A sulfur-containing carbon source temperature-controlled coated silicon-tin-based negative electrode material, a preparation method and application thereof, a negative electrode, and a lithium ion battery

Abstract

The application discloses a sulfur-containing carbon source temperature control coated silicon-tin-based negative electrode material and a preparation method and application thereof, a negative electrode and a lithium ion battery, and relates to the technical field of lithium ion battery negative electrode materials. A silicon-tin-based composite material with a silicon-tin-based phase and a metal phase is used as a precursor, in-situ carbonization modification is performed on the precursor by using a sulfur-containing organic carbon source at a gradient temperature, and a high-performance sulfur-containing carbon source temperature control coated silicon-tin-based negative electrode material is prepared. The application has the advantages of simple and controllable process, low cost, high first coulomb efficiency of the prepared material, excellent cycle stability, suitability for large-scale production, and wide application prospect in the field of lithium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material, its preparation method and application, anode, and lithium-ion battery. Background Technology

[0002] With the rapid development of the new energy industry, the market has put forward higher requirements for the energy density and cycle life of lithium-ion batteries. At present, the theoretical specific capacity of commercial graphite anodes is low (372 mAh / g) and there is a safety hazard of lithium dendrite growth, which makes it difficult to meet the demand. Silicon-based anodes have become the preferred material for the next generation due to their advantages such as ultra-high theoretical specific capacity (3579 mAh / g), low discharge potential and abundant reserves. Silicon-tin composite materials combine the high capacity of silicon and the excellent conductivity of tin, but their industrialization still faces three major challenges: (1) Silicon expands drastically during charging and discharging, which easily leads to the pulverization and shedding of materials; (2) Volume changes cause the SEI film to repeatedly break and regenerate, continuously consuming active lithium and electrolyte, increasing polarization; (3) The low intrinsic electronic conductivity and lithium-ion diffusion rate of silicon restrict the rate performance.

[0003] Sulfur-containing carbon source coating modification provides a new approach for the comprehensive modification of silicon-tin-based anode materials. The introduction of sulfur can not only improve the ionic conductivity of the material by forming a fast ion conductor phase of metal sulfide, but also participate in the formation of the SEI film, producing a more stable and highly conductive SEI film. However, current research on sulfur-containing carbon source-coated silicon-tin-based materials suffers from poor matching between carbonization temperature and the degree of sulfidation and carbon layer structure, resulting in limited improvement in the electrochemical performance of the material. Therefore, developing a simple, low-cost, scalable method for preparing sulfur-containing carbon source-coated silicon-tin-based anode materials that can achieve precise matching between the degree of sulfidation and carbon layer structure through temperature control has significant theoretical and practical application value. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material, its preparation method and application, anode, and lithium-ion battery. The preparation method proposed in this invention is simple to operate and easy to implement, and the prepared silicon-tin-based anode material exhibits excellent comprehensive performance in lithium-ion batteries (such as high initial coulombic efficiency and excellent cycle stability).

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: One objective of this invention is to provide a method for preparing a temperature-controlled coated silicon-tin-based anode material containing a sulfur-containing carbon source. The method uses a silicon-tin-based composite material consisting of a silicon-tin-based phase and a metallic phase as a precursor, and performs in-situ coating and carbonization modification using a sulfur-containing organic carbon source at a gradient temperature to prepare a high-performance temperature-controlled coated silicon-tin-based anode material containing a sulfur-containing carbon source. The method specifically includes the following steps: S1: A silicon-tin based composite material consisting of a silicon-tin based phase and a metallic phase was prepared by suspension melting combined with rapid quenching technology; S2: The silicon-tin-based composite material is refined by sand milling with anhydrous ethanol as the grinding medium to obtain silicon-tin-based composite material powder with uniform particle size, thereby increasing the contact area between the material and the sulfur-containing carbon source and ensuring the uniformity of subsequent coating. S3: Disperse silicon-tin based composite powder in deionized water, add sulfur-containing organic carbon source, and magnetically stir at room temperature to make the carbon source uniformly adsorbed on the surface of the powder. Then place it in a forced-air drying oven to dry and obtain carbon source supported precursor composite. S4: Manually grind and sieve the carbon source-supported precursor composite, load it into a corundum ceramic boat, and place it in the constant temperature zone of a tube furnace. Introduce protective gas into the tube furnace. After the atmosphere inside the furnace is completely replaced, heat it to the specified temperature, hold it at that temperature, and then turn off the heating device. Allow the furnace to cool down naturally to room temperature to obtain the sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material.

[0006] Furthermore, in step S1, the silicon-tin based phase is a Si-Sn solid solution phase, specifically Si 95 Sn5 solid solution; the metallic phase is elemental Sn phase; the particle size of the silicon-tin based composite material is 1-10 μm.

[0007] Further, in step S1, the specific method of combining suspension melting with rapid quenching technology is as follows: high-purity silicon powder and high-purity tin powder are mixed at a mass ratio of 95:5 and then subjected to induction suspension melting at a melting temperature of 1400-1600℃. After melting, the mixture is rapidly cooled to room temperature using rapid quenching technology to obtain Si. 95 A silicon-tin based composite material consisting of a Sn5 solid solution phase and a elemental Sn metallic phase.

[0008] Further, in step S2, the process parameters of the sand milling technology are: the sand milling speed is 500-5000 r / min, the sand milling time is 20-40 min, and the solid-liquid ratio of anhydrous ethanol to silicon-tin based composite material during the sand milling process is 1:2-5.

