A lithium-ion battery silicon and silicon alloy composite negative electrode material and preparation method thereof

Abstract

A lithium-ion battery silicon and silicon alloy composite negative electrode material and its preparation method belong to the technical field of electrochemical energy storage battery electrode material preparation technology. The composite negative electrode material includes nano-ferrosilicon alloy, nano-aerosolized silicon and coated carbon. The mass ratio of nano-ferrosilicon alloy is 30-50wt.%, nano-aerosolized silicon is 10-20wt.%, and coated carbon is 30-60wt.%. First, nano-ferrosilicon alloy powder prepared by arc plasma torch technology and nano-aerosolized silicon powder prepared by arc evaporation technology are ball-milled in proportion and evenly mixed and dried to obtain mixed powder A; secondly, mixed powder A is deposited by CVD method and carbon pre-coated to obtain mixed powder B; finally, mixed powder B is ball-milled with an organic carbon source in proportion and sieved, and then calcined for carbon coating modification to obtain a composite negative electrode material. The synergistic effect of the three components in the negative electrode material of the present invention can achieve long-term and high-density energy storage of silicon-based negative electrode materials, and its comprehensive electrochemical performance is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of electrode materials for electrochemical energy storage batteries, and relates to a ferrosilicon alloy composite negative electrode material for a lithium-ion battery and a preparation method thereof. Background Art

[0002] With the rapid development and continued growth of the new energy vehicle industry, the demand for high-power, high-capacity, and highly safe lithium-ion power batteries is becoming increasingly urgent. Currently, the mainstream carbon anode materials and ferrosilicon alloy nano-anode materials on the market lack competitiveness in the application of next-generation high-capacity power batteries due to their limited theoretical specific capacity. Furthermore, various silicon-carbon anode materials have been unable to effectively address the problem of overall electrode failure and poor cycling performance caused by the high volume expansion of silicon during the lithium embedding process. Consequently, the overall silicon addition level is limited, and the high capacity of silicon cannot be fully utilized.

[0003] Therefore, how to increase the usage of silicon while limiting the impact of silicon volume expansion is a key issue that needs to be solved in the development of silicon-based negative electrode materials. Summary of the Invention

[0004] In view of the deficiencies in the art, the object of the present invention is to provide a lithium-ion battery silicon and silicon alloy composite negative electrode material and a preparation method thereof with high specific capacity and good cycle stability and relatively low preparation cost.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A lithium-ion battery silicon and silicon alloy composite negative electrode material includes nano-ferrosilicon alloy, nano-aerosol silicon and coated carbon. Based on the total mass of the composite negative electrode material as 100%, the mass ratio of the nano-ferrosilicon alloy accounts for 30-50wt.%, the mass ratio of the nano-aerosol silicon accounts for 10-20wt.%, and the mass ratio of the coated carbon accounts for 30-60wt.%.

[0007] The nano-silicon ferrosilicon alloy is prepared by arc plasma torch technology and is composed of a two-phase mixture of nano-silicon and nano-FeSi2 uniformly dispersed at the nanoscale. Based on the total mass of the nano-silicon ferrosilicon alloy as 100%, the mass ratio of the nano-silicon accounts for 80wt.%, the mass ratio of the nano-FeSi2 alloy phase accounts for 20wt.%, and the particle size distribution range is 5 to 150nm.

[0008] The described nano-aerogel silicon is prepared by an arc evaporation technique and consists of a mixture of silicon oxide SiOx (0 < x ≤ 2) and nano-silicon. The silicon oxide SiOx has an amorphous (non-crystalline structure) flocculent structure, and the nano-silicon is in the form of crystalline nano-silicon particles with a particle size distribution range of 5 - 50 nm, which are uniformly dispersed within the amorphous flocculent structure of the silicon oxide SiOx. Based on 100% of the total mass of the nano-aerogel silicon, the mass ratio of the nano-silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

[0009] The described carbon coating consists of graphite carbon deposited by CVD and amorphous carbon obtained by high-temperature calcination and pyrolysis of phenolic resin.

