Carbon nanotube porous silicon composite electrode material and preparation method thereof

Abstract

This application relates to the field of lithium-ion battery anode materials technology, and discloses a carbon nanotube porous silicon composite electrode material and its preparation method. The material is made of porous silicon powder, multi-walled carbon nanotubes, ammonium lignosulfonate, water-soluble ammonium polyphosphate, and polyethyleneimine. The preparation process employs a two-step dynamic induced agglomeration process, causing the polymer to crosslink on the surface of silicon particles to form a gel network. This network is then pyrolyzed at high temperature to transform into a mesoporous carbon matrix layer coating the porous silicon, with multi-walled carbon nanotubes intercalating within to construct a conductive network. Simultaneously, the water-soluble ammonium polyphosphate is pyrolyzed into an amorphous polyphosphate phase and distributed in the interfacial gaps. This invention utilizes the structural flexibility of the amorphous polyphosphate to absorb and buffer the volume expansion stress of porous silicon during lithium insertion / extraction, combined with the efficient electron and ion transport channels provided by the carbon network, effectively mitigating the pulverization of the active material and improving the long-cycle stability of the electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a carbon nanotube porous silicon composite electrode material and its preparation method. Background Technology

[0002] With the rapid development of portable electronic devices and the new energy vehicle industry, the market demand for high-energy-density lithium-ion batteries is constantly increasing. The specific capacity of traditional graphite anode materials has approached its theoretical limit, making it difficult to meet the demand for further improvements in battery energy density. Silicon materials, due to their high theoretical specific capacity and suitable lithium intercalation potential, are considered to be the most promising anode materials for next-generation high-energy-density lithium-ion batteries.

[0003] Despite its capacity advantage, silicon undergoes dramatic volume expansion and contraction during the lithium insertion and extraction processes of charging and discharging. This repeated volume deformation generates significant mechanical stress within the active material particles, causing them to pulverize and fragment. As the particles break down, the exposed fresh silicon surface reacts with the electrolyte, leading to repeated rupture and regeneration of the solid electrolyte interfacial film, continuously consuming the active lithium ions and electrolyte within the battery. Furthermore, the dramatic deformation of the active material disrupts the established conductive network within the electrodes, causing some silicon particles to detach from the conductive agent or current collector, increasing the contact resistance within the electrodes, ultimately resulting in a rapid decline in battery cycle capacity.

[0004] To address the volume expansion issue of silicon-based anodes, existing technologies primarily employ modification methods such as porous design and surface carbon coating. The pores within porous silicon can provide space for volume expansion to some extent, while the surface carbon layer can improve the material's electronic conductivity. However, carbon coatings prepared using conventional processes often exhibit rigidity. After repeated charge-discharge deformation of the silicon particles, the rigid carbon shell struggles to withstand internal stress and is prone to cracking, losing its protective function for the core particles. Furthermore, during conventional liquid-phase or mechanical mixing processes, due to differences in surface properties between components, silicon particles and conductive media such as carbon nanotubes are prone to agglomeration, resulting in weak interfacial bonding. This phase-separated structure is highly susceptible to failure under the stress of electrochemical cycling, making it difficult to maintain the integrity of the composite material's mechanical structure over the long term. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a carbon nanotube porous silicon composite electrode material and its preparation method. This solves the problem that silicon-based anode materials typically undergo significant volume deformation during charge-discharge cycles. This repeated expansion and contraction can easily lead to the pulverization and peeling of active materials, and to some extent, cause unstable growth of the solid electrolyte interface film, thereby affecting the connectivity of the conductive network inside the electrode and resulting in the decay of the battery's long-cycle capacity.

[0006] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a carbon nanotube porous silicon composite electrode material, which adopts the following technical solution: A carbon nanotube porous silicon composite electrode material is prepared by high-temperature pyrolysis of the following raw materials in parts by weight: 100 parts of porous silica powder; 2-8 parts of multi-walled carbon nanotubes; Ammonium lignosulfonate, 30-50 parts; the sodium ion content of the ammonium lignosulfonate is less than 100 ppm on a dry basis; 5-8 parts of water-soluble ammonium polyphosphate; Polyethyleneimine 4.5–10 parts; The composite electrode material includes a porous silicon core, a carbon matrix coating layer with a mesoporous structure located outside the porous silicon core, and a phosphorus-containing interface phase located between the porous silicon core and the carbon matrix coating layer. The multi-walled carbon nanotubes are at least partially dispersed and interspersed within the carbon matrix coating layer; The phosphorus-containing interface phase is a phosphorus-containing amorphous phase containing a POP bond structure.

