Radiation star-like nanosilicon-carbon composite material, preparation method and application thereof

Abstract

The application discloses a kind of radiating star-like nano silicon-carbon composite material and preparation method and application, belong to lithium ion battery material technical field.Its preparation method includes: under the action of surfactant and catalyst, silicon source is hydrolyzed to obtain radiating star-like silicon dioxide, then radiating star-like silicon dioxide is reduced into radiating star-like nano silicon material by metal hot reduction method, radiating star-like nano silicon material and organic carbon source, carbon nanomaterial liquid phase ball milling are mixed, spray drying is carried out after sintering, and radiating star-like nano silicon-carbon composite material is obtained.Nanometer silicon-carbon negative electrode material with the above special structure can effectively alleviate the negative influence generated by its volume expansion in the cycle process, and reduce lithium ion diffusion distance, improve electrochemical reaction efficiency.

Description

Technical Field

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

[0002] Batteries are ideal energy storage devices that achieve the conversion between chemical energy and electrical energy by combining reaction electrodes in a container filled with electrolyte. Among them, lithium-ion batteries have attracted widespread attention and research due to their advantages such as high capacity, good cycle stability, portability, and environmental friendliness. The use of lithium-ion batteries has also greatly facilitated people's daily lives. Lithium-ion batteries are mainly composed of several parts such as positive electrode, negative electrode, electrolyte, separator and shell. The properties of positive and negative electrode materials have a crucial impact on the battery's performance such as capacity, energy density and cycle life. The ideal negative electrode material needs to have the characteristics of low working point, high capacity, high first efficiency, low cost and good cycle stability. Based on the above, the most commercialized negative electrode material at present is graphite-based carbon material. However, the theoretical lithium storage capacity of graphite is -370mAh / g, which is increasingly unable to meet people's demand for high-power and high-energy density batteries. People have found that Si and Li can generate a series of LixSi alloy compounds with a theoretical capacity of up to 4200mAh / g and a low working voltage (<0.4V vs Li / Li + ); and silicon is abundant in the earth's crust and is non-toxic and harmless, so silicon-based materials are considered to be one of the most promising negative electrode materials.

[0003] The significant volume expansion of silicon-based materials during their alloying reaction with lithium and their poor electrical conductivity are major factors restricting their development. The stress generated by the repeated volume contraction and expansion of silicon during charge and discharge can lead to cracking and pulverization of the electrode material, poor cycling stability, and rapid degradation of electrochemical performance. Furthermore, the solid electrolyte interphase (SEI) formed at the electrode-electrolyte interface repeatedly destroys and grows, accompanied by irreversible consumption of the electrolyte. To practically apply silicon-based anode materials, the design of stable nanostructures and simplified synthesis processes are essential.

[0004] In view of this, it is necessary to provide a radial star-shaped nano-silicon-carbon composite material and a preparation method and application thereof. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a radial star-shaped nano-silicon-carbon composite material and its preparation method and application.

[0006] The present invention solves the technical problem by adopting the following technical solutions.

[0007] The present invention provides a radial star-shaped nano-silicon-carbon composite material, which includes a matrix and a carbon layer coated on at least a portion of the matrix surface. The matrix includes a radial star-shaped nano-silicon material and a carbon nano-material, and the total carbon content of the radial star-shaped nano-silicon-carbon composite material is 50-90%.

[0008] The present invention also provides a method for preparing the above-mentioned radial star-shaped nano-silicon-carbon composite material, which comprises:

[0009] The radiating star-shaped silicon dioxide is reduced into radiating star-shaped nano-silicon material by metal thermal reduction method;

[0010] The obtained radiating star-shaped nano-silicon material, carbon nano-material and organic carbon source are mixed and sintered to obtain a radiating star-shaped nano-silicon-carbon composite material.

[0011] The present invention also provides a negative electrode plate, wherein the negative electrode active material in the negative electrode plate includes the above-mentioned radial star-shaped nano silicon-carbon composite material.

[0012] The present invention also provides a lithium battery, which includes the above-mentioned negative electrode plate.

[0013] The present invention has the following beneficial effects:

[0014] The present invention provides a radial star-shaped nano-silicon-carbon composite material, as well as a preparation method and application. The radial star-shaped nano-silicon-carbon composite material comprises a substrate and a carbon layer coated on at least a portion of the substrate surface. The substrate comprises a radial star-shaped nano-silicon material and a carbon nano-material, and the total carbon content of the radial star-shaped nano-silicon-carbon composite material is 50-90%. The preparation process includes: hydrolyzing a silicon source under the action of a surfactant and a catalyst, and adjusting the size and morphology of the silicon dioxide by adjusting the surfactant concentration and ratio to obtain radial star-shaped silicon dioxide; then reducing the radial star-shaped nano-silicon material using a metallothermic reduction method; and finally mixing and sintering the radial star-shaped nano-silicon material, the carbon nano-material, and an organic carbon source to obtain the radial star-shaped nano-silicon-carbon composite material. The pores in the star-shaped morphology of the radial star-shaped nano-silicon material after accumulation can effectively buffer the volume change of the material during the charge and discharge process. The composite carbon nano-material can further increase the conductivity of the material and buffer the volume change of silicon. The radial star-shaped nano-silicon material and the carbon nano-material are in situ coated to fix and stabilize the material structure. Ultimately, the prepared radial star-shaped nano-silicon-carbon composite material is suitable as the negative electrode active material of the lithium-ion battery, thereby enabling the prepared lithium-ion battery to exhibit excellent capacity and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 Schematic diagram of the matrix structure of the radial star-shaped nano-silicon-carbon composite material prepared in Example 1 of the present invention;

