Nano silicon-carbon composite material, preparation method thereof and lithium ion battery

Abstract

The invention provides a nanometer silicon-carbon composite material, a preparation method thereof and a lithium ion battery. The composite material comprises nanometer silicon particles, a first carbon matrix and a second carbon layer. The preparation method of the nano silicon-carbon composite material comprises the following steps: (1) contacting a porous carbon material with a silicon source-containing solution to obtain a material A; (2) uniformly mixing the material A with a reducing agent-containing solution, and treating to obtain a material B; (3) introducing a treating agent into the material B to prepare a silicon-carbon composite material precursor; (4) uniformly mixing the silicon-carbon composite material precursor with the carbon material precursor C to obtain a material D; and (5) in the presence of the carbon material precursor E, carrying out aging treatment on the material D, and then drying and pyrolyzing to obtain the silicon-carbon composite material. According to the preparation method, the nano silicon-carbon composite material with high specific capacity and long cycle stability can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and relates to a lithium-ion battery negative electrode material and a preparation method thereof, and in particular to a nano-silicon-carbon composite material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The rapid development of new energy electric vehicle technology requires high-quality specific energy for the battery system within its three-electric system (battery, motor, and electronic control) to achieve long driving range. In current power battery development systems, the use of high-capacity positive and negative electrode materials is the material foundation for achieving high specific energy for power batteries. The widely used graphite negative electrode material currently has a specific capacity exceeding 360 mAh / g, approaching its theoretical specific capacity of 372 mAh / g.

[0003] To achieve higher specific capacities, there is an urgent need to develop a new generation of anode materials with high lithium storage capacity. Among the numerous high-capacity anode material systems, silicon-based anode materials are gradually becoming the next generation of power lithium-ion battery anode materials that can replace graphite due to their high theoretical specific capacity (4200mAh / g), abundant content, and slightly higher lithium insertion potential than graphite, resulting in a lower risk of rapid lithium deposition. Currently, companies including Tesla, CATL, Weilan New Energy Technology, and Huawei have developed silicon-based anode batteries and implemented application demonstrations in electric vehicles, mobile phones, and other fields.

[0004] At present, silicon-based negative electrode materials mainly include silicon oxide, silicon carbon, silicon nanowires and porous micron silicon systems. Among them, silicon oxide and silicon carbon systems have comprehensive advantages in price, specific capacity, cycle stability and other aspects, and have become the next generation of preferred negative electrode materials for power batteries to replace graphite negative electrodes. Conventional silicon carbon is prepared by crushing to obtain nano-silicon particles from crystalline silicon materials, and then compounding with carbon materials through a secondary coating method. To achieve nano-size silicon particles, not only high-performance equipment and energy consumption are required, but also when silicon particles reach a critical size of 80nm or less for volume expansion, they are more likely to agglomerate, making it difficult to achieve uniform compounding with carbon materials in an ideal state. Therefore, the cycle stability of various current silicon carbon technologies is somewhat different from the practical level requirements. Due to its unique lithium ion process, silicon oxide materials will have a large irreversible capacity during the first lithium ion, and the development leads to the loss of active lithium in the positive electrode.

[0005] CN114188512A discloses a silicon-carbon composite material, its preparation method, and application. Silicon particles are mixed with carbon particles to obtain silicon-carbon mixed particles, and the mixed particles are coated with a graphite phase, C3N4, to prepare a carbon-coated silicon-carbon composite material. The carbon coating layer simultaneously achieves the composite of silicon and graphite materials and the surface coating of the composite material. However, because the graphite and silicon are only physically mixed, the graphite does not limit the structural changes of silicon during the charge and discharge process. The cyclic stability of the composite material is difficult to effectively guarantee. Only the capacity retention rate (85% to 95.3%) after 100 cycles is given, and the performance after longer cycles is not given. Summary of the Invention

[0006] To address the challenges of existing technologies, this invention breaks through the traditional approach to preparing silicon-carbon materials. By adopting a "small-to-large" approach, the silicon-carbon composite is prepared by in-situ reduction within the mesoporous structure of the carbon material. Simultaneously, vapor deposition and in-situ polymerization are employed to coat the silicon-carbon composite with a nanocarbon layer. By leveraging the confinement and support properties of the carbon material's mesopores, along with the secondary coating of the heterogeneous carbon layer, a silicon-carbon composite with high specific capacity and long-term cycling stability is achieved.

[0007] The first aspect of the present invention provides a nano-silicon-carbon composite material, which includes nano-silicon particles, a first carbon matrix and a second carbon layer; the nano-silicon particles are embedded in the pore structure of the first carbon matrix, and the second carbon layer is wrapped around the outer surface of the first carbon matrix. The first carbon matrix is ​​porous carbon, and the second carbon layer is an amorphous carbon layer.

