CN116779816A

CN116779816A - Porous silicon-carbon-based composite material, preparation method thereof, negative electrode and lithium ion battery

Info

Publication number: CN116779816A
Application number: CN202310836336.0A
Authority: CN
Inventors: 张怀文; 张少波; 王浩; 张小龙
Original assignee: Anhui Keda Purui Energy Technology Co ltd
Current assignee: Fujian Keda New Energy Technology Co ltd
Priority date: 2023-07-07
Filing date: 2023-07-07
Publication date: 2023-09-19

Abstract

The application provides a porous silicon-carbon-based composite material and a preparation method thereof, a negative electrode and a lithium ion battery, and relates to the technical field of electrochemical elements. The porous silicon-carbon-based composite material comprises a porous silicon-carbon composite bracket, nano silicon particles and a coated carbon layer; wherein the porous silicon-carbon composite scaffold comprises uniformly dispersed nano silicon-containing particles; the nano silicon particles are attached to the surface of the porous silicon-carbon composite bracket and are dispersed inside and outside the pores of the porous silicon-carbon composite bracket; the mass sum of the nano silicon-containing particles and the nano silicon particles accounts for 30-85 wt% of the porous silicon-carbon-based composite material. The application also provides a preparation method of the material, and a negative electrode and an electrochemical device applying the material. The porous silicon-carbon-based composite material provided by the application overcomes the defect that the silicon-carbon composite material for the lithium ion battery in the prior art has no obvious improvement on the electrochemical performance of the lithium ion battery.

Description

Porous silicon-carbon-based composite material, preparation method thereof, negative electrode and lithium ion battery

Technical Field

The application relates to the technical field of electrochemical elements, in particular to a porous silicon-carbon-based composite material, a preparation method thereof, a negative electrode and a lithium ion battery.

Background

At present, the conventional lithium ion negative electrode material is mainly a graphite negative electrode, but the theoretical specific capacity of the graphite negative electrode is only 372mAh/g, and along with the development of technology, the commercialized graphite negative electrode is close to the theoretical value, and is difficult to further promote. The theoretical capacity of silicon is up to 4200mAh/g, the detachment potential is lower (less than 0.5V), the voltage platform is slightly higher than that of graphite, lithium is difficult to separate out during charging, the safety performance is better, the earth reserves are rich, the environment is friendly, the research and application potential is high, and the silicon-silicon composite electrode material becomes a hot spot for research and development in novel electrode materials. However, in the process of charging and discharging silicon, the lithium intercalation and deintercalation cycle can generate serious silicon volume expansion and contraction, so that the collapse of a material structure and the pulverization and the peeling of an electrode are caused, the connection between an active material and a current collector is influenced, and the electron transmission is not facilitated; on the other hand, the volume effect causes the solid electrolyte interface (SEI film) formed between the silicon-based material and the electrolyte to be destroyed, and forms a new SEI film at the new interface, the active material and the electrolyte are gradually lost, and the battery capacity is further reduced sharply, and the cycle performance is seriously deteriorated.

In order to solve the technical problem, the prior art mainly adopts the following processes: and (3) carrying out wet grinding on silicon powder in a solvent, adding graphite or other carbon materials for wet mixing after the granularity is qualified, carrying out atomization drying on the uniformly mixed slurry by a spray dryer, compounding the spray-dried powder with the carbon materials such as asphalt, and carrying out high-temperature carbonization and mechanical shaping to obtain the silicon-carbon composite material. However, the carbon material used in the wet mixing has smaller specific surface, the available pore number is small, nano silicon particles are enriched on the surface layer of the carbon material, and the space provided by the carbon material for the volume expansion of silicon is limited; when the silicon-carbon composite material is compounded with carbon materials such as asphalt and the like, mechanical mixing is adopted, physical acting force is relied among material particles, the particle size of spray-dried powder is larger, asphalt particles are coated on the surface of the spray-dried powder and are filled in the pores of the powder, and a carbonized carbon layer is not compact and has poor coating effect, so that the capacity of the silicon-carbon composite material is exerted and the cycle performance is poor.

Disclosure of Invention

The application aims to provide a porous silicon-carbon-based composite material so as to overcome the defect that the silicon-carbon composite material for a lithium ion battery in the prior art has no obvious improvement on the electrochemical performance of the lithium ion battery.

Another object of the present application is to provide a method for preparing a porous silicon carbon-based composite material.

It is still another object of the present application to provide a negative electrode.

It is still another object of the present application to provide an electrochemical device.

In a first aspect, the application discloses a porous silicon-carbon based composite material, comprising a porous silicon-carbon composite bracket, nano silicon particles and a coated carbon layer;

wherein the porous silicon-carbon composite scaffold comprises uniformly dispersed nano silicon-containing particles; the nano silicon particles are attached to the surface of the porous silicon-carbon composite bracket and are dispersed inside and outside the pores of the porous silicon-carbon composite bracket;

the mass ratio of the nano silicon-containing particles and the nano silicon particles in the porous silicon-carbon-based composite material is 30-85 wt%, wherein the mass ratio of the nano silicon-containing particles to the nano silicon particles is (10:1) - (1:10).

Further, in some embodiments of the present application, the mass ratio of the nano silicon-containing particles in the porous silicon-carbon based composite material is 10wt% to 50wt%, and the mass ratio of the porous carbon material is 10wt% to 65wt%; the mass ratio of the nano silicon particles is 5-40 wt%, and the mass ratio of the coated carbon layer is 5-30 wt%.

Further, in some embodiments of the applicationThe specific surface area of the porous silicon-carbon composite bracket is 350-950m ² Per g, pore volume of 0.2-0.6cm ³ /g。

Further, in some embodiments of the application, the nano-silicon-containing particles have a median particle diameter D50 of 100nm or less and a grain size of less than 10nm.

Further, in some embodiments of the application, the average particle size of the nano-silicon particles is no greater than 10nm.

Further, in some embodiments of the present application, the porous silicon carbon-based composite material has a specific surface area of 2 to 20m ² /g。

Further, in some embodiments of the present application, the nano-silicon-containing particles are at least one of silicon powder, silicon oxide, silicon dioxide, silicon alloy.

In a second aspect, the present application provides a method for preparing a porous silicon carbon-based composite material, including:

providing a carbonaceous organic material and a siliceous raw material having a particle size of a nano-scale;

mixing the carbon-containing organic matter and the silicon-containing raw material, drying and curing to obtain a silicon-containing composite material precursor;

carbonizing the silicon-containing composite material precursor to obtain a porous silicon-carbon composite bracket;

utilizing organic silicon source gas to chemically vapor deposit nano silicon particles on the porous silicon-carbon composite bracket, and enabling part or all of the nano silicon particles to enter the pores of the porous silicon-carbon composite bracket to obtain a composite material;

And coating the composite material by using a carbon source at a temperature for decomposing the carbon source to obtain the porous silicon-carbon-based composite material.

