Silicon-based phase and metal phase composite silicon-based composite material as well as preparation method and application thereof in low-temperature lithium ion battery

Abstract

The invention discloses a silicon-based phase and metal phase composite silicon-based composite material as well as a preparation method and application thereof in a low-temperature lithium ion battery, and relates to the technical field of lithium ion battery negative electrode materials. According to the invention, a silicon-based original material compounded by a silicon-based phase and a metal phase is used as a precursor, and is converted into the silicon-based composite material through polydopamine carbon coating. The silicon-based negative electrode material prepared in the invention shows excellent chemical stability and mechanical stability under the condition of low temperature (-30 DEG C), and has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery negative electrode materials, and in particular to a silicon-based composite material of a silicon-based phase and a metal phase, a preparation method thereof, and an application thereof in low-temperature lithium ion batteries. Background Art

[0002] With the rapid development of new clean energy sources, the demand for energy storage batteries is increasing. Lithium-ion batteries are widely researched and applied due to their advantages such as high energy density, long cycle life, and lack of memory effect. Currently, the theoretical capacity of graphite anodes of 372 mAh / g is insufficient to meet the demand for high energy density in lithium-ion batteries. Silicon anode materials have attracted much attention due to their high theoretical specific capacity of 3579 mAh / g, relatively low discharge voltage plateau (approximately 0.4 V to lithium potential), non-toxicity, and abundant reserves, making them the preferred anode material for next-generation lithium-ion batteries.

[0003] However, in actual application, silicon-based negative electrodes still face the following key challenges: (1) Silicon materials undergo large volume changes during the process of lithium insertion and removal, which can easily cause the material performance to decay. The huge internal stress causes the material to reach its mechanical limit and break and pulverize. In severe cases, the active material falls off the electrode, loses electrical contact and becomes inactive, ultimately causing the electrode capacity to decay rapidly. (2) The problem of solid electrolyte interface film (SEI) on the surface of silicon materials. The SEI on the surface cannot adapt to the volume change of silicon during the cycle and repeatedly breaks and forms again. The broken silicon particles expose new surfaces and contact with the electrolyte, which will also form new SEI. Both of these situations will lead to the continuous consumption of active lithium and electrolyte in the battery and the continuous thickening of SEI, which will hinder the electrical contact of the active material, cause the polarization of the battery to increase, and lead to a decrease in the battery cycle stability. (3) The inherent electronic conductivity of silicon is low (3.16×10 -6 Siemens per centimeter), the lithium ion diffusion rate is low (10 -15 ~10 -12 square centimeters per second), which is not conducive to the transmission of electrons and leads to slow lithium insertion and extraction kinetics, seriously limiting the full utilization of silicon capacity and the performance of battery rate performance.

[0004] On the other hand, with the expansion of lithium-ion battery application conditions, conventional lithium-ion batteries can no longer effectively store energy under low-temperature conditions such as aerospace (~-50 degrees Celsius), aviation and military industries (~-40 degrees Celsius). Under low-temperature conditions, the slow lithium storage kinetics of electrode materials is an important reason for the degradation of battery performance. Compared with positive electrode materials, negative electrode materials not only have a degradation of lithium storage performance (capacity reduction and cycle instability) at low temperatures, but also pose safety risks due to the growth of lithium dendrites. Therefore, Si negative electrodes still have the following technical problems at low temperatures: (1) Low reversible capacity: The ion conduction speed is too slow at low temperatures, resulting in severe polarization of the battery and reduced reversible capacity; at the same time, lithium insertion is difficult at low temperatures, and there is asymmetry in lithium insertion and extraction. (2) Poor cycle stability: At low temperatures, the lithium deposition of the electrode reacts with the electrolyte, and the deposition of its products causes the SEI thickness to continue to increase; the SEI formed under the action of polar groups in the electrolyte is more susceptible to low temperatures. (3) Poor rate performance: At low temperatures, ion diffusion in the bulk phase is too slow, significantly increasing the charge transfer impedance. At the same time, the desolvation problem slows down the transport across the SEI, thus affecting its rate performance. (4) Poor safety performance: At low temperatures, the ion conduction rate in the electrolyte slows down, and the reaction kinetics with the electrode surface weakens, increasing the impedance of the electrode / electrolyte interface. A large amount of lithium is deposited on the electrode surface, further generating lithium dendrites and "dead lithium". Lithium dendrites can pierce the diaphragm, causing the battery to short-circuit and causing safety issues.

[0005] In response to the above problems, researchers have carried out a lot of work in recent years, mainly focusing on the following directions: (1) SEI optimization: First, optimize the electrolyte composition and select appropriate electrolyte additives, such as film-forming additives (such as fluoroethylene carbonate (FEC) [], vinylene carbonate (VC) etc.) to optimize the SEI formation speed and mechanical properties under extremely low temperature conditions; Second, use chemical means to prepare native SEI on the surface of the material and coat the second phase on the surface of the material. This second phase is often a substrate material that is conducive to the formation of a stable SEI. (2) Improvement of conductivity: The modification method to improve ionic conductivity under extremely low temperature conditions is mainly to optimize the electrolyte composition, select appropriate solvents, electrolyte additives, etc. to improve the ionic conductivity of lithium-ion batteries at low temperatures; the method to improve electronic conductivity at extremely low temperatures is mainly composite modification (introduction of high conductive phase / fast ion conductor). The composite of silicon with carbon, metal, and conductive polymers can enhance the overall conductivity of the negative electrode material. Although the above strategies can enhance conductivity to a certain extent, their modification effect on the improvement of the intrinsic electronic conductivity of silicon materials is still limited. In order to solve the problems of low energy density, short life and great safety risks of lithium batteries at low temperatures, it is urgent to explore a silicon-based negative electrode material with high lithium storage capacity and fast lithium storage kinetics at low temperatures. Summary of the Invention

[0006] In response to the above problems, the present invention provides a silicon-based composite material composed of a silicon-based phase and a metal phase, a preparation method thereof, and an application in low-temperature lithium-ion batteries. The preparation method proposed in the present invention is simple to operate and easy to implement, and the prepared silicon-based negative electrode material exhibits excellent comprehensive performance under low-temperature conditions of lithium-ion batteries.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a method for preparing a silicon-based composite material composed of a silicon-based phase and a metal phase, using a silicon-based raw material composed of a silicon-based phase and a metal phase as a precursor, and converting it into a silicon-based composite material by polydopamine carbon coating, which specifically comprises the following steps: S1: Suspension melting combined with rapid quenching technology is used to obtain silicon-based raw materials composed of silicon-based phase and metal phase; S2: mixing the above silicon-based raw material with the conductive agent, and obtaining a silicon-based raw material-conductive agent powder material by sand grinding technology; S3: Pour the above silicon-based raw material-conductive agent powder material into tris(hydroxymethyl)aminomethane hydrochloride buffer solution, ultrasonicate for a period of time, add a certain amount of dopamine, continue ultrasonication, then place the sample on a magnetic stirrer in the air and stir continuously at a certain speed for several hours, and vacuum dry the sample; manually grind the dried sample through a 200-mesh sieve and pour it into a porcelain boat, and place it in a tube furnace; introduce gas into the tube furnace, heat to a specified temperature at a certain heating rate, and then keep it warm for several hours. After the end, cool it down with the furnace to obtain the silicon-based composite material.

