A porous carbon composite material, a preparation method thereof and a lithium ion battery

Abstract

The application provides a kind of porous carbon composite material and its preparation method and lithium ion battery, belongs to battery material technical field.Preparation method includes the following steps: organic template agent, crosslinking agent, dispersing agent, lithium supplement agent and porous carbon precursor solution are mixed, hydrothermal reaction is carried out, and intermediate material is obtained;The intermediate material is carbonized and then activated with an activator to obtain a porous carbon composite material.The application uses a template method and a lithium supplement agent to prepare a porous carbon composite material with a spherical structure, high pore volume and uniform pore size distribution.The porous carbon composite material as a silicon carrier exhibits excellent silicon storage capacity and structural stability, effectively alleviates the volume expansion during charging and discharging, enhances the compression resistance of the material, and is beneficial to the construction of a stable electrode interface.The silicon-carbon composite material prepared based on this has obvious improvement effect in power performance, cycle performance and initial efficiency.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a porous carbon composite material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Silicon-based materials are considered the most promising candidates for next-generation high-energy-density lithium-ion battery anodes due to their extremely high theoretical specific capacity. However, silicon faces significant volume changes during charge and discharge, leading to electrode material pulverization, continuous growth of the solid electrolyte interphase (SEI) film, and eventual failure, severely hindering its commercial application. To overcome this challenge, silicon-carbon composite materials have emerged, consisting of porous carbon and nano-silicon deposited within the pores, coated with amorphous carbon. The porous carbon serves as both a conductive network and a buffer for the volume expansion of silicon, while the outer amorphous carbon coating further stabilizes the interface and inhibits excessive SEI film growth.

[0003] However, due to the uncontrollable size of the pores in porous carbon materials and the large number of nano- and micro-pores, the amount of nano-silicon that can be accommodated in the material is low and the expansion is large; the high impedance of the porous carbon core and the large number of defects result in high impedance and poor compressive strength of the material.

[0004] Although some researchers have improved the electronic and ionic conductivity of materials by doping the material internally and coating it with an outer layer, the improvement is limited; or by preparing a spherical structure to reduce expansion and improve compressive strength, but this will increase impedance.

[0005] Therefore, how to improve the power performance of porous carbon while reducing its volume expansion, thereby improving the electrochemical performance of silicon-carbon composites, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a porous carbon composite material, its preparation method, and a lithium-ion battery. This invention employs a synergistic strategy of template method and lithium supplementation agent to prepare a porous carbon composite material with a spherical structure, high pore volume, and uniform pore size distribution. This method effectively reduces the defect density of the carbon skeleton, improves the ion diffusion coefficient, and significantly enhances the material's initial coulombic efficiency and rate performance. The porous carbon composite material prepared using this method exhibits excellent silicon storage capacity and structural stability when used as a silicon carrier. It not only effectively alleviates volume expansion during charge and discharge processes and enhances the material's compressive strength but also facilitates the construction of a stable electrode interface. The silicon-carbon composite material prepared in this way shows significant improvements in power performance, cycle performance, and initial efficiency.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a porous carbon composite material, the method comprising the following steps:

[0009] An organic template agent, crosslinking agent, dispersant, lithium supplementer, and porous carbon precursor solution are mixed and subjected to a hydrothermal reaction to obtain an intermediate material.

[0010] The intermediate material is carbonized and then activated with an activator to obtain the porous carbon composite material.

[0011] This invention utilizes a synergistic strategy of template method and lithium supplementation to prepare porous carbon composite materials with spherical structure, high pore volume, and uniform pore size distribution. This method effectively reduces the defect density of the carbon skeleton, improves the ion diffusion coefficient, and significantly enhances the material's initial coulombic efficiency and rate performance. The porous carbon composite material prepared using this method exhibits excellent silicon storage capacity and structural stability when used as a silicon support. It not only effectively alleviates volume expansion during charge and discharge processes and enhances the material's compressive strength but also facilitates the construction of a stable electrode interface. The silicon-carbon composite material prepared in this way shows significant improvements in power performance, cycle performance, and initial efficiency.

[0012] Preferably, the organic template agent includes any one or a combination of at least two of lithium pyruvate, lithium diacetate, lithium acetate, lithium naphthalenesulfonate, lithium citrate, or lithium gluconate.

[0013] Preferably, the crosslinking agent includes any one or a combination of at least two of maleic anhydride, acetic anhydride, benzoic anhydride or chromic anhydride.

[0014] Preferably, the dispersant comprises any one or a combination of at least two of polyvinyl alcohol, F127 polyether ester, or polyacrylate.

[0015] Preferably, the lithium supplement includes any one or a combination of at least two of Li5FeO4, Li6CoO4, Li2O2, LiNiO2 or Li2MnO3.

[0016] Preferably, the porous carbon precursor solution is a glycosyl compound solution.

[0017] Preferably, the glycosyl compound solution contains any one or a combination of at least two of glucose, sucrose, starch, or cellulose, and the solvent is deionized water.

