Synergistically modified silicon-carbon negative electrode material, preparation method thereof, negative electrode and battery

Abstract

This invention provides a synergistically modified silicon-carbon anode material, its preparation method, an anode, and a battery. The synergistically modified silicon-carbon anode material includes a silicon-carbon composite material and a coating layer on the surface of the silicon-carbon composite material. The coating layer is a conductive polymer doped with fluorine (F) and y, where y is selected from one or more of Cl, I, and Br. Coating the silicon-carbon material with the F and Y doped conductive polymer allows the conductive polymer to combine mechanical flexibility with high electronic conductivity, buffering silicon volume expansion and constructing a stable conductive framework. F induces the formation of a stable SEI film rich in LiF, while y maintains the framework structure and enhances conductivity. The functions of the two are decoupled and synergistic, and the electron-withdrawing effect of F further stabilizes the y-doped framework. Ultimately, a dual continuous electron and ion transport network and synergistic stability of the interface and bulk phase are achieved within the same coating layer, significantly improving the cycle and rate performance of the silicon-carbon anode.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery materials technology, specifically relating to synergistically modified silicon-carbon anode materials, their preparation methods, anodes, and batteries. Background Technology

[0002] With the growth of the portable electronics and electric vehicle markets, the demand for high-energy-density lithium-ion batteries is increasing. Currently, the theoretical specific capacity of silicon anodes (4200 mAh·g) is... -1 ) is approximately equivalent to a commercial graphite anode (372 mAh·g) -1 With a silicon-carbon anode material that is ten times more potent than lithium-ion batteries and has a suitable operating voltage (0.4V), it is a very promising anode material. Furthermore, silicon is abundant in the Earth's crust, inexpensive, and environmentally friendly. However, converting silicon-carbon anode materials into industrial-scale lithium-ion battery anodes is not a simple process. During cycling, silicon is affected by lithium ions (Li₂O₃). + The embedding of ) will result in a huge volume expansion (>300%), with Li + As the Si is extracted, its volume shrinks, and this volume change occurs repeatedly with each cycle. This volume change not only leads to repeated cracking and fragmentation of Si but also causes disintegration, breakage, and electrical isolation between Si and the electrode. Continuous fragmentation also causes the solid electrolyte interphase (SEI) layer to be continuously damaged and thickened, rapidly consuming the electrolyte and Li. + This results in low coulombic efficiency (CE) of silicon anodes, rapid capacity decay, and a sharp decline in stability. The most common solution currently is to use a carbon coating to suppress the volume expansion of silicon and prevent direct contact between silicon and the electrolyte, thereby reducing side reactions and improving coulombic efficiency. However, carbon coating itself has some defects that limit the performance of silicon anodes.

[0003] In the aforementioned silicon-carbon composite materials, the drastic volume changes of silicon during charge-discharge cycles—repeatedly stretching the carbon layer—make this physical contact interface highly susceptible to separation after long-term cycling, leading to protection failure. Even with further carbon coating, the volume changes of silicon still cause repeated rupture and repair of the solid electrolyte interphase (SEI) film on the surface. This process continuously consumes electrolyte and active lithium, resulting in increased battery polarization and continuous capacity decay. Furthermore, while the carbon coating layer is relatively stable, its mechanical properties (such as hardness and flexibility) differ from those of silicon itself. This mismatch exacerbates interface instability under stress. Simultaneously, imperfect structures such as defects and oxygen-containing functional groups on the carbon material surface catalyze electrolyte decomposition, leading to excessive SEI film formation, thereby intensifying internal side reactions and lithium loss. In addition, the carbon coating layer is typically amorphous or non-crystalline, with poor conductivity, resulting in a significant decrease in high-rate charge-discharge capacity, increased polarization under high current, and ineffective capacity utilization.

[0004] Therefore, there is an urgent need to develop a new type of carbon material that can precisely control the carbon framework, has high interfacial stability, good conductivity and structural designability, so as to effectively bear the volume change of silicon and reduce side reactions, thereby promoting the practical application of silicon anodes. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned problems of the prior art, and its purpose is to provide synergistically modified silicon-carbon anode materials, anodes and batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, a synergistically modified silicon-carbon anode material is provided, comprising a silicon-carbon composite material and a coating layer covering the surface of the silicon-carbon composite material, wherein the coating layer is a conductive polymer doped with both F (fluorine) and Y, and the Y is selected from one or more of Cl, I, and Br.

[0007] Furthermore, the silicon-carbon anode material includes a porous carbon matrix and silicon particles distributed within the pores of the porous carbon matrix.

[0008] Furthermore, the porous carbon matrix is ​​a phosphorus-doped porous carbon matrix.

[0009] Furthermore, the phosphorus doping amount in the porous carbon matrix is ​​0.1~5wt%.

[0010] Furthermore, the molecular formula of the F and Y co-doped conductive polymer is (C a H b X) n ·Y n×α ·F n×β Where X is one or more of H, S, N, and O, and Y is one or more of Cl, I, and Br; where a≥b; 1≤n≤1000; 0<α<0.4, 0<β<0.3.

[0011] Furthermore, the conductive polymer is selected from one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, and PBFDO (poly(benzodifurandione)); Furthermore, the thickness of the coating layer is 0.5~50nm.