[0008] Specifically, in step S1, the silicon-based phase is a Si-Sn solid solution phase, collectively referred to as a Si-Sn phase; the content of Sn in the Si-Sn phase does not exceed a molar fraction of 1 to 30% of the total amount of Si-Sn.

[0009] Specifically, in step S1, the metal phase is (1) any one of Y, Er, and Ce among the rare earth elements; or (2) any one of Bi and other metal elements having a melting point less than 1000 degrees Celsius and a boiling point less than 2200 degrees Celsius; or (3) any one of Ni and other metal elements having a melting point greater than 1000 degrees Celsius and a boiling point less than 5000 degrees Celsius; and the metal phase accounts for 2% to 20% of the molar fraction of the silicon-based composite material.

[0010] Specifically, in step S1, the specific method of combining suspension smelting with rapid quenching technology is as follows: S11: placing a mixture of bulk raw materials Si, Sn and metal M in a graphite crucible and performing vacuum suspension induction melting in an argon atmosphere to obtain a mixed ingot; after the mixed ingot is cooled, the surface graphite is polished off, the ingot is cleaned with kerosene for 30 minutes, and ultrasonicated with ethanol for 1 hour; after drying at room temperature, the ingot is placed in a copper crucible and again subjected to vacuum suspension induction melting three times in an argon atmosphere to achieve compositional uniformity, thereby obtaining a Si-Sn-M composite ingot composed of a silicon-based phase and a metal phase; S12: The Si-Sn-M composite material ingot obtained by the above-mentioned induction melting is mechanically crushed, and blocks of appropriate size are selected and placed in a quartz tube. Suspension melting is carried out in a vacuum rotary quenching furnace under an argon atmosphere. By gradually increasing the heater power, when the material is completely melted and jumps in the form of a flame in the quartz tube, the melt is transmitted through a nozzle carrying an argon flow and sprayed onto a high-speed rotating copper roller. After cooling, the rapidly quenched product is collected to obtain a silicon-based original material composite of a silicon-based phase and a metal phase.

[0011] More specifically, in step S11, the vacuum degree during vacuum suspension induction melting is 4×10 -3 Pa; in step S12, the vacuum degree of the vacuum quenching furnace is 6.0×10 -3 ~3.0×10 -3 Pa, the pressure in the furnace is -0.1~-0.02 MPa, the pressure of the argon gas flow in the nozzle that conveys the spray-cast melt is 0.4~3 atmospheres, and the linear speed of the copper roller is 10~150 m / s.

[0012] Specifically, in step S2, the silicon-based raw material and the conductive agent are mixed in a mass ratio of 4:1; the conductive agent is (1) any one or more of industrial furnace black, channel black, thermal black, high-temperature graphitized carbon black, and acetylene black in the carbon black conductive agent; or (2) any one or more of artificial graphite and natural graphite in the graphite conductive agent; or (3) any one or more of fiber and nanotube conductive agents; or (4) any one or more of graphene conductive agents; or (5) any one or more of biomass carbon.

[0013] Specifically, in step S2, the sand milling technology: the rotation speed is 300-8000 rpm, the sand milling time is 10-200 minutes, and the grinding medium is any one or more of ethanol, acetone or deionized water.

[0014] Specifically, in step S3, the ratio of the amount of silicon-based raw material-conductive agent powder material to tris(hydroxymethyl)aminomethane hydrochloride buffer is 1 gram:150 milliliters; the ultrasonic time is 30 minutes; the mass ratio of the silicon-based raw material-conductive agent powder material to dopamine is 100:1~20:1; the ultrasonic time is continued for 20 minutes; the speed of the magnetic stirrer is 100~1000 rpm, and the time is 10~24 hours; the vacuum drying temperature is 30~120 degrees Celsius; the heating rate is 1~10 degrees Celsius / minute, the heating temperature is 500~1000 degrees Celsius, and the holding time is 0.5~2 hours; the gas introduced into the tubular furnace is any one or more of argon, nitrogen, hydrogen, argon-hydrogen mixture, and oxygen.

[0015] The present invention also provides a silicon-based composite material of a silicon-based phase and a metal phase prepared by the above-mentioned preparation method.

[0016] The present invention also provides the application of the silicon-based phase and metal phase composite silicon-based composite material prepared by the above-mentioned preparation method in low-temperature lithium-ion batteries. The activation is carried out for 3 cycles (at a current density of 150 mA / g) at a room temperature of 28 degrees Celsius, and then applied at minus 30 degrees Celsius.

