Porous long-circulation silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of electrode materials, and provides a porous long-circulation silicon-carbon negative electrode material and a preparation method thereof. The preparation method comprises the following steps: preparing SiO2 microspheres through sol-gel reaction, generating silicon dioxide particles through hydrolysis and polycondensation reaction, forming a SiO2 (at) MgO composite structure, carrying out high-temperature reduction reaction on the SiO2 (at) MgO composite structure and magnesium powder, and carrying out chemical etching to form a porous silicon substrate; the method comprises the following steps: preparing a PANI material, forming an LATP layer by using precursor sol, improving the ionic conductivity of the binder, introducing an active functional group on the surface of PANI coated LATP, and then forming a functionalized binder through photo-initiation polymerization reaction; li3PS4 solid electrolyte is prepared, and a conductive protection layer is coated with polydopamine, so that the combination of the electrolyte and a silicon negative electrode is enhanced; and dispersing the porous silicon-carbon composite material, Li3PS4 (at) PDA and PANI (at) LATP binder to prepare the porous long-circulation silicon-carbon negative electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode material preparation, and relates to a porous long-cycle silicon-carbon anode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and light weight. With the increasing requirements for the performance of lithium-ion batteries in these fields, the graphite anode material commonly used in current commercial batteries, although having good cycle stability and a low lithium intercalation potential, is difficult to meet the needs of the next generation of high-energy-density batteries. Especially under high-rate charge and discharge and long-term cycling conditions, due to its low specific capacity and limited electrochemical performance, the graphite anode cannot meet the growing market demand for high-performance batteries, and the cycle performance of traditional graphite anode materials has been difficult to meet the requirements. Therefore, developing anode materials with higher cycle performance has become the core of current research.

[0003] As a new type of anode material, silicon has become an important candidate for future lithium-ion battery anode materials due to its extremely high theoretical specific capacity and abundant reserves. However, the practical application of silicon materials still faces multiple challenges. During the charge and discharge process, silicon will cause a large volume expansion due to the insertion and extraction of lithium ions, resulting in particle fragmentation, electrode structure failure, and rapid capacity decay. In addition, the surface of silicon is prone to side reactions with the electrolyte to form an unstable solid electrolyte interface (SEI), further accelerating the performance decay. These problems seriously limit the application of silicon materials in actual lithium-ion batteries. To alleviate the volume expansion problem of silicon materials and improve their electrochemical performance, silicon-carbon composite materials have been widely studied. By compounding silicon particles with carbon materials, the conductivity and mechanical flexibility of the carbon materials can be used to provide a buffer space for silicon, reduce the impact of volume expansion, and improve the conductivity. However, traditional silicon-carbon composite materials still have problems with insufficient cycle performance in practical applications. Therefore, it is of great significance to develop a porous long-cycle silicon-carbon anode material. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a porous long-cycle silicon-carbon anode material and a preparation method thereof. By preparing a porous silicon matrix to buffer volume expansion, using a carbon coating to improve conductivity and interface protection, introducing a Li3PS4@PDA composite material to enhance lithium ion conduction and interface stability, and designing a PANI@LATP binder to provide electronic conductivity and mechanical support, the actual production needs can be met.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a porous long-cycle silicon-carbon anode material, and the preparation method includes:

[0007] A1. Add tetraethyl orthosilicate to an ethanol aqueous solution, add ammonia water and raise the temperature to a first temperature for stirring reaction. After centrifugal washing, SiO2 microspheres are obtained. Immerse the SiO2 microspheres in a magnesium nitrate ethanol solution, ultrasonically disperse them, dry them at a second temperature, transfer them to a muffle furnace and calcine them at a third temperature to obtain SiO2@MgO. Then, mix SiO2@MgO and Pluronic F-127 in absolute ethanol, stir at room temperature and then perform rotary evaporation to obtain a template material. Mix the template material with magnesium powder, place it in a tube furnace, heat it to a fourth temperature in an Ar / H2 atmosphere for heat preservation, and after natural cooling, corrode it successively with hydrochloric acid and hydrofluoric acid, and wash and dry it with deionized water to obtain a porous silicon matrix.

[0008] S1. Mix aniline and concentrated sulfuric acid, add ammonium persulfate and continuously stir. Place it in a water bath at a first temperature and continuously stir. Filter, wash, dry and transfer it to a tube furnace, heat it to a fifth temperature for heat preservation to obtain PANI nanomaterials. Immerse the PANI nanomaterials in a precursor sol and raise the temperature gradientially, then immerse them in a CTAB solution, apply a DC electric field and stir, and then perform segmented calcination to obtain PANI@LATP. Immerse PANI@LATP in a toluene solution of 3-aminopropyltriethoxysilane, reflux at 80 °C, add glycidyl methacrylate and CuBr, adjust the temperature to 60 °C for reflux reaction, adjust the temperature to 50 °C and then add lipoic acid to react to obtain a pre-product. Disperse the pre-product and tetra-armed polyethylene glycol lipoic acid in N,N-dimethylformamide, add a photoinitiator and irradiate with ultraviolet light, and freeze-dry to obtain a PANI@LATP binder;

[0009] S2. Disperse phosphorus pentasulfide and lithium carbonate in absolute acetonitrile, reflux at a second temperature and then add polydopamine microspheres, adjust the temperature to a sixth temperature for reaction, wash and dry to obtain Li3PS4@PDA;

[0010] S3. Heat the porous silicon matrix to a fourth temperature in an argon atmosphere and then introduce acetylene. After heat preservation, naturally cool it to obtain a silicon-carbon composite material. Disperse the silicon-carbon composite material and Li3PS4@PDA in N-methylpyrrolidone, add the PANI@LATP binder after uniform dispersion, and stir evenly to obtain a porous long-cycle silicon-carbon anode material.

[0011] Tetraethyl orthosilicate is a common silicon source. In a mixed system of water and alcohol solvents, hydrolysis and polycondensation reactions are achieved through the sol-gel method, and finally silicon dioxide is formed. In this process, ammonia water acts as an alkaline catalyst and plays an important role. Its alkaline environment can accelerate the cleavage of the siloxane bond in the tetraethyl orthosilicate molecule and promote its rapid hydrolysis to form silicic acid. Subsequently, as the reaction proceeds, water or alcohol is removed through polycondensation reactions between silicic acid molecules, gradually forming Si-O-Si bonds and constructing a three-dimensional silicon dioxide network structure. After sufficient reaction time, SiO2 microspheres with uniform morphology and good dispersibility are formed. The surface of the SiO2 microspheres has a large number of hydroxyl groups, and these hydroxyl groups provide active sites for subsequent chemical functionalization. When the SiO2 microspheres are immersed in a magnesium nitrate ethanol solution, magnesium ions in the solution undergo electrostatic adsorption or coordination with the hydroxyl groups on the surface of the SiO2 microspheres and are evenly adsorbed on the surface of the microspheres. During the drying process, ethanol volatilizes, and magnesium ions are gradually deposited on the surface of the microspheres, forming a uniformly distributed magnesium precursor layer. In the subsequent calcination process, magnesium nitrate decomposes to form magnesium oxide, and this magnesium oxide layer uniformly covers the surface of the SiO2 microspheres, forming a SiO2@MgO composite structure. At high temperatures, SiO2@MgO undergoes a strong reduction reaction with magnesium powder (Mg), and SiO2 is reduced to silicon and magnesium oxide is formed. In this process, the MgO coating layer plays an important synergistic function. The calcined MgO layer ensures its uniform distribution on the surface of each particle through tight binding with SiO2, thereby improving the contact conditions between magnesium powder and SiO2. This uniform interfacial contact improves the efficiency of the reduction reaction and avoids the non-uniformity of the reaction. In addition, due to the high thermal conductivity of MgO, it can help evenly disperse heat during the high-temperature reduction process, preventing local overheating or overly intense reactions, thereby enhancing the controllability of the reaction. More importantly, the MgO coating layer can effectively inhibit the agglomeration of SiO2 particles at high temperatures. SiO2 is prone to sintering or agglomeration due to the driving force of the surface energy of the particles at high temperatures, while the MgO coating layer forms a physical isolation between the particles, reducing the possibility of direct contact between the particles, thereby maintaining the dispersibility and initial morphology of the particles. In addition, MgO itself has a high melting point and excellent thermal stability and does not undergo phase changes or decomposition within the experimental temperature range. This stability enables MgO to act as a protective layer throughout the high-temperature preparation process, preventing the morphology of SiO2 particles from being damaged during the reduction reaction. After the reduction reaction is completed, MgO partially transforms from the initial coating layer into a by-product of the reduction reaction (newly formed MgO) and is distributed on the surface and pores of the silicon particles. Subsequently, the product is acid-etched with hydrochloric acid to remove the excess MgO.The corrosive effect of hydrochloric acid not only removes MgO but also leaves a pore structure in the silicon matrix. The presence of these pores greatly increases the specific surface area of the porous silicon and simultaneously regulates its pore size distribution, thus providing sufficient reaction interfaces and lithium-ion diffusion channels for the electrochemical reactions of lithium-ion batteries. The MgO coating layer not only protects the SiO2 microspheres from sintering and agglomeration during the high-temperature reduction process but also lays the foundation for the formation of the porous silicon matrix through the removal process after the reaction. Its functions cover the uniformity of the reaction, the maintenance of the particle morphology, and the regulation of the pore structure, which is a key step in achieving the preparation of high-performance porous silicon matrices. The formed porous silicon matrix not only has a high specific surface area and abundant pores but also improves the cycling performance and rate performance of the anode material for lithium-ion batteries through its structural characteristics.

