Method for preparing double-coated silicon-carbon composite material, electrode and lithium battery

Abstract

The application belongs to the technical field of lithium batteries, and relates to a preparation method of a double-coated silicon-carbon composite material, an electrode and a lithium battery.The method comprises the following steps: placing a lithium dopant and a MOF material in a first organic solvent, adding a template agent and a catalyst, reacting, filtering, freeze-drying and obtaining a gel composite; in an inert atmosphere, the gel composite is heated to a first preset temperature, carbon dioxide is introduced at a preset flow rate, the temperature is lowered, the gel composite is soaked in mixed acid, pickling is performed, vacuum drying is performed, and a porous carbon composite material is obtained; liquid silane, a phosphine derivative, a dispersing agent, the porous carbon composite material and a silane coupling agent are added to a second organic solvent, spray drying is performed, primary carbonization is performed, and a silicon-carbon precursor material is obtained; resin is dissolved in a third organic solvent, a fast ion conductor and the silicon-carbon precursor material are added, secondary carbonization is performed, the temperature is lowered to a second preset temperature, a reducing gas is introduced, and a double-coated silicon-carbon composite material is obtained; the conductivity is improved, the interface stability is improved, and the full charge swelling is reduced.

Description

Technical Field

[0001] This application belongs to the field of lithium battery technology, and particularly relates to the preparation method of double-coated silicon-carbon composite material, electrodes and lithium batteries. Background Technology

[0002] Porous carbon is a precursor material for silicon-carbon composites. Currently, the electronic or ionic conductivity of the material is mainly improved by doping with heteroatoms. However, the carbon matrix is ​​made of biomass materials such as resin and coconut shell, resulting in small pore volume and large expansion, which reduces the performance of silicon-carbon composites. In addition, the current silicon-carbon composites have high resistivity, which reduces the electrochemical performance of lithium batteries.

[0003] Existing silicon-carbon composite materials suffer from problems such as small pore volume, large expansion, high resistivity, and reduced electrochemical performance of lithium batteries. Summary of the Invention

[0004] This application provides a method for preparing a double-coated silicon-carbon composite material, an electrode, and a lithium battery, aiming to solve to some extent the problems of small pore volume, large expansion, high resistivity, and reduced electrochemical performance of lithium batteries caused by silicon-carbon composite materials.

[0005] In a first aspect, this application provides a method for preparing a double-coated silicon-carbon composite material, comprising:

[0006] S1, lithium dopant and MOF material are soaked in a first organic solvent, then template agent and organic catalyst are added, mixed evenly, reacted, filtered, and freeze-dried to obtain a gel composite.

[0007] S2, In an inert atmosphere, the gel composite is heated to the first preset temperature, carbon dioxide gas is introduced at a preset flow rate, and then cooled to the ambient temperature. The obtained material is then added to a mixed acid solution for soaking, followed by acid washing, and then vacuum drying to obtain a porous carbon composite material.

[0008] S3, liquid silane, phosphine derivative, dispersant, porous carbon composite material and silane coupling agent are added to the second organic solvent and mixed evenly, then spray dried and carbonized once to obtain silicon-carbon precursor material.

[0009] S4, the resin is dissolved in a third organic solvent and dispersed evenly, then fast ion conductor and silicon-carbon precursor material are added, and secondary carbonization is carried out. After that, the temperature is cooled to a second preset temperature, and then a reducing gas is introduced for reduction treatment to obtain a double-coated silicon-carbon composite material.

[0010] In one embodiment, in step S1, the mass ratio of lithium dopant:MOF material:first organic solvent:spherical template agent:organic catalyst is (1~5):100:(500~1000):(5~1):(1~5).

[0011] The reaction temperature is 100℃~200℃, and the time is 1h~6h;

[0012] The freeze-drying temperature was -40℃ and the time was 24 hours.

[0013] In one embodiment, in step S1, the lithium dopant is any one or a combination of lithium iron phosphate, lithium nickel phosphate, lithium manganese phosphate, and lithium cobalt phosphate.

[0014] The MOF material is any one or a combination of ZIF-8, ZIF-67, MOF-74, chromium-based MIL-101, iron-based MIL-101, Mg-MOF-74, and Ni-MOF-74;

[0015] The first organic solvent is any one or a combination of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate;

[0016] The template agent is either polystyrene microspheres or tetramethylammonium hydroxide;

[0017] The organic catalyst is any one or a combination of ferrocene, ferrous oxalate, ferric citrate, and copper acetate.

[0018] In one embodiment, in step S2, the first preset temperature is 900℃~1100℃, the preset flow rate is 100ml / min~500ml / min, and the time for introducing carbon dioxide gas is 30 minutes~300 minutes;

[0019] The mass ratio of nitric acid to hydrochloric acid in the mixed acid solution was 1:1, and the soaking time was 12 hours.

