, in step S2, the lithium source gas... The phosphorus source gas is any one of lithium acetate, lithium citrate, lithium formate, and lithium isobutyrate; the phosphorus source gas is any one of tetramethylfluorourea hexafluorophosphate, tripolyphosphate, 2,3-dibromo-1-propanol phosphate, 2-ethylhexyl phosphate, ethyl dichlorophosphate, vinyl phosphate, and 2-butoxyethanol phosphate; the crosslinking gas is any one of di-tert-butane peroxide, di-tert-butane peroxide, isononanoyl peroxide, tert-amyl peroxide, tert-butyl hydroperoxide, tert-butanol peroxide, hydroxyisopropylbenzene peroxide, diisopropylbenzene peroxide, benzoyl peroxide, and dibenzoyl peroxide. S3: The modified porous carbon obtained in step S2 is fed into a fluidized bed and heated to 450-550℃ under an inert gas atmosphere. A silane mixed gas is introduced at a flow rate of 100-300 ml / min for 60-600 minutes to obtain silicon-carbon material. Preferably, in step S3, the silane mixed gas is any one of methanesilane, ethylsilane, monochlorosilane, dichlorosilane, and monochlorosilane mixed with nitrogen, and the volume ratio of the two is 1-5:10. S4: Transfer the silicon-carbon material obtained in step S3 to the atomic vapor deposition reaction chamber, evacuate to 1-10 Torr, heat to 200-400°C, introduce an inert carrier gas carrying solid electrolyte composite vapor to deposit on its surface for 30-300 minutes; then, introduce fluorinated carbon derivative gas at a flow rate of 10-60 ml / min for pyrolysis deposition for 60-600 minutes to obtain atomic layer deposition silicon-carbon composite material; preferably, in step S4, the volume ratio of solid electrolyte composite vapor to inert carrier gas is 1-5:1, and the total flow rate is 10-60 ml / min; the inert carrier gas... The mixture includes any one or more of helium, argon, or xenon; the solid electrolyte complex vapor is formed by mixing any one of the solid electrolytes, namely lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium germanium aluminum phosphate, or lithium titanium aluminum phosphate, with MOF material, and the mass ratio of the two is 0.5-2:1; the fluorinated carbon derivative gas is any one of carbon tetrafluoride, hexafluoroethane, and trichlorofluoromethane; preferably, the MOF material is any one of ZIF-8 (2-methylimidazolium-zinc nitrate), ZIF-67 (2-methylimidazolium-cobalt nitrate), MIL-101 (iron-terephthalic acid), and MIL-53 (aluminum-terephthalic acid).

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] Based on the above-described implementation schemes, this application further proposes the following specific embodiments: First, it should be noted that the reagent raw materials used in the following specific embodiments and comparative examples of the present invention are sourced from the following: Unless otherwise specified, all raw materials are ordinary commercially available products.

[0021] It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] Example 1: A method for preparing an atomic layer deposition silicon-carbon composite material, comprising the following steps: S1: Mix 100g epoxy resin, 1000g acetone solution of 2% ferric chloride evenly, and react at 80℃ for 3 hours. After filtration, the resulting material is carbonized at 400℃ for 2 hours. Then, the material obtained from the low-temperature carbonization is mixed with 8g potassium carbonate and carbonized at 1200℃ for 2 hours. The material obtained from the medium-temperature carbonization is then acid-washed with 500ml of 0.1mol / L mixed acid (hydrochloric acid: hydrofluoric acid volume ratio = 1:1) to obtain porous carbon material. S2: Transfer the porous carbon material obtained in step S1 to a tube furnace. First, argon inert gas is introduced to purge the air from the tube, and the vacuum is evacuated to 5 Pa. Then, the material is heated to 650°C. At a total flow rate of 5 ml / min, lithium acetate gas, tetramethylfluorourea hexafluorophosphate gas, and di-tert-butane peroxide gas (in order, with a volume ratio of 1:1:1) are introduced to modify the pores of the porous carbon material for 30 minutes. Then, the temperature is raised to 1200°C, and carbon dioxide gas is introduced at a flow rate of 30 ml / min to expand the pores for 150 minutes to obtain modified porous carbon. S3: The modified porous carbon obtained in step S2 above is fed into a fluidized bed and heated to 500°C under a nitrogen inert gas atmosphere. A mixture of silane and nitrogen gas (silane:nitrogen volume ratio = 3:10) is introduced at a flow rate of 200 ml / min for 300 minutes to obtain silicon-carbon material. S4: Transfer the silicon-carbon material obtained in step S3 above into the atomic vapor deposition (ALD) reaction chamber, evacuate to 5 Torr, heat to 300°C, introduce nitrogen inert carrier gas, and deposit lithium lanthanum zirconium oxygen vapor (mass ratio of lithium lanthanum zirconium oxygen: ZIF-8 = 1:1) on its surface, wherein the volume ratio of lithium lanthanum zirconium oxygen vapor to nitrogen inert carrier gas is 1:5, the total flow rate is 30 ml / min, and the deposition time is 150 minutes; then introduce carbon tetrafluoride gas and perform pyrolysis deposition at a flow rate of 30 ml / min for 300 minutes to obtain atomic layer deposition silicon-carbon composite material.