[0007] By adopting the above technical solution, a composite material that helps suppress volume expansion and improve the long-term cycling stability of the electrode is obtained due to the use of a multi-component synergistic system of porous silica powder, multi-walled carbon nanotubes, ammonium lignosulfonate, water-soluble ammonium polyphosphate, and polyethyleneimine. The microstructure evolution and mechanism of action of this composite electrode material are mainly reflected in the following processes: In the liquid phase stage of constructing the composite material, the ammonium lignin sulfonate molecular chains in the system carry sulfonic acid groups ( - SO3 - Polyethyleneimine contains anionic groups such as NH3, while its molecular chain has different levels of amino groups. With changes in environmental conditions, the amino groups of polyethyleneimine undergo protonation to transform into polycations (-NH3). + This positively charged structure self-assembles with the negatively charged ammonium lignosulfonate based on electrostatic attraction; during this process, the amino groups of polyethyleneimine also undergo a certain degree of chemical cross-linking with the oxygen-containing functional groups of ammonium lignosulfonate. The above polymer components gradually form a relatively uniform three-dimensional hydrogel network on the surface and near the pores of the porous silica powder, thereby embedding and fixing the multi-walled carbon nanotubes and water-soluble ammonium polyphosphate.

[0008] Following subsequent high-temperature inert calcination, the three-dimensional polymer network, under dehydration and carbonization, evolves into a mesoporous carbon matrix layer covering the exterior of the porous silicon powder. Polyethyleneimine, as a nitrogen-rich precursor, promotes in-situ nitrogen doping within the carbon matrix, altering the local electron cloud distribution and improving the conductivity and electrolyte wettability of the carbon layer. Simultaneously, the small-molecule gases generated during pyrolysis etch the nascent carbon framework, inducing mesoporous structures and providing pathways for lithium-ion migration. Meanwhile, multi-walled carbon nanotubes are dispersed and interspersed within the carbon matrix, supplementing the long-range conductive network.

[0009] In addition, water-soluble ammonium polyphosphate undergoes deamination and polycondensation during the pyrolysis stage, and the reaction process is roughly as follows: (NH4PO3) n →(HPO3) n +nNH3↑; The polyphosphoric acid generated after gas release undergoes cross-linking and rearrangement at high temperature, transforming into an amorphous polyphosphate glass phase with a POP network structure. Since this amorphous phase tends to distribute within the interfacial gaps between the mesoporous carbon layer and porous silicon particles, and possesses a certain degree of glassy structural flexibility, when the porous silicon undergoes volume expansion during electrochemical lithium intercalation, this polyphosphate phase can absorb and disperse localized mechanical stress, transforming the deformation of individual particles into limited compression of internal gaps. This, in turn, delays the transmission of stress to the macroscopic electrode layer, helping to maintain the integrity of the electrode structure.

[0010] Preferably, the raw materials are in the following weight proportions: 100 parts porous silica powder, 5 parts multi-walled carbon nanotubes, 40 parts ammonium lignosulfonate, 6.5 parts water-soluble ammonium polyphosphate, and 7 parts polyethyleneimine.

[0011] By adopting the above technical solution, the charge distribution of the anionic and cationic polymers in the system tends to be balanced, thereby promoting the formation of a relatively complete coating layer on the porous silicon surface. At the same time, the amorphous polyphosphate glass phase derived according to this ratio has a more suitable volume duty cycle, which provides stress buffer space while reducing the obstruction to the lithium-ion solid-phase transport interface.

[0012] Preferably, the specific preparation method of the ammonium lignosulfonate is as follows: the aqueous solution of ammonium lignosulfonate is subjected to ion exchange treatment through a chromatography column packed with ammonium-type strong acid cation exchange resin, the effluent is collected and spray-dried to obtain the product.