[0009] Further, in step S3, the sulfur-containing organic carbon source is L-cysteine ​​or 2-hydrogen sulfate, and the sulfur-containing organic carbon source accounts for 5% of the mass of the silicon-tin-based composite material powder; the magnetic stirring speed is 300-500 r / min, the stirring time is 12-24 h; and the drying temperature is ≤20℃.

[0010] Further, in step S4, the sieve size is 200 mesh; the protective gas is an argon-hydrogen mixture with a volume ratio of argon to hydrogen of 9:1 and a gas flow rate of 50-100 sccm; the heating rate is 5℃ / min, the specified temperature is 500-700℃, and the holding time is 3h.

[0011] Another objective of this invention is to provide a sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material prepared by the above-described preparation method.

[0012] Another objective of this invention is to provide an application of a sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material in lithium-ion batteries.

[0013] Another objective of this invention is to provide a silicon-tin-based anode for lithium-ion batteries, comprising the aforementioned sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material. Specifically, using commercially available electrolytic copper foil (8-12 μm thick) as the current collector, the sulfur-containing carbon-coated silicon-tin-based anode material is used as the active material and mixed with 2.3 wt% sodium alginate aqueous binder at a mass ratio of 4:1. The mixture is stirred in a planetary mixer at 300 r / min for 2-4 hours to prepare a slurry with uniform viscosity. The slurry is coated onto the surface of the copper current collector using a doctor blade coating method, dried in a vacuum oven at 80°C for 12 hours, and then compacted by roller pressing under a pressure of 20 MPa for 60 seconds. Finally, it is cut into electrode sheets of specified specifications to obtain the silicon-tin-based anode for lithium-ion batteries.

[0014] Another objective of this invention is to provide a lithium-ion battery, which uses a silicon-tin based negative electrode, and the positive electrode is selected from any one of LiFePO4, LiCoO2, ternary layered materials, and lithium-rich manganese-based materials. The separator is a Celgard-2400 type polyolefin separator, and the electrolyte is a 1 mol / L LiPF6 electrolyte. The solvent is ethylene carbonate (EC), ethyl methyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1. 10 wt% of fluoroethylene carbonate (FEC) is added to the electrolyte as a film-forming additive. The CR2025 type coin cell lithium-ion battery is assembled in an anhydrous and oxygen-free glove box filled with high-purity argon (water and oxygen content <0.1 ppm) in the following order: "positive electrode shell - positive electrode sheet - separator - electrolyte - negative electrode sheet - gasket - spring sheet - negative electrode shell".

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation process is simple and controllable, and suitable for large-scale production: This invention abandons the complex template method and vapor deposition method of traditional nano-modification, and adopts the process route of suspension melting-rapid quenching-sand milling-in-situ carbon coating. All processes are conventional processes that are mature in industry. The equipment is simple to operate, the process parameters are easy to control, the production efficiency is high, and there is no need for expensive precious metal catalysts and special reagents, which greatly reduces the production cost and is suitable for large-scale industrial production. (2) Temperature control achieves precise matching of structure and performance: This invention achieves precise matching of the degree of sulfidation of the material and the degree of graphitization of the carbon layer by adjusting the carbonization temperature of 500-700℃. Among them, 600℃ is the optimal carbonization temperature. At this temperature, the conversion ratio of Sn to SnS is moderate. The SnS fast ion conductor phase formed can significantly improve the electronic and ionic conductivity of the material. At the same time, the degree of graphitization of the amorphous carbon layer is adapted to the volume buffering requirements of the material. The bonding force between the carbon layer and the silicon-tin matrix is ​​the strongest. (3) Multi-dimensional solution to the core defects of silicon-tin based materials: The present invention uses in-situ coating of sulfur-containing carbon source to form a nanoscale amorphous carbon layer on the surface of the material, which can effectively buffer the volume expansion during the charging and discharging process, prevent the material from breaking, pulverizing and falling off from the current collector; the sulfur and nitrogen non-metallic elements remaining in the carbon layer can participate in the formation of SEI film, prepare a more stable and highly conductive SEI film, and reduce the consumption of active lithium and electrolyte; the SnS fast ion conductor phase formed in the matrix can significantly improve the lithium ion diffusion rate and electronic conductivity, improve the lithium insertion and extraction dynamics of the material, and solve the defects of volume expansion, SEI film instability and insufficient intrinsic conductivity of silicon-tin based materials to a certain extent. (4) Excellent electrochemical performance of the material: The material prepared by the present invention under the optimal process at 600℃ has a capacity retention rate (66.85%) after 300 cycles that is significantly higher than that of the uncoated sample (5.81%) and the sample without sulfur carbon source coating (37.66%), which confirms the synergistic effect of in-situ coating of sulfur carbon source and temperature control process on improving the cycle stability of the material; (5) The raw materials are environmentally friendly and economical, and have strong compatibility: The sulfur-containing carbon source used in this invention is L-cysteine, which is widely available and inexpensive. The anhydrous ethanol, deionized water, sodium alginate and other reagents used are all safe, environmentally friendly and pollution-free, which meets the requirements of green chemistry development. The silicon-tin based anode material obtained is fully compatible with the cathode material, separator and electrolyte of conventional commercial lithium-ion batteries. It does not require major modifications to the existing lithium-ion battery production process and can be directly applied to the preparation of various types of lithium-ion batteries, with broad application prospects. Attached Figure Description