[0017] The application is specifically as follows: using copper foil used for conventional commercial lithium-ion battery negative electrodes as a current collector, the silicon-based composite material is evenly mixed with a binder (sodium alginate aqueous binder) and a conductive agent used in the preparation of conventional lithium-ion battery negative electrodes in a ratio of (80:20). The mixing process can be carried out by sand milling, ball milling or other stirring and mixing methods. After preparing a slurry, the slurry is coated on a copper current collector, and finally prepared into a negative electrode material through roller pressing, drying and cutting. The negative electrode material is used as the negative electrode, and conventional lithium-ion battery positive electrode materials such as LiFePO4, LiCoO2, ternary materials and lithium-rich manganese-based materials are used as the positive electrode. The lithium-ion battery is assembled with a separator and electrolyte conventionally used in lithium-ion batteries.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The equipment used in the present invention for preparing silicon-based negative electrode materials by polydopamine carbon coating is simple to operate, and the synthesis process is efficient and rapid; (2) The silicon-based negative electrode material prepared by polydopamine carbon coating in the present invention is low in cost and has excellent performance, and is an ideal silicon-based negative electrode material suitable for low-temperature lithium-ion batteries; (3) The raw materials used in the present invention are widely available, and the chemical reagents used are safe, environmentally friendly, and pollution-free, meeting the requirements of green chemistry; (4) The silicon-based negative electrode material prepared in the present invention exhibits excellent chemical stability and mechanical stability under low temperature (minus 30 degrees Celsius) conditions and has excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is the powder X-ray diffraction spectrum of the Si-Sn based material prepared by carbon coating with polydopamine in Example 1; Figure 2 This is the SEM morphology of the Si-Sn based material prepared by carbon coating with polydopamine in Example 1; Figure 3 The cycling performance of the Si-Sn-based negative electrode material prepared by carbon coating with polydopamine in Example 1 at a current density of 75 mA / g at -30 degrees Celsius; Figure 4 This is the powder X-ray diffraction spectrum of the Si-Sn-Ce based material prepared by carbon coating with polydopamine in Example 2; Figure 5 (a) Transmission electron microscopy (TEM) morphology of Si-Sn-Ce based materials prepared by polydopamine carbon coating in Example 2, (b) EDS spectrum of Si-Sn-Ce based materials prepared by polydopamine carbon coating; Figure 6 This is the XPS spectrum of Si-Sn-Ce based material prepared by carbon coating with polydopamine in Example 2; Figure 7 The cycling performance of the Si-Sn-M negative electrode material in Example 2-6 at a current density of 75 mA / g at -30 degrees Celsius; Figure 8 This is the powder X-ray diffraction spectrum of the Si-Sn-Bi based material prepared by carbon coating with polydopamine in Example 3; Figure 9 (a) Transmission electron microscopy (TEM) morphology of Si-Sn-Bi based materials prepared by carbon coating with polydopamine in Example 3, (b) EDS spectrum of Si-Sn-Bi based materials prepared by carbon coating with polydopamine; Figure 10 This is the XPS spectrum of Si-Sn-Bi based material prepared by carbon coating with polydopamine in Example 3; Figure 11 This is the powder X-ray diffraction spectrum of the Si-Sn-Er based material prepared by carbon coating with polydopamine in Example 4; Figure 12 (a) Transmission electron microscopy (TEM) morphology of Si-Sn-Er based materials prepared by carbon coating with polydopamine in Example 4, (b) EDS spectrum of Si-Sn-Er based materials prepared by carbon coating with polydopamine; Figure 13 This is the powder X-ray diffraction spectrum of the Si-Sn-Ni based material prepared by carbon coating with polydopamine in Example 5; Figure 14 (a) Transmission electron microscopy (TEM) morphology of Si-Sn-Ni based materials prepared by carbon coating with polydopamine in Example 5, (b) EDS spectrum of Si-Sn-Ni based materials prepared by carbon coating with polydopamine; Figure 15 This is the powder X-ray diffraction spectrum of the Si-Sn-Y based material prepared by carbon coating with polydopamine in Example 6; Figure 16 (a) Transmission electron microscopy (TEM) morphology of Si-Sn-Y based materials prepared by carbon coating with polydopamine in Example 6 (b) EDS spectrum of Si-Sn-Y based materials prepared by carbon coating with polydopamine; Figure 17 This is a powder X-ray diffraction spectrum of the Si-Sn based material prepared in Comparative Example 1 without using the polydopamine carbon coating technology; Figure 18 This is the SEM morphology of the Si-Sn based material prepared in Comparative Example 1 without using the polydopamine carbon coating technology; Figure 19 The cycling performance of the Si-Sn-based / Si-Sn-M-based materials prepared in Comparative Examples 1-3 without using the polydopamine carbon coating technology at a current density of 75 mA / g at -30 degrees Celsius; Figure 20 The XRD patterns of the Si-Sn-Ce based material prepared in Comparative Example 2 without using the polydopamine carbon coating technology and the Si-Sn-Ce based material prepared in Comparative Example 3 without high temperature carbonization; Figure 21 This is the SEM morphology of the Si-Sn-Ce based material prepared in Comparative Example 2 without using the polydopamine carbon coating technology; Figure 22 This is the SEM morphology of the Si-Sn-Ce based material prepared without high temperature carbonization in Comparative Example 3. DETAILED DESCRIPTION

[0020] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] Unless otherwise specified, the instruments, reagents, and materials used in the following examples are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods and detection methods used in the following examples are all conventional experimental methods and detection methods available in the prior art, unless otherwise specified.

[0022] Example 1 1. Preparation of Si by polydopamine carbon coating 95 Sn5 composite material: S1: Si is obtained by suspension melting combined with rapid quenching technology 95 Sn5 original material: (1) Place the mixture of bulk raw materials Si and Sn in a graphite crucible under an argon atmosphere with a vacuum degree of 4×10 -3 Pa, vacuum suspension induction melting was performed to obtain a mixed ingot; after the mixed ingot was cooled, the surface graphite was polished off, kerosene was cleaned for 30 minutes, and ethanol was ultrasonicated for 1 hour; after drying at room temperature, the ingot was placed in a copper crucible and placed in an argon atmosphere with a vacuum degree of 4×10 -3 Under the condition of Pa, vacuum suspension induction melting was carried out three times to achieve the uniformity of composition, and a Si-Sn composite ingot with a silicon-based phase and a metal phase was obtained; (2) The Si-Sn composite material ingot obtained by induction melting was mechanically crushed, and blocks of appropriate size were selected and placed in a quartz tube. The vertical distance between the nozzle of the quartz tube and the copper roller was adjusted to about 3-5 microns. The vacuum was 4×10 -3 In a vacuum rotary quenching furnace, suspension melting is carried out under an argon atmosphere (chamber pressure is -0.05 MPa). By gradually increasing the heater power, when the material is completely melted and jumps in the form of a flame in the quartz tube, the melt is transmitted through a nozzle carrying an argon flow (spray pressure is 0.15 MPa) and sprayed onto a high-speed rotating (linear speed is 30 m / s) copper roller. After cooling, the rapid quenching product is collected to obtain Si composite of silicon-based phase and metal phase. 95 Sn5 original material; S2: The above Si 95 Sn5 raw material was mixed with conductive agent (4:1) and sand milled (speed 1500 rpm, time 40 min, grinding medium ethanol) to obtain Si 95 Sn5 original material - conductive agent powder material; S3: 1g Si 95 Sn5 raw material-conductive agent powder material was poured into 150 ml tris (hydroxymethyl) aminomethane hydrochloride buffer, ultrasonicated for 30 minutes, and 0.05 g dopamine (Si 95 The mass ratio of Sn5 raw material-conductive agent powder material to dopamine was 20:1), and ultrasonication was continued for 20 minutes. After that, the sample was placed on a magnetic stirrer in air and stirred continuously at 500 rpm for 12 hours. The sample was placed in a vacuum oven at 60 degrees Celsius. The dried sample was manually ground through a 200-mesh sieve and poured into a porcelain boat, which was placed in a tube furnace. Argon-hydrogen mixed gas (9:1) was introduced into the tube furnace and heated to 600 degrees Celsius at a heating rate of 5 degrees Celsius / minute and then kept warm for 1 hour. After the end, the temperature was cooled with the furnace to obtain Si 95 Sn5 composite material.

[0023] Figure 1 Preparation of Si for polydopamine carbon coating 95The X-ray diffraction (XRD) pattern of the Sn5 sample revealed the presence of Si (JCPDS 27-1402) and Sn (JCPDS 04-0673) phases in the composite material, as well as a conductive agent added during the sanding process. This indicates that no alloy phase was formed between Si and Sn during the preparation process. Due to the insensitivity of the XRD instrument to surface elements, other elements were not detected at this time. Figure 2 This is the SEM morphology of the material. The surface of the material is loose. The flaky black substance is SFG-6 conductive agent. The particle size is mainly in the range of 200 nanometers to 1 micron. The overall morphology is a typical mechanical crushing morphology.

