Silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of negative electrode materials, in particular to a silicon-carbon negative electrode material and a preparation method and application thereof. The preparation method comprises the following steps: S1, adding a porous silicon material and an organic carbon source into an ethanol solution, then adding transition metal salt, carrying out uniform ultrasonic dispersion, and carrying out spray drying to obtain a powder sample; s2, performing a high-temperature carbonization process on the powder sample obtained in the step S1 to obtain pSi-C-M; and S3, the pSi-C-M obtained in the S2 is heated to a certain temperature under atmosphere protection, then carbon-containing gas is introduced, heat preservation is conducted for a period of time, cooling is conducted to the room temperature, and the pSi-C-M-C is obtained. The pores or the surface of the porous silicon material are filled with the organic carbon source through a spraying method, so that the electron transmission capability can be improved, the structural stability can be improved, and the tap density can be improved; meanwhile, a chemical vapor deposition method is used for outer layer carbon wrapping, permeation of electrolyte is isolated, the specific surface area is reduced, and the mechanical strength of the material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and particularly relates to a silicon-carbon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of new energy vehicles and portable electronic devices, the demand for high-energy density batteries is increasing continuously. Silicon-based anode materials are regarded as key materials for improving the energy density of batteries due to their high theoretical specific capacity (about 4200 mAh / g). Problems such as particle cracking, pulverization, electrode expansion, and active material shedding caused by the volume expansion of silicon anode materials during the lithium deintercalation / insertion process, thus leading to the attenuation of electrochemical performance. In addition, the high surface activity of silicon anode materials causes serious interfacial side reactions, consumes the stock of active lithium, and results in their low Coulomb efficiency.

[0003] Researchers have used a large number of methods to improve the performance of silicon anode materials, such as modification by means of nanosizing, surface coating, element doping, etc., which greatly improves the commercial application prospects of silicon materials. At present, introducing a carbon matrix on the silicon surface to construct a silicon-carbon composite material is one of the most promising solutions. Carbon materials can not only improve the conductivity of the electrode, but also serve as a buffer material for the expansion of silicon, which is the future direction of its commercialization. By changing the preparation process of silicon-carbon materials, their electrochemical stability and lower expansion rate can be improved.

[0004] For example, in the literature "Suitable Thickness of Carbon Coating Layers for Silicon Anode", Jinsen Gao et al. used chemical vapor deposition to coat an amorphous carbon layer on the surface of nanosilicon. The prepared Si@C composite material exhibited excellent electrical conductivity and strong mechanical strength, retaining a capacity of 3019 mAh / g at 0.2 A / g and 1647 mAh / g at a current density of 5 A / g. A suitable carbon coating can effectively alleviate the volume expansion of the battery and the instability of the SEI film. In "Microsized Silicon / Carbon Composite Anodes through In Situ Polymerization of Phenolic Resin onto Silicon Microparticles for High-Performance Lithium-Ion Batteries", Xiang Guo et al. designed a silicon / carbon (Si / C) composite anode by in situ polymerizing phenolic resin (PF) on SiMPs and coating them with pyrolysis. After 400 cycles at 2 A / g, it was 1283 mAh / g, and the full battery using lithium iron phosphate and μSi@PF could maintain 87.7% of its capacity.

[0005] In the literature "Silicon@Graphene Composite Prepared by Spray-drying Method as Anode for Lithium Ion Batteries", Mingru Su et al. prepared a Silicon@Graphene composite material as the anode material by combining the spray-drying method with a low-temperature reduction technique. The Silicon@Graphene powder is in the shape of a micron-sized sphere, and the nanosilicon particles are embedded in the three-dimensional conductive network assembled by graphene sheets. When the mass ratio of silicon to graphene oxide reaches 1:4, it has a high initial capacity of 1298.1 mAh / g at a current density of 100 mA / g. In the literature "Three-dimensional Porous Pitch-derived Carbon Coated Si Nanoparticles-CNT Composite Microsphere with Superior Electrochemical PePRormance for Lithium Ion Batteries", Gi Dae Park et al. successfully synthesized a three-dimensional porous pitch-derived carbon-coated silicon nanoparticle-carbon nanotube (Si-CNT@PC) composite microsphere through a spray pyrolysis and subsequent pitch infiltration process. Uniformly distributed Si nanoparticles, acid-treated multi-walled CNTs, and polystyrene (PS) nanoparticles form a porous-structured Si-CNT composite microsphere through spray pyrolysis. The pitch dissolved in tetrahydrofuran is uniformly infiltrated and then carbonized to obtain the Si-CNT@PC microsphere. Compared with the uncoated carbon Si-CNT microsphere, the uniquely structured Si-CNT@PC microsphere has superior electrochemical performance.