[0023] This application conducted SEM (scanning electron microscopy) morphology tests on the atomic layer deposition silicon-carbon composite material obtained in Example 1. The test results are as follows: Figure 1 As shown, we through Figure 1 It can be seen that the silicon-carbon composite material exhibits a spherical structure with a particle size between 5-10 μm and a uniform size distribution.

[0024] Example 2: A method for preparing an atomic layer deposition silicon-carbon composite material, comprising the following steps: S1: Mix 100g glucose, 1000g cobalt chloride in acetone solution evenly, and react at 80℃ for 3 hours. Filter the resulting material and carbonize it at 300℃ for 3 hours. Then mix the material obtained from the low-temperature carbonization with 5g potassium hydroxide and carbonize it at 1000℃ for 3 hours. Wash the material obtained from the medium-temperature carbonization with 500ml of 0.1mol / L mixed acid (hydrochloric acid: hydrofluoric acid volume ratio = 1:1) to obtain porous carbon material. S2: Transfer the porous carbon material obtained in step S1 to a tube furnace. First, purge the air in the tube with nitrogen inert gas, evacuate to 1 Pa, and heat to 500°C. Then, at a total flow rate of 1 ml / min, simultaneously introduce lithium citrate gas, tripolyphosphate gas, and ditert-butane peroxide gas (in order, with a volume ratio of 2:2:0.5) to modify the pores in the porous carbon material for 60 minutes. After that, raise the temperature to 1000°C and introduce carbon dioxide at a flow rate of 10 ml / min to expand the pores for 300 minutes to obtain modified porous carbon. S3: The modified porous carbon obtained in step S2 above is fed into a fluidized bed and heated to 450°C under a nitrogen inert gas atmosphere. A silane mixed gas (silane: nitrogen volume ratio = 1:10) is introduced at a flow rate of 100 ml / min for 600 minutes to obtain silicon-carbon material. S4: Transfer the silicon-carbon material obtained in step S3 above into the atomic vapor deposition (ALD) reaction chamber, evacuate to 1 Torr, heat to 400°C, introduce nitrogen inert carrier gas, and deposit lithium lanthanum titanium oxygen vapor (mass ratio of lithium lanthanum titanium oxygen: ZIF-67 = 0.5:1) on its surface, wherein the volume ratio of lithium lanthanum titanium oxygen vapor to nitrogen inert carrier gas is 1:1, the total flow rate is 10 ml / min, the deposition time is 300 minutes, and then hexafluoroethane gas is introduced and pyrolysis deposition is carried out at a flow rate of 10 ml / min for 600 minutes to obtain atomic layer deposition silicon-carbon composite material.