[0020] In one embodiment, in step S3, the mass ratio of liquid silane:phosphine derivative:dispersant:porous carbon composite material:silane coupling agent is 100:(10~30):(1~5):(100~200):(10~20).

[0021] The temperature for one carbonization is 1000℃~1300℃, and the time is 1h~6h;

[0022] In step S4, the mass ratio of resin: third organic solvent: silicon carbide precursor material: fast ion conductor is (2~10):(50~200):100:(1~5).

[0023] The secondary carbonization temperature is 700℃~800℃, and the time is 1h~3h;

[0024] The second preset temperature is 400℃~600℃, and the reduction treatment time is 1h~3h.

[0025] In one embodiment, in step S3, the silane coupling agent is any one or a combination of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyl, and N-β-aminoethyl-γ-aminopropyltrimethoxysilane;

[0026] The dispersant is any one or a combination of polyvinylpyrrolidone, castor oil acid, methylcellulose, hydroxypropyl methylcellulose, polyvinyl alcohol, and sodium stearate;

[0027] The liquid silane is any one or a combination of propyltrichlorosilane, dimethylchlorosilane, trichloroethylsilane, methylvinyldichlorosilane, triisopropylchlorosilane, and phenyldichlorosilane;

[0028] The phosphine derivative is any one or a combination of (benzoylmethylene)triphenylphosphine, (acetylmethylene)triphenylphosphine, and cyanomethylenetrimethylphosphine;

[0029] The second organic solvent is N-methylpyrrolidone.

[0030] In one embodiment, in step S4, the resin is any one or a combination of phenolic resin, furfural resin, epoxy resin, and urea-formaldehyde resin.

[0031] The third organic solvent is any one or a combination of xylene, ethyl acetate, acetone, and toluene;

[0032] The fast ion conductor is any one or a combination of lithium titanium aluminum phosphate, lithium zirconium phosphate, and lithium aluminum silicate;

[0033] The reducing gas is any one or a combination of hydrogen, carbon monoxide, and hydrogen sulfide.

[0034] Secondly, this application provides a double-coated silicon-carbon composite material, which is prepared by the method for preparing the double-coated silicon-carbon composite material described in any one of the contents of the first aspect.

[0035] Thirdly, this application provides an electrode comprising a double-coated silicon-carbon composite material prepared by any of the methods for preparing double-coated silicon-carbon composite materials described in the first aspect, or a double-coated silicon-carbon composite material as described in the second aspect.

[0036] Fourthly, this application provides a lithium battery, including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the electrode described in the third aspect.

[0037] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0038] The advantages of this application compared to the prior art are:

[0039] The preparation method of the double-coated silicon-carbon composite material of this application includes the following steps: S1, immersing lithium dopant and MOF material in a first organic solvent, then adding a template agent and an organic catalyst, mixing evenly, reacting, filtering, and freeze-drying to obtain a gel composite; S2, heating the gel composite to a first preset temperature in an inert atmosphere, introducing carbon dioxide gas at a preset flow rate, cooling to ambient temperature, then immersing the obtained material in a mixed acid solution, acid washing, and vacuum drying to obtain a porous carbon composite material; S3, adding liquid silane, phosphine derivatives, dispersant, porous carbon composite material, and silane coupling agent to a second organic solvent, mixing evenly, then spray drying, and performing a first carbonization to obtain a silicon-carbon precursor material; S4, dissolving resin in a third organic solvent and dispersing evenly, then adding a fast ion conductor and silicon-carbon precursor material, performing a second carbonization, then cooling to a second preset temperature, and then introducing a reducing gas for reduction treatment to obtain the double-coated silicon-carbon composite material. Compared with the prior art, the MOF material has a large pore volume and large pore size, and the template agent... The formation of porous carbon layers by the plate-forming agent and organic catalyst improves the pore volume, pore size, and specific surface area of ​​the silicon-carbon composite material. Lithium dopants reduce defects and replenish lithium, improving ionic conductivity. Phosphorus in phosphine dops the uniformly dispersed nano-silicon after the decomposition of liquid silane, improving the power performance of the silicon-carbon composite material. Silane coupling agents form coupling structures between porous carbons, reducing the expansion of the silicon-carbon composite material and improving the wettability of the electrolyte. The primary carbonization of alkane forms the first layer of amorphous carbon coating, and the secondary carbonization of resin forms the second layer of carbon coating and is doped with fast ion conductors, resulting in fewer defects in the silicon-carbon composite material and further improving its ionic conductivity, thus increasing the first charge-discharge efficiency of the lithium battery. The secondary carbon coating reduces the volume effect of silicon, further reducing expansion and also reducing gas production. Through the synergistic effect of porous carbon framework, nano-silicon, phosphorus doping, double carbon layer coating, and fast ion conductor doping, a silicon-carbon composite material is formed, thereby improving the conductivity of the silicon anode, reducing volume expansion, improving SEI interface stability, and ultimately improving the electrochemical performance of the lithium battery. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the SEM test of the silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0042] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0043] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0044] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0045] The terms "first" and "second" are used only to describe the purpose and to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the provisions of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0046] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0047] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0048] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0049] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0050] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0051] Existing silicon-carbon composite materials suffer from problems such as small pore volume, large expansion, high resistivity, and reduced electrochemical performance of lithium batteries.

