CN118800896B

CN118800896B - Preparation method of doped silicon-carbon composite anode material

Info

Publication number: CN118800896B
Application number: CN202411280752.8A
Authority: CN
Inventors: 许迪新; 任睿银; 赵玉明; 李阁; 王亚鹏
Original assignee: Shanxi Fuji New Energy Material Technology Co ltd; Beijing One Gold Amperex Technology Ltd
Current assignee: Shanxi Fuji New Energy Material Technology Co ltd; Beijing One Gold Amperex Technology Ltd
Priority date: 2024-09-13
Filing date: 2024-09-13
Publication date: 2024-11-15
Anticipated expiration: 2044-09-13
Also published as: CN118800896A

Abstract

本发明公开了一种掺杂硅碳复合负极材料的制备方法，是以多孔碳为基底，均匀涂覆于沉积收集装置内壁，在和收集装置联通的真空蒸镀炉中加热硅源和金属掺杂源形成蒸汽，扩散至收集装置，进行多孔碳材料的硅沉积和掺杂，然后烧结，最后进行碳包覆，得到所述掺杂硅碳复合负极材料。掺杂金属元素在内部以硅酸盐键合网络形式均匀分布在硅碳材料中，经过金属原位掺杂后，在氧化亚硅内部形成了惰性键合网络，起到提高首次库伦效率减少不可逆锂损失的作用，具有更好的循环稳定性和更高的首次效率。

The present invention discloses a method for preparing a doped silicon-carbon composite negative electrode material, which is based on porous carbon, uniformly coated on the inner wall of a deposition collection device, and heated in a vacuum evaporation furnace connected to the collection device to form steam, diffused to the collection device, and silicon deposition and doping of the porous carbon material are performed, and then sintered, and finally carbon coated to obtain the doped silicon-carbon composite negative electrode material. The doped metal element is uniformly distributed in the silicon-carbon material in the form of a silicate bonding network. After metal in-situ doping, an inert bonding network is formed inside the silicon oxide, which plays a role in improving the first coulomb efficiency and reducing irreversible lithium loss, and has better cycle stability and higher first efficiency.

Description

Preparation method of doped silicon-carbon composite anode material

Technical Field

The invention belongs to the technical field of battery cathodes, and particularly relates to a preparation method of a silicon-carbon doped composite cathode material.

Background

With the rapid development of new energy technology, secondary batteries such as lithium ion batteries are increasingly widely applied in the fields of electric automobiles, wearable devices and the like. However, with the continuous increase in consumer expectations for battery performance, conventional graphite negative electrode materials have failed to meet the stringent requirements of high performance batteries, particularly fast-charging batteries, for the negative electrode materials. In the popularization of battery technology, a rapid charging function has become an urgent need of the public. Therefore, developing a negative electrode material that can meet the fast charge requirements of high performance batteries has become a key challenge for the battery industry at present.

At present, the precursors of the silicon-based anode material are mainly silicon and silicon oxide, and compared with the silicon oxide, the silicon has higher capacity (up to 4200 mAh/g), but has larger volume expansion rate (300 percent), which is not beneficial to improving the cycle stability and safety of the lithium ion battery. The silicon oxide can irreversibly generate lithium oxide and lithium silicate with lithium ions in the charge and discharge process, plays a role in buffering the volume expansion of the lithium silicon alloy in the circulation process, and has longer cycle life and higher safety. However, the silicon oxide has larger volume expansion problem (150 percent) as well, the active material is crushed and pulverized due to severe volume expansion, and then the active material falls off from the current collector to lose electrical contact, and the SEI film is continuously broken and regenerated, and the process consumes a large amount of active lithium and electrolyte, so that the capacity attenuation and aging of the battery are accelerated, the service life, the safety and the cycling stability of the battery are seriously influenced, and electrochemical inert lithium oxide and lithium silicate are generated in the first lithium intercalation process of the silicon oxide, so that the first coulombic efficiency of the silicon oxide serving as a negative electrode material is seriously reduced due to irreversible lithium consumption, and the advantages of the silicon-based negative electrode material cannot be effectively exerted.