[0016] Figure 1 The following are the powder X-ray diffraction pattern, Raman pattern and Fourier transform infrared pattern of the Si-Sn based anode material prepared by L-cysteine ​​coating at 500℃ in Example 1. Figure 2 The figures for Example 1 are: (a) the first charge-discharge curve of Si-Sn based anode material prepared by L-cysteine ​​coating at 500℃; (b) the cycling performance at a current density of 1500 mA / g; and (c) and (d) the EIS curves before cycling and after 300 cycles at a current density of 1500 mA / g, respectively. Figure 3 The following are the powder X-ray diffraction pattern, Raman pattern and Fourier transform infrared pattern of the Si-Sn based anode material prepared by L-cysteine ​​coating at 600℃ in Example 2. Figure 4 The XPS spectra of C 1s, Si 2p, P 2p and Sn 4d of Si-Sn-based anode material powder prepared by L-cysteine ​​coating at 600℃ in Example 2 are shown. Figure 5 This is the TEM image of the Si-Sn-based anode material prepared by L-cysteine ​​coating at 600℃ in Example 2; Figure 6 The figures for Example 2 are: (a) the first charge-discharge curve of the Si-Sn-based anode material prepared by L-cysteine ​​coating at 600℃; (b) the cycling performance at a current density of 1500 mA / g; and (c) and (d) the EIS curves before cycling and after 300 cycles at a current density of 1500 mA / g, respectively. Figure 7 The following are the powder X-ray diffraction pattern, Raman pattern and Fourier transform infrared pattern of Si-Sn based anode material prepared by L-cysteine ​​coating at 700℃ in Example 3; Figure 8 The figures for Example 3 are: (a) the first charge-discharge curve of Si-Sn based anode material prepared by L-cysteine ​​coating at 700℃; (b) the cycling performance at a current density of 1500 mA / g; and (c) and (d) the EIS curves before cycling and after 300 cycles at a current density of 1500 mA / g, respectively. Figure 9 The figures for Example 4 are: (a) the initial charge-discharge curves of the Si-Sn-based anode material prepared by 2-hydrogen sulfate coating at 500°C, and (b) the cycle performance at a current density of 1500 mA / g. Figure 10 The graphs show the first charge-discharge curves at 150 mA / g and the cycling performance at 1500 mA / g for Si-Sn-based anode material without L-cysteine ​​coating after sand milling at 500 °C, as well as the cycling performance at 1500 mA / g for the Si-Sn-based anode material of Comparative Example 1. Figure 11The figures for Comparative Example 2 are: (a) the first charge-discharge curves at 150 mA / g and (b) the cycling performance at 1500 mA / g of the Si-Sn-based anode material after L-cysteine ​​carbonization and mixing and milling at 500 °C without L-cysteine ​​coating. Figure 12 The figures for Comparative Example 3 are the first charge-discharge curves of Si-Sn based anode materials prepared by citric acid coating at 500℃ (a) 150 mA / g and (b) the cycle performance at a current density of 1500 mA / g. Figure 13 The figures for Comparative Example 4 are the first charge-discharge curves of Si-Sn-based anode materials prepared by L-cysteine ​​coating at 800℃, and the cycle performance at a current density of 1500 mA / g, respectively. Detailed Implementation

[0017] To make the objectives and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0018] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0019] In all embodiments and comparative examples of this invention, the silicon powder and tin powder used were 99.99% high-purity powders, L-cysteine, citric acid, and sodium alginate were analytical grade reagents, and anhydrous ethanol, ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, LiPF6, and fluoroethylene carbonate were battery-grade reagents. The testing equipment used included an X-ray diffractometer (XRD, Cu Kα radiation), a Raman spectrometer (excitation wavelength 532 nm), a Fourier transform infrared spectrometer (FT-IR, KBr pellet method), and a blue battery testing system.

[0020] Example 1 1. Preparation of Si by L-cysteine ​​coating 95 The Sn5 anode material specifically includes the following steps: S1: Using a combination of suspension melting and rapid quenching technology, 95g of high-purity silicon powder and 5g of high-purity tin powder were mixed at a mass ratio of 95:5 and then subjected to induction suspension melting at a melting temperature of 1500℃. After melting, the mixture was rapidly cooled to room temperature using rapid quenching technology to obtain Si. 95 A silicon-tin based composite material (particle size 1-10 μm) consisting of Sn5 solid solution phase and elemental Sn metallic phase.

[0021] S2: The silicon-tin based composite material was refined by grinding with anhydrous ethanol as the grinding medium and a solid-liquid ratio of 1:3 at 3000 r / min for 30 min using sand milling technology to obtain silicon-tin based composite material powder with uniform particle size. S3: Disperse 10g of silicon-tin-based composite material powder in deionized water, add 0.5g of L-cysteine ​​(5% by mass), and stir magnetically at 400r / min for 12h at room temperature to allow L-cysteine ​​to be uniformly adsorbed on the surface of the powder. Then place it in an 18℃ forced-air oven to dry and obtain carbon source supported precursor composite. S4: The carbon source-supported precursor composite was manually ground and passed through a 200-mesh sieve. It was then placed in a corundum ceramic boat and placed in a tube furnace. An argon-hydrogen mixture (argon to hydrogen volume ratio of 9:1) was introduced into the tube furnace at a flow rate of 80 sccm. The temperature was increased to 500℃ at 5℃ / min and held for 3 hours. The furnace was then allowed to cool naturally to room temperature to obtain a sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material.