[0012] Silicon, as the anode material of lithium-ion batteries, undergoes volume expansion and contraction during charge and discharge processes. However, the mechanical stress caused by this volume change can lead to the pulverization of silicon particles and damage the structural integrity of the electrode, thereby reducing the interfacial stability of the anode material and ultimately resulting in a rapid decline in the battery's capacity and deterioration of its cycling performance. Therefore, in order to improve the service life and electrochemical performance of silicon-based anode materials, it is necessary to introduce structures or components that can relieve the volume expansion stress in the material design to optimize its mechanical and chemical stability. During the preparation of silicon-carbon anodes, the reduction reaction of silicon is a key process. Using metallic magnesium as a reducing agent, silicon dioxide is reduced to elemental silicon under high-temperature conditions. This process not only realizes the transformation of SiO2 into high-purity silicon but also regulates the structure of the silicon matrix. During the reduction process, the generated MgO fills or occupies part of the volume of the original SiO2 particles, prompting the formation of a pore structure between silicon particles. Subsequently, the residual MgO and the unreacted SiO2 template are removed by etching with hydrochloric acid and hydrofluoric acid. These treatments further expand the pores, forming a porous silicon matrix with a high specific surface area and abundant pores. This porous structure not only relieves the volume expansion of silicon during charge and discharge but also provides abundant channels for the transport and storage of lithium ions. It is worth noting that this reduction reaction is carried out in an inert atmosphere (Ar / H2), and the weak reducing property of H2 further reduces the risk of silicon particles being oxidized at high temperatures, thus generating high-purity elemental silicon. The generation of high-purity silicon improves the electronic conductivity of the material, which is crucial for the electrochemical performance of the anode material. Silicon has a high theoretical specific capacity, and compared with traditional graphite anode materials, the capacity advantage of silicon is significant. The silicon generated in the reduction reaction can form an alloy with lithium ions through a lithiation reaction, which provides active sites for the storage of lithium ions and significantly enhances the specific capacity of the anode material. In addition, due to the porous structure generated by the reduction reaction, the pore network of the porous silicon matrix provides abundant channels for the diffusion of lithium ions. This structure significantly reduces the diffusion resistance of lithium ions, enabling lithium ions to quickly pass through the electrode material, thereby enhancing the rate performance of the material. The pore structure also allows the electrolyte to fully infiltrate the entire silicon matrix, increasing the contact area between the electrode and the electrolyte and further promoting the transport efficiency of lithium ions. The formed pore distribution and optimized structural stability enable the porous silicon matrix to maintain a high capacity during long-term charge and discharge cycles, demonstrating excellent cycling stability.

[0013] In addition to the contribution of the pore structure, MgO itself also plays an important role in the porous silicon anode material. MgO is a material with high hardness and high melting point, having good mechanical stability. After the reduction reaction, although most of the MgO is corroded and removed, there are still a small number of residual MgO particles distributed inside or on the surface of the porous silicon matrix. These residual MgO particles act as a structural support, forming a "hard-soft" composite structure, in which the hard MgO and the relatively soft porous silicon together constitute the composite material. Such a composite structure can absorb part of the stress when the silicon particles expand due to lithiation, preventing direct extrusion and fragmentation between the silicon particles. Specifically, the residual MgO particles play the following roles in the material: (1) Buffering volume expansion: The residual MgO particles, as a mechanical support, can effectively disperse the stress generated during silicon expansion, reducing the damage to the overall structure of the material caused by expansion; (2) Enhancing mechanical strength: The residual MgO fills inside or on the surface of the porous silicon matrix, providing additional mechanical strength for the composite material, thus reducing the phenomenon of silicon particles cracking due to expansion and contraction during charge and discharge; (3) Maintaining the integrity of the pore structure: The presence of MgO stabilizes the framework structure of the porous silicon to a certain extent. Even after multiple charge and discharge cycles, the pore network can still maintain its integrity. Maintaining the integrity of the pore structure is particularly important for the long cycle performance of the material. The pores not only provide a path for the diffusion of lithium ions but also provide a buffer space for the volume expansion of silicon. If the pores collapse during cycling, it will lead to an increase in the density of the electrode, a decrease in the electrolyte permeability, and a reduction in the lithium ion transport efficiency, thus causing a rapid decay of the electrochemical performance. Therefore, the composite structure composed of residual MgO and porous silicon is of great significance in improving the cycle performance of the material. The porous silicon matrix prepared by the reduction reaction of silicon exhibits multiple advantages in terms of structure and performance. The generation of high-purity silicon provides excellent conductivity and high specific capacity for the material; the porous structure provides rich channels for the transport and storage of lithium ions and buffers the volume expansion of silicon; the residual MgO particles further enhance the stability of the material through mechanical support.

[0014] The preparation of polyaniline (PANI) is carried out by chemical oxidative polymerization, which is a common method for preparing conductive polymers. The core mechanism is that aniline monomers undergo chemical polymerization under the action of an oxidant in an acidic solution. In this experiment, sulfuric acid provides an acidic environment, enabling aniline molecules to be protonated to form cationic aniline. The protonated aniline cations are more stable in an acidic medium. In the reaction, ammonium persulfate acts as a strong oxidant and reacts with aniline monomers to generate aniline radical cations. Aniline radical cations are highly reactive intermediates, which combine with each other through coupling reactions to gradually form a conjugated molecular chain composed of imine and amine units, and finally form polyaniline. After the preparation is completed, PANI needs to be further heat-treated to improve its performance. During the holding and calcination process, PANI undergoes partial carbonization reactions. The main role of carbonization is to remove low-molecular-weight organic components, such as unreacted aniline monomers or low-molecular-weight polyanilines during the reaction process. This process not only reduces the defects in the material but also further improves the order of PANI molecular chains by introducing the conjugated structure of partial carbon bonds, thus significantly enhancing the electron transport ability of the material. In addition, calcination also improves the thermal stability and antioxidant properties of PANI, endowing it with better stability in high-temperature and electrochemical working environments. This carbonized PANI material has high conductivity and can be used as part of an electronic conductive network to compensate for the insufficient conductivity of the silicon-carbon negative electrode. At the same time, its antioxidant and thermal stability can extend the service life of the negative electrode material. After carbonization, the PANI nanomaterials are immersed in the precursor sol and further coated with an LATP coating by the sol-gel method. LATP is a solid electrolyte with excellent lithium-ion conductivity and chemical stability. The preparation of the LATP coating uses titanium tetraisopropoxide as the titanium source, aluminum nitrate nonahydrate as the aluminum source, and lithium dihydrogen phosphate as the lithium source, and is realized by the sol-gel method. In this system, titanium tetraisopropoxide first undergoes a hydrolysis reaction to generate titanium oxide intermediates. Subsequently, the aluminum source and the lithium source interact with the intermediates to form a mixed metal oxide precursor sol. After the PANI material is immersed in the precursor sol, due to the action of liquid surface tension, the sol uniformly covers the surface of the PANI particles. To form a stable LATP coating, the sol system is treated by gradient heating to form a continuous and dense coating that firmly adheres to the surface of PANI. The LATP coating plays an important role in the silicon-carbon negative electrode: (1) Improving lithium-ion conductivity: LATP provides a fast migration channel for lithium ions and improves the ion transport ability of the negative electrode material; (2) Isolating silicon particles from the electrolyte: The LATP coating can effectively block the direct contact between silicon particles and the electrolyte, reduce the decomposition reaction of the electrolyte and the disordered growth of the solid electrolyte interface (SEI) film on the silicon surface, thereby improving the cycle life of the electrode; (3) Improving chemical stability: LATP has good chemical stability within the electrochemical working potential range.

