Porous silicon-carbon composite negative electrode material and preparation method thereof

Abstract

The application provides a porous silicon-carbon composite negative electrode material and a preparation method thereof, and belongs to the technical field of battery negative electrode materials.The porous silicon-carbon composite negative electrode material takes porous carbon as a matrix, and nano-silicon is deposited in the holes on the outer surface of the porous carbon matrix; the particle size of the porous silicon-carbon composite negative electrode material is 5-50 mu m, and the pore size of the holes on the porous carbon matrix is 50-500 nm.The porous silicon-carbon composite negative electrode material has good electrochemical performance, and the method is simple in process, low in cost and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery negative electrode material preparation, and particularly relates to a porous silicon-carbon composite negative electrode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of electric vehicles and portable electronic devices, especially the demand of electric vehicles for higher cruising range, high specific energy battery systems gradually become a research hotspot. Graphite is the main negative electrode material for commercial application of lithium ion batteries at present, however, its theoretical capacity is low (372 mAh / g), which can only provide very limited energy density, and it is difficult to meet the current demand. Silicon is the most promising next-generation lithium ion battery negative electrode material, and its theoretical capacity at room temperature is as high as 3579 mAh / g, but the huge volume expansion (>300%) during lithium deintercalation limits its practical application.

[0003] In order to solve the above problems, researchers have proposed various solutions, mainly including material nanocrystallization, silicon structure design and preparation of silicon-carbon composite materials. Studies have shown that when the size of silicon particles is less than 150 nm, the volume expansion will not cause the particles to be crushed, and the damage to the electrode structure is smaller. The main mechanism of silicon-carbon composite forms, such as core-shell, yolk-shell or embedded structure, is to relieve the internal stress caused by volume expansion and improve the electrical conductivity of the material.

[0004] Patent CN110098380A mixes nano-silicon and etched carbon material by ball milling, embeds nano-silicon into the internal space of the carbon material pores, and then performs carbon coating treatment on the ball-milled sample to obtain a composite material. However, commercial nano-silicon particles are basically prepared by laser etching method, and the use of nano-silicon as raw material directly has high cost. In addition, the ball milling process is easy to cause oxidation and agglomeration of silicon particles, and it is difficult for nano-silicon to be uniformly distributed in the internal space of the carbon material pores, which will cause obvious deterioration of the electrochemical performance of the material.

[0005] Patent CN102214817A deposits a nano-silicon layer on the surface of the carbon material by a chemical vapor deposition process, and then further deposits a nano-carbon layer. However, during the thermal decomposition process of the silicon source precursor, it is difficult to control the agglomeration growth and furnace wall growth trend of silicon. In addition, the volume effect limiting ability of the nano-carbon layer to the silicon layer is limited, and it is difficult to maintain the stability of the electrochemical performance of the composite material. SUMMARY

[0006] The application provides a porous silicon-carbon composite negative electrode material and a preparation method thereof. The porous silicon-carbon composite negative electrode material provided by the application has good electrochemical performance, the method is simple, low in cost and suitable for industrial production.

[0007] In order to achieve the above object, the application provides a porous silicon-carbon composite negative electrode material, which takes porous carbon as a matrix, and nano-silicon is deposited in the pores on the outer surface of the porous carbon matrix; the particle size of the porous silicon-carbon composite negative electrode material is 5-50 μm, and the pore size of the pores on the porous carbon matrix is 50-500 nm.

[0008] The application provides a preparation method of the porous silicon-carbon composite negative electrode material, comprising the following steps:

[0009] 1) ultrasonic treatment of a metal salt solution and a carbon precursor to obtain a mixture;

[0010] 2) hydrothermal reaction and drying of the mixture in sequence to obtain a dried material;

[0011] 3) heating of the dried material to 400-1100 ℃ in a protective atmosphere for 1-6 h, closing the protective atmosphere, introducing a silicon source gas, and continuing to heat for 1-2 h, and then cooling to room temperature to obtain the porous silicon-carbon composite negative electrode material.

[0012] Preferably, the metal salt in step 1) is one or more of ferric chloride, cupric chloride, nickel chloride, zinc chloride, chromic chloride, cupric nitrate, nickel nitrate, chromic nitrate, ferric acetate and cupric acetate; the solvent for dissolving the metal salt is ionic water, ethanol, N,N-dimethylformamide, N,N-dimethylpyrrolidone, dimethyl sulfoxide or tetrahydrofuran; and the concentration of the metal salt in the metal salt solution is 0.01-1 g / mL.