[0022] Figure 1 (a) Preparation of Si for L-cysteine ​​coating 95 X-ray diffraction (XRD) patterns of Sn5 anode material samples revealed the presence of Si and Sn phases. The Si peak exhibited the highest intensity, indicating that Si is the main phase, fully leveraging its high theoretical specific capacity. Simultaneously, the Sn peak was clearly present, and the SnS characteristic peak was significant, confirming the successful introduction of sulfur and its sulfidation reaction, forming the SnS phase. As a fast ion conductor, SnS effectively improves the electronic conductivity and ion transport efficiency of the electrode. Sn-based sulfides can reduce electrode reaction resistance and accelerate Li... + Diffusion. Its presence can effectively alleviate the inherent defects of poor intrinsic conductivity and low lithium-ion diffusion rate of Si. Figure 1 In the Raman spectrum of (b), 1347 cm⁻¹ -1 (D peak) and 1586cm -1 The G peak corresponds to amorphous carbon formed by the carbonization of L-cysteine. ID / IG = 0.914 indicates that the degree of graphitization of the carbon layer is within a reasonable range, and an appropriate amount of carbon layer defects can provide sufficient Li. + Adsorption and migration of active sites, while possessing a certain degree of graphitization to ensure electronic conduction efficiency, avoiding the problems of decreased conductivity due to excessive defects or insufficient active sites due to excessive graphitization. Figure 1 (c) is its infrared spectrum, at 673 cm⁻¹ -1 and 1611cm -1Sulfur-oxygen bonds were detected at the interface, confirming that sulfur was successfully introduced into the material. The synergistic effect of sulfur and oxygen bonds can optimize the composition and structure of the SEI film, enhance its mechanical stability and ionic conductivity, and further improve the electrode cycle performance.

[0023] 2. Preparation of Si-Sn based anode material anode sheet and test cell, and testing of electrode electrochemical performance: A silicon-tin based anode material prepared using L-cysteine ​​coating technology was mixed with sodium alginate aqueous binder at a mass ratio of 80:20, with the sodium alginate binder concentration being 2.3 wt%. The mixture was coated onto a copper current collector, dried in an oven, and the electrode sheet was compacted under a pressure of 20 MPa for 60 seconds to form an electrode sheet. These were then punched into 10 mm diameter discs and assembled into CR2025 coin cells using lithium sheets as the counter electrode to test the electrochemical performance of the electrodes. Battery assembly was completed in an argon-filled glove box. The separator used was a Celgard-2400 lithium-ion battery-specific separator. An electrolyte with a concentration of 1 mol / L was prepared using LiPF6 as the solute and a composite solvent of ethylene carbonate (EC), ethyl methyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, with 10 wt% fluoroethylene carbonate (FEC) additive added. After assembly, the electrode was allowed to stand for 12 hours before electrochemical performance testing. A constant current testing method was used to test the specific capacity and cycle performance of the electrode on an electrochemical testing instrument, with a voltage window of 0.01-1.5V.

[0024] In Example 1, the initial charge-discharge curves of the negative electrode material as a lithium-ion battery negative electrode at a current density of 150 mA / g are as follows: Figure 2 (a) Its initial charge reversible specific capacity is 1474.50 mAh / g, its initial coulombic efficiency is 71.23%, and its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 2 (b) After 300 cycles, the capacity retention was 58.13%, indicating generally poor electrochemical performance. Figure 2 (c) and (d) show the EIS impedance diagrams before and after 300 cycles. The impedance values ​​before and after the cycles are significantly higher than the other two groups, with the largest semicircle diameter at high frequencies. This indicates that the carbon layer formed at this temperature may have a loose structure, incomplete coating, or low crystallinity, leading to an unstable electrode / electrolyte interface and a large charge transfer impedance (Rct). Simultaneously, the slope of the low-frequency line is relatively gentle, indicating that lithium ion diffusion in the bulk material is also difficult. Therefore, the slow interfacial reaction kinetics of the sample prepared at 500℃ is a significant reason for its relatively poor electrochemical performance, although its electrochemical performance is still better than the comparative example. This testing method was used in all embodiments of this invention.