[0012] Secondly, a method for preparing synergistically modified silicon-carbon anode materials is provided, including: S1. Under an inert atmosphere, phosphorus source is used to dope the porous carbon matrix with phosphorus; S2. Silicon is deposited onto the phosphorus-doped porous carbon matrix to obtain a silicon-carbon composite material with silicon particles loaded in the pores of the porous carbon matrix. S3. Using halogen Y source, conductive polymer monomer A, fluorine-containing conductive polymer monomer B and oxidant as raw materials, in-situ polymerization is carried out to coat the surface of silicon-carbon composite material with an F and Y doped conductive polymer layer; Y is selected from one or more of Cl, I and Br.

[0013] Thirdly, a negative electrode is provided, including the silicon-carbon negative electrode material described in the first aspect or the silicon-carbon negative electrode material prepared by the preparation method described in the second aspect.

[0014] Fourthly, a battery is provided, including the negative electrode described in the third aspect.

[0015] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: By coating the surface of silicon-carbon anode materials with a conductive polymer doped with both fluorine (F) and halogen fluorine (Y), the conductive polymer coating layer itself has good mechanical flexibility, which can play a buffering and restraining role during the volume expansion / contraction of silicon particles. The F-doped conductive polymer can induce the formation of a LiF-rich SEI film on the surface of silicon-carbon anode materials, while halogen fluorine doping constructs a high electronic conductivity framework. The Y embedded in the interchain acts as a structural pillar, maintaining the stability of the polypyrrole oxidized framework. The dual doping of Y and fluorine in the conductive polymer achieves a synergistic improvement effect on performance such as cycle performance and rate performance. The two act at different spatial sites in the conductive polymer, and their co-doping achieves functional decoupling. Furthermore, the electron-withdrawing effect of F helps to stabilize the polypyrrole oxidized doped state, indirectly protecting the conductivity stability of the Y-doped framework. The high electronic conductivity provided by Y allows the interface optimization function of F to be fully utilized, thereby simultaneously realizing the construction of a dual continuous electron and ion transport network and the interface-bulk phase synergistic stability within the same coating layer.

[0016] P doping of porous carbon can expand the carbon interlayer spacing, promote rapid lithium-ion diffusion, and introduce an n-type doping effect, improving the intrinsic electronic conductivity of the carbon matrix. Furthermore, the incorporation of P atoms into the carbon lattice creates local defects and micro-strains, which can suppress brittle fracture of the carbon framework under cyclic stress, allowing porous carbon to more persistently buffer the internal stress generated by silicon expansion and prevent overall electrode pulverization. Simultaneously, P doping of porous carbon amplifies the improvement effect of F and Y dual-doped conductive polymer coating, further forming a dual synergistic effect: F and Y doping of PPy mainly optimizes the outer electron transport and SEI film, while P doping of porous carbon optimizes the ion transport kinetics of the core. The two form an electron-ion dual transport channel, achieving synergistic modification through internal and external linkage. Moreover, the electron-rich surface forms interfacial dipoles and chemical bonds with the electron-deficient nitrogen / halogen atoms in the F and Y doped conductive polymers, significantly enhancing the interfacial bonding between the coating layer and the carbon substrate, and also constructing accelerated Li-Li at the interface. +The electric field gradient of migration. P doping can stabilize the dense SEI film rich in LiF formed by F participation, suppress local excessive reduction reaction, and amplify the ion conductivity buffering effect and side reaction suppression effect of the conductive polymer layer, thereby significantly improving the performance of the anode material, such as rate performance and cycle performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a TEM image of the silicon-carbon anode material prepared in Example 1.

[0019] Figure 2 The images show the HAADF and EDS of the silicon-carbon anode material prepared in Example 1, where (a) is the HAADF image, and (b), (c), and (d) are the EDS images of F, P, and Cl, respectively.

[0020] Figure 3 XPS image of the negative electrode of the battery assembled from the silicon-carbon composite material prepared in Example 1 after 5 cycles at 0.1C.

[0021] Figure 4 XPS image of the negative electrode of the battery assembled from the silicon-carbon composite material prepared for Comparative Example 5 after 5 cycles at 0.1C. Detailed Implementation

[0022] Some embodiments provide synergistic effect modified silicon-carbon anode materials, including silicon-carbon composite materials and a coating layer covering the surface of the silicon-carbon composite material, wherein the coating layer is a conductive polymer doped with F and Y, and Y is selected from one or more of Cl, I, and Br.

[0023] This invention involves coating a silicon-carbon anode material with a conductive polymer doped with both phosphorus (F) and halogen (Y). The F-doped conductive polymer induces the formation of a LiF-rich SEI film on the silicon-carbon anode material surface. This LiF-rich SEI film exhibits excellent ionic conductivity and chemical stability, effectively passivating the silicon surface and inhibiting continuous electrolyte reduction and decomposition while ensuring lithium-ion insertion / extraction. This reduces irreversible capacity loss and improves electrode cycle performance. The halogen (Y) doping constructs a high electronic conductivity framework. High electronic conductivity ensures a stable electron transport channel between silicon particles and the conductive network, preventing capacity decay due to conductive network breakage. Simultaneously, the Y intercalated in the chains acts as a structural pillar, maintaining the stability of the polypyrrole oxidized framework and preventing loss of conductivity due to doped state collapse during cycling. The polypyrrole coating itself possesses good mechanical flexibility, providing buffering and constraint during silicon particle volume expansion / contraction.