[0010] A preparation method for a silicon and silicon alloy composite negative electrode material of a lithium-ion battery, which is used to prepare the above-mentioned silicon and silicon alloy composite negative electrode material of a lithium-ion battery. The preparation method of the silicon and silicon alloy composite negative electrode material of a lithium-ion battery includes the following steps:

[0011] (1) Uniformly mix and dry by ball milling the nano-scale ferrosilicon alloy powder prepared by an arc plasma torch technique and the nano-scale aerogel silicon powder prepared by an arc evaporation technique in proportion to obtain a mixed powder A.

[0012] (2) Use CVD method to deposit on the mixed powder A in a vacuum rotary furnace, and perform carbon pre-coating treatment to obtain a mixed powder B.

[0013] (3) After ball milling, screening the mixed powder B with an organic carbon source in proportion, and then calcining for carbon coating modification to obtain the final composite negative electrode material C containing nano-ferrosilicon alloy, aerogel silicon and carbon coating.

[0014] In the above technical solution, further, the ball milling parameters in step (1) are: ball-to-material ratio 10:1 (mass ratio), rotation speed 600 revolutions per minute, ball milling time 3 hours, drying temperature in the drying oven 150 °C, and drying time 1 hour;

[0015] In the above technical solution, further, the conditions for carbon pre-coating treatment of the mixed powder A by CVD method in step (2) are: rotation speed of the rotary furnace is 5 revolutions per minute, heating rate is 5 - 10 °C / min, deposition temperature is between 600 - 900 °C, deposition time is 1 - 4 hours; the gaseous carbon source in the vacuum rotary furnace is at least one of methane, propylene or acetylene, the gas pressure is 2 kPa, and the gas flow rate is 5 L min

[0015] ,

[0014] , , <0000​​​​In the above technical solution, further, in the step (3), the organic carbon source is one or more of phenolic resin, glucose, citric acid, sucrose, polyvinyl alcohol, asphalt, etc., and the ball milling parameters are: ball-to-material ratio 10:1 (mass ratio), rotation speed 800 rpm, ball milling time 3 hours, 400 mesh sieve screening; calcination is carried out under an inert atmosphere, the calcination temperature is 800-1100 ° C, the calcination time is 2-4 hours, the inert atmosphere is one of argon and nitrogen or a mixture of the two, the flow rate is 20m 3 / h.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects:

[0018] The active material portion of the composite negative electrode material of the present invention is a ferrosilicon alloy nanomaterial prepared by arc plasma torch technology and an aerosolized silicon nanomaterial prepared by arc plasma evaporation technology. It can give full play to the high capacity characteristics of nano-scale uniformly dispersed nano-silicon in the ferrosilicon alloy and nano-silicon wrapped by flocculent SiOx in the aerosolized silicon. At the same time, with the help of the three-dimensional skeleton support of nano-FeSi2 and the flocculent SiOx, the volume expansion of nano-silicon in the lithium embedding process is fully buffered and constrained. The composite negative electrode greatly increases the amount of elemental silicon added, while combining the three-dimensional skeleton support of the ferrosilicon alloy and the flocculent SiOx to fully constrain the dispersion and volume expansion of nano-silicon. Furthermore, the surface of the composite nanoparticles (here referred to as mixed powder A) is pre-uniformly coated with a thin layer of graphite carbon in a vacuum rotary kiln by CVD pre-coating carbon, and then it is mixed with an organic carbon source by ball milling and calcined for final carbon coating modification, so that the overall conductivity of the composite negative electrode material and the stability during the cycle are fully guaranteed. In this structure, active nano-silicon provides high capacity, the alloy phase constrains silicon's volume expansion from the inside, the aerosolized silicon further buffers this expansion, and the carbon confinement layer mitigates volume expansion and contraction from the outside, insulating the electrolyte and improving the material's initial coulombic efficiency. The synergistic effect of these three elements enables long-term, high-density energy storage in silicon-based anode materials.