[0024] 2. Preparation of Si-Sn composite material negative electrode sheet and test battery and electrode electrochemical performance test at -30 degrees Celsius: A silicon-based composite material prepared by polydopamine carbon coating technology was mixed with an aqueous sodium alginate binder at a mass ratio of 80:20, with a sodium alginate binder concentration of 1.2 wt%. The mixed slurry was applied to a copper current collector and dried in an oven. The electrode sheet was compacted by holding it at 20 MPa for 60 seconds to form an electrode sheet. The sheet was then punched into 10 mm diameter discs and assembled into CR2025 button cells using a lithium sheet as the counter electrode to test the electrochemical performance of the electrodes. The cells were assembled in an argon-filled glove box. A Celgard-2400 separator, specifically designed for lithium-ion batteries, was used as the separator. A 1 mol / L electrolyte solution was prepared using LiPF6 as the solute and a 1:1:1 volume ratio of ethylene carbonate (EC), ethyl methyl carbonate (DMC), and diethyl carbonate (DEC) as the solvent. 10 wt% of fluoroethylene carbonate (FEC) was added as an additive.

[0025] The specific capacity and cycle performance of the electrode were tested on an electrochemical tester using a constant current test method with a voltage window of 0.01-1.5 volts. The composite material obtained in Example 1 was used as a negative electrode for a lithium-ion battery. Before low-temperature testing, it was activated for three cycles at room temperature (28 degrees Celsius) at a current density of 150 mA / g. The cycle performance was then tested at -30 degrees Celsius at a current density of 75 mA / g. Figure 3 The first reversible capacity is 1122.18 mAh / g, and after 200 cycles, the capacity is maintained at 993.01 mAh / g, with a capacity retention rate of 88.5%, which is much better than the electrochemical performance of Comparative Example 1. 95 Sn5 material, due to the surface amorphous carbon has certain mechanical properties, can 95 Sn5 material is in-situ coated to ensure the carbon layer and Si 95The good bonding strength between Sn5 materials has a significant effect on promoting the cycling stability of samples at low temperatures. The embodiments of the present invention all adopt this test method.

[0026] Example 2 1. The same method as in Example 1 was used, except that the third phase metal element cerium was introduced and Si was prepared by polydopamine carbon coating. 90 Sn5Ce5 composite material: S1: Si composite of silicon-based phase and metal phase is obtained by suspension melting combined with rapid quenching technology 90 Sn5Ce5 original material: (1) Place the mixture of bulk raw materials Si, Sn, and Ce in a graphite crucible under an argon atmosphere with a vacuum degree of 4×10 -3 Pa, vacuum suspension induction melting was performed to obtain a mixed ingot; after the mixed ingot was cooled, the surface graphite was polished off, kerosene was cleaned for 30 minutes, and ethanol was ultrasonicated for 1 hour; after drying at room temperature, the ingot was placed in a copper crucible and placed in an argon atmosphere with a vacuum degree of 4×10 -3 Under the condition of Pa, vacuum suspension induction melting was carried out three times to achieve the uniformity of composition, and an ingot of Si-Sn-Ce composite material composed of silicon-based phase and metal phase was obtained; (2) The Si-Sn-Ce composite material ingot obtained by induction melting was mechanically crushed, and blocks of appropriate size were selected and placed in a quartz tube. The vertical distance between the nozzle of the quartz tube and the copper roller was adjusted to about 3-5 microns. The vacuum was 4×10 -3 In a vacuum rotary quenching furnace, suspension melting is carried out under an argon atmosphere (chamber pressure is -0.05 MPa). By gradually increasing the heater power, when the material is completely melted and jumps in the form of a flame in the quartz tube, the melt is transmitted through a nozzle carrying an argon flow (spray pressure is 0.15 MPa) and sprayed onto a high-speed rotating (linear speed is 30 m / s) copper roller. After cooling, the rapid quenching product is collected to obtain Si composite of silicon-based phase and metal phase. 90 Sn5Ce5 original material; S2: Si 90 The Sn5Ce5 raw material was mixed with a conductive agent (4:1) and sand milled (speed 1500 rpm, time 40 min, grinding medium ethanol) to obtain Si 90 Sn5Ce5 original material - conductive agent powder material; S3: 1g Si 90The Sn5Ce5 raw material-conductive agent powder material was poured into 150 ml of tris (hydroxymethyl) aminomethane hydrochloride buffer solution, and after ultrasonication for 30 minutes, 0.05 g of dopamine was added (the mass ratio of active substance to dopamine was 20:1), and ultrasonication was continued for 20 minutes. After that, the sample was placed on a magnetic stirrer in air and stirred continuously at 500 rpm for 12 hours. The sample was placed in a vacuum oven at 60 degrees Celsius; the dried sample was manually ground through a 200-mesh sieve and poured into a porcelain boat, which was placed in a tube furnace; an argon-hydrogen mixed gas (9:1) was introduced into the tube furnace, and heated to 600 degrees Celsius at a heating rate of 5 degrees Celsius / minute and kept warm for 1 hour. After the end, the temperature was lowered with the furnace to obtain Si 90 Sn5Ce5 composite material.

[0027] Figure 4 This is the X-ray diffraction (XRD) pattern of the sample. XRD analysis reveals that the composite material contains Si (JCPDS 27-1402) and Sn (JCPDS 04-0673) phases, as well as CeO2 (JCPDS 43-1002) and a conductive agent added during the sanding process. Cerium, a third phase element, is easily oxidized. During the preparation process, oxygen was introduced. Cerium oxide acts as a sacrificial agent to protect silicon from hydrogen fluoride attack, and the resulting CeF2 serves as an anti-corrosion component of the SEI. Figure 5 (a) TEM morphology of the material shows that the composite material surface is successfully coated with a layer of carbon with a thickness of about 4.5 nanometers. EDS is further used to clarify the distribution of Si, Sn, Ce, C, N, and O in the bulk phase of the material. The results are as follows: Figure 5 (b). It can be found that the overall distribution in the bulk phase is uniform, and there is an inconspicuous segregation phenomenon at the scale of 500 nanometers. The reason may be that some self-polymerized dopamine is attached to the surface of the material particles, or the self-polymerized dopamine reacts with the dopamine on the surface of the particles again. In addition, the size of the silicon grains in the material is significantly smaller than 500 nanometers. The addition of cerium can inhibit the growth of silicon grains during smelting and rapid quenching. Smaller grains can provide larger grain boundaries and phase boundaries, which is conducive to the rapid diffusion of lithium ions in them, and will have a great effect on improving the kinetic properties of the material. Evaluation of carbon-coated Si by XPS 90 The chemical environment of Si, Sn, Ce, N, C, and O inside the Sn5Ce5 sample, such as Figure 6 As shown. Figure 6 (a) It can be seen that the 2p XPS peak of Si includes Si 0 and Si 3+ , where Si 3+The presence of a SiOx oxide layer on the particle surface indicates that this layer is still present. This is due to the susceptibility of Si-based materials to oxidation in air. The XRD results previously showed the absence of SiOx diffraction peaks, indicating that the SiOx content on the surface of the material is extremely low and does not significantly affect its electrochemical performance. Figure 6 (b) The 3d Sn in SnO2 appears 4+ , it is speculated that the sample was oxidized due to exposure to air. Figure 6 The chemical environment of Ce in (c) includes Ce element, Ce-Si alloy phase, Ce-Sn alloy phase, and CeOx, which means that the addition of Ce also affects the second conductive phase. The interface contact problem between semiconductors is transformed into the problem of heterojunction inside the semiconductor and the contact problem between metal and semiconductor at the interface (including the contact between Ce and Sn, Si and Ce). After surface modification, Figure 6 The XPS of N in (d) shows that the N element has successfully penetrated into the surface SiOx layer. Figure 6 (e) The two new peaks at 284.35 volts and 284.8 volts in the C 1s spectrum correspond to the CN / CO and CC bonds, respectively. Figure 6 (f) The enhanced peaks at 531.9 eV (C=O) and 533.4 eV (C-OH) further confirm the carbon-coated Si 90 Formation of carboxyl groups on the surface of Sn5Ce5 samples.

