Silicon-based composite material, method for preparing the same, and lithium ion battery

Abstract

The application provides a silicon-based composite material and a preparation method thereof, and a lithium ion battery. The silicon-based composite material comprises Si-O-C spherical structures, and the ratio of the number of Si-O bonds to the number of Si-C bonds in the silicon-based composite material is greater than 2. Therefore, the silicon-based composite material can have a high specific capacity. Meanwhile, the spherical structure of the silicon-based composite material and the buffer framework formed by Si-O-C therein can make the silicon-based composite material have a good cycle capacity retention rate and a low cycle expansion, so that the silicon-based composite material is suitable for use in a lithium ion battery.

Description

Technical Field

[0001] This application relates to the field of energy storage materials, and in particular to a silicon-based composite material, a method for preparing the silicon-based composite material, and a lithium-ion battery. Background Technology

[0002] The ever-increasing energy density requirements for lithium-ion batteries in the power battery field have brought them close to their theoretical specific capacity (372 mAh / g). Common graphite-based anode materials can no longer meet the demands for high capacity and long lifespan. Silicon-based anode materials, on the other hand, have a theoretical specific capacity (~4200 mAh / g) that is more than 10 times that of graphite anode materials, making them one of the hot topics in current anode material research.

[0003] However, silicon-based anode materials have poor intrinsic conductivity. During lithium intercalation, the enormous volume expansion (~400%) causes damage to the solid electrolyte interphase (SEI) film, leading to the repeated formation of new SEI films. This results in continuous electrolyte consumption and thickening, causing a large expansion rate. Simultaneously, the large volume change also leads to particle pulverization, affecting the electrical contact between particles and between the battery's active materials and current collectors, causing a decrease in specific capacity and poor cycle performance. Therefore, to achieve higher specific capacity and improved cycle stability in silicon-based anode materials, improvements are needed. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a silicon-based composite material with high specific capacity and good cycle stability.

[0005] To address the aforementioned issues, this application discloses a silicon-based composite material comprising a Si-OC spherical structure, wherein the ratio of the number of Si-O bonds to the number of Si-C bonds in the silicon-based composite material is greater than 2.

[0006] Optionally, the surface of the Si-OC spherical structure is coated with a carbon material layer.

[0007] Optionally, the O / Si molar ratio in the Si-OC spherical structure is 1 to 2;

[0008] Optionally, the C / Si molar ratio in the Si-OC spherical structure is 0.5 to 3.5;

[0009] Optionally, the Si-OC spherical structure includes SiO4 structural units and SiO3C structural units; wherein the mass fraction of the SiO3C structural units is greater than the mass fraction of the SiO4 structural units.

[0010] Optionally, a ratio of a mass fraction of the SiO3C to a mass fraction of the SiO4 is greater than 2.

[0011] Optionally, the Si-O-C spherical structure further comprises SiO4 structural units, SiO3C structural units, and SiO2C2 structural units; wherein a ratio of a sum of mass fractions of the SiO4 structural units and the SiO3C structural units to a mass fraction of the SiO2C2 structural units is greater than 2.

[0012] Optionally, a surface of the Si-O-C spherical structure is coated with a carbon material layer, and the carbon material layer comprises an inorganic carbon material layer.

[0013] Optionally, in a capacitance-voltage characteristic curve of the silicon-based composite material, a capacity in a 0-0.1V interval accounts for 20-50% of a total capacity of the silicon-based composite material, and a capacity in a 0.1-0.6V interval accounts for 50-80% of the total capacity of the silicon-based composite material.

[0014] Optionally, a Wadell sphericity of the silicon-based composite material is greater than 0.95.

[0015] Optionally, a particle size span of the silicon-based composite material is less than or equal to 1.20.

[0016] Optionally, the silicon-based composite material comprises Si microcrystals, and a size of the Si microcrystals is 1-10nm.

[0017] Optionally, a specific surface area of the silicon-based composite material is 2.0-9.5m 2 / g.

[0018] Optionally, a particle size D50 of the silicon-based composite material is 0.3-5.8μm.

[0019] The application further discloses a preparation method of the silicon-based composite material.

[0020] A siloxane raw material, a phenolic raw material, an aldehyde raw material, and a catalyst are added into a solvent, and then uniformly mixed to obtain an oil phase;

[0021] The oil phase is added dropwise into an aqueous phase containing an emulsifier to obtain an oil-in-water emulsion;

[0022] The oil-in-water emulsion is formed into a gel in an environment with a pH value of 11-12, and then dried and heat-treated to obtain the silicon-based composite material.

[0023] Optionally, the step of adding the siloxane raw material, the phenolic raw material, the aldehyde raw material, and the catalyst into the solvent, and then uniformly mixing to obtain the oil phase specifically comprises:

[0024] adding silicone raw materials and phenolic raw materials into a solvent, and mixing to obtain a second solution;

[0025] adding aldehyde raw materials and a catalyst into the second solution, and mixing to obtain an oil phase.

[0026] Optionally, the step of adding the oil phase dropwise into an aqueous phase containing an emulsifier to obtain an oil-in-water emulsion comprises:

[0027] adding an emulsifier into deionized water to obtain an aqueous phase, and adding the oil phase dropwise into the aqueous phase to obtain an oil-in-water emulsion.

[0028] Optionally, the step of forming a gel from the oil-in-water emulsion, drying, and then heat treating to obtain a silicon-based composite material comprises:

[0029] standing still under a water bath or an oil bath at 25-100°C to generate a gel;

[0030] drying the gel to obtain precursor microspheres, and heat treating the precursor microspheres to obtain a silicon-based composite material.

[0031] Optionally, the method further comprises:

[0032] heat treating the silicon-based composite material based on a carbon source to obtain a silicon-based composite material coated with a carbon material layer;

[0033] Optionally, the step of heat treating the silicon-based composite material based on a carbon source to obtain a silicon-based composite material coated with a carbon material layer comprises:

[0034] mixing the silicon-based composite material with the carbon source, and then heat treating to obtain a silicon-based composite material coated with a carbon material layer.

[0035] Optionally, the step of adding silicone raw materials and phenolic raw materials into a solvent, and mixing to obtain a second solution comprises:

[0036] adding a pH adjusting solution into the solvent to adjust the pH value to be between 11 and 12 to obtain a first solution;

[0037] adding silicone raw materials and phenolic raw materials into the first solution, and mixing to obtain a second solution;

[0038] Optionally, the step of adding the oil phase dropwise into an aqueous phase containing an emulsifier to obtain an oil-in-water emulsion comprises:

[0039] adding an emulsifier into the aqueous phase, adding a pH adjusting solution to adjust the pH value to be between 11 and 12, and adding the oil phase dropwise into the aqueous phase;

[0040] Optionally, the step of forming the oil-in-water emulsion into a gel in the environment of pH 11-12 comprises:

[0041] adding a pH adjusting solution to the oil-in-water emulsion to adjust the pH value to be between 11-12, and forming the oil-in-water emulsion into a gel.

[0042] Optionally, the O / Si molar ratio of the siloxane raw material is ≤1.

[0043] Optionally, the siloxane raw material comprises at least one of aromatic siloxane, octamethyltetrasiloxane, decamethyltetrasiloxane, 1,3-divinyltetramethyldisiloxane, octamethyltrisiloxane.

[0044] Optionally, the phenolic raw material comprises at least one of resorcinol, m-aminophenol, bisphenol A.

[0045] Optionally, the aldehyde raw material comprises formaldehyde.

[0046] Optionally, the pH adjusting solution comprises ammonia or urea with a concentration of 0.1-2 mol / L.

[0047] Optionally, the catalyst comprises platinum divinyltetramethyl-disiloxane complex and / or dibutyltin dilaurate.

[0048] Optionally, the emulsifier comprises at least one of polysorbate-80, polysorbate-60, polysorbate-40, and polysorbate-20.

[0049] Optionally, the carbon source comprises at least one of solid-phase carbon source, liquid-phase carbon source, and gas-phase carbon source.

[0050] Optionally, the solid-phase carbon source comprises at least one of citric acid, glucose, pitch, phenol formaldehyde resin, and furfuryl resin.

[0051] Optionally, the liquid-phase carbon source comprises at least one of low-temperature liquid pitch, furfuryl alcohol, glycidyl methacrylate, and triethylene glycol dimethacrylate.

[0052] Optionally, the gas-phase carbon source comprises at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone, and benzene.

[0053] Optionally, the mass ratio between the phenolic raw material and the siloxane raw material is 1:2-8.

[0054] Optionally, the volume ratio between the aldehyde raw material and the first solution is 1:50-250.

[0055] Optionally, the volume ratio between the pH adjusting solution and the solvent is 1:30-100.

[0056] Optionally, the catalyst accounts for 0.5%-15% of the mass of the siloxane raw material.

[0057] Optionally, the emulsifier accounts for 1%-20% of the mass of the aqueous phase.

[0058] Optionally, the mass ratio between the oil phase and the aqueous phase is 1:20-100.

[0059] The application also discloses a lithium ion battery containing the silicon-based composite material or the silicon-based composite material prepared by the method.

[0060] Compared with the prior art, the application has the following advantages:

[0061] The silicon-based composite material provided by the application has a ratio of the number of Si-O bonds to the number of Si-C bonds greater than 2, so that the silicon-based composite material has a high specific capacity. Meanwhile, the spherical structure of the silicon-based composite material and the buffer skeleton formed by Si-O-C can make the silicon-based composite material have a good cycle capacity retention rate and a low cycle expansion, so that the silicon-based composite material is suitable for use in a lithium ion battery.