[0019] Therefore, the silicon and silicon alloy composite negative electrode material obtained by the present invention can achieve a specific capacity of 900mAh g at a high current density of 0.3C. -1 After 200 cycles, the capacity retention rate is more than 90%, and the first coulombic efficiency is ≥85%. Compared with existing silicon-based negative electrode materials, its comprehensive electrochemical performance has been greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the process flow of the method of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of the silicon and silicon alloy composite negative electrode material prepared in Example 2;

[0022] Figure 3 Electrochemical performance diagram of the silicon and silicon alloy composite anode material prepared in Example 3. Detailed implementation manners

[0023] To better understand the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The embodiments are only used to explain the present invention and will not constitute any limitation to the present invention. For the operation methods without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions or the conditions recommended by the manufacturers.

[0024] The process flow of the method for the ferrosilicon alloy / aerogel silicon / carbon composite anode material of the present invention is as Figure 1 shown, specifically including:

[0025] Example 1:

[0026] (1) Uniformly mix the nanoscale ferrosilicon alloy powder prepared by the arc plasma torch technology and the nanoscale aerogel silicon powder prepared by the arc evaporation technology in a mass ratio of 30:10 by ball milling. The ball-to-material ratio is 10:1, the rotation speed is 500 rpm, the ball milling time is 2 h, and then dry to obtain the mixed powder A; specifically:

[0027] The nanoscale ferrosilicon alloy prepared by the arc plasma torch technology is composed of a two-phase mixture of nanoscale silicon and nanoscale FeSi2 uniformly dispersed at the nanoscale. Calculated based on 100% of the total mass of the nanoscale ferrosilicon alloy, the mass ratio of the nanoscale silicon accounts for 80 wt.%, and the mass ratio of the nanoscale FeSi2 alloy phase accounts for 20 wt.%. The particle size distribution range is 5 - 150 nm.

[0028] The nanoscale aerogel silicon prepared by the arc evaporation technology is composed of a mixture of silicon oxide SiOx (0 < x ≤ 2) and nanoscale silicon. The silicon oxide SiOx is in an amorphous flocculent structure, and the nanoscale silicon is in the form of crystalline nanoscale silicon particles with a particle size range of 5 - 50 nm, and is uniformly dispersed in the amorphous flocculent structure of the silicon oxide SiOx; calculated based on 100% of the total mass of the nanoscale aerogel silicon, the mass ratio of the nanoscale silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

[0029] (2) Add the mixed powder A into a vacuum rotary furnace, introduce a mixed gas of argon and acetylene, heat it to 600 °C at a rate of 5 °C / min, perform gas-phase chemical deposition for carbon pre-coating, keep the temperature for reaction for 1 h, deposit a carbon coating layer on the surface of the mixed powder A, naturally cool to room temperature, and take it out to obtain the pre-carbon-coated mixed powder B;

[0030] (3) Mix the mixed powder B and phenolic resin evenly by ball milling at a mass ratio of 40:60, with a ball-to-material ratio of 10:1, a rotation speed of 800 rpm, and a ball milling time of 3 h. After screening through a 400-mesh sieve, a calcined precursor is obtained. The precursor is placed in an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, heated to 800 °C at a rate of 10 °C / min, held for reaction for 2 h, naturally cooled to room temperature, and taken out to obtain the final composite anode material containing nano-silicon iron alloy, aerogel silicon, and coated carbon. In the obtained composite anode material, based on 100 wt.% of the total mass of the composite anode material, the mass ratio of the nano-silicon iron alloy accounts for 30 wt.%, the mass ratio of nano-aerogel silicon accounts for 10 wt.%, and the mass ratio of coated carbon accounts for 60 wt.%.

[0031] From the transmission electron microscope images of the composite anode material, it can be seen that the nano-silicon iron alloy and aerogel silicon nanoparticles are evenly distributed, there are agglomerated large particles, and amorphous carbon uniformly covers the particle surface. The data and analysis of the electrochemical performance diagram are shown in Table 1. The specific capacity is 2152 mAh g -1 at a current density of 0.1 C, and the capacity retention rate is above 87% after 200 cycles at 0.3 C.