[0028] 2. Si 90 Preparation of Sn5Ce5 composite material negative electrode sheet and test battery and electrode electrochemical performance test at -30 degrees Celsius: The negative electrode sheet was prepared and the battery was assembled in the same manner as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius, except that a binder with a concentration of 1.8% was used.

[0029] The first charge-discharge curve of the composite material obtained in Example 2 as the negative electrode of a lithium-ion battery at a current density of 75 mA / g at -30 degrees Celsius is as follows: Figure 7 The reversible specific capacity of the first charge is 1158.16 mAh / g, and the capacity is maintained at 1298.97 mAh / g after 78 cycles, with a capacity retention rate of 1158.16%, which is significantly improved compared with the performance in Example 1. 90 Sn5Ce5 composite material, the mechanical properties of the surface amorphous carbon, can 90 Sn5Ce5 composite material is in-situ coated to ensure that the carbon layer is closely connected to the Si 90The strong bonding between the Sn5Ce5 materials and the residual nitrogen on the carbon layer's surface also effectively enhance the carbon layer's charge interface transfer capability and electronic conductivity. Furthermore, the introduction of a third phase, the lanthanide metal Ce, for bulk doping helps mitigate volume expansion. Dynamically, this shortens the bulk Si band gap while transforming the bulk-phase interface from a Schottky contact to an Ohmic contact, optimizing carrier transport efficiency at low temperatures and improving the material's carrier transport capacity at low temperatures. These two synergistic mechanisms contribute to enhanced cycling stability at -30°C.

[0030] Example 3 1. The same method as in Example 1 was used, except that the third phase metal element bismuth was introduced and Si was prepared by polydopamine carbon coating. 90 Sn5Bi5 composite materials Figure 8 This is the X-ray diffraction (XRD) pattern of the sample. Testing shows that the composite material contains Si (JCPDS 27-1402) and Sn (JCPDS 04-0673) phases, as well as Bi (JCPDS 44-1246) and a conductive agent added during the sanding process. This indicates that Si, Sn, and Bi did not form alloy phases during the preparation process. As a soft metal element, Bi plays a certain role in suppressing the volume expansion of silicon. Figure 9 (a) is the TEM morphology of the material, and the thickness of the carbon coating layer is about 3.75 nanometers. Figure 9 (b) In order to clarify the distribution of Si, Sn, Bi, C, N, and O elements in the bulk phase of the material through EDS, it can be found that each element is uniformly distributed in the bulk phase as a whole, and there is also an insignificant segregation phenomenon at the scale of 500 nanometers. The reason is similar to that in Example 2. It may be that some self-polymerized dopamine is attached to the surface of the material particles, or the self-polymerized dopamine reacts with the dopamine on the surface of the particles again. In addition, the size of the silicon grains in the material is significantly smaller than 500 nanometers. This shows that the introduction of bismuth also plays the same role as cerium in refining the grains. By inhibiting the growth of silicon grains during smelting and rapid quenching, it provides a larger grain boundary and phase boundary area, promotes the rapid diffusion of lithium ions therein, and improves the material dynamics. Evaluation of carbon-coated Si by XPS 90 The chemical environment of Si, Sn, Bi, N, C, and O inside the Sn5Bi5 sample is shown in the following figure. Figure 10 As shown. Figure 10 (a) It can be seen that the 2p XPS peak of Si is similar to that of Example 2, including Si 0 and Si 3+ , where Si 3+ The intensity is significantly higher, indicating that there is still a SiOx oxide layer on the surface of the particles, which is attributed to the fact that silicon-based materials are easily oxidized in the air. Figure 8 The XRD shows that there is no SiOx diffraction peak, so the SiOx content in this layer on the surface of the material is low, and it is speculated that it will not have a significant impact on its electrochemical performance. Figure 10 (b) The 3d Sn in SnO2 shows obvious Sn 4+ , it is speculated that the sample was oxidized due to exposure to air. Figure 10 (c) The XPS of N shows that N has successfully penetrated into the surface SiOx layer. After surface modification, Figure 10 (d) The two new peaks at 284.08 eV and 284.8 eV in the C1s spectrum correspond to the CN / CO and CC bonds, respectively. Figure 10 (e) The enhanced peaks at 531.9 eV (C=O) and 533.4 eV (C-OH) further confirm the carbon-coated Si 90 The formation of carboxyl groups on the surface of Sn5Bi5 samples. No relevant information about Bi was detected, and it is speculated that the instability of bismuth had a certain impact on the sample detection during the characterization process.

[0031] 2. Si 90 Preparation of Sn5Bi5 composite material negative electrode sheet and test battery and electrode electrochemical performance test at -30 degrees Celsius: The negative electrode sheet was prepared and the battery was assembled using the same method as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius. Figure 7 As shown, the composite material obtained in Example 3 as the negative electrode of a lithium-ion battery has a first charge reversible specific capacity of 935.58 mAh / g at a current density of 75 mAh / g at minus 30 degrees Celsius. After 75 cycles, the capacity is maintained at 1377.7 mAh / g, and the capacity retention rate is 147.3%. This is attributed to the lithium affinity of metallic bismuth, which has certain advantages in optimizing interfacial reaction behavior. At the same time, some preferential diffusion paths are constructed for lithium ion diffusion at low temperatures, and the bismuth metal is soft and can absorb the stress generated by the expansion of the bulk phase by deformation. It is further confirmed that after polydopamine carbon coating, the N element formed at the interface of the material reacts with the lithium salt to generate Li3N during the charge and discharge process. As an inorganic component of SEI, it can guide lithium electrodeposition and create a weak solvation environment by reducing the Li+ solvent coordination at low temperatures, thereby promoting the migration of lithium ions in the electrolyte. It also has good thermodynamic stability and high conductivity, which plays an important role in improving the electrochemical cycle stability of the sample at minus 30 degrees Celsius.