[0015] To further improve the uniformity and adhesion of the LATP coating, the PANI@LATP material was immersed in a CTAB solution and an electric field was applied. CTAB is a cationic surfactant that can interact with the surface of LATP particles through electrostatic adsorption, thereby improving the uniformity of the coating. When an electric field is applied, the ion migration rate in the LATP coating increases, further promoting the densification of the coating. In addition, the electric field also induces charge interactions between the surface of PANI and the LATP layer, enhancing the binding strength between the two. This process enables the LATP coating to cover the surface of PANI more tightly and densely, providing excellent electrical conductivity, ion transport ability, and chemical stability for subsequent electrochemical applications. PANI prepared by chemical oxidative polymerization has high electrical conductivity and thermal stability after preliminary carbonization, and can provide a reliable electronic conduction network for the silicon-carbon negative electrode. Subsequently, an LATP coating was deposited on the surface of PANI by the sol-gel method. The presence of LATP significantly improves the lithium-ion conductivity of the negative electrode, while isolating the direct contact between silicon particles and the electrolyte, reducing side reactions and increasing the cycle life. The uniformity and adhesion of the LATP coating were further optimized by CTAB and electric field-assisted modification, enabling the material to exhibit excellent performance in an electrochemical environment.

[0016] The PANI@LATP was immersed in a toluene solution of 3-aminopropyltriethoxysilane and heated under reflux. The silyl group in the 3-aminopropyltriethoxysilane molecule undergoes hydrolysis in the reaction system to form silanol. The generated silanol molecules have high chemical activity and can react with the hydroxyl groups present on the surface of the LATP or PANI material through a condensation reaction, eliminating water molecules to form a silicon-oxygen-silicon bond. The silanol in the 3-aminopropyltriethoxysilane molecule covalently binds to the hydroxyl groups on the material surface, forming stable silicon-oxygen-silicon bonds on the material surface. This reaction not only firmly attaches 3-aminopropyltriethoxysilane to the surface of LATP or PANI but also introduces amino groups onto the material surface. These amino groups do not participate in the condensation reaction but remain on the material surface, serving as active sites in subsequent chemical reactions and providing a chemical reaction basis for the binding of epoxy groups and polymerization reactions. After the silanization modification is completed, glycidyl methacrylate and lipoic acid are added to the system to introduce epoxy groups and disulfide bonds respectively, and the reaction occurs under suitable temperature conditions. The epoxy group in the glycidyl methacrylate molecule has high chemical activity and can undergo a nucleophilic ring-opening reaction with the amino groups introduced on the silanized surface. The carbon atom in the epoxy group is vulnerable to attack by nucleophiles. After the amino group reacts with the epoxy group as a nucleophile, a stable hydroxyl-amine covalent bond is formed. Through this reaction, the epoxy group in GMA is firmly bound to the surface of the PANI@LATP material, further providing active sites for subsequent cross-linking polymerization reactions. At the same time, the carboxyl group in the lipoic acid molecule can undergo an esterification reaction with the hydroxyl groups present on the material surface, generating an ester bond through dehydration. This process firmly binds the lipoic acid molecule to the material surface. In addition, the disulfide bond in the lipoic acid molecule endows the material with key flexibility and antioxidant properties. In the application of silicon-based anode materials, the disulfide bond provides mechanical flexibility and can buffer stress during the severe volume expansion of silicon particles during charge and discharge processes. At the same time, the antioxidant property improves the stability of the material in electrochemical cycles. The obtained pre-product is further polymerized with tetra-arm polyethylene glycol lipoic acid and a photoinitiator to construct a highly cross-linked polymer network. These free radicals can initiate the polymerization reaction of the active terminal groups in the tetra-arm polyethylene glycol lipoic acid molecule with the epoxy groups or other reaction sites on the material surface, forming a highly cross-linked three-dimensional polymer network. This polymer network provides flexibility through the polyethylene glycol molecular segments and enhances the mechanical strength and adhesion ability of the material through the cross-linked structure. In addition, the formation of the cross-linked network can effectively prevent the material from falling off due to volume changes during multiple charge and discharge processes of silicon particles, thus significantly improving the cycle stability of the electrode.Through photo-initiated free radical polymerization, a highly cross-linked polymer network is formed on the material surface. This network not only acts as a binder, improving the bonding strength of the internal components of the material, but also significantly enhances the flexibility and electrochemical stability of the material through flexible molecular chains and antioxidant structures, enabling it to better adapt to the complex mechanical and chemical environments generated during the charge and discharge processes of the silicon-based anode.

[0017] Phosphorus pentasulfide is a strong electrophilic compound, and its chemical properties mainly originate from the phosphorus-sulfur bonds in the molecule, which have high reactivity. After being dispersed in anhydrous acetonitrile, the phosphorus pentasulfide molecules are partially dissolved, and their phosphorus-sulfur bonds are activated by the polar environment of the solvent molecules, making the phosphorus atoms in phosphorus pentasulfide exhibit strong electrophilicity. In this state, the phosphorus atoms in phosphorus pentasulfide are vulnerable to attack by nucleophiles, thus triggering chemical reactions. In the reaction system, lithium carbonate acts as a lithium source and participates in the reaction together with phosphorus pentasulfide. Lithium carbonate dissociates under heating conditions to generate lithium ions and carbonate ions. Among them, the carbonate ion is a strong nucleophile and can actively attack the electrophilic phosphorus atoms in the phosphorus pentasulfide molecule. Specifically, the carbonate ion uses its oxygen atom as a nucleophilic center to undergo a nucleophilic substitution reaction with the phosphorus atoms in the phosphorus pentasulfide molecule, gradually releasing carbon dioxide gas while triggering the cleavage and recombination of the phosphorus pentasulfide molecular structure. During the reaction process, the phosphorus and sulfur atoms in phosphorus pentasulfide combine with the lithium ions in the solution to finally form lithium thiophosphate (Li3PS4). Li3PS4 is an important solid electrolyte, and its crystal structure contains abundant lithium ion migration channels. These channels are formed by the arrangement between sulfide ions and phosphate ions in the structure, enabling lithium ions to migrate rapidly in the lattice with low activation energy, showing excellent ionic conduction performance.