[0017] Figure 2 This is the XRD spectrum of the radial star-shaped nano-silicon-carbon composite material prepared in Example 1 of the present invention;

[0018] Figure 3 This is the specific capacity-voltage curve of the first charge and discharge of a button cell made of the radial star-shaped nano-silicon-carbon composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] The following specifically describes a radial star-shaped nano-silicon-carbon composite material, a preparation method, and an application thereof provided in an embodiment of the present invention.

[0021] In a first aspect, an embodiment of the present invention provides a radial star-shaped nano-silicon-carbon composite material, which includes a matrix and a carbon layer coated on at least a portion of the surface of the matrix, wherein the matrix includes a radial star-shaped nano-silicon material and a carbon nano-material, and the total carbon content in the radial star-shaped nano-silicon-carbon composite material is 50-90%.

[0022] Radiating star-shaped silica nanoparticles (SMSNS) are surrounded by a unique star-shaped relief structure, exhibiting excellent properties such as a large specific surface area, uniform particle size, and strong adsorption capacity. Generally, the smaller the average particle size of a nanoparticle, the greater its specific surface area. However, the unique star-shaped relief structure of SMSNS allows it to maintain a high specific surface area over a wide particle size range. Furthermore, the special star-shaped relief structure reduces the diffusion path of lithium ions, and the gaps between the materials provide a buffer for volume changes. Combining the aforementioned radiating star-shaped silicon nanoparticles with carbon nanomaterials as a matrix, the composite carbon nanomaterial further increases the material's conductivity and buffers silicon volume changes. Coating at least a portion of the matrix with a carbon layer not only buffers and constructs a continuous and uniform conductive network, but also stabilizes and stabilizes the material structure. The resulting composite material, when used as an electrode material, can effectively mitigate the volume expansion of silicon during charge and discharge and reduce the diffusion distance of lithium ions, thereby improving its electrochemical performance as an electrode material and, in turn, enhancing the specific capacity and cycling performance of lithium batteries. It should be further explained that the total carbon in the radial star-shaped nano-silicon-carbon composite material includes the carbon content of the carbon nano-material and the carbon layer covering the surface.

[0023] In an optional embodiment, the matrix includes a radiating star-shaped nano-silicon material, and a carbon nano-material located on the surface of the radiating star-shaped nano-silicon material and / or in the star-shaped gaps;

[0024] Preferably, the carbon nanomaterial includes a first carbon nanomaterial and a second carbon nanomaterial, wherein the first carbon nanomaterial is a carbon nanotube, and the second carbon nanomaterial is at least one of graphite nanosheets, graphene, acetylene black, and carbon black;

[0025] Preferably, the size of the radiating star-shaped nano-silicon material is 40-200 nm;

[0026] Preferably, the thickness of the carbon layer coated on at least part of the substrate surface is 0.5-8 nm, more preferably 1-4 nm;

[0027] Preferably, the composite carbon nanotubes have a diameter of 2-50 nm and a length of 2-100 μm, the graphite nanosheets have a thickness of 3-20 nm, and the graphene has a thickness of 0.4-3 nm.

[0028] The radial star-shaped nano-silicon-carbon composite material provided in the embodiment of the present invention has a matrix comprising radial star-shaped nano-silicon material and carbon nano-material located on the surface of the radial star-shaped nano-silicon material and / or in the star-shaped gaps. The carbon nano-material comprises carbon nanotubes, and at least one of graphite sheets, graphene, acetylene black, and carbon black. Figure 1It can be seen that: in the matrix, the carbon nanotubes are interpenetrated and wound on the radial star-shaped nanosilicon material to form a three-dimensional network structure, and graphite sheets, graphene, acetylene black, carbon black and other carbon materials are distributed in the three-dimensional network structure; the composite material with the special structure can effectively alleviate the negative effects caused by the volume expansion in the cycle process, and improve the electrochemical reaction efficiency.

[0029] In a second aspect, the embodiment of the present application provides a preparation method of the radial star-shaped nanosilicon-carbon composite material, which comprises the following steps:

[0030] The radial star-shaped nanosilicon material is prepared by reducing the radial star-shaped silicon dioxide by a metal reduction method;

[0031] The radial star-shaped nanosilicon material, the carbon nanomaterial and the organic carbon source are mixed and sintered to obtain the radial star-shaped nanosilicon-carbon composite material.