[0052] To address the aforementioned problems to some extent, firstly, this application provides a method for preparing a double-coated silicon-carbon composite material, comprising:

[0053] S1, lithium dopant and MOF material are soaked in a first organic solvent, then template agent and organic catalyst are added, mixed evenly, reacted, filtered, and freeze-dried to obtain a gel composite.

[0054] S2, In an inert atmosphere, the gel composite is heated to the first preset temperature, carbon dioxide gas is introduced at a preset flow rate, and then cooled to the ambient temperature. The obtained material is then added to a mixed acid solution for soaking, followed by acid washing, and then vacuum drying to obtain a porous carbon composite material.

[0055] S3, liquid silane, phosphine derivative, dispersant, porous carbon composite material and silane coupling agent are added to the second organic solvent and mixed evenly, then spray dried and carbonized once to obtain silicon-carbon precursor material.

[0056] S4, the resin is dissolved in a third organic solvent and dispersed evenly, then fast ion conductor and silicon-carbon precursor material are added, and secondary carbonization is carried out. After that, the temperature is cooled to a second preset temperature, and then a reducing gas is introduced for reduction treatment to obtain a double-coated silicon-carbon composite material.

[0057] In this embodiment, the MOF material has a large pore volume and pore size. The template agent and organic catalyst form a porous carbon layer, which improves the pore volume, pore size and specific surface area of ​​the silicon-carbon composite material. The lithium dopant reduces defects and replenishes lithium, improving ionic conductivity. Phosphorus in the phosphine dopes the uniformly dispersed nano-silicon after the decomposition of liquid silane, improving the power performance of the silicon-carbon composite material. The silane coupling agent forms a coupling structure between the porous carbons, reducing the expansion of the silicon-carbon composite material and improving the wettability of the electrolyte. The alkanes undergo primary carbonization to form the first layer of amorphous carbon coating, and the resin undergoes secondary carbonization. The formation of a second carbon coating and doping with fast ion conductors reduces defects in the silicon-carbon composite material, further improving its ionic conductivity and increasing the initial charge-discharge efficiency of the lithium battery. The secondary carbon coating also reduces the volume effect of silicon, further reducing expansion and gas production. Through the synergistic effect of porous carbon framework, nano-silicon, phosphorus doping, double carbon coating, and fast ion conductor doping, a silicon-carbon composite material is formed, thereby improving the conductivity of the silicon anode, reducing volume expansion, and improving SEI interface stability, thus enhancing the electrochemical performance of the lithium battery.

[0058] Step S1 involves the preparation of a porous gel precursor. A large-pore-volume, large-diameter MOF material serves as the initial porous framework, carbon source, and metal source. The MOF material undergoes pyrolysis to form a porous carbon / metal oxide composite with a high specific surface area. A lithium dopant provides the lithium source, allowing lithium to be pre-intercalated or coordinated with the MOF, improving ionic conductivity and stabilizing the structure. A template agent is used for pore expansion or creation; it carbonizes during subsequent high-temperature decomposition and removal to form a mesoporous / macroporous porous structure, increasing the pore volume of the porous carbon and reducing its expansion. An organic catalyst serves as a precursor for catalytic graphitization or carbon nanotube growth, resulting in a highly anisotropic carbon layer and a stronger carbon network structure, which also improves electronic conductivity. The reaction in the first organic solvent ensures uniform bonding of the components. Freeze-drying preserves the porous structure, providing a rich foundation of hierarchical channels and conductive networks for subsequent silicon loading and ion transport.

[0059] Step S2 in this embodiment involves the preparation and activation of a porous carbon framework. CO2 is introduced at a first preset temperature for physical / chemical activation, where CO2 reacts with amorphous carbon to generate CO, thereby etching the carbon to create more pores. This increases the specific surface area and porosity of the carbon material, improves the silicon loading capacity, and alleviates volume expansion. Acid washing removes metallic impurities (such as iron and zinc), leaving the porous carbon framework and preventing interference from these impurities on electrochemical performance. The process of heating the gel composite to the first preset temperature, introducing carbon dioxide gas at a preset flow rate, and cooling to ambient temperature all occur in an inert atmosphere. This prevents the combustion of carbon and organic matter when heated in air or oxygen, and also avoids the severe oxidation of carbon upon cooling.