[0062] The preparation method of the silicon-based composite material provided by the application prepares the silicon-based composite material by using a sol-gel method. In the preparation process, the pH value is adjusted to be between 11 and 12, so that no gelatinous precipitate is generated in the preparation process, so that the finally prepared silicon-based composite material has good fluidity and has a high tap density and a high discharge specific capacity, thereby having excellent electrochemical performance. The oil phase is added dropwise into the aqueous phase to form an oil-in-water emulsion, so that a plurality of sol molecules generated in the hydrolysis and condensation reaction can be simultaneously coated in a layer of water coating layer, thereby promoting the generation of the micron-sized Si-O-C spherical silicon-based composite material. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 is an electron microscope image of the silicon-based composite material prepared in Example 1 of the application;

[0064] Figure 2 is an electron microscope image of the silicon-based composite material prepared in Example 2 of the application;

[0065] Figure 3 is an electron microscope image of the silicon-based composite material prepared in Example 3 of the application. DETAILED DESCRIPTION

[0066] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0067] In order to make the silicon-based negative electrode material have a higher specific capacity and improve the cycle stability of the silicon-based negative electrode material, the present application provides a silicon-based composite material, which comprises a Si-O-C spherical structure, and the ratio of the number of Si-O bonds to the number of Si-C bonds in the silicon-based composite material is greater than 2

[0068] Specifically, in the Si-O-C spherical structure, Si mainly forms Si-O bonds with O, and a small amount of unbound Si elements exist, C elements mainly exist in the form of free C around the matrix composed of Si-O bonds, and the ratio of the number of Si-O bonds to the number of Si-C bonds is greater than 2, so that the silicon-based composite material can have a higher specific capacity. At the same time, the spherical structure of the silicon-based composite material and the buffer framework formed by Si-O-C can make the silicon-based composite material have a better cycle capacity retention rate and a lower cycle expansion. Among them, according to the change of reaction conditions, the ratio of the number of Si-O bonds to the number of Si-C bonds in the silicon-based composite material can be greater than 2, greater than 2.5, greater than 3, greater than 3.5, greater than 4, greater than 4.5, greater than 5, greater than 5.5, greater than 6, greater than 6.5, greater than 7, greater than 7.5, etc.

[0069] The silicon-based composite material prepared in the present application can not have a porous structure. Therefore, the silicon-based composite material of the present application can have a higher tap density compared with battery materials having a porous structure. Compared with a porous structure, it can better adapt to the volume change during cycling. At the same time, it can avoid the collapse of the Si-O-C spherical structure under the action of a large stress, which will cause the electrolyte to penetrate into the internal pores, resulting in the deterioration of the electrochemical performance. Therefore, the silicon-based negative electrode material prepared in the present application has a rigid structure with a higher hardness from the inside to the outside, which is more conducive to maintaining the structural stability and improving the electrochemical performance.

[0070] In an embodiment of the present application, the surface of the Si-O-C spherical structure is coated with a carbon material layer. By coating the surface of the Si-O-C spherical structure with a carbon material layer, the initial coulumb efficiency (ICE) can be effectively improved.

[0071] In an embodiment of the present application, the Si-O-C spherical structure comprises SiO4 structural units and SiO3C structural units; wherein the mass fraction of the SiO3C structural units is greater than the mass fraction of the SiO4 structural units.

[0072] Preferably, the ratio of the mass fraction of the SiO3C structural unit to the mass fraction of the SiO4 structural unit is greater than 2. Depending on the change of reaction conditions, the ratio of the mass fraction of the SiO3C structural unit to the mass fraction of the SiO4 structural unit can be greater than 2, greater than 2.5, greater than 3, greater than 3.5, greater than 4, greater than 4.5, greater than 5, etc.

[0073] In an embodiment of the present application, the Si-O-C spherical structure further comprises a SiO2C2 structural unit; wherein the ratio of the sum of the mass fraction of the SiO4 structural unit and the mass fraction of the SiO3C structural unit to the mass fraction of the SiO2C2 structural unit is greater than 2.

[0074] Depending on the change of reaction conditions, the ratio of the sum of the mass fraction of the SiO4 structural unit and the mass fraction of the SiO3C structural unit to the mass fraction of the SiO2C2 structural unit can be greater than 2, greater than 2.5, greater than 3, greater than 3.5, greater than 4, greater than 4.5, greater than 5, etc.

[0075] Preferably, the ratio of the sum of the mass fraction of the SiO4 structural unit and the mass fraction of the SiO3C structural unit to the mass fraction of the SiO2C2 structural unit is between 2 and 4.

[0076] Specifically, both the SiO4 structural unit and the SiO3C structural unit are reversible phases, both of which have high specific capacity, and the specific capacity of both structural units can be more than three times higher than that of graphite.

[0077] The SiO3C structural unit can have a higher reversible specific capacity, and the silicon-based composite material can have a higher reversible specific capacity when the silicon-based composite material contains more SiO3C structural units.

[0078] The SiO2C2 structural unit, which can also be included in the Si-O-C spherical structure, is a reversible phase, which can also increase the reversible specific capacity of the silicon-based composite material, but its reversible specific capacity is lower than that of the SiO4 structural unit and the SiO3C structural unit.

[0079] In summary, the silicon-based composite material can tend to contain more SiO4 structural units and SiO3C structural units with high specific capacity, and contain less SiO2C2 structural units. The SiOC3 structural unit and the SiC4 structural unit containing more Si-C bonds can be less than the SiO2C2 structural unit, so that the silicon-based composite material can not contain or contain less SiOC3 structural units and inert SiC4 structural units with low specific capacity, so that the silicon-based composite material as a whole can have high specific capacity.

[0080] In an embodiment of the present application, the O / Si molar ratio in the Si-O-C spherical structure is 1-2, and the C / Si molar ratio is 0.5-3.5.

[0081] Specifically, the Si-O-C spherical structure mainly contains SiO4 structural units, SiO3C structural units, and possibly a small amount of SiO2C2 structural units, and hardly contains SiOC3 structural units and SiC4 structural units. Therefore, the O / Si molar ratio in the Si-O-C spherical structure is between 1 and 2.

[0082] In addition to the SiO4 structural units, SiO3C structural units, and SiO2C2 structural units, the Si-O-C spherical structure can also contain a certain amount of C dispersed in the Si-O-C spherical structure. Therefore, the C / Si molar ratio of the Si-O-C spherical structure can be between 0.5 and 3.5. When the O / Si molar ratio of the Si-O-C spherical structure is between 1 and 2, and the C / Si molar ratio is between 0.5 and 3.5, the C dispersed in the Si-O-C spherical structure can also provide a certain reversible capacity, so that the Si-O-C spherical structure can obtain a higher reversible capacity as the C / Si molar ratio increases.

[0083] In an embodiment of the present application, the coating layer comprises an inorganic carbon material layer. The inorganic carbon material layer can effectively improve the electrical conductivity of the Si-O-C spherical structure, which can form a good conductive network with the C free on the surface and inside the Si-O-C spherical structure, further improving the initial coulombic efficiency of the material. Moreover, the inorganic carbon material layer is coated on the surface of the Si-O-C spherical structure, which does not affect the morphology and amorphous structure of the Si-O-C spherical structure, ensuring that the Si-O-C spherical structure can maintain its good specific capacity and cycle stability.

[0084] In an embodiment of the present application, in the capacity-voltage characteristic curve of the silicon-based composite material, the capacity in the 0-0.1 V interval accounts for 20-50% of the overall capacity of the silicon-based composite material, and the capacity in the 0.1-0.6 V interval accounts for 50-80% of the overall capacity of the silicon-based composite material.

[0085] Specifically, in the capacitance-voltage characteristic curve of the silicon-based composite material, the 0-0.1V interval can correspond to the process of lithium ion embedding into the crystalline silicon, and the 0.1-0.6V interval can correspond to the process of lithium ion embedding into the Si-O-C glass phase. In the case that the capacity in the 0.1-0.6V interval accounts for 50-80% of the overall capacity of the silicon-based composite material, it can be known that the silicon-based composite material mainly forms the Si-O-C glass phase, and the Si-O-C glass phase can have a higher reversible specific capacity and coulombic efficiency, thereby further improving the reversible specific capacity of the silicon-based composite material.

[0086] In an embodiment of the present application, the wadell sphericity of the silicon-based composite material is greater than 0.95.

[0087] Specifically, the spherical structure can have higher flowability and bulk density, and the higher the wadell sphericity of the silicon-based composite material, the more easily the negative electrode material with good electrochemical performance can be obtained in the processing process of the lithium ion battery negative electrode material.

[0088] In an embodiment of the present application, the (D90-D10) / D50 of the silicon-based composite material is less than 1.20.

[0089] Wherein, D90 is the particle size of the cumulative distribution of 90% of the particles, D10 is the particle size of the cumulative distribution of 10% of the particles, and D50 is the particle size of the cumulative distribution of 50% of the particles, also known as the median particle size.

[0090] Specifically, an ideal battery material needs to have a relatively narrow particle size distribution. Previous studies have shown that too much fine powder will cause the continuously consumed electrolyte of the battery material with too high activity during the cycle to cause the capacity retention rate to deteriorate. The large particles with greater expansion are prone to cause particle pulverization during the cycle, which is easy to cause the continuous thickening of SEI, and the SiO x The lithium insertion and extraction of the material itself will also be more difficult. Therefore, narrowing the particle size distribution can improve the cycle performance of the material.

[0091] The (D90-D10) / D50 of the silicon-based composite material in the present application is less than or equal to 1.20. According to the change of the reaction conditions, the particle size span can be 1.20, 1.15, 1.10, 1.05, 1.00, 0.95, 0.90, etc. Therefore, the silicon-based composite material can have a relatively uniform particle size. The relatively uniform particle size can make the silicon-based composite material avoid the above problems while further having a higher bulk density, so as to obtain a negative electrode material with good electrochemical performance and cycle performance.

[0092] In an embodiment of the present application, the median particle size (D50) of the silicon-based composite material is 0.3-5.8 μm. Depending on the reaction conditions, the median particle size can be 5.8 μm, 5.5 μm, 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, 0.5 μm, 0.3 μm, etc.

[0093] The moderate particle size can avoid the case that the silicon-based composite material has too large specific surface area due to too small particle size, which causes the particles to easily agglomerate, resulting in the deterioration of the performance of the lithium ion battery negative electrode material after processing, and the case that the battery negative electrode material with too high activity continuously consumes electrolyte during cycling, causing the deterioration of the capacity retention rate.

[0094] In an embodiment of the present application, the specific surface area of the silicon-based composite material is 2 m 2 / g-9.5 m 2 / g. Depending on the reaction conditions, the specific surface area can be 9.5 m 2 / g, 8 m 2 / g, 7 m 2 / g, 6 m 2 / g, 5 m 2 / g, 4 m 2 / g, 3 m 2 / g, 2 m 2 / g, etc. The moderate specific surface area can avoid the case that the lithium ion battery negative electrode material has deteriorated performance due to too large specific surface area.