[0025] Example 3: A method for preparing an atomic layer deposition silicon-carbon composite material, comprising the following steps: S1: Mix 100g of furfural resin and 600g of 5wt% nickel chloride in acetone solution until homogeneous, and react at 80℃ for 3 hours. After filtration, the resulting material is carbonized at 500℃ for 1 hour. Then, the material obtained from the low-temperature carbonization is mixed with 10g of sodium carbonate and carbonized at 1300℃ for 1 hour. The material obtained from the medium-temperature carbonization is then acid-washed with 500ml of 0.1mol / L mixed acid (hydrochloric acid: hydrofluoric acid volume ratio = 1:1) to obtain porous carbon material. S2: Transfer the porous carbon material obtained in step S1 to a tube furnace. First, introduce nitrogen inert gas to purge the air from the tube. Then, evacuate to 10 Pa and heat to 900 °C. Then, at a total flow rate of 10 ml / min, simultaneously introduce lithium formate gas, ethyl dichlorophosphate gas, and benzoyl peroxide gas (in order, with a volume ratio of 0.5:0.5:2) to modify the pores in the porous carbon material for 60 minutes. Then, raise the temperature to 1300 °C and introduce carbon dioxide at a flow rate of 50 ml / min to expand the pores for 30 minutes to obtain modified porous carbon. S3: The modified porous carbon obtained in step S2 above is fed into a fluidized bed and heated to 550°C under a nitrogen inert gas atmosphere. A mixture of monochlorosilane gas (monochlorosilane: nitrogen volume ratio = 5:10) is introduced at a flow rate of 300 ml / min for 600 minutes to obtain silicon-carbon material. S4: Transfer the silicon-carbon material obtained in step S3 above into the atomic vapor deposition (ALD) reaction chamber, evacuate to 10 Torr, heat to 400°C, introduce nitrogen inert carrier gas, and carry a mixed vapor of lithium aluminum germanium phosphate (mass ratio of lithium aluminum germanium phosphate to MIL-101 = 2:1) to deposit on its surface. The volume ratio of the mixed vapor of lithium aluminum germanium phosphate to nitrogen inert carrier gas is 5:1, the total flow rate is 60 ml / min, the deposition time is 30 minutes, and then trichlorofluoromethane gas is introduced and pyrolyzed at a flow rate of 60 ml / min for 60 minutes to obtain atomic layer deposition silicon-carbon composite material.

[0026] Comparative Example 1: The remaining technical solutions of Comparative Example 1 are the same as those of Example 1, except that in Comparative Example 1, step S1 is cancelled, and the porous carbon material in step S2 is replaced with commercially available porous carbon (model: YP-50F, manufacturer: Kuraray Co., Ltd., Japan).

[0027] Comparative Example 2: The remaining technical solutions of Comparative Example 2 are the same as those of Example 1, except that in step S2 of Comparative Example 2, lithium acetate gas is not introduced, and tetramethylfluorourea hexafluorophosphate gas and di-tert-butane peroxide gas are used to modify the porous carbon.

[0028] Comparative Example 3: The remaining technical solutions of Comparative Example 3 are the same as those of Example 1, except that in Comparative Example 3, step S4 is omitted, and the silicon-carbon material obtained in step S3 is directly used as the product obtained in Comparative Example 3.

[0029] To verify the technical effects achieved by the embodiments of this application, the materials obtained in the above embodiments 1-3 and comparative examples 1-3 were subjected to the following physicochemical property tests: The pore volume, pore size, and specific surface area of ​​the porous carbon materials used in Examples 1-3 and Comparative Examples 1-3 were tested according to the national standards GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method" and GB / T7702.20-2008 "Detection of Pore Volume of Coal-based Activated Carbon". The specific surface area and tap density of the materials obtained in Examples 1-3 and Comparative Examples 1-3 were tested according to the national standard GB / T38823-2020 "Silicon Carbon". The powder resistivity of the materials obtained in Examples 1-3 and Comparative Examples 1-3 was then tested using a four-probe tester. The test results are shown in Table 1.

[0030] As can be seen from Table 1 above, the silicon-carbon composite materials and their corresponding porous carbon materials provided in Examples 1-3 are significantly better than those in Comparative Examples 1-3 in terms of pore volume, specific surface area and powder resistivity. The main reason is that the embodiments of this application reduce the defects of silicon-carbon composite materials by creating pores with activators and doping them with elements such as lithium and heteroatoms in the pores to improve the electronic conductivity of the material, thereby reducing the powder resistivity of silicon-carbon composite materials.