[0060] Step S3 of this embodiment involves the introduction of a silicon / phosphorus source and primary carbonization coating. Liquid silane has a low decomposition temperature and good wettability with porous carbon. Liquid silane (silicon source) and phosphine derivative (phosphorus source) are impregnated into porous carbon through solution mixing, and spray drying achieves uniform coating. Primary carbonization causes silane to decompose at high temperature, generating nano-silicon (Si) in situ within the carbon framework. The phosphine derivative decomposes to provide phosphorus (P), enabling P doping, thereby improving conductivity, or forming a buffer phase SiPx phase to stabilize the structure, and forming silicon-phosphorus compounds or doping with phosphorus. Simultaneously, the pyrolysis of various alkane substances generates amorphous carbon coating, and the silane coupling agent enables the formation of a coupled secondary particle structure between porous carbon particles. Primary carbonization forms the first carbon coating layer, and spray drying ensures uniform dispersion of the precursor.

[0061] Step S4 in this embodiment involves secondary carbonization coating and reduction treatment. The silicon-carbon precursor is coated a second time with a resin solution, and a fast-ion conductor is added to reduce defects. The secondary carbonization forms a continuous, robust, and denser conductive second carbon coating layer, effectively binding silicon particles and maintaining electrode integrity. Coating with a fast-ion conductor (such as a solid electrolyte material) can accelerate the reduction of Li... + Migration on particle surfaces; low-temperature reducing gas treatment further purifies the material, reduces the surface oxide layer and may optimize the fast ion conductor interface. The reduction treatment also reduces surface SiO2, improving the first charge and discharge efficiency of the lithium battery; double carbon coating, with the inner layer (first layer) from primary carbonization and the outer layer (second layer) from secondary carbonization, greatly alleviates the volume effect of silicon, reduces the gas production of silicon-carbon composite materials, and improves the ion diffusion coefficient of the material, thereby increasing conductivity. Fast ion conductor doping also improves the rate performance and cycle performance of the lithium battery.

[0062] In one embodiment, in step S1, the mass ratio of lithium dopant:MOF material:first organic solvent:spherical template agent:organic catalyst is (1~5):100:(500~1000):(5~1):(1~5); the reaction temperature is 100℃~200℃, and the time is 1h~6h; the freeze-drying temperature is -40℃, and the time is 24h.

[0063] In one embodiment, in step S1, the lithium dopant is any one or a combination of lithium iron phosphate, lithium nickel phosphate, lithium manganese phosphate, and lithium cobalt phosphate; the MOF material is any one or a combination of ZIF-8, ZIF-67, MOF-74, chromium-based MIL-101, iron-based MIL-101, Mg-MOF-74, and Ni-MOF-74; the second organic solvent is any one or a combination of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate; the template agent is any one of polystyrene microspheres and tetramethylammonium hydroxide; and the organic catalyst is any one or a combination of ferrocene, ferrous oxalate, ferric citrate, and copper acetate.

[0064] In one embodiment, in step S2, the first preset temperature is 900℃~1100℃, the preset flow rate is 100ml / min~500ml / min, the carbon dioxide gas is introduced for 30 minutes~300 minutes, the mass ratio of nitric acid to hydrochloric acid in the mixed acid solution is 1:1, and the soaking time is 12h.

[0065] In one embodiment, in step S3, the mass ratio of liquid silane:phosphine derivative:dispersant:porous carbon composite material:silane coupling agent is 100:(10~30):(1~5):(100~200):(10~20); the temperature of the first carbonization is 1000℃~1300℃, and the time is 1h~6h.

[0066] In one embodiment, in step S4, the mass ratio of resin: third organic solvent: silicon carbide precursor material: fast ion conductor is (2~10):(50~200):100:(1~5); the secondary carbonization temperature is 700℃~800℃, and the time is 1h~3h; the second preset temperature is 400℃~600℃, and the reduction treatment time is 1h~3h.

[0067] In one embodiment, in step S3, the silane coupling agent is any one or a combination of γ-aminopropyltriethoxysilane (i.e., KH550), γ-methacryloyloxypropyl (i.e., KH570), and N-β-aminoethyl-γ-aminopropyltrimethoxysilane (i.e., KH792); the dispersant is any one or a combination of polyvinylpyrrolidone, castor oil acid, methylcellulose, hydroxypropyl methylcellulose, polyvinyl alcohol, and sodium stearate; the liquid silane is any one or a combination of propyltrichlorosilane, dimethylchlorosilane, trichloroethylsilane, methylvinyldichlorosilane, triisopropylchlorosilane, and phenyldichlorosilane; the phosphine derivative is any one or a combination of (benzoylmethylene)triphenylphosphine, (acetylmethylene)triphenylphosphine, and cyanomethylenetrimethylphosphine; and the second organic solvent is N-methylpyrrolidone.