[0032] Example 4 1. The same preparation method as in Example 1 was used, except that a third phase metal element, erbium, was introduced and Si was prepared by polydopamine carbon coating. 90 Sn5Er5 composite material.

[0033] Figure 11 is the X-ray diffraction (XRD) pattern of the sample. Except for the generation of ErSi2 (JCPDS 12-0037), the other processes are basically the same as those in Example 2. Figure 12 (a) is the TEM morphology of the material. The surface of the sample is also covered with a layer of carbon with a thickness of about 4 nanometers. Figure 12 In (b), the Si, Sn, Er, C, and N elements are uniformly distributed in the material as a whole, and subtle segregation occurs in some areas. The reason is similar to that in Example 2, which may be that some self-polymerized dopamine adheres to the surface of the material particles, or the self-polymerized dopamine reacts with the dopamine on the surface of the particles again.

[0034] 2. Si 90 Preparation of Sn5Er5 composite material negative electrode sheet and test battery and electrode electrochemical performance test at -30 degrees Celsius: The negative electrode sheet was prepared and the battery was assembled using the same method as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius. Figure 7 As shown, the composite material obtained in Example 4 as the negative electrode of a lithium-ion battery has a first charge reversible specific capacity of 957.31 mAh / g at a current density of 75 mAh / g at -30 degrees Celsius. After 99 cycles, the capacity remains at 927.04 mAh / g, and the capacity retention rate is 96.8%, which is significantly improved compared with the electrochemical performance of Example 1. This shows that the introduction of the third phase lanthanide transition metal erbium element for bulk doping, and the resulting ErSi2 as a buffer layer between the metal electrode and the highly doped silicon is conducive to the alleviation of volume expansion and the suppression of the Fermi pinning effect at the interface. In terms of dynamics, the buffer layer acts as a "bridge", shortening the energy band gap of the bulk Si while realizing the transformation of the bulk phase and the phase boundary interface from Schottky contact to ohmic contact, optimizing the carrier transport efficiency, and improving the carrier transport capacity of the material at low temperatures. Furthermore, since dopamine can self-polymerize in an alkaline environment to form a dark brown amorphous network polymer called polydopamine (PDA), it can adhere tightly to the surface of the material, enhancing the adhesion between the active material and the binder and current collector, significantly improving the cycling stability of the sample at -30°C. Furthermore, the presence of amino groups (-NH2) in the dopamine monomer allows it to be well coated on the material surface after carbonization, maintaining the material's structure. Furthermore, nitrogen remains in the carbon layer, which helps improve the charge transfer capability and electronic conductivity of the carbon layer at low temperatures.

[0035] Example 5 1. The same method as in Example 1 was used, except that the third phase metal element nickel was introduced and Si was prepared by polydopamine carbon coating. 90 Sn5Ni5 composite material.

[0036] Figure 13 The X-ray diffraction (XRD) pattern of the sample shows that the composite material contains Si (JCPDS 27-1402) and Sn (JCPDS 04-0673) phases, as well as NiSi2 (JCPDS 43-0989), and a conductive agent added during the sanding process. NiCO3 (JCPDS 12-0771) was also detected, indicating that Si and Ni formed an alloy phase during the preparation process. Furthermore, the introduction of a third phase of nickel also generated NiCO3 during the carbon coating process, suggesting that this inorganic phase may play a role in the sample's cycling stability. Figure 14 (a) is the TEM morphology of the material. The sample is relatively uniformly coated and the thickness of the carbon layer is about 6 nanometers. Figure 14 (b) EDS is used to illustrate the distribution of Si, Sn, Ni, C, and N elements in the bulk phase of the material. The elements are uniformly distributed overall, with subtle segregation in some areas. The reason is similar to that in Example 2, possibly because some self-polymerized dopamine adheres to the surface of the material particles, or the self-polymerized dopamine reacts again with the dopamine on the particle surface.

[0037] 2. Si 90 Preparation of Sn5Ni5 composite negative electrode sheet and test battery and electrode electrochemical performance test at -30 degrees Celsius: The negative electrode sheet was prepared and the battery was assembled using the same method as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius. Figure 7 As shown, the composite material obtained in this embodiment 5 as the negative electrode of a lithium ion battery has a first charge reversible specific capacity of 1053.22 mAh / g at a current density of 75 mAh / g at -30 degrees Celsius. After 83 cycles, the capacity is maintained at 1153.55 mAh / g, and the capacity retention rate is 109.5%, which is significantly improved compared with the electrochemical performance of Example 1. This shows that the third phase nickel element is introduced for bulk doping. In addition to the role of NiSi2, the formation of NiCO3 also provides a certain inorganic component for the interface composition during the charge and discharge process of the sample, which has a significant effect on the conductivity and stability of the sample at low temperatures. More importantly, after the polydopamine carbon is coated, the amorphous carbon and residual N element formed on the surface of the material also have a significant effect on the optimization of the electrode interface and the charge transfer ability, which can effectively improve the electrochemical performance of the sample at -30 degrees Celsius.

[0038] Example 6 1. The same preparation method as in Example 1 was used, except that a third phase metal element, yttrium, was introduced and Si was coated with polydopamine carbon. 90 Sn5Y5 composite material.

[0039] Figure 15 : This is the X-ray diffraction (XRD) pattern of the sample. After testing, the composite material contains Si (JCPDS 27-1402) and Sn (JCPDS 04-0673) phases, as well as YSi2 (JCPDS 11-0596), and a conductive agent added during the sanding process. The overall results are similar to those of Example 5. Figure 16 (a) is the TEM morphology of the material. The surface of the sample is successfully coated with a layer of amorphous carbon, and the thickness of the carbon layer is about 5 nanometers, which once again proves the feasibility of this method. Figure 16 In (b), the elements are uniformly distributed as a whole, with subtle segregation in some areas. The reason is similar to that in Example 2, which may be that some self-polymerized dopamine adheres to the surface of the material particles, or the self-polymerized dopamine reacts with the dopamine on the particle surface again.

[0040] 2. Si 90 Preparation of Sn5Y5 composite material negative electrode sheet and test battery and electrode electrochemical performance test at -30 degrees Celsius: The test cell was prepared in the same manner as in Example 1 and its electrochemical performance was tested. Figure 7 As shown, the composite material obtained in Example 5 as the negative electrode of a lithium-ion battery has a first charge reversible specific capacity of 930.51 mAh / g at a current density of 75 mAh / g at -30 degrees Celsius. After 101 cycles, the capacity is maintained at 890.19 mAh / g, and the capacity retention rate is 95.67%, indicating that the introduction of the third phase yttrium element for bulk doping, and the generated YSi2 has the same effect as NiSi2. Therefore, the cyclic stability of the polydopamine carbon-coated sample at minus 30 degrees Celsius is significantly improved, which can be attributed to the following points: First, dopamine can self-polymerize in an alkaline environment to form a black-brown amorphous network polymer-polydopamine (PDA), which can adhere tightly to the surface of the material, enhance the adhesion between the active substance and the binder and current collector, and alleviate the volume expansion of the silicon negative electrode; second, the presence of amino groups (-NH2) in the dopamine monomer can be well coated on the surface of the material after carbonization, maintain the structure of the material, and enhance the cyclic stability of the sample in the electrochemical process; third, after high-temperature annealing, the nitrogen element in polydopamine will remain in the carbon layer on the surface of the sample, which is beneficial to improve the charge interface transfer ability and electronic conductivity of the carbon layer, thereby improving the electrochemical performance of the sample at low temperatures.