[0031] To further verify the technical effects achieved in this application, the materials obtained in Examples 1-3 and Comparative Examples 1-3 above were used as negative electrode active materials to prepare coin cells according to the following method: The negative electrode active material, binder, conductive agent, and solvent were mixed (in the order of 70g:15g:15g:300mL), stirred to form a slurry, and then coated onto copper foil. After drying and pressing, a negative electrode sheet was obtained. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The electrolyte was a LiPF6 solution with a concentration of 1mol / L, and the solvent was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1. A lithium metal sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator. Each coin cell was assembled in an argon-filled glove box. Then, the coin cells obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to the following performance tests: (1) Electrochemical performance was tested on the Wuhan Landian CT2001A battery tester. The charge and discharge voltage range was 0.005V to 2.0V, and the charge and discharge rate was 0.1C. The discharge specific capacity and initial efficiency of the corresponding coin cell were tested. At the same time, the cycle performance (0.1C / 0.1C, 100 cycles) of the corresponding coin cell was tested. (2) Full charge expansion test: Test the thickness D1 of the electrode after rolling, and test the thickness D2 when fully charged to 100% SOC. Full charge expansion = (D2-D1) / D1; (3) The lithium-ion diffusion coefficient was tested by GITT; The test results are shown in Table 2 below:

[0032] As shown in Table 2 above, compared with the comparative examples, the silicon-carbon composite materials prepared in each embodiment have higher specific capacity, higher initial efficiency, and higher diffusion coefficient. This is mainly because: in the preparation process of each embodiment, lithium and its heteroatoms are doped, which improves the electronic and ionic conductivity of the material, reduces polarization, and improves the discharge specific capacity and initial efficiency; simultaneously, because each embodiment deposits a solid electrolyte on the surface of the silicon-carbon composite material using atomic vapor deposition, it improves the ionic conductivity and rate performance, and the coating on the surface of the silicon-carbon composite material restricts the expansion of the core nano-silicon, improving cycle performance; Specifically, Comparative Example 1, due to the lack of activator for further pore expansion and the absence of catalyst to alter the anisotropy of the carbon layer, resulted in a higher electronic conductivity and lower pore volume in the porous carbon, leading to a lower specific capacity and diffusion coefficient in the obtained material. Comparative Example 2, due to the lack of lithium and heteroatoms deposited on the inner wall of the porous carbon, resulted in a lower defect level and higher impedance in the obtained material, leading to a lower initial efficiency and a deviated diffusion coefficient. Comparative Example 3, due to the lack of a solid electrolyte composite material coating, resulted in higher impedance, a lower lithium-ion diffusion coefficient, and increased full-charge expansion due to the confined expansion of nano-silicon.

[0033] To further verify the technical effects achieved in this application, this application also prepared negative electrode sheets by doping the materials obtained in Examples 1-3 and Comparative Examples 1-3 with 92% artificial graphite, using ternary material LiNi 0.6 Co 0.2 Mn 0.2 O2 was used as the positive electrode material; LiPF6 was used as the electrolyte, and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 was used as the solvent; a Celgard 2400 membrane was used as the separator to prepare 5Ah pouch cells corresponding to Examples 1-3 and Comparative Examples 1-3; the following performance tests were performed on each pouch cell: 1. Cyclic performance test: The battery's cycle performance was tested for 500 cycles at a charge / discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, and a temperature of 25±3℃. 2. HPPC Performance Testing: Charging DCR was measured at different SOCs (10%, 30%, 50%, 70%, 90%) using 3C charging and 4C discharging rates. The test results for the pouch batteries are shown in Table 3:

[0034] As shown in Table 3 above, the cycle performance and rate performance of the soft-pack battery obtained by using the silicon-carbon composite material provided in Examples 1-3 of this application are significantly better than those of Comparative Examples 1-3. The main reason is that the silicon-carbon composite material provided in Examples 1-3 of this application is coated with a solid electrolyte, which restricts the expansion of the core and improves the ionic conductivity, thereby increasing the diffusion coefficient of the material, reducing the DCR, and improving the cycle performance.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0036] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing an atomic layer deposition silicon-carbon composite material, characterized in that, The following steps are included: S1: According to the mass ratio of porous carbon precursor: catalyst: activator = 100:10-30:5-10, the porous carbon precursor and catalyst solution are mixed evenly and reacted at a temperature not lower than 70℃ for at least 2.5 hours. After filtration, the mixture is carbonized at a low temperature of 300-500℃ for 1-3 hours. Then, the material obtained from the low temperature carbonization is mixed with the activator and carbonized at a medium temperature of 1000-1300℃ for 1-3 hours. The material obtained from the medium temperature carbonization is then acid-washed to obtain the porous carbon material. S2: Transfer the porous carbon material obtained in step S1 to a tube furnace, introduce inert gas to purge the air inside the tube, evacuate to 1-10 Pa, and heat to 500-900℃. Then, at a total flow rate of 1-10 ml / min, simultaneously introduce lithium source gas, phosphorus source gas, and their crosslinking gas to modify the pores of the porous carbon material for 10-60 minutes. Afterward, raise the temperature to 1000-1300℃, and introduce carbon dioxide gas at a flow rate of 10-50 ml / min to expand the pores for 30-300 minutes. To modify porous carbon; the phosphorus source gas is any one of tetramethylfluorourea hexafluorophosphate, tripolyphosphate, 2,3-dibromo-1-propanol phosphate, 2-ethylhexyl phosphate, ethyl dichlorophosphate, vinyl phosphate, and 2-butoxyethanol phosphate; the crosslinking gas is any one of di-tert-butane peroxide, isononanoyl peroxide, tert-amyl peroxide, tert-butyl hydroperoxide, tert-butanol peroxide, cumene peroxide, dicumene peroxide, benzoyl peroxide, and dibenzoyl peroxide. S3: The modified porous carbon obtained in step S2 is fed into a fluidized bed and heated to 450-550℃ under an inert gas atmosphere. A silane mixed gas is introduced at a flow rate of 100-300 ml / min for 60-600 minutes to obtain silicon-carbon material. S4: Transfer the silicon-carbon material obtained in step S3 to the atomic layer vapor deposition reaction chamber, evacuate to 1-10 Torr, heat to 200-400°C, introduce an inert carrier gas, and deposit the solid electrolyte composite vapor on its surface for 30-300 minutes; then, introduce fluorinated carbon derivative gas at a flow rate of 10-60 ml / min for pyrolysis deposition for 60-600 minutes to obtain the atomic layer deposited silicon-carbon composite material; the solid electrolyte composite vapor is formed by mixing any one of the solid electrolytes lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium germanium aluminum phosphate, or lithium titanium aluminum phosphate with the MOF material, with a mass ratio of 0.5-2:1; The atomic layer deposition silicon-carbon composite material adopts a core-shell encapsulation structure consisting of a core and an outer shell, wherein the core is a multi-element doped silicon-carbon material and the outer shell is a solid electrolyte composite layer; the mass ratio of the core to the outer shell is 80-95:5-20.

2. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, In step S1, the porous carbon precursor is any one of glucose, asphalt, epoxy resin, phenolic resin, furfural resin, polyethylene glycol, polyamide resin, and cellulose; the catalyst is any one of ferric chloride, nickel chloride, cobalt chloride, ferric nitrate, nickel nitrate, and cobalt nitrate, with a concentration of 1-5 wt% in the catalyst solution; and the activator is any one of potassium carbonate, potassium hydroxide, sodium carbonate, and sodium hydroxide.

3. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, In step S1, the pickling process includes: pickling the material obtained by medium-temperature carbonization with a 0.1 mol / L mixed acid, wherein the mixed acid is hydrochloric acid and hydrofluoric acid in a volume ratio of 1:

1.

4. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, In step S2, the lithium source gas is any one of lithium acetate, lithium citrate, lithium formate, and lithium isobutyrate.

5. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, In step S3, the silane mixed gas is any one of silane, silane, monochlorosilane, and dichlorosilane mixed with nitrogen, and the volume ratio of the two is 1-5:

10.

6. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, In step S4, the inert carrier gas includes any one or a mixture of several of helium, argon, or xenon; the fluorinated carbon derivative gas is any one of carbon tetrafluoride, hexafluoroethane, and trichlorofluoromethane.

7. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, The MOF material is any one of ZIF-8, ZIF-67, MIL-101, and MIL-53.

8. The method for preparing the atomic layer deposition silicon-carbon composite material according to claim 1, characterized in that, In step S4, the volume ratio of the solid electrolyte complex vapor to the inert carrier gas is 1-5:1, and the total flow rate is 10-60 ml / min.

9. The application of an atomic layer deposition silicon-carbon composite material prepared by a method according to any one of claims 1-8, characterized in that, The atomic layer deposited silicon-carbon composite material is used as the active material raw material for preparing battery electrodes.

10. The application of the atomic layer deposition silicon-carbon composite material obtained by the preparation method according to claim 9, characterized in that, The atomic layer deposited silicon-carbon composite material is used as the active material raw material for the negative electrode sheet of a lithium-ion battery.

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