[0068] In one embodiment, in step S4, the resin is any one or a combination of phenolic resin, furfural resin, epoxy resin, and urea-formaldehyde resin; the third organic solvent is any one or a combination of xylene, ethyl acetate, acetone, and toluene; the fast ion conductor is any one or a combination of lithium titanium aluminum phosphate, lithium zirconium phosphate, and lithium aluminum silicate; and the reducing gas is any one or a combination of hydrogen, carbon monoxide, and hydrogen sulfide.

[0069] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0070] Example 1

[0071] A method for preparing a double-coated silicon-carbon composite material, comprising:

[0072] S1, 3g of lithium iron ferrite and 100g of ZIF-8 were added to 800g of dimethyl carbonate for soaking, then 10g of polystyrene microspheres and 3g of ferrocene were added and mixed evenly, and then transferred to a high-pressure reactor and reacted at 150℃ for 3h. After filtration, the resulting material was freeze-dried at -40℃ for 24h to obtain a gel composite.

[0073] S2, the gel composite was transferred to a tube furnace under an inert atmosphere and heated to 1000℃. Carbon dioxide gas was introduced at a flow rate of 300 ml / min for 150 min. Then, the temperature was lowered to room temperature (25℃), and the resulting material was added to a mixed acid solution (nitric acid: hydrochloric acid mass ratio of 1:1) for soaking for 12 h for acid washing. The material was then vacuum dried at 80℃ for 24 h to obtain a porous carbon composite material.

[0074] S3, 100g propyltrichlorosilane, 20g (benzoylmethylene)triphenylphosphine, 3g polyvinylpyrrolidone, 150g porous carbon composite material and 15g KH550 silane coupling agent were added to 500g N-methylpyrrolidone and mixed evenly. The mixture was then spray-dried and the resulting material was carbonized once at 1200℃ for 3h to obtain silicon-carbon precursor material.

[0075] S4, 5g of phenolic resin was dissolved in 100g of xylene and dispersed evenly. Then, 3g of lithium titanium aluminum phosphate and 100g of silicon-carbon precursor material were added, and secondary carbonization was carried out at 750℃ for 2h. After that, the temperature was lowered to 500℃ and carbon monoxide reducing gas was introduced for reduction treatment for 2h to obtain double-coated silicon-carbon composite material.

[0076] 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 exhibits a secondary granular structure with a uniform size distribution and a particle size of 5 micrometers to 10 micrometers.

[0077] Example 2

[0078] A method for preparing a silicon-carbon composite material includes the following steps:

[0079] S1, 1g of lithium-rich nickel oxide and 100g of ZIF-67 material were added to 500g of ethylene carbonate for soaking. Then, 5g of tetramethylammonium hydroxide and 1g of ferrous oxalate were added and mixed evenly. The mixture was then transferred to a high-pressure reactor and reacted at 100℃ for 6h. After filtration, the resulting material was freeze-dried at -40℃ for 24h to obtain a gel composite.

[0080] S2, the gel composite was transferred to a tube furnace under an inert atmosphere and heated to 900℃. Carbon dioxide gas was introduced at a flow rate of 100 ml / min for 300 min. Then the temperature was lowered to room temperature (25℃). The resulting material was added to a mixed acid solution (nitric acid: hydrochloric acid mass ratio 1:1) and soaked for 12 h for acid washing. It was then vacuum dried at 80℃ for 24 h to obtain a porous carbon composite material.

[0081] S3, 100g of dimethylchlorosilane, 10g of (acetylmethylene)triphenylphosphine, 1g of castor oil acid, 100g of porous carbon composite material and 10g of KH570 silane coupling agent were added to 500g of N-methylpyrrolidone and mixed evenly. The mixture was then spray-dried, and the resulting material was carbonized once at 1000℃ for 6h to obtain silicon-carbon precursor material.

[0082] S4, 2g of furfural resin was dissolved in 50g of toluene and dispersed evenly. Then, 1g of lithium zirconium phosphate and 100g of silicon-carbon precursor material were added and mixed evenly. The mixture was then subjected to secondary carbonization at 700℃ for 3h. After that, the temperature was lowered to 400℃ and hydrogen reducing gas was introduced for reduction treatment for 3h to obtain double-coated silicon-carbon composite material.