[0024] The dual doping of conductive polymers with Y and fluorine achieves a synergistic improvement effect on cycling performance and rate performance. The two act at different spatial sites in the conductive polymer, with F located on the ring and Y located between chains, so there is no doping competition. The electron-withdrawing effect of F also helps to stabilize the oxidized doped state of polypyrrole, indirectly protecting the conductivity stability of the Y-doped backbone. Meanwhile, the high electronic conductivity provided by Y allows the interface optimization function of F to be fully utilized, thereby simultaneously realizing the construction of an electron-ion dual continuous transport network and the interface-bulk phase synergistic stability within the same coating layer.

[0025] In some preferred embodiments, the silicon-carbon composite material includes a porous carbon matrix and silicon particles distributed within the porous carbon pores; the porous carbon matrix is ​​a phosphorus-doped porous carbon matrix. P doping of porous carbon can expand the carbon interlayer spacing, promote rapid lithium-ion diffusion, and introduce an n-type doping effect, improving the intrinsic electronic conductivity of the carbon matrix. Furthermore, the incorporation of P atoms into the carbon lattice creates local defects and micro-strains, which can suppress brittle fracture of the carbon framework under cyclic stress, allowing porous carbon to more persistently buffer the internal stress generated by silicon expansion and prevent overall electrode pulverization. Simultaneously, P doping of porous carbon amplifies the improvement effect of F and Y dual-doped conductive polymer coating, further forming a dual synergistic effect: F and Y doping of PPy mainly optimizes the outer electron transport and SEI film, while P doping of porous carbon optimizes the ion transport kinetics of the core. The two form an electron-ion dual transport channel, achieving synergistic modification through internal and external linkage. Moreover, the electron-rich surface forms interfacial dipoles and chemical bonds with the electron-deficient nitrogen / halogen atoms in the F and Y doped conductive polymers, significantly enhancing the interfacial bonding between the coating layer and the carbon substrate, and also constructing accelerated Li-Li at the interface. +The electric field gradient of migration. P doping can stabilize the dense SEI film rich in LiF formed by F participation, suppress local excessive reduction reaction, and amplify the ion conductivity buffering effect and side reaction suppression effect of the conductive polymer layer, thereby significantly improving the performance of the anode material, such as rate performance and cycle performance.

[0026] In some preferred embodiments, the phosphorus doping amount in the porous carbon matrix is ​​0.1~5wt%, for example 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt%, 3.2wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt%, etc.

[0027] In some embodiments, the carbon source of the porous carbon matrix is ​​selected from one or more of resin-based carbon, biomass carbon, coal, and petroleum coke.

[0028] In some embodiments, the average pore size of the porous carbon matrix is ​​1~10nm, such as 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc.

[0029] In some embodiments, the silicon particles are silicon nanoparticles; the particle size of the silicon particles is 0.5~10nm, for example 0.5nm, 1nm, 2nm, 3nm, 4nm, 5nm, 8nm, 10nm, etc.

[0030] In some embodiments, the silicon mass percentage in the silicon-carbon composite material is 10-90%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0031] In some embodiments, a carbon coating layer may be provided between the coating layer and the porous carbon matrix, or no carbon coating layer may be provided.

[0032] In some preferred embodiments, the molecular formula of the F and Y co-doped conductive polymer is (C a H b X) n ·Y n×α ·F n×βWherein, X is one or more of H, S, N, and O, and Y is one or more of Cl, I, and Br; where a ≥ b; 1 ≤ n ≤ 1000; 0 < α < 0.4, for example 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.2, 0.25, 0.3, 0.35, etc., preferably 0.01~0.2; 0 < β < 0.3, for example 0.005, 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.2, 0.25, preferably 0.005~0.1.

[0033] In some preferred embodiments, the conductive polymer is selected from one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, and PBFDO (poly(benzodifurandione)).

[0034] In some preferred embodiments, the thickness of the coating layer is 0.5~50nm, preferably 3~10nm, such as 3nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc.

[0035] Some embodiments provide a method for preparing synergistically modified silicon-carbon anode materials, including: S1. Under an inert atmosphere, phosphorus source is used to dope the porous carbon matrix with phosphorus; S2. Silicon is deposited onto the phosphorus-doped porous carbon matrix to obtain a silicon-carbon composite material with silicon particles loaded in the pores of the porous carbon matrix. S3. Using halogen Y source, conductive polymer monomer A, fluorine-containing conductive polymer monomer B and oxidant as raw materials, in-situ polymerization is carried out to coat the surface of silicon-carbon composite material with an F and Y doped conductive polymer layer; Y is selected from one or more of Cl, I and Br.

[0036] In the above preparation method, because Y and F have different doping modes, they act at different spatial sites in the conductive polymer. F is located on the ring and Y is located between chains. Therefore, there is no competitive effect between the two doping methods, which improves the doping effect.

[0037] The halogen Y source and the oxidant can be the same substance or different substances.

[0038] In some preferred embodiments, step S1 includes: S31. Disperse the silicon-carbon composite material in a solvent, add conductive polymer monomer A and fluorinated conductive polymer monomer B, stir and mix thoroughly so that conductive polymer monomer A and fluorinated conductive polymer monomer B are uniformly adsorbed on the surface of silicon-carbon particles to obtain a suspension. S32. The temperature of the suspension is lowered to 0~5℃, an inert gas is introduced, and the pH value is adjusted to 2~3. A halogen Y compound is added to the suspension. The halogen Y compound has strong oxidizing properties (i.e., in this method, the halogen Y compound is both a halogen Y source and an oxidant). The mixture is stirred at low temperature (0~5℃) to carry out a polymerization reaction. After the reaction is completed, the mixture is separated into solid and liquid components and washed to obtain a silicon-carbon composite material coated and modified with F and Y dual-doped conductive polymers.

