Carbon material, silicon-carbon negative electrode material, and preparation method for and use of silicon-carbon negative electrode material

Abstract

The present disclosure relates to the technical field of battery negative electrode materials, and disclosed are a carbon material, a silicon-carbon negative electrode material, and a preparation method for and a use of the silicon-carbon negative electrode material. In the negative electrode material, silicon is distributed within pores of a porous substrate, and the volume expansion of silicon in a lithium deintercalation process is suppressed by using the pore structure of the porous substrate, thereby improving the cycle performance of the negative electrode material. The silicon-carbon composite material exhibits high sphericity, avoids poor compression resistance due to numerous edges and corners during rolling, and can mitigate the problems of continuous formation of solid electrolyte interface (SEI) films, reduced capacity and poor cycle performance caused by low strength. Porous carbon is prepared using a nanoscale carbon nanotube, facilitating improvement of the electrical conductivity of the porous carbon; and in addition, a tin or germanium element doped into the negative electrode material facilitates deintercalation of lithium ions by lowering the energy barrier of lithium ion transition, thereby improving the initial coulombic efficiency.

Description

Carbon material, silicon-carbon negative electrode material, and preparation method and application thereof

[0001] Cross-reference to Related Applications

[0002] The present disclosure claims priority to a Chinese patent application No. 2024108896162, entitled "Negative electrode material, preparation method and application" and filed with the China Patent Office on July 4, 2024;

[0003] and a Chinese patent application No. 2024112386533, entitled "Silicon-carbon composite material, preparation method and application thereof" and filed with the China Patent Office on September 4, 2024;

[0004] and a Chinese patent application No. 2024113194738, entitled "Preparation method of porous carbon, porous carbon, negative electrode material and secondary battery" and filed with the China Patent Office on September 20, 2024, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0005] The present disclosure relates to the technical field of battery negative electrode materials, in particular to a carbon material, a silicon-carbon negative electrode material, and a preparation method and application thereof. BACKGROUND

[0006] Firstly, silicon is currently the negative electrode material with the largest theoretical capacity, with a specific capacity as high as 4200 mAh / g, far higher than the theoretical capacity of graphite (the theoretical capacity of graphite negative electrode material is only 372 mAh / g), and has the advantages of low lithium intercalation potential and low cost, and is expected to replace graphite as the next generation of lithium ion battery negative electrode material. However, silicon as a negative electrode material is accompanied by severe volume expansion and contraction during lithium intercalation and deintercalation, which leads to easy pulverization of the material, and the material falls off from the current collector and loses electrochemical performance.

[0007] Due to the structural stability of carbon materials, the volume change during charging and discharging is relatively small, and it has good cycle stability, and is similar in chemical properties to silicon, so silicon and carbon are often compounded to achieve the purpose of improving the volume expansion effect of silicon and improving the electrochemical stability thereof. However, the negative electrode material obtained by the existing silicon-carbon compounding method has poor cycle performance, which is the second problem to be solved.

[0008] Secondly, the lithium ion battery is indispensable in the fields of traditional 3C consumer electronics, new energy power batteries, large power power plants, and large energy storage power stations, etc. As a traditional battery negative electrode material, the actual capacity of graphite has gradually approached its theoretical true capacity with the progress of technology. Under this background, silicon negative electrode with higher theoretical capacity is considered as the best candidate for the next generation of high-capacity batteries. In order to inhibit the expansion of silicon during charging and discharging and improve the conductivity of silicon element, silicon needs to be coated in a porous carbon substrate with high specific surface.

[0009] In the process of battery production, there is a certain requirement for the strength of the silicon-carbon composite material to prevent particle breakage caused by rolling, thereby causing silicon particles to be exposed and causing serious volume expansion during charging and discharging, affecting the performance of the battery. The strength of the silicon-carbon composite material is related to various factors, such as material particle size, silicon content, morphology, etc. The particle breakage caused by rolling is greatly related to the morphology of the silicon-carbon material. Irregular silicon-carbon composite materials will cause mutual extrusion between particles during rolling in the process of battery production, thereby causing the breakage of irregular edges and corners, and the shedding of internal active substances, which is not conducive to the formation of a stable SEI film, and is the first problem to be solved.

[0010] Finally, as a high-performance lithium ion battery negative electrode material, the silicon-based material has advantages such as high theoretical capacity (about 4200 mAh / g, much higher than 372 mAh / g of graphite) and low lithiation potential, but also has some challenges, including low conductivity and low lithium activity.

[0011] The low conductivity of the silicon-based material limits the diffusion speed of lithium ions and the efficiency of electron transmission, which in turn affects the rate performance and cycle stability of the battery. Existing solutions include doping or coating conductive materials to improve conductivity, but directly doping conductive materials into the silicon-based material has limited effect on improving the conductivity of the silicon-based material; the low lithium activity of the silicon-based material is due to the large volume expansion and contraction during lithiation / delithiation, which in turn causes poor contact between the active material and the current collector.

[0012] In the application of silicon-based materials in lithium ion battery negative electrodes, low conductivity and low lithium activity are two major challenges. How to effectively improve the conductivity and lithium activity of silicon-based materials and in turn improve the performance of lithium ion batteries is the third problem to be solved. SUMMARY

[0013] The purpose of the present disclosure is to provide a carbon material, a silicon-carbon negative electrode material, a preparation method and application thereof, and a detection method of a silicon-carbon composite material.

[0014] Firstly, the present disclosure provides a negative electrode material, a preparation method and application, which improves the cycle performance of the negative electrode material.

[0015] The present disclosure is implemented as follows:

[0016] In a first aspect, the present disclosure provides a negative electrode material, comprising a porous substrate, silicon elements distributed in the pores of the porous substrate, and a carbon coating on the surface of the porous substrate, wherein the silicon content of the negative electrode material is 30wt%-80wt%, the resistivity is less than 5Ω·cm, and the value of W is >8, where W = silicon content / resistivity, the unit of silicon content is wt%, and the unit of resistivity is Ω·cm.

[0017] In an optional embodiment, the specific surface area of the negative electrode material is 4m 2 / g-9m 2 / g.

[0018] And / or, the D50 of the negative electrode material is 1μm-15μm;

[0019] And / or, the tap density of the negative electrode material is 0.7g / cm 3 -1.5g / cm 3 .

[0020] In a second aspect, the present disclosure also provides a preparation method of the negative electrode material according to any one of the preceding embodiments, comprising:

[0021] Low-temperature adsorption, placing the porous substrate in an environment containing a silicon source gas and adsorbing the silicon source gas;

[0022] High-temperature pyrolysis, heating the porous substrate adsorbed with the silicon source gas to decompose the silicon source gas, obtaining a porous substrate loaded with nanosilicon in the pore structure;

[0023] Coating treatment, forming a carbon coating layer on the porous substrate loaded with nanosilicon in the pore structure, obtaining the negative electrode material.

[0024] In an optional embodiment, the low-temperature adsorption step is carried out in a low-temperature adsorption device, and the low-temperature adsorption step ends when the silicon source gas is discharged from the tail gas outlet of the low-temperature adsorption device during low-temperature adsorption;

[0025] Optionally, the low-temperature adsorption temperature is 25°C-200°C, the pressure is 0.0001KPa-0.3KPa, and the time is 1h-30h; more optionally, the low-temperature adsorption temperature is 30°C-150°C, the pressure is 0.001KPa-0.1KPa, and the time is 2h-25h;

[0026] Optionally, the silicon source is selected from at least one of monosilane, disilane, dichlorodisilane, and trichlorosilane;

[0027] Optionally, the silicon source gas further comprises an inert gas, wherein the volume fraction of the silicon source is 50vol%-99vol%.

[0028] In an optional embodiment, the high-temperature pyrolysis step is performed in a high-temperature pyrolysis device, and the high-temperature pyrolysis step ends when the tail gas outlet of the high-temperature pyrolysis device does not emit hydrogen in the gas;

[0029] Optionally, the high-temperature pyrolysis temperature is 300-800℃, the pressure is 0.01-5KPa, and the time is 1-50h; more optionally, the high-temperature pyrolysis temperature is 400-700℃, the pressure is 0.01-3KPa, and the time is 1-40h;

[0030] In an optional embodiment, the porous substrate satisfies at least one of the following A-G:

[0031] A, SPAN value <1.5;

[0032] B, Dv50 is 2-20μm

[0033] C, the specific surface area of the porous substrate is 400m 2 / g-2000m 2 / g, optionally 900m 2 / g-2000m 2 / g;

[0034] D, the average pore size is 1.2-7.0nm, optionally 1.5-5.0nm;

[0035] E, the pore volume is 0.3cm 3 / g-2.0cm 3 / g, optionally 0.5cm 3 / g-1.8cm 3 / g;

[0036] F, the pore size concentration is 0.3-6.0, calculated as (P V 90-P V 10) / P V 50, optionally 0.3-8:

[0037] G, the porous substrate is selected from at least one of porous carbon, porous metal oxide, coordination polymer and porous metal, and porous ceramic, optionally porous carbon.

[0038] In an optional embodiment, the coating treatment includes passing a carbon-containing gas source into a reactor containing the porous substrate loaded with nanosilicon in the pore structure to perform carbon deposition to form a carbon coating layer;

[0039] Optionally, the carbon deposition temperature is 300-1300℃, and the carbon deposition time is 1-10h; optionally, the carbon deposition temperature is 400-1000℃, and more optionally, 400-600℃;

[0040] Optionally, the carbon-containing gas source comprises a carbon source gas selected from an alkane gas with a cracking temperature within the carbon deposition temperature range.

[0041] Optionally, the carbon-containing gas source further comprises an inert gas.

[0042] Optionally, the volume fraction of the carbon source gas in the carbon-containing gas source is 50-99vol%.

[0043] In a third aspect, the present disclosure further provides a negative electrode tab comprising the negative electrode material of any one of the preceding embodiments or the negative electrode material prepared by the method of any one of the preceding embodiments.

[0044] In a fourth aspect, the present disclosure further provides a secondary battery comprising the negative electrode tab of the preceding embodiments.

[0045] In a fifth aspect, the present disclosure further provides an electrical equipment comprising the secondary battery of the preceding embodiments.

[0046] The negative electrode material, the preparation method and the application in the present disclosure have the following beneficial effects:

[0047] The negative electrode material in the present disclosure distributes silicon in the pores of the porous substrate, utilizes the pore structure of the porous substrate to inhibit the volume expansion of silicon during lithium extraction and embedding, and further improves the cycle performance of the negative electrode material.

[0048] In the preparation method of the negative electrode material in the present disclosure, the silicon source is first adsorbed in the cavities of the porous substrate; then the temperature in the furnace is raised, and the silane is decomposed in the cavities to obtain nano-silicon particles deposited in the cavities, thereby reducing the content of floating silicon.

[0049] Secondly, the present disclosure provides a silicon-carbon composite material and a preparation method and application thereof. The silicon-carbon composite material has high sphericity, avoids poor compression resistance caused by many edges and corners during rolling, and prevents particle breakage. The silicon-carbon composite material can improve the problem of continuous formation of a solid electrolyte interface (SEI) film, capacity weakening, and cycle deterioration caused by low strength.

[0050] To achieve the above-mentioned purposes, the present disclosure adopts the following technical solutions:

[0051] In a sixth aspect, the present disclosure provides a silicon-carbon composite material, which comprises active material particles, and the active material particles comprise a skeleton of spherical porous carbon and nano-silicon particles.

[0052] The strength of the silicon-carbon composite material is defined by the following formula:

[0053] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of the silicon-carbon composite material before pressing, m 2 / g.

[0054] Preferably, the specific surface area of the silicon-carbon composite material is 2-5 m 2 / g.

[0055] Preferably, the strength of the silicon-carbon composite material under a pressure of 450 MPa for 30 s is above 90%.

[0056] Preferably, the sphericity of the spherical porous carbon is ≥80%.

[0057] Preferably, the spherical porous carbon contains uniformly distributed micropores and / or mesopores inside.

[0058] Preferably, the total pore volume of the spherical porous carbon with an average pore diameter less than 4 nm is ≥0.7 cm 3 / g.

[0059] Preferably, the mesopore ratio of the spherical porous carbon is <20%, and the micropore ratio is >80%.

[0060] Preferably, the particle size of the spherical porous carbon is 1-60 μm; wherein, the D 10 particle size of the spherical porous carbon is 3-7 μm; the D 50 particle size is 8-13 μm; the D 90 particle size is 15-40 μm.

[0061] Preferably, the nano-silicon particles are deposited in the pores of the spherical porous carbon.

[0062] Preferably, the content of silicon in the silicon-carbon composite material is 40-60%.

[0063] Preferably, the specific capacity of the silicon-carbon composite material is >1500 mAh / g, preferably >1800 mAh / g.

[0064] Preferably, the capacity retention rate of the silicon-carbon composite material after 200 cycles is >90%.

[0065] In a seventh aspect, the present disclosure provides a preparation method of the silicon-carbon composite material according to the first aspect, the preparation method comprising the following steps:

[0066] Mixing low-carbon source microspheres, high-carbon source resin and solvent to obtain a mixed solution;

[0067] The mixture is subjected to spray drying treatment to obtain small spherical particles;

[0068] The small spherical particles are subjected to carbonization treatment and activation treatment in sequence to obtain spherical porous carbon;

[0069] The spherical porous carbon is subjected to gas phase deposition to obtain the silicon-carbon composite material.

[0070] Preferably, the residual carbon content of the low-carbon-source microspheres is ≤40%.

[0071] Preferably, the residual carbon content of the high-carbon-source resin is 50-70%.

[0072] Preferably, the low-carbon-source microspheres include any one or a combination of at least two of polystyrene microspheres, polylactic acid microspheres or polyvinylidene fluoride microspheres.

[0073] Preferably, the high-carbon-source resin is phenolic resin and / or phenolic resin derivative.

[0074] Preferably, the mass ratio of the low-carbon-source microspheres to the high-carbon-source resin is 1:(1-5).

[0075] Preferably, the solvent includes an alcohol solvent, preferably ethanol.

[0076] Preferably, the solid content of the mixture is 30-60 wt%.

[0077] Preferably, the mixture further includes 5-10 wt% of carbon nanotubes.

[0078] Preferably, the mixture further includes a conductive polymer, which includes any one or a combination of at least two of polyacetylene, polythiophene, polypyrrole or polyaniline.

[0079] Preferably, the process parameters of the spray drying treatment include: a centrifugal disc rotation speed of 24,000-30,000 rpm; an air inlet temperature of 160-230°C; a feeding speed of 1.2-4 L / h; and a frequency of an air blower of 40-50 Hz.

[0080] Preferably, the carbonization treatment is performed at a temperature of 400-900°C for 3-10 h.

[0081] Preferably, the activation treatment is performed by a physical activation method.

[0082] Preferably, the step of physical activation is performed by introducing an activation gas into the carbon microspheres obtained after the carbonization treatment to perform physical activation.

[0083] Preferably, the activation gas includes carbon dioxide and / or water vapor.

[0084] Preferably, the temperature of the physical activation is 800-1000℃, and the time of the physical activation is 7-20h.

[0085] Preferably, the activation process further comprises a step of removing impurities: after the activation process, the porous carbon microspheres are washed with acid to remove impurities, and then washed with water and dried.

[0086] Preferably, the acid washing uses a 5-8wt% hydrochloric acid solution.

[0087] Preferably, the temperature of the acid washing is 20-100℃, and the time of the acid washing is 1-24h.

[0088] Preferably, the temperature of the drying is 70-90℃.

[0089] Preferably, the deposition gas source of the vapor deposition is a mixed gas of a protective gas and a silicon source gas.

[0090] Preferably, the protective gas comprises any one or a combination of at least two of nitrogen, neon, argon, krypton, xenon or radon.

[0091] Preferably, the silicon source gas comprises any one or a combination of at least two of monosilane, disilane, dichlorodisilane or trichlorosilane.

[0092] Preferably, the silicon source gas further comprises a carbon source gas, and the carbon source gas comprises any one or a combination of at least two of methane, ethane, acetylene or ethylene.