Further, in some embodiments of the application, the mass ratio of the carbonaceous organics to the siliceous feedstock is (100:5) - (100:60).

Further, in some embodiments of the present application, the carbon-containing organic matter is selected from a polymer selected from at least one of a phenolic resin, a polyethylene glycol, a polyether polyester resin, a polyamide resin, a polyimide resin, a polyvinylpyrrolidone, an epoxy resin, a urea-formaldehyde resin, cellulose, and the like, or a monomer forming the polymer.

Further, in some embodiments of the application, when the carbon-containing organic is a precursor or monomer for forming the polymer, after the mixing, before the drying, further comprising: polymerizing the precursor or monomer at a temperature at which the precursor or monomer forms the polymer.

Further, in some embodiments of the application, the carbonizing the silicon-containing composite precursor comprises:

carbonizing the precursor of the silicon-containing composite material for 1-6 h at the temperature of 400-1000 ℃.

Further, in some embodiments of the present application, chemical vapor deposition of nano-silicon particles on the porous silicon carbon composite scaffold using a organosilicon source gas comprises:

under the inert gas environment of 450-950 ℃, utilizing organic silicon source gas as a silicon source, and performing chemical vapor deposition on nano silicon particles on the porous silicon-carbon composite bracket; the deposition time is 1 h-8 h.

Further, in some embodiments of the present application, the organosilicon source gas is at least one of silane, dichlorosilane, trichlorosilane, silicon tetrachloride, silicon tetrafluoride, disilane, and the like.

Further, in some embodiments of the present application, the carbon source is selected from at least one of a gas phase carbon source, a solid phase carbon source.

Further, in some embodiments of the present application, the carbon source is a gas phase carbon source, and coating the composite material with the carbon source at a temperature that decomposes the carbon source to obtain a porous silicon carbon based composite material comprises:

and (3) in a protective gas environment at 400-1000 ℃, enabling the gas-phase carbon source to be cracked and deposited on the surface of the composite material to form a carbon coating, so as to obtain the porous silicon-carbon-based composite material.

Further, in some embodiments of the present application, the carbon source is a solid phase carbon source, and coating the composite material with the carbon source at a temperature that decomposes the carbon source to obtain a porous silicon carbon based composite material comprises:

Mixing the composite material and the solid phase carbon source;

sintering under the inert gas environment of 400-1000 ℃ to obtain the porous silicon-carbon-based composite material;

or (b)

Heating and melting the solid-phase carbon source into liquid;

coating the liquid on the surface of the composite material by using a spraying process;

sintering under the inert gas environment of 400-1000 ℃ to obtain the porous silicon-carbon-based composite material.

In a third aspect, the application provides a negative electrode, which comprises the porous silicon-carbon-based composite material in the first aspect or the porous silicon-carbon-based composite material prepared by the preparation method of the porous silicon-carbon-based composite material in the second aspect.

Further, in some embodiments of the application, the negative electrode has a reversible capacity of not less than 1800mAh/g and a first efficiency of greater than 85% in a coin cell test.

Further, in some embodiments of the application, the negative electrode has a charge-discharge capacity retention of greater than 80% after 1400 charge and discharge cycles in a 18650 cylindrical battery test.

In a fourth aspect, the application also provides a lithium ion battery, which comprises the porous silicon-carbon-based composite material in the first aspect or the porous silicon-carbon-based composite material in the second aspect, or the porous silicon-carbon-based composite material prepared by the preparation method of the porous silicon-carbon-based composite material in the third aspect.

The application has the beneficial effects that:

the application provides a porous silicon-carbon-based composite material, which adopts a porous silicon-carbon composite bracket uniformly dispersed with nano silicon-containing particles as a porous bracket, and attaches small-size nano silicon particles in the porous bracket, and then coats a carbon coating layer to form the porous silicon-carbon-based composite material, wherein the silicon content in the composite material can reach 30-85 wt%, and the charge-discharge capacity of a negative electrode based on the porous silicon-carbon-based composite material is improved; in addition, the nano silicon-containing particles are dispersed in the porous bracket, so that the porous bracket can be utilized to provide better expansion buffering for the nano silicon-containing particles; and the nano silicon-containing particles dispersed in the porous silicon-carbon composite bracket can also realize the uniform dispersion of the nano silicon-containing particles in the porous silicon-carbon composite bracket and improve the binding force of the nano silicon-containing particles and the porous silicon-carbon composite bracket. Meanwhile, the nano silicon-containing particles and the small-size nano silicon particles adopted by the porous silicon-carbon-based composite material are respectively distributed in the porous support and the gaps of the porous support, so that the absolute value of the volume expansion of silicon in the porous silicon-carbon-based composite material can be reduced, and the cycling stability of the negative electrode based on the porous silicon-carbon-based composite material is improved. In addition, the nano silicon-containing particles and the small-size nano silicon particles are respectively distributed, so that the specific surface area requirement and the pore requirement of the porous support material can be properly reduced, the preparation difficulty is reduced, the nano silicon particles can enter the pores of the porous support as much as possible, the adhesion quantity of the nano silicon particles is improved, and the charge-discharge capacity of a battery based on the composite material is improved.

The application also provides a preparation method of the porous silicon-carbon-based composite material, which is characterized in that nano silicon-containing particles and polymers are carbonized to form a porous silicon-carbon composite bracket with large specific surface area and small average pore diameter, and then small-size nano silicon particles are deposited on the surface of the porous silicon-carbon composite bracket through a chemical vapor deposition process, so that the defect of too low silicon content in the porous silicon-carbon-based composite material due to insufficient nano silicon particle deposition caused by small specific surface area and large pore diameter of the porous silicon-carbon composite bracket is avoided; meanwhile, the average particle diameter of the nano silicon particles formed by the chemical vapor deposition process is small, and the nano silicon particles can enter the porous silicon-carbon composite bracket, so that the silicon content of the porous silicon-carbon-based composite material is improved, and the charge-discharge capacity of a battery based on the composite material is further improved; meanwhile, the volume expansion of silicon can be reduced, and the cycle performance of the battery based on the composite material is improved.