At present, the volume expansion and the first coulombic efficiency of the silicon-based anode material are improved mainly through element doping and carbon cladding. The carbon-coated silicon oxide anode material combines the advantages of silicon and carbon, aims to overcome some challenges of silicon materials in lithium ion batteries, reserves expansion space for the volume expansion of silicon by the composite material prepared by compositing silicon and carbon, and overcomes the defects of poor silicon conductivity and unstable Solid Electrolyte Interface (SEI) film to a certain extent. Although carbon-coated silica negative electrode materials theoretically have high specific capacities and small volume expansions, there are some drawbacks in practical applications. First, the first time efficiency of the carbon-coated silica anode material is generally low, which means that the number of lithium ions capable of effectively participating in the reaction during the first charge and discharge is small. Second, while carbon coating can alleviate the bulk expansion of silicon to some extent, the carbon coating can crack during long-term cycling, resulting in reduced material properties. In the prior art, the carbon fiber is coated in a mode of coating the carbon fiber, but the preparation cost of the carbon fiber is high, and the processing of the silicon oxide layer can influence the fiber structure of the silicon oxide layer, so that the silicon oxide layer is not beneficial to large-scale production.

Elemental doping is a strategy commonly used for modification of silicon oxide and this approach typically involves the incorporation of metallic elements into the silicon oxide material for improving the performance of the silicon oxide negative electrode material in lithium ion batteries. By doping a small amount of metal elements in the silicon oxide structure, the loss of irreversible lithium can be reduced, thereby improving the first coulombic efficiency of the battery. Meanwhile, the metal silicate uniformly dispersed in the silica structure can suppress the volume expansion of the material to some extent. In the existing doping technology, some doping elements can stabilize the structure of the material, and structural damage or phase change possibly occurring in the charge-discharge process is reduced. The stability is not only beneficial to prolonging the cycle life of the battery, but also can improve the coulomb efficiency of the battery, but is limited by intrinsic defects of materials, types and concentrations of doping elements and other factors, the improvement effect is probably not obvious, and the high requirement of the fast-charging battery on the performance of the anode material is difficult to meet, so that the existing doping mode cannot fully excite and utilize the synergistic effect between the doping elements.

Patent CN114906853a discloses a method for preparing an element doped silica/carbon composite material. The method takes doping source, silicon and silicon dioxide as raw materials to prepare element doped silicon oxide; coating the crushed element doped silicon oxide with a carbon layer by vapor deposition to obtain the element doped silicon oxide/carbon composite material. According to the method, the element doping is carried out on the silicon oxide, so that the carrier concentration is improved, or the high-conductivity metal is introduced, so that the lithium ion transmission rate of the material is improved, the element doped silicon oxide/carbon composite material has high-rate charge-discharge performance, the defect of low lithium ion transmission rate of the traditional silicon oxide is overcome, and the rate performance is improved. However, although the doping of the elements may improve the electrochemical performance, the problem of volume expansion of the silicon oxide during the charge and discharge process cannot be effectively solved, and the cycling stability and the service life of the material may be sacrificed while the high energy density is pursued. In order to successfully popularize a silicon-based anode material into practical application, the key point is to develop a solution which can effectively solve three main core challenges faced by the silicon-based anode material while maintaining the advantage of high energy density of the silicon-based material: the initial coulombic efficiency is low, the cyclic stability is poor and the multiplying power performance is insufficient.

Disclosure of Invention

The invention aims to solve the problems that the existing silicon-based material has poor electrochemical performance, irreversible phase is formed in the first charge and discharge process, meanwhile, the rate performance of the silicon crystal region is obviously reduced due to the agglomeration phenomenon in the battery cycle process, the first coulomb efficiency of the anode material is further low, the cycle life is low and the like, so that the invention provides a porous carbon deposited silicon oxide, then a silicon carbon anode material filled with doped silicon oxide is formed, and the preparation method and the application thereof, and the first coulomb efficiency, the rate performance and the cycle performance of the anode material of the current lithium ion battery are improved.