[0093] Preferably, the volume ratio of the protective gas to the silicon source gas is (10-30):(70-90).

[0094] Preferably, the content of the carbon source gas accounts for 0-30% of the total volume of the silicon source gas.

[0095] Preferably, the deposition amount of the vapor deposition to the amount of the material put in is (0.4-1.5):1.

[0096] Preferably, the temperature of the vapor deposition is 300-800℃, and the time of the vapor deposition is 5-10h.

[0097] In an eighth aspect, the present disclosure provides a use of the silicon-carbon composite material according to the first aspect in the preparation of a battery negative electrode material.

[0098] In a ninth aspect, the present disclosure provides a detection method of a silicon-carbon composite material, which comprises the following steps:

[0099] Obtaining the specific surface area of the silicon-carbon composite material before pressing, and denoted as S1;

[0100] The silicon-carbon composite material is subjected to compaction treatment to break the sample, so as to obtain the specific surface area of the broken silicon-carbon composite material after pressing, and is denoted as S2;

[0101] The specific surface area change rate of the silicon-carbon composite material is calculated by the following formula I to characterize the strength of the silicon-carbon composite material;

[0102] The strength of the silicon-carbon composite material is defined by the following formula:

[0103] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material before pressing, m 2 / g; S1 represents the specific surface area of the silicon-carbon composite material after pressing, m 2 / g.

[0104] Preferably, the rate of the compaction treatment is 8-12 mm / min, preferably 10 mm / min.

[0105] Preferably, the holding time of the compaction treatment is 10-50 s, preferably 30 s.

[0106] Preferably, the pressure of the compaction treatment is 450-500 MPa.

[0107] The silicon-carbon composite material, the preparation method and the application thereof in the present disclosure have the following beneficial effects compared with the prior art:

[0108] (1) The present disclosure utilizes the morphology of carbon microspheres and the high carbon content of phenolic resin to synthesize a carbon base with good sphericity, and the particle size of the carbon microspheres can be well controlled by the spray drying technology, and the particle size uniformity is good.

[0109] (2) Compared with irregular resin-based silicon-carbon composite materials, the silicon-carbon material synthesized by this method has higher strength and does not have biomass-based natural macroporous pores inside.

[0110] (3) The silicon-carbon negative electrode material disclosed in the present disclosure has high sphericity, which avoids poor compression resistance caused by many edges and corners during the rolling process, and can improve the continuous generation of solid electrolyte interface (SEI) film caused by low strength, capacity weakening, and cycle deterioration.

[0111] (4) The present disclosure quantifies the strength of the silicon-carbon composite material by comparing the specific surface area change rate before and after pressing, uses a formula to characterize the strength and limits the strength range of the silicon-carbon composite material, avoids the problems such as sample without adhesion, easy to be pressed off, platform period, error data and only single particle evaluation in the traditional detection of silicon-carbon negative electrode material strength by nanoindentation.

[0112] Finally, the present disclosure provides a method for preparing porous carbon, porous carbon, negative electrode material and secondary battery, which helps to improve the electrical conductivity of silicon-based materials.

[0113] The present disclosure is implemented as follows:

[0114] In a tenth aspect, the present disclosure provides a method for preparing porous carbon, comprising:

[0115] Granulation, drying and granulation are performed on the phenolic resin microsphere suspension to obtain a powder; the nanometer carbon nanotubes are dispersed in the phenolic resin microspheres;

[0116] Carbonization, the powder is sequentially subjected to second solidification, pre-oxidation and carbonization to obtain the porous carbon.

[0117] In an optional embodiment, the average length of the nanometer carbon nanotubes is 20-50 nm, and the average aspect ratio is 1.5-5;

[0118] And / or, in the phenolic resin microsphere suspension, the mass ratio of nanometer carbon nanotubes to the total mass of phenolic raw materials and aldehyde raw materials is 1:(1.5-10);

[0119] And / or, the doped source is dispersed in the phenolic resin microspheres, the doped source is at least one of germanium source and tin source, the germanium source is selected from at least one of ortho-germanate, metagermanate, dihydrogen germanate and tetrahydrogen germanate, and the tin source is selected from at least one of tin chloride, tin nitrate and tin sulfate;

[0120] And / or, the doped source is dispersed in the phenolic resin microspheres, and the mass ratio of nanometer carbon nanotubes to doped source in the phenolic resin microsphere suspension is (5-10):1.

[0121] In an optional embodiment, the method for preparing the phenolic resin microsphere suspension comprises: mixing a dispersant, a doped source, a phenolic raw material, an aldehyde raw material and a catalyst with an aqueous solution in which nanometer carbon nanotubes are dispersed and performing heat preservation to obtain a prepolymer solution;

[0122] Mixing the prepolymer solution with a curing agent to perform first solidification to obtain the phenolic resin microsphere suspension.

[0123] Preferably, the method for preparing the phenolic resin microsphere suspension satisfies at least one of the following characteristics A-G:

[0124] A. The dispersant is selected from at least one of F127, PVA, PEG and sodium silicate;

[0125] B. The aldehyde raw material is selected from at least one of formaldehyde and furfural;

[0126] C. the phenolic raw material is selected from at least one of phenol and resorcinol, and the mass ratio of the phenolic raw material to the aldehyde raw material is 1:(0.8-1.2);

[0127] D. the catalyst is selected from at least one of sodium hydroxide and lithium hydroxide, and the ratio of the catalyst to the total mass of the phenolic raw material and the aldehyde raw material is 1:(25-35);

[0128] E. the holding time is 4h-6h, and the temperature is 75℃-85℃;

[0129] F. the curing agent is selected from at least one of hexamethylenetetramine and ammonia water, and the ratio of the curing agent to the total mass of the phenolic raw material and the aldehyde raw material is 1:(11-15);

[0130] G. the first curing temperature is 90℃-95℃, and the first curing time is 2h-8h.

[0131] In an optional embodiment, the preparation method of the aqueous solution in which the nanometer carbon nanotubes are dispersed comprises: ultrasonic stirring a mixture of nanometer carbon nanotubes and water to obtain the aqueous solution in which the nanometer carbon nanotubes are dispersed; and the preparation method of the aqueous solution in which the nanometer carbon nanotubes are dispersed satisfies at least one of the following characteristics a-c:

[0132] a. the ultrasonic frequency is 50Hz-70Hz; the stirring rate is 50rpm-200rpm; and the ultrasonic stirring time is 30min-60min;

[0133] b. the solid content in the aqueous solution in which the nanometer carbon nanotubes are dispersed is 0.1wt%-10wt%;

[0134] c. the nanometer carbon nanotubes are obtained by ball milling a carbon nanotube raw material, and the ball milling parameters include: a ball-to-material ratio of (20-50):1, a ball mill rotation speed of 500rpm-2000rpm, and an inert gas atmosphere.

[0135] In an optional embodiment, the mixture of the phenolic resin microsphere suspension and the water-soluble binder is subjected to spray drying to obtain the powder, and the spray drying parameters include: an inlet air temperature of 160℃-200℃, an outlet air temperature of 80℃-120℃, a feeding speed of 100mL / h-300mL / h, and a centrifugal atomization disc rotation speed of 23000rpm-27000rpm;

[0136] And / or, the water-soluble binder is selected from at least one of a water-soluble resin, starch, dextrin, and polyvinyl alcohol;

[0137] And / or, the volume ratio of the phenolic resin microsphere suspension to the water-soluble binder is 1:(0.5-4).

[0138] In an optional embodiment, the second curing temperature is 100-140°C, and the second curing time is 1-4h.

[0139] And / or, the pre-oxidation temperature is 280-320°C, the pre-oxidation time is 1-5h, and the pre-oxidation temperature rising rate is 1-5°C / min.

[0140] And / or, the carbonization temperature is 800-1000°C, the carbonization time is 4-8h, and the carbonization temperature rising rate is 4-6°C / min.

[0141] In an optional embodiment, the porous carbon is further activated by an activating agent to obtain activated porous carbon, the activation temperature is 700-1100°C, the activation time is 2-30h, and the mass ratio of the porous carbon to the activating agent is 1:(0.5-4).

[0142] In an eleventh aspect, the present disclosure provides a porous carbon prepared by the preparation method of the preceding embodiments.

[0143] Preferably, the porous carbon satisfies at least one of the following ①-④:

[0144] ①The pore volume is in the range of 0.3-1.4cm 3 / g. 3 / g.

[0145] ②The specific surface area is in the range of 800-2600m 2 / g. 2 / g.

[0146] ③The average pore size is in the range of 1.65-3.02nm.

[0147] ④The particle size D50 is in the range of 4-30μm.

[0148] In a twelfth aspect, the present disclosure provides a negative electrode material comprising the porous carbon of the preceding embodiments and silicon and / or carbon distributed on the porous carbon.

[0149] In a thirteenth aspect, the present disclosure provides a secondary battery comprising the negative electrode material of the preceding embodiments.

[0150] The preparation method of the porous carbon, the porous carbon, the negative electrode material and the secondary battery in the present disclosure have the following beneficial effects:

[0151] In the present disclosure, the nanoscale carbon nanotubes are used to prepare the porous carbon. Firstly, the good conductivity of the carbon nanotubes helps to improve the electrical conductivity of the porous carbon. Meanwhile, the size of the carbon nanotubes has an important influence on the electrical conductivity of the porous carbon. Generally, increasing the length of the carbon nanotubes can form a continuous conductive path, which is more conducive to improving the electrical conductivity of the porous carbon and the mechanical strength of the porous carbon. However, the longer carbon nanotubes are prone to agglomeration and have poor dispersion stability, which is not conducive to the uniform distribution of the carbon nanotubes in the suspension and the improvement of the electrical conductivity of the porous carbon. Therefore, the nanoscale carbon nanotubes are used in the present disclosure, which is more conducive to improving the electrical conductivity of the porous carbon. In addition, a small amount of tin or germanium element doping can promote the deintercalation of lithium ions, reduce the residual dead lithium, and improve the initial efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0152] In order to more clearly illustrate the specific embodiments of the present disclosure or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present disclosure, and other drawings can also be obtained by those skilled in the art without creative labor.

[0153] FIG. 1 is a technical route diagram for preparing the negative electrode material in Example 1-1 of the present disclosure.

[0154] FIG. 2 is a SEM image of the negative electrode material prepared in Example 1-1 of the present disclosure.

[0155] FIG. 3 is a SEM image of the negative electrode material prepared in Comparative Example 1-6 of the present disclosure.

[0156] FIG. 4 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 2-1.

[0157] FIG. 5 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 2-2.

[0158] FIG. 6 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Example 2-3.

[0159] FIG. 7 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Comparative Example 2-1.

[0160] FIG. 8 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Comparative Example 2-2.

[0161] FIG. 9 is a scanning electron microscope image of the carbonized small balls prepared in Comparative Example 2-3.

[0162] FIG. 10 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in Comparative Example 2-4.

[0163] Fig. 11 is a particle size distribution graph of the silicon-carbon negative electrode material prepared in Example 2-1.

[0164] Fig. 12 is a N2 adsorption-desorption isotherm graph of the silicon-carbon negative electrode material prepared in Example 2-1.

[0165] Fig. 13 is a SEM graph of the porous carbon material prepared in Example 3-1. DETAILED DESCRIPTION

[0166] Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. Clear indications to the contrary are needed to establish that any term in this disclosure cannot be interpreted in accordance with the ordinary and customary meaning. In the present disclosure, the use of “or” means “and / or” unless otherwise stated. Moreover, the use of the term “including” as well as other forms such as “include”, “includes” for indicating components, elements and / or parts of a list of elements is not limited to the recited components, elements, and / or parts thereof. Instead, means that other undescribed components, elements, and / or parts are optionally present in addition to the described components, elements, and / or parts.

[0167] The technical solutions of the present disclosure will be described clearly and completely in connection with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present disclosure.

[0168] The features and performances of the present disclosure will be further described in detail in connection with the embodiments.

[0169] Firstly, the present disclosure provides a negative electrode material, a preparation method and an application, specifically including the following contents.

[0170] The negative electrode material provided by the present disclosure includes a porous substrate, silicon elements distributed in the pores of the porous substrate, and carbon coated on the surface of the porous substrate. The silicon content in the negative electrode material is 30wt%-80wt%, the resistivity is less than 5Ω·cm, and the value of W is >8, where W=silicon content / resistivity, the unit of silicon content is wt%, and the unit of resistivity is Ω·cm.

[0171] Specifically, the silicon content in the negative electrode material can be 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, or any value between 30wt% and 80wt%. Increasing the silicon content in the negative electrode material is beneficial to improve the capacity of the negative electrode material. However, since silicon as a negative electrode material is accompanied by serious volume expansion and shrinkage during lithium intercalation and delithiation, it will affect the cycle performance of the negative electrode material. Therefore, the content of silicon should not be too much.

[0172] In the prior art, when preparing the negative electrode material, a large amount of silicon exists on the surface of the negative electrode material, i.e., forming floating silicon. Since the porous substrate cannot buffer the volume expansion of the floating silicon during the storage of lithium, and the existence of the floating silicon also affects the uniformity of the carbon coating, thereby being not conducive to the cycle performance of the negative electrode material.

[0173] In order to ensure the cycle performance of the negative electrode material while improving the capacity of the negative electrode material as much as possible, the negative electrode material in the present disclosure reduces the existence of floating silicon as much as possible, distributes the silicon in the pores of the porous substrate, uses the pore structure of the porous substrate to inhibit the volume expansion of the silicon during the deintercalation of lithium, and thereby improves the cycle performance of the negative electrode material.

[0174] In the embodiments of the present disclosure, as the content of floating silicon increases, the resistivity of the material increases. In the embodiments, the resistivity of the negative electrode material can be specifically less than 1 Ω·cm, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, or any value less than 5 Ω·cm. The larger the W is, the lower the proportion of floating silicon is. In the embodiments, the value of W of the negative electrode material can be specifically 8, 9, 10, 20, any value greater than 20, or any value greater than 8.

[0175] In the present disclosure, the carbon is also coated on the porous substrate, which is conducive to further relieving the volume expansion of the negative electrode material during the intercalation of lithium, and improving the electrical conductivity. In some embodiments, the content of the carbon coating layer in the silicon-carbon composite negative electrode material is 0.5wt%-10wt%.

[0176] In the optional embodiments, the specific surface area of the negative electrode material is 4m 2 / g-9m 2 / g, and can be specifically any value between 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, or 4m 2 / g-9m 2 / g. Increasing the specific surface area can increase the number of active sites for deintercalation of lithium, which is conducive to the deintercalation of lithium. However, too large specific surface area is not conducive to improving the cycle performance of the negative electrode material.

[0177] In the optional embodiments, the D50 of the negative electrode material is 1 μm-15 μm, and can be specifically 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, or any value between 1 μm and 15 μm. If the particle size of the negative electrode material is too large, the path for deintercalation of lithium at the center position increases, and the difficulty of deintercalation of lithium increases.

[0178] In the optional embodiments, the tap density of the negative electrode material is 0.7g / cm3 -1.5g / cm 3 , specifically, can be any value between 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 or 0.7g / cm 3 -1.5g / cm 3 , increasing the tap density is conducive to increasing the energy density of the material, but too high tap density will reduce the pore structure, and the difficulty of lithium extraction will increase.

[0179] The preparation method of the negative electrode material according to any one of the preceding embodiments comprises:

[0180] low-temperature adsorption, placing the porous substrate in an environment containing a silicon source gas and adsorbing the silicon source gas;

[0181] high-temperature pyrolysis, heating the porous substrate adsorbed with the silicon source gas to decompose the silicon source gas, to obtain a porous substrate with nano-silicon loaded in the pore structure;

[0182] coating treatment, forming a carbon coating layer on the porous substrate with nano-silicon loaded in the pore structure, to obtain the negative electrode material.