[0083] Example 3

[0084] A method for preparing a porous carbon composite material includes the following steps:

[0085] Step S1: 5g of lithium cobalt oxide and 100g of MOF-74 were added to 500g of ethylene carbonate for soaking. Then, 15g of polystyrene microspheres and 5g of ferric citrate were added and mixed evenly. The mixture was then transferred to a high-pressure reactor and reacted at 200℃ for 1h. After filtration, the resulting material was freeze-dried at -40℃ for 24h to obtain a gel composite.

[0086] Step S2: Transfer the gel composite to a tube furnace under an inert atmosphere, heat it to 1100℃, introduce carbon dioxide gas at a flow rate of 500 ml / min for 30 min, then cool it to room temperature (25℃), add the obtained material to a mixed acid solution (nitric acid: hydrochloric acid mass ratio of 1:1) for soaking for 12 h for acid washing, and vacuum dry at 80℃ for 24 h to obtain a porous carbon composite material.

[0087] Step S3: Add 100g of trichloroethylsilane, 30g of cyanomethylenetrimethylphosphine, 5g of methylcellulose, 200g of porous carbon composite material and 20g of KH792 silane coupling agent to 1000g of N-methylpyrrolidone and mix evenly. Spray dry the mixture and carbonize the resulting material at 1300℃ for 1h to obtain silicon-carbon precursor material.

[0088] Step S4: Dissolve 10g of epoxy resin in 200g of toluene and disperse evenly. Then add 5g of lithium aluminum silicate and 100g of silicon-carbon precursor material, and perform secondary carbonization at 800℃ for 1h. After that, cool down to 600℃ and introduce hydrogen reducing gas for reduction treatment for 1h to obtain double-coated silicon-carbon composite material.

[0089] Example 4

[0090] Compared with Comparative Example 1: the addition of 3g of lithium-rich lithium ferrite in step S1 is changed to the addition of 1g of lithium-rich lithium ferrite, and the rest is the same as in Example 1.

[0091] Example 5

[0092] Compared with Example 1: the addition of 10g of polystyrene microspheres in step S1 is changed to the addition of 1g of polystyrene microspheres, and the rest is the same as in Example 1.

[0093] Example 6

[0094] The difference from Example 1 is that the addition of 20g of (benzoylmethylene) triphenylphosphine in step S3 is replaced by the addition of 10g of (benzoylmethylene) triphenylphosphine, while the rest is the same as in Example 1.

[0095] Example 7

[0096] The difference from Example 1 is that the addition of 20g of (benzoylmethylene) triphenylphosphine in step S3 is replaced by the addition of 30g of (benzoylmethylene) triphenylphosphine, while the rest is the same as in Example 1.

[0097] Comparative Example 1 differs from Example 1 in that lithium-rich lithium iron phosphate is not added in step S1, but otherwise it is the same as Example 1.

[0098] Comparative Example 2 differs from Example 1 in that ZIF-8 is not added in step S1, but otherwise it is the same as Example 1.

[0099] Comparative Example 3 differs from Example 1 in that polystyrene microspheres are not added in step S1, but otherwise it is the same as Example 1.

[0100] Comparative Example 4, compared with Example 1, did not add (benzoylmethylene)triphenylphosphine in step S3, and was otherwise the same as Example 1.

[0101] Performance / Data Testing:

[0102] 1. Physicochemical properties:

[0103] The specific surface area and powder compaction density of the silicon-carbon composite materials prepared in Examples 1-7 and Comparative Examples 1-4 were tested according to the national standard GBT-38823-2020 "Silicon-Carbon". Simultaneously, the resistivity of the silicon-carbon composite powder was tested using a four-probe tester. The gas production of the silicon-carbon composite powder was also tested; specifically, m1 grams of material powder was added to deionized water to prepare a 10wt% concentration, soaked at 45℃ for 48 hours, and the corresponding gas production V1 was measured. The gas production ratio (gas production ratio = V1 / m1) was calculated. The test results are shown in Table 1.

[0104] Table 1. Physicochemical property test data of each embodiment and comparative example.

[0105]

[0106] As shown in Table 1, the lithium dopant in the silicon-carbon composite materials of each embodiment has high ionic conductivity, which reduces powder resistance. Simultaneously, the addition of a template pore-forming agent increases the pore volume and specific surface area of ​​the silicon-carbon composite material, resulting in superior performance compared to the comparative examples. Comparative Example 1, lacking lithium-rich lithium iron phosphate, suffers from a reduced ion diffusion rate, increased powder resistance, reduced porosity after carbonization, and decreased specific surface area. Comparative Example 2, lacking ZIF-8 material, experiences reduced porosity, leading to a decrease in specific surface area. Comparative Example 3, lacking polystyrene microspheres, reduces the tap density and compaction density of the silicon-carbon material. Comparative Example 4, lacking phosphine compounds (i.e., no phosphorus doping), increases the powder resistance of the silicon-carbon material.