The application also provides a negative electrode, which adopts the porous silicon-carbon-based composite material with high silicon content, large specific surface area and small absolute value of silicon expansion and contraction as a negative electrode material, the porous silicon-carbon-based composite material adopts the porous silicon-carbon-based composite material with large specific surface area and small pore diameter as a bracket, small-size nano silicon particles are deposited in pores, a sufficient volume expansion space is provided for silicon, the possibility of crushing after the silicon volume expansion when the negative electrode is embedded with lithium is reduced, the corrosion of electrolyte is blocked, and the cycle performance of the negative electrode and the lithium ion extraction speed are improved. The reversible capacity of the negative electrode provided by the application can reach 1800mAh/g, the first efficiency is higher than 85%, the retention rate can still be higher than 80% after 1400 charge and discharge cycles, and the electrical property is excellent.

The application also provides an electrochemical device which adopts the cathode with high charge and discharge capacity, high efficiency and excellent cycle performance and has good electrical performance.

Drawings

Fig. 1 is an SEM image of a porous silicon carbon based composite scaffold provided in example 1 of the present application;

FIG. 2 is an XRD pattern of a porous SiON-based composite scaffold according to example 1 of the present application;

FIG. 3 is a first charge-discharge curve of a button cell of the porous SiON-based composite material according to example 1 of the present application;

fig. 4 is a cycle curve of 18650 cylindrical batteries of the porous silicon carbon-based composite provided in example 1 of the present application at a 1C/1C rate.

Detailed Description

For a better explanation of the present application, the main content of the present application is further elucidated with reference to the embodiments of the present application, and is further elucidated with reference to the specific examples, but the content of the present application is not limited to the following examples.

The inventor provides a porous silicon-carbon-based composite material, which comprises a porous silicon-carbon composite bracket, nano silicon particles and a coated carbon layer;

The mass sum of the nano silicon-containing particles and the nano silicon particles accounts for 30-85 wt% of the porous silicon-carbon-based composite material.

The porous silicon-carbon composite scaffold is a composite scaffold containing carbon and nano silicon-containing particles, wherein the carbon structure is a porous carbon structure formed by carbonizing an organic carbon source at high temperature; the nano silicon-containing particles are uniformly distributed in the porous carbon structure and are tightly combined with the porous carbon structure. The term "the nano silicon particles are attached to the surface of the porous silicon-carbon composite scaffold and dispersed inside and outside the pores of the porous silicon-carbon composite scaffold" means that the nano silicon particles are uniformly dispersed in the pores and on the surface of the porous silicon-carbon composite scaffold, namely: some or all of the nano silicon particles enter the pores of the porous silicon-carbon composite scaffold.

In the present application, the content of the silicon element in the porous silicon-carbon based composite material is preferably 30wt% to 85wt% in terms of mass fraction, and the content of the silicon element in the porous silicon-carbon based composite material may be any one of 32wt%, 40wt%, 46wt%, 53wt%, 64wt%, 70wt%, 79wt% by way of example; preferably, the content of silicon element in the porous silicon-carbon-based composite material is 35-70 wt%; the content of silicon element in the porous silicon-carbon-based composite material is 40-55wt%, namely the content of silicon element and the content of carbon element in the porous silicon-carbon-based composite material are about 1:1, so that the porous silicon-carbon-based composite material has excellent electrochemical performance, the silicon element provides higher specific capacity, the carbon element promotes the conductivity of the material, reduces the internal resistance, improves the dynamics of nano silicon in the anode material, and simultaneously isolates the erosion of electrolyte, thereby the material has high first reversible capacity, high first coulomb efficiency and good cycle performance.

In order to achieve the ratio of the sum of the masses of the nano silicon-containing particles and the nano silicon particles in the porous silicon-carbon based composite material, the mass ratio of the nano silicon-containing particles in the porous silicon-carbon composite support and the distribution of the silicon element content in the nano silicon particles and the coated carbon layer can be adjusted within a certain range. However, the content of nano silicon-containing particles in the porous silicon-carbon composite bracket is not too high or too low, because the content of nano silicon-containing particles is too high, the specific surface area of the porous silicon-carbon composite bracket is too low, the chemical vapor deposition of organic silicon source gas on the bracket is not facilitated, the nano silicon-containing particles are easy to agglomerate, the dispersion uniformity is poor, the coating effect of the porous carbon material is poor, and therefore the first coulomb efficiency and the cycle performance of the silicon-carbon composite material cannot be obviously improved; if the content of the nano silicon-containing particles is too low, the capacity of the porous silicon-carbon-based composite material is affected; meanwhile, the nano silicon particles on the porous silicon-carbon composite support are not too high, because more nano silicon particles are distributed on the surface of the porous silicon-carbon composite support, bare silicon nano particles can appear when the proportion of coated carbon is low, the silicon nano particles can be oxidized, the capacity and the first coulombic efficiency of the porous silicon-carbon composite material are affected, and the porous silicon-carbon composite material is in direct contact with electrolyte in the charge-discharge cycle process of the battery, so that the cycle performance of the cathode material is affected. Therefore, in the porous silicon-carbon based composite material, the mass ratio of the nano silicon-containing particles can be 10-50 wt%, and the mass ratio of the porous carbon material is 10-65 wt%; the mass ratio of the nano silicon particles is 5-40 wt%, and the mass ratio of the coated carbon layer is 5-30 wt%. In addition, in the preparation process, the mass ratio of the nano silicon-containing particles in the porous silicon-carbon composite scaffold can be 5-60 wt%, the mass ratio of the porous carbon material can be 40-95 wt%, and preferably, the mass ratio of the nano silicon-containing particles in the porous silicon-carbon composite scaffold can be 20-35 wt%. And further preferably, the mass ratio of the nano silicon particles in the porous silicon carbon-based composite material may be 20wt% to 35wt%, and the mass ratio of the coated carbon layer may be 5wt% to 10wt%.

In the application, the nano silicon-containing particles can be at least one of crystalline silicon powder, silicon oxide, silicon dioxide and silicon alloy with short-range order, wherein the median particle diameter (D50) size of the nano silicon-containing particles is not higher than 100nm, and meanwhile, the grain size is not higher than 10nm, so that the mechanical fragmentation caused by volume expansion is relieved in the charging and discharging process, and meanwhile, the dynamic property is improved. In addition, when the nano silicon-containing particles are silicon alloy, the silicon alloy adopted by the nano silicon-containing particles contains silicon, metal X and oxygen, wherein the metal X can be any one or a combination of a plurality of magnesium, copper, aluminum, zinc, iron, manganese, titanium, lithium, calcium and the like.