[0018] After the preparation of Li3PS4 is completed, in order to further improve its stability and the binding performance between particles, polydopamine (PDA) microspheres are introduced for surface modification. Polydopamine is a kind of biomimetic polymer material, which is prepared by the self-oxidation and self-polymerization reaction of dopamine. The PDA molecular chain is rich in various active functional groups, including phenolic hydroxyl groups, amino groups and amide structures. These functional groups have extremely high chemical reaction activity and adhesion performance, enabling PDA to physically adsorb and chemically bond with the surfaces of various materials. Under high-temperature conditions, PDA microspheres are introduced into the reaction system to form a composite with Li3PS4. The phenolic hydroxyl groups and amino groups on the surface of PDA can form stable interactions with the sulfur or phosphorus atoms exposed on the surface of Li3PS4 particles through hydrogen bonding or weak chemical bonds. Specifically, the phenolic hydroxyl groups can form hydrogen bonds with the sulfur atoms in the sulfides on the surface of Li3PS4, while the amino groups can bind to the phosphorus atoms on the surface of Li3PS4 through electrostatic interactions or weak chemical bonds. Under the combined action of this physical adsorption and chemical bonding, PDA is gradually and uniformly deposited on the surface of Li3PS4 particles, and finally Li3PS4@PDA is formed. Li3PS4 is a material that is vulnerable to the external environment. In particular, moisture and oxygen have a great destructive effect on its performance. When in contact with moisture, Li3PS4 will undergo a decomposition reaction to generate by-products such as hydrogen sulfide, resulting in a significant decrease in the ionic conductivity of the material. By coating a layer of PDA on the surface of Li3PS4, the intrusion of external moisture and oxygen can be effectively isolated, thereby significantly improving the environmental stability of Li3PS4. In addition, the PDA coating can also reduce the possibility of side reactions between Li3PS4 and oxygen in the air, and extend the service life of the material. In addition to having a protective effect, PDA also has excellent adhesion and mechanical flexibility. The rich functional groups on its surface can enhance the interaction between Li3PS4 particles and reduce the resistance at the particle interface. This effect helps to improve the overall ionic conductivity of the material, and at the same time, by enhancing the close contact between particles, the performance of the composite material in the electrode is more excellent.

[0019] Under high-temperature conditions (650 - 680 °C), the surface structure of the porous silicon substrate is activated to a certain extent. The thermal energy at high temperature causes some of the chemical bonds on the silicon surface (such as silicon-oxygen bonds or silicon-hydrogen bonds) to be partially broken or rearranged, thereby exposing more unsaturated bonds or active sites. These active sites can significantly enhance the adsorption capacity of the silicon substrate surface for external molecules (such as acetylene) and provide ideal reaction sites for subsequent chemical vapor deposition reactions. This surface activation phenomenon not only increases the contact area with the reaction gas but also creates more favorable conditions for the deposition of carbon atoms. When acetylene gas is introduced into the reaction system, its molecules undergo thermal decomposition at high temperature to generate active carbon atoms and hydrogen. During this process, the triple bond (C≡C) in the acetylene molecule is broken due to the input of high-temperature energy, producing individual carbon atoms. These carbon atoms have extremely high chemical activity and can quickly undergo physical adsorption and chemical bonding with the silicon substrate surface and gradually deposit on the surface of the silicon particles through chemical vapor deposition. As the reaction time extends, these carbon atoms accumulate in a layered form on the silicon surface and finally form a uniform carbon coating that completely covers the surface of the silicon particles. The introduction of this carbon coating is of great significance for the electrochemical performance of silicon-based electrode materials. During the charge and discharge process of lithium-ion batteries, silicon, as the anode material, has attracted much attention due to its extremely high specific capacity. However, silicon undergoes significant volume expansion during the lithium intercalation reaction, and this expansion effect will cause cracking and pulverization of the silicon particles, thereby damaging the electrode structure and reducing the cycle life of the battery. After introducing the carbon coating, the flexibility and mechanical stability of the carbon material can play a buffering role, absorbing the mechanical stress caused by volume expansion and preventing the pulverization of silicon particles. In addition, the carbon coating can also maintain the integrity of the silicon particles to a certain extent, thereby maintaining the structural stability of the electrode. On the other hand, due to its excellent electronic conductivity, the carbon material not only provides a fast electron migration channel but also can reduce the overall impedance and improve the rate performance of the battery. At the same time, the carbon coating also plays an isolation and protection role. After covering the surface of the silicon particles, it can effectively isolate the direct contact between silicon and the electrolyte. When silicon contacts the electrolyte, it is easy to induce side reactions, leading to the unstable growth of the solid electrolyte interface phase (SEI), and these unstable SEI layers will consume the electrolyte and lithium ions, thereby causing capacity decay. The presence of the carbon coating can slow down these adverse reactions, thereby enhancing the cycle stability and long-term service life of the electrode.

[0020] Polyaniline (PANI) is an important conductive polymer, and its unique molecular structure enables it to provide excellent electron conduction ability through doping and dedoping effects. In electrode materials, PANI can not only serve as part of the conductive network to reduce the electron impedance of the electrode, but also buffer the volume expansion effect of the silicon-carbon composite material through its flexible molecular chain. This flexible property allows PANI to adapt to the expansion and contraction of silicon particles during the charge and discharge process of the electrode material, thereby avoiding the accumulation of mechanical stress in the material and prolonging the cycle life of the electrode. Lithium aluminum titanium phosphate (LATP) is a high-performance solid electrolyte with good lithium-ion conduction ability. In electrode materials, LATP can not only improve the overall ionic conduction performance of the electrode, but also enhance the lithium-ion migration efficiency inside the electrode, thereby improving the rate performance of the battery. In addition, the phosphate ions in the LATP crystal structure can form weak chemical bonds with the surface of the silicon-carbon composite particles, and this bonding can further enhance the structural stability of the composite material and prevent the separation and shedding of particles. Generally speaking, the introduction of the PANI@LATP binder realizes the synergistic optimization of electron and ion conduction. PANI provides an efficient electron conductive network, while LATP constructs a fast lithium-ion migration channel. The two work together to significantly improve the electrochemical performance of the silicon-carbon composite electrode. At the same time, the chemical bonding between LATP and silicon-carbon particles and the flexible adhesion of PANI enhance the structural integrity and cycle stability of the electrode.

[0021] As a preferred technical solution of the present invention, in step A1, the volume ratio of tetraethyl orthosilicate to the ethanol aqueous solution is 1:5.

[0022] In some alternative embodiments, the mass fraction of the ethanol aqueous solution is 9-11 wt.%, for example, it can be 9.0 wt.%, 9.2 wt.%, 9.4 wt.%, 9.6 wt.%, 9.8 wt.%, 10.0 wt.%, 10.2 wt.%, 10.4 wt.%, 10.6 wt.%, 10.8 wt.% or 11.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] In some alternative embodiments, the mass fraction of the ammonia water is 20-25 wt.%, for example, it can be 20.0 wt.%, 20.5 wt.%, 21.0 wt.%, 21.5 wt.%, 22.0 wt.%, 22.5 wt.%, 23.0 wt.%, 23.5 wt.%, 24.0 wt.%, 24.5 wt.% or 25.0 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] In some alternative embodiments, the volume ratio of tetraethyl orthosilicate to ammonia water is 12:5.

[0025] In some alternative embodiments, the first temperature is 40 - 50 °C. For example, it can be 40.0 °C, 41.0 °C, 42.0 °C, 43.0 °C, 44.0 °C, 45.0 °C, 46.0 °C, 47.0 °C, 48.0 °C, 49.0 °C or 50.0 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0026] In some alternative embodiments, the stirring reaction time at the first temperature is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] In some alternative embodiments, the mass fraction of the magnesium nitrate ethanol solution is 13 wt.%.

[0028] In some alternative embodiments, the ultrasonic dispersion time is 30 - 40 min. For example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] In some alternative embodiments, the second temperature is 80 - 90 °C. For example, it can be 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C or 90 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] In some alternative embodiments, the third temperature is 500 - 600 °C. For example, it can be 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 570 °C, 580 °C, 590 °C or 600 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] In some alternative embodiments, the calcination time is 3 - 4 h. For example, it can be 3.0 h, 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h or 4.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0032] In some alternative embodiments, the mass ratio of SiO2@MgO to Pluronic F-127 is 5:3.

[0033] In some alternative embodiments, the mass-volume ratio of SiO2@MgO to absolute ethanol is 1 g: 40 mL.