[0013] Preferably, the carbon precursor in step 1) is one or more of glucose, sucrose, gelatin, starch, cellulose, lignin, carboxymethyl cellulose, glycine, folic acid, phenolic resin, furan resin and polyvinylpyridine.

[0014] Preferably, the mass ratio of the metal salt to the carbon precursor in step 1) is 1:5-1:50.

[0015] Preferably, the temperature of the hydrothermal reaction in step 2) is 60-200 ℃, and the time is 2-36 h; and the drying mode is natural drying, air drying, vacuum drying or freeze drying.

[0016] Preferably, the protective atmosphere in step 3) is nitrogen, hydrogen, argon or hydrogen-argon mixed gas.

[0017] Preferably, the silicon source in step 3) is one or more of monosilane, monochlorosilane, dichlorosilane, trichlorosilane, silicon chloride and silane.

[0018] Preferably, in step 3), the heating rate is 1-10℃ / min; the flow rate of the silicon source gas is 0.15L / min-15L / min.

[0019] Preferably, in step 3), after cooling to room temperature, a sieving treatment is further performed, and the mesh size of the sieve is 200-2500 mesh.

[0020] Compared with the prior art, the application has the following advantages and positive effects:

[0021] (1) In the application, the nano-silicon particles in the composite material are derived from chemical vapor deposition, which greatly reduces the material manufacturing cost compared with the industrial laser etching technology; and compared with high-energy ball milling, the oxidation of the particles can be avoided.

[0022] (2) In the application, by adjusting the reaction atmosphere, the synthesis of porous carbon and the deposition of nano-silicon can be realized in one step, and the preparation process is simple and easy to implement. The metal salt plays a dual role of carbon substrate activation and pore formation and silicon source catalytic decomposition, which is low in equipment corrosion and environmental pollution compared with KOH activator; on the other hand, after activation and pore formation, the residual metal compounds at the pore positions can be used as silicon source decomposition catalysts to directionally induce silicon to deposit inside the outer pores of the porous carbon.

[0023] (3) Through the catalyst, on the one hand, the energy barrier of silicon source decomposition can be reduced, thereby reducing the chemical vapor deposition reaction temperature; on the other hand, the catalyst directionally induces silicon to deposit inside the outer pores of the porous carbon substrate, suppresses the agglomeration and furnace wall deposition trend of the decomposed silicon, reduces the specific surface area of the porous carbon, and improves the first coulomb efficiency. Moreover, the silicon particles are confined inside the pores, which slows down the volume effect on the destruction of the electrode, and greatly improves the electrochemical stability of the material. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of the prepared porous silicon-carbon composite material;

[0025] Wherein 1 is the outer pore of the carbon substrate; 2 is the inner pore of the carbon substrate; 3 is the silicon nanoparticle; and 4 is the metal salt catalyst. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0027] The application provides a porous silicon-carbon composite negative electrode material, which is based on porous carbon, and nano-silicon is deposited in the pores on the outer surface of the porous carbon base; the particle size of the porous silicon-carbon composite negative electrode material is 5-50 mu m, and the pore size of the pores on the porous carbon base is 50-500 nm.

[0028] The porous silicon-carbon composite negative electrode material provided by the application has the nano-silicon deposited in the pores on the outer surface of the porous carbon base, which can reduce the specific area of the porous carbon and improve the initial coulombic efficiency; in addition, the silicon particles are confined in the interior of the pores, the confinement effect can relieve the internal stress caused by the volume expansion of silicon, slow down the damage of the volume effect to the electrode, and improve the stability of the electrode material; meanwhile, the pores in the interior of the porous carbon base are reserved, which can maximize the reservation of the lithium storage sites and give the composite material higher capacity; in addition, the direct contact of the high specific surface area porous carbon with the electrolyte can form irreversible SEI, causing the initial capacity loss, the outer pores are filled with silicon, and the interior pores are reserved, which can greatly relieve the direct contact with the electrolyte, thereby improving the initial efficiency of the material.

[0029] The application provides a preparation method of the porous silicon-carbon composite negative electrode material.