[0018] Preferably, the mass ratio of the organic template agent, crosslinking agent, dispersant, lithium supplementer, and porous carbon precursor solution is (10-30):(1-5):(1-5):(1-5):500, wherein the organic template agent is selected from the range of "10-30", for example, 10, 15, 20, 25, or 30, the crosslinking agent is selected from the range of "1-5", for example, 1, 2, 3, 4, or 5, the dispersant is selected from the range of "1-5", for example, 1, 2, 3, 4, or 5, and the lithium supplementer is selected from the range of "1-5", for example, 1, 2, 3, 4, or 5.

[0019] In this invention, the specified mass ratio of organic template agent, crosslinking agent, dispersant, lithium supplementer, and porous carbon precursor solution is beneficial for forming a stable and structurally controllable precursor gel system in solution. Specifically: the organic template agent, at this ratio, effectively guides the assembly of glycosyl precursor molecules to form a uniform micelle or liquid crystal phase, providing an initial template for subsequent porous structures; the crosslinking agent moderately promotes the crosslinking and curing of precursor molecules, stabilizing the template structure and preventing its collapse during subsequent processing; the dispersant ensures that all components, especially hydrophobic or easily agglomerated lithium supplementers, are uniformly dispersed in the aqueous phase, achieving molecular-level uniform mixing; and an appropriate amount of lithium supplementer can be uniformly distributed in the material matrix, avoiding the excessive introduction of impurity phases that affect conductivity, while ensuring effective active lithium compensation during electrochemical processes. This optimized ratio ensures the synergistic effect of each functional component, which is a key prerequisite for ultimately obtaining porous carbon composite materials with high specific surface area, regular pore structure, low defect density, and excellent lithium supplementation effect. If the ratio is unbalanced, it can easily lead to problems such as incomplete template structure, component segregation, disordered channels, or poor lithium replenishment effect.

[0020] Preferably, the temperature of the hydrothermal reaction is 50-100℃, for example, it can be 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃.

[0021] Preferably, the hydrothermal reaction time is 1-6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0022] Preferably, the carbonization temperature is 700-1000℃, for example, 700℃, 800℃, 900℃ or 1000℃.

[0023] Preferably, the carbonization treatment time is 1-6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0024] Preferably, the carbonization process includes mixing intermediate materials and an alkaline reagent, and then carbonizing them.

[0025] This invention involves carbonizing an intermediate material with a basic reagent, achieving an integrated and synergistic enhancement of the "carbonization-activation" process. Specifically, during high-temperature carbonization, the basic reagent not only acts as a traditional activator but also, through redox reactions (such as… Selective etching of the carbon framework creates abundant micropores and mesopores, significantly increasing the specific surface area and pore volume of the material. Simultaneously, alkali metal ions can penetrate into the carbon interlayer at high temperatures, catalyzing graphitization and effectively reducing the defect density and disorder of the carbon material, thus improving its electronic conductivity. More importantly, this step, combined with the pre-organized structure formed by the aforementioned template method, allows alkaline etching to proceed along the template-guided path, resulting in more regular channels and a more concentrated pore size distribution. Furthermore, the alkaline environment helps decompose or transform residual organic template agents and crosslinking agents in the precursor, allowing some of their decomposition products to participate in the construction of the carbon structure or pore formation, avoiding impurity residue. This integrated treatment simplifies the process flow, and the simultaneous carbonization and activation result in a porous carbon composite material with a highly conductive network, a well-developed pore structure, and a stable framework, providing an ideal carrier for subsequent loading of active materials (such as silicon). Separating carbonization and activation makes it difficult to achieve this simultaneous optimization of structure and conductivity, and easily leads to process complexity and increased energy consumption.

[0026] Preferably, the alkaline reagent includes any one or a combination of at least two of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, or sodium bicarbonate.

[0027] Preferably, the mass ratio of the intermediate material to the alkaline reagent is 100:(100-500), for example, it can be 100:100, 100:200, 100:300, 100:400 or 100:500, etc.

[0028] Preferably, the activator comprises water vapor.

[0029] Preferably, the activation treatment temperature is 900-1300℃, for example, it can be 900℃, 1000℃, 1100℃, 1200℃ or 1300℃.

[0030] Preferably, the activation treatment time is 30-300 min, for example, it can be 30 min, 50 min, 100 min, 200 min or 300 min.

[0031] Preferably, coal-based pitch is also added during the mixing process of the intermediate material and the alkaline reagent. For example, the coal-based pitch may be medium-temperature coal pitch, high-temperature coal pitch, or modified coal pitch.

[0032] In this invention, coal-based pitch serves as a binder and supplementary carbon source. Its function is twofold: during the carbonization stage, the softened coal-based pitch binds primary carbon particles, forming secondary spherical aggregates with high mechanical strength and bulk density; simultaneously, its carbonization products combine with the pore structure generated by alkaline etching to construct a continuous and highly conductive carbon skeleton. This multi-level porous conductive network, synergistically formed by "coal-based pitch reinforcing the secondary structure" and "alkaline reagent creating pores," fundamentally improves the material's compaction density, structural stability, and electron transport dynamics, thereby effectively reducing impedance.