[0107] 2. Button cell battery test:

[0108] The silicon-carbon composite materials from Examples 1-7 and Comparative Examples 1-4 were used as negative electrode materials for lithium-ion batteries to assemble coin cells. The specific preparation method for the negative electrode material was as follows: a binder, conductive agent, and solvent were added to the silicon-carbon composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled. The binder used was LA136D binder, the conductive agent was conductive carbon black SP, and the solvent was double-distilled water. The negative electrode sheet was prepared according to the following ratio: silicon-carbon composite material: SP: LA136D: double-distilled water 80g:15g:15g:300mL. A lithium metal sheet was used as the positive electrode. The electrolyte was LiPF6 / ethylene carbonate EC + diethyl carbonate DEC, with LiPF6 as the electrolyte and a 1:1 volume ratio of EC and DEC as the solvent. The electrolyte concentration was 1.3mol / 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 performed using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 1.5V, and the charge / discharge rate was 0.1C. The initial discharge capacity and initial efficiency of the coin cells were tested, along with cycle performance (0.2C / 0.2C, 100 cycles) and the expansion of the negative electrode at full charge (100% SOC). This involved dissecting the coin cells to test the expansion rate of the negative electrode. The test results are shown in Table 2.

[0109] Table 2 Electrochemical performance test data of coin cells in each embodiment and comparative example.

[0110]

[0111] As can be seen from Table 2, the lithium dopant in each embodiment reduces lithium ion loss during charging and discharging, and improves the first-cycle efficiency and cycle performance; at the same time, the addition of a template agent reduces expansion and further improves cycle performance. The performance of each embodiment is better than that of the comparative examples in all aspects.

[0112] 3. Soft-pack battery test:

[0113] The silicon-carbon composite materials in Examples 1-7 and Comparative Examples 1-4 were mixed with 92% 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 Using O2 as the positive electrode, LiPF6 as the electrolyte, and ethylene carbonate EC, diethyl carbonate DEC, and dimethyl carbonate DMC as the solvents in a volume ratio of 1:1:1, the electrolyte concentration was 1.1 mol / L. A 2Ah soft-pack battery was prepared using Celgard 2400 membrane as the separator.

[0114] 3.1 HPPC Ratio Performance Test:

[0115] 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℃. Resistance was measured under different state of charge (SOC) conditions (90%, 70%, 50%, 30%, 10%) at 3C charging, and discharged at 4.0C. The results are shown in Table 3.

[0116] Table 3. Resistance test data of the rate performance of the pouch cells in each embodiment and comparative example.

[0117]

[0118] As shown in Table 3, since lithium ions need to migrate during battery charging, the silicon-carbon composite materials of each embodiment have lower powder resistivity. Furthermore, the lithium dopant increases the lithium ion diffusion rate of the material and reduces the DC resistance (DCR). The soft-pack batteries of silicon-carbon composite materials in Examples 1-7 have significantly lower impedance than those in Comparative Examples 1-4, meaning that the charging time is shorter.

[0119] 3.2 Cyclic performance test:

[0120] The obtained soft-pack battery was 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 its charge DCR (50%SOC, 1.0C) was tested after 500 cycles. The test results are shown in Table 4.

[0121] Table 4. Test data on the cycle performance of the pouch batteries in each embodiment and comparative example.

[0122]

[0123] As can be seen from Table 4, the lithium-ion batteries prepared using the silicon-carbon composite materials obtained in Examples 1-7 have significantly better cycle performance than those prepared using Comparative Examples 1-4 because the silicon-carbon composite materials of each example have lower expansion and lower powder resistivity, which reduces the lithium ions consumed by repeated repair of the SEI interface during charging and discharging.