[0032] Example 2:

[0033] (1) Evenly mix the nano-scale silicon iron alloy powder prepared by the arc plasma torch technology and the nano-scale aerogel silicon powder prepared by the arc evaporation technology by ball milling at a ratio of 50:20, with a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, and a ball milling time of 2 h, and dry to obtain the mixed powder A; specifically:

[0034] The nano-silicon iron alloy prepared by the arc plasma torch technology is composed of a two-phase mixture of nano-silicon and nano-FeSi2 uniformly dispersed at the nano-scale. Based on 100% of the total mass of the nano-silicon iron alloy, the mass ratio of the nano-silicon accounts for 80 wt.%, and the mass ratio of the nano-FeSi2 alloy phase accounts for 20 wt.%, and the particle size distribution range is 5 - 150 nm.

[0035] The nano-aerogel silicon prepared by the arc evaporation technology is composed of silicon oxide SiOx (0 < x ≤ 2) and nano-silicon mixture. Among them, the silicon oxide SiOx is an amorphous flocculent structure, and the nano-silicon is crystalline nano-silicon particles with a particle size range of 5 - 50 nm, and is uniformly dispersed in the amorphous flocculent structure of the silicon oxide SiOx; based on 100% of the total mass of the nano-aerogel silicon, the mass ratio of the nano-silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

[0036] (2) Mixed powder A was added to a vacuum rotary furnace, and a mixed gas of argon and methane was introduced. The temperature was raised to 700°C at a rate of 6°C / min for vapor phase chemical deposition. The mixture was kept at this temperature for 1.5 hours to deposit a carbon coating layer on the surface of the mixed powder A. The mixture was naturally cooled to room temperature and taken out to obtain a pre-carbon-coated mixed powder B.

[0037] (3) The mixed powder B and glucose were evenly mixed by ball milling in a ratio of 70:30, with a ball-to-material ratio of 10:1, a rotation speed of 800 rpm, and a ball milling time of 3 h. After screening through a 400-mesh sieve, a calcined precursor was obtained. The precursor was placed in an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, and then heated to 900°C at a rate of 6°C / min, kept at this temperature for 3 hours, and naturally cooled to room temperature. The final composite negative electrode material containing nano-ferrosilicon alloy, aerosol-condensed silicon, and coated carbon was obtained. In the resulting composite negative electrode material, based on 100wt.% of the total mass of the composite negative electrode material, the mass ratio of the nano-ferrosilicon alloy accounted for 50wt.%, the mass ratio of the nano-aerosol-condensed silicon accounted for 20wt.%, and the mass ratio of the coated carbon accounted for 30wt.%.

[0038] Figure 2 This is a scanning electron microscope image of the composite negative electrode material of Example 2. It can be seen that the nano-silicon ferrosilicon alloy and aerosol-condensed silicon nanoparticles are evenly distributed, with agglomerated tiny particles present, and amorphous carbon evenly covering the particle surface. The electrochemical performance data and analysis are shown in Table 1. The specific capacity at a current density of 0.1C is 2052 mAh g -1 , after 200 cycles at 0.3C, the capacity retention rate is over 89%.

[0039] Example 3:

[0040] (1) Nano-sized ferrosilicon alloy powder prepared by arc plasma torch technology and nano-sized aerosol silicon powder prepared by arc evaporation technology were uniformly mixed by ball milling in a ratio of 40:15, with a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, a ball milling time of 2 h, and dried to obtain mixed powder A; specifically:

[0041] The nano-silicon ferrosilicon alloy prepared by arc plasma torch technology is composed of a two-phase mixture of nano-silicon and nano-FeSi2 uniformly dispersed at the nanoscale. Based on the total mass of the nano-silicon ferrosilicon alloy as 100%, the mass ratio of the nano-silicon accounts for 80wt.%, the mass ratio of the nano-FeSi2 alloy phase accounts for 20wt.%, and the particle size distribution ranges from 5 to 150nm.