[0033] Preferably, the mass ratio of the intermediate material, the alkaline reagent, and the coal-based pitch is 100:(100-500):(5-15), wherein the alkaline reagent can be selected in the range of "100-500", for example, 100, 200, 300, 400, or 500, and the coal-based pitch can be selected in the range of "5-15", for example, 5, 10, or 15.

[0034] Preferably, the softening point of the coal-based pitch is 50-100℃, for example, it can be 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃.

[0035] Preferably, the preparation method includes the following steps:

[0036] (1) Add organic template agent, crosslinking agent, dispersant and lithium supplement to sugar compound solution and mix evenly. Then transfer to high pressure reactor and carry out hydrothermal reaction at 50-100℃ for 1-6h. After drying, intermediate material is obtained.

[0037] The mass ratio of the organic template agent, crosslinking agent, dispersant, lithium supplementer and glycosyl compound solution is (10-30):(1-5):(1-5):(1-5):500; the mass concentration of the glycosyl compound solution is 1-10 wt% (e.g., it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%, etc.).

[0038] (2) The intermediate material, alkaline reagent and coal-based pitch are mixed and then carbonized at 700-1000℃ for 1-6 hours. After that, the temperature is raised to 900-1300℃ and water vapor is introduced at a flow rate of 100-500mL / min (e.g., 100mL / min, 200mL / min, 300mL / min, 400mL / min or 500mL / min, etc.) for 30-300 minutes to activate the porous carbon composite material.

[0039] The mass ratio of the intermediate material, alkaline reagent and coal-based pitch is 100:(100-500):(5-15).

[0040] In a second aspect, the present invention provides a porous carbon composite material, which is prepared by the preparation method described in the first aspect.

[0041] Thirdly, the present invention provides a silicon-carbon composite material, wherein the raw materials for preparing the silicon-carbon composite material include the porous carbon composite material described in the second aspect.

[0042] Fourthly, the present invention provides a method for preparing a silicon-carbon composite material as described in the third aspect, the method comprising the following steps:

[0043] Silicon-carbon materials are obtained by depositing nano-silicon in porous carbon composite materials.

[0044] Lithium sulfonate is coated onto the surface of the silicon-carbon material to obtain the silicon-carbon composite material.

[0045] This invention involves coating the surface of silicon-carbon materials with lithium sulfonate. Lithium sulfonate has advantages such as strong solvation ability and high ion diffusion coefficient, which is beneficial to improving the rate performance of silicon-carbon materials.

[0046] Preferably, the method for depositing nano-silicon includes vapor deposition.

[0047] Preferably, in the vapor deposition method, the parameters include: a deposition temperature of 450-550℃, for example, 450℃, 500℃, or 550℃; a deposition time of 60-300min, for example, 60min, 100min, 200min, or 300min; a gas source including silane gas and inert gas; and a gas flow rate of 100-500mL / min, for example, 100mL / min, 200mL / min, 300mL / min, 400mL / min, or 500mL / min.

[0048] Preferably, the volume ratio of the silane gas to the inert gas is (1-5):10, for example, it can be 1:10, 2:10, 3:10, 4:10 or 5:10, etc.

[0049] Preferably, the silane gas includes any one or a combination of at least two of the following: silane, disilane, dichlorosilane, trichlorosilane, tetrachlorosilane, or silicon tetrafluoride.

[0050] Preferably, the inert gas includes nitrogen.

[0051] Preferably, after depositing nano-silicon, the surface of the nano-silicon is further passivated to form silicon oxide.

[0052] In this invention, passivation aims to controllably oxidize the surface of nano-silicon generated by vapor deposition, forming a dense and appropriately thick silicon oxide passivation layer. This passivation layer has the following key functions: First, as a physical barrier, it significantly reduces the direct contact area between the highly active nano-silicon and the electrolyte, thereby effectively suppressing the continuous consumption of active lithium and electrolyte decomposition caused by side reactions during charging and discharging; Second, it possesses good lithium-ion conductivity and structural stability, which helps to induce the formation of a thin and stable solid electrolyte interphase (SEI) film in the early stages of cycling, reducing the repeated growth and rupture of the SEI film in subsequent cycles; Third, moderate surface oxidation can alleviate the absolute volumetric strain of the pure silicon phase during lithium insertion / extraction, improving the structural integrity of the material. This passivation treatment is a crucial step in improving the initial coulombic efficiency of silicon-carbon composite materials, extending cycle life, and maintaining high-rate performance. If this step is omitted, the extremely high surface activity of the nascent nano-silicon will lead to severe irreversible capacity loss and rapid capacity decay.