In order to achieve the above effects, the invention provides a preparation method of a doped silicon-carbon composite anode material, which comprises the following steps:

(S1) preparing porous carbon, a binder and a solvent into slurry, vacuum defoaming, coating the slurry on the inner wall of a collecting device, volatilizing the solvent under the condition of heating in an inert atmosphere, and enabling a porous carbon material to be adhered on the inner wall of the collecting device;

(S2) forming steam from the mixture of a silicon source and a metal doping source in a vacuum evaporation furnace communicated with a collecting device, wherein the steam enters the collecting device through diffusion, and the collecting device is maintained at 500-600 ℃ to deposit and dope the porous carbon material adhered to the inner wall of the collecting device; the silicon source is a mixture of silicon and silicon oxide, the metal doping source is metal simple substance and/or metal compound, and the metal is alkali metal and/or alkaline earth metal;

(S3) transferring the collecting device into a sintering furnace under inert atmosphere, heating for sintering, and cooling to obtain the doped silicon-carbon material;

and (S4) doping the silicon-carbon material for carbon coating to obtain the doped silicon-carbon composite anode material.

The silicon-carbon doped composite anode material is prepared by taking porous carbon as a substrate, uniformly coating the porous carbon inside a deposition collecting device, then carrying out vacuum vapor deposition to form a silicon-carbon composite material filled with doped silicon and silicon oxide, wherein metals are uniformly distributed in the silicon-carbon material in a silicate bonding network mode inside; the metal element is selected from one or more of alkali metal or alkaline earth metal.

Compared with the prior simple mixing technology, the method has the advantages that the porous carbon is coated on the inner wall of the collecting device, so that metal doped silicon oxide can be uniformly deposited inside the porous carbon, the pore structure of the porous carbon is not damaged in subsequent treatment, the high specific surface area of the porous carbon is kept, the stability of the internal structure of the porous carbon is enhanced, the particle cracking of a Si crystal region in an electrochemical process is reduced, and the first coulomb efficiency is improved; the porous structure of the porous carbon can be fully utilized, the contact area between the porous carbon and electrolyte is increased, and the reaction activity is improved; and provides a good support and conductive network for the metal doped silicon oxide, which is helpful for improving the electrochemical performance. In addition, the preparation method of the invention can simplify the subsequent treatment process by coating the porous carbon in the collecting device in advance, especially in a high vacuum environment, can effectively reduce impurity pollution and ensures that the deposited silicon-carbon composite material has higher purity. The vacuum evaporation method has the advantages of simple film forming method and easy operation, and is suitable for large-scale production and application.

Further, in the step (S1), the porous carbon is selected from one or more of activated carbon fiber, carbon nano tube, carbon molecular sieve and carbon aerogel, the particle size of the porous carbon is 5-10 μm, the specific surface area is 1500-2500m ²/g, and the pore volume is 0.8-1.1cm ³/g. The thickness of the slurry coating is 1-2cm, and the coating layer cannot be too thick, otherwise it may be peeled off from the collecting device in a subsequent process. The porous structure rich in porous carbon reserves space for the volume expansion of silicon, greatly relieves the volume expansion rate of silicon in the charge and discharge process, effectively increases the conductivity of a silicon negative electrode by introducing carbon, and provides a large number of channels for the diffusion of lithium ions. The binder is at least one selected from vinylidene fluoride (PVDF), sodium carboxymethylcellulose (CMC) and Polytetrafluoroethylene (PTFE); the solvent is at least one selected from H ₂ O, butyl acetate, N-methyl pyrrolidone and N, N-dimethylformamide. The preparation of the slurry is not particularly limited, and the materials can be uniformly mixed, for example, the slurry is stirred for 1 to 5 hours under the condition of the rotating speed of 50 to 100 rpm; vacuum defoamation is to vacuumize in a collecting device, and continuously maintain the vacuum degree for 0.5-1h when the bubbles in the material are observed to be basically disappeared; the inert atmosphere is nitrogen and/or argon, and the solvent is volatilized and removed under the heating condition, and is dried for 5-10 hours at 60-90 ℃ so as to volatilize and remove the solvent, so that the porous carbon material is firmly adhered to the inner wall of the collecting device. The shape of the collecting device is not particularly limited, such as a cylindrical shape, a cube shape.