[0008] Furthermore, as a specific embodiment, the first carbon substrate is porous carbon with a specific surface area of ​​200 to 3000 m 2 / g, with a multi-level pore structure of micropores-mesopores-macropores, in which the mesopores are concentrated in the range of 2 to 10 nm.

[0009] Furthermore, as a specific embodiment, based on the weight of the nano-silicon-carbon composite material, the silicon mass content is 10% to 70%, preferably 30% to 60%; the silicon particle size is 2 to 10 nm, preferably 3 to 5 nm, and the silicon particles are uniformly distributed in the pore structure of the first carbon matrix in a mosaic form.

[0010] Furthermore, as a specific embodiment, the second carbon layer has a thickness of 2 to 3 nm and is uniformly coated on the outer surface of the first carbon matrix.

[0011] Furthermore, the specific capacity of the nano-silicon-carbon composite material is 600 to 2000 mAh / g.

[0012] A second aspect of the present invention provides a method for preparing a nano-silicon-carbon composite material, comprising the following steps:

[0013] (1) fully contacting the porous carbon material with a silicon source solution under contact conditions to obtain material A;

[0014] (2) Under an inert atmosphere, the material A obtained in step (1) is mixed with a solution containing a reducing agent to obtain material B;

[0015] (3) introducing a treating agent into the material B obtained in step (2), and then washing and drying to obtain a silicon-carbon composite material precursor;

[0016] (4) uniformly mixing the silicon-carbon composite material precursor obtained in step (3) with the carbon material precursor C to obtain material D;

[0017] (5) In the presence of a carbon material precursor E, the material D obtained in step (4) is aged, and then dried and pyrolyzed to obtain a silicon-carbon composite material.

[0018] Furthermore, as a specific embodiment, the porous carbon material in step (1) has the following pore structure characteristics: containing micropores less than 2nm and mesopores of 2-10nm, and the specific surface area of ​​the porous carbon is 200-3000m 2 / g, pore volume of 0.5~3.0cm 3 / g, of which the pore volume of 2-10 nm mesopores is 0.45-2.8 cm 3 / g.

[0019] Furthermore, as a specific embodiment, the porous carbon in step (1) can be derived from one or more composite compositions of alkali-activated resin-based porous carbon, petroleum coke-based porous carbon, biomass-based porous carbon, porous graphene, carbon nanotubes, activated acetylene black, activated carbon fibers, etc.

[0020] Furthermore, as a specific embodiment, the silicon source solution in step (1) includes a silicon source and an organic solvent, wherein the silicon source can be selected from one or more of methyl orthosilicate, tetraethyl orthosilicate, methyltrimethoxysilane, silicon tetrachloride, trichlorosilane, trimethylchlorosilane, phenylchlorosilane, methylphenylchlorosilane, methylvinylchlorosilane, and vinyltrichlorosilane, preferably one or more of trichlorosilane, trimethylchlorosilane, silicon tetrachloride, and vinyltrichlorosilane; and the organic solvent is one or more of toluene, benzene, tetrahydrofuran, and diethyl ether.

[0021] Furthermore, as a specific embodiment, the reducing agent solution in step (2) comprises a reducing agent and an organic solvent, wherein the reducing agent used can be selected from one or more of sodium 2-hydrogen bis(dimethoxyethoxy)aluminate, lithium tri(tert-butoxy)aluminum hydride, diisobutylaluminum hydride, lithium aluminum hydride, etc., and the organic solvent is one or more of toluene, benzene, tetrahydrofuran, and diethyl ether. The concentration of the reducing agent solution is 1 to 15 mol / L, preferably 5 to 10 mol / L.

[0022] Furthermore, as a specific embodiment, the molar ratio of the reducing agent to the silicon source is 5 to 1:1, preferably 2 to 1:1.

[0023] Furthermore, as a specific embodiment, the inert atmosphere in step (2) can be one or more of nitrogen, helium, neon, argon, krypton, and xenon.

[0024] Furthermore, as a specific implementation method, the processing time in step (2) is 3 to 10 hours.

[0025] Furthermore, as a specific embodiment, the treating agent in step (3) is one or more of a mixed solution of ethyl acetate and toluene (volume ratio 1-3:1), anhydrous methanol, and a sodium hydroxide aqueous solution (preferably with a mass concentration of 5% to 20%).

[0026] Furthermore, as a specific embodiment, the molar ratio of the treating agent to the reducing agent in step (3) is 1 to 15:1, preferably 3 to 10:1.