[0039] In some embodiments, in step S11, the solvent is one or more of water, ethanol, organic solvents, etc.

[0040] In some preferred embodiments, the halogen Y compound may be selected from one or more of FeCl3 and its hydrate, FeBr3, KIO3, and NaIO4.

[0041] In some preferred embodiments, the molar ratio of the halogen Y compound to the total molar ratio of the conductive polymer monomer A and the fluorinated conductive polymer monomer B is (1.0~2.5):1, for example 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, etc.

[0042] In some preferred embodiments, in step S32, one or more of acetic acid solution, acetic acid-sodium acetate buffer solution, and hydrochloric acid solution are used to adjust the pH value.

[0043] In some embodiments, the phosphorus source is selected from one or more of phosphates (including but not limited to diammonium hydrogen phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, ammonium phosphate, sodium phosphate, etc.), phosphoric acid, phytic acid, and phosphine.

[0044] In some embodiments, the conductive polymer monomer A is one or more of pyrrole, aniline, acetylene, thiophene, and benzodifurandione; In some embodiments, the fluorinated conductive polymer monomer B is one or more of 3-fluoropyrrole, 3,4-difluoropyrrole, 2-fluoroaniline, 3-fluoroaniline, 4-fluoroaniline, 3,5-difluoroaniline, 3-fluorothiophene, and 3,4-difluorothiophene.

[0045] In some preferred embodiments, the molar ratio of the fluorinated conductive polymer monomer B to the conductive polymer monomer A is 9~9.99:1~0.01, for example 9:1, 9.1:0.9, 9.2:0.8, 9.3:0.7, 9.4:6, 9.5:0.5, 9.6:0.4, 9.7:0.3, 9.8:0.2, 9.9:0.1, 9.92:0.08, 9.94:0.06, 9.96:0.04, 9.98:0.02, 9.99:0.01, etc.

[0046] In some preferred embodiments, the ratio of the total mass of the fluorinated conductive polymer monomer B and the conductive polymer monomer A to the mass of the silicon-carbon composite material is 1:(10~100), for example, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, etc.

[0047] In some embodiments, the inert atmosphere is a nitrogen atmosphere, an argon atmosphere, or an atmosphere of other kinds.

[0048] In some embodiments, in step S1, the phosphorus doping temperature is 25~900℃, and the phosphorus doping temperature is related to the phosphorus source; the phosphorus doping time is 2~24h.

[0049] In step S1, phosphorus doping can be achieved using existing conventional processes, such as the following process: Porous carbon powder was added to an aqueous solution of NH4H2PO4, stirred and impregnated at room temperature, vacuum dried and ground, and then placed in a tube furnace under a N2 atmosphere. The temperature was raised to 600~800℃ and held, and then cooled to room temperature with the furnace. Residual phosphate was removed by washing with deionized water, and then vacuum dried to obtain phosphorus-doped porous carbon.

[0050] In some embodiments, in step S2, the temperature of silicon deposition is 400~600℃; the deposition time is 4~20h; the silicon source is one or more of conventional gaseous silicon precursors such as silane, silane, propane, and halosilane, and an inert gas such as N2 can be used as a carrier.

[0051] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0052] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0053] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0054] Example 1 This embodiment provides a silicon-carbon anode material, the preparation process of which is as follows: S1, phosphorus-doped porous carbon matrix, the specific process flow is as follows: Porous carbon powder was added to an 18wt% NH4H2PO4 aqueous solution at a solid-liquid ratio of 1:6, stirred and impregnated at room temperature for 3 hours, separated by solid-liquid separation, vacuum dried at 80℃ for 12 hours, ground and sieved, placed in a tube furnace and heated to 700℃ at 3℃ / min under N2 atmosphere, held for 3 hours, cooled to room temperature with the furnace, washed 3-5 times with deionized water to remove residual phosphate, and vacuum dried at 80℃ to obtain P-doped porous carbon.

[0055] S2, the preparation process of silicon-carbon anode material is as follows: Silicon infiltration: Take an appropriate amount of phosphorus-doped porous carbon and put it into a fluidized bed. Perform chemical vapor deposition in silane gas for 10 hours at a deposition temperature of 480℃. Wait for the silicon deposition to be completed to prepare a porous carbon matrix with silicon nanoparticles deposited on it. S3, F, Cl doped ppy coating: S31. Add deionized water to the reaction vessel, add phosphorus-doped silicon carbon material, disperse it ultrasonically, then add pyrrole and 3-fluoropyrrole, stir for 30 min to allow the pyrrole monomer to be uniformly adsorbed on the surface of the silicon carbon particles, and obtain a suspension; wherein the molar ratio of pyrrole to 3-fluoropyrrole is 9.6:0.4, and the ratio of the total mass of pyrrole and 3-fluoropyrrole to the mass of silicon carbon material is 1:50; S32. Place the three-necked flask in an ice-water bath and lower the temperature of the reaction system to 0°C with continuous stirring. Simultaneously, purge with nitrogen to remove air and prevent monomer oxidation. Slowly add an acetate-sodium acetate buffer solution to the suspension to adjust the pH to 3.0. Then, add a ferric chloride solution to the reaction system, where the molar ratio of ferric chloride to the total molar ratio of pyrrole to 3-fluoropyrrole is 1.2:1. Continue stirring at 0°C for 24 hours to ensure complete polymerization. After the reaction, vacuum filter the product and wash thoroughly with deionized water and anhydrous ethanol to remove unreacted monomers, oxidants, and byproducts. Finally, dry in a vacuum drying oven at 80°C for 24 hours to obtain the Cl-F dual-doped PPy-coated silicon-carbon composite material, with an average coating thickness of approximately 5 nm.