[0025] Example 2 1. The same method as in Example 1 was used, except that Si was prepared at a carbonization temperature of 600°C. 95 Sn5 anode material Figure 3 (a) Preparation of Si for L-cysteine ​​coating 95 The X-ray diffraction (XRD) pattern of the Sn5 anode material sample showed that as the preparation temperature increased, the SnS peaks were slightly enhanced overall, and the characteristic peaks of the SnS (120) and SnS (111) crystal planes were clearer, indicating that the degree of sulfidation was further improved compared with Example 1 and the conversion ratio of Sn to SnS increased. However, the Sn (200) and Sn (101) peaks were still clearly present, indicating that the sulfidation reaction was not completely carried out. Figure 3 In the Raman spectrum of (b), 1351 cm⁻¹ -1 With 1636cm -1 The D and G peaks at the location correspond to amorphous carbon formed by carbonization, with ID / IG=0.862. Compared to Example 1, the degree of graphitization is significantly increased, carbon layer defects are reduced, and the mechanical strength of the carbon layer can be improved. Figure 3 (c) Infrared characterization still detected sulfur-oxygen bonds, confirming the stable presence of sulfur and its ability to improve electrode chemical performance. Figure 4 Its XPS spectrum shows the presence of C–C, C–S, Si–O, and Si on the material surface. 0 SnS / C–S, SiS, and Sn 4+ Sn 0 The presence of sulfur in various chemical states, including C–S bonds, indicates successful sulfur doping into the carbon framework. This enhances the conductivity of the carbon layer, introduces defect sites, and promotes lithium-ion diffusion. The presence of SiS and SnS suggests that sulfur forms a stable sulfide interface layer with silicon and tin, potentially enhancing the adhesion between the carbon layer and active particles and mitigating structural damage caused by volume expansion during cycling. Simultaneously, Si… 0 and Sn 0 The presence of this indicates that some active substances remain in a metallic state, which is beneficial for electron conduction. Figure 5 TEM images of the carbon layer show a uniform carbon coating thickness, indicating that agglomeration does not occur at this temperature. Overall, the sulfur-doped carbon coating structure is stable at this temperature, and the sulfide interface layer helps improve the electrode's cycle stability and rate performance.

[0026] 2. Preparation of Si-Sn based anode material anode sheet and test cell, and testing of electrode electrochemical performance: The test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested. Example 2 yielded the first charge-discharge curve of the negative electrode material used as the negative electrode in a lithium-ion battery at a current density of 150 mA / g, as shown below. Figure 6(a) Its first-charge reversible specific capacity is 3421.36 mAh / g, its first-charge coulombic efficiency is 70.12%, and its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 6 (b) After 300 cycles, the capacity retention was 66.85%, which is superior to the electrochemical performance of the comparative example and Example 1. This further confirms that the Si prepared by carbon coating with an organic carbon source... 95 Sn5 material, due to the mechanical properties of its surface amorphous carbon, can react with Si. 95 In-situ coating of Sn5 material ensures the adhesion between the carbon layer and Si. 95 The Sn5 materials exhibit good bonding between each other, and the sulfur element remains in the carbon layer, which helps to improve the charge interface transfer ability and electronic conductivity of the carbon layer, thus significantly promoting the cycling stability of the sample. Figure 6 (c) and (d) show the impedance spectra before and after 300 cycles. Before and after cycling, the diameter of the high-frequency semicircle significantly decreases, indicating a significant reduction in charge transfer impedance. This is attributed to the higher temperature promoting more complete pyrolysis and graphitization of the carbon source, forming a denser and more conductive carbon coating layer, which improves the electronic conductivity of the electrode and stabilizes the interface. However, the improvement in the low-frequency slope is limited, and the impedance increase after cycling is still significant, suggesting that the bonding force between the carbon layer structure and the matrix, or its own mechanical strength, is not yet optimal at this temperature, and the interface stability needs further improvement during long-term cycling.

[0027] Example 3 1. The same method as in Example 1 was used, except that Si was prepared at a carbonization temperature of 700°C. 95 Sn5 anode material Figure 7 (a) Preparation of Si for L-cysteine ​​coating 95 The X-ray diffraction (XRD) pattern of the Sn5 anode material sample showed a significant decrease in the SnS peak intensity compared to Example 2, indicating a reduced degree of sulfidation, a lower conversion rate of Sn to SnS, the formation of H2S in the intermediate stage, and an increase in Sn phase residue. Insufficient sulfidation prevents SnS from fully utilizing its advantages as a fast ion conductor, hindering the improvement of both electronic and ionic conductivity of the electrode. Furthermore, excessive Sn phase residue exacerbates the volume expansion effect during charge and discharge, leading to electrode structure damage and rapid capacity decay. Figure 7 In the Raman spectrum of (b), 1331 cm⁻¹ -1 With 1596cm -1The D and G peaks at the location correspond to amorphous carbon, with ID / IG=0.855. The degree of graphitization is further reduced compared to Example 2, and the number of defects in the carbon layer increases. Although this can increase the number of active sites, the electronic conduction efficiency drops significantly, making it impossible to form a continuous and stable conductive network. This makes it difficult to alleviate the problem of poor intrinsic conductivity of Si. At the same time, the mechanical strength of the carbon layer is weakened, which cannot effectively buffer the volume expansion of Si, resulting in a decrease in the stability of the SEI film. Figure 7 (c) Although the infrared characterization still detected sulfur-oxygen bonds and nitrogen-hydrogen bonds, the insufficient degree of sulfidation prevented the full play of the interface modification effect of nitrogen and sulfur elements, and the electrode electrochemical performance was further inferior to that of Example 1 and Example 2.