[0095] Optionally, the silicon-based composite material contains Si microcrystals with a size of 1 nm-10 nm. The moderate size of the Si microcrystals can bring higher cycle performance to the lithium ion battery. Depending on the reaction conditions, the size of the Si microcrystals can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc.

[0096] The present application also discloses a preparation method of a silicon-based composite material, which comprises:

[0097] adding siloxane raw materials, phenolic raw materials, aldehyde raw materials, and a catalyst in a solvent, and mixing uniformly to obtain an oil phase;

[0098] dropping the oil phase into an aqueous phase containing an emulsifier to obtain an oil-in-water emulsion;

[0099] forming a gel from the oil-in-water emulsion under the condition of pH value 11-12, drying, and then performing heat treatment to obtain a silicon-based composite material.

[0100] The standing time under water bath or oil bath can be 6-24 hours.

[0101] The pH adjusting solution can include ammonia or urea, and the concentration thereof is 0.1-2 mol / L.

[0102] The solvent can include a mixed solution of ethanol and deionized water.

[0103] The temperature range for controlling the sol to gel is 25-100℃. Specifically, the temperature for controlling the sol to gel can be 25℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc., and the present application does not limit this.

[0104] Specifically, the present application uses a sol-gel method to prepare the silicon-based composite material. In the preparation process, by adjusting the pH value to be between 11 and 12, no gel-like precipitate is generated in the preparation process, so that the finally prepared silicon-based composite material can have good flowability, and has high tap density and specific discharge capacity, thereby having excellent electrochemical performance. Dropping the oil phase into the water phase forms an oil-in-water emulsion, which can promote the hydrolysis and condensation reaction of the multiple sol molecules to be coated in a layer of water coating, thereby promoting the generation of micron-sized Si-O-C spherical particles.

[0105] Specifically, the silicon-based composite material is prepared by a sol-gel method, and by adjusting the pH value, the nucleation and generation speed of the sol can be controlled. When the nucleation speed is much greater than the generation speed, a large number of crystal nuclei will be formed in the solution, and at this time the growth speed of the crystal nuclei is very slow, so these crystal nuclei will agglomerate and eventually form a gel-like precipitate. Such a sample not only has no spherical structure in terms of morphology, but also has low tap density and poor electrochemical performance. When the nucleation speed is much less than the growth speed, the solution has a small number of crystal nuclei, and at this time the growth speed of the crystal nuclei is very large, so there is no agglomeration phenomenon in the generation process of the crystal. The crystal has a good generation and growth environment, and finally a large-particle-size spherical structure with good morphology characteristics is obtained, thereby obtaining a silicon-based composite material with good comprehensive performance.

[0106] The present application adjusts the pH value to be between 11 and 12, reduces the supersaturation of the solution, so that the nucleation rate tends to decrease compared with the growth rate in the process of crystal generation, so that there are fewer crystal nuclei in the solution. These crystal nuclei have good growth space, and ultimately particles with moderate particle size will be obtained. At the same time, due to the pH value between 11 and 12, the pH value fluctuates less, so that the reaction is carried out under relatively stable pH conditions, and a silicon-based composite material with concentrated particle size distribution is obtained. In addition, since the solution is in an alkaline environment at this time, small particles in the solution have a larger solubility than large particles, and the alkaline environment promotes the dissolution of small particles. The newly generated particles can orderly arrange and grow on larger crystals, which is conducive to the growth of the crystals. In larger particles, the internal particles have different activity from the corner particles. Specifically, the internal particles have lower activity than the corner particles due to stronger binding force, while the corner particles are more active. Therefore, the alkaline solution can interact with the corner particles, and the synthesized particles have good morphology and can present a spherical structure. The spherical structure has high flowability and bulk density, which improves the electrochemical performance of the silicon-based composite material.

[0107] If the pH value is not adjusted, it may affect the morphology of the finally formed precursor microspheres, and a large number of "fluff" structures may exist on the particle surface, which will greatly increase the specific surface area of the material. The increase in specific surface area will increase the side reactions, thereby affecting the capacity retention rate during cycling, and also causing the expansion caused by the thickening of the SEI film to increase. The fluff structure and low tap density will both bring about poor material processing performance. In the present application, by reasonably adjusting the pH value to be between 11 and 12 and controlling the reaction temperature range, the silicon-based composite material prepared has a smooth surface and a narrow particle size distribution, which helps to improve the cycling performance of the material.

[0108] Low temperature is conducive to the formation of small particles, and high temperature is conducive to the formation of larger particles. In order to obtain spherical particles with larger particle size and higher bulk density, a higher reaction temperature should be selected. However, too high a reaction temperature will increase energy consumption, and the evaporation of the solution system during the reaction will greatly affect the accurate and continuous measurement of the pH value of the reaction. With the increase of the reaction temperature, the specific discharge capacity slightly increases, and the bulk density shows a decreasing trend. By controlling the oil bath or water bath temperature to be between 25 and 100°C during preparation, the silicon-based composite material prepared has moderate particle size and a narrow particle size distribution.

[0109] The prepared silicon-based composite material is in the order of microns, is not easy to agglomerate, and has moderate specific surface area, which can avoid the case that the specific surface area of the silicon-based composite material is too large due to too small particle size, the particles are easy to agglomerate, and the performance of the processed lithium ion battery negative material is deteriorated, and the case that the battery negative material with too high activity continuously consumes electrolyte during cycling to cause the capacity retention rate to deteriorate. At the same time, the prepared silicon-based composite material can have a relatively narrow particle size distribution and a good spherical appearance, so that the cycle performance of the material is further improved.

[0110] The prepared silicon-based composite material has a ratio of the number of Si-O bonds to the number of Si-C bonds greater than 2, and the Si-C bonds are dominant. 2+ The Si-C bonds are dominant, which can ensure that the prepared silicon-based composite material has similar specific capacity and initial coulombic efficiency to commercial SiO x Under the premise of similar specific capacity and initial coulombic efficiency, the capacity retention rate of the material is further improved and the expansion is reduced.

[0111] In the preparation process, the precursor microspheres are heat treated based on the carbon source, so that the surface of the Si-O-C spherical structure in the silicon-based composite material can be coated with a carbon material layer. During the heat treatment of the precursor microspheres, the phenolic resin formed by the reaction of the phenolic raw material and the aldehyde raw material is carbonized to form free C in the Si-O-C spherical structure, and the carbon material layer and the free C in the Si-O-C spherical structure form a more complete and thinner C layer conductive network, which can improve the initial coulombic efficiency without significantly reducing the specific capacity of the material, and can further optimize the cycle performance of the Si-O-C material as a lithium ion battery negative material.

[0112] In an embodiment of the present application, the step of adding a siloxane raw material, a phenolic raw material, an aldehyde raw material, and a catalyst in a solvent to obtain an oil phase after mixing uniformly specifically includes:

[0113] The siloxane raw material and the phenolic raw material are added to the solvent, and a second solution is obtained after mixing uniformly;

[0114] The aldehyde raw material and the catalyst are added to the second solution, and an oil phase is obtained after mixing uniformly.

[0115] In a specific implementation, the step of adding a siloxane raw material, a phenolic raw material, an aldehyde raw material, and a catalyst in a solvent to obtain an oil phase after mixing uniformly specifically includes:

[0116] The siloxane raw material and the phenolic raw material are added to the solvent, and a second solution is obtained after mixing uniformly at a stirring speed of 100-400 r / min for 30-180 minutes;

[0117] The aldehyde raw material and the catalyst are added to the second solution, and an oil phase is obtained after mixing uniformly at a stirring speed of 100-400 r / min for 0-30 minutes.

[0118] In an embodiment of the present application, the step of adding the oil phase droplets into the water phase containing the emulsifier to obtain the oil-in-water emulsion comprises:

[0119] adding the emulsifier into deionized water to obtain a water phase; and adding the oil phase droplets into the water phase to obtain an oil-in-water emulsion.

[0120] In an embodiment of the present application, the step of forming the oil-in-water emulsion into a gel, drying, and then heat treating to obtain the silicon-based composite material comprises:

[0121] standing still in a water bath or oil bath at 25-100℃ to form a gel;

[0122] drying the gel to obtain precursor microspheres, and heat treating the precursor microspheres to obtain the silicon-based composite material.

[0123] In an embodiment of the present application, the method further comprises:

[0124] heat treating the silicon-based composite material based on a carbon source to obtain a silicon-based composite material coated with a carbon material layer;

[0125] In an embodiment of the present application, the step of heat treating the silicon-based composite material based on a carbon source to obtain a silicon-based composite material coated with a carbon material layer comprises:

[0126] mixing the silicon-based composite material with the carbon source and then heat treating to obtain a silicon-based composite material coated with a carbon material layer.

[0127] The temperature for heat treating the precursor microspheres is determined according to actual needs, for example, the temperature range can be set to 600-1000℃, which can be 600℃, 700℃, 800℃, 900℃, 1000℃, etc., and the present application does not limit this.

[0128] The temperature for heat treating the silicon-based composite material is determined according to actual needs, for example, the temperature range can be set to 600-1000℃, which can be 600℃, 700℃, 800℃, 900℃, 1000℃, etc., and the present application does not limit this.

[0129] The heat treatment equipment can be a rotary furnace, a tube furnace, a box furnace, a roller kiln, a tunnel kiln, a push plate kiln, etc., and the present application does not limit this.

[0130] Under high-temperature heat treatment, the precursor microspheres compounded by siloxane and phenolic resin are carbonized, and polarization is basically eliminated, thereby forming a silicon-based composite mainly composed of Si, C, O and H. Specifically, Si, O and part of C form Si(O,C)4 tetrahedral structures, mainly including basic units of SiC4, SiOC3, SiO2C2, SiO3C and SiO4, and the remaining C exists in the form of free carbon. The content of SiO3C, which has the highest reversible specific capacity, is the most, followed by SiO4, and the content of SiO2C2 is less than SiO4. The content of H in Si-O-C composite microspheres is extremely small, some of which exist in the form of C-H bond on the periphery of free carbon, and some of which exist in the form of Si-H bond.