[0034] In some alternative embodiments, the time for stirring at room temperature is 12 - 13 h, for example, it can be 12.0 h, 12.1 h, 12.2 h, 12.3 h, 12.4 h, 12.5 h, 12.6 h, 12.7 h, 12.8 h, 12.9 h or 13.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0035] In some alternative embodiments, the mass ratio of SiO2@MgO to magnesium powder is 1:16.

[0036] In some alternative embodiments, the volume ratio of Ar to H2 is 95:5.

[0037] In some alternative embodiments, the fourth temperature is 650 - 680 °C, for example, it can be 650 °C, 653 °C, 656 °C, 659 °C, 662 °C, 665 °C, 668 °C, 671 °C, 674 °C, 677 °C or 680 °C, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0038] In some alternative embodiments, the holding time at the fourth temperature is 5 - 6 h, for example, it can be 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h or 6.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the concentration of hydrochloric acid is 1 M.

[0040] In some alternative embodiments, the mass fraction of hydrofluoric acid is 5 wt.%.

[0041] As a preferred technical solution of the present invention, in step S1, the mass-volume ratio of aniline to concentrated sulfuric acid is 1 g: 5 mL.

[0042] In some alternative embodiments, the mass ratio of aniline to ammonium persulfate is 2:1.

[0043] In some alternative embodiments, the continuous stirring time under the water bath condition is 12 - 13 h. For example, it can be 12.0 h, 12.1 h, 12.2 h, 12.3 h, 12.4 h, 12.5 h, 12.6 h, 12.7 h, 12.8 h, 12.9 h or 13.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative embodiments, the fifth temperature is 200 - 220 °C. For example, it can be 200 °C, 202 °C, 204 °C, 206 °C, 208 °C, 210 °C, 212 °C, 214 °C, 216 °C, 218 °C or 220 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative embodiments, the heat preservation time at the fifth temperature is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] In some alternative embodiments, the solute in the precursor sol is tetra - isopropyl titanate, aluminum nitrate nonahydrate and lithium dihydrogen phosphate, and the volume - mass ratio is 25 mL:8 g:12 g. The solvent is a mixed solution of ethanol / acetyl and acetone with a volume ratio of 4:1, and the volume ratio of tetra - isopropyl titanate to the solvent is 25:130.

[0047] In some alternative embodiments, the gradient heating is as follows: keep the temperature at 50 °C for 2 h, 80 °C for 1 h, and 120 °C for 30 min.

[0048] The concentration of the CTAB solution is 0.01 M.

[0049] In some alternative embodiments, the voltage of the direct - current electric field is 30 V.

[0050] In some alternative embodiments, the staged calcination is as follows: calcine at 300 °C for 2 h with a heating rate of 1 °C / min, and then calcine at 550 °C for 3 h with a heating rate of 2 °C / min.

[0051] In some alternative embodiments, the mass - volume ratio of PANI@LATP to 3 - aminopropyltriethoxysilane is 2 g:5 mL.

[0052] In some alternative embodiments, the volume ratio of 3 - aminopropyltriethoxysilane to toluene in the toluene solution of 3 - aminopropyltriethoxysilane is 1:7.

[0053] In some alternative embodiments, the reflux reaction time at 80 °C is 12 - 13 h. For example, it can be 12.0 h, 12.1 h, 12.2 h, 12.3 h, 12.4 h, 12.5 h, 12.6 h, 12.7 h, 12.8 h, 12.9 h or 13.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0054] In some alternative embodiments, the volume ratio of the toluene solution of 3 - aminopropyltriethoxysilane to glycidyl methacrylate is 20:1.

[0055] In some alternative embodiments, the volume - mass ratio of glycidyl methacrylate to CuBr is 10 mL:0.5 g.

[0056] In some alternative embodiments, the reflux reaction time at 60 °C is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0057] In some alternative embodiments, the mass ratio of lipoic acid to PANI@LATP is 1:2.

[0058] In some alternative embodiments, the reaction time for adding lipoic acid is 3 - 4 h. For example, it can be 3.0 h, 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h or 4.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0059] In some alternative embodiments, the mass ratio of tetra - arm polyethylene glycol lipoic acid to PANI@LATP is 1:5.

[0060] In some alternative embodiments, the mass - volume ratio of tetra - arm polyethylene glycol lipoic acid to N,N - dimethylformamide is 1 g:50 mL.

[0061] In some alternative embodiments, the photoinitiator is Irgacure 2959, and its mass ratio to PANI@LATP is 1:100.

[0062] In some alternative embodiments, the ultraviolet irradiation time is 30 - 40 min, for example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0063] As a preferred technical solution of the present invention, in step S2, the mass ratio of phosphorus pentasulfide to lithium carbonate is 8:5.

[0064] In some alternative embodiments, the mass - volume ratio of lithium carbonate to anhydrous acetonitrile is 1 g:40 mL.

[0065] In some alternative embodiments, the reflux reaction time at the second temperature is 6 - 7 h, for example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0066] In some alternative embodiments, the mass ratio of phosphorus pentasulfide to polydopamine microspheres is 4:1.

[0067] In some alternative embodiments, the sixth temperature is 180 - 190 °C, for example, it can be 180 °C, 181 °C, 182 °C, 183 °C, 184 °C, 185 °C, 186 °C, 187 °C, 188 °C, 189 °C or 190 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0068] In some alternative embodiments, the reaction time at the sixth temperature is 12 - 13 h, for example, it can be 12.0 h, 12.1 h, 12.2 h, 12.3 h, 12.4 h, 12.5 h, 12.6 h, 12.7 h, 12.8 h, 12.9 h or 13.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0069] As a preferred technical solution of the present invention, in step S3, the gas flow rate of argon is 100 sccm, and the gas flow rate of acetylene is 20 sccm.

[0070] In some alternative embodiments, the mass ratio of the silicon - carbon composite material, Li3PS4@PDA to the PANI@LATP binder is 100:3:3.

[0071] In some alternative embodiments, the mass-volume ratio of the silicon-carbon composite material to N-methylpyrrolidone is 1 g: 4 mL.

[0072] In a second aspect, the present invention provides a porous long-cycle silicon-carbon anode material prepared by using the preparation method described in the first aspect.

[0073] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) A porous silicon matrix is prepared by a template method to form a porous structure, which alleviates the volume expansion of silicon during charge and discharge, reduces the risk of stress concentration and particle pulverization, enhances the mechanical stability of the electrode, and MgO can effectively disperse the stress generated during silicon expansion, reduce the damage of the expansion to the overall structure of the material, provide additional mechanical strength for the composite material, and maintain its integrity; (2) PANI is a conductive polymer, and its flexible molecular chain can buffer the volume expansion of silicon particles, while providing an efficient electron conduction channel, reducing the impedance of the electrode. Introducing LATP into the binder can not only improve the ionic conductivity of the electrode, but also enhance the structural stability of the composite material by binding the phosphate ions of LATP to the surface of the silicon-carbon composite material; (3) Li3PS4 is a solid electrolyte with high lithium-ion conductivity, and the polydopamine coating on the surface of Li3PS4 further enhances the interfacial stability of the material. The PDA coating can not only protect Li3PS4 from moisture and oxygen erosion, but also form stable physical adsorption or weak chemical bonding with the silicon-carbon composite material through its abundant functional groups (such as phenolic hydroxyl groups and amine groups) on the surface, improving the overall interfacial stability of the composite material; (4) By means of chemical vapor deposition, a carbon coating is uniformly introduced on the surface of the porous silicon. This carbon coating not only has good electron conductivity, can provide a fast electron transport channel for silicon particles, reduce the overall impedance of the electrode, but also can isolate the direct contact between silicon and the electrolyte, inhibit the excessive growth of the SEI layer, and reduce the irreversible capacity loss. Description of the Drawings

[0074] Figure 1 TEM image of the porous silicon matrix prepared in Example 1 of the present invention (scale bar: 200 nm);

[0075] Figure 2 TEM image of the porous silicon matrix prepared in Example 1 of the present invention (scale bar: 50 nm);

[0076] Figure 3 SEM image of the PANI@LATP binder prepared in Example 1 of the present invention. Detailed Embodiments

[0077] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0078] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been further purified.