[0027] Furthermore, as a specific embodiment, the washing in step (3) is generally performed by first washing with an alcohol solvent and then washing with water; the alcohol solvent can generally be ethanol.

[0028] Furthermore, as a specific embodiment, the drying temperature in step (3) is 50-100° C., and the drying time is 6-24 hours.

[0029] Furthermore, as a specific embodiment, the treatment agent can be introduced in step (3) by spraying the treatment agent into the material B obtained in step (2) in the form of ultrasonic spray.

[0030] Furthermore, as a specific embodiment, the carbon material precursor C in step (4) can be selected from asphalt or phenolic compounds, and the asphalt can be at least one of petroleum-based asphalt and coal-based asphalt; the softening point of asphalt is generally 75-120°C; the asphalt is heated to a molten state when used; the phenolic compound can be at least one of resorcinol, phenol, phloroglucinol, hydroquinone, cresol, aminophenol, nitrophenol, naphthol, and chlorophenol, preferably at least one of resorcinol, phenol, phloroglucinol, and hydroquinone; the phenolic compound needs to be dissolved in a solvent when used, and the solvent can be an ethanol aqueous solution with a solution concentration of 0.5-5 mol / L.

[0031] Furthermore, as a specific embodiment, the carbon material precursor E in step (5) is an aldehyde compound, and the aldehyde compound can be specifically selected from at least one of formaldehyde, acetaldehyde, adipaldehyde, valeraldehyde, terephthalaldehyde, lauryl aldehyde (dodecanal), tridecanal, myristic aldehyde (tetradecanal), benzaldehyde, phenylacetaldehyde, phenylpropionic aldehyde, cinnamaldehyde, lily-of-the-valley aldehyde, vanillin, and ethyl vanillin, preferably at least one of formaldehyde, acetaldehyde, adipaldehyde, valeraldehyde, terephthalaldehyde, benzaldehyde, and phenylacetaldehyde.

[0032] Furthermore, as a specific embodiment, the molar ratio of the carbon material precursor E to the carbon material precursor C is 1 to 10:1, preferably 2 to 6:1.

[0033] Furthermore, as a specific embodiment, the aging treatment in step (5) is carried out under closed conditions, the aging temperature is 50 to 120° C., and the aging time is 2 to 48 hours.

[0034] Furthermore, as a specific embodiment, the drying temperature in step (5) is 60-120°C.

[0035] Furthermore, as a specific embodiment, the heat treatment in step (5) is carried out in the presence of an inert atmosphere, and the pyrolysis temperature is 800-1200°C; the inert atmosphere can be one or more of nitrogen, nitrogen, helium, neon, argon, krypton, and xenon.

[0036] The third aspect of the present invention provides a nano-silicon-carbon composite material obtained by the above preparation method.

[0037] A fourth aspect of the present invention provides a lithium-ion battery, comprising the nano-silicon-carbon composite material described above.

[0038] Compared with the prior art, the nano-silicon-carbon composite material, its preparation method, and lithium-ion battery provided by the present invention have one or a combination of the following technical effects:

[0039] The nanoscale carbon-coated silicon-carbon composite material provided by the present invention has silicon particles with a size of 2 to 10 nm and is confined in the pore structure of the carbon matrix. By using nano-sized silicon material as a lithium storage active material, the discharge specific capacity of the silicon-carbon composite material can be significantly improved, and the optimal discharge specific capacity can reach 2000 mAh / g; by coating with a heterogeneous structure second carbon layer, the bonding stability of the silicon-carbon composite material is further improved, thereby improving the electrochemical cycle stability performance of the silicon-carbon composite material.

[0040] In the preparation method of nano-scale carbon-coated silicon-carbon composite material provided by the present invention, the silicon loading and the nano-size of silicon in the silicon-carbon composite material are regulated by regulating the pore structure of the carbon material; the in-situ reduction technology is used to regulate the compatibility of the silicon source precursor and the type of reducing agent, thereby achieving high reliability in preparing nano-sized active silicon, thereby achieving high discharge specific capacity of silicon.

[0041] In the method for preparing nano-scale carbon-coated silicon-carbon composite materials provided by the present invention, a combination of physical confinement and chemical reduction is adopted, and safe silicon-based and carbon-based precursors are used to reduce the operating conditions requirements for process equipment, thereby having significant low cost and high safety characteristics. The raw materials used are safer than the raw materials such as silane gas used in the current various chemical vapor deposition methods for preparing silicon-carbon materials, and a quasi-liquid phase uniform reaction environment is adopted to obtain a highly uniform material structure. The present invention has simple structural requirements for the equipment and high safety of the material synthesis process. Combining the above two aspects, the material prepared by the present invention has lower cost and therefore has higher comprehensive economic efficiency.