[0183] In the preparation method of the negative electrode material disclosed in the present disclosure, the porous substrate first plays an adsorption role on the silicon source, adsorbing the silicon source in the cavities of the porous substrate; then the temperature in the furnace is raised, so that the silane decomposes in the cavities, to deposit nano-silicon particles in the cavities, so as to reduce the influence of the volume expansion of lithium storage by silicon on the cycle performance of the negative electrode material.

[0184] The decomposition of the silicon source in the cavities releases gas, and the escape of the gas forms a cavity structure in the deposited silicon, to provide sufficient buffer space for the volume expansion of the nano-silicon particles during the subsequent lithium extraction process, so as to improve the stability of the negative electrode material.

[0185] The silicon deposition mode of "adsorption first and decomposition later" disclosed in the present disclosure significantly improves the deposition efficiency and the utilization rate of the silicon source when the deposition amount of silicon is equivalent or the deposition time is the same; the lithium ion battery assembled by using the silicon-carbon negative electrode material prepared by the preparation method disclosed in the present disclosure has more excellent cycle stability and initial coulombic efficiency.

[0186] In an optional embodiment, the low-temperature adsorption step is performed in a low-temperature adsorption device, and the low-temperature adsorption step ends when the silicon source gas is discharged from the tail gas outlet of the low-temperature adsorption device; the low-temperature adsorption device can be a deposition furnace or other device capable of realizing low-temperature adsorption; when the gas leaving the tail gas outlet contains the silicon source gas, it indicates that the adsorption of the porous substrate to the silicon source gas has been saturated; at this time, if the silicon source gas continues to be introduced, part of the silicon source gas will be adsorbed on the surface of the porous substrate, and the silicon obtained by subsequent high-temperature pyrolysis will be deposited on the surface of the porous substrate to form floating silicon, thereby increasing the content of floating silicon.

[0187] In an optional embodiment, the low-temperature adsorption temperature is 25-200°C, and specifically can be 25°C, 50°C, 75°C, 100°C, 125°C, 150°C, 175°C, 200°C, or any value between 25°C and 200°C; the low-temperature adsorption pressure is 0.0001-0.3 KPa, and specifically can be 0.0001-0.3 KPa or any value between 0.0001 KPa and 0.3 KPa; the low-temperature adsorption time is 1-30 h, and specifically can be 1 h, 3 h, 5 h, 10 h, 15 h, 20 h, 30 h, or any value between 1 h and 30 h; more optionally, the low-temperature adsorption temperature is 30-150°C, the pressure is 0.001-0.1 KPa, and the time is 2-25 h.

[0188] The low pressure during low-temperature adsorption is conducive to promoting the adsorption of the porous substrate to the silicon source gas and improving the adsorption efficiency; if the pressure is increased, the gas molecules will gather on the surface of the porous material and cannot effectively diffuse into the cavities of the porous substrate, which will form surface floating silicon on the substrate surface and affect the cycle stability of the silicon-carbon negative electrode material.

[0189] The low-temperature adsorption step uses a relatively low temperature, which can effectively reduce the movement and diffusion of the silicon source gas molecules and improve the adsorption effect of the porous substrate to the silicon source gas; however, if the temperature is too low, the gas molecules will move too slowly and disperse unevenly after entering the porous substrate, which will cause the nanosilicon particles obtained by subsequent pyrolysis to agglomerate and affect the stability of the negative electrode material.

[0190] In an optional embodiment, the silicon source is at least one selected from the group consisting of monosilane, disilane, dichlorodisilane, and trichlorosilane;

[0191] In an optional embodiment, the silicon source gas further contains an inert gas, and the volume fraction of the silicon source is 50%-99%. The presence of the inert gas is conducive to improving safety.

[0192] In an optional implementation, the high-temperature pyrolysis step is carried out in a high-temperature pyrolysis device. During high-temperature pyrolysis, the high-temperature pyrolysis step ends when the exhaust gas discharged from the tail gas outlet of the high-temperature pyrolysis device does not contain hydrogen. The silicon source gas decomposes and releases hydrogen. If no hydrogen is discharged from the tail gas outlet, the high-temperature pyrolysis step can be considered to have ended.

[0193] In an optional embodiment, the high-temperature pyrolysis temperature is 300℃-800℃, specifically any value between 300℃, 300℃, 300℃, 300℃, 300℃, 800℃, or 300℃-800℃; the high-temperature pyrolysis pressure is 0.01Kpa-5Kpa, specifically any value between 0.01Kpa, 0.1Kpa, 1Kpa, 2Kpa, 3Kpa, 4Kpa, 5Kpa, or 0.01Kpa-5Kpa; the high-temperature pyrolysis time is 1... h-50h; specifically, it can be any value between 1h, 3h, 5h, 10h, 20h, 30h, 40h, 50h or 1h-50h; more preferably, the high-temperature pyrolysis temperature is 400℃-700℃, the pressure is 0.01Kpa-3KPa, and the time is 1h-40h; the high-temperature pyrolysis step should provide a relatively high temperature to ensure that the silicon source gas is fully pyrolyzed, while maintaining a relatively low pressure to ensure that the adsorbed silicon source gas continues to remain in the cavities of the porous substrate.

[0194] In an optional implementation, the porous substrate satisfies at least one of the following AG:

[0195] A. SPAN value < 1.5, specifically it can be any value of 1.5, 1.2, 0.9, 0.6, 0.3, or < 1.5; the porous substrate has a relatively uniform particle size distribution, which is beneficial to obtaining a negative electrode material with a uniform particle size distribution.

[0196] B. Dv50 is 2μm-20μm, specifically it can be any value between 2μm, 5μm, 10μm, 15μm, 20μm or 2μm-20μm; the particle size of the porous substrate will affect the particle size of the negative electrode material, so the particle size of the porous substrate also needs to be selected reasonably.

[0197] C. The specific surface area of ​​the porous substrate is 400 m². 2 / g-2000m 2 / g, specifically 400m 2 / g、800m 2 / g、1200m 2 / g, 1600m 2 / g、2000m 2 / g or any value between 2μm and 20μm; optionally 900m 2 / g-2000m2 / g; the increase of the specific surface area of the porous substrate is conducive to increasing the amount of adsorbed silicon source gas, but too large specific surface area of the porous substrate leads to too high silicon content in the negative electrode material, which is not conducive to improving the cycle performance; in addition, the specific surface area of the porous substrate is partially inherited to the negative electrode material, thereby affecting the specific surface area of the negative electrode material.

[0198] D, the average pore size is 1.2 nm-7.0 nm, specifically, it can be 1.2 nm, 3 nm, 5 nm, 7.0 nm or any value between 1.2 nm and 7.0 nm, optionally 1.5 nm-5.0 nm; too large pore size is not conducive to uniform dispersion of deposited silicon, and too small pore size cannot accommodate the volume expansion of lithium intercalated silicon, both of which are not conducive to improving the cycle performance of the negative electrode material.

[0199] E, the pore volume is 0.3 cm 3 / g-2.0 cm 3 / g, specifically, it can be 0.3 cm 3 / g, 0.6 cm 3 / g, 0.9 cm 3 / g, 1.2 cm 3 / g, 1.5 cm 3 / g, 2.0 cm 3 / g or 0.3 cm 3 / g-2.0 cm 3 / g, optionally 0.5 cm 3 / g-1.8 cm 3 / g; too large pore volume, the strength of the porous substrate is relatively low, and too small pore volume cannot accommodate enough silicon source gas, resulting in reduced silicon content in the negative electrode material.

[0200] F, the pore size concentration is 0.3-6.0, specifically, it can be 0.3, 1, 2, 4, 6.0 or any value between 0.3 and 6.0, and the calculation method is (P V 90-P V 10) / P V 50, optionally 0.3-8: wherein PV refers to the pore volume, and the relatively uniform pore volume is conducive to relatively uniform adsorption of silicon in the cavities of the porous substrate, thereby facilitating uniform distribution of deposited silicon in the porous substrate.

[0201] G, the porous substrate is selected from at least one of porous carbon, porous metal oxide, coordination polymer and porous metal, and porous ceramic, and is optionally porous carbon; the porous carbon substrate can provide a certain capacity while adsorbing silicon source gas, and has good stability.

[0202] In an optional embodiment, the coating process comprises carbon deposition by introducing a carbon-containing gas source into a reactor in which the porous substrate loaded with nanosilicon is placed, to form a carbon coating layer;

[0203] Optionally, the carbon deposition temperature is 300-1300℃, and specifically can be 300℃, 600℃, 900℃, 1100℃, 1300℃, or any value between 300-1300℃, and the carbon deposition time is 1-10h, and specifically can be 1h, 3h, 5h, 7h, 10h, or any value between 1-10h; optionally, the carbon deposition temperature is 400-1000℃, and more optionally 400-600℃.

[0204] Optionally, the carbon-containing gas source comprises a carbon source gas selected from an alkane gas with a cracking temperature in the carbon deposition temperature range.

[0205] Optionally, the carbon-containing gas source further comprises an inert gas.

[0206] Optionally, the volume fraction of the carbon source gas in the carbon-containing gas source is 50-99vol%.

[0207] The embodiments of the present disclosure further provide a negative electrode tab of the present disclosure, comprising the negative electrode material of any one of the preceding embodiments or the negative electrode material prepared by the method of any one of the preceding embodiments.

[0208] The embodiments of the present disclosure further provide a secondary battery of the present disclosure, comprising the negative electrode tab of the preceding embodiments, which has excellent cycle stability, high reversible specific capacity, and high initial coulombic efficiency.

[0209] The embodiments of the present disclosure further provide an electrical equipment of the present disclosure, comprising the secondary battery of the preceding embodiments.

[0210] Secondly, the present disclosure provides a silicon-carbon composite material, a preparation method and application thereof, specifically comprising the following contents.

[0211] The embodiments of the present disclosure provide a silicon-carbon composite material, which comprises active material particles, and the active material particles comprise a skeleton of spherical porous carbon and nanosilicon particles.

[0212] The strength of the silicon-carbon composite material is defined by the following formula:

[0213] Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of the silicon-carbon composite material before pressing, m 2 / g.

[0214] In the present disclosure, a silicon-carbon composite material with high sphericity is prepared by depositing nano-silicon particles into the pores of a spherical porous carbon framework through chemical deposition; at the same time, the silicon-carbon composite material is subjected to compaction treatment, and it is found that most of the particles are broken after being pressed using an electron microscope, and the particles are mainly through cracks, which increases the specific surface area of the particles, i.e. the degree of particle breakage can be quantified by comparing the specific surface areas before and after the particles are characterized, and it is found that the compaction density and the applied pressure have a good linear correlation with the specific surface area after being pressed, so the strength is characterized by the change rate of the specific surface area before and after being pressed.

[0215] In an optional embodiment, the specific surface area of the silicon-carbon composite material is 2-5 m 2 / g, for example, it can be 2 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m 2 / g, 4.5 m 2 / g, 5 m 2 / g, etc.

[0216] In an optional embodiment, the strength of the silicon-carbon composite material under a pressure of 450 MPa for 30 s is above 90%, for example, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc.

[0217] In an optional embodiment, the sphericity of the spherical porous carbon is ≥80%, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0218] In an optional embodiment, the spherical porous carbon contains uniformly distributed micropores and / or mesopores inside.

[0219] In an optional embodiment, the total pore volume of the spherical porous carbon with an average pore size of less than 4 nm is ≥0.7 cm 3 / g, for example, it can be 0.7 cm 3 / g, 0.75 cm 3 / g, 0.8 cm 3 / g, 0.85 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, etc.

[0220] In an optional embodiment, the mesoporous carbon of the spherical porous carbon is <20%, for example, it can be 19%, 18%, 17%, 16%, 15%, 14%, 12%, 10%, 8%, 6%, 4%, 2%, 1%, etc.

[0221] In an optional embodiment, the microporosity of the spherical porous carbon is >80%, for example, it can be 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc.

[0222] In an optional embodiment, the particle size of the spherical porous carbon is 1 to 60 μm, for example, it can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc.

[0223] In an optional embodiment, the D of the spherical porous carbon 10 The particle size is 3 to 7 μm, for example, it can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, etc.

[0224] In an optional embodiment, the D of the spherical porous carbon 50 The particle size is 8–13 μm, for example, it can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, etc.

[0225] In an optional implementation, D 90 The particle size is 15–40 μm, for example, it can be 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, etc.

[0226] In an optional embodiment, the nano-silicon particles are deposited in the pores of the spherical porous carbon.

[0227] In an optional embodiment, the silicon content in the silicon-carbon composite material is 40% to 60%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, etc.

[0228] In an optional embodiment, the specific capacity of the silicon-carbon composite material is > 1500 mAh / g, for example, can be 1501 mAh / g, 1505 mAh / g, 1510 mAh / g, 1550 mAh / g, 1600 mAh / g, 1650 mAh / g, 1700 mAh / g, 1750 mAh / g, 1780 mAh / g, 1790 mAh / g, 1800 mAh / g, 1820 mAh / g, 1830 mAh / g, 1840 mAh / g, 1850 mAh / g, 1860 mAh / g, 1870 mAh / g, 1880 mAh / g, 1890 mAh / g, 1900 mAh / g, etc., preferably the specific capacity is > 1800 mAh / g.

[0229] In an optional embodiment, the capacity retention rate of the silicon-carbon composite material at 200 cycles is > 90%, for example, can be 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc.

[0230] The present disclosure also provides a preparation method of the silicon-carbon composite material according to any one of the preceding embodiments of the present disclosure, the preparation method comprising the following steps:

[0231] Mixing the low-carbon-source microspheres, the high-carbon-source resin, and the solvent to obtain a mixed solution;

[0232] Spray drying the mixed solution to obtain small spherical particles;

[0233] Carrying out carbonization treatment and activation treatment on the small spherical particles in sequence to obtain spherical porous carbon;

[0234] Carrying out gas-phase deposition on the spherical porous carbon to obtain the silicon-carbon composite material.

[0235] The present disclosure utilizes the mixing of microspheres with low synthetic carbon content and resin liquid with high carbon source, and then forms small spheres through spray drying treatment. The particle size of the spherical carbon is regulated by regulating the solidification conditions of the spray drying. The spherical carbon with high carbon content and good sphericity is prepared. Further, the pores are formed through chemical and physical methods. In the process of carbonization and activation pore formation, there is no hollow phenomenon, and there are no large pores in the interior, which does not weaken the strength. Thus, the spherical porous carbon with high sphericity and high strength is prepared. Finally, through gas-phase deposition, the nano-silicon particles are deposited in the pores of the spherical porous carbon skeleton, and the silicon-carbon composite material with high sphericity is prepared. At the same time, the higher the sphericity, the better the compression resistance in the rolling process due to the presence of many edges. The continuous formation of the solid electrolyte interface (SEI) film due to low strength, capacity weakening, and cycle deterioration are improved. In particular, the strength of the spherical silicon-carbon composite material under a pressure of 450 MPa for 30 s is more than 90%, but the strength of the irregular silicon-carbon composite material is less than 90%.

[0236] In an optional embodiment, the low-carbon-source microspheres have a residual carbon content of ≤40%, such as 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.

[0237] In an optional embodiment, the high-carbon-source resin has a residual carbon content of 50-70%, such as 50%, 55%, 60%, 65%, 70%, etc.

[0238] In an optional embodiment, the low-carbon-source microspheres include any one or a combination of at least two of polystyrene microspheres, polylactic acid microspheres, or polyvinylidene fluoride microspheres. The high-carbon-source resin is a phenolic resin and / or a phenolic resin derivative.

[0239] In an optional embodiment, the mass ratio of the low-carbon-source microspheres to the high-carbon-source resin is 1:(1-5), such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, etc.

[0240] In an optional embodiment, the solvent includes an alcohol solvent, preferably ethanol;

[0241] In an optional embodiment, the solid content of the mixed solution is 30-60wt%, such as 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, etc.

[0242] In an optional embodiment, the mixed solution further includes 5-10wt% carbon tubes, such as 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, etc.

[0243] It should be noted that, in the present disclosure, in addition to the fusion of the microspheres with the high-carbon-source resin, a certain amount of carbon tubes can also be added to further increase the electrical conductivity of the silicon-carbon composite material.