In order to enable nano silicon particles to be better deposited on the surface of the porous silicon-carbon composite bracket and enter the pores of the porous silicon-carbon composite bracket, the specific surface area of the porous silicon-carbon composite bracket is not too low, and the pore diameter of the pores of the porous silicon-carbon composite bracket is not too high. The porous silicon-carbon composite bracket with the excessively low specific surface area is easy to cause less deposition of nano silicon particles, is mainly concentrated on the surface of the porous silicon-carbon composite bracket, and has poor distribution uniformity; too small specific surface area and too large pore diameter can also lead to aggregation and concentration of silicon-containing nano particles, poor uniformity of distribution in the porous carbon material, insufficient space when the silicon volume expands in the charging and discharging process, and influence the cycle performance of the cathode based on the composite material. In addition, the porous silicon-carbon composite bracket has high specific surface area, is favorable for immersing nano silicon particles, has higher requirements on materials, and has higher preparation process difficulty. Therefore, in the application, the porous silicon-carbon composite scaffold is preferably a porous silicon-carbon composite scaffold with a specific surface area of 350-950m ² Per g, pore volume of 0.2-0.6cm ³ Porous Si-C composite scaffold per g, and further preferably having a specific surface area of 400-800m ² Per g, pore volume of 0.25-0.5cm ³ Porous silicon-carbon composite scaffold/g.

In some embodiments, the average particle size of the nano silicon particles is not higher than 10nm, so that the absolute expansion volume of the nano silicon particles is reduced, the dynamic characteristics of the nano silicon particles are improved, and the phenomenon that the distance of the nano silicon particles for excessively increasing the volume expansion of lithium ions to intercalate into a silicon material in the charge and discharge process of a battery is influenced due to poor conductivity of the nano silicon particles is avoided, so that the speed of lithium ion deintercalation and the cycle stability of the battery are influenced. Still more preferably, the average particle diameter of the nano-silicon particles is 2 to 5nm. The nano silicon particles with the particle size of less than 3nm are selected, so that the nano silicon particles can enter the pores of the porous silicon-carbon composite bracket, and the anode material with better cycle stability can be obtained.

In some embodiments, the porous silicon carbon based composite has a specific surface area of 2 to 20m ² /g。

In order to better realize the application, the inventor also provides a preparation method of the porous silicon-carbon-based composite material, which comprises the following steps:

mixing the carbon-containing organic matter and the silicon-containing raw material, and drying and curing to obtain a silicon-containing composite material precursor;

Wherein the nanoscale silicon-containing feedstock is used to provide nanoscale silicon-containing particles. In the actual preparation process, the nano silicon-containing particles can be obtained by wet grinding of silicon-containing raw materials in a solvent or dry grinding without a solvent, wherein the solvent adopted in the wet grinding can be one or more of methanol, benzyl alcohol, ethanol, ethylene glycol, propanol, isopropanol, propylene glycol, butanol, n-butanol, isobutanol, amyl alcohol, neopentyl alcohol and octanol. Wherein the grinding process is a conventional process in the prior art, and thus is not described in detail in the present application.

In some embodiments, the mass ratio of the carbonaceous organics to the siliceous feedstock is (100:5) - (100:60). Wherein the silicon-containing feedstock herein is understood to be nano-silicon-containing particles.

In the preparation process provided by the application, the raw materials for forming the porous silicon-carbon composite scaffold adopt nano silicon-containing particles and carbon-containing organic matters serving as carbon sources to be mixed to form a precursor, and then the precursor is dried, solidified and carbonized. Compared with a silicon-carbon composite material formed by taking carbon materials such as graphite and the like as raw materials and silicon-containing raw materials, the silicon-containing material can enter the composite bracket, the distribution in the composite bracket is more uniform, the uniformity is better, and the connection between carbon and silicon-containing raw materials in the composite is more compact. In addition, the porous silicon-carbon composite bracket formed by the method has smaller aperture and larger specific surface area, is more beneficial to the deposition of nano silicon particles and provides sufficient volume expansion space for silicon under working conditions.

In the present application, the carbon-containing organic matter may be a carbon-containing polymer or may be a monomer that can form a carbon-containing polymer by polymerization, wherein the monomer may be a carbon-containing monomer or a carbon-containing oligomer. Illustratively, the carbon-containing organic matter is selected from at least one of phenolic resin, polyethylene glycol, polyether polyester resin, polyamide resin, polyimide resin, polyvinylpyrrolidone, epoxy resin, urea resin, cellulose.

When the carbonaceous organic material is a carbonaceous monomer or a carbonaceous oligomer, after the mixing and before the drying, the method further comprises: the carbon-containing monomer or oligomer is polymerized at a temperature at which the carbon-containing monomer or oligomer is polymerized to form the polymer. The polymerization temperature and polymerization conditions may be adjusted according to the carbon-containing monomer or the carbon-containing oligomer used, or may be adjusted according to the catalyst or initiator used. Illustratively, the carbon-containing monomer is phenolic resin or bisphenol A, the catalyst used is hexamethylenetetramine, the curing temperature is 150 ℃, and the time for the whole polymerization curing reaction of the carbon-containing monomer is 4 hours.

After polymerization, the polymer is cured by heat preservation at a temperature at which the polymer is cured, and then a carbonization step is performed.

In some embodiments, the carbonization process comprises:

carbonizing the precursor of the silicon-containing composite material for 1-6 h at the temperature of 400-1000 ℃. Wherein the carbonization process is performed in an inert gas environment. The inert gas used in the present application may be a conventional inert gas such as: helium, neon, argon, krypton. Still other processes of the present application require a shielding gas environment, wherein the shielding gas employed is one or more of nitrogen or an inert gas.

In the application, the carbonization temperature of the precursor of the silicon-containing composite material is not too high or too low, because the specific surface area and pore volume of the porous silicon-carbon composite support show a tendency of rising and then reducing, in a certain temperature range, the pyrolysis speed of the polymer is increased along with the rising of the temperature, and non-carbon atoms are easy to deviate; however, the temperature continues to rise, and the porous carbon contracts, so that a small amount of closed pores appear; the carbonization time is not too long or too short, because the carbonization time is too short, the carbonization degree is low, and the polymer is not completely pyrolyzed; the carbonization time is too long, the porous carbon is excessively ablated, part of the structure is destroyed, and the specific surface area is reduced. Further preferably, the carbonization temperature of the precursor of the silicon-containing composite material is 550-900 ℃ and the carbonization time is 2-5 h.

In some embodiments, chemical vapor deposition of nano-silicon particles on the porous silicon-carbon composite scaffold using a organosilicon source gas comprises:

The organic silicon source gas used in the present application may be a conventional silicon-containing organic gas, and may specifically be at least one of monosilane, dichlorosilane, trichlorosilane, disilane, silicon tetrachloride, silicon tetrafluoride, and the like.

In the chemical vapor deposition device, the flow rate of the organic silicon source gas is 1L/min-5L/min, and the flow rate cannot be too low so as to ensure the safety and the production efficiency.