[0013] By adopting the above technical solution, the interference of free metallic sodium ions in commercially available industrial-grade raw materials is reduced. Trace amounts of sodium ions may cause excessive graphitization of the carbon precursor during the high-temperature pyrolysis stage, increasing the rigidity of the carbon layer and weakening its strain capacity. Furthermore, residual sodium ions can easily induce side reactions during electrochemical cycling. The sodium removal process using resin pretreatment can largely suppress material property fluctuations caused by alkali metal impurities.

[0014] Preferably, the BET specific surface area of ​​the composite electrode material is 140–150 m². 2 / g, with mesopores concentrated in a pore size of 8.0–8.5 nm; and the nitrogen-containing configuration on the surface of the composite electrode material includes pyridine nitrogen and pyrrole nitrogen doped at the edges of the carbon lattice.

[0015] By adopting the above technical solution, a relatively coordinated specific surface area and pore structure are formed. This combination of specific surface area and mesopore size allows the electrolyte to penetrate into the pores of the active material while also helping to control the excessive growth of the solid electrolyte interfacial film. The pyridine nitrogen and pyrrole nitrogen doped at the edge of the carbon matrix often possess lone pairs of electrons, making them suitable as auxiliary adsorption sites for lithium ions, thus positively promoting the overall lithium insertion / extraction kinetics of the material.

[0016] Secondly, the present invention provides a method for preparing a carbon nanotube porous silicon composite electrode material, employing the following technical solution: A method for preparing a carbon nanotube porous silicon composite electrode material includes the following steps: (1) Alkaline dispersion: Porous silica powder, multi-walled carbon nanotubes, ammonium lignosulfonate and water-soluble ammonium polyphosphate are added sequentially to a liquid medium. Ammonia solution is added to adjust the pH of the system to be alkaline. The mixture is stirred and dispersed at a constant temperature to obtain a homogeneous alkaline slurry. (2) Addition of polyethyleneimine: While maintaining a constant system temperature, add an aqueous solution of polyethyleneimine to the alkaline slurry and continue stirring to homogenize the reaction; (3) Two-step dynamic induction of coagulation: In the first stage, the system temperature is kept constant and acid solution is added dropwise to the liquid surface of the system to reduce the pH of the system to the first set value; in the second stage, the system is linearly heated and acid solution is added dropwise during the heating process until the pH of the system drops to the second set value and then the acid solution is stopped. Then the temperature is continued to rise to the target aging temperature and the gel is obtained by isothermal aging. (4) Dehydration, drying and pulverization: The gel is centrifuged and vacuum dried in sequence, the dried material is mechanically ground and sieved, and the precursor particles are collected. (5) High-temperature pyrolysis: The precursor particles are calcined under inert gas protection by programmed heating. After the heat treatment is completed, the material is cooled with the furnace and sieved to obtain the composite electrode material.

[0017] By adopting the above technical solution, a controllable assembly process for composite electrode material precursors is provided, the preparation mechanism of which mainly depends on the dynamic adjustment of polymer conformation by environmental parameters: In the initial alkaline dispersion, the higher pH value allows the ammonium lignosulfonate molecular chains to remain relatively extended, enabling them to disperse and adhere more uniformly to the vicinity of silica particles and carbon nanotubes. Because the alkaline conditions inhibit the protonation of the amine groups in the polyethyleneimine molecules, the subsequently added polyethyleneimine does not immediately undergo disordered electrostatic aggregation with the ammonium lignosulfonate, thus maintaining the initial homogeneity of the mixed slurry.

[0018] The process then proceeds to the stage of adding acid dropwise. During the isothermal decrease of acid, the amino groups of polyethyleneimine gradually protonate as the pH of the system decreases, generating positively charged cation sites. These newly generated sites then electrostatically bind to the anionic groups of ammonium lignosulfonate, forming a preliminary organic protective layer around the silicon particles and reducing the tendency for secondary aggregation between particles.