[0042] In the preparation method of nano-scale carbon-coated silicon-carbon composite materials provided by the present invention, an in-situ preparation technology of nano-silicon with confined mesopore size is proposed, which can effectively ensure that the silicon particles are smaller than the critical size of the lithium complex reaction, thereby obtaining reliable cycle stability performance and solving the problem of poor cycle stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the SEM image of the silicon-carbon composite material prepared in Example 1.

[0044] Figure 2 This is the first charge and discharge curve of the silicon-carbon composite material obtained in Example 1.

[0045] Figure 3 1 is the cyclic stability curve of the silicon-carbon composite material obtained in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0046] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any form.

[0047] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0048] In this document, unless otherwise expressly stated, all percentages and contents are based on mass.

[0049] In this paper, the specific surface area and pore size distribution curves of the samples were analyzed using nitrogen adsorption-desorption curves using a QuantaChrome Autosorb IQ2 microporous physical adsorption instrument. The sample treatment conditions were: the material was treated at 300°C for 6 hours, and the nitrogen adsorption isotherm was measured at 77K. The total specific surface area was calculated using the BET equation from the nitrogen adsorption isotherm within the relative pressure range (P / P0) = 0.05 to 0.3. The micropore specific surface area was calculated using the T-plot method within the relative pressure range (P / P0) = 0.2 to 0.8. The total pore volume was calculated as the volume corresponding to the adsorption amount at a relative pressure close to 1. The mesopore diameter was calculated using the BJH method, and the micropore diameter was calculated using the DFT method.

[0050] In this article, the electrochemical testing method is as follows: a 2016-type button battery shell is used to stack the working electrode (silicon-based negative electrode prepared in the embodiment of this application), the diaphragm (Celgare2400), and the counter electrode (80μm metal lithium sheet) in sequence, and the thickness is matched with a stainless steel sheet so that the total thickness of the battery contents is 1200-1300μm. The battery is sealed with a small hydraulic button battery packaging machine. All charge and discharge tests are carried out on a CT2001A Land battery testing system. The charge and discharge specific capacity is calculated based on the mass of the active material in the electrode.

[0051] Example 1

[0052] The specific surface area is 1700m 2 / g, and the mesopore volume is 2.7 cm 3 / g, 0.5g of petroleum coke-based porous carbon with a mesopore size distribution of 5 to 10nm, take 2g of methyltrimethoxysilane, dissolve it in 0.5ml of tetrahydrofuran, and impregnate it into the porous carbon; then, under a nitrogen atmosphere, take 10g of 2-hydrogen bis(dimethoxyethoxy) sodium aluminate and dissolve it in 5ml of toluene to prepare it as a reducing agent, take 1ml of the reducing agent solution and impregnate it into the above-mentioned porous carbon containing the silicon source, and let it stand for 4h. Take 2ml of ethyl acetate and 1ml of toluene to prepare a mixed solution, and use ultrasonic spray to spray 3ml of the above mixed solution onto the surface of the porous carbon after standing for 4h. The obtained material is washed with ethanol and water, and then dried in an 80℃ oven for 24h to obtain a primary product of silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, mix 0.15g of molten petroleum-based coated asphalt with 1g of the primary silicon-carbon composite material, and place it in polytetrafluoroethylene container A. Take 1g of adipaldehyde and place it in polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed inside container B. Container B is sealed and placed in a 100°C oven for aging for 24 hours. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 900°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 62wt%.

[0053] A nano-silicon-carbon composite material, used as the active material, was mixed with acetylene black and a binder (PVDF) in a mass ratio of 9:0.5:0.5. The mixture was then ground in a mortar. N-methylpyrrolidone was added as a solvent, and the mixture was thoroughly ground into a uniform slurry. This slurry was then applied to a coated copper foil with a spatula to create a silicon-based anode. At a current density of 100 mA / g, the device achieved a discharge capacity of 1801 mAh / g, an initial efficiency of 89%, and a capacity retention of 82% after 700 cycles.

[0054] Example 2

[0055] The specific surface area is 1800m 2 / g, and the mesopore volume is 2.8cm 3 / g, 0.5g of petroleum coke-based porous carbon with a mesopore size distribution of 3 to 10nm, 1g of silicon tetrachloride is dissolved in 1.5ml of toluene, and impregnated into the porous carbon; then, under a nitrogen atmosphere, 15g of diisobutylaluminum hydride is dissolved in 10ml of toluene as a reducing agent, 1ml of the reducing agent solution is impregnated into the above-mentioned porous carbon containing the silicon source, and allowed to stand for 4 hours. Take 2ml of anhydrous methanol and spray it onto the surface of the porous carbon after standing for 4 hours by ultrasonic spraying. The obtained material is washed with ethanol and water, and then dried in an 80°C oven for 24 hours to obtain a primary product of the silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, dissolve 0.5g of phloroglucinol in 5ml of a mixed solution of ethanol and water, take 1ml of the phloroglucinol solution and evenly mix it with 1g of the primary silicon-carbon composite material, and place it in polytetrafluoroethylene container A. Take 5g of formaldehyde and place it in polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed in container B. Container B is sealed and placed in a 90°C oven for aging for 24 hours. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 1000°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 60%.