[0032] The embodiment of the present application provides a preparation method of a radial star-shaped nanosilicon-carbon composite material, which comprises the following steps:

[0033] The radial star-shaped silicon dioxide is obtained by hydrolyzing a silicon source under the action of a surfactant and a catalyst;

[0034] The radial star-shaped nanosilicon material is obtained by calcining the mixture of the radial star-shaped silicon dioxide and the active metal powder;

[0035] The radial star-shaped nanosilicon material, the carbon nanomaterial and the organic carbon source are mixed by liquid phase ball milling, and then are sintered after spray drying to obtain the radial star-shaped nanosilicon-carbon composite material.

[0036] The preparation method of the radial star-shaped nanosilicon-carbon composite material provided by the embodiment of the present application first hydrolyzes a silicon source under the action of a surfactant and a catalyst; the surfactant is used as a morphology control agent, and the concentration and the ratio of different surfactants in the synthesis process are controlled to regulate the size and the morphology of the silicon dioxide, so as to obtain the radial star-shaped silicon dioxide; then the radial star-shaped nanosilicon material is obtained by mixing the radial star-shaped silicon dioxide with an active metal powder and performing high-temperature calcination; finally, the radial star-shaped nanosilicon material, the carbon nanomaterial and the organic carbon source are mixed and sintered, and the carbon layer can be coated on at least part of the surfaces of the radial star-shaped nanosilicon material and the carbon nanomaterial by high-temperature carbonization of the organic carbon source, so as to obtain the radial star-shaped nanosilicon-carbon composite material.

[0037] In an optional embodiment, the preparation of the radiating star-shaped nanosilicon-carbon composite material comprises the following steps: hydrolyzing a silicon source under the action of a surfactant and a catalyst to obtain radiating star-shaped silicon dioxide; then mixing the radiating star-shaped silicon dioxide and active metal powder uniformly and performing high-temperature calcination to obtain radiating star-shaped nanosilicon material; and then mixing the radiating star-shaped nanosilicon material with an organic carbon source and carbon nanomaterials by liquid-phase ball milling, performing spray drying, and then performing sintering to obtain the radiating star-shaped nanosilicon-carbon composite material.

[0038] In an optional embodiment, the preparation of the radiating star-shaped silicon dioxide comprises the following steps: adding a surfactant and a catalyst into water, heating and stirring until completely dissolved; then mixing with a silicon source to obtain a mixed solution, continuously stirring the mixed solution until white precipitates are generated; and then washing and drying the separated white precipitates to obtain the radiating star-shaped silicon dioxide.

[0039] Preferably, the silicon source comprises at least one of orthosilicate, aminopropyl triethoxysilane, and diethoxydimethylsilane, and the concentration of the silicon source in the mixed solution is 0.5-0.8 mol / L.

[0040] Preferably, the surfactant comprises at least one of cetyltrimethylammonium bromide, cetyltrimethylammonium p-toluenesulfonate, cetyltrimethylammonium chloride, octadecyltrimethylammonium chloride, and dodecyl dimethyl benzyl ammonium chloride, and preferably, the surfactant is at least one of cetyltrimethylammonium bromide and cetyltrimethylammonium p-toluenesulfonate; and the concentration of the surfactant in the mixed solution is 0.02-0.1 mol / L.

[0041] Preferably, the catalyst comprises at least one of triethanolamine and 2-amino-2-hydroxymethyl-1,3-propanediol, and the concentration of the catalyst in the mixed solution is 0.005-0.04 mol / L.

[0042] Preferably, the heating temperature is 45-98℃, and more preferably, 70-85℃.

[0043] Preferably, the reaction time of the continuous stirring is 1-24 h.

[0044] Preferably, the drying temperature of the white precipitates is 25-60℃.

[0045] In the above preparation process of the radiating star-shaped silicon dioxide, a silicon-containing compound is used as a silicon source, and a surfactant is used as a morphology control agent. By adjusting the concentration and ratio of the surfactant during the synthesis process, the size and morphology of the silicon dioxide can be controlled. Ultimately, the radiating star-shaped silicon dioxide with controllable particle size and adjustable specific surface area is obtained, and the dispersion is relatively uniform and the mechanical strength is high.

[0046] In an optional embodiment, the preparation of the radiating star-shaped nanosilicon material comprises: uniformly mixing radiating star-shaped silicon dioxide and active metal powder, calcining under the protection of a first inert gas, immersing the cooled product in acid, and washing and drying the separated precipitate to obtain the product.

[0047] Preferably, the calcining temperature is 650-1300°C, and the calcining time is 2-15h, more preferably, the calcining temperature is 900-1150°C.

[0048] Preferably, the first inert gas is argon or nitrogen.

[0049] Preferably, the active metal powder comprises at least one of magnesium powder, aluminum powder and zinc powder, and the mass ratio of the active metal powder to the radiating star-shaped silicon dioxide is 1:(2-10).

[0050] Preferably, the acid used for the immersion comprises at least one of hydrofluoric acid, hydrochloric acid and nitric acid, the concentration of the acid is 1-6mol / L, and the immersion time is 2-8h.