[0019] When the process progresses to the second stage of heating and continuous acid reduction, driven by thermodynamic factors, the movement rate of polymer chain segments accelerates, exposing more potential reaction sites. Combined with the further reduction in pH, the cross-linking reactions between macromolecules are deeply activated. This dual induction by heat and acid causes the originally loose electrostatic network to gradually transform into a three-dimensional hydrogel phase with a certain structural strength. Finally, through a period of isothermal aging, the cross-linked network undergoes localized shrinkage and conformational rearrangement, effectively encapsulating various internal powder materials and providing a structurally stable precursor morphology for the pyrolysis and carbonization stage.

[0020] Preferably, in step (1), the liquid medium is deionized water; the constant temperature during dispersion is set to 20-30℃; an ammonia solution with a mass concentration of 3-8wt% is added to adjust the pH value of the system to 10.2-10.8 and maintain it stable; the stirring and dispersion time is 1.5-2.5 hours. In step (2), the pure polyethyleneimine is pretreated by dissolving and preparing it, specifically: pure polyethyleneimine with a weight average molecular weight of 25000 is dissolved in deionized water, and stirred continuously at room temperature until completely dissolved to prepare a homogeneous polyethyleneimine aqueous solution with a mass fraction of 20wt% for addition; the continuous stirring time after addition is 0.8-1.5 hours.

[0021] By adopting the above technical solution, the parameter configuration helps to establish a better initial mixing state. Controlling the initial pH between 10.2 and 10.8 maintains the spatial extension of lignin molecules while keeping the surface of silica particles negatively potential, thus mitigating particle sedimentation through electrostatic repulsion. Using polyethyleneimine with a molecular weight of 25,000 aims to balance the number of crosslinking nodes with the processing viscosity of the solution; pre-preparing it into a low-concentration aqueous solution effectively alleviates the problems of excessively high local concentrations and uneven dispersion that easily occur when directly adding high-viscosity raw materials.

[0022] Preferably, in step (3), the acid solution is a glacial acetic acid solution with a mass concentration of 3-8 wt%, and the pH decrease rate is controlled to be constant at 0.10-0.15 pH / min during the droplet addition process; the first set value is 7.8-8.2; the second set value is 4.8-5.2; in the second stage, the linear heating rate of the system is controlled at 0.8-1.2℃ / min, the target aging temperature is 60-70℃, and the isothermal aging time is 0.8-1.5 hours.

[0023] By adopting the above technical solution, a relatively stable reaction kinetic control process was formed. Controlling the acidity decrease rate at 0.10-0.15 pH / min moderated the polymer protonation process, reducing instantaneous agglomeration caused by sudden changes in the local environment. By controlling the reaction conditions in stages, the system first formed a primary coating layer in a weakly alkaline range of pH 7.8-8.2, and then further reduced the acidity to a slightly acidic environment of pH 4.8-5.2 through a heating rate of 0.8-1.2 °C / min, promoting the densification of the gel structure. This control of process parameters helps maintain the uniformity of the gel phase transition process, thereby reducing the possibility of macroscopic phase separation of the precursor during preparation.

[0024] Preferably, in step (4), the vacuum drying process is controlled at a temperature of 110–130°C, a vacuum degree of -0.08 MPa to -0.10 MPa, and a baking time of 10–14 hours; the D50 particle size of the collected precursor particles is controlled within the range of 10–15 μm. The specific implementation method of step (5) is as follows: the precursor particles are placed in a tube furnace, nitrogen gas with a flow rate of 0.5–1.5 L / min is introduced for atmosphere protection, and the temperature is heated to 750–850°C at a heating rate of 2–5°C / min, and then kept at a constant temperature for calcination for 3–5 hours.

[0025] By employing the above technical solution, negative pressure dehydration under vacuum helps to reduce the damage to the gel skeleton pores caused by capillary shrinkage stress. The subsequent gentle heating pyrolysis process (2-5℃ / min) allows the gases generated by the decomposition of organic matter to escape smoothly, forming internal mesopores in conjunction with vapor phase etching. The set final calcination temperature range of 750-850℃ takes into account both the microcrystalline evolution requirements of the carbonaceous precursor to ensure electrical conductivity and the physical and thermal stability of the porous silicon structure. At the same time, this temperature range covers well the operating window for the thermal conversion of water-soluble ammonium polyphosphate to the polyphosphate glass phase.