[0030] 1) ultrasonic treatment of a metal salt solution and a carbon precursor to obtain a mixture;

[0031] 2) sequentially performing hydrothermal reaction and drying on the mixture to obtain a dried material;

[0032] 3) transferring the dried material into a protective atmosphere, heating to 400-1100 DEG C for 1-6 h, closing the protective atmosphere, introducing a silicon source gas, continuing to heat for 1-2 h, and cooling to room temperature to obtain the porous silicon-carbon composite negative electrode material.

[0033] The present application carries out ultrasonic treatment on the metal salt solution and the carbon precursor to obtain a mixture. In the present application, the metal salt is preferably one or more of ferric chloride, cupric chloride, nickel chloride, zinc chloride, chromium chloride, copper nitrate, nickel nitrate, chromium nitrate, ferric acetate and cupric acetate; the solvent used to dissolve the metal salt is preferably ionic water, ethanol, N,N-dimethylformamide, N,N-dimethylpyrrolidone, dimethyl sulfoxide or tetrahydrofuran; and the concentration of the metal salt in the metal salt solution is preferably 0.01-1 g / mL. In the present application, the metal salt plays a role in activating the carbon substrate and creating pores on one hand, and the metal compound remaining at the position of the pores can act as a catalyst for the decomposition of silicon source and induce the deposition of silicon inside the pores of the porous carbon, thereby inhibiting the agglomeration of the decomposed silicon and the deposition of the silicon on the furnace wall, reducing the specific surface area of the porous carbon and improving the initial coulomb efficiency. In addition, the addition of the metal salt as a catalyst can also reduce the energy barrier of the decomposition of the silicon source, thereby reducing the chemical vapor deposition reaction temperature. In addition, the silicon particles are confined inside the pores, which slows down the damage of the volume effect to the electrode and greatly improves the electrochemical stability of the material.

[0034] In the present application, the carbon precursor is preferably one or more of glucose, sucrose, gelatin, starch, cellulose, lignin, carboxymethyl cellulose, glycine, folic acid, phenolic resin, furan resin and polyvinylpyridine. In the present application, the precursor contains abundant functional groups, which can be partially preserved after carbonization. The remaining heteroatoms and functional groups can act as lithium storage sites on one hand to improve the lithium storage capacity, and can improve the electrical conductivity of the material on the other hand. In the present application, the mass ratio of the metal salt to the carbon precursor is preferably 1:5-1:50. In the present application, the power of the ultrasonic treatment is 100-250 W and the time is 30-60 min. In the present application, the metal salt solution and the carbon precursor are mixed by ultrasonic treatment.

[0035] After obtaining the mixture, the present application carries out hydrothermal reaction and drying on the mixture in sequence to obtain a dried material. In the present application, the temperature of the hydrothermal reaction is preferably 60-200°C and the time is preferably 2-36 h. In the present application, the hydrothermal reaction makes the carbon precursor undergo two stages of "dissolution-recrystallization", which can reduce the agglomeration of components and improve the consistency of particles. More importantly, the surface of the carbon precursor after the hydrothermal reaction has abundant functional groups, which can effectively adsorb metal ions and thus facilitate the uniform dispersion of the metal catalyst.

[0036] In the present application, the drying method is preferably natural drying, blast drying, vacuum drying or freeze drying, more preferably vacuum drying or freeze drying. In the present application, the vacuum degree during vacuum drying is 0.01-0.1 MPa. During freeze drying, the temperature is -100-10°C and the vacuum degree is 1-50 Pa. In the present application, vacuum drying or freeze drying can maximize the avoidance of the pollution of the material by moisture, oxygen or other impurities in the environment.

[0037] After obtaining the dried material, the present application transfers the dried material into a protective atmosphere, heats it to 400-1100°C for 1-6 h, closes the protective atmosphere, introduces a silicon source gas, continues to heat for 1-2 h, cools to room temperature, and obtains a porous silicon-carbon composite negative electrode material. In the present application, the protective atmosphere is nitrogen, hydrogen, argon or a hydrogen-argon mixture. In the present application, the heating rate during heating is preferably 1-10°C / min. In the present application, the silicon source is preferably one or more of monosilane, monochlorosilane, dichlorosilane, trichlorosilane, silicon chloride and silane. In the present application, the flow rate during the introduction of the silicon source gas is 0.15 L / min-15 L / min. After cooling to room temperature, the present application preferably further performs a sieving treatment, and the mesh size of the sieve is preferably 200-2500 mesh. The present application preferably transfers the dried material into a CVD reaction furnace for treatment. The present application does not have special limitations on the specific structure of the CVD reaction furnace, and a commercially available product in the art can be used. For example, a tube furnace, a rotary furnace and a fluidized bed can be used, and the CVD reaction furnace preferably has double gas paths, one of which is used for introducing the protective atmosphere and the other of which is used for introducing the silicon source gas.