[0056] The silicon-based negative electrode material was prepared in the same manner as in Example 1. It was used as the active material to prepare a silicon-based negative electrode. At a current density of 100 mA / g, the discharge specific capacity was 1501 mAh / g, the first efficiency was 89%, and the capacity retention rate was 83% after 500 cycles.

[0057] Example 3

[0058] The specific surface area is selected as 900m 2 / g, and the mesopore volume is 1.2cm 3 / g, 0.5g of petroleum coke-based porous carbon with a mesopore size distribution of 3-5nm, 0.5g of trimethylchlorosilane was dissolved in 0.5ml of tetrahydrofuran and impregnated into the porous carbon; then, under a nitrogen atmosphere, 5g of lithium aluminum hydride was dissolved in 10ml of toluene as a reducing agent, 1ml of the reducing agent solution was impregnated into the above-mentioned porous carbon containing the silicon source, and the reaction was allowed to stand for 5h. 2ml of ethyl acetate and 1ml of toluene were prepared into a mixed solution, and 3ml of the mixed solution was sprayed onto the surface of the porous carbon after standing for 5h by ultrasonic spraying. The obtained material was washed with ethanol and water, and then dried in an oven at 120℃ for 24h to obtain a primary product of silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, dissolve 0.5g of hydroquinone in a mixed solution of 5ml of ethanol and water, take 1ml of the hydroquinone solution and evenly mix it with 1g of the primary silicon-carbon composite material, and place it in polytetrafluoroethylene container A. Take 5g of adipaldehyde and place it in polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed in container B. Container B is sealed and placed in a 100°C oven for aging for 48 hours. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 900°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 54%.

[0059] The silicon-based negative electrode material was prepared in the same manner as in Example 1. It was used as the active material to prepare a silicon-based negative electrode. At a current density of 100 mA / g, the discharge specific capacity was 850 mAh / g, the first efficiency was 91%, and the capacity retention rate was 88% after 500 cycles.

[0060] Example 4

[0061] Take 0.5g of activated acetylene black (specific surface area 350m 2 / g, pore volume 0.7cm 3 / g), take 1g of phenylchlorosilane and dissolve it in 0.5ml of ether, and immerse it in acetylene black; then, under an inert atmosphere, take 4g of lithium tri(tert-butoxy)aluminum hydride and dissolve it in 5ml of toluene to prepare a reducing agent, take 0.5ml of the reducing agent solution and immerse it in the acetylene black containing the silicon source, and let it react for 6 hours. Take 10wt% sodium hydroxide solution and spray 4ml of it onto the surface of the material after standing and reacting for 6 hours by ultrasonic spraying. The obtained material is washed with ethanol and water, and then dried in an 80℃ oven for 24 hours to obtain a primary silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, dissolve 0.5g of phenol in a mixed solution of 5ml of ethanol and water, take 1ml of the phenol solution and evenly mix it with 1g of the primary silicon-carbon composite material, and place it in polytetrafluoroethylene container A. Take 5g of benzaldehyde and place it in polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed in container B. Container B is sealed and placed in a 90°C oven for aging for 24 hours. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 900°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 41%.

[0062] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 720 mAh / g at a current density of 100 mA / g, an initial efficiency of 93%, and a capacity retention rate of 88% after 2000 cycles.

[0063] Example 5

[0064] Take 0.5g carbon nanotubes (specific surface area 1230m 2 / g, pore volume 1.1cm 3 / g), take 1g of methylvinyldichlorosilane and mix it with 0.5ml of ether, and impregnate it into the carbon nanotubes; then, under an inert atmosphere, take 1g of diisobutylaluminum hydride and mix it with 10ml of toluene to prepare a reducing agent, take 1ml of the reducing agent solution and impregnate it into the above-mentioned carbon nanotubes carrying the silicon source, and let it react for 5 hours. Take 1ml of ethyl acetate and 1ml of toluene, and then further mix it with 2ml of anhydrous methanol, and use ultrasonic spray to spray 4ml of the above-mentioned mixed solution onto the surface of the composite material after standing for 5 hours. The obtained material is washed with ethanol and water, and then dried in an 80°C oven for 12 hours to obtain a primary product of the silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, dissolve 0.5g of naphthol in 5ml of a mixed solution of ethanol and water (1:1, volume ratio), take 1ml of the naphthol solution and evenly mix it with 1g of the primary silicon-carbon composite material, and place it in a polytetrafluoroethylene container A. Take 3g of tridecaldehyde and place it in a polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed in container B. Container B is sealed and placed in a 100°C oven for aging for 24h. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 850°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 40%.