[0006] Although the core-shell structured silicon-carbon effectively improves the electrochemical stability of silicon materials, the brittle carbon layer is not sufficient to overcome the stress impact during silicon expansion, and it will still cause the pulverization of silicon particles and the deterioration of the solid electrolyte interface during long-term lithium deintercalation and intercalation processes, ultimately resulting in the failure of the silicon electrode. At the same time, due to the low tap density and compaction density of silicon-carbon, it further hinders its commercial application. Summary of the Invention

[0007] The object of the present invention is to propose a silicon-carbon anode material, its preparation method and application in view of the above-mentioned deficiencies of the prior art.

[0008] The first object of the present invention is to provide a preparation method of a silicon-carbon anode material, which includes the following steps:

[0009] S1: Add the porous silicon material and the organic carbon source into an ethanol solution, then add the transition metal salt. After ultrasonic dispersion to uniformity, a spray solution is obtained. The spray solution is spray-dried to obtain a powder sample;

[0010] S2: Under the protection of an atmosphere, the powder sample obtained in S1 is subjected to a high-temperature carbonization process in a two-stage heating manner to obtain pSi@C@M;

[0011] S3: Under the protection of an atmosphere, heat the pSi@C@M obtained in S2 to a certain temperature, then introduce a carbon-containing gas, keep it warm for a period of time, and cool it to room temperature and take it out to obtain pSi@C@M@C.

[0012] Further, in S1, the porous silicon material is micron-scale three-dimensional porous silicon.

[0013] Further, in S1, the organic carbon source is one or more of phenolic resin, glucose, sucrose, citric acid, and urea.

[0014] Further, in S1, the mass ratio of the porous silicon material to the organic carbon source is 1:0.2 - 2; preferably 1:0.2 - 1.0; more preferably 1:0.4 - 1.0; most preferably 1:0.8.

[0015] In the present invention, by controlling the mass ratio of the porous silicon material to the organic carbon source, the degree of filling of the organic carbon source in the pores of the porous silicon material and the thickness of the surface are controlled. If the filling degree is insufficient, it may be difficult to alleviate excessive volume expansion, and the tap density is insufficient, and the conductive transport network is discontinuous, ultimately affecting the performance of the sample; if the filling degree is too high, during the subsequent heat treatment process, the excessive content of the organic carbon source may increase the oxidation degree of the silicon material and the capacity of the final silicon-carbon product. Therefore, the control of the mass ratio of the porous silicon material to the organic carbon source in the present invention is extremely important.

[0016] Further, the addition amount of the transition metal salt is 1 - 5% of the total mass of the silicon material and the organic carbon source; preferably 3%.

[0017] In the present invention, by controlling the addition amount of the transition metal salt to be only within 5%, and in-situ catalyzing the formation of a carbon nanotube conductive network and metal carbide, the conductivity of the anode material is further improved, and the cycle and rate performance are highly improved. An excessive addition content cannot form a CNT conductive network.

[0018] Further, in S1, the transition metal salt is one or more of iron, nickel, cobalt salts, etc.; preferably nickel acetate.

[0019] The present invention controls the formation and content of CNTs by controlling the type and addition amount of transition metal salts. If the type and addition amount are not properly controlled, the CNT conductive network and transition metal carbides cannot be formed, which affects the conductivity of the material and ultimately affects the electrochemical performance and expansion rate of the material. Therefore, the control of the type and addition amount of transition metal salts in the present invention is extremely important.

[0020] Further, in the step S1, the solid content of the spray solution is 8-20%, preferably 8-15%, and more preferably 12%.

[0021] Further, in the step S1, in the spray operation, the inlet temperature is 100-200°C, preferably 120-180°C, and more preferably 160°C; the feeding rate is 5-30 ml / min, preferably 10 ml / min; the flow rate is 10-50 ml / min, preferably 20-40 ml / min, and more preferably 30 ml / min.

[0022] The present invention controls the formation of the inlaid model structure of the silicon-carbon material and the uniform filling degree of the organic carbon source by controlling factors such as the solid content, inlet temperature, feeding rate, and gas flow rate during the spraying process. If factors such as the solid content, inlet temperature, feeding rate, and gas flow rate are not properly controlled, the carbon layer cannot be uniformly filled into the pores or surface of the porous silicon material, resulting in uneven carbon distribution and affecting the electrochemical performance of the material. Therefore, the control of the solid content, inlet temperature, feeding rate, and flow rate in the present invention is extremely important.

[0023] Further, in the step S2, the inert atmosphere is one or more of atmospheres such as Ar, Ar / H2, N2, etc.; preferably Ar / H2.