In some embodiments, the carbon source is selected from at least one of a gas phase carbon source, a solid phase carbon source.

After the nano silicon particles are deposited, a carbon coating layer is coated on the surface of the composite bracket by using a gas phase carbon source or a solid phase carbon source in order to play a better protection role. Wherein, the gas phase carbon source can be at least one of carbon-containing gas organic matters such as methane, ethane, acetylene, propane, propylene, acetone, propanol, butane, liquefied gas and the like; the solid carbon source can be at least one of carbon-containing solid organic matters such as glucose, sucrose, asphalt, epoxy resin, phenolic resin, furfural resin and the like which are solid at normal temperature.

The coating process of the carbon coating can be adjusted according to the different carbon sources adopted.

Illustratively: when the carbon source is a gas-phase carbon source, the gas-phase carbon source is cracked and deposited on the surface of the composite material to form a coated carbon layer in a protective gas environment at 400-1000 ℃ to obtain the porous silicon-carbon-based composite material. In this example, the gas-phase carbon source introduction flow rate is 1L/min to 15L/min, preferably 2L/min to 10L/min. The deposition time is 1 h-8 h.

Illustratively: when the carbon source is a solid-phase carbon source, coating the composite material with the carbon source at a temperature at which the carbon source is decomposed to obtain a porous silicon-carbon-based composite material, comprising:

mixing the composite material and the solid phase carbon source;

In addition, when the carbon source is a solid-phase carbon source, the coating process may further include the following specific steps:

heating and melting the solid-phase carbon source into liquid;

When the carbon source is a solid-phase carbon source, the sintering temperature used in the sintering step is 400 to 1000 ℃ and the sintering time is 1 to 6 hours. The sintering curve of the solid-phase carbon source can be adjusted according to whether the solid-phase carbon source is melted into liquid coating. Illustratively, when the solid phase carbon source is directly mixed with the composite material, the sintering curve is at a constant temperature of 650 ℃ for 2 hours; when the solid-phase carbon source is heated and melted into liquid, the sintering curve of the solid-phase carbon source is kept at the constant temperature of 450 ℃ for 3 hours when the coating composite material is sprayed.

In some embodiments, the negative electrode has a reversible capacity of not less than 1800mAh/g and a first efficiency of greater than 85% in a coin cell test.

In some embodiments, the negative electrode has a charge-discharge capacity retention of greater than 80% after 1400 charge and discharge cycles in a 18650 cylindrical battery test.

The present application will be described in more detail with reference to the following examples, which are not intended to limit the scope of the application.

Wherein the silicon-containing material is micron silicon-grade particles, the median particle size D50 is 1-1000 mu m, and if the silicon-containing material is silicon alloy, the mass content of silicon in the silicon alloy is more than or equal to 65%;

example 1:

The embodiment of the application provides a preparation method of a porous silicon-carbon-based composite material, which specifically comprises the following steps:

s1, 180g of micron silicon powder is taken and put into 1000mL of absolute ethyl alcohol to be ground, so as to obtain nano silicon slurry with the average particle size of 95 nm; adding 600g of phenolic resin mixture into the nano silicon powder slurry, wherein the mixture is prepared from phenolic resin, bisphenol A and hexamethylenetetramine according to a certain proportion, and stirring and mixing to obtain mixed slurry; evaporating the mixed slurry under reduced pressure at normal temperature under stirring to remove absolute ethyl alcohol to obtain a precursor of the silicon-containing composite material;

s2, placing the precursor of the silicon-containing composite material in a box furnace, taking nitrogen as a protective gas, and carbonizing at 800 ℃ for 120min to obtain a porous silicon-carbon composite bracket;

s3, placing the porous silicon-carbon composite bracket in a CVD furnace liner, introducing inert gas at a flow rate of 5L/min to remove air in the CVD furnace, heating to 600 ℃ after the oxygen content is lower than 100ppm, introducing silane gas at a flow rate of 2L/min on the premise of keeping the flow rate of the inert gas unchanged, and performing chemical vapor deposition for 3.5 hours to enable silicon particles to be deposited in the pores of the porous silicon-carbon composite bracket, thereby obtaining a composite material;

s4, introducing inert gas into the CVD furnace at a flow of 8L/min to remove silane gas, introducing acetylene gas at a flow of 3L/min, heating to 700 ℃, performing chemical vapor deposition of a carbon source for 2h, depositing carbon particles formed after the decomposition of the acetylene gas on the surface of the composite material to form a carbon coating layer, and cooling to obtain the porous silicon-carbon-based composite material, wherein SEM characterization results and XRD characterization results are shown in figures 1 and 2.

Example 2

s1, 180g of silicon oxide is taken and put into 1000mL of butanol to be ground to obtain silicon oxide slurry with the average particle size of 88 nm; adding the silica slurry into 600g of polyethylene glycol, and stirring and mixing to obtain mixed slurry; spray drying the slurry to obtain silicon-containing precursor composite particles with the average particle diameter of 18 mu m;

s2, placing the precursor of the silicon-containing composite material into a tube furnace, taking argon as a protective gas, and carbonizing at 400 ℃ for 90min to obtain a porous silicon-carbon composite bracket;

s3, placing the porous silicon-carbon composite bracket in a CVD furnace liner, introducing inert gas at a flow rate of 2L/min to remove air in the CVD furnace, heating to 450 ℃ after the oxygen content is lower than 100ppm, introducing disilane gas at a flow rate of 1L/min on the premise of keeping the inert gas flow rate unchanged, and performing chemical vapor deposition for 8 hours to enable silicon particles to be deposited in the pores of the porous silicon-carbon composite bracket, thereby obtaining a composite material;

and S4, introducing inert gas into the CVD furnace at a speed of 2L/min to remove disilane gas, introducing methane gas at a flow of 1L/min, heating to 800 ℃, performing chemical vapor deposition of a carbon source for 8 hours, depositing carbon particles formed after decomposing the methane gas on the surface of the composite material to form a carbon coating layer, and cooling to obtain the porous silicon-carbon-based composite material.