[0051] The above radiating star-shaped nanosilicon material is obtained by high-temperature calcining of radiating star-shaped silicon dioxide and active metal powder. The radiating star-shaped silicon dioxide is reduced to obtain the radiating star-shaped nanosilicon material, and the active metal is oxidized to the corresponding oxide. The reduction reaction is carried out in a first inert gas atmosphere to avoid oxidation of the raw materials. The reaction is carried out at a temperature of 650-1300°C. If the temperature is too low, the reduction reaction will be difficult to proceed or will not be complete. If the reaction temperature is higher than the above-mentioned temperature, other impurity phases may be generated. The product is immersed in acid to remove the metal oxide and a small amount of unreacted radiating star-shaped silicon dioxide.

[0052] In an optional embodiment, the preparation of the radiating star-shaped nanosilicon-carbon composite material comprises: uniformly mixing radiating star-shaped nanosilicon material, carbon nanomaterial and organic carbon source in ethanol solution according to a ratio, spray drying, and sintering in a second inert atmosphere to obtain the product.

[0053] Preferably, the organic carbon source comprises at least one of pitch, glucose, sucrose, starch, citric acid, ascorbic acid, polyethylene glycol, polyvinylpyrrolidone and polyaniline.

[0054] Preferably, the mass ratio of the organic carbon source: carbon nanomaterial: radiating star-shaped nanosilicon material is (2-5):(0.5-4):1; the carbon nanomaterial comprises a first carbon nanomaterial and a second carbon nanomaterial, the first carbon nanomaterial is carbon nanotube, the second carbon nanomaterial is at least one of graphite nanosheet, graphene, acetylene black and carbon black, and the mass ratio of the first carbon nanomaterial to the second carbon nanomaterial is (0.05-0.2):1.

[0055] Preferably, the total carbon content in the radial star-shaped nano-silicon-carbon composite material is 50-90%;

[0056] Preferably, the volume ratio of ethanol to water in the ethanol-water solution is 1:1;

[0057] Preferably, the ball milling speed is 200-600 r / min, and the ball milling time is 2-8 h;

[0058] Preferably, the sintering temperature is 300-800°C and the sintering time is 3-12h;

[0059] Preferably, the second inert atmosphere is argon or nitrogen.

[0060] In the above-mentioned preparation process of the radial star-shaped nano-silicon-carbon composite material, the radial star-shaped nano-silicon material, the organic carbon source, and the carbon nano-material are ball-milled and evenly mixed in an ethanol aqueous solution according to a proportion, and then spray-dried to obtain a relatively complete granular material. After sintering, a carbon coating layer is easily formed on the surface of the radial star-shaped nano-silicon material and the carbon nano-material, which can not only form a structurally stable composite material, but also can buffer and construct a continuous and uniform conductive network.

[0061] As can be seen from the above, the present invention designs and prepares a radial star-shaped nano-silicon-carbon composite structural material. Using a silicon-containing compound as a silicon source and a surfactant as a morphology control agent, radial star-shaped nano-silicon dioxide is first prepared. Then, a radial star-shaped nano-silicon material is synthesized by reduction using a metallothermic reduction method. The radial star-shaped nano-silicon material is then mixed with an organic carbon source and a carbon nano-material by liquid-phase ball milling, spray-dried, and sintered to obtain a radial star-shaped nano-silicon-carbon composite material. The pores present in the star-shaped nano-silicon material after accumulation in the silicon-carbon composite material can effectively buffer the material's volume change during charge and discharge. The composite carbon nano-material can further increase the material's conductivity and buffer the silicon's volume change. The carbon layer coated on at least a portion of the surface can improve the material's stability. The resulting composite material as a whole exhibits low volume expansion during charge and discharge. The prepared radial star-shaped nano-silicon-carbon composite structural material exhibits excellent capacity and cycle stability when used in lithium-ion batteries.

[0062] In a third aspect, an embodiment of the present invention further provides a negative electrode plate, wherein the negative electrode active material in the negative electrode plate includes the above-mentioned radial star-shaped nano-silicon-carbon composite material.

[0063] It should be noted that the negative electrode active layer of the negative electrode sheet may include components such as a negative electrode active material, a binder, and a conductive agent. The negative electrode active material contained in the negative electrode active layer includes the aforementioned nano-radiative star-shaped silicon-carbon composite material of the present invention, or a nano-radiative star-shaped silicon-carbon composite material prepared by the aforementioned preparation method of the present invention. The mass percentage of the radiative star-shaped nano-silicon-carbon composite material in the negative electrode active layer is 85%-95%.

[0064] In some embodiments, the binder may include at least one of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and a chitosan derivative. The binder may comprise 2% to 5% by weight of the negative electrode active layer.

[0065] In some embodiments, the conductive agent may include graphite, carbon black, acetylene black, graphene, carbon fiber, C 60 The content of the conductive agent in the negative electrode active layer may be 1 wt% to 5 wt%.

[0066] In some embodiments, the preparation process of the negative electrode sheet can be: mixing the negative electrode active material, the conductive agent and the binder to obtain an electrode slurry, coating the electrode slurry on the current collector, and preparing the negative electrode sheet through steps such as drying, rolling, and die cutting.

[0067] In a fourth aspect, an embodiment of the present invention further provides a lithium battery, which includes the above-mentioned negative electrode plate.