[0244] In an optional embodiment, the mixed solution further includes a conductive polymer, which includes any one or a combination of at least two of polyacetylene, polythiophene, polypyrrole, or polyaniline.

[0245] It should be noted that, in the present disclosure, in addition to the fusion of the microspheres with the high-carbon-source resin, a certain amount of conductive polymer can also be added to increase the active defects, thereby further increasing the electrical conductivity of the silicon-carbon composite material.

[0246] In an alternative embodiment, the spray drying process parameters include: the centrifugal disc rotation speed is 24000-30000 rpm; the inlet air temperature is 160-230℃; the feed rate is 1.2-4 L / h; the air blower frequency is 40-50 Hz.

[0247] In an alternative embodiment, the centrifugal disc rotation speed is 24000-30000 rpm, for example, it can be 24000 rpm, 25000 rpm, 26000 rpm, 27000 rpm, 28000 rpm, 29000 rpm, 30000 rpm, etc.

[0248] In an alternative embodiment, the inlet air temperature is 160-230℃, for example, it can be 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, etc.

[0249] In an alternative embodiment, the feed rate is 1.2-4 L / h, for example, it can be 1.2 L / h, 1.4 L / h, 1.6 L / h, 1.8 L / h, 2 L / h, 2.2 L / h, 2.4 L / h, 2.6 L / h, 2.8 L / h, 3 L / h, 3.2 L / h, 3.4 L / h, 3.6 L / h, 3.8 L / h, 4 L / h, etc.

[0250] In an alternative embodiment, the air blower frequency is 40-50 Hz, for example, it can be 40 Hz, 42 Hz, 44 Hz, 46 Hz, 48 Hz, 50 Hz, etc.

[0251] In an alternative embodiment, the carbonization treatment temperature is 400-900℃, for example, it can be 400℃, 450℃, 500℃, 550℃, 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, etc.

[0252] In an alternative embodiment, the carbonization treatment time is 3-10 h, for example, it can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc.

[0253] In an alternative embodiment, the activation treatment includes physical activation and / or chemical activation.

[0254] In an alternative embodiment, the activation treatment is performed by physical activation.

[0255] In an alternative embodiment, the step of physical activation is: introducing an activation gas into the carbon microspheres obtained after the carbonization treatment to perform physical activation.

[0256] In an optional embodiment, the activating gas comprises carbon dioxide and / or water vapor.

[0257] In an optional embodiment, the temperature of the physical activation is 800-1000℃, for example, it can be 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃, 1000℃, etc.

[0258] In an optional embodiment, the time of the physical activation is 7-20h, for example, it can be 7h, 8h, 9h, 10h, 12h, 14h, 16h, 18h, 20h, etc.

[0259] In an optional embodiment, the activating treatment further comprises a step of removing impurities: after the activating treatment, the porous carbon microspheres are washed with acid to remove impurities, and then washed with water and dried.

[0260] In an optional embodiment, the acid washing uses a 5-8wt% hydrochloric acid solution, for example, it can be 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, etc.

[0261] In an optional embodiment, the temperature of the acid washing is 20-100℃, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0262] In an optional embodiment, the time of the acid washing is 1-24h, for example, it can be 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc.

[0263] In an optional embodiment, the temperature of the drying is 70-90℃, for example, it can be 70℃, 75℃, 80℃, 85℃, 90℃, etc.

[0264] In an optional embodiment, the deposition gas source of the vapor deposition is a mixed gas of a protective gas and a silicon source gas.

[0265] In an optional embodiment, the protective gas comprises any one or a combination of at least two of nitrogen, neon, argon, krypton, xenon or radon.

[0266] In an optional embodiment, the silicon source gas comprises any one or a combination of at least two of monosilane, disilane, dichlorodisilane or trichlorosilane.

[0267] In an optional embodiment, the volume ratio of the protective gas to the silicon source gas is (10-30):(70-90).

[0268] wherein "10-30" can be, for example, 10, 12, 15, 18, 20, 22, 25, 28, 30, etc.

[0269] wherein "70-90" can be, for example, 70, 72, 75, 78, 80, 82, 85, 88, 90, etc.

[0270] In an optional embodiment, the ratio of the deposition amount of the vapor deposition to the feeding material is (0.4-1.5):1, which can be, for example, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0271] In an optional embodiment, the temperature of the vapor deposition is 300-800℃, which can be, for example, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc.

[0272] In an optional embodiment, the time of the vapor deposition is 5-10h, which can be, for example, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0273] In an optional embodiment, the method for preparing the silicon-carbon composite material comprises the following steps:

[0274] S1. Preparation of a low-carbon-source microsphere / high-carbon-source resin mixture:

[0275] The low-carbon-source microspheres and the high-carbon-source resin are mixed and dispersed in a solvent to obtain a mixture;

[0276] S2. Spray drying:

[0277] The mixture obtained in S1 is subjected to spray drying to obtain small spherical particles with a sphericity of >80%;

[0278] S3. Carbonization treatment:

[0279] The small spherical particles obtained in S2 are subjected to carbonization treatment in an inert atmosphere to obtain carbon microspheres after carbonization;

[0280] S4. Activation treatment:

[0281] The carbon microspheres after carbonization obtained in S3 are subjected to activation treatment to obtain porous carbon microspheres;

[0282] S5. Impurity removal:

[0283] The porous carbon microspheres obtained in S4 are subjected to acid washing to remove impurities, and then subjected to water washing and drying;

[0284] S6, chemical vapor deposition:

[0285] The impurity-removed porous carbon microspheres obtained in S5 are subjected to chemical vapor deposition to obtain the silicon-carbon composite material.

[0286] The present disclosure also provides a use of the silicon-carbon composite material according to any of the preceding embodiments in the preparation of a battery anode material.

[0287] The present disclosure also provides a detection method of a silicon-carbon composite material, which comprises the following steps:

[0288] The specific surface area of the silicon-carbon composite material before pressing is obtained and denoted as S1;

[0289] The silicon-carbon composite material is subjected to compaction treatment to break the sample, and the specific surface area of the broken silicon-carbon composite material after pressing is obtained and denoted as S2;

[0290] The specific surface area change rate of the silicon-carbon composite material is calculated by the following Formula I to characterize the strength of the silicon-carbon composite material;

[0291] The strength of the silicon-carbon composite material is defined by the following formula:

[0292] wherein P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material after pressing, m 2 / g; and S1 represents the specific surface area of the silicon-carbon composite material before pressing, m 2 / g.

[0293] The present disclosure does not limit the testing method of the specific surface area of the silicon-carbon composite material, which can be tested by BET method, for example.

[0294] The present disclosure does not limit the instrument for compaction treatment of the silicon-carbon composite material, and preferably, a compaction density instrument is used for compaction treatment.

[0295] In the present disclosure, the compaction density instrument is combined with the specific surface area instrument, and the change rate of the specific surface area before and after pressing is compared to quantify the strength of the silicon-carbon anode material. It is found by using an electron microscope to characterize the silicon-carbon material after pressing that most of the particles are broken, and the particles are mainly through cracks, which increases the specific surface area of the particles. Therefore, the degree of particle breakage is quantified by characterizing the specific surface area of the particles before and after pressing.

[0296] In an optional embodiment, the particle size distribution of the silicon-carbon powder can also be tested according to the provisions of GB / T 19077, and the particle size of the silicon-carbon composite material can be controlled to be the same D(50) if two types of the same sample are compared.

[0297] In an optional embodiment, the compaction treatment can be performed under the condition that the sample is broken, and the suitable pressure and displacement of pressing and unloading, the pressure holding pressure and the pressure holding time are set to make the particles of the sample broken under the same pressure (i.e., to ensure that the pressing time and the pressure holding time can crush the sample).

[0298] In an optional embodiment, the specific process of the compaction treatment is as follows: a certain amount of the silicon-carbon powder sample is weighed in the sample bin of the compaction density instrument; the compaction test conditions are set: the suitable pressure and displacement of pressing and unloading, the pressure holding pressure and the pressure holding time are set to make the particles of the sample broken under the same pressure (i.e., to ensure that the pressing time and the pressure holding time can crush the sample); after the test is completed, the sample is taken out using the rod retractor, and the sample after pressing is collected; and the collected sample is mixed for testing.

[0299] In an optional embodiment, the compaction treatment is performed at a rate of 8-12 mm / min, for example, 8 mm / min, 9 mm / min, 10 mm / min, 11 mm / min, 12 mm / min, etc., and preferably 10 mm / min.

[0300] In an optional embodiment, the pressure holding time of the compaction treatment is 10-50 s, for example, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, etc., and preferably 30 s.

[0301] In an optional embodiment, the pressure of the compaction treatment is 450-500 MPa, for example, 450 MPa, 460 MPa, 470 MPa, 480 MPa, 490 MPa, 500 MPa, etc.

[0302] Finally, the present disclosure provides a preparation method of porous carbon, porous carbon, a negative electrode material and a secondary battery, and specifically includes the following contents.

[0303] The present disclosure further provides a preparation method of porous carbon, comprising:

[0304] Granulation, drying and granulation are performed on the phenolic resin microsphere suspension to obtain a powder; the nanocarbon nanotubes are dispersed in the phenolic resin microspheres;

[0305] Carbonization, the powder is sequentially subjected to the second solidification, pre-oxidation and carbonization to obtain the porous carbon.

[0306] In the embodiments of the present disclosure, the nanoscale carbon nanotubes are used to prepare the porous carbon. First, the good electrical conductivity of the carbon nanotubes helps to improve the electrical conductivity of the porous carbon. Meanwhile, the size of the carbon nanotubes has an important influence on the electrical conductivity of the porous carbon. Generally, increasing the length of the carbon nanotubes can form a continuous conductive path, which is more conducive to improving the electrical conductivity of the porous carbon and the mechanical strength of the porous carbon. However, the longer carbon nanotubes are prone to agglomeration and have poor dispersion stability, which is not conducive to the uniform distribution of the carbon nanotubes in the suspension and the improvement of the electrical conductivity of the porous carbon. Therefore, the nanoscale carbon nanotubes are used in the present disclosure, which is more conducive to improving the electrical conductivity of the porous carbon.

[0307] In optional embodiments, the average length of the nanocarbon nanotubes is 20 nm-50 nm, and specifically can be 20 nm, 30 nm, 40 nm, 50 nm, or any value between 20 nm and 50 nm; and the average aspect ratio is 1.5-5, and specifically can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any value between 1.5 and 5.

[0308] The size of the nanocarbon nanotubes is within a suitable range, which is conducive to the nanocarbon nanotubes being wrapped by the phenolic resin microspheres. On the one hand, the wrapping by the phenolic resin microspheres can inhibit the agglomeration of the carbon nanotubes, which is conducive to improving the dispersion stability of the carbon nanotubes. On the other hand, if the size of the carbon nanotubes is too large, the carbon nanotubes are difficult to be wrapped by the phenolic resin microspheres, which may also affect the sphericity and pore structure of the subsequent porous carbon, and further affect the electrical properties of the negative electrode material prepared from the porous carbon.

[0309] In optional embodiments, in the phenolic resin microsphere suspension, the mass ratio of the nanocarbon nanotubes to the total mass of the phenolic raw material and the aldehyde raw material is 1:(1.5-10), and specifically can be 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10, or any value between 1 and 1:(1.5-10).

[0310] Although the introduction of the nanocarbon nanotubes into the phenolic resin microspheres is conducive to improving the electrical conductivity, if the amount is too large, the uniformity of the distribution of the nanocarbon nanotubes may be reduced, which further affects the electrical properties of the negative electrode material prepared from the porous carbon.

[0311] In optional embodiments, the doped source is further dispersed in the phenolic resin microspheres. The doped source is at least one of a germanium source and a tin source. The germanium source is at least one of a germanate, a metagermanate, dihydrogen germanate, and tetrahydrogen germanate. The tin source is at least one of tin chloride, tin nitrate, and tin sulfate.

[0312] Introducing germanium or tin elements in the porous carbon is beneficial to expand the lattice size, and further improve the ion conductivity, reduce the energy barrier, make the lithium deintercalation easier, reduce the generation of dead lithium, and thus improve the initial efficiency of the silicon-carbon negative electrode. In addition, in the present embodiment, the doping source is introduced into the phenolic resin microspheres, which is more beneficial to the uniform distribution of the doping source in the porous carbon.

[0313] In an optional embodiment, the doping source is also dispersed in the phenolic resin microspheres, and the mass ratio of the nanometer carbon nanotubes to the doping source in the phenolic resin microsphere suspension is (5-10):1, and specifically can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or any value between (5-10):1.

[0314] Introducing a small amount of germanium or tin elements in the porous carbon is more beneficial to the "local expansion" effect, and further beneficial to the transport of Li ions, but if the amount is too large, it may have the opposite effect, i.e. the "narrow channel" effect dominates, thereby increasing the migration energy barrier of Li ions, increasing the content of "dead lithium", and further affecting the electrical properties of the negative electrode material prepared from the porous carbon.

[0315] In an optional embodiment, the preparation method of the phenolic resin microsphere suspension comprises: mixing a dispersing agent, a doping source, a phenolic raw material, an aldehyde raw material, a catalyst, and an aqueous solution in which nanometer carbon nanotubes are dispersed, and performing heat preservation to obtain a prepolymer solution;

[0316] Mixing the prepolymer solution with a curing agent to perform a first curing to obtain the phenolic resin microsphere suspension.

[0317] In the mixing step, the purpose of the dispersing agent is to promote the uniform dispersion of the nanometer carbon nanotubes and inhibit their agglomeration, therefore, the dispersing agent is usually added to the aqueous solution first, and then the doping source, the phenolic raw material, the aldehyde raw material, and the catalyst are added.

[0318] In the present embodiment, an aqueous solution in which CNTs are uniformly dispersed is first obtained, and phenolic resin microspheres with nanometer carbon nanotubes as the core are generated by polymerization in the aqueous solution in which CNTs are uniformly dispersed, which is more beneficial to ensuring that the phenolic resin microspheres wrap the nanometer carbon nanotubes.

[0319] Preferably, the preparation method of the phenolic resin microsphere suspension satisfies at least one of the following characteristics A-G:

[0320] A. The dispersing agent is selected from at least one of F127 (poloxamer 407), PVA (polyvinyl alcohol), PEG (polyethylene glycol), and sodium silicate;

[0321] B. The aldehyde raw material is selected from at least one of formaldehyde and furfural;

[0322] C. the phenolic raw material is selected from at least one of phenol and resorcinol, and the mass ratio of the phenolic raw material to the aldehyde raw material is 1:(0.8-1.2), specifically can be 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2 or any value between 1:(0.8-1.2);

[0323] D. the catalyst is selected from at least one of sodium hydroxide and lithium hydroxide, and the ratio of the total mass of the catalyst to the phenolic raw material and the aldehyde raw material is 1:(25-35), specifically can be 1:25, 1:27, 1:29, 1:31, 1:33, 1:35 or any value between 1:(25-35);

[0324] E. the holding time is 4h-6h, specifically can be 4h, 5h, 6h or any value between 4h-6h; the temperature is 75℃-85℃, specifically can be 75℃, 80℃, 85℃ or any value between 75℃-85℃;

[0325] F. the curing agent is selected from at least one of hexamethylenetetramine and ammonia water, and the ratio of the total mass of the curing agent to the phenolic raw material and the aldehyde raw material is 1:(11-15), specifically can be 1:11, 1:12, 1:13, 1:14, 1:15 or any value between 1:(11-15);

[0326] G. the first curing temperature is 90℃-95℃, specifically can be 90℃, 93℃, 95℃ or any value between 90℃-95℃, and the first curing time is 2h-8h, specifically can be 2h, 5h, 8h or any value between 2h-8h.

[0327] By selecting the raw materials and synthesis conditions of the synthetic phenolic resin, the pore structure of the porous carbon is adjusted, and the cross-linked polymerized nanospheres can be changed into solid phenolic resin nanospheres by curing.