[0026] This invention provides a carbon nanotube porous silicon composite electrode material and its preparation method. It has the following beneficial effects: 1. This invention introduces water-soluble ammonium polyphosphate into the raw materials, causing it to undergo deammoniation and polycondensation during high-temperature pyrolysis, transforming it into an amorphous polyphosphate glass phase. This amorphous phase is distributed in the gaps between the mesoporous carbon matrix layer and the porous silicon powder. When the porous silicon undergoes volume expansion during lithium insertion / extraction, the polyphosphate phase absorbs and disperses local deformation stress through its structural flexibility, alleviating the pulverization and peeling problems caused by repeated volume changes in the active material particles, and helping to maintain the mechanical structural integrity of the electrode material during long-term cycling.

[0027] 2. This invention utilizes a polymer network formed by the crosslinking of ammonium lignosulfonate and polyethyleneimine, which is then transformed into an in-situ coated mesoporous carbon matrix layer through high-temperature carbonization. This layer, in conjunction with multi-walled carbon nanotubes, constructs a continuous electron conduction network. Polyethyleneimine, as a precursor, retains the pyridine and pyrrole nitrogen structures within the carbon layer. Combined with the mesoporous channels generated by pyrolysis gas etching, this improves the electrolyte wettability of the material while shortening the lithium-ion transport path, thereby enhancing the charge transfer rate and overall lithium insertion / extraction kinetics of the composite electrode material.

[0028] 3. This invention employs a two-step dynamic induced agglomeration process to prepare the precursor. First, under isothermal conditions, slow acid reduction induces the formation of a primary coating of polymer chains on the porous silicon surface. Subsequently, linear heating and further acid reduction induce densification of the gel network. This segmented, controlled reaction condition liquid-phase assembly method suppresses disordered aggregation of components in the initial mixing stage, ensuring uniform encapsulation of silicon powder and carbon nanotubes by the polymer shell, reducing the risk of macroscopic phase separation, and improving the uniformity of the final product's microstructure. Attached Figure Description

[0029] Figure 1 The rheological change trend diagrams of the slurry systems of Example 1 and Comparative Example 2 of the present invention during the gelation process are shown. Figure 2The above are XPS high-resolution spectra of the samples of Example 1, Comparative Example 1 and Comparative Example 3 of the present invention; wherein, (a) is the N1s high-resolution spectrum of the samples of Example 1, Comparative Example 1 and Comparative Example 3, and (b) is the P2p high-resolution spectrum of the samples of Example 1, Comparative Example 1 and Comparative Example 3. Figure 3 The BJH pore size distribution curves of the samples from Example 1, Comparative Example 3, and Comparative Example 4 of the present invention are shown. Figure 4 The graphs show the delithiation specific capacity curves of the composite electrode materials prepared in Example 1, Comparative Examples 2 and 4 of this invention during 500 consecutive long-cycle tests, and the coulombic efficiency curve of Example 1. Figure 5 This is a comparison chart of the electrode thickness expansion rates of Embodiment 1, Comparative Example 1, and Comparative Example 4 of the present invention; Figure 6 The cross-section of a single particle of the composite electrode material prepared in Example 1 of this invention is shown in the EDS radial line scan spectrum of the relative content distribution of elements (Si, C, P, etc.) from the porous silicon core to the outer carbon matrix coating layer. Figure 7 The images show the morphology of a single particle cross-section and the EDS elemental mapping of the composite electrode material prepared in Example 1 of this invention; where (a) is a transmission electron microscope (TEM) cross-sectional morphology image, (b) is a high-angle annular dark field (HAADF-STEM) morphology image, (c), (d), and (e) are independent mapping images of Si, C, and P elements, respectively, and (f) is a superimposed mapping image of Si, C, and P elements. Figure 8 This is a comparison curve showing the distribution of the relative content of P element along the radial line scan distance in the cross-section of a single particle of the composite electrode material prepared in Example 1 and Comparative Example 2 of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0032] Porous silica powder, CAS number 7440-21-3, D50 particle size 2.5μm, porosity 40%, BET specific surface area 25m². 2 / g.