[0053] Preferably, the parameters during the passivation process include: an air flow rate of 10-50 mL / min, such as 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, or 50 mL / min; a passivation time of 60-300 min, such as 60 min, 100 min, 200 min, or 300 min; and a passivation temperature of room temperature, such as 25℃±5℃.

[0054] Preferably, the mass ratio of lithium sulfonate to silicon carbide is (1-5):100, for example, it can be 1:100, 2:100, 3:100, 4:100 or 5:100, etc.

[0055] Preferably, the lithium sulfonate includes any one or a combination of at least two of lithium trifluoromethanesulfonate, lithium perfluorohexanesulfonate, lithium perfluorobutylsulfonate, lithium 4-vinylbenzenesulfonate, or lithium dinonylnaphthalenesulfonate.

[0056] Preferably, the step of coating the surface of the silicon-carbon material with lithium sulfonate includes: mixing the silicon-carbon material and the coating solution containing lithium sulfonate, and then sintering.

[0057] Preferably, the mass fraction of the lithium sulfonate coating solution is 1-20 wt%, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, or 20 wt%.

[0058] Preferably, the sintering temperature is 350-800℃, for example, it can be 350℃, 450℃, 550℃, 650℃, 750℃ or 800℃.

[0059] Preferably, the sintering time is 1-6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0060] Preferably, in the lithium sulfonate coating solution, the organic solvent includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, or ethylene carbonate.

[0061] Fifthly, the present invention provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises a porous carbon composite material as described in the second aspect, or comprises a silicon-carbon composite material as described in the third aspect.

[0062] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] This invention utilizes a synergistic strategy of template method and lithium supplementation to prepare porous carbon composite materials with spherical structure, high pore volume, and uniform pore size distribution. This method effectively reduces the defect density of the carbon skeleton, improves the ion diffusion coefficient, and significantly enhances the material's initial coulombic efficiency and rate performance. The porous carbon composite material prepared using this method exhibits excellent silicon storage capacity and structural stability when used as a silicon support. It not only effectively alleviates volume expansion during charge and discharge processes and enhances the material's compressive strength but also facilitates the construction of a stable electrode interface. The silicon-carbon composite material prepared in this way shows significant improvements in power performance, cycle performance, and initial efficiency. Attached Figure Description

[0065] Figure 1 This is a SEM image of the silicon-carbon composite material prepared in Example 1 of this invention. Detailed Implementation

[0066] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0067] Example 1

[0068] This embodiment provides a method for preparing porous carbon composite materials, the method comprising the following steps:

[0069] (1) Add 20g lithium pyruvate, 3g maleic anhydride, 3g polyvinyl alcohol and 3g Li5FeO4 to 500g glucose aqueous solution (mass concentration of 5wt%) and mix evenly. Then transfer to a high pressure reactor and carry out hydrothermal reaction at 80℃ for 3h. Filter and then vacuum dry at 80℃ for 24h to obtain intermediate material.

[0070] The mass ratio of lithium pyruvate, maleic anhydride, polyvinyl alcohol, Li5FeO4 and glucose aqueous solution is 20:3:3:3:500.

[0071] (2) Mix 100g of the intermediate material, 200g of potassium hydroxide and 10g of coal-based pitch evenly, compress into blocks, and then perform carbonization treatment at 750℃ for 3h. After that, raise the temperature to 1100℃ and pass water vapor through at a flow rate of 300mL / min for 180min to perform activation treatment to obtain the porous carbon composite material.

[0072] The mass ratio of the intermediate material, potassium hydroxide, and coal-based pitch is 100:200:10; the coal-based pitch is a medium-temperature coal pitch with a softening point of about 80°C.

[0073] This embodiment also provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0074] (a) The porous carbon composite material prepared above is transferred to a fluidized bed, nitrogen is introduced to exhaust the gas, and then heated to 500°C. A mixed gas consisting of silane gas and nitrogen gas with a volume ratio of 3:10 is introduced at a flow rate of 300 mL / min for 180 min for vapor deposition. Then, the temperature is cooled to room temperature of 25°C, and air is introduced at a flow rate of 30 mL / min for 180 min for passivation to form silicon oxide, thus obtaining silicon-carbon material.

[0075] (b) Add 3g of lithium trifluoromethanesulfonate to 90g of dimethyl carbonate solvent and mix well to prepare a coating solution containing lithium trifluoromethanesulfonate; the mass fraction of the coating solution is 10wt%.

[0076] The coating solution containing lithium trifluoromethanesulfonate and 100g of the silicon-carbon material are mixed evenly and then transferred to a reaction vessel. Argon gas is first introduced to purge the air in the vessel, and then the mixture is heated to 650°C and sintered for 3 hours to obtain the silicon-carbon composite material. The mass ratio of lithium trifluoromethanesulfonate in the coating solution to the silicon-carbon material is 3:100.

[0077] Figure 1 The SEM image of the silicon-carbon composite material prepared in this embodiment is shown. As can be seen from the image, the material exhibits a granular structure with a uniform size distribution and a particle size between 5 and 10 μm.