[0328] In an optional embodiment, the preparation method of the water solution dispersing nanometer carbon nanotubes comprises: ultrasonic stirring a mixture of nanometer carbon nanotubes and water to obtain the water solution dispersing nanometer carbon nanotubes; and the preparation method of the water solution dispersing nanometer carbon nanotubes satisfies at least one of the following characteristics a-c:

[0329] a. The ultrasonic frequency is 50-70 Hz, specifically, it can be 50 Hz, 60 Hz, 70 Hz or any value between 50-70 Hz; the stirring rate is 50-200 rpm, specifically, it can be 50 rpm, 100 rpm, 150 rpm, 200 rpm or any value between 50-200 rpm; the ultrasonic stirring time is 30-60 min, specifically, it can be 30 min, 40 min, 50 min, 60 min or any value between 30-60 min, the ultrasonic and stirring are carried out at the same time, which is beneficial to the dispersion of nanometer carbon nanotubes and the stability of the aqueous solution.

[0330] b. The solid content in the aqueous solution containing dispersed nanometer carbon nanotubes is 0.1-10 wt%, specifically, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% or any value between 0.1-10 wt%, which is beneficial to the dispersion of nanometer carbon nanotubes and the stability of the aqueous solution.

[0331] c. The nanometer carbon nanotubes are obtained by ball milling the carbon nanotube raw material, and the ball milling parameters include: the ball-to-material ratio is (20-50):1, specifically, it can be 20:1, 30:1, 40:1, 50:1 or any value between 20-50:1, the ball mill speed is 500-2000 rpm, specifically, it can be 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm or any value between 500-2000 rpm, and the gas is inert gas atmosphere. First, the carbon nanotube raw material is ball milled to obtain nanometer carbon nanotubes with appropriate particle size, which is beneficial to improve the uniformity and stability of the dispersion of nanometer carbon nanotubes in the aqueous solution, and is more beneficial to the wrapping of carbon nanotubes during the subsequent synthesis of phenolic resin.

[0332] In an optional embodiment, the mixture of the phenolic resin microsphere suspension and the water-soluble binder is subjected to spray drying to obtain the powder, and the spray drying parameters include: an inlet air temperature of 160-200°C, specifically 160°C, 170°C, 180°C, 190°C, 200°C, or any value between 160°C and 200°C; an outlet air temperature of 80-120°C, specifically 80°C, 90°C, 100°C, 110°C, 120°C, or any value between 80°C and 120°C; a feeding speed of 100-300 mL / h, specifically 100 mL / h, 200 mL / h, 300 mL / h, or any value between 100 mL / h and 300 mL / h; and a centrifugal atomization disc rotating speed of 23,000-27,000 rpm, specifically 23,000 rpm, 25,000 rpm, 27,000 rpm, or any value between 23,000 rpm and 27,000 rpm.

[0333] The spray drying can realize simultaneous drying and granulation, which is conducive to improving the efficiency, and in addition, the spray drying is conducive to improving the sphericity of the powder, and further conducive to improving the sphericity of the porous carbon finally prepared.

[0334] In an optional embodiment, the water-soluble binder is selected from at least one of a water-soluble resin, starch, dextrin, and polyvinyl alcohol.

[0335] In an optional embodiment, the volume ratio of the phenolic resin microsphere suspension to the water-soluble binder is 1:(0.5-4), specifically 1:0.5, 1:1, 1:2, 1:3, 1:4, or any value between 1:(0.5-4).

[0336] The addition of the binder can adjust the slurry viscosity to a reasonable range suitable for spray drying, and in addition, the amount and type of the water-soluble binder can affect the particle size of the powder and the pore structure of the porous carbon.

[0337] In an optional embodiment, the second curing temperature is 100-140°C, specifically 100°C, 110°C, 120°C, 130°C, 140°C, or any value between 100°C and 140°C, and the second curing time is 1-4 h, specifically 1 h, 2 h, 3 h, 4 h, or any value between 1 h and 4 h.

[0338] This curing can reduce the water content of the material on the one hand, and on the other hand, it is conducive to improving the cross-linking degree of the resin, which further affects the pore structure, thermal stability, and mechanical strength of the porous carbon.

[0339] In an optional embodiment, the pre-oxidation temperature is 280-320°C, specifically 280°C, 290°C, 300°C, 310°C, 320°C, or any value between 280-320°C, the pre-oxidation time is 1-5h, specifically 1h, 2h, 3h, 4h, 5h, or any value between 1-5h, and the pre-oxidation temperature rising rate is 1-5°C / min, specifically 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, or any value between 1-5°C / min; at the pre-oxidation temperature, the cross-linking degree of the resin is further improved, the stability of the porous carbon is further improved, and more pore structures are formed.

[0340] In an optional embodiment, the carbonization temperature is 800-1000°C, specifically 800°C, 900°C, 1000°C, or any value between 800-1000°C, the carbonization time is 4-8h, specifically 4h, 5h, 6h, 7h, 8h, or any value between 4-8h, and the carbonization temperature rising rate is 4-6°C / min, specifically 4°C / min, 5°C / min, 6°C / min, or any value between 4-6°C / min.

[0341] During the carbonization process, the organic components in the phenolic resin are decomposed, leaving a carbon skeleton, and forming a porous carbon, wherein a higher pyrolysis temperature is conducive to generating a more stable carbon skeleton and a more developed pore structure.

[0342] In an optional embodiment, the method further comprises activating the porous carbon with an activating agent to obtain activated porous carbon, the activation temperature is 700-1100°C, specifically 700°C, 800°C, 900°C, 1000°C, 1100°C, or any value between 700-1100°C, the activation time is 2-30h, specifically 2h, 5h, 10h, 15h, 20h, 25h, 30h, or any value between 2-30h, and the mass ratio of the porous carbon to the activating agent is 1:(0.5-4), specifically 1:0.5, 1:1, 1:2, 1:3, 1:4, or any value between 1:(0.5-4).

[0343] The activation step can affect the pore structure and specific surface area of the porous carbon, and thus is conducive to improving the performance of the negative electrode material prepared therefrom, wherein the activating agent is classified into a physical activating agent and a chemical activating agent, the physical activating agent is commonly CO2, water, etc., and the chemical activating agent is KOH, NaOH, phosphoric acid, etc.

[0344] The disclosure also provides a porous carbon prepared by the preparation method described in the foregoing embodiments.

[0345] Preferably, the porous carbon satisfies at least one of the following ①-④:

[0346] ① the pore volume ranges from 0.3 cm 3 / g to 4 cm 3 / g;

[0347] ② the specific surface area ranges from 800 m 2 / g to 2600 m 2 / g;

[0348] ③ the average pore size is 1.65 nm to 3.02 nm;

[0349] ④ the particle size D50 ranges from 4 μm to 30 μm.

[0350] The porous carbon satisfying the above requirements is beneficial to improving the performance of the negative electrode material prepared therefrom.

[0351] The embodiment of the present disclosure further provides a negative electrode material, comprising the porous carbon of the preceding embodiment and silicon and / or carbon distributed on the porous carbon.

[0352] In some embodiments, the prepared porous carbon is placed in a deposition furnace for CVD vapor deposition to obtain a silicon-carbon material, the temperature in the furnace is 400°C to 800°C, the silicon source is one or two of monosilane, disilane and trichlorosilane, the silane deposition time is 2h to 12h; after the deposition is completed, a carbon source is introduced for vapor coating, wherein the carbon source is one or two of methane, acetylene and ethylene, the thickness of the carbon coating layer is 1-10nm, and the mass ratio of the carbon coating layer to the final silicon-carbon negative electrode material is 1-5%, and the mass ratio of the nano-silicon particles is 30%-80%.

[0353] The embodiment of the present disclosure further provides a secondary battery comprising the negative electrode material of the preceding embodiment.

[0354] The features and performance of the negative electrode material, the preparation method and the application of the present disclosure are further described in detail below in combination with embodiments.

[0355] Embodiment 1-1

[0356] The embodiment provides a preparation method of a negative electrode material, and a technical route map is shown in FIG. 1, comprising the following steps:

[0357] (1) low-temperature adsorption, a porous carbon substrate (the average pore size is 4.5 nm, the pore volume is 1.0 cm 3 / g, the Dv50 is 7.8 μm, and the specific surface area is 1873 m 2The material (SPAN value: 1.2, pore size concentration: 2.4) is placed in a vapor deposition furnace, the furnace temperature is adjusted to 100°C, the pressure in the furnace is adjusted to 0.05 KPa, a mixed gas composed of 70 vol% silane and 30 vol% nitrogen is introduced at a flow rate of 10 L / min, the exhaust gas is observed by a mass spectrometer, and when silane gas appears in the exhaust gas after 12 h of heat preservation treatment, the low-temperature adsorption step is completed, at which time the introduction of silane gas is stopped and nitrogen is continuously introduced.

[0358] (2) After high-temperature pyrolysis and low-temperature adsorption, the furnace temperature is adjusted to 550°C, the pressure in the furnace is adjusted to 1.5 KPa, nitrogen is continuously introduced, the exhaust gas is observed by a mass spectrometer, and when the hydrogen content in the exhaust gas is reduced to 0 after 15 h of heat preservation treatment, the high-temperature pyrolysis step is completed.

[0359] (3) After the high-temperature pyrolysis step, the temperature in the furnace is adjusted to 800°C, a mixed gas composed of 60 vol% acetylene and 40 vol% nitrogen is introduced at a flow rate of 10 L / min, the deposition time is 2 h, and after the carbon coating is completed, the temperature is lowered to room temperature. After the material is dispersed, sieved, and de-magnetized, a silicon-carbon negative electrode material is obtained, and the SEM is shown in FIG. 2.

[0360] Example 1-2: Increase of low-temperature adsorption pressure

[0361] This example provides a method for preparing a negative electrode material, which is basically the same as Example 1-1, except that the pressure in the furnace in step (1) is adjusted to 0.15 KPa.

[0362] Example 1-3: Decrease of low-temperature adsorption pressure

[0363] This example provides a method for preparing a negative electrode material, which is basically the same as Example 1-1, except that the pressure in the furnace in step (1) is adjusted to 0.0008 KPa.

[0364] Example 1-4: Increase of low-temperature adsorption temperature

[0365] This example provides a method for preparing a negative electrode material, which is basically the same as Example 1-1, except that the temperature in the furnace in step (1) is adjusted to 180°C.

[0366] Example 1-5: Decrease of low-temperature adsorption temperature

[0367] This example provides a method for preparing a negative electrode material, which is basically the same as Example 1-1, except that the pressure in the furnace in step (1) is adjusted to 30°C.

[0368] Comparative Example 1-1: Too high low-temperature adsorption pressure

[0369] This comparative example provides a method for preparing a negative electrode material, which is substantially the same as Example 1-1, except that the pressure in the furnace in step (1) is adjusted to 1 KPa.

[0370] Comparative Example 1-2: Low adsorption temperature is too low

[0371] This comparative example provides a method for preparing a negative electrode material, which is substantially the same as Example 1-1, except that the temperature in the furnace in step (1) is adjusted to 10°C.

[0372] Comparative Example 1-3: Low adsorption temperature is too high

[0373] This comparative example provides a method for preparing a negative electrode material, which is substantially the same as Example 1-1, except that the pressure in the furnace in step (1) is adjusted to 250°C.

[0374] Comparative Example 1-4: The low adsorption step is ended before silane appears in the tail gas of low adsorption

[0375] This comparative example provides a method for preparing a negative electrode material, which is substantially the same as Example 1-1, except that the heat preservation time in step (1) is adjusted to 10 h.

[0376] Comparative Example 1-5: The low adsorption step is continued after silane appears in the tail gas of low adsorption

[0377] This example provides a method for preparing a negative electrode material, which is substantially the same as Example 1-1, except that the heat preservation time in step (1) is adjusted to 15 h.

[0378] Comparative Example 1-6

[0379] This example provides a method for preparing a negative electrode material, which comprises the following steps:

[0380] (1) A porous carbon material (average pore size of 4.5 nm, pore volume of 0.98 cm 3 / g, Dv50 of 7.5 μm, specific surface area of 1847 m 2 / g, SPAN value of 1.2, and pore size concentration of 2.8) as a substrate is placed in a deposition furnace at a temperature of 550°C; a mixed gas composed of 70 vol% silane and 30 vol% acetylene is introduced into the deposition furnace at a flow rate of 10 L / min, and the tail gas pipe pressure valve is adjusted so that the pressure in the furnace is always maintained at 1.5 KPa, and the gas is continuously introduced for 12 h, so that silicon particles and carbon particles are continuously nucleated and deposited inside the pores of the porous carbon material;

[0381] (2) After the silicon-carbon deposition is completed, the deposition furnace is heated to 800℃, a mixed gas composed of 60vol% acetylene and 40vol% nitrogen is introduced at a flow rate of 10L / min, and the deposition time is 2h. After the carbon coating is completed, the temperature is lowered to room temperature. After the material is dispersed, sieved, and de-magnetized, the silicon-carbon negative electrode material is obtained. The SEM is shown in FIG.3.

[0382] Comparative Examples 1-7

[0383] The present embodiment provides a preparation method of a negative electrode material, including the following steps:

[0384] The present embodiment is basically the same as Comparative Example 1-6, except that the aeration time in step (1) is adjusted to 15h.

[0385] Test Example 1-1

[0386] The composition and structure of the negative electrode material obtained in the above examples and comparative examples are characterized, wherein the specific surface area is measured by using a U.S. Micromeritics TriStar3020 specific surface area and pore size analyzer device, D50 is tested by using a Mastersizer3000 laser diffraction technology, and the tap density is tested by a tap density instrument. The specific test results are shown in Table 1-1:

[0387] Table 1-1

[0388] Application Example 1-1

[0389] The negative electrode material prepared in each example is assembled into a battery, specifically including the following steps.

[0390] (1) Preparation of positive electrode sheet: the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), conductive agent SuperP, carbon nanotube, and binder polyvinylidene fluoride (PVDF) are uniformly mixed with N-methyl pyrrolidone (NMP) at a mass ratio of 97:1:0.5:1.5 to prepare a positive electrode slurry (solid content of 70%) on the positive and negative sides of the current collector aluminum foil. After drying at 100℃, cold pressing is performed at room temperature under a pressure of 4MPa, followed by edge cutting, sheet cutting, striping, and welding of the tabs to prepare a positive electrode sheet.

[0391] (2) Preparation of negative electrode sheet: under a nitrogen protective atmosphere, the solvent N-methyl pyrrolidone (NMP) and the binder PVDF are uniformly stirred and mixed, then the conductive agent SuperP is added and stirred and mixed, followed by the addition of the negative electrode active substance and thorough stirring and mixing to prepare a negative electrode slurry (solid content of 50%).

[0392] The above negative electrode slurry is coated on the front and back of the current collector copper foil, dried at 100°C, cold-pressed at room temperature under 4 MPa, then trimmed, cut, striped, and welded to form a negative electrode sheet.

[0393] (3) Assembly of lithium ion battery

[0394] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence with the separator between the positive and negative electrode sheets to obtain a bare cell by winding. The bare cell is placed in an aluminum plastic shell package and dried at 100°C under a relative vacuum pressure of -0.95x105Pa to a moisture content of 100 ppm or less. An electrolyte is injected into the dried bare cell, wherein the electrolyte is composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) (EC: EMC: DEC volume ratio = 1:1:1) and LiPF6 (1.0M), and the battery is packaged, rested, formed (0.02C constant current charging for 2h, 0.1C constant current charging for 2h), shaped, and tested for capacity (binning) to obtain a soft-packaged liquid lithium ion battery.

[0395] During battery assembly, five batteries are prepared for each test, and five sets of data are tested. The final performance is the average of the five sets of data.