[0124] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0125] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0126] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0127] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing a double-coated silicon-carbon composite material, characterized in that, include: S1, lithium dopant and MOF material are soaked in a first organic solvent, then template agent and organic catalyst are added, mixed evenly, reacted, filtered, and freeze-dried to obtain a gel composite. S2, In an inert atmosphere, the gel composite is heated to the first preset temperature, carbon dioxide gas is introduced at a preset flow rate, and then cooled to the ambient temperature. The obtained material is then added to a mixed acid solution for soaking, followed by acid washing, and then vacuum drying to obtain a porous carbon composite material. S3, liquid silane, phosphine derivative, dispersant, porous carbon composite material and silane coupling agent are added to the second organic solvent and mixed evenly, then spray dried and carbonized once to obtain silicon-carbon precursor material. S4, dissolve the resin in the third organic solvent and disperse it evenly, then add fast ion conductor and silicon-carbon precursor material, and perform secondary carbonization. Then cool it down to the second preset temperature, and then introduce a reducing gas for reduction treatment to obtain double-coated silicon-carbon composite material. The template agent is either polystyrene microspheres or tetramethylammonium hydroxide. The organic catalyst is any one or a combination of ferrocene, ferrous oxalate, ferric citrate, and copper acetate; The phosphine derivative is any one or a combination of (benzoylmethylene)triphenylphosphine, (acetylmethylene)triphenylphosphine, and cyanomethylenetrimethylphosphine. The phosphine derivative decomposes to provide P, achieving P doping and forming silicon-phosphine compounds, which form a buffer phase to stabilize the structure. Among them, the gas production ratios of the double-coated silicon-carbon composite materials are 0.014 ml / mg, 0.021 ml / mg, 0.032 ml / mg, 0.035 ml / mg, 0.041 ml / mg, 0.043 ml / mg, and 0.045 ml / mg; The preset flow rate is 100ml / min to 500ml / min, the first preset temperature is 900℃ to 1100℃, and the second preset temperature is 400℃ to 600℃.

2. The method for preparing the double-coated silicon-carbon composite material as described in claim 1, characterized in that, In step S1, the mass ratio of lithium dopant:MOF material:first organic solvent:spherical template agent:organic catalyst is (1~5):100:(500~1000):(5~1):(1~5). The reaction temperature is 100℃~200℃, and the time is 1h~6h; The freeze-drying temperature was -40℃ and the time was 24 hours.

3. The method for preparing the double-coated silicon-carbon composite material as described in claim 1, characterized in that, In step S1, the lithium dopant is any one or a combination of lithium iron phosphate, lithium nickel phosphate, lithium manganese phosphate, and lithium cobalt phosphate. The MOF material is any one or a combination of ZIF-8, ZIF-67, MOF-74, chromium-based MIL-101, iron-based MIL-101, Mg-MOF-74, and Ni-MOF-74; The first organic solvent is any one or a combination of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

4. The method for preparing the double-coated silicon-carbon composite material as described in claim 1, characterized in that, In step S2, the carbon dioxide gas is introduced for 30 minutes to 300 minutes. The mass ratio of nitric acid to hydrochloric acid in the mixed acid solution was 1:1, and the soaking time was 12 hours.

5. The method for preparing the double-coated silicon-carbon composite material as described in claim 1, characterized in that, In step S3, the mass ratio of liquid silane:phosphine derivative:dispersant:porous carbon composite material:silane coupling agent is 100:(10~30):(1~5):(100~200):(10~20). The temperature for one carbonization is 1000℃~1300℃, and the time is 1h~6h; In step S4, the mass ratio of resin: third organic solvent: silicon carbide precursor material: fast ion conductor is (2~10):(50~200):100:(1~5). The secondary carbonization temperature is 700℃~800℃, and the time is 1h~3h; The reduction process takes 1 to 3 hours.

6. The method for preparing the double-coated silicon-carbon composite material as described in claim 1, characterized in that, In step S3, the silane coupling agent is any one or a combination of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyl, and N-β-aminoethyl-γ-aminopropyltrimethoxysilane; The dispersant is any one or a combination of polyvinylpyrrolidone, castor oil acid, methylcellulose, hydroxypropyl methylcellulose, polyvinyl alcohol, and sodium stearate; The liquid silane is any one or a combination of propyltrichlorosilane, dimethylchlorosilane, trichloroethylsilane, methylvinyldichlorosilane, triisopropylchlorosilane, and phenyldichlorosilane; The second organic solvent is N-methylpyrrolidone.

7. The method for preparing the double-coated silicon-carbon composite material as described in claim 1, characterized in that, In step S4, the resin is any one or a combination of phenolic resin, furfural resin, epoxy resin, and urea-formaldehyde resin. The third organic solvent is any one or a combination of xylene, ethyl acetate, acetone, and toluene; The fast ion conductor is any one or a combination of lithium titanium aluminum phosphate, lithium zirconium phosphate, and lithium aluminum silicate; The reducing gas is any one or a combination of hydrogen, carbon monoxide, and hydrogen sulfide.

8. A double-coated silicon-carbon composite material, characterized in that, The double-coated silicon-carbon composite material is prepared by any one of claims 1 to 7.

9. An electrode, characterized in that, This includes the double-coated silicon-carbon composite material prepared by the method for preparing the double-coated silicon-carbon composite material according to any one of claims 1 to 7, or the double-coated silicon-carbon composite material according to claim 8.

10. A lithium battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The negative electrode is the electrode as described in claim 9.

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