[0033] Multi-walled carbon nanotubes, CAS number 7440-44-0, with an outer diameter of 10 nm to 20 nm, a length of 5 μm to 15 μm, and a purity of ≥98 wt% (Note: Multi-walled carbon nanotubes are allotropes of carbon, and in industry they often share the basic CAS number of elemental carbon).

[0034] Ammonium lignosulfonate, CAS No. 8061-53-8, is a water-soluble anionic polymer with a main chain containing phenylpropane structural units and sulfonic acid groups and hydroxyl groups. Its weight-average molecular weight (Mw) is 10,000, and its degree of sulfonation is 1.5 mmol / g. (Na...) + The residual amount is less than 100 ppm.

[0035] Water-soluble ammonium polyphosphate, CAS number 68333-79-9, chemical formula (NH4). n+2 P n O 3n+1 It is a short-chain inorganic polymer with a degree of polymerization n of 20. The molecular chain morphology is a linear repeating unit arrangement. Its solubility in water at 25℃ is 25g / 100mL.

[0036] Polyethyleneimine, CAS number 9002-98-6, has a branched molecular structure. The molecular chain contains repeating units of primary, secondary, and tertiary amines, with the chemical formula of the repeating unit being (C2H5N). n The weight-average molecular weight (Mw) is 25,000, and the molecular weight distribution index (PDI) is 2.5.

[0037] Preparation Example 1: This preparation example is used to remove possible residual sodium ion impurities from commercially available ammonium lignin sulfonate, and specifically includes the following steps: (1) Ion exchange treatment: Dissolve 500g of commercially available industrial grade ammonium lignosulfonate in 1500g of deionized water to prepare an aqueous solution; pass the aqueous solution through a chromatography column packed with ammonium-type strong acid cation exchange resin at a flow rate of 20mL / min, so that the trace amount of free Na+ in the aqueous solution can undergo ion exchange with NH4+ on the resin. (2) Spray drying and testing: Collect the effluent and then send it into a centrifugal spray dryer for drying at an inlet air temperature of 180°C and an outlet air temperature of 80°C. Collect the refined ammonium lignosulfonate solid powder. Use an inductively coupled plasma atomic emission spectrometer to test the solid powder and confirm that the Na+ content on a dry basis is less than 100 ppm. Seal it for later use.

[0038] Preparation Example 2: Since polyethyleneimine, with a weight-average molecular weight (Mw) of 25,000, is a highly viscous liquid at room temperature, direct addition makes rapid and homogeneous dispersion difficult. Therefore, it is necessary to prepare an aqueous solution of polyethyleneimine in advance, which includes the following steps: (1) Dissolving and preparing: Accurately weigh 100g of pure polyethyleneimine viscous liquid and place it in a glass beaker, then add 400g of deionized water; (2) Stirring and homogenization: Turn on the magnetic stirrer at room temperature and stir continuously at 500 rpm for 2 hours until the polyethyleneimine is completely dissolved and there is no stringing phenomenon, so as to obtain a homogeneous polyethyleneimine aqueous solution with a mass fraction of 20 wt%, which is ready for use.

[0039] In subsequent embodiments, the amount of polyethyleneimine added refers to the net mass of pure polyethyleneimine. In actual operation, the amount is calculated based on a 20wt% concentration and the aqueous solution is measured and added.

[0040] Example 1: This embodiment provides a method for preparing a carbon nanotube porous silicon composite electrode material, specifically including the following steps: (1) Alkaline dispersion: 400g of deionized water was added to a planetary biaxial power mixer with a temperature control jacket and a top exhaust valve. The jacket temperature was set to 25°C. 100g of porous silica powder, 5g of multi-walled carbon nanotubes, 40g of ammonium lignosulfonate solid obtained in Preparation Example 1, and 6.5g of water-soluble ammonium polyphosphate were added in sequence. The mixer was turned on, and the revolution speed was set to 30rpm and the rotation speed to 400rpm. The top exhaust valve was opened at the same time. A 5wt% ammonia solution was slowly added dropwise to the slurry to adjust the pH value of the system to 10.5 and maintain it stable. The mixture was stirred and dispersed for 2 hours at a temperature of 25°C and the above pH conditions.