[0078] Example 2

[0079] This embodiment provides a method for preparing porous carbon composite materials, the method comprising the following steps:

[0080] (1) 10g lithium diacetate, 1g acetic anhydride, 5g F127 polyether ester and 5g Li6CoO4 were added to 500g sucrose aqueous solution (mass concentration of 1wt%) and mixed evenly. Then the mixture was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 50°C for 6h. After filtration, the mixture was vacuum dried at 80°C for 24h to obtain intermediate material.

[0081] The mass ratio of lithium diacetate, acetic anhydride, F127 polyether ester, Li6CoO4 and sucrose aqueous solution is 10:1:5:5:500.

[0082] (2) Mix 100g of the intermediate material, 100g of sodium hydroxide and 5g of coal-based pitch evenly, press into blocks, and then perform carbonization treatment at 700℃ for 6h. After that, raise the temperature to 900℃ and pass water vapor through at a flow rate of 100mL / min for 300min to perform activation treatment to obtain the porous carbon composite material.

[0083] The mass ratio of the intermediate material, sodium hydroxide, and coal-based pitch is 100:100:5; the coal-based pitch is a low-temperature coal pitch with a softening point of about 50°C.

[0084] This embodiment also provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0085] (a) The porous carbon composite material prepared above is transferred to a fluidized bed, nitrogen is introduced to exhaust the gas, and then heated to 450°C. A mixture of silane gas and nitrogen gas with a volume ratio of 1:10 is introduced at a flow rate of 100 mL / min for 300 min of vapor deposition. Then the temperature is cooled to room temperature of 25°C, and air is introduced at a flow rate of 10 mL / min for 300 min of passivation to form silicon oxide, thus obtaining silicon-carbon material.

[0086] (b) 1g of lithium perfluorohexanesulfonate was added to 60g of dimethyl carbonate solvent and mixed evenly to prepare a coating solution containing lithium perfluorohexanesulfonate; the mass fraction of the coating solution was 5wt%.

[0087] The coating solution containing lithium perfluorohexane sulfonate and 100g of the silicon-carbon material are mixed evenly and then transferred to a reaction vessel. Argon gas is first introduced to purge the air in the vessel, and then the mixture is heated to 500°C and sintered for 6 hours to obtain the silicon-carbon composite material. The mass ratio of lithium perfluorohexane sulfonate in the coating solution to the silicon-carbon material is 1:100.

[0088] Example 3

[0089] This embodiment provides a method for preparing porous carbon composite materials, the method comprising the following steps:

[0090] (1) Add 30g lithium acetate, 5g benzoic anhydride, 5g polyacrylate and 5g LiNiO2 to 500g starch aqueous solution (mass concentration of 10wt%) and mix evenly. Then transfer to high pressure reactor and carry out hydrothermal reaction at 100℃ for 1h. Filter and then vacuum dry at 80℃ for 24h to obtain intermediate material.

[0091] The mass ratio of lithium acetate, benzoic anhydride, polyacrylate, LiNiO2 and starch aqueous solution is 30:5:5:5:500.

[0092] (2) Mix 100g of the intermediate material, 300g of potassium carbonate and 15g of coal-based pitch evenly, press into blocks, and then perform carbonization treatment at 1000℃ for 1h. After that, raise the temperature to 1300℃ and pass water vapor through at a flow rate of 500mL / min for 30min to perform activation treatment to obtain the porous carbon composite material.

[0093] The mass ratio of the intermediate material, potassium carbonate, and coal-based pitch is 100:300:15; the coal-based pitch is a high-temperature coal pitch with a softening point of about 100°C.

[0094] This embodiment also provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0095] (a) The porous carbon composite material prepared above is transferred to a fluidized bed, nitrogen is introduced to exhaust the gas, and then heated to 550°C. A mixed gas consisting of dichlorosilane and nitrogen with a volume ratio of 3:10 is introduced at a flow rate of 500 mL / min for 60 min of vapor deposition. Then, the temperature is cooled to room temperature of 25°C, and air is introduced at a flow rate of 50 mL / min for 60 min of passivation to form silicon oxide, thus obtaining silicon-carbon material.

[0096] (b) Add 5g of lithium perfluorobutyl sulfonate to 75g of dimethyl carbonate solvent and mix well to prepare a coating solution containing lithium perfluorobutyl sulfonate; the mass fraction of the coating solution is 20wt%.

[0097] The coating solution containing lithium perfluorobutyl sulfonate and 100g of the silicon-carbon material are mixed evenly and then transferred to a reaction vessel. Argon gas is first introduced to purge the air in the vessel, and then the mixture is heated to 800°C and sintered for 1 hour to obtain the silicon-carbon composite material. The mass ratio of lithium perfluorobutyl sulfonate in the coating solution to the silicon-carbon material is 5:100.