Example 3

s1, 180g of ferrosilicon is taken and put into 1000mL of isopropanol to be ground, so as to obtain nano ferrosilicon slurry with the average grain diameter of 79 nm; adding the nano ferrosilicon alloy slurry into 600g of polyvinylpyrrolidone, and stirring and mixing to obtain mixed slurry; evaporating the solvent from the mixed slurry under reduced pressure, and drying to obtain a silicon-containing composite material precursor;

s2, placing the precursor of the silicon-containing composite material in a muffle furnace, and carbonizing at 1000 ℃ for 360min by taking helium as a protective gas to obtain a porous silicon-carbon composite bracket;

s3, placing the porous silicon-carbon composite bracket in a CVD furnace liner, introducing inert gas at a rate of 10L/min to remove air in the CVD furnace, heating to 950 ℃ after the oxygen content is lower than 100ppm, introducing dichlorosilane gas at a rate of 5L/min to enable the CVD furnace to carry out chemical vapor deposition for 1h under the premise of keeping the inert gas flow unchanged, and enabling silicon particles to be deposited in the pores of the porous silicon-carbon composite bracket to obtain a composite material;

and S4, introducing inert gas into the CVD furnace at a flow rate of 10L/min to remove dichlorosilane gas, introducing acetone gas at a flow rate of 6.5L/min, heating to 1000 ℃, performing chemical vapor deposition of a carbon source for 1h, depositing carbon particles formed after the decomposition of the acetone gas on the surface of the composite material to form a carbon coating layer, and cooling to obtain the porous silicon-carbon-based composite material.

Example 4

Compared with the embodiment 1, in the embodiment, asphalt is used as a carbon source in the step S4, the silane deposited composite material and asphalt obtained in the step S3 are placed in a VC mixer according to a mass ratio of 1:0.1, the frequency of the VC mixer is adjusted to 150Hz, the mixing time is 1h, then the VC mixer is placed in a box-type furnace, nitrogen is introduced, the temperature is raised to 750 ℃, the temperature is kept for 4h, and then the porous silicon-carbon based composite material is obtained after cooling to room temperature.

Example 5

In this example, compared with example 1, the mass of the nano silicon powder adopted in step S1 is 90g, the mass of the carbon-containing organic matter is 600g, and the rest steps are the same as in example 1, so as to obtain the porous silicon-carbon-based composite material.

Example 6

In this example, compared with example 1, the mass of the nano silicon powder adopted in step S1 is 270g, the mass of the carbon-containing organic matter is 600g, and the rest steps are the same as in example 1, so as to obtain the porous silicon-carbon-based composite material.

Comparative example 1

In this comparative example, step S2 was omitted, and the remaining steps were the same as in example 1, to obtain a comparative porous silicon carbon-based composite material 1.

Comparative example 2

In this comparative example, compared with example 1, the silicon-containing raw material was not added in step S1, and the remaining steps were the same as in example 1, to obtain a comparative porous silicon carbon-based composite material 2.

Comparative example 3

In this comparative example, the carbon source added in step S1 was graphite, and the remaining steps were the same as in example 1, to obtain a comparative porous silicon carbon-based composite material 3.

Comparative example 4

In this comparative example, compared with example 1, the carbon source added in step S1 was graphite, and after step S1, the obtained silicon-containing composite precursor was mixed in 160g of pitch before step S2, and then step S2 was performed, and the remaining steps were the same as in example 1, to obtain comparative porous silicon-carbon-based composite 4.

Comparative example 5

In this comparative example, compared with example 1, the mass of the nano silicon powder used in step S1 was 18g, the mass of the carbonaceous organic material was 600g, and the remaining steps were the same as in example 1, to obtain a comparative porous silicon carbon-based composite material 5.

Comparative example 6

In this comparative example, compared with example 1, the mass of the nano silicon powder used in step S1 was 400g, the mass of the carbonaceous organic material was 600g, and the remaining steps were the same as in example 1, to obtain a comparative porous silicon carbon-based composite material 6.

Comparative example 7

The comparative example, compared with example 1, comprises the following steps:

s1, 60g of micron silicon powder is taken and put into 1200mL of absolute ethyl alcohol to be ground, so as to obtain nano silicon powder slurry with the average particle size of 89 nm; adding 800g of polyvinylpyrrolidone into the nano silicon powder slurry, and stirring and mixing to obtain mixed slurry; evaporating the mixed slurry under reduced pressure at normal temperature under stirring to remove absolute ethyl alcohol to obtain a precursor of the silicon-containing composite material;

S2, placing the precursor of the silicon-containing composite material in a tube furnace, taking nitrogen gas as protective gas, and carbonizing at 700 ℃ for 150min to obtain a porous silicon-carbon composite bracket;

s3, placing the porous silicon-carbon composite bracket in a CVD furnace liner, introducing inert gas at a flow rate of 6L/min to remove air in the CVD furnace, heating to 550 ℃ after the oxygen content is lower than 100ppm, introducing disilane at a flow rate of 1.5L/min on the premise of keeping the inert gas flow rate unchanged, and performing chemical vapor deposition for 1h to enable silicon particles to be deposited in the pores of the porous silicon-carbon composite bracket, thereby obtaining a composite material;

and S4, introducing inert gas into a CVD furnace at a speed of 6L/min to remove disilane gas, introducing acetylene gas at a speed of 2.5L/min, heating to 850 ℃, performing chemical vapor deposition of a carbon source for 7h, depositing carbon particles formed after the decomposition of the acetylene gas on the surface of the composite material to form a carbon coating layer, and cooling to obtain the comparative porous silicon-carbon-based composite material 7.

Comparative example 8

s1, grinding 320g of micron silicon powder in 1200mL of absolute ethyl alcohol to obtain nano silicon powder slurry with the average particle size of 92 nm; adding the nano silicon powder slurry into 500g of polyethylene glycol, and stirring and mixing to obtain mixed slurry; spray drying the slurry to obtain a silicon-containing composite material precursor with an average particle diameter of 15.3 mu m;

S2, placing the precursor of the silicon-containing composite material in a muffle furnace, taking argon gas as protective gas, and carbonizing at 800 ℃ for 180min to obtain a porous silicon-carbon composite bracket;

s3, placing the porous silicon-carbon composite support in a CVD furnace liner, introducing inert gas at a flow rate of 10L/min to remove air in the CVD furnace, heating to 500 ℃ after the oxygen content is lower than 100ppm, introducing silane gas at a flow rate of 5L/min, and performing chemical vapor deposition for 8 hours to enable silicon particles to be deposited in the pores of the porous silicon-carbon composite support, thereby obtaining a composite material;

and S4, introducing inert gas into the CVD furnace at a flow rate of 5L/min to remove silane gas, introducing methane gas at a flow rate of 2L/min, heating to 750 ℃, performing chemical vapor deposition of a carbon source for 1.5h, depositing carbon particles formed after decomposing the methane gas on the surface of the composite material to form a carbon coating layer, and cooling to obtain the comparative porous silicon-carbon-based composite material 8.

Comparative example 9

Compared with the embodiment 1, the nano silicon powder adopted in the step S1 is micron silicon powder, the particle size is 148nm after grinding, and the rest steps are the same as the embodiment 1, so that the comparative porous silicon carbon-based composite material 9 is obtained.