[0131] Optionally, in the process of heat treating the precursor microspheres to form the silicon-based composite, the precursor microspheres can be placed in a reducing atmosphere, which is beneficial to the formation of a more reversible Si-O-C glass phase for lithium ions, and the Si-O-C glass phase can have a higher reversible specific capacity and coulombic efficiency.

[0132] In an embodiment of the present application, the step of drying the gel to obtain the precursor microspheres includes: drying the gel at 60-100°C for 30-60 min to obtain the precursor microspheres. The drying method can include centrifugation, suction filtration, spray drying, etc.

[0133] In an embodiment of the present application, the pH value can be adjusted in different steps according to actual needs.

[0134] Therefore, the step of adding siloxane raw materials and phenolic raw materials to the solvent and mixing uniformly to obtain a second solution can include: adding a pH adjusting solution to the solvent to adjust the pH value to be between 11 and 12 to obtain a first solution; adding siloxane raw materials and phenolic raw materials to the first solution and mixing uniformly to obtain a second solution.

[0135] The step of adding the oil phase dropwise into the water phase containing the emulsifier to obtain an oil-in-water emulsion can include: adding an emulsifier and a pH adjusting solution to the water phase to adjust the pH value to be between 11 and 12, and adding the oil phase dropwise into the water phase.

[0136] The step of forming a gel from the oil-in-water emulsion under the condition of a pH value of 11-12 can include: adding a pH adjusting solution to the oil-in-water emulsion to adjust the pH value to be between 11 and 12, and forming a gel from the oil-in-water emulsion.

[0137] In an embodiment of the present application, the O / Si molar ratio in the siloxane raw materials is ≤1.

[0138] Specifically, by setting the O / Si molar ratio of the siloxane raw material to be ≤1, the O / Si molar ratio of the prepared silicon-based composite material is avoided to be too high. In the case that the O / Si molar ratio of the siloxane raw material is appropriate, the silicon-based composite material can be more inclined to form SiO3C structural units with better specific capacity, so that the silicon-based composite material can obtain higher specific capacity.

[0139] The siloxane raw material includes at least one of aromatic siloxane, octamethyltetrasiloxane (C8H 24 O4Si4), decamethyltetrasiloxane (C 10 H 30 O3Si4), 1,3-divinyltetramethyldisiloxane (C8H 18 OSi2), octamethyltrisiloxane (C8H 24 O2Si3).

[0140] By reasonably selecting the siloxane raw material, the prepared silicon-based composite material is more inclined to generate SiO3C structural units and SiO4 structural units with higher reversible specific capacity, and less generate SiC4 structural units and SiOC3 structural units with lower specific capacity.

[0141] In an embodiment of the present application, the phenolic raw material includes at least one of resorcinol, m-aminophenol, and bisphenol A. By reasonably selecting the siloxane raw material, the prepared silicon-based composite material is more inclined to generate SiO3C structural units and SiO4 structural units with higher reversible specific capacity, and less generate SiC4 structural units and SiOC3 structural units with lower specific capacity.

[0142] In an embodiment of the present application, the aldehyde raw material can include formaldehyde. By reasonably selecting the siloxane raw material, the prepared silicon-based composite material is more inclined to generate SiO3C structural units and SiO4 structural units with higher reversible specific capacity, and less generate SiC4 structural units and SiOC3 structural units with lower specific capacity.

[0143] In an embodiment of the present application, the catalyst includes platinum divinyltetramethyl-disiloxane complex and / or dibutyltin dilaurate. By selecting a phenolic functional silane that can be used as an adhesion promoter. Promote the hydrolysis and condensation reaction between siloxane and phenolic aldehyde, so that they can generate a 3D body phase macromolecular network with larger molecular weight, generating μm-level spheres.

[0144] In an embodiment of the present application, the emulsifier includes at least one of polysorbate-80, polysorbate-60, polysorbate-40, and polysorbate-20.

[0145] Specifically, the emulsifier is selected from emulsifiers with HLB in the range of 8-18, so that the oil phase can be more easily added to the water phase to generate an oil-in-water (O-W) emulsion. The multiple sol molecules generated by the hydrolysis and condensation reaction can be simultaneously coated in a layer of water, thereby facilitating the generation of micron-sized Si-O-C spherical particles.

[0146] In an embodiment of the present application, the carbon source includes at least one of a solid-phase carbon source, a liquid-phase carbon source, and a gas-phase carbon source.

[0147] In an embodiment of the present application, the solid-phase carbon source includes at least one of organic solid carbon sources of citric acid, glucose, pitch, phenolic resin, and furfuryl resin. In the case of using a solid carbon source, the cooled Si-O-C composite microspheres can be mixed with the carbon source uniformly, placed in a furnace, and pyrolyzed by introducing a protective gas such as nitrogen, argon, helium, neon, krypton, and xenon, etc. to make the carbon source crack and coat the surface of the Si-O-C composite microspheres.

[0148] The mixing method can include mixing by a VC mixer, fusion, ball milling, suction filtration, heating reflux, three-dimensional mixing, fluidized bed mixing, etc.

[0149] In an embodiment of the present application, the liquid-phase carbon source includes at least one of organic liquid carbon sources of low-temperature liquid pitch, furfuryl alcohol, glycidyl methacrylate, and triethylene glycol dimethacrylate. In the case of using a liquid carbon source, the cooled Si-O-C composite microspheres can be mixed with the carbon source uniformly, placed in a furnace, and pyrolyzed by introducing a protective gas such as nitrogen, argon, helium, neon, krypton, and xenon, etc. to make the carbon source crack and coat the surface of the Si-O-C composite microspheres.

[0150] The mixing method can include mixing by a VC mixer, fusion, ball milling, suction filtration, heating reflux, three-dimensional mixing, fluidized bed mixing, etc.

[0151] In an embodiment of the present application, the gas-phase carbon source includes at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone, and benzene. In the case of using a gas-phase carbon source, the cooled Si-O-C composite microspheres can be placed in a furnace and pyrolyzed by introducing a gas-phase carbon source to make amorphous carbon deposit on the surface of the Si-O-C composite microspheres.

[0152] In an embodiment of the present application, the solvent can include deionized water and / or ethanol, and in the case of including deionized water and ethanol, the mass ratio between the ethanol and the deionized water is 1:0-10. For example, 1:0, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0153] In one embodiment of the present application, the mass ratio between the phenolic raw material and the siloxane raw material is 1:2-8. For example, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, etc.

[0154] In addition, the mass ratio between the phenolic raw material and the second solution is 1:100-300, for example, 1:100, 1:150, 1:200, 1:250, 1:300, etc.

[0155] In one embodiment of the present application, the volume ratio between the aldehyde raw material and the first solution is 1:50-250. For example, 1:50, 1:100, 1:150, 1:250, etc.

[0156] In one embodiment of the present application, the volume ratio between the pH adjusting solution and the solvent is 1:30-100. For example, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, etc.

[0157] In one embodiment of the present application, the catalyst accounts for 0.5%-15% of the mass of the siloxane raw material. For example, 0.5%, 1%, 2%, 5%, 7%, 10%, 13%, 15%, etc.

[0158] In one embodiment of the present application, the emulsifier accounts for 1%-20% of the mass of the aqueous phase. For example, 1%, 2%, 5%, 7%, 10%, 13%, 15%, 17%, 20%, etc.

[0159] In one embodiment of the present application, the mass ratio between the oil phase and the aqueous phase is 1:20-100. For example, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, etc.

[0160] By reasonably selecting the ratio of various raw materials, the reaction speed is controlled under the premise of ensuring sufficient reaction, thereby improving the sphericity of the prepared microspheres and narrowing the range of particle size. And it can be more inclined to generate SiO3C structural units, SiO4 structural units with higher reversible specific capacity, and less SiC4 structural units, SiOC3 structural units with lower specific capacity.

[0161] In the prior art, the sol-gel method is used to prepare the silicon-based composite material, and irregular morphology is easily generated, or although spherical structure is generated, the particle size is small (nanometer level). If the silicon-based composite material with μm size is needed to be produced, the pressure resistance of the equipment is usually required to be high, and special equipment is needed to be used. In the present application, by screening the reaction raw materials and the proportion, and by controlling the reaction conditions in the reaction process, the spherical particles with μm size can be obtained, and the particles do not have the phenomenon of adhesion, and have good dispersibility.

[0162] The present application also discloses a lithium ion battery comprising the silicon-based composite material as described in the present application or the silicon-based composite material prepared by the method as described in the present application.

[0163] The following are typical but non-limiting examples of the present application:

[0164] Example 1

[0165] (1) 30ml of 1mol / L ammonia water was dispersed in a mixed solution of 2000ml of water and 1000ml of ethanol, and stirred at a speed of 300r / min for 1h to adjust the pH value to be between 11 and 12, to obtain a second solution;

[0166] (2) 100ml of octamethyltrisiloxane (density 0.82g / cm3) and 10g of resorcinol were slowly added, and stirring was continued at a speed of 200r / min for 30min to obtain a first solution;

[0167] (3) 14ml of formaldehyde solution was further added dropwise in the first solution, platinum divinyltetramethyl-disiloxane complex (1% of the mass of octamethyltrisiloxane) was added to the mixture, and then stirring was carried out at a speed of 200r / min for 15min to obtain an oil phase;

[0168] (4) In another container, 20wt% of polysorbate-80 was added to ionized water to obtain an aqueous phase. The mass ratio of the aqueous phase and the oil phase was 50:1.

[0169] (5) After the aqueous phase and the oil phase were respectively mixed uniformly, the oil phase was added dropwise into the aqueous phase to form an oil-in-water emulsion while stirring;

[0170] (6) The emulsion was heated in a water bath at 80℃ for 24h, and in this process, the oil phase liquid was quickly gelatinized and solidified to generate a gel;

[0171] (7) The gel was centrifuged, washed and dried to obtain methyl poly silyl-phenolic resin composite microspheres;

[0172] (8) The dried methylsilsesquioxane-phenol formaldehyde resin composite microspheres were carbonized in a tube furnace under argon atmosphere at 800°C for 6 hours to obtain black Si-O-C composite microspheres.