[0024] Further, in the step S2, the two-stage heating is respectively heating to 400-800°C, preferably 600°C, at a rate of 1-10°C / min, preferably 5°C / min, and holding for 2.0 h; then heating to 900-1100°C, preferably 950°C, at a rate of 1-10°C / min, preferably 5°C / min, and holding for 3.0 h.

[0025] The selection of the heating rate and holding temperature for the two-stage heating in the present invention is very crucial. The purpose of the first-stage holding is pre-carbonization, allowing the transition metal salt to catalytically decompose the organic carbon source to generate carbon nanotubes and construct a conductive network; the second stage is to improve the graphitization degree. If the heating rate is too fast and the holding temperature is too low, the carbonization reaction will be insufficient, thereby affecting the carbon composition and structure of the material and ultimately affecting the electrochemical performance; if the heating rate is too slow and the holding temperature is too high, the internal thermal stress of the material will increase, thereby causing cracks and fragmentation of the material, and will also lead to excessive graphitization, thereby increasing the brittleness of the material and affecting its structural stability.

[0026] Further, in S3, the heat preservation temperature is 600-900°C; preferably 700-800°C; more preferably 700°C.

[0027] Further, in S3, the carbon-containing gas is one or more of methane, benzene, and acetylene gas; preferably acetylene.

[0028] Further, in S3, the feeding rate of the carbon-containing gas is 2-10 ml / min, and the heat preservation time is 0.2-3 h; preferably 4-8 ml / min, more preferably 5 ml / min; the heat preservation time is 1 h.

[0029] The control of the heat preservation temperature and the gas ventilation rate in the CVD process of the present invention is very crucial, which directly affects the thickness of the outer carbon coating. If the thickness of the outer coating is too low, it may not effectively protect the internal silicon material, resulting in side reactions with the electrolyte and affecting the cycle stability and safety of the battery. On the contrary, if the thickness of the outer coating is too high, it may increase the internal resistance of the material and affect the diffusion rate of lithium ions, thereby affecting the rate performance and charge-discharge efficiency of the battery.

[0030] The second object of the present invention is to provide a silicon-carbon negative electrode material prepared by the above preparation method.

[0031] The present invention obtains a silicon-carbon material at a low temperature (below 1200°C) while ensuring structural stability, which is used as a negative electrode material for lithium-ion batteries and can improve the electrochemical performance of the material.

[0032] The third object of the present invention is to provide an application of the silicon-carbon negative electrode material as described above, used as a negative electrode material for lithium batteries.

[0033] The present invention fills the pores and surfaces of porous silicon materials with organic carbon sources by spray method. The obtained silicon-carbon composite material has an irregular block structure. With porous silicon as the matrix, carbon materials and metal carbides are distributed in the pores of porous silicon, and the porous silicon and carbon materials are in an interlocking model structure. On the one hand, it can improve the tap density and compaction density of the material and reduce the specific surface area, greatly reducing the degree of side reactions and improving the cycle stability of the material; on the other hand, the high carbon content and stable structure effectively enhance the electron transport ability. At the same time, during the subsequent cycle process, the carbon layer is difficult to fall off, effectively inhibiting the expansion of silicon, maintaining good cycle stability and reducing the expansion rate.

[0034] The present invention combines the spraying method with the chemical vapor deposition method to fill the pores or surfaces of porous silicon materials with an organic carbon source, which can improve the electron transport ability, enhance the structural stability, and increase the tap density. At the same time, the outer carbon layer prepared by the chemical vapor deposition method will fill the voids of the previous organic carbon, wrap the entire structure, isolate the penetration of the electrolyte, reduce the porosity and specific surface area of the silicon-carbon material, and improve the mechanical strength of the material. The synergistic effect of the internal organic carbon source and the external CVD carbon layer endows the obtained silicon-carbon particles with excellent structural stability, forms a continuous conductive network, and significantly improves the electron conductivity of the silicon-based material.

[0035] In addition, the preparation method of the present invention is simple, the process is short, the preparation temperature is low, and the potential safety hazards during the preparation process are low. The raw materials of the present invention are cheap and easily available, which is conducive to saving production costs and large-scale commercial production. Brief Description of the Drawings

[0036] Figure 1 XRD patterns of pS@PRC@Ni (a) and pSi@PRC@Ni@C (b) in Example 1 of the present invention;

[0037] Figure 2a Scanning electron microscope image of pS@PRC@Ni in Example 1 of the present invention;

[0038] Figure 2b Scanning electron microscope image of pSi@PRC@Ni@C in Example 1 of the present invention;

[0039] Figure 3 Transmission electron microscope images of pS@PRC@Ni (a) and pSi@PRC@Ni@C (b) in Example 1 of the present invention;

[0040] Figure 4 Tap density graphs (a) and BET graphs (b) of pS@PRC@Ni and pSi@PRC@Ni@C in Example 1 of the present invention;