[0056] TEM images of the obtained Cl, F dual-doped PPy-coated silicon-carbon composite material are shown below. Figure 1 As shown, by Figure 1 It can be seen that the average thickness of the coating layer is approximately 10 nm; its HAADF and EDS images are as follows. Figure 2 As shown, by Figure 2 It can be seen that F, Cl, and P are uniformly distributed on the silicon-carbon composite material, indicating that the doping of F, Cl, and P has been successfully achieved.

[0057] Example 2 The difference between this embodiment and Embodiment 1 is that in step S3, the mass ratio of pyrrole monomer to silicon-carbon material is 1:25, the average thickness of the coating layer is about 10 nm, and the other conditions are the same as in Embodiment 1.

[0058] Example 3 The difference between this embodiment and Embodiment 1 is that in step S3, the mass ratio of pyrrole monomer to silicon-carbon material is 1:12, the average thickness of the coating layer is 20 nm, and the other conditions are the same as in Embodiment 1.

[0059] Example 4 The difference between this embodiment and Embodiment 1 is that, in step S3, the molar ratio of pyrrole to 3-fluoropyrrole is 9.95:0.05.

[0060] Example 5 The difference between this embodiment and Embodiment 1 is that porous carbon-phosphorus doping is not performed, i.e. step S1 is omitted, while the remaining conditions are the same as in Embodiment 1.

[0061] Comparative Example 1 The difference between this comparative example and Example 1 is that step S3 is replaced by the following step: S31. Add deionized water to the reaction vessel, add phosphorus-doped silicon carbon material, disperse it ultrasonically, then add pyrrole and 3-fluoropyrrole, stir for 30 min to allow the pyrrole monomer to be uniformly adsorbed on the surface of the silicon carbon particles, and obtain a suspension; wherein the molar ratio of pyrrole to 3-fluoropyrrole is 9.5:0.5, and the ratio of the total mass of pyrrole and 3-fluoropyrrole to the mass of silicon carbon material is 1:50; S32. Place the three-necked flask in an ice-water bath and lower the temperature of the reaction system to 0°C with continuous stirring. Simultaneously, purge with nitrogen to remove air and prevent monomer oxidation. Add an acetate-sodium acetate buffer solution to the suspension to adjust the pH to 3.0. Then, add an ammonium persulfate solution to the reaction system, where the molar ratio of ammonium persulfate to the total molar ratio of pyrrole to 3-fluoropyrrole is 1:1. Continue stirring at 0°C for 24 hours to ensure complete polymerization. After the reaction, vacuum filter the product and wash thoroughly with deionized water and anhydrous ethanol to remove unreacted monomers, oxidants, and byproducts. Finally, dry in a vacuum drying oven at 80°C for 24 hours to obtain the F-doped PPy-coated silicon-carbon composite material with an average coating thickness of approximately 5 nm.

[0062] Comparative Example 2 The difference between this comparative example and Example 1 is that step S3 is different, while all other conditions are the same as in Example 1. S31. Add deionized water to the reaction vessel, add phosphorus-doped silicon carbon material, disperse it ultrasonically, then add pyrrole, stir for 30 minutes to allow the pyrrole monomer to be uniformly adsorbed on the surface of the silicon carbon particles, and obtain a suspension; the mass ratio of pyrrole to silicon carbon particles is 1:50. S32. Place the three-necked flask in an ice-water bath and lower the temperature of the reaction system to 0°C with continuous stirring. Simultaneously, purge with nitrogen to remove air and prevent monomer oxidation. Slowly add an acetate-sodium acetate buffer solution to the suspension to adjust the pH to 3.0. Then, add a ferric chloride solution to the reaction system, with a molar ratio of ferric chloride to pyrrole of 1.2:1. Continue stirring at 0°C for 24 hours to ensure complete polymerization. After the reaction, vacuum filter the product and wash thoroughly with deionized water and anhydrous ethanol to remove unreacted monomers, oxidants, and byproducts. Finally, dry in a vacuum drying oven at 80°C for 24 hours to obtain a Cl-doped PPy-coated silicon-carbon composite material with an average coating thickness of approximately 5 nm.

[0063] Comparative Example 3 The difference between this comparative example and Example 1 is that: conductive polymer doping is not performed, only porous carbon-phosphorus doping is performed, step S3 is changed, and the other conditions are the same as in Example 1. Step S3 is as follows: S31. Add deionized water to the reaction vessel, add phosphorus-doped silicon carbon material, disperse it by ultrasonication, then add py and continue stirring for 30 minutes to make the pyrrole monomer uniformly adsorbed on the surface of the silicon carbon particles. The mass ratio of pyrrole monomer to phosphorus-doped silicon carbon material is 1:50. S32. Slowly add an acetate-sodium acetate buffer solution to the above mixed solution to adjust the pH of the system to 3.0. Then place the three-necked flask in an ice-water bath and lower the temperature of the reaction system to 0°C with continuous stirring. At the same time, nitrogen gas is introduced to remove air and prevent the monomer from being oxidized; ammonium persulfate solution is slowly added dropwise, with a molar ratio of ammonium persulfate to pyrrole monomer of 1:1, and the reaction is continued at 0°C with stirring for 24 hours to ensure complete polymerization. After the reaction, the product is vacuum filtered and thoroughly washed with deionized water and anhydrous ethanol to remove unreacted monomers, oxidants, and byproducts. Finally, it is dried in a vacuum drying oven at 80°C for 24 hours to obtain PPy-coated silicon-carbon composite material with an average coating thickness of 5 nm.