[0079] Example 1

[0080] This example provides a preparation method for a porous long-cycle silicon-carbon anode material. The preparation method specifically includes the following steps:

[0081] A1. Add 60 mL of tetraethyl orthosilicate to 300 mL of 9.3 wt.% ethanol aqueous solution, add 25 mL of 22 wt.% ammonia water and heat to 44 °C for stirring reaction for 6.4 h. After centrifugation and washing, SiO2 microspheres are obtained. Immerse the SiO2 microspheres in 200 mL of 13 wt.% magnesium nitrate ethanol solution, ultrasonically disperse for 31 min and dry at 87 °C, transfer to a muffle furnace and calcine at 520 °C for 3.2 h to obtain SiO2@MgO. Then mix 5 g of SiO2@MgO with 3 g of Pluronic F-127 in anhydrous ethanol, stir at room temperature for 12.2 h and then rotary evaporate to obtain a template material. Mix the template material with 80 g of magnesium powder, place it in a tube furnace, heat to 660 °C in an Ar / H2 atmosphere and hold for 5.2 h. After natural cooling, corrode with 1 M hydrochloric acid and 5 wt.% hydrofluoric acid in sequence, wash with deionized water and dry to obtain a porous silicon matrix;

[0082] S1. Mix 10 g of aniline with 50 mL of concentrated sulfuric acid, add 5 g of ammonium persulfate and continuously stir. Place it in a water bath at 44 °C and continuously stir for 12.1 h. Filter, wash, dry and transfer it to a tube furnace. Heat it to 205 °C and keep it warm for 2.4 h to obtain PANI nanomaterials. Immerse the PANI nanomaterials in the precursor sol and gradually increase the temperature. Keep it warm at 50 °C for 2 h, at 80 °C for 1 h, and at 120 °C for 30 min. Then immerse it in a 0.01 M CTAB solution, apply a 30 V DC electric field and stir. Then carry out segmented calcination, which is calcined at 300 °C for 2 h with a heating rate of 1 °C / min, and at 550 °C for 3 h with a heating rate of 2 °C / min to obtain PANI@LAT P. Immerse 10 g of PANI@LATP in 200 mL of a toluene solution of 3-aminopropyltriethoxysilane, reflux at 80 °C for 12.2 h, add 10 mL of glycidyl methacrylate and 0.5 g of CuBr, adjust the temperature to 60 °C and reflux for 6.3 h, adjust the temperature to 50 °C and then add 5 g of lipoic acid and react for 3.3 h to obtain a pre-product. Disperse the pre-product and 2 g of tetra-arm polyethylene glycol lipoic acid in 100 mL of N,N-dimethylformamide, add 0.1 g of Irgacure 2959 and irradiate with ultraviolet light for 33 min, and freeze-dry to obtain the PANI@LATP binder.

[0083] S2. Disperse 8 g of phosphorus pentasulfide and 5 g of lithium carbonate in 200 mL of anhydrous acetonitrile, reflux at 82 °C for 6.9 h, then add 2 g of polydopamine microspheres, adjust the temperature to 188 °C and react for 12.2 h, wash and dry to obtain Li3PS4@PDA.

[0084] S3. Heat the porous silicon matrix to 650 °C in an argon atmosphere and then introduce acetylene. After keeping it warm for 3 h, naturally cool it to obtain a silicon-carbon composite material. Disperse 10 g of the silicon-carbon composite material and 0.3 g of Li3PS4@PDA in 40 mL of N-methylpyrrolidone. After dispersing evenly, add 0.3 g of the PANI@LATP binder and stir evenly to obtain a porous long-cycle silicon-carbon anode material.

[0085] Figure 1 This is the TEM image of the porous silicon matrix prepared in this example, and it can be seen that it has an obvious pore structure. Figure 2 This is the TEM image of the porous silicon matrix prepared in this example. Figure 3 This is the SEM image of the PANI@LATP binder prepared in this example.

[0086] Example 2

[0087] This example provides a preparation method of a porous long-cycle silicon-carbon anode material. The specific preparation method includes the following steps:

[0088] A1. Add 60 mL of tetraethyl orthosilicate to 300 mL of a 10.8 wt.% ethanol aqueous solution. Add 25 mL of 25 wt.% ammonia water and raise the temperature to 41 °C, then stir and react for 6.8 h. After centrifugal washing, SiO2 microspheres are obtained. Immerse the SiO2 microspheres in 200 mL of a 13 wt.% magnesium nitrate ethanol solution, ultrasonically disperse for 38 min and dry at 81 °C. Transfer to a muffle furnace and calcine at 580 °C for 3.9 h to obtain SiO2@MgO. Then, mix 5 g of SiO2@MgO with 3 g of Pluronic F-127 in anhydrous ethanol, stir at room temperature for 12.9 h, and then rotary evaporate to obtain a template material. Mix the template material with 80 g of magnesium powder, place it in a tube furnace, heat up to 670 °C in an Ar / H2 atmosphere, hold for 5.9 h, and after natural cooling, corrode successively with 1 M hydrochloric acid and 5 wt.% hydrofluoric acid, wash with deionized water and dry to obtain a porous silicon matrix;

[0089] S1. Mix 10 g of aniline with 50 mL of concentrated sulfuric acid, add 5 g of ammonium persulfate and continuously stir. Place it in a 48 °C water bath and continuously stir for 12.8 h. Filter, wash, dry and transfer to a tube furnace, heat up to 210 °C and hold for 2.1 h to obtain PANI nanomaterials. Immerse the PANI nanomaterials in the precursor sol and raise the temperature gradient, hold at 50 °C for 2 h, hold at 80 °C for 1 h, hold at 120 °C for 30 min, then immerse in a 0.01 M CTAB solution, apply a 30 V DC electric field and stir, and then perform segmented calcination, which is calcined at 300 °C for 2 h with a heating rate of 1 °C / min, and calcined at 550 °C for 3 h with a heating rate of 2 °C / min to obtain PANI@LAT P. Immerse 10 g of PANI@LATP in 200 mL of a toluene solution of 3-aminopropyltriethoxysilane, reflux at 80 °C for 12.8 h, add 10 mL of glycidyl methacrylate and 0.5 g of CuBr, adjust the temperature to 60 °C and reflux for 6.1 h, adjust the temperature to 50 °C and then add 5 g of lipoic acid and react for 3.7 h to obtain a pre-product. Disperse the pre-product and 2 g of tetra-armed polyethylene glycol lipoic acid in 100 mL of N,N-dimethylformamide, add 0.1 g of Irgacure 2959 and irradiate with ultraviolet light for 38 min, and freeze-dry to obtain a PANI@LATP binder;

[0090] S2. Disperse 8 g of phosphorus pentasulfide and 5 g of lithium carbonate in 200 mL of anhydrous acetonitrile, reflux at 89 °C for 6.2 h, then add 2 g of polydopamine microspheres, adjust the temperature to 182 °C and react for 12.8 h, wash and dry to obtain Li3PS4@PDA;

[0091] S3. Heat the porous silicon matrix to 680 °C in an argon atmosphere, then introduce acetylene. After maintaining the temperature for 3 h, cool it naturally to obtain a silicon-carbon composite material. Disperse 10 g of the silicon-carbon composite material and 0.3 g of Li3PS4@PDA in 40 mL of N-methylpyrrolidone. After uniform dispersion, add 0.3 g of PANI@LATP binder and stir evenly to obtain a porous long-cycle silicon-carbon anode material.