[0042] The nano-aerogel silicon prepared by the arc evaporation technology consists of a mixture of silicon oxide SiOx (0 < x ≤ 2) and nano-silicon. The silicon oxide SiOx has an amorphous flocculent structure, and the nano-silicon is crystalline nano-silicon particles with a particle size range of 5 - 50 nm, and is uniformly dispersed within the amorphous flocculent structure of the silicon oxide SiOx. Calculated based on 100% of the total mass of the nano-aerogel silicon, the mass ratio of the nano-silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

[0043] (2) Add the mixed powder A to a vacuum rotary furnace, introduce a mixed gas of argon and methane, heat it to 750 °C at a rate of 7 °C / min, carry out vapor-phase chemical deposition, hold the reaction for 3 h, deposit a carbon coating layer on the surface of the mixed powder A, naturally cool to room temperature, and take out to obtain the pre-carbon-coated mixed powder B;

[0044] (3) Ball-mill and mix the mixed powder B and citric acid evenly at a ratio of 55:45, with a ball-to-material ratio of 10:1, a rotation speed of 800 revolutions / min, and a ball-milling time of 3 h. After screening through a 400-mesh sieve, a calcination precursor is obtained. Place the precursor in an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, heat it to 950 °C at a rate of 10 °C / min, hold the reaction for 3.5 h, naturally cool to room temperature, and take out to obtain the final composite anode material containing nano-silicon iron alloy, aerogel silicon, and coated carbon. In the obtained composite anode material, calculated based on 100 wt.% of the total mass of the composite anode material, the mass ratio of the nano-silicon iron alloy accounts for 40 wt.%, the mass ratio of the nano-aerogel silicon accounts for 15 wt.%, and the mass ratio of the coated carbon accounts for 45 wt.%.

[0045] Figure 3 It is the electrochemical performance diagram of the silicon and silicon alloy composite anode material prepared in Example 3. The specific capacity is 1816 mAh g at a current density of 0.1C -1 , and the capacity retention rate is above 98% after 200 cycles at 0.3C.

[0046] Example 4:

[0047] (1) Ball-mill and uniformly mix the nano-scale silicon iron alloy powder prepared by the arc plasma torch technology and the nano-scale aerogel silicon powder prepared by the arc evaporation technology at a ratio of 30:20, with a ball-to-material ratio of 10:1, a rotation speed of 500 revolutions / min, and a ball-milling time of 2 h, and dry to obtain the mixed powder A; Specifically:

[0048] The nano-sized ferrosilicon alloy prepared by the arc plasma torch technology is composed of a two-phase mixture of nano-sized silicon and nano-sized FeSi₂ uniformly dispersed at the nano-scale. Calculated based on 100% of the total mass of the nano-sized ferrosilicon alloy, the mass ratio of the nano-sized silicon accounts for 80 wt.%, and the mass ratio of the nano-sized FeSi₂ alloy phase accounts for 20 wt.%. The particle size distribution range is 5 - 150 nm.

[0049] The nano-sized aerogel silicon prepared by the arc evaporation technology is composed of a mixture of silicon oxide SiOx (0 < x ≤ 2) and nano-sized silicon. The silicon oxide SiOx has an amorphous flocculent structure, and the nano-sized silicon is crystalline nano-sized silicon particles with a particle size range of 5 - 50 nm, and is uniformly dispersed within the amorphous flocculent structure of the silicon oxide SiOx; calculated based on 100% of the total mass of the nano-sized aerogel silicon, the mass ratio of the nano-sized silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

[0050] (2) Add the mixed powder A into a vacuum rotary furnace, introduce a mixed gas of argon and acetylene, heat it to 850 °C at a rate of 8 °C / min, carry out gas-phase chemical deposition, keep the temperature for reaction for 3.5 h, deposit a carbon coating layer on the surface of the mixed powder A, cool it naturally to room temperature, and take out to obtain the pre-carbon-coated mixed powder B;

[0051] (3) Ball-mill and mix the mixed powder B and polyvinyl alcohol evenly at a ratio of 50:50, with a ball-to-material ratio of 10:1, a rotation speed of 800 revolutions / min, and a ball-milling time of 3 h. After screening through a 400-mesh sieve, a calcined precursor is obtained. Place the precursor in an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, heat it to 1050 °C at a rate of 9 °C / min, keep the temperature for reaction for 4 h, cool it naturally to room temperature, and take out to obtain the final composite anode material containing nano-sized ferrosilicon alloy, aerogel silicon, and coated carbon. In the obtained composite anode material, calculated based on 100 wt.% of the total mass of the composite anode material, the mass ratio of the nano-sized ferrosilicon alloy accounts for 30 wt.%, the mass ratio of the nano-sized aerogel silicon accounts for 20 wt.%, and the mass ratio of the coated carbon accounts for 50 wt.%.