[0396] Test Example 3

[0397] The battery cycle performance is tested on a newwei device, specifically:

[0398] At 25°C, first discharge at 0.1C to 0.005V, then discharge at 0.08C to 0.001V, discharge at 0.05C to 0.001V, and discharge at 0.02C to 0.001V, and stand for 10 min; then charge at 0.1C to 1.5V and stand for 10 min, record the charge and discharge capacity after the first cycle, and calculate the first coulombic efficiency; cycle 100 times according to the above method, record the charge and discharge capacity after 100 times, and calculate the capacity retention rate after 100 cycles. The same method is used for testing and calculating the capacity retention rate after 500 cycles; the resistivity is tested by a semiconductor powder resistivity tester (30MPa four-probe V1.4) at 25°C, and the specific test results are shown in Tables 1-2.

[0399] Table 1-2

[0400] From the data of Examples 1-1 to 1-3 and Comparative Example 1-1, it can be seen that, in the low-temperature adsorption step, maintaining a lower pressure in the deposition furnace can effectively promote the adsorption of the porous substrate, and increasing the degree of negative pressure can promote the improvement of the adsorption efficiency of the substrate; reducing the degree of negative pressure causes the gas molecules to gather on the surface of the porous material and fail to effectively diffuse into the substrate, forming surface floating silicon on the substrate surface and affecting the cycle stability of the silicon-carbon negative electrode material.

[0401] From the data of Examples 1-1, 1-4, 1-5 and Comparative Examples 1-2, 1-3, it can be seen that, in the low-temperature adsorption step, a relatively low temperature can effectively reduce the movement and diffusion of silane gas molecules and improve the adsorption effect of the substrate on silane gas; however, if the adsorption temperature is too low, the gas molecules move too slowly and are not uniformly dispersed in the porous substrate after entering the substrate, resulting in agglomeration after subsequent pyrolysis and affecting the stability of the negative electrode material.

[0402] From Examples 1-1 and Comparative Examples 1-4, 1-5, it can be seen that determining the end time of the low-temperature adsorption step by the time at which silane appears in the tail gas pipe can effectively control the amount of silane deposition and avoid excessive deposition that causes surface floating silicon.

[0403] From Examples 1-1 and Comparative Examples 1-6, 1-7, it can be seen that the amount of silane deposited by Comparative Example 1-6 in the same time is significantly lower than that of Example 1-1, and Comparative Example 1-6 cannot effectively control the deposition position of silane, resulting in surface floating silicon and a significant increase in the resistivity of the material; only by appropriately extending the deposition time can a deposition amount comparable to that of Example 1-1 be achieved, but in Comparative Example 1-7, the floating silicon phenomenon is more obvious, which not only causes an increase in the resistivity of the material but also seriously affects the cycle stability of the material and shortens the service life of the battery.

[0404] The lithium ion battery assembled from the silicon-carbon negative electrode material prepared by the present disclosure has excellent cycle stability, with a capacity retention rate of up to 90% or more, and a maximum of 96%, after 100 cycles; a capacity retention rate of up to 80% or more, and a maximum of 87%, after 500 cycles; a low powder resistance of less than 8 Ω·cm, and high reversible specific capacity and first coulombic efficiency.

[0405] The features and properties of the silicon-carbon composite material, the preparation method and application thereof in the present disclosure are further described in detail below in conjunction with the examples.

[0406] Some of the raw material parameters in the following examples are shown below:

[0407] Low-carbon source carbon microspheres: Beijing Deke Daojin Technology Co., Ltd.; Model: PSC002000, residual carbon content: 15-20%, particle size: 2 um.

[0408] High carbon source solid resin: Guangzhou Shuangli Rubber Raw Material Trade Co., Ltd.; Model: 9003-35-4, residual carbon content 50-70%.

[0409] Example 2-1

[0410] The present embodiment provides a silicon-carbon composite material prepared by the following steps:

[0411] S1, mix and disperse 15% carbon microspheres with residual carbon content and 55% resin with a mass ratio of 1:1 in anhydrous ethanol to form a spray liquid with a solid content of 30%.

[0412] S2, spray the above spray liquid: spray solidification conditions: atomizing disc rotation speed: 28000 rpm, air inlet temperature: 175℃, feeding speed: 1.8L / h, air blower frequency: 50Hz, spray particle size: 5-20μm carbon microsphere particles.

[0413] S3, heat treat the above solidified carbon microsphere particles under nitrogen atmosphere, heating rate is 10℃ / min, heat treatment temperature is 400℃, carbonization is carried out for 5h to obtain carbonized carbon microspheres.

[0414] S4, put the above carbonized carbon microspheres into a well-sealed rotary kiln, rotate the kiln at a frequency of 30Hz, and introduce water vapor at a flow rate of 12L / min, the rotary kiln has a heating rate of 10℃ / min, and the temperature is raised to 900℃ and kept for 8h, then cooled to room temperature to obtain the material.

[0415] S5, soak the material obtained in S4 with 6.5% HCl and heat to 60℃ for 1h, then wash with pure water until neutral, and dry at 80℃ to obtain spherical porous carbon.

[0416] The sphericity of the spherical porous carbon is 92.5%; the spherical porous carbon contains uniformly distributed micropores and mesopores, and the average pore size of the spherical porous carbon is 1.89nm; the total pore volume of the spherical porous carbon with an average pore size less than 4nm is 0.84cm 3 / g; the mesopore ratio of the spherical porous carbon is 19%, and the micropore ratio is 81%; the particle size of the spherical porous carbon is 8.3μm; the D 10 particle size of the spherical porous carbon is 3.5μm; the D 50 particle size of the spherical porous carbon is 8.3μm; the D 90 particle size of the spherical porous carbon is 19.8μm.

[0417] S6, the spherical porous carbon material obtained in S5 is placed into a rotary kiln with good sealing, the kiln is rotated, a mixed gas of a deposition gas source and a silicon source is introduced as a protective gas, the mixed gas is a mixture of nitrogen and monosilane (the volume ratio of nitrogen to monosilane is 20:80), the deposition amount is 0.6 times the amount of the material, the deposition temperature is 500 DEG C, and the deposition time is 6 hours, to obtain the silicon-carbon composite material.

[0418] FIG. 4 is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 2-1. As shown in FIG. 4, the low-carbon microspheres are combined with the high-carbon resin base, the particle size of the spherical carbon is controlled by spray drying, the carbon base with high carbon and good sphericity is prepared, and the carbon base pellets prepared by this method do not have the phenomenon of hollowing in the process of carbonization and alkali activation, and do not have large pores in the interior, which causes weakening of the strength.

[0419] Example 2-2

[0420] This example provides a silicon-carbon composite material, which is different from Example 2-1 only in that the spray solidification conditions of S2 are different, and the specific conditions are as follows:

[0421] S2, the spray liquid is subjected to a spray experiment: spray solidification conditions: atomizing disc rotation speed: 28000 rpm, air inlet temperature: 190 DEG C, feeding speed: 2.3 L / h, air blower frequency: 50 Hz, and the sprayed particle size is 6-40 pm carbon microsphere particles.

[0422] FIG. 5 is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 2-2. As shown in FIG. 5, the low-carbon microspheres are combined with the high-carbon resin base, the particle size of the spherical carbon is controlled by spray drying, the carbon base with high carbon and good sphericity is prepared, and the carbon base pellets prepared by this method do not have the phenomenon of hollowing in the process of carbonization and alkali activation, and do not have large pores in the interior, which causes weakening of the strength.

[0423] Example 2-3

[0424] This example provides a silicon-carbon composite material, which is different from Example 2-1 only in that the spray solidification conditions of S2 are different, and the specific conditions are as follows:

[0425] S2, the spray liquid is subjected to a spray experiment: spray solidification conditions: atomizing disc rotation speed: 28000 rpm, air inlet temperature: 190 DEG C, feeding speed: 2.3 L / h, air blower frequency: 50 Hz, and the sprayed particle size is 6-40 pm carbon microsphere particles.

[0426] Figure 6 is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 2-3. As shown in Figure 6, by combining low-carbon microspheres with a high-carbon resin base and controlling the particle size of the spherical carbon through spray drying, a carbon base with high carbon content and good sphericity is prepared; and using this method to prepare carbon base pellets, there is no hollow phenomenon and no large pores in the interior during the carbonization and alkali activation pore-forming processes, which does not weaken the strength.

[0427] Example 2-4

[0428] This example provides a silicon-carbon composite material, which differs from Example 2-1 in that in S1, the mass ratio of the low-carbon microspheres to the high-carbon resin is 1:5, and the other steps are completely consistent with Example 2-1.

[0429] Example 2-5

[0430] This example provides a silicon-carbon composite material, which differs from Example 2-1 in that the carbonization treatment temperature in S3 is 600°C; the carbonization treatment time is 10h, and the other steps are completely consistent with Example 2-1.

[0431] Example 2-6

[0432] This example provides a silicon-carbon composite material, which differs from Example 2-1 in that the carbonization treatment temperature in S3 is 900°C; the carbonization treatment time is 3h, and the other steps are completely consistent with Example 2-1.

[0433] Example 2-7

[0434] This example provides a silicon-carbon composite material, which differs from Example 2-1 in that the activation temperature in S4 is 800°C, and the activation time is 20h, and the other steps are completely consistent with Example 2-1.

[0435] Example 2-8

[0436] This example provides a silicon-carbon composite material, which differs from Example 2-1 in that the activation temperature in S4 is 1000°C, and the activation time is 7h, and the other steps are completely consistent with Example 2-1.

[0437] Example 2-9

[0438] This example provides a silicon-carbon composite material, which differs from Example 2-1 in that the deposition amount to the material ratio is 0.4, the deposition temperature is 300°C, and the deposition time is 10h, and the other steps are completely consistent with Example 2-1.

[0439] Example 2-10

[0440] The embodiment provides a silicon-carbon composite material, which is prepared through the following steps:

[0441] Comparative example 2-1

[0442] The comparative example provides a silicon-carbon composite material, which is prepared through the following steps:

[0443] S1, dispersing resin with a residual carbon content of 55% in anhydrous ethanol to form a spraying liquid with a solid content of 30%.

[0444] S2, performing a spraying experiment on the spraying liquid: spraying and solidifying conditions: atomizing disc rotating speed: 28000 rpm, air inlet temperature: 175 DEG C, feeding speed: 1.8 L / h, air blower frequency: 50 Hz, and the spraying particle size is 5-20 mu m carbon microsphere particles with a sphericity of 70-80%.

[0445] S3, performing heat treatment on the solidified carbon microsphere particles in a nitrogen atmosphere, the heating rate is 10 DEG C / min, the heat treatment temperature is 400 DEG C, and the carbonization is performed for 5 h, so that carbonized carbon microspheres are obtained.

[0446] S4, placing the carbonized carbon microspheres into a rotary kiln furnace with good sealing, rotating the kiln furnace at a frequency of 30 Hz, and introducing water vapor with a flow rate of 12 L / min, the heating rate of the rotary kiln furnace is 10 DEG C / min, the temperature is increased to 900 DEG C, and the temperature is kept for 8 h, and then the temperature is cooled to room temperature to obtain a material.

[0447] S5, soaking the material obtained in S4 in 6.5% HCl and heating to 60 DEG C for stirring for 1 h, then washing with pure water until neutral, and drying at 80 DEG C, so that the spherical porous carbon is obtained.

[0448] S6, placing the spherical porous carbon material obtained in S5 into a rotary kiln furnace with good sealing, rotating the kiln furnace at a frequency of 40 Hz, and introducing a deposition gas source which is a mixed gas of a protective gas and a silicon source: a mixed gas of nitrogen and monosilane (the volume ratio of nitrogen to monosilane is 20:80), the deposition amount to the feeding material ratio is 0.6, the deposition temperature is 500 DEG C, and the deposition time is 6 h, so that the silicon-carbon composite material is obtained.

[0449] Fig. 7 is an electron microscope image of the silicon-carbon composite material prepared in the comparative example 2-1, as shown in Fig. 7, no low-carbon source microspheres are added, only a high-carbon source resin liquid is used for spray drying granulation, and the sphericity of the silicon-carbon composite material prepared by the method is poor.

[0450] Comparative example 2-2

[0451] The comparative example provides a silicon-carbon composite material prepared by the following steps:

[0452] S1, the resin with a carbon residue of 55% is dissolved in anhydrous ethanol to form a resin solution with a solid content of 30%, and then the resin solution is cured in a vacuum oven at 120°C for 4h.

[0453] S2, the carbonized carbon particles are heat treated under a nitrogen atmosphere at a heating rate of 10°C / min, the heat treatment temperature is 400°C, and the treatment time is 5h to obtain a pre-carbonized material.

[0454] S3, the pre-carbonized material is crushed to uniform particles of millimeter level by a crusher for standby use.

[0455] S4, the carbonized carbon microspheres are placed in a well-sealed rotary kiln, the kiln is rotated at a frequency of 30Hz, water vapor is introduced at a flow rate of 12L / min, the heating rate of the rotary kiln is 10°C / min, and the temperature is raised to 900°C, and then the temperature is maintained for 8h, and then cooled to room temperature to obtain a material.

[0456] S5, the material obtained in S4 is soaked in 6.5% HCl and heated to 60°C for 1h, then washed with pure water until neutral, and dried at 80°C.

[0457] S6, the material in S5 is crushed to D50=5-12μm by using a jet mill.

[0458] S7, the material obtained in S6 is placed in a well-sealed rotary kiln, the kiln is rotated at a frequency of 40Hz, and a mixed gas of deposition gas source as protective gas and silicon source is introduced: a mixed gas of nitrogen and silane (volume ratio of nitrogen to silane is 20:80), the deposition amount is 0.6 times the amount of the material, the deposition temperature is 500°C, and the deposition time is 6h to obtain the silicon-carbon composite material.

[0459] Figure 8 is an electron microscope image of the silicon-carbon composite material prepared in Comparative Example 2-2, as shown in Figure 8, without adding low-carbon microspheres and without using spray drying, the obtained silicon-carbon composite material presents an irregular state.

[0460] Comparative Example 2-3

[0461] The comparative example provides a carbon microsphere particle prepared by the following steps:

[0462] S1, the carbon microspheres with a carbon residue of 15% are directly cured in a vacuum oven at 120°C for 4h.

[0463] S2, heat-treating the carbon microspheres after curing under a nitrogen atmosphere at a heating rate of 10°C / min and at a heat-treatment temperature of 400°C for 5h to carbonize.

[0464] Figure 9 is an electron microscope image of the silicon material prepared in Comparative Example 2-3. As shown in Figure 9, the carbonized microspheres collapsed and became hollow.

[0465] Comparative Example 2-4

[0466] This comparative example provides a silicon-carbon composite material, which differs from Example 2-1 in that, in S1, the mass ratio of the carbon microspheres with a residual carbon content of 15% to the resin with a residual carbon content of 55% is 2:1, and the other steps are identical to those of Example 2-1.

[0467] Comparative Example 2-5

[0468] This comparative example provides a silicon-carbon composite material, which differs from Example 2-1 in that, in S1, the mass ratio of the carbon microspheres with a residual carbon content of 15% to the resin with a residual carbon content of 55% is 1:6, and the other steps are identical to those of Example 2-1.

[0469] Comparative Example 2-6

[0470] This comparative example provides a silicon-carbon composite material, which is prepared by the following steps:

[0471] S1, mixing and dispersing the carbon microspheres with a residual carbon content of 15% and the resin with a residual carbon content of 55% in anhydrous ethanol at a mass ratio of 1:1 to form a spray liquid with a solid content of 30%.

[0472] S2, stirring and heating the mixture to cure for 8h to form carbon microspheres with a sphericity of 60-70%.

[0473] S3, heat-treating the carbon microspheres after curing under a nitrogen atmosphere at a heating rate of 10°C / min and at a heat-treatment temperature of 400°C for 5h to carbonize the carbon microspheres.

[0474] S4, placing the carbonized carbon microspheres in a rotary kiln with good sealing, rotating the kiln at a frequency of 30Hz, introducing water vapor at a flow rate of 12L / min, and heating the rotary kiln at a rate of 10°C / min to 900°C, maintaining the temperature for 8h, and then cooling to room temperature to obtain the material.