[0038] The biggest challenge in the preparation of silicon nanoparticles by the CVD process at present is that there is competition between the agglomeration and growth of product molecules and the adsorption of product molecules on the substrate, i.e. it is difficult to achieve the deposition of silicon only on the carbon substrate. Therefore, the introduction of a catalyst on the surface of the substrate can induce the deposition of the silicon source on the surface of the substrate. However, the volume expansion of the silicon layer coated on the surface during the electrochemical reaction is still unavoidable, resulting in the crushing and falling off of the material. In the present application, the metal salt not only acts as a catalyst, but also activates the pore formation. After pore formation, the metal salt remains in the pores, so that the deposition of silicon in the pores can be induced in a directional manner. The structure of the prepared porous silicon-carbon composite material is shown in Figure 1 .

[0039] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in conjunction with examples, but they should not be understood as limitations on the scope of protection of the present application.

[0040] Example 1

[0041] In a 100 mL hydrothermal kettle, 60 mL of deionized water was added, followed by 3 g of iron chloride and 60 g of glucose, and the mixture was stirred uniformly by ultrasonic (power 150 W, time 30 min). The hydrothermal kettle containing the mixture was transferred to an oven, and the hydrothermal reaction was carried out at 80°C for 10 h. The obtained reaction solution was transferred to a freeze dryer for freeze drying (temperature -50°C, vacuum degree 5 Pa, time 24 h). Then the dried sample was transferred to a CVD reaction furnace, the air in the furnace was pumped out by opening the vacuum pump, and the furnace chamber was cleaned by opening the argon valve, and the operation was repeated 3 times to exhaust the air in the reaction furnace. Argon was continuously introduced, and the temperature was increased to 600°C at a rate of 3°C / min, and after 1 h of heat preservation, the temperature was kept unchanged, and silane gas (silane gas is monochlorosilane, gas flow rate is 0.2 L / min) was introduced for 1 h, and the reaction was completed. After cooling to room temperature, the sample was taken out through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0042] Example 2

[0043] In a 100 mL hydrothermal kettle, 60 mL of deionized water was added, followed by 1 g of copper acetate and 50 g of gelatin, and the mixture was stirred uniformly by ultrasonic (power 150 W, time 45 min). The hydrothermal kettle containing the mixture was transferred to an oven, and the hydrothermal reaction was carried out at 120°C for 6 h. After the reaction was completed, the hydrothermal kettle was cooled to room temperature, and the obtained reaction solution was vacuum dried (temperature 25°C, vacuum degree 0.01 Mpa, time 24 h) to obtain dried material. The dried material was transferred to a CVD reaction furnace, the air in the furnace was pumped out by opening the vacuum pump, and the furnace chamber was cleaned by opening the argon valve, and the operation was repeated 3 times to exhaust the air in the reaction furnace. The temperature was increased to 500°C at a rate of 2°C / min, and after 1 h of heat preservation, the argon valve was closed, the temperature was kept unchanged, and monochlorosilane gas was introduced for 1 h (gas flow rate is 0.5 L / min) to complete the reaction. After cooling to room temperature, the sample was taken out through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0044] Example 3

[0045] In a 100 mL hydrothermal kettle, 60 mL of deionized water was added, followed by 6 g of nickel chloride and 60 g of sucrose, and the mixture was ultrasonically mixed (power 150 W, time 30 min). The hydrothermal kettle containing the mixture was transferred to an oven, and a hydrothermal reaction was performed at 150°C for 10 h. After the reaction, the hydrothermal kettle was cooled to room temperature, and the obtained reaction solution was transferred to a freeze dryer for freeze-drying (temperature -50°C, vacuum degree 5 Pa, time 24 h). The dried material was then transferred to a CVD reaction furnace, the vacuum pump was turned on to extract the air in the furnace, the argon valve was opened to clean the furnace chamber, and the operation was repeated three times to remove the air in the reaction furnace. The temperature was increased to 600°C at a rate of 3°C / min, and after 1 h of heat preservation, the argon valve was closed, the temperature was kept unchanged, and silane gas was introduced for 2 h (gas flow rate 1 L / min) to end the reaction. After cooling to room temperature, the product was taken out and passed through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0046] Example 4