[0098] Example 4

[0099] The difference between this embodiment and Embodiment 1 is that the amount of Li5FeO4 added is adjusted so that the mass ratio of Li5FeO4 to glucose aqueous solution in step (1) is 0.5:500.

[0100] The remaining preparation methods and parameters are consistent with those in Example 1.

[0101] Example 5

[0102] The difference between this embodiment and embodiment 1 is that the amount of Li5FeO4 added is adjusted so that the mass ratio of Li5FeO4 to glucose aqueous solution in step (1) is 10:500.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 6

[0105] The difference between this embodiment and embodiment 1 is that the amount of coal-based pitch added is adjusted so that the mass ratio of intermediate material to coal-based pitch in step (2) is 100:20.

[0106] The remaining preparation methods and parameters are consistent with those in Example 1.

[0107] Example 7

[0108] The difference between this embodiment and embodiment 1 is that coal-based pitch is not added in step (2).

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 8

[0111] The difference between this embodiment and Embodiment 1 is that air is not introduced for passivation in step (a).

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Comparative Example 1

[0114] The difference between this comparative example and Example 1 is that Li5FeO4 is not added in step (1).

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Comparative Example 2

[0117] The difference between this comparative example and Example 1 is that lithium pyruvate is not added in step (1).

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Comparative Example 3

[0120] The difference between this comparative example and Example 1 is that step (b) is omitted.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Performance testing

[0123] 1. The pore volume and pore size of the porous carbon composite materials obtained in the above examples and comparative examples were tested according to the national standard GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method"; the specific surface area and tap density of the porous carbon composite materials were tested according to the national standard GB / T38823-2020 "Silicon Carbon"; and the powder resistivity of the porous carbon composite materials was tested using a four-probe tester.

[0124] The test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] II. Using the porous carbon composite materials provided in the above embodiments and comparative examples as the negative electrode material for lithium-ion batteries, coin cells were prepared according to the following method:

[0128] A binder, conductive agent, and solvent were added to a porous carbon composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain a negative electrode sheet. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The ratio of porous carbon:SP:LA132:NMP was 60g:15g:25g:300mL. The electrolyte was a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent was a mixture of EC and DEC with 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. The assembly was carried out in an argon-filled glove box to obtain a coin cell.

[0129] The electrochemical performance of the coin cell was tested using a CT2001A battery tester from Wuhan Landian Electronics Co., Ltd. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The discharge specific capacity and initial efficiency of the corresponding coin cell were tested. The diffusion coefficient of the porous carbon composite material was tested using GITT.

[0130] The test results are shown in Table 2.

[0131] Table 2

[0132]

[0133] As can be seen from Tables 1 and 2, the porous carbon composite material obtained by the technical solution provided by the present invention has low powder resistivity and high initial efficiency and diffusion coefficient. This is because the use of template method, the doping of lithium supplement and the introduction of coal-based pitch synergistically reduce its irreversible capacity and improve the diffusion coefficient and initial efficiency of the material, thereby increasing the pore volume and thus improving the specific capacity of the material.

[0134] III. Using the silicon-carbon composite materials provided in the above embodiments and comparative examples as the negative electrode material for lithium-ion batteries, coin cells were prepared according to the following method:

[0135] A binder, conductive agent, and solvent were added to a silicon-carbon composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain a negative electrode sheet. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The ratio of silicon-carbon material:SP:LA132:NMP was 70g:15g:15g:300mL. The electrolyte was a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent was a mixture of EC and DEC with 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. The assembly was carried out in an argon-filled glove box to obtain a coin cell.

[0136] Electrochemical performance tests were conducted on the coin cell battery using a CT2001A battery tester from Wuhan Landian Electronics Co., Ltd. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The discharge specific capacity and initial efficiency of the corresponding coin cell battery were tested. At the same time, the room temperature charge DCR (50% SOC) and cycle performance (0.1C / 0.1C, 100 cycles) of the corresponding coin cell battery were tested.

[0137] The test results are shown in Table 3.

[0138] Table 3

[0139]

[0140] As shown in Table 3, the silicon-carbon composite material prepared based on the porous carbon composite material provided by the present invention has significantly improved in terms of initial efficiency and expansion. This is because the doping of the lithium replenishing agent in the present invention causes it to release lithium ions during charging and discharging, which reduces its irreversible capacity and increases the diffusion coefficient of the material, thereby improving the cycle performance. At the same time, the silicon-carbon material is coated with lithium sulfonate, which has the characteristics of strong solvation ability, which can effectively restrain the expansion of the core silicon and improve the cycle performance.