Further, in the step (S1), the mass ratio of the porous carbon, the binder and the solvent is 100:2-5:50-80,

Further, in the step (S2), further, the alkali metal is lithium, sodium, potassium, and the alkaline earth metal is magnesium, calcium; the metal compound is at least one of an oxide, hydroxide, carbonate, bicarbonate, and halide salt of a metal (such as a metal chloride, a metal bromide, and preferably a metal chloride); such as lithium carbonate, lithium hydroxide, lithium nitrate, sodium carbonate, sodium bicarbonate, sodium oxide, sodium chloride, magnesium oxide, magnesium carbonate, calcium oxide, calcium carbonate, calcium bicarbonate, calcium hydroxide.

Further, in the step (S2), the silicon has a particle size of 2-4 μm, the silicon oxide has a particle size of 5-8 μm, the silicon oxide has a particle size 1-5 μm larger than the silicon particle size, and the metal doping source has a particle size of 5-20 μm. Preferably, when the metal doping source is an alkali metal simple substance and/or an alkali metal compound, the particle diameter is 15-20 μm; when the metal doping source is alkaline earth metal simple substance and/or alkaline earth metal compound, the particle size is 7-12 μm. The size of the particle size of the feedstock affects the surface area, collision frequency, mass transfer rate and number of active sites per mass of the reactive species, and therefore, controlling the particle size of the feedstock is an important process parameter in the manufacturing process. The particle size is related to the reaction rate, if the particle size is too small, the reaction rate is too fast, so that the porous carbon coating can not be uniformly deposited in the porous carbon coating, and the deposition effect is poor; the particle size is too large, the reaction rate is too slow, the deposition amount is too small within the same time, the reactant cannot be completely deposited, and the reactant can be uniformly deposited in the porous carbon coating layer within the reaction time due to the proper particle size. The size of the particle size depends on the material and the different components have different most preferred particle size ranges. Through a great deal of experiments, the inventor unexpectedly obtains the silicon source and the doping source in the particle size range, and the doped silicon-carbon composite material with the optimal electrochemical performance can be obtained.

Further, in step (S2), the mass ratio of the silicon source to the metal doping source is 3-5:1, such as 4-4.5:1; in the silicon source, the mass ratio of silicon to silicon oxide is 3-7:1, such as 3-4:1, a step of; the oxide of silicon is silicon dioxide and/or silicon oxide; the mass ratio of the silicon source of step (S2) to the porous carbon of step (S1) is 1.2-2:1, preferably 1.6-1.8:1.

Further, in the step (S2), the vacuum high temperature condition is that the temperature is raised to 1250-1450 ℃ under 0.1-10Pa and the temperature is kept for 10-20 hours, so as to form the steam of silicon and metal. The generated steam is diffused into a collecting device with lower temperature, the temperature of the collecting device is maintained at 500-600 ℃, and the deposition of silicon and the doping of a metal source are completed.

Under the high-temperature vacuum condition, silicon and silicon oxide are evaporated from a solid state to a gaseous state to be combined into SiO _x, wherein the metal oxide is reduced into a simple substance by silicon and is doped with SiO _x in situ to form metal silicate, and the metal silicate is uniformly deposited in a porous carbon material adhered to the inner wall of the collecting device under the driving of temperature difference.

Further, in the step (S3), the temperature is increased to 600-900 ℃ for sintering for 6-10h.

Further, in the step (S4), a carbon coating process is well known in the art, specifically, a carbon-containing process gas is introduced, the carbon-containing process gas contacts with the doped silicon-carbon material in the step (S3) under heating condition, the carbon-containing process gas is pyrolyzed, and a carbon layer is deposited on the surface of the doped silicon-carbon material to form a dense carbon coating layer. Preferably, the carbon-containing process gas is selected from at least one of methane, ethane, propane, ethylene and acetylene, the heating temperature is 800-950 ℃, the flow rate of the carbon-containing process gas is independently 5-15L/min, and the total inlet amount of the carbon-containing process gas enables the carbon of the carbon coating layer to account for 3-5wt% of the total mass of the doped silicon-carbon composite anode material.