[0052] From the transmission electron microscope images of the composite anode material, it can be seen that the nano-sized ferrosilicon alloy and aerogel silicon nanoparticles are evenly distributed, there are aggregated large particles, and amorphous carbon uniformly covers the particle surface. The electrochemical performance diagram data and analysis are shown in Table 1. The specific capacity is 1786 mAh g -1 at a current density of 0.1C, and the capacity retention rate is above 94% after 200 cycles at 0.3C.

[0053] Example 5:

[0054] (1) Nano-sized ferrosilicon alloy powder prepared by arc plasma torch technology and nano-sized aerosol silicon powder prepared by arc evaporation technology were uniformly mixed by ball milling in a ratio of 50:10, with a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, a ball milling time of 2 h, and dried to obtain mixed powder A;

[0055] (2) Mixed powder A was added to a vacuum rotary furnace, and a mixed gas of argon and propylene was introduced. The temperature was raised to 950°C at a rate of 5°C / min for vapor phase chemical deposition. The mixture was kept at this temperature for 3 hours to deposit a carbon coating layer on the surface of the mixed powder A. The mixture was naturally cooled to room temperature and taken out to obtain a pre-carbon-coated mixed powder B.

[0056] (3) The mixed powder B and asphalt were evenly mixed by ball milling in a ratio of 60:40, with a ball-to-material ratio of 10:1, a rotation speed of 800 rpm, and a ball milling time of 3 h. After screening through a 400-mesh sieve, a calcined precursor was obtained. The precursor was placed in an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, and then heated to 1100°C at a rate of 10°C / min, kept at this temperature for reaction for 1.5 minutes, and naturally cooled to room temperature. The final composite negative electrode material containing nano-ferrosilicon alloy, aerosol-condensed silicon, and coated carbon was obtained. In the resulting composite negative electrode material, based on 100wt.% of the total mass of the composite negative electrode material, the mass ratio of the nano-ferrosilicon alloy accounted for 50wt.%, the mass ratio of the nano-aerosol-condensed silicon accounted for 10wt.%, and the mass ratio of the coated carbon accounted for 40wt.%.

[0057] Transmission electron microscopy images of the composite negative electrode material show that the nano-silicon ferrosilicon alloy and aerosol-condensed silicon nanoparticles are evenly distributed, with large agglomerated particles present, and amorphous carbon evenly covering the particle surface. Electrochemical performance data and analysis are shown in Table 1. The specific capacity at a current density of 0.1C is 1636 mAh g -1 , after 200 cycles at 0.3C, the capacity retention rate is above 85%.

[0058] Comparative Example 1:

[0059] (1) The nano-sized ferrosilicon alloy powder prepared by arc plasma torch technology was ball-milled with a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, a ball-milling time of 2 h, and dried to obtain powder A; specifically:

[0060] The nano-silicon ferrosilicon alloy prepared by arc plasma torch technology is composed of a two-phase mixture of nano-silicon and nano-FeSi2 uniformly dispersed at the nanoscale. Based on the total mass of the nano-silicon ferrosilicon alloy as 100%, the mass ratio of the nano-silicon accounts for 80wt.%, the mass ratio of the nano-FeSi2 alloy phase accounts for 20wt.%, and the particle size distribution ranges from 5 to 150nm.