[0047] In a 100 mL hydrothermal kettle, 60 mL of deionized water was added, followed by 3 g of chromium nitrate and 60 g of polyvinylpyridine, and the mixture was ultrasonically mixed (power 250 W, time 30 min). The hydrothermal kettle containing the mixture was transferred to an oven, and a hydrothermal reaction was performed at 200°C for 6 h. After the reaction, the hydrothermal kettle was cooled to room temperature, and the reaction solution was freeze-dried (temperature -50°C, vacuum degree 5 Pa, time 24 h). The dried material was then transferred to a CVD reaction furnace, the vacuum pump was turned on to extract the air in the furnace, the argon valve was opened to clean the furnace chamber, and the operation was repeated three times to remove the air in the reaction furnace. The temperature was increased to 800°C at a rate of 4°C / min, and after 1 h of heat preservation, the argon valve was closed, the temperature was kept unchanged, and trichlorosilane gas was introduced for 1 h (gas flow rate 1 L / min) to end the reaction. After cooling to room temperature, the product was taken out and passed through a 2000 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0048] Example 5

[0049] In a 100 mL hydrothermal kettle, 60 mL of deionized water was added, followed by 6 g of zinc chloride and 30 g of cellulose, and the mixture was uniformly mixed by ultrasonic stirring (power 100 W, time 60 min). The hydrothermal kettle containing the mixture was transferred to an oven, and a hydrothermal reaction was performed at 120°C for 5 h. After the reaction, the hydrothermal kettle was cooled to room temperature, and the obtained reaction solution was vacuum dried (temperature 25°C, vacuum degree 0.01 Mpa, time 24 h). Then, the dried material was transferred to a CVD reaction furnace, the air in the furnace was pumped out by opening the vacuum pump, and the furnace chamber was cleaned by opening the argon valve and repeating the operation three times to remove the air in the reaction furnace. The temperature was increased to 450°C at a rate of 2.5°C / min, and the argon valve was closed after 3 h of heat preservation. The temperature was kept unchanged, and silane gas was introduced for 1 h (gas flow rate 2 L / min) to end the reaction. After cooling to room temperature, the product was taken out and sieved through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0050] Comparative Example 1

[0051] The difference between Example 1 and Comparative Example 1 is that no iron chloride is added, and the specific operation is as follows:

[0052] In a 100 mL hydrothermal kettle, 60 mL of deionized water was added, followed by 60 g of glucose, and the mixture was uniformly mixed by ultrasonic stirring (power 150 W, time 30 min). The hydrothermal kettle containing the mixture was transferred to an oven, and a hydrothermal reaction was performed at 80°C for 10 h. The obtained reaction solution was transferred to a freeze dryer for freeze drying (temperature -50°C, vacuum degree 5 Pa, time 24 h). Then, the dried sample was transferred to a CVD reaction furnace, the air in the furnace was pumped out by opening the vacuum pump, and the furnace chamber was cleaned by opening the argon valve and repeating the operation three times to remove the air in the reaction furnace. Argon gas was continuously introduced, and the temperature was increased to 600°C at a rate of 3°C / min. After 1 h of heat preservation, the temperature was kept unchanged, and monochlorosilane gas was introduced (gas flow rate 0.2 L / min) for 1 h to end the reaction. After cooling to room temperature, the product was taken out and sieved through a 1250 mesh screen to obtain a silicon-carbon composite negative electrode material.