[0041] Figure 5 Electrochemical cycling performance graphs of pS@PRC@Ni and pSi@PRC@Ni@C in Example 1 of the present invention;

[0042] Figure 6 Rate performance graphs of pS@PRC@Ni and pSi@PRC@Ni@C in Example 1 of the present invention;

[0043] Figure 7 Scanning electron microscope image of pSi@PRC@Ni@BC in Example 2 of the present invention;

[0044] Figure 8 Scanning electron microscope image of nSi@PRC@Ni@C in Comparative Example 1 of the present invention;

[0045] Figure 9 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 2 of the present invention;

[0046] Figure 10 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 3 of the present invention;

[0047] Figure 11 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 4 of the present invention;

[0048] Figure 12 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 5 of the present invention;

[0049] Figure 13 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 6 of the present invention.

[0050] Figure 14 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 7 of the present invention;

[0051] Figure 15 This is the electrochemical cycling performance graph of pSi@PRC@Ni@C for Comparative Example 8 of the present invention. Detailed implementation manners

[0052] The following are specific examples of the present invention and in combination with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these examples.

[0053] Example 1

[0054] A preparation method for constructing a silicon-carbon anode material by spray method, comprising the following steps:

[0055] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material (prepared by the method disclosed in 2017103229177), pour pSi and phenolic resin into an ethanol solution at a ratio of 1:0.8, design the solid content to be 12%, add 3% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, and perform spraying, and cool to room temperature to obtain pSi@PR@Ni;

[0056] (2) Heat the sample obtained in (1) under Ar / H2 conditions, heat it to 600 °C at a rate of 5 °C / min and hold for 2 h, then heat it to 950 °C at a rate of 5 °C / min and hold for 3 h, and cool to room temperature to obtain pS@PRC@Ni;

[0057] (3) The sample obtained in (2) was heated to 700 °C at a rate of 5 °C / min under an Ar atmosphere, and then acetylene gas was introduced at a rate of 5 ml / min. After holding for 1 h, it was cooled to room temperature to obtain pSi@PRC@Ni@C.

[0058] Experimental results

[0059] Figure 1 are the XRD patterns of pS@PRC@Ni and pSi@PRC@Ni@C. From the XRD patterns, it can be seen that the XRD spectra of the prepared composite materials basically coincide with that of pure silicon, indicating that the materials are mainly composed of silicon and no new chemical reactions occur to generate new phases; the characteristic diffraction peaks of the materials can be observed, and these peaks correspond to the silicon crystal planes (111), (220), (311), (400), (331), (422), etc. respectively; no other miscellaneous peaks are found in the XRD patterns, indicating that no new phases are generated during the preparation process, so it can be inferred that the materials have a high purity and are mainly composed of silicon; at the same time, there is a relatively broad bread-like peak between 20° and 24°, and this peak corresponds to the amorphous carbon after the pyrolysis of phenolic resin.

[0060] Figure 2a and 2b are the scanning electron microscope images of pS@PRC@Ni and pSi@PRC@Ni@C. No obvious porous morphology can be seen from the scanning electron microscope image of pS@PRC@Ni, which indicates that the phenolic resin carbon is well filled in the pores of porous silicon; after CVD carbon coating, the scanning electron microscope image of pSi@PRC@Ni@C shows better uniformity and consistency on the material surface, which is very important for ensuring the stability and reliability of battery performance. Uniform carbon coating can provide better electrochemical performance and cycling stability.

[0061] Figure 3 are the transmission electron microscope images of pS@PRC@Ni and pSi@PRC@Ni@C. The pores of the raw material porous silicon cannot be seen from the transmission electron microscope image of pS@PRC@Ni either, but the obvious boundary skeleton of the porous silicon can be seen, which further indicates that the phenolic resin is uniformly filled in the pores of the porous silicon; while the transmission electron microscope image of pSi@PRC@Ni@C shows that the material is in an irregular block shape after CVD carbon coating, and the whole structure is completely wrapped in the carbon layer, which is crucial for evaluating the structural stability performance of the material.

[0062] Figure 4 are the tapped density and BET of pSi, pS@PRC@Ni and pSi@PRC@Ni@C. As the preparation process progresses, from the raw material pSi to pS@PRC@Ni, and then to pSi@PRC@Ni@C, the tapped density changes from 0.31 g / cm 3 →0.68 g / cm 3 →0.77 g / cm3 , gradually and steadily increase. The specific surface area decreases from 50 m 2 / g to 18 m 2 / g and then to 6 m 2 / g, gradually and steadily decrease, and prepare a silicon-carbon anode material with high tap density and low specific surface area, laying a good foundation for commercialization.