The porous carbon substrate in the silicon-carbon composite anode material obtained by the method provides a volume expansion space required by the lithium intercalation process of the silicon-based anode material, so that the crushing and pulverization of silicon oxide micron particles can be prevented, and the cycling stability of the material is further improved; in addition, the porous structure of carbon can effectively shorten the transmission path of lithium ions and electrons in the battery, inhibit the aggregation of crystal regions of the SiO _x material in the cyclic process, and effectively improve the rate capability and cyclic stability of the material through a proper stabilization treatment process; and after metal in-situ doping, an inert bonding network is formed in the silicon oxide, so that the structural modulus of the material can be directly improved, pores are formed in particles, the volume expansion rate of the material is reduced, and therefore capacity attenuation caused by volume change is restrained.

Drawings

FIG. 1 is a schematic diagram of an apparatus for preparing a doped silicon-carbon composite negative electrode material according to the present invention;

FIG. 2 is an X-ray diffraction spectrum of the doped silicon-carbon composite anode material prepared in example 1;

FIG. 3 is a scanning electron micrograph of the doped silicon-carbon composite negative electrode material prepared in example 1;

fig. 4 is a first charge-discharge diagram of the doped silicon-carbon composite anode material prepared in example 1.

Detailed Description

The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples.

The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, are commercially available.

FIG. 1 is a schematic diagram of an apparatus for preparing a doped silicon-carbon composite anode material according to the present invention. Wherein: 1-vacuum evaporation furnace wall, 2-reaction zone, 3-collection zone, 4-collection device, 5-vacuum pipeline, 6-circulating water cooling chamber, 7-circulating water outlet pipe and 8-circulating water inlet pipe.

Example 1

(S1) pretreatment: the inside of the cylindrical collecting device is first washed with absolute ethanol to ensure that the porous carbon material can be uniformly coated on the surface thereof. Then, 10kg of a porous carbon material having a particle size of 6.5 μm and a pore volume of 1cm ³/g, a specific surface area of 1800 m ²/g, 0.2kg of a binder (CMC), and 6kg of a solvent H ₂ O were taken, mixed in a stirrer at a rotation speed of 50 r/min for 2H to form a slurry, the slurry was transferred to the inside of a vacuum vessel and gradually evacuated to a vacuum environment, and a defoaming treatment was started, and when it was observed that bubbles in the material had substantially disappeared, the vacuum state in the vessel was maintained for 60 minutes to ensure thorough defoaming, and then the porous carbon was firmly adhered to the inner layer of the collecting device by uniformly smearing the slurry on the inner wall of the collecting device, coating a thickness of 2cm, and drying 6H under an argon atmosphere at 80 ℃.

(S2) mixing 13.5kg of silicon oxide with the particle size of 8.0 mu m, 4.5kg of silicon powder with the particle size of 4.0 mu m and 4kg of lithium oxide with the particle size of 16.0 mu m uniformly to obtain a mixture, adding the mixture into a reactor in a vacuum evaporation furnace with the vacuum degree of less than 1pa, heating to 1300 ℃ at the heating rate of 10 ℃/min, preserving heat for 20h, always controlling the temperature of a deposition condensation collection area at 600 ℃, and naturally cooling to room temperature after the reaction is finished to obtain the massive porous carbon deposition silicon oxide composite material.

And (S3) transferring the collection device after the deposition to a sintering furnace under the inert atmosphere with the ventilation flow of 5-L/min, heating to 800 ℃ at the heating rate of 1 ℃/min, and sintering to 7h, and naturally cooling to room temperature under the protection of the inert atmosphere to obtain the blocky porous carbon deposition pre-lithium silicon oxide anode material.

And (S4) crushing the material obtained in the step (S3), adding the crushed material into a coating furnace, filling nitrogen to remove air, heating to 920 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1.5h, stabilizing, then filling acetylene gas at a flow rate of 10L/min for 3h, dehydrogenating acetylene, converting into a compact carbon layer to coat the material, closing the acetylene gas, keeping the heating for 2h, and cooling and discharging to obtain the product doped silicon-carbon composite anode material. The carbon coating layer accounts for 3.6wt% of the total mass of the doped silicon-carbon composite anode material.

Fig. 2 is an X-ray diffraction spectrum of the doped silicon-carbon composite anode material prepared in example 1.