[0068] It should be noted that the lithium battery provided by the embodiments of the present invention includes essential components such as a positive electrode, a negative electrode, a separator, and an electrolyte, as well as other necessary or auxiliary components. The negative electrode sheet is the negative electrode sheet described in the embodiments of the present invention above. The positive electrode is a counter electrode and is a metal lithium sheet.

[0069] Since the secondary battery provided by the embodiment of the present invention includes the negative electrode plate mentioned above, that is, the negative electrode active layer contained in the negative electrode plate contains the above-mentioned radial star-shaped nano-silicon-carbon composite material, the secondary battery provided by the embodiment of the present invention has low internal resistance and the negative electrode material has sufficient buffer space during the cycle process, so that the secondary battery provided by the embodiment of the present invention has good cycle performance and high energy density.

[0070] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0071] Example 1

[0072] Weigh 1.822 g (0.005 mol) of CTAB and 0.0746 g (0.0005 mol) of triethanolamine and dissolve them in 100 mL of deionized water. Heat to 65°C and continue stirring. After both are completely dissolved, add 10.42 g (0.05 mol) of ethyl orthosilicate. Stir to produce a white precipitate. Keep reacting for 3 h.

[0073] The white precipitate was filtered, washed three times with deionized water, and then dried in a vacuum drying oven at room temperature to obtain radiating star-shaped silica.

[0074] The radiating star-shaped silica and magnesium powder were mixed and ground uniformly at a mass ratio of 2:1. The mixture was placed in a corundum boat and placed in a tube furnace. The temperature was raised to 650°C at a rate of 5°C / min under a nitrogen atmosphere and held for 5 hours. The mixture was then cooled to room temperature to obtain an active metal oxide / silicon composite.

[0075] The active metal oxide / silicon complex was dispersed in 2 mol / L hydrochloric acid and stirred for 3 hours. The mixture was then filtered, and the precipitate was washed with deionized water and dried to obtain a radiating star-shaped nano-silicon material.

[0076] The obtained radial star-shaped nano-silicon material, asphalt, graphene and carbon nanotubes were added to a ball mill at a mass ratio of 1:0.5:1:0.5, and water and ethanol were added at a volume ratio of 1:1. After adding ball mill beads, the mixture was ball milled at a speed of 400 r / min for 3 hours to mix evenly, and then spray-dried. The powder was heated to 400°C at a rate of 5°C / min in a nitrogen atmosphere and sintered for 4 hours to obtain a radial star-shaped nano-silicon-carbon composite material.

[0077] Figure 1 Schematic diagram of the matrix structure of the radial star-shaped nano-silicon-carbon composite material prepared in Example 1 of the present invention; Figure 2 The XRD spectrum of the radial star-shaped silicon-carbon composite material prepared in Example 1 of the present invention shows that the radial star-shaped silicon-carbon composite material contains carbon and silicon; Figure 3 The specific capacity-voltage curve of the first charge and discharge of the button battery prepared from the radial star-shaped silicon-carbon composite material prepared in Example 1 of the present invention shows that the discharge platform voltage of the composite material is less than 0.1V, the first discharge capacity is 1189.9mAh / g, and the discharge capacity is 933.9mAh / g.

[0078] Example 2

[0079] Take 2.732 g (0.006 mol) of CTAT and 0.0746 g (0.0005 mol) of triethanolamine, dissolve them in 100 mL of deionized water, heat to 80°C and continue to stir, after both are completely dissolved, add 15.496 g (0.07 mol) of aminopropyl triethoxysilane, continue to stir for 5 h, and a white precipitate is produced.

[0080] Filter the above white precipitate, wash it three times with deionized water, then place the precipitate in a vacuum drying oven at room temperature to dry, and obtain the radiating star-shaped silica.

[0081] Mix the radiating star-shaped silica with aluminum powder at a mass ratio of 3:1, grind them uniformly, place them in a corundum boat, and put them into a tube furnace, heat to 750°C at a rate of 5°C / min under a nitrogen atmosphere, and keep the temperature for 6 h. Then cool to room temperature to obtain the active metal oxide / silicon composite.

[0082] Disperse the above active metal oxide / silicon composite into 2 mol / L concentrated nitric acid and stir for 2 h, then filter the mixture, wash and dry the precipitate to obtain the radiating star-shaped nanosilicon material.

[0083] Add the obtained radiating star-shaped nanosilicon material, polyethylene glycol, graphene, graphite sheet, and carbon nanotube at a mass ratio of 1:0.25:0.25:0.5:0.5 into a ball mill jar, add water and ethanol at a volume ratio of 1:1, put in the ball mill beads, and mill at a speed of 400 r / min for 3 h to mix uniformly, then spray dry, and sinter the powder at a rate of 5°C / min to 400°C under a nitrogen atmosphere for 4 h to obtain the radiating star-shaped nanosilicon-carbon composite material.

[0084] Example 3

[0085] Take 2.278 g (0.005 mol) of CTAT, 0.364 g (0.001 mol) of CTAB, and 0.0931 g (0.001 mol) of 2-amino-2-hydroxymethyl-1,3-propanediol, dissolve them in 100 mL of deionized water, heat to 85°C and continue to stir, after both are completely dissolved, add 10.655 g (0.07 mol) of methyl silicate, continue to stir for 6 h, and a white precipitate is produced.