[0063] Electrochemical performance test

[0064] Mix the active material, carbon black (Super P Li), and polyacrylic acid solution (PAA, 4.5 wt.%) in a mass ratio of 70:10:20 to form a slurry, and cast the slurry on a copper foil. After vacuum drying at 80 °C for 24 h, roll-press the electrode to increase the electrode density, and cut it into circular discs with a diameter of 12 mm. Assemble a coin-type half-cell (CR2032) in a glove box filled with argon. The counter electrode is a pure lithium foil, and a Celgard 2400 film is used as the separator. The electrolyte is a mixture of lithium hexafluorophosphate (LiPF6, 1 mol L -1 ) and fluoroethylene carbonate (FEC) (10 vol.%) dissolved in ethylene carbonate / diethyl carbonate (EC / DEC, volume ratio 1:1). The battery performance test is carried out on a battery tester (Wuhan Blue Electronic Co., Ltd., Land CT2001A), and the voltage range is 0.01 - 1.0 V (V vs. Li / Li + ). The first three cycles are carried out at a current density of 0.1 A g -1 , and then the cycles are carried out at a current density of 1 A g -1 to evaluate the cycle performance of the half-cell. The rate performance test is carried out at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A g -1 .

[0065] Figure 5Electrochemical cycling performance graphs of pS@PRC@Ni and pSi@PRC@Ni@C. After cycling 3 laps at a current density of 0.1 A / g and then undergoing long-term cycling at 1 A / g, pSi@PRC@Ni@C exhibits more stable electrochemical performance than pS@PRC@Ni. Although due to the higher carbon content, the initial reversible specific capacity of pS@PRC@Ni@C is lower than that of pS@PRC@Ni, the structure of pS@PRC@Ni@C is more stable, with better cycling stability in the later stage and a higher reversible specific capacity. At a current density of 1 A / g, pS@PRC@Ni@C still retains a reversible specific capacity of 1125 mAh / g after 300 cycles, and the capacity retention rate is 69.7% (compared with the 4th cycle), while pS@PRC@Ni only retains a reversible specific capacity of 782 mAh / g after 300 cycles, and the capacity retention rate is 41.9% (compared with the 4th cycle), demonstrating the better cycling stability of pS@PRC@Ni@C.

[0066] Figure 6 Rate performance graphs of pS@PRC@Ni and pSi@PRC@Ni@C. After cycling 5 laps at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g and then returning to a current density of 0.1 A / g for another 5 laps, pSi@PRC@Ni@C shows higher discharge specific capacities in all cases, indicating that pSi@PRC@Ni@C can operate at different charge-discharge rates and maintain stable electrochemical performance.

[0067] Example 2

[0068] A preparation method for constructing a silicon-carbon anode material by spray method, comprising the following steps:

[0069] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material. Pour pSi and phenolic resin into an ethanol solution at a ratio of 1:1.2, with a designed solid content of 12%, add 3% nickel acetate, ultrasonic for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, and perform spraying. Cool to room temperature to obtain pSi@PR@Ni;

[0070] (2) Heat the sample obtained in (1) under Ar / H2 conditions at a rate of 5 °C / min to 600 °C and hold for 2 h, then heat to 950 °C at a rate of 5 °C / min and hold for 3 h, and cool to room temperature to obtain pS@PRC@Ni;

[0071] (3) Heat the sample obtained in (2) in an Ar atmosphere at a rate of 5 °C / min to 700 °C, then introduce benzene-containing gas at a rate of 5 ml / min, hold for 1 h, and cool to room temperature to obtain pSi@PRC@Ni@C.

[0072] Figure 7 The scanning electron microscope image of pSi@PRC@Ni@BC shows that increasing the content of phenolic resin results in the complete encapsulation of porous silicon by carbon. In addition, benzene is used as the carbon source for the outer coating to isolate the infiltration of the electrolyte, reduce interfacial side reactions, and effectively alleviate volume expansion.

[0073] Comparative Example 1

[0074] A preparation method for constructing a silicon-carbon anode material by spray method includes the following steps:

[0075] (1) Select nano-silicon nSi with a particle size of 50 - 200 nm as the raw material. Dissolve nSi and phenolic resin in ethanol at a ratio of 1:0.8, adjust the solid content to 12%, add 3% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, then perform spraying and cool to room temperature to obtain nSi@PR@Ni;

[0076] (2) Heat the sample obtained in (1) from room temperature to 600 °C at a rate of 5 °C / min under Ar / H2 atmosphere and hold for 2 h, then heat to 950 °C at a rate of 5 °C / min and hold for 3 h, and then cool to room temperature to obtain nSi@PRC@Ni;

[0077] (3) Heat the sample obtained in (2) to 700 °C at a rate of 5 °C / min under Ar atmosphere, then introduce acetylene gas at a rate of 5 ml / min, hold for 1 h, and then cool to room temperature to obtain nSi@PRC@Ni@C.