[0141] A comparison of Examples 1 and 4-5 shows that if the mass ratio of lithium supplementer to porous carbon precursor solution is too small, i.e., the amount of lithium supplementer added is too low, then although a certain amount of lithium supplementer is added, its effect on compensating for active lithium is limited, and its contribution to improving the initial coulombic efficiency is insufficient (e.g., the initial efficiency in Example 4 is 88.5%), and its effect on improving the electronic conductivity of the material is not significant (the powder resistivity is 3.45 Ω·cm). If the mass ratio of lithium supplementer to porous carbon precursor solution is too large, then excessive lithium supplementer may agglomerate in the material, resulting in uneven distribution, or generate excessive electrochemically inert residues during high-temperature treatment. This will not only partially block the pores of the carbon material, leading to a decrease in specific surface area (1905 m² in Example 5). 2 The diffusion coefficient (diffusion coefficient = 4.85 × 10⁻⁶ g) may also introduce additional impedance, which is detrimental to the optimization of the overall dynamic properties of the material (diffusion coefficient = 4.85 × 10⁻⁶ g). -8 cm 2 / s).

[0142] A comparison of Examples 1 and 6 shows that if the mass ratio of intermediate material to coal-based pitch is too small, i.e., the amount of coal-based pitch added is too large, it is not conducive to the development of the material's pore structure. Excessive coal-based pitch will form an excessively thick carbon layer after carbonization, partially covering and blocking the initial channels created by the template agent and alkaline activation, resulting in a decrease in the material's specific surface area (1750 m²). 2 / g) and pore volume (0.75cm) 3 The specific capacity of the silicon-carbon composite material decreased significantly (1850.1 mAh / g), which weakened its ability to store silicon as a silicon carrier and ultimately reduced the discharge specific capacity (1850.1 mAh / g).

[0143] A comparison of Examples 1 and 7 shows that without the addition of coal-based pitch, the material lacks an effective binder phase to construct secondary particles, resulting in loose bonding between primary particles and a significant decrease in tap density (0.41 g / cm³). This loose structure leads to incomplete electron conduction pathways, increased powder resistivity (5.68 Ω·cm), and a decrease in ion diffusion coefficient (1.02 × 10⁻⁶). - 8 cm 2 / s). This is reflected in the final silicon-carbon composite material, which exhibits poor electrode structure stability, a higher volume expansion rate (90.3%), and is affected in terms of cycle performance (88.3%) and rate performance (DCR of 29.4 mΩ).

[0144] A comparison of Examples 1 and 8 shows that if air is not introduced for passivation during the preparation of the silicon-carbon material, the newly deposited highly active nano-silicon surface lacks a stable silicon oxide protective layer. This makes silicon more susceptible to continuous and severe side reactions with the electrolyte during subsequent battery cycles, leading to increased irreversible consumption of active lithium and excessive growth of the solid electrolyte interphase (SEI) film. Therefore, despite the intact porous carbon support structure, the cycle stability of the resulting silicon-carbon composite material decreases (capacity retention rate is 88.9%), and the volume expansion control capability is also slightly weakened (expansion rate is 89.1%).

[0145] A comparison of Example 1 and Comparative Example 1 shows that without the addition of a lithium replenishing agent, the material lacks an additional active lithium source to compensate for the irreversible lithium loss caused by the formation of the solid electrolyte interphase (SEI) film during the first charge-discharge process, resulting in a significant decrease in the initial coulombic efficiency (83.1%) of the porous carbon anode. Simultaneously, the lack of the potential catalytic effect of the transition metal elements in the lithium replenishing agent leads to a relatively low degree of graphitization and numerous defects in the carbon material, resulting in poorer electronic conductivity (powder resistivity 5.34 Ω·cm) and weak ion diffusion ability (0.65 × 10⁻⁶). -8 cm 2 The overall electrochemical performance of the silicon-carbon composite material was severely limited (first-time efficiency 92.2%, cycle retention 87.3%, DCR 35.6mΩ).

[0146] A comparison of Example 1 and Comparative Example 2 shows that without the addition of an organic template agent, the hydrothermal reaction system lacks structural guidance, and the formation of the precursor gel tends to be disordered. This results in the final carbon material failing to form a regular spherical morphology and a uniform mesoporous structure; its pore size distribution is relatively wide, and although the most probable pore sizes are similar, the pore volume and specific surface area (1618 m²) are significantly different. 2 / g, 0.71cm 3 The density (g / cm³) is significantly lower, and the tap density (0.45 g / cm³) is also poor. This structural defect makes it insufficient to buffer volume expansion after silicon loading. The silicon-carbon composite material exhibits the highest full charge expansion rate (107.3%) and the worst cycle performance (capacity retention rate 85.5%).

[0147] As can be seen from the comparison between Example 1 and Comparative Example 3, if the silicon-carbon material is not coated with lithium sulfonate, the material surface lacks an interface modification layer with high lithium-ion conductivity and good mechanical flexibility. During cycling, the huge volume expansion of the silicon core cannot be effectively restrained and buffered, leading to the accumulation of internal stress and accelerated structural damage, resulting in poor electrode integrity. At the same time, the exposed surface is more prone to electrolyte decomposition, forming a thick and unstable SEI film. Therefore, despite the same carrier and silicon deposition process, the electrochemical performance of the uncoated material is comprehensively degraded: the cycle capacity decays the fastest (retention rate 84.1%), the volume expansion rate is large (104.5%), and the interface impedance is significantly increased (DCR is 38.2 mΩ).