[0028] 2. Preparation of Si-Sn based anode material anode sheet and test cell, and testing of electrode electrochemical performance: The test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested. Example 3 yielded the first charge-discharge curve of the negative electrode material used as the negative electrode in a lithium-ion battery at a current density of 150 mA / g, as shown below. Figure 8 (a) Its initial reversible specific capacity is 2252.36 mAh / g, and its initial coulombic efficiency is 63.92%, with a decrease in initial efficiency. Its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 8 (b) After 300 cycles, the capacity retention was 53.95%, which is slightly lower than the cycling performance at 600℃, but still significantly better than Comparative Example 1. L-cysteine-coated Si 95 In Sn5 material, the amorphous carbon layer on the surface can mitigate the pulverization caused by volume expansion, ensuring the adhesion between the carbon layer and Si. 95 The Sn5 materials exhibit good bonding between each other, and the sulfur element remains in the carbon layer, which helps to improve the charge interface transfer ability and electronic conductivity of the carbon layer, thus significantly promoting the cycling stability of the sample. Figure 8 (c) and (d) show their EIS impedance plots. The impedance values ​​decrease further both before and after 300 cycles, but the impedance increase slightly rebounds after cycling, possibly due to excessive graphitization of the carbon layer or sulfur decomposition, leading to increased carbon layer brittleness and susceptibility to microcracks during cycling. Despite this, the overall impedance remains low, indicating that high-temperature treatment is beneficial for forming a highly conductive carbon network, but structural stability and interface matching must be considered. Overall, 600℃ is the optimal treatment temperature, balancing conductivity and cycling stability.

[0029] Example 4 The test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested. The difference was that L-cysteine ​​was replaced with 2-hydrogen sulfate-coated Si. 95Sn5 anode material. The first charge-discharge curve of the anode material obtained in Example 4 as a lithium-ion battery anode at a current density of 150 mA / g is shown below. Figure 9 (a) Its first-charge reversible specific capacity is 2623.36 mAh / g, its first coulombic efficiency is 80.92%, and its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 9 (b) After 300 cycles, the capacity retention was 60.83%, which is also significantly better than the comparative example. Si prepared by coating with 2-hydrogen sulfate 95 The Sn5 material demonstrates that sulfur enhances the charge transfer capacity and electronic conductivity of the carbon layer, significantly contributing to the cycling stability of the sample.

[0030] Comparative Example 1 The preparation process is basically the same as in Example 1, except that L-cysteine ​​coating technology is not used, and the raw material is Si after sand milling. 95 The Sn5 anode material was used to prepare a test battery using the same method as in Example 1, and its electrochemical performance was tested.

[0031] The initial charge-discharge curves at a current density of 150 mA / g are as follows: Figure 10 (a) Its first-charge reversible specific capacity is 3762.34 mAh / g, its first coulombic efficiency is 76.79%, and its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 10 (b) After 300 cycles, the capacity retention rate was 5.81%, and the negative electrode material obtained in Comparative Example 1 basically lost its electrochemical activity. This indicates that the sample without L-cysteine ​​coating has extremely poor cycling stability, exhibits severe volume expansion, and the active material may detach from the current collector, leading to the loss of electrochemical activity.

[0032] Si without L-cysteine ​​coating 95The lack of a carbon layer on the surface of Sn5 materials means they cannot buffer the dramatic volume expansion of the silicon substrate during charge and discharge, leading to electrode material pulverization and breakage, and delamination of the active material from the current collector, resulting in failure. Simultaneously, without the interfacial modification of a sulfur-doped carbon layer, the SEI film forms directly on the surface of the silicon-tin particles, repeatedly rupturing and regenerating under volume change stress, continuously consuming active lithium and electrolyte, causing a sharp increase in electrode impedance and rapid capacity decay. In stark contrast, the sulfur-doped carbon layer formed by in-situ L-cysteine ​​coating in this example not only effectively buffers volume expansion and maintains electrode structural integrity but also significantly improves the electronic conductivity and interfacial stability of the electrode by forming a SnS fast ion conductor phase and participating in SEI film construction. This comparative example fully demonstrates the crucial role of in-situ sulfur-containing carbon source coating in improving the cycle stability of silicon-tin based anode materials. Therefore, it further proves that the amorphous coating layer formed on the sample surface prepared by L-cysteine ​​coating can effectively alleviate sample volume expansion, and the inorganic material formed during charge and discharge has high conductivity and good mechanical properties, which has a significant effect on improving the electrochemical performance of the sample.

[0033] Comparative Example 2 The preparation process is basically the same as in Example 1, except that L-cysteine ​​coating technology is not used. Instead, L-cysteine ​​is carbonized and then combined with Si after sand milling. 95 Sn5 anode material was stirred, coated, and assembled into a battery. The test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested.

[0034] The initial charge-discharge curves at a current density of 150 mA / g are as follows: Figure 11 (a) Its first-charge reversible specific capacity is 1623.1 mAh / g, its first-charge coulombic efficiency is 74.64%, and its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 11 (b) The capacity retention rate was 37.66% after 300 cycles. This indicates that the physically mixed carbonized L-cysteine ​​and the active material could not form a uniform coating layer, resulting in the loss of electrochemical activity of the sample.

[0035] The main reason for the poor performance of this comparative example is that carbonizing L-cysteine ​​separately before physically mixing it with the active material fails to form a continuous, uniform, and tightly bonded sulfur-doped carbon coating layer on the surface of the silicon-tin particles. This non-in-situ mixing method results in only a loose physical contact between the carbon material and the active material, lacking effective interfacial bonding. During charge and discharge, the carbon layer is easily peeled off from the particle surface, failing to buffer the drastic volume expansion of the silicon substrate. Simultaneously, the exposed silicon-tin surface directly contacts the electrolyte, causing the SEI film to continuously rupture and regenerate under repeated volume change stress, continuously consuming active lithium and electrolyte, leading to increased electrode impedance and rapid capacity decay. Furthermore, free carbon particles may block ion diffusion channels in the electrode, further deteriorating electrochemical performance. In stark contrast, the in-situ coating process in this example allows L-cysteine ​​to be uniformly deposited on the surface of the silicon-tin particles during pyrolysis, forming a sulfur-doped carbon layer with good mechanical properties and electronic conductivity, and synergistically improving the cycle stability of the electrode by forming a SnS fast ion conductor phase. This comparative example further demonstrates the crucial role of in-situ carbon coating in improving the electrochemical performance of silicon-tin based anode materials. Therefore, it is further demonstrated that the amorphous coating layer formed on the surface of the sample prepared by carbon coating with organic carbon source can effectively alleviate the volume expansion of the sample and has a significant effect on improving the electrochemical performance of the sample.