[0078] Figure 8 The scanning electron microscope of nSi@PRC@Ni@C shows that when using nSi as the silicon source, a three-dimensional porous spherical structure is obtained after spraying, which has an obvious porous structure. Its specific surface area is too high, which is not conducive to the application and performance in the full cell.

[0079] Comparative Example 2

[0080] A preparation method for constructing a silicon-carbon anode material by spray method includes the following steps:

[0081] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material. Dissolve pSi and phenolic resin in ethanol at a ratio of 1:0.1, adjust the solid content to 12%, add 3% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, then perform spraying and cool to room temperature to obtain pSi@PR@Ni;

[0082] (2) The sample obtained in (1) was heated to 600 °C at a rate of 5 °C / min under Ar / H2 conditions and held for 2 h, then heated to 950 °C at a rate of 5 °C / min and held for 3 h, and cooled to room temperature to obtain pSi@PRC@Ni;

[0083] (3) The sample obtained in (2) was heated to 700 °C at a rate of 5 °C / min under Ar atmosphere, and then acetylene gas was introduced at a rate of 5 ml / min and held for 1 h, and cooled to room temperature to obtain pSi@PRC@Ni@C.

[0084] Figure 9 It is the electrochemical cycling performance graph of pSi@PRC@Ni@C (pSi: phenolic resin = 1:0.1). At a current density of 1 A / g, the reversible specific capacity is 966 mAh / g after 300 cycles.

[0085] In this comparative example, the addition amount of phenolic resin is too low, which is difficult to inhibit swelling, reduce the structural stability, and at the same time cause the electron transport network to be discontinuous, affecting the conductivity of the electrode and the cycling performance of the battery.

[0086] Comparative Example 3

[0087] A preparation method for constructing a silicon-carbon anode material by spray method, comprising the following steps:

[0088] (1) Porous silicon with a particle size of 3-5 μm was selected as the raw material. pSi and phenolic resin were poured into an ethanol solution at a ratio of 1:0.8, the solid content was adjusted to 25%, 3% nickel acetate was added, and ultrasonic treatment was carried out for 30 min. The inlet temperature was adjusted to 160 °C, the feeding rate was 10 ml / min, and the flow rate was 30 ml / min, and then spraying was carried out and cooled to room temperature to obtain pSi@PR@Ni;

[0089] (2) The sample obtained in (1) was heated to 600 °C at a rate of 5 °C / min under Ar / H2 conditions and held for 2 h, then heated to 950 °C at a rate of 5 °C / min and held for 3 h, and cooled to room temperature to obtain pSi@PRC@Ni;

[0090] (3) The sample obtained in (2) was heated to 700 °C at a rate of 5 °C / min under Ar atmosphere, and then acetylene gas was introduced at a rate of 5 ml / min and held for 1 h, and cooled to room temperature to obtain pSi@PRC@Ni@C.

[0091] Figure 10 It is the electrochemical cycling performance graph of pSi@PRC@Ni@C (the solid content of the solution is 25%). At a current density of 1 A / g, the reversible specific capacity is 513 mAh / g after 300 cycles.

[0092] In this comparative example, the solid content is relatively high, and there is too much porous silicon and phenolic resin in a single droplet, resulting in severe agglomeration during the spraying process, forming porous spherical particles, which seriously affects the particle size and morphology of the silicon-carbon material, and further has a greater impact on the cycling performance.

[0093] Comparative Example 4

[0094] A preparation method for constructing a silicon-carbon anode material by spray method, comprising the following steps:

[0095] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material, pour pSi and phenolic resin into an ethanol solution according to a ratio of 1:0.8, adjust the solid content to 12%, add 10% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, and perform spraying. After cooling to room temperature, take out to obtain pSi@PR@Ni;

[0096] (2) Heat the sample obtained in (1) to 600 °C at a rate of 5 °C / min under Ar / H2 conditions and hold for 2 h, then heat to 950 °C at a rate of 5 °C / min and hold for 3 h, and cool to room temperature to obtain pSi@PRC@Ni;

[0097] (3) Heat the sample obtained in (2) to 700 °C at a rate of 5 °C / min under an Ar atmosphere, then introduce acetylene gas at a rate of 5 ml / min, hold for 1 h, and cool to room temperature to obtain pSi@PRC@Ni@C.

[0098] Figure 11 It is the electrochemical cycling performance diagram of pSi@PRC@Ni@C (10% nickel acetate). At the same time, at a current density of 1 A / g, the reversible specific capacity is 896 mAh / g after 300 cycles.