[0086] Filter the above white precipitate, wash it three times with deionized water, then place the precipitate in a vacuum drying oven at room temperature to dry, and obtain the radiating star-shaped silica.

[0087] The radiating star-shaped silica and aluminum powder were mixed in a mass ratio of 3:1, ground evenly, placed in a corundum boat, and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was raised to 750°C at a rate of 5°C / min and held for 6 hours. The temperature was then cooled to room temperature to obtain an active metal oxide / silicon composite.

[0088] The active metal oxide / silicon complex was dispersed in 2 mol / L nitric acid and stirred for 2 h. The mixture was then filtered, and the precipitate was washed with deionized water and dried to obtain a radiating star-shaped nano-silicon material.

[0089] The obtained radial star-shaped nano-silicon material, glucose, graphene, graphite sheets and carbon nanotubes were added to a ball mill at a mass ratio of 1:0.5:1:0.25:0.25, and water and ethanol were added at a volume ratio of 1:1. After adding ball mill beads, the mixture was ball milled at a speed of 400 r / min for 3 hours to mix evenly, and then spray-dried. The powder was heated to 400°C at a rate of 5°C / min in a nitrogen atmosphere and sintered for 4 hours to obtain a radial star-shaped nano-silicon-carbon composite material.

[0090] Example 4

[0091] 2.734 g (0.006 mol) of CTAT, 0.32 g (0.001 mol) of CTAC, and 0.0746 g (0.0005 mol) of triethanolamine were weighed and dissolved in 100 mL of deionized water. The mixture was heated to 85°C and stirred continuously. After both were completely dissolved, 11.862 g (0.08 mol) of diethoxydimethylsilane was added and stirred continuously for 10 h to produce a white precipitate.

[0092] The white precipitate was filtered, washed three times with deionized water, and then dried in a vacuum drying oven at room temperature to obtain radiating star-shaped silica.

[0093] Radiating star-shaped silica and zinc powder were mixed in a mass ratio of 3:1, ground evenly, placed in a corundum boat, and placed in a tube furnace. The mixture was heated to 900°C at a rate of 5°C / min under a nitrogen atmosphere and held at that temperature for 6 hours. The mixture was then cooled to room temperature to obtain an active metal oxide / silicon composite.

[0094] The active metal oxide / silicon complex was dispersed in 5 mol / L nitric acid and stirred for 2 hours. The mixture was then filtered, and the precipitate was washed with deionized water and dried to obtain a radiating star-shaped nano-silicon material.

[0095] The obtained radial star-shaped nano-silicon material, polyvinyl pyrrolidone, graphene, graphite particles and carbon nanotubes were added to a ball mill at a mass ratio of 1:0.25:0.25:0.5:1, and water and ethanol were added at a volume ratio of 1:1. After adding ball mill beads, the mixture was ball milled at a speed of 400 r / min for 3 hours to mix evenly, and then spray-dried. The powder was heated to 400°C at a rate of 5°C / min in a nitrogen atmosphere and sintered for 4 hours to obtain a radial star-shaped nano-silicon-carbon composite material.

[0096] Comparative Example 1

[0097] The steps are similar to those in Example 1, except that CTAB and triethanolamine are not added during the preparation of the radial star-shaped silica, thereby obtaining a spherical nano-silicon-carbon composite material.

[0098] Comparative Example 2

[0099] The steps are similar to those in Example 1, except that in the compounding step, only graphene and carbon nanotubes are added to the obtained radial star-shaped nano-silicon material for mixing, without adding asphalt as an organic carbon source, and the mass ratio of the radial star-shaped nano-silicon material, graphene and carbon nanotubes is 1:1.25:0.75, maintaining the carbon content in the composite material without decreasing, and finally obtaining a radial star-shaped nano-silicon-carbon composite material.

[0100] Comparative Example 3

[0101] The steps are similar to those in Example 1, except that the mass of the added carbon material and organic carbon source are reduced to 20% of that in Example 1, and the final total carbon accounts for less than 50% of the total mass of the radial star-shaped nano-silicon-carbon composite material.

[0102] Comparative Example 4

[0103] The steps are similar to those in Example 1, except that in the compounding step, only asphalt is added to the obtained radial star-shaped nano-silicon material without adding graphene and carbon nanotubes, and the mass ratio of the radial star-shaped nano-silicon material to the asphalt is 1:2.

[0104] Battery performance test:

[0105] The radial star-shaped nano-silicon-carbon composite material provided in the above examples and comparative examples was used as the active material, and a battery was assembled as follows:

[0106] Preparation of positive electrode sheet: Mix the active material, SP (conductive carbon black) and sodium carboxymethyl cellulose (CMC) in a mass ratio of 6:2:2, add an appropriate amount of deionized water and stir with a ball mill for 2 hours to obtain a positive electrode slurry; add the prepared slurry on aluminum foil, evenly scrape it with a scraper, dry it at 130 ° C, and then roll it. Place the front of the rolled electrode close to the punched area, and punch out the sheets in sequence to obtain the positive electrode sheet.