[0036] Comparative Example 3 The preparation process was basically the same as in Example 1, except that citric acid was used instead of L-cysteine ​​organic carbon source for coating. The preparation process was the same as in Example 1, and the test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested. The initial charge-discharge curves at a current density of 150 mA / g are shown below. Figure 12 (a) Its first-charge reversible specific capacity is 2259.67 mAh / g, its first coulombic efficiency is 70.46%, and its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 12 (b) After 300 cycles, the capacity retention rate was 50.88%. The cycling performance of the negative electrode material obtained in this comparative example is better than that of Comparative Example 1 and Comparative Example 2, but worse than that of all examples. This indicates that L-cysteine ​​coating at 600°C can significantly enhance its cycling stability.

[0037] The main reason for the poor performance of this comparative example is that citric acid, as a common organic carbon source, can only form an amorphous carbon layer after carbonization, lacking the chemical modification effect of sulfur. Although the carbon layer itself can provide a certain volume buffer and electronic conductivity, it cannot form a SnS fast ion conductor phase, nor can it leverage the interface optimization effect brought about by sulfur's participation in SEI film construction. In contrast, L-cysteine, as a sulfur-containing carbon source, not only forms a carbon layer during carbonization but also achieves uniform sulfur doping. It reacts with Sn in the silicon-tin matrix to generate a SnS fast ion conductor phase, significantly improving the ionic conductivity of the material. At the same time, sulfur participates in the formation of the SEI film, making it more stable and dense, reducing the consumption of active lithium. In addition, the sulfur-doped carbon layer has a stronger interfacial bond with the silicon-tin matrix, which can more effectively buffer volume expansion. This comparative example fully demonstrates that relying solely on ordinary carbon layer coating is insufficient to fully realize the performance potential of silicon-tin based anode materials. In-situ coating with sulfur-containing carbon sources plays an irreplaceable role in achieving a synergistic improvement in the structural stability and electrochemical performance of electrode materials. Therefore, it is further demonstrated that the amorphous coating layer formed on the surface of the sample prepared by L-cysteine ​​coating can more effectively alleviate the volume expansion of the sample. The inorganic material formed during the charge and discharge process has high conductivity and good mechanical properties, which has a significant effect on improving the electrochemical performance of the sample.

[0038] Comparative Example 4 The same method as in Example 1 was used, except that Si was prepared at a carbonization temperature of 800°C. 95 Sn5 anode material. A test battery was prepared using the same method as in Example 1, and its electrochemical performance was tested. The first charge-discharge curves of this comparative example 4, obtained using the anode material as a lithium-ion battery anode, at a current density of 150 mA / g are shown below. Figure 13 (a) Its initial reversible specific capacity is 1452.36 mAh / g, and its initial coulombic efficiency is 63.92%, with a decrease in initial efficiency. Its cycling performance at a current density of 1500 mAh / g ranks among the best. Figure 13 (b) After 300 cycles, the capacity retention rate was 53.95%, which is relatively poor compared to the cycling performance at 500-700℃.

[0039] The main reason for the poor performance of this comparative example is that the excessively high carbonization temperature (800℃) leads to unfavorable structural evolution of the material. On the one hand, SnS undergoes a decomposition reaction under a high-temperature reducing atmosphere (argon-hydrogen mixture): SnS + H2 → Sn + H2S↑, which significantly reduces the content of the SnS fast ion conductor phase in the matrix, thus losing its positive role in improving ionic conductivity and buffering volume expansion. On the other hand, the carbon layer becomes excessively graphitized at excessively high temperatures, increasing the ID / IG ratio and increasing carbon layer defects. Although conductivity is improved to some extent, the carbon layer becomes more brittle and its mechanical strength decreases, making it difficult to effectively buffer the severe volume expansion of the silicon matrix, leading to carbon layer cracking and SEI film instability during cycling. In summary, 800℃ exceeds the optimal temperature control window for this system. The decomposition of the SnS phase and the degradation of the carbon layer together lead to a decrease in the cycling stability and coulombic efficiency of the electrode, further verifying that 600℃ is the preferred temperature for sulfur-containing carbon source-coated silicon-tin based anode materials.

[0040] In addition to the above embodiments: In some other embodiments of the present invention, the suspension melting temperature of step S1 is 1400°C or 1600°C.

[0041] In some other embodiments of the present invention, the milling speed in step S2 is 500 r / min, the milling time is 40 min, and the solid-liquid ratio of anhydrous ethanol to silicon-tin based composite material during the milling process is 1:2.

[0042] In some other embodiments of the present invention, the milling speed in step S2 is 5000 r / min, the milling time is 20 min, and the solid-liquid ratio of anhydrous ethanol to silicon-tin based composite material during the milling process is 1:5.