[0092] Example 3

[0093] This example provides a preparation method of a porous long-cycle silicon-carbon anode material. The preparation method specifically includes the following steps:

[0094] A1. Add 60 mL of tetraethyl orthosilicate to 300 mL of 10.2 wt.% ethanol aqueous solution, add 25 mL of 20 wt.% ammonia water and heat to 49 °C for stirring reaction for 6.1 h. After centrifugal washing, obtain SiO2 microspheres. Immerse the SiO2 microspheres in 200 mL of 13 wt.% magnesium nitrate ethanol solution, ultrasonically disperse for 36 min and place in an oven at 89 °C for drying. Transfer to a muffle furnace and calcine at 550 °C for 3.6 h to obtain SiO2@MgO. Then mix 5 g of SiO2@MgO and 3 g of Pluronic F-127 in anhydrous ethanol, stir at room temperature for 12.4 h and then rotary evaporate to obtain a template material. Mix the template material with 80 g of magnesium powder, place it in a tube furnace, heat to 650 °C in an Ar / H2 atmosphere, maintain the temperature for 5.7 h, and after natural cooling, corrode successively with 1 M hydrochloric acid and 5 wt.% hydrofluoric acid, wash with deionized water and dry to obtain a porous silicon matrix;

[0095] S1. Mix 10 g of aniline with 50 mL of concentrated sulfuric acid, add 5 g of ammonium persulfate and continuously stir. Place it in a water bath at 41 °C and continuously stir for 12.5 h. Filter, wash, dry and transfer it to a tubular furnace. Heat it up to 220 °C and keep it warm for 2.8 h to obtain PANI nanomaterials. Immerse the PANI nanomaterials in the precursor sol and increase the temperature gradient. Keep it warm at 50 °C for 2 h, 80 °C for 1 h, and 120 °C for 30 min. Then immerse it in a 0.01 M CTAB solution, apply a 30 V DC electric field and stir. Then carry out segmented calcination, which is 2 h of calcination at 300 °C with a heating rate of 1 °C / min and 3 h of calcination at 550 °C with a heating rate of 2 °C / min to obtain PANI@LAT P. Immerse 10 g of PANI@LATP in 200 mL of a toluene solution of 3-aminopropyltriethoxysilane, reflux at 80 °C for 12.4 h, add 10 mL of glycidyl methacrylate and 0.5 g of CuBr, adjust the temperature to 60 °C and reflux for 6.9 h, adjust the temperature to 50 °C and add 5 g of lipoic acid and react for 3.1 h to obtain a pre-product. Disperse the pre-product and 2 g of tetra-armed polyethylene glycol lipoic acid in 100 mL of N,N-dimethylformamide, add 0.1 g of Irgacure 2959 and irradiate with ultraviolet light for 31 min, and freeze-dry to obtain the PANI@LATP binder;

[0096] S2. Disperse 8 g of phosphorus pentasulfide and 5 g of lithium carbonate in 200 mL of anhydrous acetonitrile, reflux at 81 °C for 6.1 h, then add 2 g of polydopamine microspheres, adjust the temperature to 183 °C and react for 12.4 h, wash and dry to obtain Li3PS4@PDA;

[0097] S3. Heat the porous silicon matrix to 660 °C in an argon atmosphere and then introduce acetylene. Keep it warm for 3 h and then cool it naturally to obtain a silicon-carbon composite material. Disperse 10 g of the silicon-carbon composite material and 0.3 g of Li3PS4@PDA in 40 mL of N-methylpyrrolidone. After dispersing evenly, add 0.3 g of the PANI@LATP binder and stir evenly to obtain a porous long-cycle silicon-carbon anode material.

[0098] Example 4

[0099] This example provides a preparation method of a porous long-cycle silicon-carbon anode material. The preparation method specifically includes the following steps:

[0100] A1. Add 60 mL of tetraethyl orthosilicate to 300 mL of 9.9 wt.% ethanol aqueous solution. Add 25 mL of 24 wt.% ammonia water and heat up to 46 °C, then stir and react for 6.5 h. After centrifugal washing, SiO2 microspheres are obtained. Immerse the SiO2 microspheres in 200 mL of 13 wt.% magnesium nitrate ethanol solution, ultrasonically disperse for 33 min and dry at 83 °C. Transfer to a muffle furnace and calcine at 560 °C for 3.1 h to obtain SiO2@MgO. Then, mix 5 g of SiO2@MgO with 3 g of Pluronic F-127 and add them to anhydrous ethanol. Stir at room temperature for 12.7 h and then rotary evaporate to obtain the template material. Mix the template material with 80 g of magnesium powder, place it in a tube furnace, heat up to 680 °C in an Ar / H2 atmosphere and hold for 5.2 h. After natural cooling, etch with 1 M hydrochloric acid and 5 wt.% hydrofluoric acid in sequence, wash with deionized water and dry to obtain the porous silicon matrix;

[0101] S1. Mix 10 g of aniline with 50 mL of concentrated sulfuric acid, then add 5 g of ammonium persulfate and continuously stir. Place it in a 45 °C water bath and continuously stir for 12.7 h. Filter, wash, dry and transfer to a tube furnace. Heat up to 215 °C and hold for 2.6 h to obtain PANI nanomaterials. Immerse the PANI nanomaterials in the precursor sol and increase the temperature gradient. Hold at 50 °C for 2 h, 80 °C for 1 h, and 120 °C for 30 min. Then immerse in 0.01 M CTAB solution, apply a 30 V DC electric field and stir. Then carry out segmented calcination, which is 2 h of calcination at 300 °C with a heating rate of 1 °C / min, and 3 h of calcination at 550 °C with a heating rate of 2 °C / min to obtain PANI@LAT P. Immerse 10 g of PANI@LATP in 200 mL of toluene solution of 3-aminopropyltriethoxysilane, reflux at 80 °C for 12.7 h, add 10 mL of glycidyl methacrylate and 0.5 g of CuBr, adjust the temperature to 60 °C and reflux for 6.5 h, then adjust the temperature to 50 °C and add 5 g of lipoic acid and react for 3.5 h to obtain the pre-product. Disperse the pre-product and 2 g of tetra-arm polyethylene glycol lipoic acid in 100 mL of N,N-dimethylformamide, add 0.1 g of Irgacure 2959 and irradiate with ultraviolet light for 37 min, and then freeze-dry to obtain the PANI@LATP binder;

[0102] S2. Disperse 8 g of phosphorus pentasulfide and 5 g of lithium carbonate in 200 mL of anhydrous acetonitrile, reflux at 85 °C for 6.6 h, then add 2 g of polydopamine microspheres, adjust the temperature to 186 °C and react for 12.7 h, wash and dry to obtain Li3PS4@PDA;

[0103] S3. Heat the porous silicon matrix to 670 °C in an argon atmosphere, then introduce acetylene. After holding the temperature for 3 h, cool it naturally to obtain a silicon-carbon composite material. Disperse 10 g of the silicon-carbon composite material and 0.3 g of Li3PS4@PDA in 40 mL of N-methylpyrrolidone. After uniform dispersion, add 0.3 g of PANI@LATP binder and stir evenly to obtain a porous long-cycle silicon-carbon anode material.

[0104] Comparative Example 1

[0105] This comparative example provides a preparation method of a porous long-cycle silicon-carbon anode material. The difference from Example 1 is that the mass of lipoic acid in S1 is 1 g, which is 4 g less than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0106] Comparative Example 2

[0107] This comparative example provides a preparation method of a porous long-cycle silicon-carbon anode material. The difference from Example 1 is that the mass of lipoic acid in S1 is 10 g, which is 5 g more than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0108] Comparative Example 3

[0109] This comparative example provides a preparation method of a porous long-cycle silicon-carbon anode material. The difference from Example 1 is that the mass of phosphorus pentasulfide in S1 is 2 g, which is 6 g less than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0110] Comparative Example 4

[0111] This comparative example provides a preparation method of a porous long-cycle silicon-carbon anode material. The difference from Example 1 is that the mass of phosphorus pentasulfide in S1 is 13 g, which is 5 g more than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0112] Test method: After stirring the prepared silicon-carbon anode material evenly, coat it evenly on a copper foil current collector using a coating device, bake it in a vacuum drying oven at 80 °C for 12 h, then press it evenly through a rolling machine, and finally use a punching machine to make a circular pole piece with a diameter of 14 mm; then use a lithium metal sheet as the counter electrode, a polypropylene membrane as the separator, and an electrolyte of a mixed solution of 1 mol / L lithium hexafluorophosphate and ethylene carbonate and dimethyl carbonate with an equal volume ratio. Assemble it into a 2025 button cell in a vacuum glove box filled with high-purity nitrogen for electrochemical performance testing. During the test, charge and discharge cycles are carried out at a rate of 0.1C, the voltage range is 0 - 1.5V, the number of cycles is 100 times and 300 times, and the battery after 100 cycles is disassembled to measure the volume expansion rate of the pole piece. The test results are shown in Table 1.