[0107] Battery assembly process: In a glove box, the negative electrode shell, spring, steel sheet, lithium sheet, separator, positive electrode sheet, and positive electrode shell are assembled in this order. During the process, 10 microliters of electrolyte are injected, and then the button cell is sealed using a sealing machine to assemble it into a button cell. The metal lithium sheet serves as the negative electrode, the Celgard 2400 microporous membrane serves as the separator, and the electrolyte is a 1.0 mol / L LiPF6 solution. The solvent of this electrolyte is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1.

[0108] Using a LAND electrochemical tester at room temperature (25°C), with the discharge cut-off voltage set at 0.01V and the charge termination voltage set at 1.5V, the 0.1C charge-discharge capacity and the capacity retention rate after 1C cycle charge-discharge of the above-mentioned button battery were tested.

[0109] The test results are shown in Table 1 below:

[0110] Table 1 Capacity of the first charge and after 100 cycles of the radial star-shaped nano-silicon-carbon composite material

[0111]

[0112] Comparing the data of Examples 1-4 and Comparative Example 1 in Table 1, it can be seen that the first coulombic efficiency and capacity retention rate after 100 cycles of the spherical nano-silicon-carbon composite material prepared without morphology control are both lower than those of the radial star-shaped nano-silicon-carbon composite material. This shows that the special star-shaped morphology has a certain improvement effect on the electrochemical performance and cycle stability of the negative electrode. Comparing the data of Examples 1, 2, 4 and Comparative Example 4, it can be seen that the combination of carbon nanomaterials also has a certain effect on the electrochemical performance of the silicon-carbon composite material. Carbon nanotubes help the material form a conductive network and have a certain volume buffering capacity. In Comparative Example 4, due to the lack of carbon nanotubes and graphite materials, the conductive network and volume buffering capacity formed are weak, and its capacity decay is fast. Comparing the data of Example 1 and Comparative Example 3, it can be seen that a certain amount of carbon compound has an improving effect on the stability of the material, making its cycle performance better. Although the proportion of silicon in Comparative Example 3 is high, the first discharge capacity is large, but the total carbon content is low, and the first coulombic efficiency and cycle performance of the obtained composite material are both reduced. From the data of Example 1 and Comparative Example 2, it can be seen that although the total carbon content in Comparative Example 2 is not reduced, there is no protective layer formed by carbon coating and a uniform conductive network, and the first coulombic efficiency and cycle stability of the material are not as good as those when an organic carbon source is added at the same time.

[0113] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A radial star-shaped nano silicon-carbon composite material, characterized in that: The radial star-shaped nano-silicon-carbon composite material comprises a matrix and a carbon layer coated on at least a portion of the matrix surface, wherein the matrix comprises radial star-shaped nano-silicon material and carbon nano-material, and the total carbon content of the radial star-shaped nano-silicon-carbon composite material is 50-90%; The radial star-shaped nano-silicon-carbon composite material is prepared by the following steps: hydrolyzing a silicon source under the action of a surfactant and a catalyst to obtain radial star-shaped silica; uniformly mixing the radial star-shaped silica and active metal powder and then calcining them to obtain a radial star-shaped nano-silicon material; then liquid-phase ball milling the radial star-shaped nano-silicon material, carbon nano-material and an organic carbon source, spray drying and then sintering to obtain the radial star-shaped nano-silicon-carbon composite material.

2. The radial star-shaped nano-silicon-carbon composite material according to claim 1, characterized in that: The matrix includes a radiating star-shaped nano-silicon material and a carbon nano-material located on the surface of the radiating star-shaped nano-silicon material and / or in the star-shaped gaps.

3. The radial star-shaped nano-silicon-carbon composite material according to claim 1, characterized in that: The carbon nanomaterial includes a first carbon nanomaterial and a second carbon nanomaterial, and the first carbon nanomaterial is a carbon nanotube, and the second carbon nanomaterial is at least one of graphite nanosheets, graphene, acetylene black, and carbon black. The mass ratio of the first carbon nanomaterial to the second carbon nanomaterial is (0.05-0.2):

1.

4. The radial star-shaped nano-silicon-carbon composite material according to claim 1, characterized in that: The size of the radiating star-shaped nano-silicon material is 40-200 nm.

5. The radial star-shaped nano-silicon-carbon composite material according to claim 1, characterized in that: The thickness of the carbon layer coated on at least a portion of the substrate surface is 0.5-8 nm.

6. The radial star-shaped nano-silicon-carbon composite material according to claim 5, characterized in that: The thickness of the carbon layer coated on at least a portion of the substrate surface is 1-4 nm.

7. A method for preparing the radial star-shaped nano-silicon-carbon composite material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Under the action of surfactant and catalyst, the silicon source is hydrolyzed to obtain radiant star-shaped silica; The radiating star-shaped silicon dioxide and active metal powder are uniformly mixed and then calcined to obtain a radiating star-shaped nano-silicon material; The radiating star-shaped nano-silicon material, carbon nano-material and organic carbon source are then mixed by liquid-phase ball milling, spray-dried and then sintered to obtain the radiating star-shaped nano-silicon-carbon composite material.