Fig. 3 is a scanning electron microscope photograph of the doped silicon carbon composite anode material prepared in example 1.

Example 2

Other conditions and operations were the same as in example 1 except that in step (S1), the binder was changed to PVDF in an amount of 0.5kg, the solvent was changed to N-methylpyrrolidone in an amount of 8 kg.

Example 3

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 12.8kg of silica powder having a particle size of 5.0 μm, 3.2kg of silica powder having a particle size of 2.0 μm, and 4kg of lithium carbonate powder having a particle size of 20. Mu.m.

Example 4

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to a silica raw material having a particle size of 12 kg and a particle size of 8.0. Mu.m, 6kg of silica powder having a particle size of 4.0. Mu.m, and 4kg of lithium oxide powder having a particle size of 16. Mu.m.

Example 5

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 15 kg of a silica raw material having a particle size of 8.0 μm, 3kg of silicon powder having a particle size of 4.0 μm, and 4kg of lithium oxide powder having a particle size of 16. Mu.m.

Example 6

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 13.5kg of a silica raw material having a particle size of 8.0 μm, 4.5kg of silicon powder having a particle size of 4.0 μm, and 6kg of a lithium oxide powder having a particle size of 16. Mu.m.

Example 7

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 13.5kg of a silica raw material having a particle size of 8.0 μm, 4.5kg of silicon powder having a particle size of 4.0 μm, and 3kg of a lithium oxide powder having a particle size of 16. Mu.m.

Example 8

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 13.5kg of silica powder having a particle size of 8.0 μm, 4.5kg of silica powder having a particle size of 4.0 μm, and 4kg of magnesia powder having a particle size of 10.0. Mu.m.

Example 9

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 13.5kg of silica powder having a particle size of 4.0 μm, 4.5kg of silica powder having a particle size of 5.0 μm, and 4kg of lithium oxide powder having a particle size of 16.0. Mu.m.

Comparative example 1

Other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 18kg of a silica raw material having a particle size of 8.0 μm, and 4kg of a lithium oxide powder having a particle size of 16. Mu.m. I.e. without adding silicon powder.

Comparative example 2

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 18kg of silicon powder having a particle size of 3.6. Mu.m, and 4kg of lithium oxide powder having a particle size of 16. Mu.m. I.e. without the addition of silica.

Comparative example 3

The other conditions and operations were the same as in example 1 except that in step (S2), the mixture was changed to 13.5kg of silica raw material having a particle size of 8.0 μm, and 4.5kg of silica powder having a particle size of 3.6. Mu.m. I.e. without the addition of lithium oxide powder.

Application example

Performance test of silicon-carbon composite material as lithium battery anode material

The electrochemical performance of the doped silicon-carbon composite anode materials prepared in the examples and the comparative examples of the invention is tested according to the following method: the silicon-carbon doped composite anode material, super P, carboxymethyl cellulose and styrene-butadiene rubber composite binder are mixed according to the mass ratio of 8:1:1, mixing to prepare slurry (the mass ratio of CMC to SBR is 1:1), uniformly coating the slurry on a copper foil by using a 200 mu m thick scraper, and then carrying out vacuum drying on the copper foil to prepare a silicon-carbon negative electrode plate 12 h; then, a metal lithium sheet is used as a counter electrode, polyolefin is used as a diaphragm, 1 mol/L LiPF ₆ (a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1) is used as an electrolyte, VC with a volume fraction of 2% and FEC with a volume fraction of 5% are added into the electrolyte, and the button cell is assembled in a Germany Braun inert gas glove box in an argon atmosphere.

And (3) carrying out charge and discharge tests on the assembled battery on a LAND charge and discharge tester, wherein the charge and discharge interval is 50 mV-1.5V, the compaction density is 1.1 g/cm ³, and after three times of charge and discharge under the current density of 0.2C (1C =1500 mA/g), the battery is charged and discharged under the current density of 0.2C, so as to obtain the capacity, the first coulombic efficiency and the cycle performance data of the material.

The silicon-based composite materials obtained in examples and comparative examples of the present invention were assembled as a negative electrode material in the same manner to a button lithium battery, and the electrochemical test results thereof are shown in table 1.