[0065] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 650 mAh / g at a current density of 100 mA / g, an initial efficiency of 92%, and a capacity retention rate of 82% after 2000 cycles.

[0066] Example 6

[0067] Take 0.25g of porous graphene (specific surface area 1430m 2 / g, pore volume 1.2cm 3 / g), take 1g of vinyltrichlorosilane and mix it with 0.5ml of toluene, and impregnate it into the porous graphene; then, under an inert atmosphere, take 1g of diisobutylaluminum hydride and mix it with 10ml of toluene to prepare a reducing agent, take 1ml of the reducing agent solution and impregnate it into the above-mentioned porous graphene containing the silicon source, and let it stand for 6 hours. Take 4ml of anhydrous methanol and spray it onto the surface of the composite material after standing for 6 hours by ultrasonic spraying. The obtained material is washed with ethanol and water, and then dried in an oven at 100°C for 24 hours to obtain a primary product of the silicon-carbon composite material. Take 1g of the primary product of the silicon-carbon composite material, dissolve 0.5g of cresol in a mixed solution of 5ml of ethanol and water (1:1, volume ratio), take 1ml of the cresol solution and evenly mix it with 1g of the primary product of the silicon-carbon composite material, and place it in a polytetrafluoroethylene container A, take 5g of tridecaldehyde, place it in a polytetrafluoroethylene container B, and place the A container containing the primary product of the silicon-carbon composite material in the container B, seal the container B, and place it in a 100°C oven for aging for 12h. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 900°C under argon protection to finally obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 39wt%.

[0068] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 620 mAh / g at a current density of 100 mA / g, an initial efficiency of 91%, and a capacity retention rate of 81% after 1500 cycles.

[0069] Comparative Example 1

[0070] Take 0.5g of 100nm nano-silicon and mix it with 0.5g of graphite, then take 0.1g of coated asphalt and mix it with the above materials under an inert atmosphere at 300℃, then heat it to 450℃, heat treat it for 2h, and cool it to room temperature; take out the sample and pyrolyze it at 1300℃ in a nitrogen atmosphere for 2h to obtain a carbon-coated silicon-carbon composite material with a silicon content of 48wt%.

[0071] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 620 mAh / g at a current density of 100 mA / g, an initial efficiency of 85%, and a capacity retention rate of 60% after 250 cycles.

[0072] Comparative Example 2

[0073] The specific surface area is selected as 150m 2 / g, pore volume of 0.3cm 3 / g, 0.5g of phenolic resin-based macroporous carbon with a pore size distribution of 200-300nm, 0.5g of trimethylchlorosilane is dissolved in 0.5ml of tetrahydrofuran and impregnated into the porous carbon; then, under a nitrogen atmosphere, 5g of lithium aluminum hydride is dissolved in 10ml of toluene as a reducing agent, 1ml of the reducing agent solution is impregnated into the above-mentioned porous carbon containing the silicon source, and the reaction is allowed to stand for 5h. 2ml of ethyl acetate and 1ml of toluene are prepared into a mixed solution, and 3ml of the mixed solution is sprayed onto the surface of the porous carbon after standing for 5h by ultrasonic spraying. The obtained material is washed with ethanol and water, and then dried in an oven at 120℃ for 24h to obtain a primary product of silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, dissolve 0.5g of hydroquinone in a mixed solution of 5ml of ethanol and water, take 1ml of the hydroquinone solution and evenly mix it with 1g of the primary silicon-carbon composite material, and place it in polytetrafluoroethylene container A. Take 5g of adipaldehyde and place it in polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed in container B. Container B is sealed and placed in a 100°C oven for aging for 48 hours. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 900°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 54%.

[0074] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 450 mAh / g at a current density of 100 mA / g, an initial efficiency of 83%, and a capacity retention rate of 45% after 100 cycles.