[0173] Example 2

[0174] (1) 30 ml of 1 mol / L urea was dispersed in a mixed solution of 2000 ml of water and 1000 ml of ethanol, and stirred at a speed of 300 r / min for 1 h to adjust the pH value to be between 11 and 12 to obtain a second solution;

[0175] (2) 100 ml of octamethyltrisiloxane (density 0.82 g / cm 3 ) and 10 g of resorcinol were slowly added, and stirring was continued at a speed of 200 r / min for 30 min to obtain a first solution;

[0176] (3) 14 ml of formaldehyde solution was further added dropwise to the first solution, and platinum divinyltetramethyl-disiloxane complex (1% of the mass of octamethyltrisiloxane) was added to the mixture, followed by stirring at a speed of 200 r / min for 15 min to obtain an oil phase;

[0177] (4) In another container, 20 wt% of polysorbate-80 was added to ionized water to obtain an aqueous phase. The mass ratio of the aqueous phase to the oil phase was 50:1.

[0178] (5) After the aqueous phase and the oil phase were each mixed uniformly, the oil phase was added dropwise to the aqueous phase under stirring to form an oil-in-water emulsion;

[0179] (6) The emulsion was heated in a water bath at 80°C for 24 hours, and in this process, the oil phase liquid was quickly gelatinized and solidified to form a gel;

[0180] (7) The gel was centrifuged, washed, and dried to obtain methylsilsesquioxane-phenol formaldehyde resin composite microspheres;

[0181] (8) The dried methylsilsesquioxane-phenol formaldehyde resin composite microspheres were carbonized in a tube furnace under argon atmosphere at 800°C for 6 hours to obtain black Si-O-C composite microspheres.

[0182] (9) Using glucose as a carbon source, the glucose and the obtained Si-O-C composite microspheres were mixed by a VC mixer, a roller kiln was used, and argon was used as a protective atmosphere for carbonization at 1000°C to obtain a silicon-based composite material coated with a carbon material layer.

[0183] Example 3:

[0184] (1) 100 ml of 0.5 mol / L ammonia water was dispersed in a mixed solution of 2000 ml of water and 1000 ml of ethanol, stirred at a speed of 200 r / min for 120 min to adjust the pH value to 11-12 to obtain a second solution;

[0185] (2) 100 ml of decamethyltetrasiloxane (0.8-0.9 g / cm 3 ) and 29 g of resorcinol were slowly added, and stirring was continued at a speed of 400 r / min for 60 min to obtain a first solution;

[0186] (3) 42 ml of formaldehyde solution was further added dropwise to the first solution, and dibutyltin dimosilicate (0.5% of the mass of decamethyltetrasiloxane) was added to the mixture, followed by stirring at a speed of 100 r / min for 20 min to obtain an oil phase;

[0187] (4) In another container, 10 wt.% of polysorbate-20 was added to ionized water to obtain an aqueous phase. The mass ratio of water to oil phase was 20:1.

[0188] (5) After the aqueous phase and the oil phase were each mixed uniformly, the oil phase was added dropwise to the aqueous phase under stirring to form an oil-in-water emulsion;

[0189] (6) The emulsion was heated at 100°C in an oil bath for 6 hours, during which the oil phase liquid quickly gelled and solidified to form a gel;

[0190] (7) The gel was centrifuged, washed, and dried to obtain methyl poly silesquioxane-phenolic resin composite microspheres;

[0191] (8) The dried methyl poly silesquioxane-phenolic resin composite microspheres were carbonized at 600°C for 1 hour under an argon atmosphere in a tube furnace to obtain black Si-O-C composite microspheres.

[0192] (9) Using low-temperature liquid pitch as a carbon source, the pitch was fused with the obtained Si-O-C composite microspheres, a rotary furnace was used, and nitrogen was used as a protective atmosphere for carbonization at 800°C to obtain a silicon-based composite material coated with a carbon material layer.

[0193] Example 4:

[0194] (1) 3000 ml of water and 500 ml of ethanol were mixed, stirred at a speed of 400 r / min for 60 min, and then 100 ml of octamethyltrisiloxane (density 0.82 g / cm 3 ) and 18 g of bisphenol A were slowly added, and stirring was continued at a speed of 100 r / min for 60 min to obtain a first solution;

[0195] (3) In the first solution, 25 ml of formaldehyde solution was added dropwise, and platinum divinyltetramethyl-disiloxane complex (3% of octamethyltrisiloxane mass) was added to the mixture, followed by stirring at 200 r / min for 25 min to obtain an oil phase;

[0196] (4) In another container, 1 wt.% of polysorbate-40 was added to ionized water to obtain an aqueous phase. The mass ratio of the aqueous phase to the oil phase was 60:1;

[0197] (5) After the aqueous phase and the oil phase were mixed uniformly, the oil phase was added dropwise to the aqueous phase under stirring to form an oil-in-water emulsion;

[0198] (6) 80 ml of 2 mol / L ammonia water was dispersed in the oil-in-water emulsion, and the emulsion was heated in a 25°C water bath for 12 hours. In this process, the oil phase liquid quickly gelled and solidified to form a gel;

[0199] (7) The gel was centrifuged, washed, and dried to obtain methyl poly silesquioxane-phenolic resin composite microspheres;

[0200] (8) The dried methyl poly silesquioxane-phenolic resin composite microspheres were carbonized at 900°C for 3 hours under an argon atmosphere in a tube furnace to obtain black Si-O-C composite microspheres.

[0201] (9) Using methane as a carbon source, placing the Si-O-C composite microspheres in a rotary furnace, passing in methane gas, and using nitrogen as a protective atmosphere, carbonization was carried out at 900°C to obtain a silicon-based composite material coated with a carbon material layer.

[0202] Example 5:

[0203] (1) 100 ml of 0.1 mol / L ammonia water was dispersed in a mixture of 4000 ml of water and 500 ml of ethanol, and stirred at a speed of 350 r / min for 90 min to adjust the pH value to 11-12 to obtain a second solution;

[0204] (2) 100 ml of 1,3-divinyltetramethyl disiloxane (density 0.81 g / mL) and 20 g of m-aminophenol were slowly added, and stirring was continued at a speed of 150 r / min for 180 min to obtain a first solution;

[0205] (3) In the first solution, 27 ml of formaldehyde solution was added dropwise, and platinum divinyltetramethyl-disiloxane complex (15% of 1,3-divinyltetramethyl disiloxane mass) was added to the mixture, followed by stirring at 400 r / min for 30 min to obtain an oil phase;

[0206] (4) In another container, add 10 wt.% of polysorbate-60 into ionized water to obtain an aqueous phase. The mass ratio of water and oil phase is 100:1;

[0207] (5) After the aqueous phase and the oil phase are mixed uniformly respectively, the oil phase is added drop by drop into the aqueous phase under stirring to form an oil-in-water emulsion;

[0208] (6) The emulsion is heated in an oil bath at 70°C for 18 hours, during which the oil phase liquid quickly gels to form a gel;

[0209] (7) The gel is centrifuged, washed, and dried to obtain methyl poly silesquioxane-phenolic resin composite microspheres;

[0210] (8) The dried methyl poly silesquioxane-phenolic resin composite microspheres are carbonized at 700°C for 5 hours in a tube furnace under an argon atmosphere to obtain black Si-O-C composite microspheres.

[0211] (9) Using acetylene as a carbon source, placing the Si-O-C composite microspheres in a rotary furnace, passing acetylene gas, and using nitrogen as a protective atmosphere, carbonization is carried out at 850°C to obtain a silicon-based composite material coated with a carbon material layer.

[0212] Example 6

[0213] (1) 30 ml of 1 mol / L ammonia water is dispersed in a mixed solution of 2000 ml of water and 1350 ml of ethanol, stirred at a speed of 300 r / min for 1 h to adjust the pH value to be between 11 and 12, to obtain a second solution;

[0214] (2) 100 ml of aromatic siloxane (density 0.9 g / cm 3 Please adjust the density) and 10 g of resorcinol are slowly added, and stirring is continued at a speed of 200 r / min for 30 min to obtain a first solution;

[0215] (3) 14 ml of formaldehyde solution is further added dropwise to the first solution, platinum divinyltetramethyl-disiloxane complex (1% of the mass of the aromatic siloxane) is added to the mixture, and then stirring is carried out at a speed of 200 r / min for 15 min to obtain an oil phase;

[0216] (4) In another container, add 20 wt.% of polysorbate-80 into ionized water to obtain an aqueous phase. The mass ratio of water and oil phase is 50:1.

[0217] (5) After the aqueous phase and the oil phase are mixed uniformly respectively, the oil phase is added drop by drop into the aqueous phase under stirring to form an oil-in-water emulsion;

[0218] (6) The emulsion is heated in a water bath at 80°C for 24 hours, during which the oil phase liquid quickly gels and solidifies to form a gel;

[0219] (7) The gel is centrifuged, washed, and dried to obtain methylsilsesquioxane-phenol resin composite microspheres;

[0220] (8) The dried methylsilsesquioxane-phenol resin composite microspheres are carbonized in a tube furnace under an argon atmosphere at 800°C for 6 hours to obtain black Si-O-C composite microspheres.

[0221] (9) Using citric acid and pitch as carbon sources, the citric acid and pitch are mixed with the obtained Si-O-C composite microspheres by a VC mixer, a roller kiln is used, and argon is used as a protective atmosphere for carbonization at 1000°C to obtain a silicon-based composite material coated with a carbon material layer.

[0222] Example 7

[0223] (1) 100 ml of 0.5 mol / L ammonia water is dispersed in a mixed solution of 1000 ml of water and 1000 ml of ethanol, stirred at a speed of 200 r / min for 120 min to adjust the pH value to between 11 and 12, and a second solution is obtained;

[0224] (2) 75 ml of octamethyltetrasiloxane (0.96 g / cm 3 ) and 29 g of resorcinol are slowly added, and stirring at a speed of 400 r / min is continued for 60 min to obtain a first solution;

[0225] (3) 42 ml of a formaldehyde solution is further added dropwise to the first solution, dibutyl tin dimetasilicate (0.5% of the mass of octamethyltetrasiloxane) is added to the mixture, and then stirring at a speed of 100 r / min is performed for 20 min to obtain an oil phase;

[0226] (4) In another container, 10 wt.% of polysorbate-20 is added to ionized water to obtain an aqueous phase. The mass ratio of water to oil is 20:1.