[0053] Comparative Example 2

[0054] The difference between Example 1 and Comparative Example 2 is that the silicon source gas is introduced at the same time as the protective atmosphere, and the specific operation is as follows:

[0055] In a hydrothermal kettle with a volume of 100 mL, 60 mL of deionized water was added, and then 3 g of iron chloride and 60 g of glucose were added. The mixture was stirred uniformly by ultrasonic stirring (power 150 W, time 30 min). The hydrothermal kettle containing the mixture was transferred to an oven, and the hydrothermal reaction was carried out at 80℃ for 10 h. The obtained reaction solution was transferred to a freeze dryer for freeze drying (temperature -50℃, vacuum degree 5 Pa, time 24 h). Then the dried sample was transferred to a CVD reaction furnace, the vacuum pump was opened to extract the air in the furnace, the argon valve was opened to clean the furnace cavity, and the operation was repeated 3 times to exhaust the air in the reaction furnace. Continuous argon was introduced, and the temperature was increased to 600℃ at a rate of 3℃ / min. The temperature was kept constant, and monochlorosilane silane gas was introduced (gas flow rate 0.2 L / min) for 1 h to complete the reaction. After cooling to room temperature, the sample was taken out through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0056] Comparative Example 3

[0057] The difference between Example 1 and Comparative Example 3 is that the amount of iron chloride is increased. The specific operation is as follows:

[0058] In a hydrothermal kettle with a volume of 100 mL, 60 mL of deionized water was added, and then 30 g of iron chloride and 60 g of glucose were added. The mixture was stirred uniformly by ultrasonic stirring (power 150 W, time 30 min). The hydrothermal kettle containing the mixture was transferred to an oven, and the hydrothermal reaction was carried out at 80℃ for 10 h. The obtained reaction solution was transferred to a freeze dryer for freeze drying (temperature -50℃, vacuum degree 5 Pa, time 24 h). Then the dried sample was transferred to a CVD reaction furnace, the vacuum pump was opened to extract the air in the furnace, the argon valve was opened to clean the furnace cavity, and the operation was repeated 3 times to exhaust the air in the reaction furnace. Continuous argon was introduced, and the temperature was increased to 600℃ at a rate of 3℃ / min. The temperature was kept constant, and monochlorosilane silane gas was introduced (gas flow rate 0.2 L / min) for 1 h to complete the reaction. After cooling to room temperature, the sample was taken out through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0059] Comparative Example 4

[0060] The method of Example 1 in patent CN114956046B was used for preparation, and the specific operation was as follows:

[0061] The 4,4'-dipyridine and copper tetrafluoroborate with a molar ratio of 2:1 were dissolved in equal volumes of methanol solvent and water, respectively, and then the pyridine solution was added dropwise into the metal salt solution and uniformly mixed. After stirring at room temperature for 4 hours, the crude product was filtered and dried to obtain a metal-organic framework material as a porous carbon substrate, which was placed in a reactor. Dimethylvinylchlorosilane and protective argon gas were introduced into the reactor to deposit in a vapor phase (600°C, 3h), and the nano-silicon deposition porous carbon substrate was obtained by natural cooling, i.e. a coating structure wrapped by the metal-organic framework material and the nano-silicon material.

[0062] Comparative Example 5

[0063] The difference between Example 1 and Comparative Example 5 is that no hydrothermal process is performed, and the specific operation is as follows:

[0064] In a hydrothermal kettle with a volume of 100 mL, 60 mL of deionized water was added, followed by 3 g of iron chloride and 60 g of glucose, and the mixture was uniformly stirred by ultrasonic stirring (power 150 W, time 30 min). The above mixture was transferred to a CVD reaction furnace, the vacuum pump was opened to extract the air in the furnace, and the argon valve was opened to clean the furnace cavity, which was repeated 3 times to exhaust the air in the reaction furnace. Argon was continuously introduced, and the temperature was increased to 600°C at a rate of 3°C / min, and after 1h of heat preservation, the temperature was kept unchanged, and silane gas (silane gas was chlorosilane, and the gas flow rate was 0.2 L / min) was introduced for 1h, and the reaction was completed. After cooling to room temperature, it was taken out through a 1250 mesh screen to obtain a porous silicon-carbon composite negative electrode material.

[0065] Performance test

[0066] The porous silicon-carbon composite material obtained in the examples and comparative examples was used as the negative electrode to prepare a battery. The negative electrode material, conductive carbon black (Super P, conductive agent), carboxymethyl cellulose (CMC, thickening agent), and styrene-butadiene rubber (SBR, binder) were mixed uniformly in a ratio of 94:2:2:2 to form a slurry, which was uniformly coated on a copper foil current collector, and then dried to obtain a negative electrode sheet. A coin cell battery was assembled in a glove box, and a metal lithium sheet was selected as the counter electrode, a polypropylene microporous membrane was used as the separator, and a 1M lithium hexafluorophosphate electrolyte (solvent was a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate) was used as the electrolyte.