[0041] Comparative Example 1 The preparation process is basically the same as that of Example 1, except that the carbon coating technology is not used and the binder concentration is 2.9%. 95 Sn5 composite material.

[0042] Figure 17 This is the XRD pattern of the sand-milled product. It contains Si (JCPDS 27-1402) and Sn (JCPDS 04-0673) phases, as well as the conductive agent added during the sand-milling process, indicating that Si and Sn did not form an alloy phase during the preparation process. The overall peak intensity of the sample is high, indicating that the sample without carbon coating has a weak amorphization. Figure 18 This is the SEM morphology of the product after sand grinding in Comparative Example 1. 95 The particle size of the Sn5 composite material is about 1 micron, which is larger than the particle size of the sample in Example 1.

[0043] The negative electrode sheet was prepared and the battery was assembled using the same method as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius. Figure 19 As shown, the negative electrode of the lithium-ion battery can hardly complete the lithium insertion and removal process under the condition of -30 degrees Celsius, and the negative electrode material obtained in this comparative example 1 loses its electrochemical activity. This shows that the performance of the sample without polydopamine carbon coating at low temperature is extremely poor, lithium ions can hardly migrate, and the charge and discharge process cannot be completed. This shows that the amorphous coating layer formed on the surface of the sample prepared by polydopamine carbon coating can effectively alleviate the volume expansion of the sample, and the introduced non-metallic elements and the inorganic substances formed during the charge and discharge process have high conductivity and good mechanical properties, which have a significant effect on improving the electrochemical performance of the sample at -30 degrees Celsius.

[0044] Comparative Example 2 The preparation process is basically the same as that of Example 2, except that no carbon coating is performed and the raw material is sand-milled Si 90 Sn5Ce5 composite material.

[0045] Figure 20 This is the XRD spectrum of the product after sand grinding. The sample composition is slightly different from the above, but it can be clearly found that the carbon coating technology makes the sample more amorphous. Figure 21 This is the SEM morphology of the sand-milled product of Comparative Example 2. The overall morphology of the sample is slightly different from the above, indicating that the carbon coating has little effect on the sample particles.

[0046] The negative electrode sheet was prepared and the battery was assembled using the same method as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius. Figure 19As shown, the negative electrode of the lithium-ion battery is also unable to complete the lithium insertion and deintercalation process under the condition of -30 degrees Celsius. The negative electrode material obtained in this comparative example 2 also loses its electrochemical activity. Compared with Example 2, the performance of the sample is extremely poor. This proves that the carbon-coated sample has a significant impact on the electrochemical performance of the sample at -30 degrees Celsius due to the effect of the coating layer and interface optimization.

[0047] Comparative Example 3 The preparation process is basically the same as that of Example 2, and the raw materials used are Si 90 The difference between the sand-polished Sn5Ce5 samples is that no high-temperature carbonization was performed during the carbon coating experiment.

[0048] The XRD patterns of the products after the experiment are listed in Figure 20 , the sample components are slightly different from the above. Figure 22 This is the SEM morphology of the sand-milled product of Comparative Example 3. The overall morphology of the sample is slightly different from the above, indicating that high-temperature carbonization has little effect on the sample particles.

[0049] The negative electrode sheet was prepared and the battery was assembled using the same method as in Example 1, and its electrochemical performance was tested at -30 degrees Celsius. Figure 19 As shown, the negative electrode of the lithium-ion battery is almost unable to complete the lithium insertion and removal process at -30 degrees Celsius. The negative electrode material obtained in Comparative Example 3 loses its electrochemical activity. Compared with Example 2, the sample is unable to undergo the lithium insertion and removal process. This proves again that without using the above-mentioned optimized preparation method, the sample obtained cannot migrate lithium ions due to the lack of interface optimization effect, and the sample loses activity. This shows that using the optimized carbon coating preparation method, the performance of the obtained sample at -30 degrees Celsius is significantly improved, which is conducive to further promotion and use.

[0050] In addition to the above embodiments: In some other embodiments of the present invention, the vacuum degree of the vacuum quenching furnace in step S1 is 6.0×10 -3 Pa, the pressure in the furnace is -0.1 MPa, the pressure of the argon gas flow in the nozzle that conveys the spray-cast melt is 0.04 MPa, and the linear speed of the copper roller is 10 m / s.

[0051] In some other embodiments of the present invention, the vacuum degree of the vacuum quenching furnace in step S1 is 3.0×10 -3 Pa, the pressure in the furnace is -0.02 MPa, the pressure of the argon gas flow in the nozzle that conveys the spray-cast melt is 0.3 MPa, and the linear speed of the copper roller is 150 m / s.

[0052] In some other embodiments of the present invention, the conductive agent in step S2 is (1) any one or more of industrial furnace black, channel black, thermal black, high-temperature graphitized carbon black, and acetylene black in the carbon black conductive agent; or (2) any one or more of artificial graphite and natural graphite in the graphite conductive agent; or (3) any one or more of fiber and nanotube conductive agents; or (4) any one or more of graphene conductive agents; or (5) any one or more of biomass carbon.

[0053] In some other embodiments of the present invention, the sand milling speed in step S2 is 300 rpm, the time is 200 minutes, and the grinding medium is acetone.

[0054] In some other embodiments of the present invention, the sand milling speed in step S2 is 8000 rpm, the time is 10 minutes, and the grinding medium is deionized water.

[0055] In some other embodiments of the present invention, in step S3, the mass ratio of the silicon-based raw material-conductive agent powder material to dopamine is 100:1; the magnetic stirring speed is 100 rpm, the stirring time is 24 hours, the vacuum drying temperature is 30 degrees Celsius, and the material is heated to 500 degrees Celsius at a heating rate of 1 degree Celsius / minute and kept warm for 2 hours.

[0056] In some other embodiments of the present invention, in step S3, the mass ratio of the silicon-based raw material-conductive agent powder material to dopamine is 50:1; the magnetic stirring speed is 1000 rpm, the stirring time is 10 hours, the vacuum drying temperature is 120 degrees Celsius, and the material is heated to 1000 degrees Celsius at a heating rate of 10 degrees Celsius / minute and kept warm for 0.5 hours.

[0057] In some other embodiments of the present invention, in step S3, the gas introduced into the tube furnace is any one or more of argon, nitrogen, hydrogen, argon-hydrogen mixture, and oxygen.