[0064] Comparative Example 4 The specific process flow for preparing silicon-carbon anode materials is as follows: S1. Silicon infiltration: Take an appropriate amount of porous carbon and put it into a fluidized bed. Perform chemical vapor deposition in silane gas for 10 hours at a deposition temperature of 580℃. Wait for the silicon deposition to be completed to prepare a porous carbon matrix with silicon nanoparticles deposited on it, which is a silicon-carbon material. S2, Conductive polymer doping: S21. Add deionized water and silicon carbon material to the reaction vessel, disperse by ultrasonication, then add py and continue stirring for 30 minutes to allow pyrrole monomer to be uniformly adsorbed on the surface of silicon carbon particles. The mass ratio of pyrrole monomer to silicon carbon material is 1:50. S22. Slowly add 1 mol / L acetic acid to the above mixed solution to adjust the pH of the system to 3.0. Then place the three-necked flask in an ice-water bath and lower the temperature of the reaction system to 0℃ with continuous stirring. At the same time, nitrogen gas is introduced to remove air and prevent the monomer from being oxidized; slowly add ammonium persulfate solution, with a molar ratio of ammonium persulfate to pyrrole monomer of 1:1, and continue to stir at 0℃ for 24 hours to ensure complete polymerization. After the reaction, the product is vacuum filtered and thoroughly washed with deionized water and anhydrous ethanol to remove unreacted monomers, oxidants, and byproducts. Finally, dry in a vacuum drying oven at 80℃ for 24 hours to obtain PPy-coated silicon-carbon composite material with an average coating thickness of 5 nm.

[0065] Comparative Example 5 The specific process flow for preparing silicon-carbon anode materials is as follows: S1. Silicon infiltration: Take an appropriate amount of porous carbon and put it into a fluidized bed. Perform chemical vapor deposition in silane gas for 10 hours at a deposition temperature of 580℃. Wait for the silicon deposition to be completed to prepare a porous carbon matrix with silicon nanoparticles deposited on it, which is a silicon-carbon material. S2, Carbon Coating: The asphalt and the silicon-carbon material obtained in step S1 are mixed at a mass ratio of 3:100 and then heat-treated and carbonized at 550°C for 2 hours under a nitrogen atmosphere to obtain the silicon-carbon composite material.

[0066] Electrode and half-cell preparation and electrochemical performance testing: Using the silicon-carbon composite materials prepared in the examples and comparative examples as negative electrode active materials, negative electrode sheets were prepared respectively. The negative electrode sheets were used to prepare CR2032 coin cells using conventional methods, and the electrical performance of the cells was tested.

[0067] The specific testing method is as follows: Half-cell assembly: CR2032 coin cells were assembled in a glove box, using a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), with a LiPF6 concentration of 1 mol / L. Charge-discharge tests were performed on the cells using a LAND battery testing system.

[0068] Cyclic specific capacity and initial efficiency test: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V, and the specific capacity was recorded as Q1; then it was discharged at a constant voltage of 0.005V until the current cutoff was 0.01C, and the specific capacity was recorded as Q2; after standing for 5 minutes, it was charged at a constant current of 0.1C to 0.8V, and the specific capacity was recorded as Q3; after standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V, and the specific capacity was recorded as Q4; after standing for 5 minutes, it was discharged at a constant current of 1.0C to 0.005V, and the specific capacity was recorded as Q5; after standing for 2 hours, the thickness of the negative electrode sheet was measured sequentially, and the average value was recorded as h1. Another coated and dried electrode sheet was taken, and the thickness of the negative electrode sheet at 5 points was measured, and the average value was recorded as h2. The initial lithium delithiation specific capacity is the specific capacity (or mass specific capacity) of the electrode material, and the ratio of the initial lithium delithiation capacity to the initial lithium insertion capacity is the initial coulombic efficiency of the battery.

[0069] 0.8V first efficiency = Q3 / (Q1+Q2)×100%; 1.5V initial efficiency = (Q3 + Q4) / (Q1 + Q2) × 100%; 1C rate discharge retention rate = Q5 / (Q3+Q4)×100%; Capacity retention test: Take three cells, let them rest for 5 minutes, then discharge them at 0.1C constant current and constant voltage to 0.005V, let them rest for 5 minutes, then discharge them at 0.02C to 0.005V, and then charge them at 0.1C constant current and constant voltage to 1.5V; let them rest for 5 minutes, then discharge them at 0.25C to 0.005V; let them rest for 5 minutes, then charge them at 0.25C constant current to 1.5V, and cycle them 50 times at a rate of 0.25C. Calculate the specific capacity retention rate by dividing the specific capacity of the 50th cycle by the charging capacity of the 1st cycle and multiplying by 100%.

[0070] Resistivity measurement methods: After compacting the silicon-carbon composite materials of Example 1 and Comparative Examples 1-4 under a pressure of 4.0 MPa, the test results were obtained using an ST2722-SD four-terminal powder resistivity tester, as shown in Table 1.