[0041] (2) Addition of polyethyleneimine: Maintain the mixer temperature at 25°C, add the aqueous solution containing 7g net weight of polyethyleneimine obtained in Preparation Example 2 to the above slurry at a uniform rate, and continue stirring for 1 hour.

[0042] (3) Two-step dynamic induced coagulation: A 5 wt% glacial acetic acid solution was added dropwise to the slurry surface using a metering pump, and the pH decrease rate was controlled at 0.12 pH / min. In the first stage, the system temperature was maintained at 25°C, and the glacial acetic acid solution was added dropwise at a uniform rate. When the pH value of the system dropped to 8.0, the second stage was started. In the second stage, the jacket temperature control system was adjusted to make the slurry system linearly heated at a heating rate of 1.0°C / min, and the glacial acetic acid solution was added dropwise during the heating process to keep the pH decrease rate of the system at 0.12 pH / min. When the pH value of the system dropped to 5.0, the addition of glacial acetic acid solution was stopped, and then the temperature was continued to rise to 65°C at the above heating rate. After the system temperature reached 65°C, the system was kept stirred and aged for 1 hour to obtain a gel.

[0043] (4) Dehydration, drying and pulverization: The obtained gel was transferred to a centrifuge and centrifuged at 3000 rpm for 15 minutes to remove the supernatant; the wet gel was placed in a vacuum drying oven and baked for 12 hours at 120℃ and -0.09 MPa; the dried material was mechanically ground and pulverized, and the precursor particles with D50 of 12 μm were collected by sieving.

[0044] (5) High-temperature pyrolysis: The precursor particles are placed in a tube furnace and nitrogen gas with a flow rate of 1.0 L / min is introduced for atmosphere protection; the temperature is raised to 800℃ at a heating rate of 3℃ / min and kept at a constant temperature for 4 hours; after calcination, the furnace is naturally cooled to room temperature and the composite electrode material is obtained by sieving.

[0045] Example 2: This embodiment provides a method for preparing a carbon nanotube porous silicon composite electrode material, specifically including the following steps: (1) Alkaline dispersion: 300g of deionized water was added to a planetary biaxial power mixer with a temperature control jacket and a top exhaust valve. The jacket temperature was set to 20°C. 100g of porous silica powder, 2g of multi-walled carbon nanotubes, 30g of ammonium lignosulfonate solid obtained in Preparation Example 1 and 5g of water-soluble ammonium polyphosphate were added in sequence. The mixer was turned on and the revolution speed was set to 20rpm and the rotation speed to 300rpm. The top exhaust valve was opened at the same time. A 3wt% ammonia solution was slowly added dropwise to the slurry to adjust the pH value of the system to 10.2 and maintain it stable. The mixture was stirred and dispersed for 1.5 hours at a temperature of 20°C and the above pH conditions.

[0046] (2) Addition of polyethyleneimine: Keep the mixer temperature at 20°C, add the aqueous solution containing 4.5g net weight polyethyleneimine obtained in Preparation Example 2 to the above slurry at a uniform rate, and continue stirring for 0.8 hours.

[0047] (3) Two-step dynamic induced coagulation: A 3wt% glacial acetic acid solution was added dropwise to the slurry surface using a metering pump, and the pH decrease rate was controlled at 0.10 pH / min. In the first stage, the system temperature was maintained at 20℃, and the glacial acetic acid solution was added dropwise at a uniform rate. When the pH value of the system dropped to 8.2, the second stage was entered. In the second stage, the jacket temperature control system was adjusted to make the slurry system linearly heated at a heating rate of 0.8℃ / min, and the glacial acetic acid solution was added dropwise during the heating process to keep the pH decrease rate of the system at 0.10 pH / min. When the pH value of the system dropped to 5.2, the addition of glacial acetic acid solution was stopped, and then the temperature was continued to rise to 60℃ at the above heating rate. After the system temperature reached 60℃, the system was kept stirred and aged for 0.8 hours to obtain a gel.