[0227] (5) After the aqueous phase and the oil phase are each mixed uniformly, the oil phase is added dropwise to the aqueous phase while stirring to form an oil-in-water emulsion;

[0228] (6) The emulsion is heated in an oil bath at 100°C for 6 hours, during which the oil phase liquid quickly gels and solidifies to form a gel;

[0229] (7) The gel is centrifuged, washed, and dried to obtain methylsilsesquioxane-phenol resin composite microspheres;

[0230] (8) The dried methylsilsesquioxane-phenol formaldehyde resin composite microspheres were carbonized in a tube furnace under argon atmosphere at 600°C for 1 hour to obtain black Si-O-C composite microspheres.

[0231] (9) Using furfuryl alcohol, glycidyl methacrylate, and triethylene glycol dimethacrylate as carbon sources, the Si-O-C composite microspheres obtained from furfuryl alcohol, glycidyl methacrylate, and triethylene glycol dimethacrylate were fused, a rotary furnace was used, and nitrogen was used as a protective atmosphere for carbonization at 800°C to obtain a silicon-based composite material coated with a carbon material layer.

[0232] Example 8

[0233] (1) 80 ml of 2 mol / L ammonia water was dispersed in 3000 ml of water, stirred at a speed of 400 r / min for 60 min to adjust the pH value to be between 11 and 12 to obtain a second solution;

[0234] (2) 100 ml of decamethyltetrasiloxane (density 0.85 g / cm 3 ) and 18 g of bisphenol A were slowly added, and stirring was continued at a speed of 100 r / min for 60 min to obtain a first solution;

[0235] (3) 25 ml of formaldehyde solution was further added dropwise to the first solution, platinum divinyltetramethyl-disiloxane complex (3% of the mass of decamethyltetrasiloxane) was added to the mixture, and then stirring was continued at a speed of 200 r / min for 25 min to obtain an oil phase;

[0236] (4) In another container, 1 wt.% of polysorbate-40 was added to ionized water to obtain an aqueous phase. The mass ratio of water to oil was 60:1;

[0237] (5) After the aqueous phase and the oil phase were each mixed uniformly, the oil phase was added dropwise to the aqueous phase while stirring to form an oil-in-water emulsion;

[0238] (6) The emulsion was heated in a water bath at 25°C for 12 hours, and in this process, the oil phase liquid quickly gelled and solidified to form a gel;

[0239] (7) The gel was centrifuged, washed, and dried to obtain methylsilsesquioxane-phenol formaldehyde resin composite microspheres;

[0240] (8) The dried methylsilsesquioxane-phenol formaldehyde resin composite microspheres were carbonized in a tube furnace under argon atmosphere at 900°C for 3 hours to obtain black Si-O-C composite microspheres.

[0241] (9) Using ethylene and propylene as carbon sources, placing Si-O-C composite microspheres in a rotary furnace, passing ethylene and propylene gas, and using nitrogen as a protective atmosphere, carbonization at 900°C to obtain a silicon-based composite material coated with a carbon material layer.

[0242] Example 9

[0243] (1) 30 ml of 1 mol / L ammonia water was dispersed in a mixed solution of 1000 ml of ethanol, stirred at a speed of 300 r / min for 1 h to adjust the pH value to 11-12 to obtain a second solution;

[0244] (2) 100 ml of octamethyltrisiloxane (density 0.82 g / cm 3 ) and 10 g of resorcinol were slowly added, and stirring was continued at a speed of 200 r / min for 30 min to obtain a first solution;

[0245] (3) 14 ml of formaldehyde solution was further added to the first solution, platinum divinyltetramethyl-disiloxane complex (1% of the mass of octamethyltrisiloxane) was added to the mixture, and then stirring was continued at a speed of 200 r / min for 15 min to obtain an oil phase;

[0246] (4) In another container, 20 wt% of polysorbate-80 was added to ionized water to obtain an aqueous phase. The mass ratio of the aqueous phase to the oil phase was 50:1.

[0247] (5) After the aqueous phase and the oil phase were each mixed uniformly, the oil phase was added dropwise to the aqueous phase under stirring to form an oil-in-water emulsion;

[0248] (6) The emulsion was heated in a water bath at 80°C for 24 h, and in this process, the oil phase liquid quickly gelled and solidified to form a gel;

[0249] (7) The gel was centrifuged, washed, and dried to obtain methyl poly silesquioxane-phenol formaldehyde resin composite microspheres;

[0250] (8) The dried methyl poly silesquioxane-phenol formaldehyde resin composite microspheres were carbonized at 800°C for 6 h under an argon atmosphere in a tube furnace to obtain black Si-O-C composite microspheres.

[0251] (9) Using phenol formaldehyde resin and furfuryl alcohol resin as carbon sources, the phenol formaldehyde resin and furfuryl alcohol resin were mixed with the obtained Si-O-C composite microspheres by a VC mixer, a roller kiln was used, and argon was used as a protective atmosphere, and carbonization at 1000°C to obtain a silicon-based composite material coated with a carbon material layer.

[0252] Example 10

[0253] (1) 100 ml of 0.5 mol / L ammonia water was dispersed in a mixed solution of 2000 ml of water and 1000 ml of ethanol, stirred at a speed of 200 r / min for 120 min to adjust the pH value to 11-12 to obtain a second solution;

[0254] (2) 100 ml of decamethyltetrasiloxane (0.8-0.9 g / cm 3 ) and 29 g of resorcinol were slowly added, and stirring was continued at a speed of 400 r / min for 60 min to obtain a first solution;

[0255] (3) 42 ml of formaldehyde solution was further added dropwise to the first solution, and dibutyltin dimethylsilicate (0.5% of the mass of decamethyltetrasiloxane) was added to the mixture, followed by stirring at a speed of 100 r / min for 20 min to obtain an oil phase;

[0256] (4) In another container, a water phase was obtained by adding 10 wt.% of polysorbate-20 to ionized water. The mass ratio of the water phase to the oil phase was 20:1.

[0257] (5) After the water phase and the oil phase were each mixed uniformly, the oil phase was added dropwise to the water phase under stirring to form an oil-in-water emulsion;

[0258] (6) The emulsion was heated in an oil bath at 100°C for 6 hours, during which the oil phase liquid quickly gelled and solidified to form a gel;

[0259] (7) The gel was centrifuged, washed, and dried to obtain methylsilsesquioxane-phenolic resin composite microspheres;

[0260] (8) The dried methylsilsesquioxane-phenolic resin composite microspheres were carbonized at 600°C for 1 hour under an argon atmosphere in a tube furnace to obtain black Si-O-C composite microspheres.

[0261] (9) Using ethane, propane, and propyne as carbon sources, the Si-O-C composite microspheres were placed in a rotary furnace, the ethane, propane, and propyne gas was introduced, and nitrogen was used as a protective atmosphere for carbonization at 900°C to obtain a silicon-based composite material coated with a carbon material layer.

[0262] Example 11

[0263] (1) 100 ml of decamethyltetrasiloxane (0.8-0.9 g / cm 3 ) and 29 g of resorcinol were slowly added in a mixed solution of 2000 ml of water and 1000 ml of ethanol, and stirring was continued at a speed of 400 r / min for 60 min to obtain a first solution;

[0264] (2) In the first solution, 42 ml of formaldehyde solution was added dropwise, and dibutyl tin dimetasilicate (0.5% of the mass of decamethyltetrasiloxane) was added to the mixture, followed by stirring at a speed of 100 r / min for 20 min to obtain an oil phase;

[0265] (3) In another container, 10 wt.% of polysorbate-20 and 100 ml of 0.5 mol / L ammonia water were added to ionized water to obtain an aqueous phase. The mass ratio of the aqueous phase to the oil phase was 20:1.

[0266] (4) After the aqueous phase and the oil phase were mixed uniformly, the oil phase was added dropwise to the aqueous phase under stirring to form an oil-in-water emulsion;

[0267] (5) The emulsion was heated in an oil bath at 100°C for 6 hours, during which the oil phase liquid was quickly gelatinized and solidified to form a gel;

[0268] (6) The gel was centrifuged, washed, and dried to obtain methyl poly siesquioxane-phenolic resin composite microspheres;

[0269] (7) The dried methyl poly siesquioxane-phenolic resin composite microspheres were carbonized in a tube furnace under an argon atmosphere at 600°C for 1 hour to obtain black Si-O-C composite microspheres.

[0270] (8) The Si-O-C composite microspheres were placed in a rotary furnace using acetone and benzene as carbon sources, and the acetone and benzene gas was introduced, and nitrogen was used as a protective atmosphere, and carbonization was carried out at 900°C to obtain a silicon-based composite material coated with a carbon material layer.

[0271] Example 12

[0272] (1) In a mixed solution of 2000 ml of water and 1000 ml of ethanol, 100 ml of vinyltrimethoxysilane (C5H 12 O3Si, density 0.97 g / cm 3 ) and 10 g of resorcinol were slowly added, and stirring was continued at a speed of 200 r / min for 30 min to obtain a first solution;

[0273] (2) In the first solution, 14 ml of formaldehyde solution was added dropwise, and platinum divinyltetramethyl-disiloxane complex (1% of the mass of octamethyltrisiloxane) was added to the mixture, followed by stirring at a speed of 200 r / min for 15 min to obtain an oil phase;

[0274] (3) In another container, 20 wt.% of polysorbate-80 was added to ionized water to obtain an aqueous phase. The mass ratio of the aqueous phase to the oil phase was 50:1.

[0275] (4) After the water phase and the oil phase are mixed evenly, the oil phase is added dropwise into the water phase under stirring to form an oil-in-water emulsion;

[0276] (5) The emulsion is heated in a water bath at 80°C for 24 hours, and in this process, the oil phase liquid quickly gels and solidifies to form a gel;

[0277] (6) The gel is centrifuged, washed, and dried to obtain polysilsesquioxane-phenolic resin composite microspheres;

[0278] (7) The dried polysilsesquioxane-phenolic resin composite microspheres are carbonized in a tube furnace under an argon atmosphere at 800°C for 6 hours to obtain black Si-O-C composite microspheres.

[0279] (8) Using glucose as a carbon source, the glucose and the obtained Si-O-C composite microspheres are mixed by a VC mixer, carbonized at 1000°C in a roller kiln using argon as a protective atmosphere to obtain a silicon-based composite material coated with a carbon material layer.