[0071] Methods for detecting charge transfer impedance: The assembled coin cells were left to stand at room temperature for 12 hours to allow the electrolyte to fully impregnate them. The cells were then discharged at a constant current of 0.1C to 0.01V (relative to Li). + / Li), and then constant voltage until current <0.02 C, so that the silicon-carbon anode completes the first lithiation (lithium intercalation). After formation, the battery is placed under OCP for 2 hours to stabilize the electrode potential. The battery is then placed in a constant temperature chamber (25℃), connected to an electrochemical workstation, and EIS parameters are set. Impedance spectrum scanning is performed at open circuit potential, and Nyquist plot is recorded. After equivalent circuit fitting of Nyquist plot, Rct is read. The results are shown in Table 1.

[0072] In Example 1, after cycling the battery assembled with the negative electrode material of Comparative Example 5 for 5 cycles at 0.1C, the coin cell was disassembled inside a glove box. After removing the negative electrode sheet, it is typically necessary to gently rinse it with a solvent such as dimethyl carbonate to remove residual electrolyte from the surface, and then dry it under vacuum for XPS testing. The XPS spectra of the negative electrode sheets of Example 1 and Comparative Example 5 are shown below. Figure 3 , Figure 4 As shown, by Figure 3 It can be seen that the signal of F is very strong, and Figure 4 No F signal was observed. Analysis suggests that this may be because the F-doped conductive polymer on the surface of the silicon-carbon anode material can induce the formation of a LiF-rich SEI film on the surface of the silicon-carbon anode material.

[0073] Table 1 As shown in Table 1, comparing Comparative Example 3 with Comparative Example 2, Comparative Example 1, and Example 1, it can be seen that compared to the undoped conductive polymer (Comparative Example 3), the resistivity and charge transfer impedance of the silicon-carbon anode material coated with the F-doped conductive polymer (Comparative Example 1) and the silicon-carbon anode material coated with the Cl-doped conductive polymer (Comparative Example 2) are both reduced. However, the resistivity and charge transfer impedance of the silicon-carbon anode material coated with the dual-doped F and Cl conductive polymer (Example 1) show a very significant reduction. Analysis suggests this may be due to the presence of Cl... - By constructing a high-speed electronic framework through doping, F optimizes Li through dipole-ion interactions. + Interfacial transport and induction of stable LiF-containing SEIs, both forming an electron-ion bicontinuous conductive network within the same coating layer, and the electron-withdrawing effect of F may make it easier for PPy chains to maintain their oxidation state, thereby enhancing Cl... - The stability and uniformity of doping achieve simultaneous optimization of electronic conduction, ion conduction, and interface stability.

[0074] Compared with Comparative Example 3 and Comparative Example 4, P doping of the carbon matrix reduced the resistivity and charge transfer impedance of the silicon-carbon anode material.

[0075] Table 2 Comparisons of Comparative Examples 3, 2, and 1 with Example 1 show that, compared to the undoped polypyrrole coating system (Comparative Example 3), the Cl-doped polypyrrole coating system (Comparative Example 2) and the F-doped polypyrrole coating system (Comparative Example 1) improved electronic and ionic conductivity. Example 1, using F-Cl dual-doped polypyrrole coating, exhibited significantly better performance than Comparative Examples 1 and 2, achieving a synergistic performance improvement. These results indicate a significant synergistic effect between F-Cl dual doping: Cl... -Doping constructs a high electronic conductivity framework, while F doping optimizes lithium-ion interface transport and induces the formation of a LiF-rich SEI film. The two are decoupled in space and function, simultaneously improving the material's electronic conductivity, ion conductivity, and interface stability, thereby significantly improving rate performance and cycle performance.

[0076] Comparing Comparative Example 4 with Comparative Example 3, it can be seen that P doping of the porous carbon matrix improves both rate performance and cycle performance. Analysis shows that this is because P doping effectively improves the intrinsic electron / ion transport characteristics of the carbon matrix by expanding the carbon interlayer spacing and incorporating n-type doping effects. Furthermore, the incorporation of P atoms into the carbon lattice creates local defects and micro-strain, which can suppress brittle fracture of the carbon framework under cyclic stress, allowing the porous carbon to more persistently buffer the internal stress generated by silicon expansion. Further comparison of Example 5 with Example 1 shows that, under the same F-Cl dual-doped polypyrrole coating conditions, P doping of the carbon matrix synergistically improves both the rate performance and cycle performance of the anode material. Analysis reveals that these synergistic effects... The reason for this may be that, even with F-Cl dual-doping coating, the high impedance of the inner layer significantly restricts the interface optimization effect of the outer coating layer under the condition of no P-doped carbon matrix. The P-doped carbon matrix has a significant amplification effect on the F-Cl dual-doped polypyrrole coating layer. As a high-speed electron / ion transport channel in the inner layer, the P-doped carbon matrix effectively reduces the overall interface impedance, allowing the electron-ion dual-channel optimization function of the outer F-Cl dual-doped polypyrrole to be fully released. Furthermore, the electron-rich surface forms interfacial dipoles and chemical bonds with the electron-deficient nitrogen / halogen atoms in the F and Y doped conductive polymers, greatly enhancing the interfacial bonding force between the coating layer and the carbon substrate. It can also construct accelerated Li at the interface. + The migrating electric field gradient allows P-doping to stabilize the dense LiF-rich SEI film formed by F-doping, suppressing local over-reduction reactions and amplifying the ion conductivity buffering effect and side reaction suppression effect of the conductive polymer layer. Therefore, this application achieves a synergistic improvement in electronic conduction, ion conduction, and interface stability of silicon-carbon composite anode materials through a cross-layer synergistic design of the P-doped carbon matrix and the F-Cl dual-doped polypyrrole coating layer.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A synergistically modified silicon-carbon anode material, characterized in that, It includes a silicon-carbon composite material and a coating layer covering the surface of the silicon-carbon composite material. The coating layer is a conductive polymer doped with both F and Y, wherein Y is selected from one or more of Cl, I, and Br.