Comparative example 10

In this comparative example, compared with example 1, the physical vapor deposition method adopted in step S3 was used to deposit nano silicon particles on the surface of the porous silicon carbon composite scaffold, and the rest of the steps were the same as example 1, so as to obtain a comparative porous silicon carbon-based composite material 10.

Experiment

The porous silicon carbon-based composite materials obtained in the above examples 1 to 6 and the comparative porous silicon carbon-based composite materials obtained in comparative examples 1 to 10 were respectively tested for physical parameters and performance parameters by the following test methods, which were specifically described as follows:

the testing method comprises the following steps:

1-pore volume

Determination of specific surface area of solid substance by GB/T19587-2017 gas adsorption BET method

Average particle diameter of 2-nano silicon-containing particles

The granularity of the nano silicon-containing slurry is obtained by adopting a Malvern laser granularity meter Mastersizer 3000 test and a GB/T19077.0-2016 granularity distribution laser diffraction method.

Silicon grain size the material was phase analyzed using an XRD diffractometer (X' Pert3 Powder) to determine the grain size of the material.

3-element content

GB/T38823-2020 silicon carbon

The results obtained from the test are shown in Table 1.

TABLE 1

The silicon content and the carbon content in the composite bracket are the mass ratio of silicon element and carbon element in the composite bracket; the content of the silicon element and the content of the carbon element in the porous silicon-carbon-based composite material are the mass ratio of the silicon element and the carbon element in the porous silicon-carbon-based composite material, the content of the silicon element comprises the sum of the mass ratio of the silicon element in the composite bracket and the silicon element in the nano silicon-containing particles in the porous silicon-carbon-based composite material, and the content of the carbon element is the mass ratio of all the carbon elements in the composite material in the porous silicon-carbon-based composite material. The mass ratio of the nano silicon-containing particles in the porous silicon-carbon-based composite material is the difference between the mass ratio of the silicon element in the porous silicon-carbon-based composite material and the mass ratio of the silicon element in the composite bracket in the porous silicon-carbon-based composite material.

As can be seen from table 1, the silicon-carbon negative electrode material prepared by the method of the present application comprises a porous silicon-carbon based composite scaffold, a vapor deposition nano silicon and a carbon coating layer, wherein the composite scaffold comprises nano silicon-containing particles and porous carbon. The grain size of the nano silicon-containing particles can be adjusted by a grinding process, and the grain size of the nano silicon is calculated to be below 10nm by Scherrer. Porous carbon with different pore volumes can be obtained through the carbonization process of carbon-containing organic matters, and the pore volume test shows that the vapor phase silicon is deposited in the pore diameter of the porous carbon. The content of the main element carbon and silicon in the porous silicon-carbon-based composite bracket and the porous silicon-carbon-based composite material can be calculated by carrying out the content test on the carbon element by a high-frequency infrared carbon-sulfur analyzer and carrying out the weight increase test on the silicon element by a box-type resistance furnace or an atmosphere furnace. In examples 1-6, the components of the porous silicon-carbon based composite scaffold and the silicon-carbon composite material prepared by the composite scaffold can be adjusted within a certain range by adjusting the proportion and the process of each step, so that the aim of optimizing the material performance is achieved.

In order to further verify electrochemical properties such as cycle performance and charge-discharge capacity of the porous silicon-carbon based composite material provided by the application, the inventors apply the porous silicon-carbon based composite materials obtained in examples 1 to 6 and the comparative composite materials obtained in comparative examples 1 to 10 to the negative electrode of the lithium ion battery, and the specific structure of the negative electrode is as follows:

The preparation method comprises the steps of mixing a negative electrode material, conductive agent carbon black (Super P), carbon nano tube and LA133 gel in a mass ratio of 91:2:2:5 in solvent pure water, homogenizing, controlling the solid content to be 45%, coating the mixture on a copper foil current collector, and carrying out vacuum drying to obtain the negative electrode plate.

The specific structure of the lithium ion battery is as follows:

the button cell was assembled in an argon atmosphere glove box using Celgard2400 membrane, 1mol/L LiPF6/EC+DMC+EMC (v/v=1:1:1) electrolyte and metallic lithium sheet as counter electrode.

The button cell is charged and discharged, the voltage interval is 5 mV-1.5V, and the current density is 80mA/g. The first reversible capacity and efficiency of the core-shell structured porous silicon anode materials in examples and comparative examples were measured.

And the performance parameters such as charge and discharge capacity, cycle performance, first efficiency and the like of the lithium ion battery are tested, and the testing method comprises the following steps:

the prepared negative electrode plate, the ternary positive electrode plate, the 1mol/L LiPF6/EC+DMC+EMC (v/v=1:1:1) electrolyte, the Celgard2400 diaphragm and the shell are assembled into 18650 cylindrical single batteries by adopting a conventional production process. On the LAND battery test system of the Wuhan Jinno electronic limited company, the charge and discharge performance of the prepared cylindrical battery is tested, and the test conditions are as follows: constant-current charge and discharge at normal temperature and 0.2C, and the charge and discharge voltage is limited to 2.75V-4.2V.

The charge-discharge curve and cycle performance obtained by the test are exemplified as those of a lithium ion battery based on the porous silicon carbon-based composite obtained in example 1 shown in fig. 3 and 4. In order to reduce the space and repetition, the data of charge-discharge curves and cycle properties of lithium ion batteries based on the porous silicon carbon-based composite materials obtained in the remaining examples and comparative examples in the present application are presented in the form of a table, which is specifically shown in table 2.

According to the measured first reversible capacity in the button cell, the core-shell structure porous silicon anode materials in the examples and the comparative examples are mixed with the same type of stable artificial graphite, and the first reversible capacity of the button cell test of the mixed powder is 450+/-5 mAh/g. And preparing a negative electrode plate by using the mixed powder snap-fastener type battery technology, wherein a positive electrode is a ternary electrode plate, a separation film and electrode liquid prepared by using a mature technology are unchanged, and the 18650 cylindrical single battery is assembled. And (3) carrying out charge and discharge test on the 18650 cylindrical single battery, wherein the voltage interval is 2.5 mV-4.2V, and the current density is 450mA/g. The button cell and 18650 cylindrical single cell test equipment are LAND cell test systems of the Wuhan Jinno electronic Co.