Table 1 electrochemical performance test

。

In summary, the preparation method of the invention is simple and efficient, and the data of examples and comparative examples show that the inert bonding network is formed inside the material prepared by the preparation method of the invention to inhibit crack generation, silicon agglomeration and reduce internal expansion of the silicon-based material, the porous structure of the porous carbon substrate effectively buffers the volume expansion of porous silica in the charge and discharge process, reduces the internal stress of particles, and inhibits the aggregation of crystal regions of the SiO _x material in the circulation process, so that the first coulomb efficiency and the circulation stability of the material are both more advantageous. In the vacuum evaporation, the three materials of silicon powder, silicon oxide and metal doping source are indispensable in the raw materials of gas source in the vacuum evaporation furnace.

Claims

1. The preparation method of the doped silicon-carbon composite anode material is characterized by comprising the following steps of:

(S1) preparing porous carbon, a binder and a solvent into slurry, vacuum defoaming, coating the slurry on the inner wall of a collecting device, volatilizing the solvent under the condition of inert atmosphere and heating, and enabling a porous carbon material to be adhered on the inner wall of the collecting device;

(S2) forming steam from the mixture of a silicon source and a metal doping source in a vacuum evaporation furnace communicated with a collecting device, wherein the steam enters the collecting device through diffusion, and the collecting device is maintained at 500-600 ℃ to deposit and dope the porous carbon material adhered to the inner wall of the collecting device; the silicon source is a mixture of silicon and silicon oxide, the metal doping source is metal simple substance and/or metal compound, and the metal is alkali metal and/or alkaline earth metal; the particle size of the silicon is 2-4 mu m, the particle size of the silicon oxide is 5-8 mu m, the particle size of the silicon oxide is 1-5 mu m larger than that of the silicon, and when the metal doping source is an alkali metal simple substance and/or an alkali metal compound, the particle size is 15-20 mu m; when the metal doping source is alkaline earth metal simple substance and/or alkaline earth metal compound, the particle size is 7-12 mu m;

2. The method according to claim 1, wherein in the step (S1), the porous carbon is one or more selected from the group consisting of activated carbon fiber, carbon nanotube, carbon molecular sieve, and carbon aerogel, the porous carbon has a particle size of 5 to 10 μm, a specific surface area of 1500 to 2500m ²/g, and a pore volume of 0.8 to 1.1cm ³/g;

And/or the thickness of the slurry coating is 1-2cm; and/or

The binder is at least one selected from vinylidene fluoride (PVDF), sodium carboxymethylcellulose (CMC) and Polytetrafluoroethylene (PTFE); the solvent is at least one selected from H ₂ O, butyl acetate, N-methyl pyrrolidone and N, N-dimethylformamide.

3. The method according to claim 1, wherein in the step (S1), the mass ratio of the porous carbon, the binder and the solvent is 100:2-5:50-80.

4. The method according to claim 1, wherein in the step (S2), the alkali metal is lithium, sodium, potassium, and the alkaline earth metal is magnesium, calcium; the metal compound is oxide, hydroxide, carbonate, bicarbonate or halogen salt of metal.

5. The method according to claim 4, wherein the metal compound is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate, sodium carbonate, sodium bicarbonate, sodium oxide, sodium chloride, magnesium oxide, magnesium carbonate, calcium oxide, calcium carbonate, calcium bicarbonate, and calcium hydroxide.

6. The method according to claim 1, wherein in the step (S2), the mass ratio of the silicon source to the metal doping source is 3 to 5:1; in the silicon source, the mass ratio of silicon to silicon oxide is 3-7:1, a step of; the oxide of silicon is silicon dioxide and/or silicon oxide; the mass ratio of the silicon source of step (S2) to the porous carbon of step (S1) is 1.2-2:1.

7. The method according to claim 1, wherein in the step (S2), the vacuum high temperature condition is that the temperature is raised to 1250-1450 ℃ under 0.1-10Pa and kept for 10-20 hours; and/or

In the step (S3), the temperature is increased to 600-900 ℃ for sintering for 6-10h.

8. A silicon carbon negative electrode material, characterized in that it is produced by the production method according to any one of claims 1 to 7.