[0280] Example 13:

[0281] (1) 100 ml of vinyltrimethoxysilane (C5H 12 O3Si, density 0.97 g / cm 3 ) and 10 g of resorcinol are slowly added to a mixed solution of 2000 ml of water and 1000 ml of ethanol, and stirring is continued at a speed of 200 r / min for 30 min to obtain a first solution;

[0282] (2) 14 ml of a formaldehyde solution is further added dropwise to the first solution, and platinum divinyltetramethyl-disiloxane complex (1% of the mass of octamethyltrisiloxane) is added to the mixture, followed by stirring at a speed of 200 r / min for 15 min to obtain an oil phase;

[0283] (3) In another container, a water phase is obtained by adding 20 wt% of polysorbate-80 to ionized water. The mass ratio of the water phase to the oil phase is 50:1.

[0284] (4) After the water phase and the oil phase are mixed evenly, the oil phase is added dropwise into the water phase under stirring to form an oil-in-water emulsion;

[0285] (5) The emulsion is heated in a water bath at 15°C for 24 hours, and in this process, the oil phase liquid quickly gels and solidifies to form a gel;

[0286] (6) The gel is centrifuged, washed, and dried to obtain polysilsesquioxane-phenolic resin composite microspheres;

[0287] (7) The dried polysilsesquioxane-phenol resin composite microspheres were carbonized in a tube furnace under argon atmosphere at 800°C for 6 hours to obtain black Si-O-C composite microspheres.

[0288] (8) The obtained Si-O-C composite microspheres were mixed with glucose as carbon source by a VC mixer, and carbonized at 1000°C in a roller kiln using argon as a protective atmosphere to obtain a silicon-based composite material coated with a carbon material layer.

[0289] Comparative Example 1

[0290] (1) 100 ml octamethyltrisiloxane (density 0.82 g / cm3) and 10 g resorcinol were slowly added to a mixed solution of 2000 ml water and 1000 ml ethanol, and stirring was continued at a speed of 200 r / min for 30 min to obtain a first solution; 3 ) and 10 g resorcinol were slowly added to a mixed solution of 2000 ml water and 1000 ml ethanol, and stirring was continued at a speed of 200 r / min for 30 min to obtain a first solution;

[0291] (2) 14 ml of a formaldehyde solution was further added dropwise to the first solution, and platinum divinyltetramethyl-disiloxane complex (1% of the mass of octamethyltrisiloxane) was added to the mixture, followed by stirring at a speed of 200 r / min for 15 min to obtain an oil phase;

[0292] (3) In another container, a water phase was obtained by adding 20 wt.% polysorbate-80 to ionized water. The mass ratio of the water phase to the oil phase was 50:1.

[0293] (4) After the water phase and the oil phase were each mixed uniformly, the oil phase was added dropwise to the water phase while stirring to form an oil-in-water emulsion;

[0294] (5) The emulsion was heated in a water bath at 80°C for 24 hours, during which the oil phase liquid quickly gelled and solidified to form a gel;

[0295] (6) The gel was centrifuged, washed, and dried to obtain methyl polysilsesquioxane-phenol resin composite microspheres;

[0296] (7) The dried methyl polysilsesquioxane-phenol resin composite microspheres were carbonized in a tube furnace under argon atmosphere at 800°C for 6 hours to obtain black Si-O-C composite microspheres.

[0297] (8) The obtained Si-O-C composite microspheres were mixed with glucose as carbon source by a VC mixer, and carbonized at 1000°C in a roller kiln using argon as a protective atmosphere to obtain a silicon-based composite material coated with a carbon material layer.

[0298] Comparative Example 2

[0299] (1) A solution containing hydrogen-containing silicone oil, di-vinyl benzene and chloroformic acid (concentration of 12 ppm) was mixed uniformly at a mass ratio of 5:4:1, and then a solid polysiloxane was synthesized after crosslinking at 100°C for 24h;

[0300] (2) The siloxane was placed in a tube furnace and sintered at high temperature under Ar protection, with an Ar flow rate of 0.2 L / min, a sintering starting temperature of 50°C, a temperature rise rate of 5°C / min to 400°C, and holding for 1h; then the temperature was raised to 1200°C at a rate of 5°C / min and held for 5h, and then the furnace was cooled down to obtain a silicon-based composite material.

[0301] The following illustrates some advantages of the embodiments of the present application compared with the prior art through specific experimental data.

[0302] Electron microscope test

[0303] A scanning electron microscope was used to confirm the spherical particle structure in the material, and energy dispersive X-ray spectroscopy (EDS) was used to characterize the uniformity of Si, O and C element distribution in the material.

[0304] Electrical performance test

[0305] Particle size: D50, D90 and D10 were measured using a laser particle size analyzer, and the value of (D90-D10) / D50 was calculated, and there was a symmetric distribution of normal distribution.

[0306] Specific surface area: the specific surface area was measured using a U.S. Micromeritics TriStar 3000 specific surface area and pore size analyzer.

[0307] Wadell sphericity test: the particle size distribution was measured using a laser particle size analyzer, and the equivalent volume diameter in each particle size range was obtained. The equivalent volume diameter was used as the particle size of all spheres in the minimum particle size distribution range, and all particles in the range were equivalent to ideal spheres, and the specific surface area in each particle size distribution range was calculated. Then the specific surface area of the spheres with the same volume as all the particles was obtained by volume percentage weighting, so that the sphericity of the Si-O-C material prepared by sol-gel method was calculated, and the specific surface area of the equivalent volume spheres / the specific surface area of the particles measured by the specific surface area analyzer.

[0308] Si crystallite size: XRD peaks were measured using a Panalytical X'Pert Pro X-ray diffractometer, and then the Si peaks in the XRD were fitted using Jade 6.5 software, so as to obtain the Si crystallite size.

[0309] Initial reversible specific capacity and initial coulombic efficiency (ICE): The negative electrode slurry was prepared according to the mass ratio of silicon-based negative electrode material, conductive carbon black, and PPA of 75:15:10, coated on copper foil, and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode to assemble a button cell in an Ar-filled glove box. The button cell was charged and discharged at a current density of 0.1C in the charge-discharge interval of 0.01-5V to obtain the initial reversible specific capacity and initial coulombic efficiency (ICE) of the button cell.

[0310] Capacity retention and electrode sheet thickness expansion rate: The negative electrode slurry was prepared according to the mass ratio of silicon-based negative electrode material and graphite mixture, Super-P, KS-6, CMC, and SBR of 92:2:2:2:2, coated on copper foil, and dried to form a negative electrode sheet. The proportion of silicon-based negative electrode material and graphite in the silicon-based negative electrode material and graphite mixture was determined by the initial reversible specific capacity of the two and the capacity required for the two. A lithium metal sheet was used as the counter electrode to assemble a button cell in an Ar-filled glove box. The button cell was repeatedly charged and discharged 50 times at a current density of 1C in the charge-discharge interval of 0.01V-5V to obtain the capacity retention and electrode sheet thickness expansion rate of the battery after 50 cycles.

[0311] XPS: The different valence states and chemical bond types of Si, O, and C elements in the silicon-based negative electrode material were analyzed. When studying the structural changes of the active material during the charge and discharge process, the active material was first removed from the simulated battery in an anaerobic glove box, cleaned with solvent DEC, and then tested after complete drying. Test instrument: VG Multilab2000 X-ray photoelectron spectrometer Test conditions: Light etching with argon ions before testing to remove impurities on the surface of the sample, excitation source is MgKα(1253.6eV), resolution 0.1eV, focused spot 400μm.

[0312] 29 Si MAS NMR standard silicon structure chemical shift: 29 Si MAS NMR( 29Si Magic Angle SpinningNuclear Magnetic Resonance Spectroscopy) instrument model is Bruker AV 300 type nuclear magnetic resonance instrument. In order to quantitative analysis, single pulse is used in the test process, instead of using cross polarization method. The pulse width is 4.5ut, theta is 54.7°, relaxation delay (i.e. the time delay of two samples) is 5 seconds, and the rotation speed is 7 kHz. The determination is carried out with TMS as the chemical shift standard. When studying the structure change of active substance in the process of charging and discharging, the active substance is first taken out from the simulated battery in the anaerobic glove box, cleaned with solvent DEC, and then tested after completely dried. By integrating the area of the nuclear magnetic peak corresponding to each silicon structure unit, the relative atomic content of the structure unit can be obtained. For example, the average composition of SiO4 structure unit, SiO3C structure unit and SiO2C2 structure unit is SiO2, SiO 3 / 2 C 1 / 4 、SiO 2 / 2C 2 / 4 , the average molecular weight is 60, 55 and 50 g / cm 3 respectively. The relative mass fraction is calculated by conversion, and the absolute mass fraction is obtained by subtracting the content of free carbon.

[0313] Infrared measurement of silicon bonding mode: American Thermo Nicolet iS20 Fourier infrared spectrometer is used. The spectral range is 2000-350cm -1 The preferred KBr beam splitter in the middle infrared region.

[0314] Free carbon content determination: German Bruker G4 ICARUS HF infrared carbon and sulfur analyzer is used. The sample is burned in a high temperature oxygen-rich state, and the carbon element contained therein is oxidized to carbon dioxide. The generated gas enters the infrared detector with the carrier gas, and the content of carbon element can be calculated by quantitatively analyzing the change of carbon dioxide signal.

[0315] Cyclic voltammetry is used to test the redox peak value of the material: two-electrode simulated battery is used to test the CV of silicon-based negative electrode material, mainly to study the oxidation-reduction reaction mechanism, reaction reversibility and other processes in the charging and discharging process. Test instrument: AUTOLAB PGSTAT30 type electrochemical workstation Test conditions: test software and analysis software NOVA1.6. Test temperature 25℃, scanning rate 0.1mV / s, voltage range 0.005V-1.5V.

[0316] The test results are as follows:

[0317] Electron microscope test

[0318] The electron microscope image of the silicon-based negative electrode material prepared in Example 1 is as follows:Figure 1 (a), 1(b) shows that the surface of the silicon-based negative electrode material particles prepared in this embodiment is smooth and round, and the sphericity of the spheres is good. Figure 1 As can be seen from (a), 1(b), the surface of the silicon-based negative electrode material particles prepared in this embodiment is smooth and round, and the sphericity of the spheres is good.