[0475] S5, soaking the material obtained in S4 in 6.5% HC1 and heating to 60°C for 1h with stirring, then washing with pure water until neutral, and drying at 80°C to obtain the spherical porous carbon.

[0476] S6, the spherical porous carbon material obtained in S5 was placed into a rotary kiln with good sealing, the kiln was rotated, the frequency was 40 Hz, the deposition gas source was a mixed gas of protective gas and silicon source: a mixed gas of nitrogen and monosilane (the volume ratio of nitrogen to monosilane was 20:80), the deposition amount was 0.6 times the amount of the material, the deposition temperature was 500 DEG C, and the deposition time was 6 h, to obtain the silicon-carbon composite material.

[0477] FIG. 10 is an electron microscope image of the carbon-silicon material prepared in Comparative Example 2-4. As shown in FIG. 10, no spray drying treatment was performed, and the sphericity of the obtained silicon-carbon composite material was low.

[0478] Comparative Example 2-7

[0479] This comparative example provides a silicon-carbon composite material, which is different from Example 2-1 in that, in S2, the spray drying treatment process parameters include: the centrifugal disc rotation speed is 20000 rpm; the air inlet temperature is 250 DEG C; the feeding speed is 4.5 L / h; and the frequency of the air blower is 35 Hz, and the other steps are completely consistent with Example 2-1.

[0480] Comparative Example 2-8

[0481] This comparative example provides a silicon-carbon composite material, which is different from Example 2-1 in that, in S2, the spray drying treatment process parameters include: the centrifugal disc rotation speed is 32000 rpm; the air inlet temperature is 150 DEG C; the feeding speed is 1.0 L / h; and the frequency of the air blower is 55 Hz, and the other steps are completely consistent with Example 2-1.

[0482] Test Example 2-1

[0483] Test sample: the silicon-carbon composite materials provided in Examples 2-1 to 2-10, and the composite materials provided in Comparative Examples 1 to 8;

[0484] Test method:

[0485] (1) Test of particle size:

[0486] A laser particle size analyzer was used to test the particle size distribution of the powder according to the provisions of GB / T 19077, and the particle size of the silicon-carbon composite material was tested.

[0487] (2) Test of strength:

[0488] The specific surface area of the silicon-carbon composite material before pressing down is tested using a specific surface area tester and recorded as S1; the silicon-carbon composite material is placed in a sample bin of a compaction density instrument for compaction treatment (compaction conditions are 10 mm / min, pressure maintaining time is 60 s, and pressure is 450 MPa) to break the sample, and then the specific surface area of the broken silicon-carbon composite material after pressing down is tested using a specific surface area tester and recorded as S2; the specific surface area change rate of the silicon-carbon composite material is calculated by the following Formula I to represent the strength of the silicon-carbon composite material.

[0489] The strength of the silicon-carbon composite material is defined by the following formula:

[0490] In the formula, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material after pressing down, m 2 / g; S1 represents the specific surface area of the silicon-carbon composite material before pressing down, m 2 / g.

[0491] (3) Capacity: at 25°C, first discharge to 0.005 V at 0.1 C, then discharge to 0.001 V at 0.08 C, discharge to 0.001 V at 0.05 C, and discharge to 0.001 V at 0.02 C, and stand for 10 min; then charge to 1.5 V at 0.1 C, stand for 10 min, and record the charge and discharge capacity after the first cycle.

[0492] (4) 200-cycle capacity retention rate: cycle 200 times in the above manner, record the charge and discharge capacity after 200 times, calculate the capacity retention rate after 200 cycles, and the 200-cycle cycle capacity retention rate = the 200th cycle discharge capacity / the first cycle discharge capacity x 100%.

[0493] The specific test results are shown in Table 2-1:

[0494] Table 2-1

[0495] As shown in Table 2-1, the specific surface area of the silicon-carbon composite material of the present disclosure is 2-5 m 2 / g; the strength of the silicon-carbon composite material under a pressure of 450 MPa for 30 s is above 90%; the specific capacity of the silicon-carbon composite material is > 1500 mAh / g, and the 200-cycle capacity retention rate of the silicon-carbon composite material is > 90%. Therefore, the silicon-carbon composite material of the present disclosure has high sphericity, avoids poor pressure resistance caused by too many edges and corners during rolling, and can improve the problem of continuous formation of solid electrolyte interface (SEI) film, capacity weakening, and cycle deterioration caused by low strength.

[0496] Fig. 11 is a particle size distribution graph of the silicon-carbon composite material prepared in Example 2-1. Fig. 12 is a N2adsorption-desorption isotherm graph of the silicon-carbon composite material prepared in Example 2-1. As shown in Figs. 11 and 12, the silicon-carbon composite material has a single-point BET specific surface area of 1,014.12875 (m2 / g) at P / Po of 0.20000:1; a total pore volume of 0.84 cm3 / g; a micropore volume of 0.68 cm3 / g; an average pore diameter of 1.89 nm; a mesopore ratio of 19%; and a micropore ratio of 81%. 2 Fig. 13 is a particle size distribution graph of the silicon-carbon composite material prepared in Example 2-2. Fig. 14 is a N2adsorption-desorption isotherm graph of the silicon-carbon composite material prepared in Example 2-2. As shown in Figs. 13 and 14, the silicon-carbon composite material has a single-point BET specific surface area of 1,014.12875 (m2 / g) at P / Po of 0.20000:1; a total pore volume of 0.84 cm3 / g; a micropore volume of 0.68 cm3 / g; an average pore diameter of 1.89 nm; a mesopore ratio of 19%; and a micropore ratio of 81%. 3 Fig. 15 is a particle size distribution graph of the silicon-carbon composite material prepared in Example 2-3. Fig. 16 is a N2adsorption-desorption isotherm graph of the silicon-carbon composite material prepared in Example 2-3. As shown in Figs. 15 and 16, the silicon-carbon composite material has a single-point BET specific surface area of 1,014.12875 (m2 / g) at P / Po of 0.20000:1; a total pore volume of 0.84 cm3 / g; a micropore volume of 0.68 cm3 / g; an average pore diameter of 1.89 nm; a mesopore ratio of 19%; and a micropore ratio of 81%. 3 Fig. 17 is a particle size distribution graph of the silicon-carbon composite material prepared in Example 2-4. Fig. 18 is a N2adsorption-desorption isotherm graph of the silicon-carbon composite material prepared in Example 2-4. As shown in Figs. 17 and 18, the silicon-carbon composite material has a single-point BET specific surface area of 1,014.12875 (m2 / g) at P / Po of 0.20000:1; a total pore volume of 0.84 cm3 / g; a micropore volume of 0.68 cm3 / g; an average pore diameter of 1.89 nm; a mesopore ratio of 19%; and a micropore ratio of 81%.

[0497] The features and performances of the method for preparing the porous carbon, the porous carbon, the negative electrode material, and the secondary battery according to the present disclosure are further described in detail below in conjunction with examples.

[0498] Example 3-1

[0499] The present example provides a method for preparing a negative electrode material, which specifically comprises the following steps:

[0500] 1) 20 g of CNT and 400 g of zirconium balls were placed in a ball mill jar, and four groups were prepared, wherein the ball milling speed was 1500 rpm, and the ball milling time was 20 h. After the four groups were uniformly mixed, they were sieved to obtain CNT particles with an average length of 20-50 nm and an average aspect ratio of 2.

[0501] 2) 27 g of the ball-mixed CNT particles were added to 500 mL of deionized water, and ultrasonic stirring and dispersion were performed, with an ultrasonic frequency of 60 Hz, an ultrasonic time of 40 min, and a stirring rate of 150 rpm. After ultrasonic treatment, a CNT dispersion aqueous solution with a solid content of 5% was obtained.

[0502] 3) 0.5 g of F127, 3 g of germanium dihydroxide, 21.5 g of phenol, 23.5 g of formaldehyde, and 1.5 g of sodium hydroxide were sequentially added to the CNT dispersion aqueous solution for oil bath treatment, with an oil bath temperature of 80°C. After 4 h of incubation, a precursor solution was obtained.

[0503] 4) To the precursor solution, 3.5 g of hexamethylenetetramine was added, and the temperature of the oil bath was increased to 95°C. After 6 h of incubation, a phenolic resin microsphere suspension was obtained.

[0504] 5) The water-soluble resin adhesive (water-soluble thermosetting phenolic resin liquid) and the phenolic resin microsphere suspension were mixed at a ratio of 1:1, and then stirred using a homogenizer for 1 h. Spray drying was then performed, with an inlet air temperature of 180°C, an outlet air temperature of 90°C, a feeding speed of 100 ml / h, and a centrifugal atomizer speed of 25,000 rpm.

[0505] 6) Collect the powder in the spray drying collection bottle, place the powder in the oven at 120℃, solidify for 2h, then in the muffle furnace, increase the temperature from room temperature to 300℃ at a rate of 3℃ / min, and keep the temperature for 2h to perform the pre-oxidation treatment.

[0506] 7) Place the pre-oxidized powder in the tube furnace to perform the carbonization treatment, introduce nitrogen into the tube furnace, increase the temperature from room temperature to 800℃ at a rate of 5℃ / min, keep the temperature for 4h, and then obtain spherical carbon.

[0507] 8) Place the spherical carbon and KOH in a ratio of 1:2.5 in the tube furnace to perform the activation at 950℃ for 3h to obtain spherical porous carbon, and the SEM image is as shown in FIG. 13.

[0508] 9) Place the spherical porous carbon in the CVD furnace, perform the vapor deposition of methane and silane in a ratio of 1:3 to obtain a spherical silicon-based negative electrode material.

[0509] Example 3-2

[0510] This example provides a preparation method of a negative electrode material, which is different from example 3-1 only in that the germanium dihydroxide in step 1) is replaced by tin chloride.

[0511] Example 3-3

[0512] This example provides a preparation method of a negative electrode material, which is different from example 3-1 only in that the ultrasonic time in step 2) is shortened to 30min.

[0513] Example 3-4

[0514] This example provides a preparation method of a negative electrode material, which is different from example 3-1 only in that the feeding speed in step 5) is increased to 300ml / h.

[0515] Example 3-5

[0516] This example provides a preparation method of a negative electrode material, which is different from example 3-1 only in that the ratio of spherical carbon to KOH in step 8) is adjusted to 1:1.

[0517] Comparative Example 3-1

[0518] This comparative example provides a preparation method of a negative electrode material, which is different from example 3-1 only in that step 1) is cancelled and no CNT is added in step 2).

[0519] Comparative Example 3-2

[0520] This comparative example provides a preparation method of a negative electrode material, which is different from example 3-1 only in that no germanium source is added in step 3).

[0521] Comparative Example 3-3

[0522] This comparative example provides a method for preparing a negative electrode material. The only difference from Example 3-1 is that step 2) is omitted, and the 27g CNT particles in step 1) are added in step 5).

[0523] Comparative Examples 3-4

[0524] This comparative example provides a method for preparing a negative electrode material, which differs from Example 3-1 only in that step 1) is omitted.

[0525] Comparative Examples 3-5

[0526] This comparative example provides a method for preparing a negative electrode material. The only difference from Example 3-1 is that steps 3-4) are cancelled, and step 5) is modified to take the CNT dispersion aqueous solution from step 2) and the water-soluble thermosetting phenolic resin liquid in a 1:1 ratio, stir with a homogenizer for 1 hour, and then spray dry. The spray drying parameters are: inlet air temperature 180℃, outlet air temperature 90℃, feed rate 100ml / h, and centrifugal atomizer speed 25000rpm.

[0527] Test Example 3-1

[0528] The negative electrode materials obtained in the above embodiments and comparative examples were tested. At the same time, the negative electrode materials obtained in the above embodiments and comparative examples were assembled into batteries. The specific steps are as follows: (1) Preparation of electrode sheet: First, the active material, binder and conductive carbon black were placed in a mortar in a ratio of 8:1:1, and 5-8 drops of N-methylpyrrolidone were added to make a slurry. The above slurry was coated on copper foil, and then placed in a vacuum oven at 80°C for 8 hours to dry. Then, the electrode sheet was sliced ​​to obtain the electrode sheet. (2) Assembly of button battery: The negative electrode shell, lithium sheet, 3-4 drops of electrolyte, PF porous polymer separator, 3-4 drops of electrolyte, electrode sheet and positive electrode shell were assembled into a half cell in sequence. The electrolyte here is a liquid composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF6 (1.0M). The battery was tested using the following steps: at 25°C, it was first discharged at 0.1C to 0.005V, then discharged at 0.08C to 0.001V, then at 0.05C to 0.001V, and finally at 0.02C to 0.001V, and then allowed to stand for 10 minutes. Next, it was charged at 0.1C to 1.5V, allowed to stand for 10 minutes, and the charge specific capacity after the first cycle was recorded. The initial coulombic efficiency was then calculated. The results are shown in Tables 3-1 and 3-2.

[0529] Table 3-1

[0530] Table 3-2

[0531] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, and not to limit them; although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure. Industrial applicability

[0532] Firstly, the present disclosure utilizes the morphology of carbon microspheres and the high carbon content of phenolic resin to synthesize carbon substrates with good sphericity, and the particle size of the carbon microspheres can be well controlled through spray drying technology, and the particle size uniformity is good. Compared with irregular resin-based silicon-carbon composite materials, the silicon-carbon material synthesized by this method has higher strength and does not have the large pore pores of biomass-based natural materials. The sphericity of the silicon-carbon negative electrode material described in the present disclosure is high, which avoids the poor compression resistance caused by the presence of many edges during the rolling process, and can improve the continuous generation of the solid electrolyte interface (SEI) film caused by low strength, capacity weakening, and cycle deterioration.

[0533] Secondly, the negative electrode material in the present disclosure distributes silicon in the pores of the porous substrate, and utilizes the pore structure of the porous substrate to inhibit the volume expansion of silicon during the deintercalation process, thereby improving the cycle performance of the negative electrode material. In the preparation method of the negative electrode material in the present disclosure, first, the silicon source is adsorbed in the cavities of the porous substrate; then the temperature in the furnace is raised, and the silane is decomposed in the cavities to obtain nano-silicon particles deposited in the cavities, thereby reducing the content of floating silicon.

[0534] Finally, in the present disclosure, nano-sized carbon nanotubes are used to prepare porous carbon. First, the good electrical conductivity of carbon nanotubes helps to improve the electrical conductivity of porous carbon, and the size of carbon nanotubes has an important influence on the electrical conductivity of porous carbon. Generally, increasing the length of carbon nanotubes can form a continuous conductive path, which is more conducive to improving the electrical conductivity of porous carbon and also more conducive to improving the mechanical strength of porous carbon. However, longer carbon nanotubes tend to agglomerate and have poor dispersion stability, which is not conducive to the uniform distribution of carbon nanotubes in the suspension, and thus is not conducive to improving the electrical conductivity of porous carbon. Therefore, in the present disclosure, nano-sized carbon nanotubes are used, which is more conducive to improving the electrical conductivity of porous carbon. In addition, a small amount of tin or germanium element doping can promote the deintercalation of lithium ions, reduce the residual dead lithium, and improve the initial efficiency.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises a porous substrate, silicon elements distributed in the pores of the porous substrate, and carbon coated on the surface of the porous substrate, wherein the silicon content of the negative electrode material is 30wt%-80wt%, the resistivity is less than 5Ω·cm, and the value of W is greater than 8, wherein W=silicon content / resistivity, the unit of silicon content is wt%, and the unit of resistivity is Ω·cm.

2. The negative electrode material according to claim 1, characterized in that, The specific surface area of the negative electrode material is 4 m 2 / g-9 m 2 / g; And / or, the D50 of the negative electrode material is 1 μm-15 μm; and / or the tap density of the negative electrode material is 0.7 g / cm3 or more 3 -1.5 g / cm3 3 .