The test items and test results are shown in Table 2:

TABLE 2

As shown in Table 2, the porous silicon-carbon-based composite material prepared by the method of the application greatly improves the comprehensive performance of the anode material through each functional component, the first reversible capacity can be more than 1800mAh/g, the first coulomb efficiency can be more than 85%, and the capacity retention rate can reach more than 80% after 1400 times of circulation. The carbonization step is not carried out in comparative example 1, and the organic carbon source is cracked and carbonized in the silane deposition process, so that the silane deposition effect is affected to a certain extent, and the initial coulombic efficiency and the cycle performance are obviously reduced. In comparative examples 2 to 5 and comparative example 7, the silicon-containing raw material is not added or the carbon source is changed in the first step, so that the total silicon content in the composite material is relatively low, the reversible capacity is low, wherein the carbon source of the composite support in comparative example 3 and comparative example 4 is graphite or graphite plus asphalt, the ratio of the carbon source to the graphite or graphite plus asphalt is small, the pores are large and the number of the carbon source is small, nano silicon-containing particles are easy to agglomerate, and the material cycle performance is obviously poor. The input proportion of nano silicon-containing particles in the comparative examples 6 and 8 is high, the nano silicon-containing particles are agglomerated in the charge and discharge process, and the porous carbon provides less pores, so that the cycle performance is affected; in particular, comparative example 8 has less carbon coating, and the material cycle performance is obviously reduced. The nano silicon-containing particles of comparative example 9 have a much larger particle diameter and a much larger grain size than those of example 1, and the cycle performance of the resulting silicon-carbon negative electrode material is inferior to that of the negative electrode material prepared in example 1, although the first reversible capacity and the first coulombic efficiency are higher. Unlike example 1, the silicon deposition process employed in comparative example 10 did not allow the nano-silicon particles to well enter the porous carbon voids, resulting in a silicon-carbon negative electrode material having poor first reversible capacity and first coulombic efficiency, and a significant decrease in cycle performance.

The present application can be implemented in other forms than the above-described forms within a range not exceeding the gist of the present application. The disclosed embodiments of the present application are examples and are not limited to these.

Claims

1. The porous silicon-carbon-based composite material is characterized by comprising a porous silicon-carbon composite bracket, nano silicon particles and a coated carbon layer;

wherein the porous silicon-carbon composite scaffold comprises nano silicon-containing particles uniformly dispersed in the porous silicon-carbon composite scaffold; the nano silicon particles are attached to the surface of the porous silicon-carbon composite bracket and are dispersed inside and outside the pores of the porous silicon-carbon composite bracket;

the mass sum of the nano silicon-containing particles and the nano silicon particles accounts for 30-85 wt% of the porous silicon-carbon-based composite material; wherein the mass ratio of the nano silicon-containing particles to the nano silicon particles is (10:1) - (1:10).

2. The porous silicon-carbon based composite of claim 1, wherein: in the porous silicon-carbon-based composite material, the mass ratio of the nano silicon-containing particles is 10-50wt%, and the mass ratio of the porous carbon material is 10-65wt%; the mass ratio of the nano silicon particles is 5-40 wt%, and the mass ratio of the coated carbon layer is 5-30 wt%; and/or

The specific surface area of the porous silicon-carbon composite bracket is 350-950m ² Per g, pore volume of 0.2-0.6cm ³ /g; and/or

The median granularity D50 of the nano silicon-containing particles is below 100nm, and the grain size is less than 10nm; and/or

The average particle size of the nano silicon particles is not higher than 10nm; and/or

The specific surface area of the porous silicon carbon-based composite material is 2-20 m ² /g; and/or

The nanometer silicon-containing particles are at least one of silicon powder, silicon oxide, silicon dioxide and silicon alloy.

3. The preparation method of the porous silicon-carbon-based composite material is characterized by comprising the following steps:

mixing the carbon-containing organic matter and the silicon-containing raw material, and drying to obtain a silicon-containing composite material precursor;

coating the composite material with a carbon source at a temperature at which the carbon source is decomposed to obtain a porous silicon-carbon-based composite material;

Preferably, the mass ratio of the carbon-containing organic matter to the silicon-containing raw material is (100:5) - (100:60);

preferably, the organic silicon source gas is at least one of silane, dichlorosilane, trichlorosilane, silicon tetrachloride, silicon tetrafluoride and disilane;

preferably, the carbon source is at least one selected from a gas phase carbon source and a solid phase carbon source.

4. The method for producing a porous silicon carbon based composite material according to claim 3, wherein the carbon-containing organic matter is selected from a polymer selected from at least one of a phenol resin, a polyethylene glycol, a polyether polyester resin, a polyamide resin, a polyimide resin, a polyvinylpyrrolidone, an epoxy resin, a urea resin, and a cellulose, or a monomer forming the polymer.

5. The method of producing a porous silicon carbon based composite material according to claim 4, wherein when the carbonaceous organic material is a carbonaceous monomer or a carbonaceous oligomer forming the polymer, further comprising, after the mixing and before the drying: polymerizing or curing the carbon-containing monomer or oligomer at a temperature at which the carbon-containing monomer or oligomer forms the polymer.

6. A method of preparing a porous silicon carbon based composite as claimed in claim 3 wherein the charring comprises:

7. The method of preparing a porous silicon-carbon based composite material according to claim 1, wherein chemical vapor deposition of nano silicon particles on the porous silicon-carbon composite scaffold using an organosilicon source gas comprises:

8. The method for producing a porous silicon carbon based composite material according to claim 3, wherein when the carbon source is a gas phase carbon source, coating the composite material with the carbon source at a temperature at which the carbon source is decomposed to obtain the porous silicon carbon based composite material, comprising:

under the protective gas environment of 400-1000 ℃, the gas-phase carbon source is cracked and deposited on the surface of the composite material to form a coated carbon layer, and the porous silicon-carbon-based composite material is obtained;

when the carbon source is a solid-phase carbon source, coating the composite material by using the carbon source at a temperature for decomposing the carbon source to obtain the porous silicon-carbon-based composite material, wherein the method comprises the following steps of:

Mixing the composite material and the solid phase carbon source;

or (b)

Heating and melting the solid-phase carbon source into liquid;

9. A negative electrode, characterized by comprising the porous silicon-carbon-based composite material according to any one of claims 1 to 2 or the porous silicon-carbon-based composite material prepared by the preparation method of the porous silicon-carbon-based composite material according to any one of claims 3 to 8.

10. The negative electrode according to claim 9, wherein the negative electrode has a reversible capacity of not less than 1800mAh/g and a first efficiency of higher than 85% in a coin cell test;

preferably, the negative electrode has a charge-discharge capacity retention of greater than 80% after 1400 charge and discharge cycles in the 18650 cylindrical battery test.

11. A lithium ion battery, characterized by comprising the porous silicon-carbon-based composite material according to any one of claims 1 to 2 or the porous silicon-carbon-based composite material prepared by the preparation method of the porous silicon-carbon-based composite material according to any one of claims 3 to 8 or the negative electrode according to claims 9 to 10.