[0099] In this comparative example, an excessive amount of nickel acetate is added as a catalyst, resulting in the inability to form a CNT conductive network and the formation of a large amount of inert transition metal carbides, ultimately leading to the failure of the electrochemical performance of the silicon-carbon material to meet the requirements.

[0100] Comparative Example 5

[0101] A preparation method for constructing a silicon-carbon anode material by spray method, comprising the following steps:

[0102] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material, pour pSi and phenolic resin into an ethanol solution according to a ratio of 1:0.8, adjust the solid content to 12%, add 3% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 80 °C, the feeding rate to 50 ml / min, and the flow rate to 50 ml / min, and perform spraying. After cooling to room temperature, take out to obtain pSi@PR@Ni;

[0103] (2) The sample obtained in (1) was heated to 600 °C at a rate of 5 °C / min under Ar / H2 conditions, held for 2 h, then heated to 950 °C at a rate of 5 °C / min and held for 3 h, and cooled to room temperature to obtain pSi@PRC@Ni;

[0104] (3) The sample obtained in (2) was heated to 700 °C at a rate of 5 °C / min under Ar atmosphere, then acetylene gas was introduced at a rate of 5 ml / min, held for 1 h, and cooled to room temperature to obtain pSi@PRC@Ni@C.

[0105] Figure 12 It is the electrochemical cycling performance graph of pSi@PRC@Ni@C (spraying parameters are not properly controlled). At a current density of 1 A / g, the reversible specific capacity is 709 mAh / g after 300 cycles.

[0106] In this comparative example, the spraying parameters are not properly controlled. Firstly, the temperature control is improper, which will cause a large amount of moisture in the precursor, resulting in the oxidation of the material during the subsequent annealing process. Inappropriate spraying speed and flow rate will also lead to inconsistent contents of porous silicon and phenolic resin in individual droplets, and the embedded structure of the silicon-carbon material cannot be formed, ultimately affecting the electrochemical performance of the silicon-carbon composite material.

[0107] Comparative Example 6

[0108] A preparation method for constructing a silicon-carbon anode material by spraying method, comprising the following steps:

[0109] (1) Porous silicon with a particle size of 3 - 5 μm was selected as the raw material. pSi and phenolic resin were poured into an ethanol solution in a ratio of 1:0.8, the solid content was adjusted to 12%, 3% nickel acetate was added, ultrasonicated for 30 min, the inlet temperature was adjusted to 160 °C, the feeding rate was 10 ml / min, and the flow rate was 30 ml / min, and then spraying was carried out. After cooling to room temperature, it was taken out to obtain pSi@PR@Ni;

[0110] (2) The sample obtained in (1) was heated to 200 °C at a rate of 20 °C / min under Ar / H2 conditions, held for 2 h, then heated to 1200 °C at a rate of 20 °C / min and held for 3 h, and cooled to room temperature to obtain pSi@PRC@Ni;

[0111] (3) The sample obtained in (2) was heated to 700 °C at a rate of 5 °C / min under Ar atmosphere, then acetylene gas was introduced at a rate of 5 ml / min, held for 1 h, and cooled to room temperature to obtain pSi@PRC@Ni@C.

[0112] Figure 13 It is the electrochemical cycling performance graph of pSi@PRC@Ni@C (two-stage carbonization temperatures are 200 °C and 1200 °C). At a current density of 1 A / g, the reversible specific capacity is 708 mAh / g after 300 cycles.

[0113] In this comparative example, the temperature of the first-stage carbonization heat treatment is relatively low. The relatively low pre-carbonization temperature may cause insufficient decomposition of the organic carbon source, which not only fails to enhance the conductivity but also affects the reversible specific capacity of the material. If the temperature of the second-stage carbonization heat treatment is too high, inert silicon carbide materials will be formed, resulting in a decrease in capacity.

[0114] Comparative Example 7

[0115] A preparation method for constructing a silicon-carbon negative electrode material by spray method, comprising the following steps:

[0116] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material. Pour pSi and phenolic resin into an ethanol solution at a ratio of 1:0.8, adjust the solid content to 12%, add 3% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, then perform spraying. After cooling to room temperature, take out to obtain pSi@PR@Ni;

[0117] (2) Heat the sample obtained in (1) under Ar / H2 conditions at a rate of 5 °C / min to 600 °C and hold for 2 h, then heat to 950 °C at a rate of 5 °C / min and hold for 3 h, and cool to room temperature to obtain pSi@PRC@Ni;

[0118] (3) Heat the sample obtained in (2) to 700 °C at a rate of 5 °C / min under an Ar atmosphere, then introduce acetylene gas at a rate of 15 ml / min, hold for 3 h, and cool to room temperature to obtain pSi@PRC@Ni@C.