[0075] Comparative Example 3

[0076] Take 0.25g of porous graphene (specific surface area 1430m 2 / g, pore volume 1.2cm 3 / g), take 1g of vinyltrichlorosilane and mix it with 0.5ml of toluene, and impregnate it into the porous graphene; then, under an inert atmosphere, take 1g of sodium borohydride and mix it with 10ml of anhydrous methanol to prepare a reducing agent, take 1ml of the reducing agent solution and impregnate it into the porous graphene containing the silicon source, and let it react for 6 hours. The obtained material is washed with ethanol and water, and then dried in an oven at 100℃ for 24 hours to obtain a silicon-carbon composite material primary product. Take 1g of the silicon-carbon composite material primary product, dissolve 0.5g of cresol in a mixed solution of 5ml of ethanol and water (1:1, volume ratio), take 1ml of the cresol solution and mix it evenly with 1g of the silicon-carbon composite material primary product, and place it in a polytetrafluoroethylene container A, take 5g of tridecaldehyde, place it in a polytetrafluoroethylene container B, and place the container A containing the silicon-carbon composite material primary product into container B, seal container B, and place it in a 100℃ oven for aging for 12 hours. The obtained material was dried and placed in a high-temperature furnace for pyrolysis at 900° C. under argon protection, ultimately obtaining a carbon-coated nano-silicon-carbon composite material with a silicon content of 39%.

[0077] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 610 mAh / g at a current density of 100 mA / g, an initial efficiency of 86%, and a capacity retention rate of 57% after 100 cycles.

[0078] Comparative Example 4

[0079] Take 0.5g carbon nanotubes (specific surface area 1230m 2 / g, pore volume 1.1cm 3 / g), take 1g of methylvinyldichlorosilane and mix it with 0.5ml of ether, and impregnate it into carbon nanotubes; then, under an inert atmosphere, take 1g of lithium borohydride and mix it with 10ml of tetrahydrofuran to prepare a reducing agent, take 1ml of the reducing agent solution and impregnate it into the above-mentioned carbon nanotubes carrying silicon source, and let it react for 5 hours. Take a mixed solution of ethyl acetate and methanol in a volume ratio of 1:1, and use ultrasonic spray to spray 4ml of the above mixed solution onto the surface of the composite material after standing for 5 hours. The obtained material is washed with ethanol and water, and then dried in an 80℃ oven for 12 hours to obtain a primary product of silicon-carbon composite material. Take 1g of the primary silicon-carbon composite material, dissolve 0.5g of naphthol in 5ml of a mixed solution of ethanol and water (1:1, volume ratio), take 1ml of the naphthol solution and evenly mix it with 1g of the primary silicon-carbon composite material, and place it in a polytetrafluoroethylene container A. Take 3g of tridecaldehyde and place it in a polytetrafluoroethylene container B. Container A containing the primary silicon-carbon composite material is placed in container B. Container B is sealed and placed in a 100°C oven for aging for 24 hours. The resulting material is dried and placed in a high-temperature furnace for pyrolysis at 850°C under argon protection to obtain a carbon-coated nano-silicon-carbon composite material with a silicon content of 41%.

[0080] The same as the preparation of silicon-based negative electrode material in Example 1, it was used as the active material to prepare a silicon-based negative electrode, which had a discharge capacity of 645 mAh / g at a current density of 100 mA / g, an initial efficiency of 82%, and a capacity retention rate of 64% after 100 cycles.

Claims

1. A nano-silicon-carbon composite material, the composite material comprising nano-silicon particles, a first carbon matrix and a second carbon layer; the nano-silicon particles are embedded in the pore structure of the first carbon matrix, the second carbon layer is wrapped around the outer surface of the first carbon matrix, the first carbon matrix is ​​porous carbon, and the second carbon layer is an amorphous carbon layer.

2. The nano-silicon-carbon composite material according to claim 1, characterized in that: The first carbon matrix is ​​porous carbon, and the specific surface area of ​​the porous carbon is 200 to 3000 m 2 / g, which has a multi-level pore structure of micropores-mesopores-macroporous.

3. The nano-silicon-carbon composite material according to claim 1, characterized in that: Based on the weight of the nano-silicon-carbon composite material, the silicon mass content is 10% to 70%, preferably 30% to 60%; the silicon particle size is 2 to 10 nm, preferably 3 to 5 nm.

4. The nano-silicon-carbon composite material according to claim 1, characterized in that: The thickness of the second carbon layer is 2 to 3 nm.

5. The nano-silicon-carbon composite material according to claim 1, characterized in that: The specific capacity of the nano-silicon-carbon composite material is 600 to 2000 mAh / g.