[0148] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a porous carbon composite material, characterized in that, The preparation method includes the following steps: An organic template agent, crosslinking agent, dispersant, lithium supplementer and porous carbon precursor solution are mixed and subjected to a hydrothermal reaction to obtain an intermediate material; The intermediate material is carbonized and then activated by adding an activator to obtain the porous carbon composite material. The carbonization process includes: mixing intermediate materials and alkaline reagents, and then carbonizing them; during the mixing of intermediate materials and alkaline reagents, coal-based pitch is also added. The organic template agent includes any one or a combination of at least two of lithium pyruvate, lithium diacetate, lithium acetate, lithium naphthalene sulfonate, lithium citrate, or lithium gluconate; The crosslinking agent includes any one or a combination of at least two of maleic anhydride, acetic anhydride or benzoic anhydride; The dispersant includes any one or a combination of at least two of polyvinyl alcohol, F127 polyether, or polyacrylate. The lithium replenishing agent includes any one or a combination of at least two of Li5FeO4, Li6CoO4, Li2O2, LiNiO2 or Li2MnO3; The porous carbon precursor solution is a glycosyl compound solution; The mass ratio of the organic template agent, crosslinking agent, dispersant, lithium supplementer and porous carbon precursor solution is (10-30):(1-5):(1-5):(1-5):500; The mass ratio of the intermediate material, alkaline reagent and coal-based pitch is 100:(100-500):(5-15).

2. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 50-100℃; The hydrothermal reaction time is 1-6 hours; The carbonization treatment temperature is 700-1000℃; The carbonization process takes 1-6 hours.

3. The preparation method according to claim 1, characterized in that, The alkaline reagent includes any one or a combination of at least two of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, or sodium bicarbonate. The mass ratio of the intermediate material to the alkaline reagent is 100:(100-500); The activator includes water vapor; The activation treatment temperature is 900-1300℃; The activation treatment time is 30-300 min; The softening point of the coal-based pitch is 50-100℃.

4. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Add organic template agent, crosslinking agent, dispersant and lithium supplement to the glycosyl compound solution and mix evenly. Then transfer to a high-pressure reactor and carry out hydrothermal reaction at 50-100℃ for 1-6 hours. After drying, the intermediate material is obtained. The mass ratio of the organic template agent, crosslinking agent, dispersant, lithium supplementer, and glycosyl compound solution is (10-30):(1-5):(1-5):(1-5):500; the mass concentration of the glycosyl compound solution is 1-10 wt%. (2) The intermediate material, alkaline reagent and coal-based pitch are mixed and then carbonized at 700-1000℃ for 1-6 hours. After that, the temperature is raised to 900-1300℃ and water vapor is introduced at a flow rate of 100-500mL / min for 30-300 minutes to activate the porous carbon composite material. The mass ratio of the intermediate material, alkaline reagent and coal-based pitch is 100:(100-500):(5-15).

5. A porous carbon composite material, characterized in that, The porous carbon composite material is prepared by the preparation method described in any one of claims 1-4.

6. A silicon-carbon composite material, characterized in that, The raw materials for preparing the silicon-carbon composite material include the porous carbon composite material described in claim 5.

7. A method for preparing the silicon-carbon composite material as described in claim 6, characterized in that, The preparation method includes the following steps: Silicon-carbon materials are obtained by depositing nano-silicon in porous carbon composite materials. Lithium sulfonate is coated onto the surface of the silicon-carbon material to obtain the silicon-carbon composite material.

8. The preparation method according to claim 7, characterized in that, The method for depositing nano-silicon includes vapor phase deposition; In the aforementioned vapor deposition method, the parameters include: deposition temperature of 450-550℃, deposition time of 60-300min, gas source including silane gas and inert gas, and gas flow rate of 100-500mL / min. After depositing nano-silicon, a passivation treatment is performed on the surface of the nano-silicon to form silicon oxide; During the passivation process, the parameters include: an air flow rate of 10-50 mL / min, a passivation time of 60-300 min, and a passivation temperature of room temperature. The mass ratio of lithium sulfonate to silicon carbide material is (1-5):100; The lithium sulfonate includes any one or a combination of at least two of lithium trifluoromethanesulfonate, lithium perfluorohexanesulfonate, lithium perfluorobutylsulfonate, lithium 4-vinylbenzenesulfonate, or lithium dinonylnaphthalenesulfonate. The step of coating the surface of the silicon-carbon material with lithium sulfonate includes: mixing the silicon-carbon material and the coating solution containing lithium sulfonate, and then sintering it; The mass fraction of the lithium sulfonate coating solution is 1-20 wt%. In the lithium sulfonate coating solution, the organic solvent includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, or ethylene carbonate.

9. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the silicon-carbon composite material as described in claim 6.

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