[0061] (2) Add powder A into a vacuum rotary furnace, introduce a mixed gas of argon and acetylene, heat it up to 600 °C at a rate of 5 °C / min, carry out gas-phase chemical deposition for carbon pre-coating, keep the temperature for reaction for 1 h, deposit a carbon coating layer on the surface of powder A, cool it naturally to room temperature, and take out to obtain pre-carbon-coated mixed powder B;

[0062] (3) Ball-mill and mix the mixed powder B and phenolic resin evenly according to a mass ratio of 40:60, with a ball-to-material ratio of 10:1, a rotation speed of 800 revolutions / min, and a ball-milling time of 3 h. After screening through a 400-mesh sieve, obtain a calcined precursor. In an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, heat it up to 800 °C at a rate of 10 °C / min, keep the temperature for reaction for 2 h, cool it naturally to room temperature, and take out to obtain the final composite anode material containing nano-silicon iron alloy coated with carbon. In the obtained composite anode material, based on 100 wt.% of the total mass of the composite anode material, the mass ratio of the nano-silicon iron alloy accounts for 40 wt.%, and the mass ratio of the coated carbon accounts for 60 wt.%.

[0063] From the transmission electron microscope images of the composite anode material, it can be seen that the nano-silicon iron alloy is evenly distributed, there are aggregated large particles, and amorphous carbon uniformly covers the particle surface. The data of the electrochemical performance diagram are shown in Table 1. Compare Comparative Example 1 with Example 1. The difference is that nano-aerogel silicon is not added. And from the data in Table 1, it can be known that the capacity retention rate of Comparative Example 1 after 200 cycles at 0.3C is only 70%.

[0064] Comparative Example 2:

[0065] (1) Ball-mill the nano-aerogel silicon powder prepared by the arc evaporation technique, with a ball-to-material ratio of 10:1, a rotation speed of 500 revolutions / min, and a ball-milling time of 2 h, and dry it to obtain powder A; Specifically:

[0066] The nano-aerogel silicon prepared by the arc evaporation technique consists of a mixture of silicon oxide SiOx (0 < x ≤ 2) and nano-silicon. Among them, the silicon oxide SiOx is in an amorphous flocculent structure, and the nano-silicon is in a crystalline nano-silicon particle state, with a particle size range of 5 - 50 nm, and is uniformly dispersed in the amorphous flocculent structure of the silicon oxide SiOx; based on 100% of the total mass of the nano-aerogel silicon, the mass ratio of the nano-silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

[0067] (2) Add powder A into a vacuum rotary furnace, introduce a mixed gas of argon and methane, heat it up to 700 °C at a rate of 6 °C / min, carry out gas-phase chemical deposition, keep the temperature for reaction for 1.5 h, deposit a carbon coating layer on the surface of powder A, cool it naturally to room temperature, and take out to obtain pre-carbon-coated mixed powder B;

[0068] (3) The mixed powder B and glucose were evenly mixed by ball milling in a ratio of 70:30, with a ball-to-material ratio of 10:1, a rotation speed of 800 rpm, and a ball milling time of 3 h. After screening through a 400-mesh sieve, a calcined precursor was obtained. The precursor was placed in an argon gas flow atmosphere with a gas flow rate of 20 m 3 / h, then raise the temperature to 900°C at a rate of 6°C / min, maintain the reaction for 2 hours, and naturally cool to room temperature. The final composite negative electrode material containing aerosolized silicon and coated carbon is obtained. In the resulting composite negative electrode material, based on 100wt% of the total mass of the composite negative electrode material, the mass ratio of the nano-aerosolized silicon accounts for 70wt%, and the mass ratio of the coated carbon accounts for 30wt%.

[0069] Scanning electron microscope images of the composite negative electrode material in Comparative Example 2 show uniform distribution of aerosolized silicon nanoparticles, the presence of agglomerated microparticles, and the uniform coating of amorphous carbon on the particle surface. Electrochemical performance data and analysis are shown in Table 1. Comparing Comparative Example 2 with Example 2 reveals that, without the addition of nano-silicon alloy, the capacity retention of Comparative Example 2 after 200 cycles at 0.3C was only 78%.

[0070] Table 1 Comparison of electrochemical performance of carbon-coated silicon-based anode materials

[0071]

[0072] The performance data in Table 1 show that the silicon and silicon alloy composite negative electrode material obtained by the present invention can achieve a specific capacity greater than 1600 mAh g at a current density of 0.1C. -1 After 200 cycles, the capacity retention rate is above 86%, and the first coulombic efficiency is ≥85%. Compared with existing silicon-based negative electrode materials, its comprehensive electrochemical performance has been greatly improved.