[0067] The assembled button cell was tested by constant current charge-discharge test, the test current was 0.5A / g, the test voltage window was 0.01-1.5V, and the test results were shown in Table 1. The test results showed that the comparative example 1 did not add metal salt catalyst ferric chloride, the carbon substrate did not form a hole structure, the CVD silicon particles were only attached to the surface of the substrate, thus showing poor cycle performance, and the capacity retention rate was only 87% after 50 cycles. The comparative example 2 simultaneously passed in argon and silicon source gas, the substrate pore forming and silicon deposition process were carried out at the same time, which caused the silicon nanoparticles to be partially deposited on the surface of the porous carbon, and the exposed part of the outer hole was slightly worse than the comparative example 1 in the first efficiency and cycle stability. In the comparative example 3, the mass ratio of metal salt catalyst to carbon substrate was 1:2, the excessive metal salt caused excessive pore forming, which led to a large number of holes exposed to the electrolyte, and on the other hand, the presence of metal salt increased the mass burden of the negative electrode material, which caused the decrease of the specific capacity. In the comparative example 4, a large amount of metal salt catalyst was used to induce the nano-silicon particles on the surface of the carbon substrate, thus showing poor electrochemical performance compared with the present application. In the comparative example 5, the hydrothermal process was not carried out, the metal salt was not uniformly distributed in the carbon precursor, which caused the prepared carbon substrate to have inconsistent hole size, thus the prepared composite material was unstable in the electrochemical reaction process.

[0068] Table 1 battery performance

[0069]

[0070]

[0071] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A method for preparing a porous silicon-carbon composite negative electrode material, characterized by, The preparation product of the preparation method is a porous silicon-carbon composite negative electrode material, the porous silicon-carbon composite negative electrode material takes porous carbon as a matrix, and nano-silicon is deposited in the holes on the outer surface of the porous carbon matrix; the particle size of the porous silicon-carbon composite negative electrode material is 5-50 μm, and the pore size of the holes on the porous carbon matrix is 50-500 nm. The preparation method comprises the following steps: 1) ultrasonic treatment of a metal salt solution and a carbon precursor to obtain a mixture; 2) sequential hydrothermal reaction and drying of the mixture to obtain a dried material; 3) heating of the dried material to 400-1100 ℃ in a protective atmosphere for 1-6 h, closing the protective atmosphere, and then introducing a silicon source gas to continue the heating for 1-2 h, and then cooling to room temperature to obtain the porous silicon-carbon composite negative electrode material; In step 1), the carbon precursor is one or more of glucose, sucrose, gelatin, starch, cellulose, lignin, carboxymethyl cellulose, glycine, folic acid, phenolic resin, furan resin and polyvinylpyridine; and the metal salt is one or more of ferric chloride, cupric chloride, nickel chloride, zinc chloride, chromium chloride, cupric nitrate, nickel nitrate, chromium nitrate, ferric acetate and cupric acetate.

2. The production method according to claim 1, characterized by, In step 1), the solvent for dissolving the metal salt is ionized water, ethanol, N,N-dimethylformamide, N,N-dimethylpyrrolidone, dimethyl sulfoxide or tetrahydrofuran; and the concentration of the metal salt in the metal salt solution is 0.01-1 g / mL.

3. The preparation method according to claim 1, characterized in that, In step 1), the mass ratio of the metal salt to the carbon precursor is 1:5-1:

50.

4. The method of claim 1, wherein, In step 2), the temperature of the hydrothermal reaction is 60-200 ℃, and the time is 2-36 h; and the drying mode is natural drying, air drying, vacuum drying or freeze drying.

5. The preparation method according to claim 1, characterized in that, In step 3), the protective atmosphere is nitrogen, hydrogen, argon or hydrogen-argon mixed gas.

6. The method of claim 1, wherein, In step 3), the silicon source is one or more of monosilane, monochlorosilane, dichlorosilane, trichlorosilane, silicon chloride and silane.

7. The preparation method according to claim 1, characterized in that, In step 3), the heating rate during heating is 1-10 ℃ / min; and the flow rate during the introduction of the silicon source gas is 0.15 L / min-15 L / min.

8. The method of claim 1, wherein, In step 3), after cooling to room temperature, the material is further sieved, and the mesh size of the sieve is 200-2500 mesh.

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