6. A method for preparing a nano-silicon-carbon composite material, comprising the following steps: (1) Under contact conditions, the porous carbon material is fully contacted with a silicon source solution to obtain material A; (2) Under an inert atmosphere, the material A obtained in step (1) is mixed with a solution containing a reducing agent to obtain material B; (3) introducing a treating agent into the material B obtained in step (2), and then washing and drying to obtain a silicon-carbon composite material precursor; (4) uniformly mixing the silicon-carbon composite material precursor obtained in step (3) with the carbon material precursor C to obtain material D; (5) In the presence of a carbon material precursor E, the material D obtained in step (4) is aged, and then dried and pyrolyzed to obtain a silicon-carbon composite material.

7. The method for preparing the nano-silicon-carbon composite material according to claim 6, wherein: The porous carbon material in step (1) has the following characteristics: it contains micropores smaller than 2 nm and mesopores of 2 to 10 nm, and the specific surface area of ​​the porous carbon is 200 to 3000 m 2 / g, pore volume of 0.5~3.0cm 3 / g, of which the pore volume of 2-10 nm mesopores is 0.45-2.8 cm 3 / g.

8. The method for preparing the nano-silicon-carbon composite material according to claim 6, wherein: The silicon source solution in step (1) comprises a silicon source and an organic solvent, wherein the silicon source is selected from one or more of methyl orthosilicate, tetraethyl orthosilicate, methyltrimethoxysilane, silicon tetrachloride, trichlorosilane, trimethylchlorosilane, phenylchlorosilane, methylphenylchlorosilane, methylvinylchlorosilane, and vinyltrichlorosilane, preferably one or more of trichlorosilane, trimethylchlorosilane, silicon tetrachloride, and vinyltrichlorosilane; and the organic solvent is one or more of toluene, benzene, tetrahydrofuran, and diethyl ether.

9. The method for preparing the nano-silicon-carbon composite material according to claim 6, wherein: The reducing agent solution in step (2) comprises a reducing agent and an organic solvent, wherein the reducing agent used is selected from one or more of sodium 2-hydrogen bis(dimethoxyethoxy)aluminate, lithium tri(tert-butoxy)aluminum hydride, diisobutylaluminum hydride, lithium aluminum hydride, etc., and the organic solvent is one or more of toluene, benzene, tetrahydrofuran, and diethyl ether.

10. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The molar ratio of the reducing agent to the silicon source is 1 to 5:1, preferably 1 to 2:

1.

11. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The treating agent in step (3) is one or more of ethyl acetate-toluene mixed solution, anhydrous methanol, and sodium hydroxide aqueous solution.

12. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The molar ratio of the treating agent to the reducing agent in step (3) is 1 to 15:1, preferably 3 to 10:

1.

13. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The method of introducing the treatment agent in step (3) is to spray the treatment agent into the material B obtained in step (2) by ultrasonic spraying.

14. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The carbon material precursor C in step (4) is selected from asphalt or phenolic compounds, and the asphalt is at least one of petroleum-based asphalt and coal-based asphalt; the softening point of the asphalt is 75-120°C; the asphalt is heated to a molten state when used; the phenolic compound is at least one of resorcinol, phenol, phloroglucinol, hydroquinone, cresol, aminophenol, nitrophenol, naphthol, and chlorophenol, preferably at least one of resorcinol, phenol, phloroglucinol, and hydroquinone; the phenolic compound needs to be dissolved in a solvent when used, and the solvent is an ethanol aqueous solution with a solution concentration of 0.5-5 mol / L.

15. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The carbon material precursor E in step (5) is an aldehyde compound, and the aldehyde compound is selected from at least one of formaldehyde, acetaldehyde, adipaldehyde, valeraldehyde, terephthalaldehyde, lauryl aldehyde, tridecaldehyde, myristic aldehyde, benzaldehyde, phenylacetaldehyde, phenylpropionic aldehyde, cinnamaldehyde, lily-of-the-valley aldehyde, vanillin, and ethyl vanillin, and is preferably at least one of formaldehyde, acetaldehyde, adipaldehyde, valeraldehyde, terephthalaldehyde, benzaldehyde, and phenylacetaldehyde.

16. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The molar ratio of the carbon material precursor E to the carbon material precursor C is 1 to 10:1, preferably 2 to 6:

1.

17. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The aging treatment in step (5) is carried out under closed conditions, the aging temperature is 50 to 120° C., and the aging time is 2 to 48 hours.

18. The method for preparing the nano-silicon-carbon composite material according to claim 6, characterized in that: The heat treatment in step (5) is carried out in an inert atmosphere, and the pyrolysis temperature is 800-1200°C.

19. A nano-silicon-carbon composite material obtained by the preparation method according to any one of claims 6 to 18.

20. A lithium-ion battery, comprising the nano-silicon-carbon composite material according to any one of claims 1 to 5 and / or the nano-silicon-carbon composite material according to claim 19.

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