[0073] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0074] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A lithium-ion battery silicon and silicon alloy composite negative electrode material, characterized in that: The composite anode material described above includes nano-silicon ferroalloy, nano-aerogel silica and coated carbon. Based on 100% of the total mass of the composite anode material, the mass ratio of the nano-silicon ferroalloy accounts for 30-50 wt.%, the mass ratio of the nano-aerogel silica accounts for 10-20 wt.%, and the mass ratio of the coated carbon accounts for 30-60 wt.%. The nano-aerogel silica is prepared by an arc evaporation technique and is silicon oxide SiOx, where 0 < x ≤ 2. It is composed of a mixture with nano-silicon, in which the silicon oxide SiOx has an amorphous flocculent structure, and the nano-silicon is crystalline nano-silicon particles with a particle size distribution range of 5-50 nm, and is uniformly dispersed within the amorphous flocculent structure of the silicon oxide SiOx.

2. A lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 1, characterized in that: The nano-silicon ferroalloy described above is prepared by an arc plasma torch technique and is composed of a two-phase mixture of nano-silicon and nano-FeSi2 uniformly dispersed at the nano-scale. Based on 100% of the total mass of the nano-silicon ferroalloy, the mass ratio of the nano-silicon accounts for 80 wt.%, and the mass ratio of the nano-FeSi2 alloy phase accounts for 20 wt.%, and the particle size distribution range is 5-150 nm.

3. The lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 1, characterized in that: Based on 100% of the total mass of the nano-aerogel silica, the mass ratio of the nano-silicon accounts for 20 wt.%, and the mass ratio of the silicon oxide SiOx accounts for 80 wt.%.

4. The lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 1, characterized in that: The coated carbon described above is composed of graphite carbon deposited by CVD and amorphous carbon obtained by high-temperature calcination and cracking of phenolic resin.

5. A method for preparing the silicon and silicon alloy composite negative electrode material for lithium-ion batteries according to any one of claims 1 to 4, characterized in that: The preparation method described above includes the following steps: (1) Uniformly mixing and drying the nano-scale silicon ferroalloy powder prepared by an arc plasma torch technique and the nano-scale aerogel silica powder prepared by an arc evaporation technique by ball milling in proportion to obtain a mixed powder A; (2) Depositing the mixed powder A by CVD method in a vacuum rotary furnace, and performing carbon pre-coating treatment to obtain a mixed powder B; (3) Mixing the mixed powder B with an organic carbon source by ball milling in proportion, screening, and then calcining for carbon coating modification to obtain the final composite anode material C containing nano-silicon ferroalloy, aerogel silica and coated carbon.

6. The method for preparing a lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 5, characterized in that: The ball milling parameters in step (1) are: ball-to-material ratio of 10:1, rotation speed of 600 revolutions per minute, ball milling time of 3 hours, drying temperature in the drying oven of 150 °C, and drying time of 1 hour.

7. The method for preparing a lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 5, characterized in that: The conditions for carbon pre-coating treatment of the mixed powder A by CVD method in step (2) are: deposition temperature of 600-900 °C, deposition time of 1-4 hours; the gas carbon source in the vacuum rotary furnace is at least one of methane, propylene or acetylene, and the surface deposited carbon layer thickness is 5-10 nm.

8. The method for preparing a lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 5, characterized in that: The organic carbon source in step (3) is one or more of phenolic resin, glucose, citric acid, sucrose, polyvinyl alcohol, asphalt.

9. The method for preparing a lithium-ion battery silicon and silicon alloy composite negative electrode material according to claim 5, characterized in that: In step (3), the ball milling parameters are: material ratio of 10:1, rotation speed of 800 revolutions per minute, ball milling time of 3 hours, screening with a 400-mesh sieve; the calcination is carried out in an inert atmosphere, the calcination temperature is 800-1100 °C, the calcination time is 2-4 hours, and the inert atmosphere is one or a mixture of argon and nitrogen.

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