[0113] Table 1 Test Results of Porous Long-Cycle Silicon-Carbon Anode Materials in Examples 1-4 and Comparative Examples 1-4

[0114]

[0115] As can be seen from Table 1, compared with Example 1, the reversible capacity and cycle capacity retention rate of the first cycle in Comparative Example 1 decreased, and the volume expansion rate after 100 cycles increased; the reversible capacity and cycle capacity retention rate of the first cycle in Comparative Example 2 decreased, and the volume expansion rate after 100 cycles increased. This is because the disulfide bond in the lipoic acid molecule participates in cross-linking to form chemical bonds during the reaction, which can enhance the mechanical strength and flexibility of the binder, improve the adaptability to the volume expansion of silicon particles, and the lipoic acid can enhance its binding force to the silicon-carbon composite through chemical interaction with the surface of PANI@LATP, reducing the shedding between particles and interface failure. Insufficient amount of lipoic acid in Comparative Example 1 will lead to a decrease in the cross-linking density of the binder and insufficient interfacial binding force. During the first cycle, the silicon particles are subjected to greater mechanical stress due to volume expansion, which may cause some silicon particles to lose contact with the conductive network, resulting in an increase in irreversible capacity loss, thus reducing the reversible capacity of the first cycle. At the same time, it cannot effectively buffer the stress caused by the repeated expansion of silicon particles during cycling, resulting in the gradual pulverization or shedding of silicon particles, serious damage to the electrode structure, capacity attenuation, and an increase in the volume expansion rate. Excessive amount of lipoic acid in Comparative Example 2 leads to too high a cross-linking degree of the binder, an increase in the rigidity of the binder. The relatively rigid binder is difficult to adapt to the volume change of silicon particles during cycling, which may lead to poor connection between silicon particles and the conductive network, reducing the reversible capacity of the first cycle. At the same time, it may cause the binder to be overly densified in structure, affecting the conduction paths of ions and electrons, resulting in a decline in cycle performance.

[0116] As can be seen from Table 1, compared with Example 1, the reversible capacity and cycle capacity retention rate of the first cycle in Comparative Example 3 decreased, and the volume expansion rate after 100 cycles increased; the reversible capacity and cycle capacity retention rate of the first cycle in Comparative Example 4 decreased, and the volume expansion rate after 100 cycles increased. Phosphorus pentasulfide reacts with lithium carbonate to generate lithium phosphorus sulfide, which plays a role in improving the ionic conductivity in the composite material. Too little amount of phosphorus pentasulfide in Comparative Example 3 results in insufficient amount of Li3PS4 generated by the reaction, leading to low lithium ion conductivity in the composite material. During the first cycle of the battery, the lithium ion transport efficiency decreases, the reversible capacity of the first cycle decreases, and the overall ionic conduction efficiency of the electrode is low. During cycling, the lithium ion transport is limited, reducing the cycle capacity retention rate. Too much amount of phosphorus pentasulfide in Comparative Example 4 forms a relatively thick covering layer, which may reduce the conductivity inside the electrode, increase the impedance of the lithium ion transport path, resulting in a decrease in the cycle capacity retention rate.

[0117] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a porous long-cycle silicon-carbon negative electrode material, characterized in that: The preparation method comprises: S1, after mixing aniline with concentrated sulfuric acid, add ammonium persulfate and transfer to a tube furnace to obtain PANI nanomaterials, immerse the PANI nanomaterials in a precursor sol and gradually increase the temperature and then immerse them in a CTAB solution, apply a DC electric field and calcine in stages to obtain PANI@LATP, immerse the PANI@LATP in a toluene solution of 3-aminopropyltriethoxysilane, add glycidyl methacrylate, CuBr, and thioctic acid to react to obtain a pre-product, mix the pre-product, four-arm polyethylene glycol thioctic acid and a photoinitiator and irradiate with ultraviolet light to obtain a PANI@LATP binder; S2, dispersing phosphorus pentasulfide and lithium carbonate in anhydrous acetonitrile, adding polydopamine microspheres after the reaction, and reacting to obtain Li3PS4@PDA; S3, heating the porous silicon substrate under an argon atmosphere and then introducing acetylene to obtain a silicon-carbon composite material, dispersing the silicon-carbon composite material and Li3PS4@PDA in N-methylpyrrolidone, and then adding PANI@LATP binder to obtain a porous long-cycle silicon-carbon negative electrode material.

2. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: The preparation method of the porous silicon substrate comprises: A1, tetraethyl orthosilicate is added to an ethanol aqueous solution, and ammonia water is added to react to obtain SiO2 microspheres, the SiO2 microspheres are immersed in a magnesium nitrate ethanol solution, ultrasonically dispersed and calcined to obtain SiO2@MgO, and then SiO2@MgO and Pluronic F-127 are added to anhydrous ethanol, and a template material is obtained by rotary evaporation, the template material is mixed with magnesium powder, and placed in a tubular furnace, and kept warm under an Ar / H2 atmosphere, and after natural cooling, hydrochloric acid and hydrofluoric acid are used for etching in sequence, and deionized water is washed and dried to obtain a porous silicon substrate.

3. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: In S1: The mass ratio of aniline to ammonium persulfate is 2:1; The solutes in the precursor sol are tetraisopropyl titanate, aluminum nitrate nonahydrate and lithium dihydrogen phosphate, with a volume mass ratio of 25 mL:8 g:12 g; the solvent is a mixture of ethanol / acetyl and acetone, with a volume ratio of 4:1; and the volume ratio of tetraisopropyl titanate to the solvent is 25:

130.

4. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: In S1: The gradient temperature increase is 50°C for 2 hours, 80°C for 1 hour, and 120°C for 30 minutes. The stepwise calcination is carried out at 300°C for 2h with a heating rate of 1°C / min, and then at 550°C for 3h with a heating rate of 2°C / min. The mass volume ratio of the PANI@LATP to 3-aminopropyltriethoxysilane is 2 g:5 mL.

5. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: In S1: The mass ratio of lipoic acid to PANI@LATP is 1:2; The mass ratio of the four-arm polyethylene glycol lipoic acid to PANI@LATP is 1:

5.

6. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: In S2: the mass ratio of phosphorus pentasulfide to lithium carbonate is 8:5; The mass ratio of phosphorus pentasulfide to polydopamine microspheres is 4:

1.

7. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: In S3: the mass ratio of the silicon-carbon composite material, Li3PS4@PDA and PANI@LATP binder is 100:3:3; The mass volume ratio of the silicon-carbon composite material to N-methylpyrrolidone is 1 g:4 mL.

8. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 2, characterized in that: In A1: the volume ratio of tetraethyl orthosilicate to ethanol aqueous solution is 1:5; The volume ratio of tetraethyl orthosilicate to ammonia water is 12:5; The mass fraction of the magnesium nitrate ethanol solution is 13 wt.%.

9. The method for preparing a porous long-cycle silicon-carbon negative electrode material according to claim 1, characterized in that: In A1: the mass ratio of SiO2@MgO to Pluronic F-127 is 5:3; The mass ratio of SiO2@MgO to magnesium powder is 1:16; The volume ratio of Ar to H2 is 95:

5.

10. A porous long-cycle silicon-carbon negative electrode material is obtained according to the preparation method according to any one of claims 1 to 9.

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