3. A method for producing the negative electrode material according to claim 1 or 2, characterized by, The method comprises: low-temperature adsorption, wherein the porous substrate is placed in an environment containing a silicon source gas and the silicon source gas is adsorbed; high-temperature pyrolysis, wherein the porous substrate adsorbed with the silicon source gas is heated to decompose the silicon source gas, thereby obtaining a porous substrate loaded with nanosilicon in the pore structure; coating treatment, wherein a carbon coating layer is formed on the porous substrate loaded with nanosilicon in the pore structure, thereby obtaining the negative electrode material.

4. The method of producing a negative electrode material according to claim 3, characterized by, The low-temperature adsorption step is performed in a low-temperature adsorption device, and the low-temperature adsorption step ends when the silicon source gas is discharged from the tail gas outlet of the low-temperature adsorption device during low-temperature adsorption; the low-temperature adsorption step satisfies at least one of the following a-c: a, the low-temperature adsorption temperature is 25°C-200°C, the pressure is 0.0001 KPa-0.3 KPa, and the time is 1 h-30 h; b, the silicon source is selected from at least one of monosilane, disilane, dichlorosilane, and trichlorosilane; c, the silicon source gas further comprises an inert gas, wherein the volume fraction of the silicon source is 50vol%-99vol%.

5. The method of producing a negative electrode material according to claim 3 or 4, characterized by, The high-temperature pyrolysis step is performed in a high-temperature pyrolysis device, and the high-temperature pyrolysis step ends when the gas discharged from the tail gas outlet of the high-temperature pyrolysis device does not contain hydrogen during high-temperature pyrolysis; The high-temperature pyrolysis temperature is 300°C-800°C, the pressure is 0.01 KPa-5 KPa, and the time is 1 h-50 h.

6. The method of producing a negative electrode material according to any one of claims 3 to 5, wherein The porous substrate satisfies at least one of the following A-G: A, the SPAN value is less than 1.5; B, the Dv50 is 2 μm-20 μm C. the specific surface area of the porous substrate is 400 m 2 / g-2000 m 2 / g, optionally 900 m 2 / g-2000 m 2 / g; D, the average pore size is 1.2 nm-7.0 nm, and optionally 1.5 nm-5.0 nm; E. pore volume of 0.3 cm 3 / g - 2.0 cm 3 / g, optionally 0.5 cm 3 / g - 1.8 cm 3 / g; F, the aperture concentration is 0.3-6.0, the calculation method is (P V 90-P V 10) / P V 50, optionally 0.3-8: G, the porous substrate is selected from at least one of porous carbon, porous metal oxide, coordination polymer, and porous metal, and porous ceramic, and optionally porous carbon.

7. The method of producing a negative electrode material according to any one of claims 3 to 6, wherein The coating treatment comprises introducing a carbon-containing gas source into a reactor in which the porous substrate loaded with nanosilicon in the pore structure is placed to perform carbon deposition, thereby forming a carbon coating layer; the coating treatment step satisfies at least one of the following (1)-(4): (1), the carbon deposition temperature is 300°C-1300°C, and the carbon deposition time is 1 h-10 h; (2), the carbon-containing gas source comprises a carbon source gas, and the carbon source gas is selected from an alkane gas with a cracking temperature within the carbon deposition temperature range; (3), the carbon-containing gas source further comprises an inert gas; (4), the volume fraction of the carbon source gas in the carbon-containing gas source is 50vol%-99vol%.

8. A negative electrode sheet characterized by comprising: The negative electrode material comprises a porous substrate, silicon elements distributed in the pores of the porous substrate, and carbon coated on the surface of the porous substrate, wherein the silicon content of the negative electrode material is 30wt%-80wt%, the resistivity is less than 5Ω·cm, and the value of W is greater than 8, wherein W=silicon content / resistivity, the unit of silicon content is wt%, and the unit of resistivity is Ω·cm.

9. A secondary battery characterized by comprising: The negative electrode material comprises a porous substrate, silicon elements distributed in the pores of the porous substrate, and carbon coated on the surface of the porous substrate, wherein the silicon content of the negative electrode material is 30wt%-80wt%, the resistivity is less than 5Ω·cm, and the value of W is greater than 8, wherein W=silicon content / resistivity, the unit of silicon content is wt%, and the unit of resistivity is Ω·cm.

10. An electrical device, comprising: The silicon-carbon composite material comprises active material particles, and the active material particles comprise a skeleton of spherical porous carbon and nanosilicon particles.

11. A silicon-carbon composite material, characterized by, ​ The strength of the silicon-carbon composite material is defined by the following equation: Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of the silicon-carbon composite material before pressing, m 2 / g.

12. The silicon-carbon composite of claim 11, wherein, The specific surface area of the silicon-carbon composite material is 2-5 m 2 / g; Preferably, the strength of the silicon-carbon composite material under a pressure of 450 MPa for 30 s is above 90%.

13. The silicon-carbon composite material of claim 11 or 12, wherein, The sphericity of the spherical porous carbon is ≥80%; Preferably, the interior of the spherical porous carbon contains uniformly distributed micropores and / or mesopores; Preferably, the average pore diameter of the spherical porous carbon is less than 4 nm and the total pore volume of pores having a diameter of less than 4 nm is > 0.7 cm3 / g 3 / g; Preferably, the mesopore ratio of the spherical porous carbon is <20%, and the micropore ratio is >80%; Preferably, the particle size of the spherical porous carbon is 1-60 μm; wherein the D50 of the spherical porous carbon is 1-60 μm. 10 The particle size is 3-7 μm; the D50 is 3-7 μm. 50 The particle size is 8-13 μm; the D50 is 8-13 μm. 90 The particle size is 15-40 μm.

14. The silicon-carbon composite of any one of claims 11-13, wherein, The nano-silicon particles are deposited in the pores of the spherical porous carbon; Preferably, the content of silicon in the silicon-carbon composite material is 40-60%; Preferably, the specific capacity of the silicon-carbon composite material is >1500 mAh / g, preferably >1800 mAh / g; Preferably, the capacity retention rate of the silicon-carbon composite material after 200 cycles is >90%.

15. A method of producing the silicon-carbon composite material according to any one of claims 11 to 14, characterized by, The preparation method comprises the following steps: Mixing low-carbon-source microspheres, high-carbon-source resin and a solvent to obtain a mixed solution; Spray drying the mixed solution to obtain small spherical particles; Carrying out carbonization treatment and activation treatment on the small spherical particles in sequence to obtain spherical porous carbon; Carrying out gas-phase deposition on the spherical porous carbon to obtain the silicon-carbon composite material.

16. The method of claim 15, wherein the silicon-carbon composite material is prepared by a process comprising: The residual carbon content of the low-carbon-source microspheres is ≤40%, and the residual carbon content of the high-carbon-source resin is 50-70%; Preferably, the low-carbon-source microspheres comprise any one or a combination of at least two of polystyrene microspheres, polylactic acid microspheres or polyvinylidene fluoride microspheres; Preferably, the high-carbon-source resin is phenolic resin and / or a derivative of phenolic resin; Preferably, the mass ratio of the low-carbon-source microspheres to the high-carbon-source resin is 1:(1-5); Preferably, the solvent comprises an alcohol solvent, preferably ethanol; Preferably, the solid content of the mixed solution is 30-60 wt%; Preferably, the mixed solution further comprises 5-10 wt% of carbon nanotubes; Preferably, the mixed solution further comprises a conductive polymer, which comprises any one or a combination of at least two of polyacetylene, polythiophene, polypyrrole or polyaniline.

17. The method of claim 15 or 16, wherein the silicon-carbon composite material is prepared by a process comprising: The spray drying process parameters comprise: a centrifugal disc rotation speed of 24000-30000 rpm; an air inlet temperature of 160-230°C; a feeding speed of 1.2-4 L / h; and a frequency of 40-50 Hz for an air blower; Preferably, the carbonization treatment is carried out at a temperature of 400-900°C for 3-10 h; Preferably, the activation treatment is carried out by a physical activation method; Preferably, the step of physical activation comprises: introducing an activation gas into the carbon microspheres obtained after the carbonization treatment to carry out physical activation; Preferably, the activation gas comprises carbon dioxide and / or water vapor; Preferably, the physical activation is carried out at a temperature of 800-1000°C for 7-20 h; Preferably, the activation treatment further comprises a step of impurity removal: after the activation treatment, the porous carbon microspheres are subjected to acid washing to remove impurities, and then subjected to water washing and drying; Preferably, the acid washing is carried out using a 5-8 wt% hydrochloric acid solution; Preferably, the acid washing is carried out at a temperature of 20-100°C for 1-24 h; Preferably, the drying is carried out at a temperature of 70-90°C. Preferably, the deposition gas source of the vapor deposition is a mixed gas of a protective gas and a silicon source gas; Preferably, the protective gas comprises any one or a combination of at least two of nitrogen, neon, argon, krypton, xenon or radon; Preferably, the silicon source gas comprises any one or a combination of at least two of monosilane, disilane, dichlorosilane or trichlorosilane; Preferably, the silicon source gas further comprises a carbon source gas, and the carbon source gas comprises any one or a combination of at least two of methane, ethane, acetylene or ethylene; Preferably, the volume ratio of the protective gas to the silicon source gas is (10-30):(70-90); Preferably, the content of the carbon source gas accounts for 0-30% of the total volume of the silicon source gas; Preferably, the deposition amount of the vapor deposition to the feeding material ratio is (0.4-1.5):1; Preferably, the temperature of the vapor deposition is 300-800℃, and the time of the vapor deposition is 5-10h.

18. Use of the silicon-carbon composite material according to any one of claims 11-14 in the preparation of a battery anode material.

19. A method for detecting the strength of a silicon-carbon composite material, characterized by, The detection method comprises the following steps: Obtaining the specific surface area of the silicon-carbon composite material before pressing, and denoted as S1; The silicon-carbon composite material is subjected to compaction treatment to break the sample, and the specific surface area of the broken silicon-carbon composite material after pressing is obtained, and denoted as S2; The specific surface area change rate of the silicon-carbon composite material is calculated by the following formula I to characterize the strength of the silicon-carbon composite material; The strength of the silicon-carbon composite material is defined by the following equation: Wherein, P represents the strength of the silicon-carbon composite material, %; S2 represents the specific surface area of the silicon-carbon composite material after pressing, m 2 / g; S1 represents the specific surface area of the silicon-carbon composite material before pressing, m 2 / g.

20. The method of claim 19, wherein the silicon-carbon composite material is characterized by, The rate of the compaction treatment is 8-12mm / min, preferably 10mm / min; Preferably, the holding time of the compaction treatment is 10-50s, preferably 30s; Preferably, the pressure of the compaction treatment is 450-500MPa.

21. A method for producing a porous carbon, characterized by, It comprises: Granulation, drying and granulation of the phenolic resin microsphere suspension to obtain a powder; The nanometer carbon nanotubes are dispersed in the phenolic resin microspheres; Carbonization, the powder is sequentially subjected to second curing, pre-oxidation and carbonization to obtain the porous carbon.

22. The method of claim 21, wherein the porous carbon is prepared by a method comprising: The average length of the nanometer carbon nanotubes is 20nm-50nm, and the average aspect ratio is 1.5-5; And / or, in the phenolic resin microsphere suspension, the mass ratio of the nanometer carbon nanotubes to the total mass of the phenolic raw material and the aldehyde raw material is 1:(1.5-10); And / or, the doping source is at least one of a germanium source and a tin source, the germanium source is at least one of germanate, metagermanate, dihydrogen germanate and tetrahydrogen germanate, and the tin source is at least one of tin chloride, tin nitrate and tin sulfate; And / or, the doping source is at least one of a germanium source and a tin source, the germanium source is at least one of germanate, metagermanate, dihydrogen germanate and tetrahydrogen germanate, and the tin source is at least one of tin chloride, tin nitrate and tin sulfate; 23. The method of claim 22, wherein the porous carbon is prepared by a method comprising: The preparation method of the phenolic resin microsphere suspension comprises: mixing a dispersing agent, a doping source, a phenolic raw material, an aldehyde raw material and a catalyst with an aqueous solution in which nanometer carbon nanotubes are dispersed and performing heat preservation to obtain a prepolymer solution; Mixing the prepolymer solution with a curing agent to perform first curing to obtain the phenolic resin microsphere suspension; Preferably, the preparation method of the phenolic resin microsphere suspension satisfies at least one of the following characteristics A-G: A. The dispersing agent is selected from at least one of F127, PVA, PEG and sodium silicate; B. The aldehyde raw material is selected from at least one of formaldehyde and furfural; C. The phenolic raw material is selected from at least one of phenol and m-dihydroxybenzene, and the mass ratio of the phenolic raw material to the aldehyde raw material is 1:(0.8-1.2); D. The catalyst is selected from at least one of sodium hydroxide and lithium hydroxide, and the mass ratio of the catalyst to the total mass of the phenolic raw material and the aldehyde raw material is 1:(25-35); E. The holding time is 4h-6h, and the temperature is 75℃-85℃; F. The curing agent is selected from at least one of hexamethylenetetramine and ammonia water, and the mass ratio of the curing agent to the total mass of the phenolic raw material and the aldehyde raw material is 1:(11-15); G. The first curing temperature is 90℃-95℃, and the first curing time is 2h-8h.

24. The method of claim 23, wherein the porous carbon is prepared by a method comprising: The preparation method of the water solution dispersed with nanometer carbon nanotubes comprises: ultrasonic stirring a mixed solution of nanometer carbon nanotubes and water to obtain the water solution dispersed with nanometer carbon nanotubes; and the preparation method of the water solution dispersed with nanometer carbon nanotubes satisfies at least one of the following characteristics a-c: a. The ultrasonic frequency is 50Hz-70Hz; the stirring rate is 50rpm-200rpm; and the ultrasonic stirring time is 30min-60min; b. The solid content in the water solution dispersed with nanometer carbon nanotubes is 0.1wt%-10wt%; c. The nanometer carbon nanotubes are obtained by ball milling a carbon nanotube raw material, and the ball milling parameters include: a ball-to-material ratio of (20-50):1, a ball mill rotation speed of 500rpm-2000rpm, and an inert gas atmosphere.

25. The method of producing porous carbon according to any one of claims 21 to 24, wherein The mixed solution of the phenolic resin microsphere suspension and the water-soluble binder is subjected to spray drying to obtain the powder, and the spray drying parameters include: an inlet air temperature of 160℃-200℃, an outlet air temperature of 80℃-120℃, a feeding speed of 100mL / h-300mL / h, and a centrifugal atomization disc rotation speed of 23000rpm-27000rpm; And / or, the water-soluble binder is selected from at least one of a water-soluble resin, starch, dextrin and polyvinyl alcohol; And / or, the volume ratio of the phenolic resin microsphere suspension to the water-soluble binder is 1:(0.5-4).

26. The method of producing porous carbon according to any one of claims 21 to 25, wherein The second curing temperature is 100℃-140℃, and the second curing time is 1h-4h; And / or, the pre-oxidation temperature is 280℃-320℃, the pre-oxidation time is 1h-5h, and the pre-oxidation heating rate is 1℃ / min-5℃ / min; And / or, the carbonization temperature is 800℃-1000℃, the carbonization time is 4h-8h, and the carbonization heating rate is 4℃ / min-6℃ / min.

27. The method of producing porous carbon according to any one of claims 21 to 26, wherein The porous carbon is activated by using an activator to obtain activated porous carbon, the activation temperature is 700℃-1100℃, the activation time is 2h-30h, and the mass ratio of the porous carbon to the activator is 1:(0.5-4).

28. A porous carbon, characterized in that, Prepared by the preparation method of any one of claims 21-27; Preferably, the porous carbon satisfies at least one of the following ①-④: 1.3 cm 3 / g-1.4 cm 3 / g; (ii) a specific surface area ranging from 800 m2 / g to 2600 m2 / g 2 (g) from 0.1 to 10% by weight of a compound of formula (I) 2 (g) from ③ average pore diameter 1.65 nm-3.02 nm; ④ particle size D50 in the range of 4 μm-30 μm.

29. A negative electrode material, characterized by, The negative electrode material according to claim 29.

30. A secondary battery characterized by comprising: The negative electrode material according to claim 29.

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