8. The preparation method according to claim 7, characterized in that The preparation of the radiating star-shaped silica comprises: adding a surfactant and a catalyst into water, heating and stirring until completely dissolved; then mixing with a silicon source to obtain a mixed solution, continuously stirring the mixed solution until a white precipitate is generated; and then washing and drying the separated white precipitate.

9. The preparation method according to claim 8, characterized in that The silicon source includes at least one of orthosilicates, aminopropyltriethoxysilane and diethoxydimethylsilane, and the concentration of the silicon source in the mixed solution is 0.5-0.8 mol / L.

10. The preparation method according to claim 8, characterized in that The surfactant includes at least one of cetyltrimethylammonium bromide, cetyltrimethylammonium p-toluenesulfonate, cetyltrimethylammonium chloride, octadecyltrimethylammonium chloride and dodecyldimethylbenzylammonium chloride.

11. The preparation method according to claim 10, characterized in that: The surfactant is at least one of cetyltrimethylammonium bromide and cetyltrimethylammonium p-toluenesulfonate; and the concentration of the surfactant in the mixed solution is 0.02-0.1 mol / L.

12. The preparation method according to claim 8, characterized in that The catalyst comprises at least one of triethanolamine and 2-amino-2-hydroxymethyl-1,3-propanediol, and the concentration of the catalyst in the mixed solution is 0.005-0.04 mol / L.

13. The preparation method according to claim 8, characterized in that The heating temperature is 45-98°C.

14. The preparation method according to claim 13, characterized in that The heating temperature is 70-85°C.

15. The preparation method according to claim 8, characterized in that The reaction time of continuous stirring is 1-24 h.

16. The preparation method according to claim 8, characterized in that The drying temperature of the white precipitate is 25-60°C.

17. The preparation method according to claim 7, characterized in that The preparation of the radial star-shaped nano-silicon material comprises: grinding and mixing the radial star-shaped silicon dioxide and active metal powder uniformly, calcining under the protection of a first inert gas, cooling and soaking in acid, and then washing and drying the separated precipitate to obtain the material.

18. The preparation method according to claim 17, characterized in that: The calcination temperature is 650-1300° C. and the calcination time is 2-15 h.

19. The preparation method according to claim 18, characterized in that The calcination temperature is 900-1150°C.

20. The preparation method according to claim 17, characterized in that The first inert gas is argon or nitrogen.

21. The preparation method according to claim 17, characterized in that The active metal powder includes at least one of magnesium powder, aluminum powder and zinc powder, and the mass ratio of the active metal powder to the radiating star-shaped silica is 1:(2-10).

22. The preparation method according to claim 17, characterized in that The acid used for soaking includes at least one of hydrofluoric acid, hydrochloric acid and nitric acid, the concentration of the acid is 1-6 mol / L, and the soaking time is 2-8 h.

23. The preparation method according to claim 7, characterized in that The preparation of the radial star-shaped nano-silicon-carbon composite material comprises: ball-milling the radial star-shaped nano-silicon material, carbon nano-material and organic carbon source in an ethanol aqueous solution according to a proportion to uniformly mix them, spray-drying them, and then sintering them under a second inert atmosphere to obtain the composite material.

24. The preparation method according to claim 23, characterized in that The organic carbon source includes at least one of asphalt, glucose, sucrose, starch, citric acid, ascorbic acid, polyethylene glycol, polyvinyl pyrrolidone, and polyaniline.

25. The preparation method according to claim 23, characterized in that The mass ratio of the organic carbon source: carbon nanomaterial: radiating star-shaped nano-silicon material is (2-5):(0.5-4):1; the carbon nanomaterial includes a first carbon nanomaterial and a second carbon nanomaterial, and the first carbon nanomaterial is a carbon nanotube, and the second carbon nanomaterial is at least one of graphite nanosheets, graphene, acetylene black, and carbon black, and the mass ratio of the first carbon nanomaterial to the second carbon nanomaterial is (0.05-0.2):

1.

26. The preparation method according to claim 25, characterized in that The total carbon content of the radial star-shaped nano-silicon-carbon composite material is 50-90%.

27. The preparation method according to claim 25, characterized in that The volume ratio of ethanol to water in the ethanol aqueous solution is 1:

1.

28. The preparation method according to claim 25, characterized in that The ball milling speed is 200-600 r / min, and the ball milling time is 2-8 h.

29. The preparation method according to claim 25, characterized in that The sintering temperature is 300-800 ℃, and the sintering time is 3-12 h.

30. The preparation method according to claim 25, characterized in that The second inert atmosphere is argon or nitrogen.

31. A negative electrode plate, characterized in that: The negative electrode active material in the negative electrode plate includes the radial star-shaped nano-silicon-carbon composite material according to any one of claims 1 to 6 or the radial star-shaped nano-silicon-carbon composite material prepared by the preparation method according to any one of claims 7 to 30.

32. The negative electrode sheet according to claim 31, characterized in that: The content of the radial star-shaped nano-silicon-carbon composite material in the negative electrode active layer is 85-95 wt %.

33. A lithium battery, characterized in that: The lithium battery comprises the negative electrode sheet according to any one of claims 31-32.

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