[0319] The electron microscope image of the silicon-based negative electrode material prepared in Example 2 is shown in (a), 1(b). Figure 2 As can be seen from (a), 1(b), the surface of the silicon-based negative electrode material particles prepared in this embodiment is smooth and round, and the sphericity of the spheres is good. Figure 2 As can be seen from (a), 1(b), the surface of the silicon-based negative electrode material particles prepared in this embodiment is smooth and round, and the sphericity of the spheres is good.

[0320] The electron microscope image of the silicon-based negative electrode material prepared in Example 3 is shown in (a), 1(b). Figure 3 As can be seen from (a), 1(b), the surface of the silicon-based negative electrode material particles prepared in this embodiment is smooth and round, and the sphericity of the spheres is good. Figure 3 As can be seen from (a), 1(b), the surface of the silicon-based negative electrode material particles prepared in this embodiment is smooth and round, and the sphericity of the spheres is good.

[0321] Electrical performance test

[0322] Examples 1-13 and Comparative Examples 1-2 were tested in the above manner, and the results are shown in Table 1 and Table 2.

[0323] Table 1

[0324]

[0325]

[0326] Table 2

[0327]

[0328] It can be seen that Examples 1-11 have better electrochemical performance than Comparative Examples 1-2. In the preparation process, by adjusting the pH value to be between 11 and 12, no gel-like precipitate is generated during the preparation process, and by controlling the temperature range for the sol to gel to be between 25-100°C, the finally prepared silicon-based composite material can have a good particle size distribution, a moderate particle size diameter, and overall good electrochemical performance.

[0329] Specifically, the main difference between Comparative Example 1 and Example 1 is that the pH value of the solution is not controlled in Comparative Example 1. This leads to the easy occurrence of gel-like precipitate in the synthesis process of the precursor microspheres, and it is difficult to form a well-structured silicon-based composite material subsequently, thereby resulting in the particle size span and electrochemical performance of the finally generated silicon-based composite material being inferior to those of Example 1.

[0330] The main difference between Example 12 and Example 1 is that vinyltrimethoxysilane (C5H 12 O3Si, density 0.97 g / cm 3 ) is used as the siloxane raw material. Here, because the O / Si ratio of the selected raw material is greater than 1, more SiOC3 with lower specific capacity is generated in the silicon-based negative electrode material prepared, so that the silicon-based composite material obtained ultimately has less SiO3C and SiO4 with higher reversible specific capacity, thereby resulting in a decrease in specific capacity and first coulombic efficiency.

[0331] The main difference between Example 13 and Example 1 is that the temperature of the water bath is 15°C. When the temperature of the water bath is lower, the particle size of the silicon-based composite material obtained will decrease significantly. Although smaller particle size will make the expansion distribution of the silicon-based composite material more uniform, which is beneficial to the improvement of cycle performance to some extent, such smaller particles will significantly increase the specific surface area of the silicon-based composite material, resulting in an increase in side reactions during the charging and discharging process of the battery, thereby causing a significant decrease in specific capacity and first coulombic efficiency of the silicon-based composite material; and the phenomenon of agglomeration is prone to occur, so that the processing performance thereof is deteriorated. Therefore, the overall electrochemical performance of the silicon-based composite material is not good.

[0332] The above provides a silicon-based composite material, a preparation method thereof, and a lithium ion battery. The principles and implementation manners of the present application are described by applying specific examples in the present text. The above description of the examples is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range will be changed; in summary, the content of the present description should not be understood as a limitation of the present application.

Claims

1. A silicon-based composite material, characterized by, The silicon-based composite material comprises Si-O-C spherical structures, and a ratio of a number of Si-O bonds to a number of Si-C bonds in the silicon-based composite material is greater than 2, the Si-O-C spherical structures comprise SiO4 structural units, SiO3C structural units, and SiO2C2 structural units; a ratio of a sum of mass fractions of the SiO4 structural units and the SiO3C structural units to a mass fraction of the SiO2C2 structural units is greater than 2, and a ratio of a mass fraction of the SiO3C structural units to a mass fraction of the SiO4 structural units is greater than or equal to 2.

5.

2. The silicon-based composite material of claim 1, wherein At least one of the following features (1) to (4) is included: (1) The Si-O-C spherical structure is coated with a carbon material layer; (2) A molar ratio of O / Si in the Si-O-C spherical structure is 1 to 2; (3) A molar ratio of C / Si in the Si-O-C spherical structure is 0.5 to 3.5; (4) The Si-O-C spherical structure is coated with a carbon material layer, and the carbon material layer comprises an inorganic carbon material layer.

3. The silicon-based composite material according to claim 1 or 2, characterized in that, At least one of the following features (1) to (6) is included: (1) In a capacitance voltage characteristic curve of the silicon-based composite material, a capacity in a 0-0.1V interval accounts for 20% to 50% of an overall capacity of the silicon-based composite material, and a capacity in a 0.1-0.6V interval accounts for 50% to 80% of the overall capacity of the silicon-based composite material; (2) A Wadell sphericity of the silicon-based composite material is greater than 0.95; (3) A (D90-D10) / D50 of the silicon-based composite material is less than or equal to 1.20; (4) The silicon-based composite material comprises Si microcrystals, and a size of the Si microcrystals is 1nm to 10nm; (5) the specific surface area of the silicon-based composite material is 2.0-9.5 m 2 / g; (6) A particle size D50 of the silicon-based composite material is 0.3μm to 5.8μm.

4. A method of preparing a silicon-based composite material, characterized by, The method comprises: adding a siloxane raw material, a phenolic raw material, an aldehyde raw material, and a catalyst in a solvent, and uniformly mixing to obtain an oil phase, wherein a molar ratio of O / Si in the siloxane raw material is less than or equal to 1, the phenolic raw material comprises at least one of resorcinol, m-aminophenol, and bisphenol A, the aldehyde raw material comprises formaldehyde, and the catalyst comprises platinum divinyltetramethyl-disiloxane complex and / or dibutyltin dilaurate; dropping the oil phase into an aqueous phase containing an emulsifier to obtain an oil-in-water emulsion, the emulsifier comprising at least one of polysorbate-80, polysorbate-60, polysorbate-40, and polysorbate-20; under an environment with a pH value of 11 to 12, forming the oil-in-water emulsion into a gel, drying, and then performing heat treatment to obtain a silicon-based composite material.

5. The method of claim 4, wherein, At least one of the following features (1) to (8) is included: (1) The step of adding a siloxane raw material, a phenolic raw material, an aldehyde raw material, and a catalyst in a solvent, and uniformly mixing to obtain an oil phase specifically comprises: adding the siloxane raw material and the phenolic raw material in the solvent, and uniformly mixing to obtain a second solution; adding the aldehyde raw material and the catalyst in the second solution, and uniformly mixing to obtain the oil phase; (2) the step of adding the oil phase into the water phase containing emulsifier to obtain the oil-in-water emulsion, comprising: adding emulsifier into deionized water to obtain the water phase; adding the oil phase into the water phase to obtain the oil-in-water emulsion; (3) the step of forming the oil-in-water emulsion into gel, drying and then heat treating to obtain the silicon-based composite material, comprising: standing in water bath or oil bath at 25-100℃ to form gel; drying the gel to obtain the precursor microspheres, and heat treating the precursor microspheres to obtain the silicon-based composite material; (4) the method further comprises: heat treating the silicon-based composite material based on carbon source to obtain the silicon-based composite material coated with carbon material layer; (5) the step of heat treating the silicon-based composite material based on carbon source to obtain the silicon-based composite material coated with carbon material layer, comprising: mixing the silicon-based composite material with the carbon source and then heat treating to obtain the silicon-based composite material coated with carbon material layer; (6) the step of adding the siloxane raw material and the phenolic raw material into the solvent and mixing uniformly to obtain the second solution, comprising: adding pH adjusting solution into the solvent to adjust the pH value to be between 11-12 to obtain the first solution; adding the siloxane raw material and the phenolic raw material into the first solution and mixing uniformly to obtain the second solution; (7) the step of adding the oil phase into the water phase containing emulsifier to obtain the oil-in-water emulsion, comprising: adding emulsifier into the water phase and adding pH adjusting solution to adjust the pH value to be between 11-12, and adding the oil phase into the water phase; (8) the step of forming the oil-in-water emulsion into gel in the environment with pH value of 11-12, comprising: adding pH adjusting solution into the oil-in-water emulsion to adjust the pH value to be between 11-12, and forming the oil-in-water emulsion into gel.

6. The method of claim 4, wherein, At least one of the following features (1) to (4) is included: (1) the siloxane raw material comprises at least one of aromatic siloxane, octamethyltetrasiloxane, decamethyltetrasiloxane, 1,3-divinyltetramethyldisiloxane, octamethyltrisiloxane; (2) the pH adjusting solution comprises ammonia and / or urea; (3) the concentration of the pH adjusting solution is 0.1 mol / L-2 mol / L; (4) the solvent comprises water and / or ethanol.

7. The method of claim 4, wherein, At least one of the following features (1) to (4) is included: (1) the mass ratio of the phenolic raw material to the siloxane raw material is 1:2-8; (2) the catalyst accounts for 0.5%-15% of the mass of the siloxane raw material; (3) the emulsifier accounts for 1%-20% of the mass of the water phase; (4) the mass ratio between the oil phase and the water phase is 1:20-100.

8. The method of claim 5, wherein, At least one of the following features (1) to (2) is included: (1) the volume ratio of the aldehyde raw material to the second solution is 1:50-250; (2) the volume ratio of the pH adjusting solution to the solvent is 1:30-100.

9. The method of claim 5, wherein, At least one of the following features (1) to (4) is included: (1) the carbon source comprises at least one of solid-phase carbon source, liquid-phase carbon source and gas-phase carbon source; (2) the solid-phase carbon source comprises at least one of citric acid, glucose, pitch, phenol formaldehyde resin and furfural resin; (3) the liquid-phase carbon source comprises at least one of low-temperature liquid-phase pitch, furfuryl alcohol, glycidyl methacrylate and triethylene glycol dimethacrylate; (4) the gas-phase carbon source comprises at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone and benzene.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the silicon-based composite material as claimed in any one of claims 1 to 3 or the silicon-based composite material prepared by the method as claimed in any one of claims 4 to 9.

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