2. The synergistically modified silicon-carbon anode material of claim 1, wherein, The silicon-carbon anode material satisfies one or more of the following characteristics: (a) the F and Y co-doped conductive polymer has a molecular formula of (C a H b X) n ·Y n×α ·F n×β ; wherein X is one or more of H, S, N, O, and Y is one or more of Cl, I, Br; wherein a > b; 1 < n < 1000; 0 < a < 0.4, 0 < β < 0.3; (b) The conductive polymer is selected from one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, and PBFDO; (c) The thickness of the coating layer is 0.5~50nm.

3. The synergistically modified silicon-carbon anode material as described in claim 1, characterized in that, The silicon-carbon anode material satisfies one or more of the following characteristics: (a) The silicon-carbon composite material comprises a porous carbon matrix and silicon particles distributed within the pores of the porous carbon matrix; (b) The porous carbon matrix is ​​a phosphorus-doped porous carbon matrix; the phosphorus doping amount in the porous carbon matrix is ​​0.1~5 wt%; (c) The carbon source of the porous carbon matrix is ​​selected from one or more of resin-based carbon, biomass carbon, coal, and petroleum coke; (d) The average pore size of the porous carbon matrix is ​​1~10 nm; (e) The silicon particles are silicon nanoparticles; the particle size of the silicon particles is 0.5~10 nm; (f) The silicon-carbon composite material contains 10-90% silicon by mass; (g) A carbon coating layer may or may not be provided between the coating layer and the porous carbon matrix.

4. A method for preparing synergistically modified silicon-carbon anode materials, characterized in that, include: S1. Under an inert atmosphere, phosphorus source is used to dope the porous carbon matrix with phosphorus; S2. Silicon is deposited onto the phosphorus-doped porous carbon matrix to obtain a silicon-carbon composite material with silicon particles loaded in the pores of the porous carbon matrix. S3. Using halogen Y source, conductive polymer monomer A, fluorine-containing conductive polymer monomer B and oxidant as raw materials, in-situ polymerization is carried out to coat the surface of silicon-carbon composite material with an F and Y doped conductive polymer layer; Y is selected from one or more of Cl, I and Br.

5. The method for preparing the synergistically modified silicon-carbon anode material as described in claim 4, characterized in that, Step S1 includes: S31. Disperse the silicon-carbon composite material in a solvent, add conductive polymer monomer A and fluorinated conductive polymer monomer B, stir and mix thoroughly so that conductive polymer monomer A and fluorinated conductive polymer monomer B are uniformly adsorbed on the surface of silicon-carbon particles to obtain a suspension. S32. The temperature of the suspension is lowered to 0~5℃, an inert gas is introduced, and the pH value is adjusted to 2~3. A halogen Y compound is added to the suspension. The halogen Y compound has strong oxidizing properties. The suspension is stirred at low temperature (0~5℃) to carry out a polymerization reaction. After the reaction is completed, the solid and liquid are separated and washed to obtain a silicon-carbon composite material modified by F and Y dual-doped conductive polymer coating.

6. The method for preparing the synergistically modified silicon-carbon anode material as described in claim 5, characterized in that, The halogen Y compound is selected from one or more of FeCl3 and its hydrate, FeBr3, KIO3, and NaIO4; The ratio of the molar amount of halogen Y compound to the total molar amount of conductive polymer monomer A and fluorinated conductive polymer monomer B is (1.0~2.5):

1.

7. The method for preparing the synergistically modified silicon-carbon anode material as described in claim 5, characterized in that, In step S32, one or more of the following are used to adjust the pH value: acetic acid solution, acetic acid-sodium acetate buffer solution, and hydrochloric acid solution.

8. The method for preparing the synergistically modified silicon-carbon anode material as described in claim 4, characterized in that, The preparation method satisfies one or more of the following characteristics: (a) The phosphorus source is selected from one or more of phosphate, phosphoric acid, phytic acid, and phosphine; (b) The conductive polymer monomer A is one or more of pyrrole, aniline, acetylene, thiophene, and benzodifurandione; (c) The fluorinated conductive polymer monomer B is one or more of 3-fluoropyrrole, 3,4-difluoropyrrole, 2-fluoroaniline, 3-fluoroaniline, 4-fluoroaniline, 3,5-difluoroaniline, 3-fluorothiophene, and 3,4-difluorothiophene; (d) The molar ratio of the fluorinated conductive polymer monomer B to the conductive polymer monomer A is 9~9.99:1~0.01; (e) The ratio of the total mass of the fluorinated conductive polymer monomer B and the conductive polymer monomer A to the mass of the silicon-carbon composite material is 1:(10~100).

9. Negative electrode, characterized in that, This includes silicon-carbon anode materials as described in any one of claims 1 to 3, or silicon-carbon anode materials prepared by the preparation method described in any one of claims 4 to 8.

10. A battery, characterized in that, Includes the negative electrode as described in claim 9.

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