[0119] Figure 14 This is the cycling performance graph of pSi@PRC@Ni@C (acetylene flow rate is 15 ml / min). At a current density of 1 A / g, the reversible specific capacity is 707 mAh / g after 300 cycles.

[0120] The acetylene flow rate used in the comparative example is too high, resulting in too high a carbon content in the silicon-carbon negative electrode material, which ultimately manifests as a decrease in the reversible specific capacity of the negative electrode material.

[0121] Comparative Example 8

[0122] A preparation method for constructing a silicon-carbon negative electrode material by spray method, comprising the following steps:

[0123] (1) Select porous silicon with a particle size of 3 - 5 μm as the raw material. Pour pSi and phenolic resin into an ethanol solution at a ratio of 1:0.8, adjust the solid content to 12%, add 3% nickel acetate, ultrasonicate for 30 min, adjust the inlet temperature to 160 °C, the feeding rate to 10 ml / min, and the flow rate to 30 ml / min, then perform spraying. After cooling to room temperature, take out to obtain pSi@PR@Ni;

[0124] (2) The sample obtained in (1) was heated to 600 °C at a rate of 5 °C / min under Ar / H2 conditions, held for 2 h, then heated to 950 °C at a rate of 5 °C / min and held for 3 h, and cooled to room temperature to obtain pSi@PRC@Ni;

[0125] (3) The sample obtained in (2) and asphalt powder were dissolved in an ethanol solvent, ultrasonically dispersed for 30 min, and dried in a water bath until the ethanol completely evaporated. The resulting powder was heated to 700 °C at a rate of 5 °C / min under an Ar atmosphere, held for 1 h, and cooled to room temperature to obtain pSi@PRC@Ni@PC.

[0126] Figure 15 It is the cycling performance diagram of pSi@PRC@Ni@PC (with asphalt as the outer carbon source). At a current density of 1 A / g, the reversible specific capacity is 734 mAh / g after 300 cycles.

[0127] In this comparative example, asphalt powder was used as the outer carbon source. It is difficult for asphalt carbon to fill the pores generated during the pyrolysis of phenolic resin carbon, which will result in too high specific surface area, leading to serious electrochemical side reactions, and ultimately reflected in the reduction of the electrochemical performance of the material, including cycling stability and reversible specific capacity.

[0128] For those not covered above, the prior art shall apply.

[0129] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration purposes and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made based on the technical essence of the present invention to the above embodiments shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-carbon anode material, characterized in that It includes the following steps: S1: Add the porous silicon material and the organic carbon source into an ethanol solution, then add the transition metal salt. After ultrasonic dispersion until uniform, a spray solution is obtained. Spray-dry the spray solution to obtain a powder sample; S2: Under the protection of an atmosphere, perform a high-temperature carbonization process on the powder sample obtained in S1 in a two-stage heating manner to obtain pSi@C@M; S3: Heat the pSi@C@M obtained in S2 to a certain temperature under the protection of an atmosphere, then introduce a carbon-containing gas, keep it warm for a period of time, cool it to room temperature and take it out to obtain pSi@C@M@C.

2. The preparation method according to claim 1, characterized in that, In S1, the porous silicon material is micron-scale three-dimensional porous silicon.

3. The preparation method according to claim 1, characterized in that, In S1, the organic carbon source is one or more of phenolic resin, glucose, sucrose, citric acid, and urea.

4. The preparation method according to claim 1, characterized in that, In S1, the mass ratio of the porous silicon material to the organic carbon source is 1:0.2 - 2; the addition amount of the transition metal salt is 1 - 5% of the total mass of the porous silicon material and the organic carbon source; the transition metal salt is one or more of iron, nickel, and cobalt salts.

5. The preparation method according to claim 1, characterized in that, In S1, the solid content of the spray solution is 8 - 20%; in the spray operation, the inlet temperature is 100 - 200°C, the feeding rate is 5 - 30 ml / min, and the flow rate is 10 - 50 ml / min.

6. The preparation method according to claim 1, characterized in that, In S2, the two-stage heating is respectively heating to 400 - 800°C at a rate of 1 - 10°C / min and keeping it warm for 2 h; then heating to 900 - 1100°C at a rate of 1 - 10°C / min and keeping it warm for 3 h.

7. The preparation method according to claim 1, characterized in that, In S3, the heat preservation temperature is 600 - 900°C.

8. The preparation method according to claim 1, characterized in that, In S3, the carbon-containing gas is one or more of methane, benzene, and acetylene gas; the introduction rate of the carbon-containing gas is 2 - 10 ml / min; the heat preservation time is 0.2 - 3 h.

9. A silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 1 - 8.

10. Use of a silicon-carbon negative electrode material as described in claim 9, characterized in that: It is used as a negative electrode material for a lithium battery.

Images