[0058] In the above examples, polydopamine was successfully coated on the surface of the silicon-based composite material. The silicon-based anode material exhibited excellent chemical and mechanical stability at low temperatures (-30 degrees Celsius) and possessed outstanding electrochemical performance.

[0059] In summary, the composite material in this embodiment is processed by induction melting and rapid quenching of the raw materials, and then sand-milling. Subsequently, polydopamine carbon coating technology is carried out. Through the polydopamine carbon coating technology, a nano-scale amorphous carbon layer is formed on the surface of the silicon composite negative electrode material. The carbon layer has a certain mechanical strength and can be used to coat the material in situ to ensure good bonding between the carbon layer and the silicon-based negative electrode, thereby alleviating the volume expansion of the silicon-based negative electrode material during lithium insertion and extraction. At the same time, after high-temperature carbonization, the non-metallic elements remaining on the surface of the material, under conditions of minus 30 degrees Celsius, form lithium compounds after contact with the electrolyte during the charge and discharge process. As a beneficial component of SEI, it has good electrical conductivity and mechanical properties. As a negative electrode material for lithium-ion batteries, the composite material particles at minus 30 degrees Celsius show excellent comprehensive capacity and cycle performance at submicron and micron scales, which is conducive to high volume capacity density of low-temperature lithium-ion batteries. The preparation method of the material is mature in technology, good in process controllability, high in yield, low in cost, and suitable for large-scale production.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-based composite material comprising a silicon-based phase and a metal phase, characterized in that: A silicon-based raw material composed of a silicon-based phase and a metal phase is used as a precursor and converted into a silicon-based composite material by polydopamine carbon coating, specifically comprising the following steps: S1: Suspension melting combined with rapid quenching technology is used to obtain silicon-based raw materials composed of silicon-based phase and metal phase; S2: mixing the above silicon-based raw material with the conductive agent, and obtaining a silicon-based raw material-conductive agent powder material by sand grinding technology; S3: Pour the above silicon-based raw material-conductive agent powder material into tris(hydroxymethyl)aminomethane hydrochloride buffer solution, ultrasonicate for a period of time, add a certain amount of dopamine, continue ultrasonication, then place the sample on a magnetic stirrer in the air and stir continuously at a certain speed for several hours, and vacuum dry the sample; manually grind the dried sample through a 200-mesh sieve and pour it into a porcelain boat, and place it in a tube furnace; introduce gas into the tube furnace, heat to a specified temperature at a certain heating rate, and then keep it warm for several hours. After the end, cool it down with the furnace to obtain the silicon-based composite material.

2. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: In step S1, the silicon-based phase is a Si-Sn solid solution phase, collectively referred to as a Si-Sn phase; the content of Sn in the Si-Sn phase does not exceed a molar fraction of 1 to 30% of the total amount of Si-Sn.

3. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: In step S1, the metal phase is (1) any one of Y, Er, and Ce among the rare earth elements; or (2) a metal element Bi having a melting point less than 1000 degrees Celsius and a boiling point less than 2200 degrees Celsius; or (3) a metal element Ni having a melting point greater than 1000 degrees Celsius and a boiling point less than 5000 degrees Celsius; and the metal phase accounts for 2% to 20% of the molar fraction of the silicon-based composite material.

4. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: In step S1, the specific method of combining suspension smelting with rapid quenching technology is as follows: S11: placing a mixture of bulk raw materials Si, Sn and metal M in a graphite crucible and performing vacuum suspension induction melting in an argon atmosphere to obtain a mixed ingot; after the mixed ingot is cooled, the surface graphite is polished off, the ingot is cleaned with kerosene for 30 minutes, and ultrasonicated with ethanol for 1 hour; after drying at room temperature, the ingot is placed in a copper crucible and again subjected to vacuum suspension induction melting three times in an argon atmosphere to achieve compositional uniformity, thereby obtaining a Si-Sn-M composite ingot composed of a silicon-based phase and a metal phase; S12: The Si-Sn-M composite material ingot obtained by the above-mentioned induction melting is mechanically crushed, and blocks of appropriate size are selected and placed in a quartz tube. Suspension melting is carried out in a vacuum rotary quenching furnace under an argon atmosphere. By gradually increasing the heater power, when the material is completely melted and jumps in the form of a flame in the quartz tube, the melt is transmitted through a nozzle carrying an argon flow and sprayed onto a high-speed rotating copper roller. After cooling, the rapidly quenched product is collected to obtain a silicon-based original material composite of a silicon-based phase and a metal phase.

5. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 4, characterized in that: In step S11, the vacuum degree during vacuum suspension induction melting is 4×10 -3 Pa; in step S12, the vacuum degree of the vacuum quenching furnace is 6.0×10 -3 ~3.0×10 -3 Pa, the pressure in the furnace is -0.1~-0.02 MPa, the pressure of the argon gas flow in the nozzle that conveys the spray-cast melt is 0.4~3 atmospheres, and the linear speed of the copper roller is 10~150 m / s.

6. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: In step S2, the silicon-based raw material and the conductive agent are mixed in a mass ratio of 4:1; the conductive agent is (1) any one or more of industrial furnace black, channel black, thermal black, high-temperature graphitized carbon black, and acetylene black in the carbon black conductive agent; or (2) any one or more of artificial graphite and natural graphite in the graphite conductive agent; or (3) any one or more of fiber and nanotube conductive agents; or (4) any one or more of graphene conductive agents; or (5) any one or more of biomass carbon.

7. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: In step S2, the sand milling technique is as follows: the rotation speed is 300-8000 rpm, the sand milling time is 10-200 minutes, and the grinding medium is any one or more of ethanol, acetone or deionized water.

8. The method for preparing a silicon-based composite material of a silicon-based phase and a metal phase according to claim 1, characterized in that: In step S3, the ratio of the silicon-based raw material-conductive agent powder material to the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is 1 gram:150 milliliters; the ultrasonic time is 30 minutes; the mass ratio of the silicon-based raw material-conductive agent powder material to dopamine is 100:1~20:1; the ultrasonic time is continued for 20 minutes; the magnetic stirrer speed is 100~1000 rpm, and the time is 10~24 hours; the vacuum drying temperature is 30~120 degrees Celsius; the heating rate is 1~10 degrees Celsius / minute, the heating temperature is 500~1000 degrees Celsius, and the holding time is 0.5~2 hours; the gas introduced into the tubular furnace is any one or more of argon, nitrogen, hydrogen, argon-hydrogen mixture, and oxygen.

9. A silicon-based composite material comprising a silicon-based phase and a metal phase, prepared by the preparation method according to any one of claims 1 to 8.

10. Use of a silicon-based composite material of a silicon-based phase and a metal phase prepared by the preparation method according to any one of claims 1 to 8 in a low-temperature lithium-ion battery, characterized in that: The low-temperature lithium-ion battery is used at minus 30 degrees Celsius.

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