[0043] In some other embodiments of the present invention, the magnetic stirring speed in step S3 is 300 r / min and the stirring time is 24 h.

[0044] In some other embodiments of the present invention, the magnetic stirring speed in step S3 is 500 r / min and the stirring time is 18 h.

[0045] In some other embodiments of the present invention, the gas flow rate of the protective gas in step S4 is 50 sccm or 100 sccm.

[0046] The sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode materials prepared in the above embodiments all exhibit excellent comprehensive performance in lithium-ion batteries (such as high initial coulombic efficiency and excellent cycle stability).

[0047] In summary, with Si 95 Using a material composed of Sn5 solid solution and elemental Sn as a precursor, after being refined by sand milling, it is then... Cysteine ​​was used as a sulfur-containing carbon source for in-situ coating. A composite material with a surface-coated amorphous carbon layer and a SnS fast-ion conductor phase in the matrix was prepared by gradient temperature (500-700℃) heat treatment under a protective atmosphere. The key to this invention is the discovery and verification that at a specific temperature of 600℃, the optimal balance between the SnS fast-ion conductor phase content and the conductivity of the carbon layer can be achieved: at this temperature, the degree of sulfidation is moderate, the SnS characteristic peak is significant, effectively improving the electronic / ionic conductivity of the material and buffering volume expansion; simultaneously, the degree of graphitization of the carbon layer (ID / IG=0.862) is optimally matched with mechanical strength, and the interfacial bonding is strong. The resulting material achieved a capacity retention of 66.85% after 300 cycles at a current density of 1500 mA / g, significantly better than other temperatures and comparative examples. This invention features a simple and controllable process, low cost, and the prepared material exhibits high initial coulombic efficiency and excellent cycle stability, making it suitable for large-scale production and showing broad application prospects in the lithium-ion battery field.

[0048] 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 within the protection scope of the present invention.

Claims

1. A method for preparing a temperature-controlled coated silicon-tin-based anode material containing a sulfur-containing carbon source, characterized in that: Using a silicon-tin-based composite material combining silicon-tin-based and metallic phases as a precursor, a high-performance sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material is prepared by in-situ coating and carbonization modification with a sulfur-containing organic carbon source under gradient temperatures. The specific steps include the following: S1: A silicon-tin based composite material consisting of a silicon-tin based phase and a metallic phase was prepared by suspension melting combined with rapid quenching technology; S2: The silicon-tin based composite material was refined by sand milling with anhydrous ethanol as the grinding medium to obtain silicon-tin based composite material powder with uniform particle size. S3: Disperse silicon-tin based composite powder in deionized water, add sulfur-containing organic carbon source, and magnetically stir at room temperature to make the carbon source uniformly adsorbed on the surface of the powder. Then place it in a forced-air drying oven to dry and obtain carbon source supported precursor composite. S4: Manually grind and sieve the carbon source-supported precursor composite, load it into a corundum ceramic boat, place it in a tube furnace, introduce protective gas into the tube furnace, heat it to the specified temperature, hold it at the temperature, and then allow it to cool naturally to room temperature to obtain the sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material.

2. The preparation method according to claim 1, characterized in that: In step S1, the silicon-tin based phase is a Si-Sn solid solution phase, specifically Si 95 Sn5 solid solution; the metallic phase is elemental Sn phase; the particle size of the silicon-tin based composite material is 1-10 μm.

3. The preparation method according to claim 1, characterized in that: In step S1, the specific method of combining suspension melting with rapid quenching technology is as follows: high-purity silicon powder and high-purity tin powder are mixed at a mass ratio of 95:5 and then subjected to induction suspension melting at a melting temperature of 1400-1600℃. After melting, the mixture is rapidly cooled to room temperature using rapid quenching technology to obtain Si. 95 A silicon-tin based composite material consisting of a Sn5 solid solution phase and a elemental Sn metallic phase.

4. The preparation method according to claim 1, characterized in that: In step S2, the process parameters of the sand milling technology are as follows: the sand milling speed is 500-5000 r / min, the sand milling time is 20-40 min, and the solid-liquid ratio of anhydrous ethanol to silicon-tin based composite material during the sand milling process is 1:2-5.

5. The preparation method according to claim 1, characterized in that: In step S3, the sulfur-containing organic carbon source is L-cysteine ​​or 2-hydrogen sulfate, and the sulfur-containing organic carbon source accounts for 5% of the mass of the silicon-tin-based composite material powder; the magnetic stirring speed is 300-500 r / min, the stirring time is 12-24 h, and the drying temperature is ≤20℃.

6. The preparation method according to claim 1, characterized in that: In step S4, the sieve size is 200 mesh; the protective gas is an argon-hydrogen mixture with a volume ratio of argon to hydrogen of 9:1 and a gas flow rate of 50-100 sccm; the heating rate is 5℃ / min, the specified temperature is 500-700℃, and the holding time is 3h.

7. The sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material prepared by any one of the preparation methods described in claims 1-6.

8. The application of the sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material as described in claim 7 in lithium-ion batteries.

9. A lithium-ion battery negative electrode, characterized in that: It includes the sulfur-containing carbon source temperature-controlled coated silicon-tin-based anode material as described in claim 7.

10. A lithium-ion battery, comprising a negative electrode, characterized in that: The negative electrode is the negative electrode described in claim 9.

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