[0048] (4) Dehydration, drying and pulverization: The obtained gel was transferred to a centrifuge and centrifuged at 2500 rpm for 10 minutes to remove the supernatant; the wet gel was placed in a vacuum drying oven and baked for 10 hours at a temperature of 110℃ and a vacuum of -0.08 MPa; the dried material was mechanically ground and pulverized, and precursor particles with a D50 of 10 μm were collected by sieving.

[0049] (5) High-temperature pyrolysis: The precursor particles are placed in a tube furnace and nitrogen gas with a flow rate of 0.5 L / min is introduced for atmosphere protection; the temperature is raised to 750℃ at a heating rate of 2℃ / min and kept at a constant temperature for 5 hours; after calcination, the furnace is naturally cooled to room temperature and the composite electrode material is obtained by sieving.

[0050] Example 3: This embodiment provides a method for preparing a carbon nanotube porous silicon composite electrode material, specifically including the following steps: (1) Alkaline dispersion: 500g of deionized water was added to a planetary biaxial power mixer with a temperature control jacket and a top exhaust valve. The jacket temperature was set to 30°C. 100g of porous silica powder, 8g of multi-walled carbon nanotubes, 50g of ammonium lignosulfonate solid obtained in Preparation Example 1, and 8g of water-soluble ammonium polyphosphate were added in sequence. The mixer was turned on, and the revolution speed was set to 40rpm and the rotation speed to 500rpm. The top exhaust valve was opened at the same time. An 8wt% ammonia solution was slowly added dropwise to the slurry to adjust the pH value of the system to 10.8 and maintain it stable. The mixture was stirred and dispersed for 2.5 hours at a temperature of 30°C and the above pH conditions.

[0051] (2) Addition of polyethyleneimine: Keep the mixer temperature at 30°C, add the aqueous solution containing 10g net weight of polyethyleneimine obtained in Preparation Example 2 to the above slurry at a uniform rate, and continue stirring for 1.5 hours.

[0052] (3) Two-step dynamic induced coagulation: 8 wt% glacial acetic acid solution was added dropwise to the slurry surface using a metering pump, and the pH decrease rate was controlled at 0.15 pH / min. In the first stage, the system temperature was maintained at 30℃, and the glacial acetic acid solution was added dropwise at a uniform rate. When the pH value of the system dropped to 7.8, the second stage was entered. In the second stage, the jacket temperature control system was adjusted to make the slurry system linearly heated at a heating rate of 1.2℃ / min, and the glacial acetic acid solution was added dropwise during the heating process to keep the pH decrease rate of the system at 0.15 pH / min. When the pH value of the system dropped to 4.8, the addition of glacial acetic acid solution was stopped, and then the temperature was continued to rise to 70℃ at the above heating rate. After the system temperature reached 70℃, the system was kept stirred and aged for 1.5 hours to obtain a gel.

[0053] (4) Dehydration, drying and pulverization: The obtained gel was transferred to a centrifuge and centrifuged at 3500 rpm for 20 minutes to remove the supernatant; the wet gel was placed in a vacuum drying oven and baked for 14 hours at a temperature of 130℃ and a vacuum of -0.095MPa to -0.10MPa; the dried material was mechanically ground and pulverized, and precursor particles with a D50 of 15μm were collected by sieving.

[0054] (5) High-temperature pyrolysis: The precursor particles are placed in a tube furnace and nitrogen gas with a flow rate of 1.5 L / min is introduced for atmosphere protection; the temperature is raised to 850℃ at a heating rate of 5℃ / min and kept at a constant temperature for 3 hours; after calcination, the furnace is naturally cooled to room temperature and the composite electrode material is obtained by sieving.

[0055] Example 4: This embodiment provides a method for preparing a carbon nanotube porous silicon composite electrode material, specifically including the following steps: (1) Alkaline dispersion: 400g of deionized water was added to a planetary biaxial power mixer with a temperature control jacket and a top exhaust valve. The jacket temperature was set to 25°C. 100g of porous silica powder, 8g of multi-walled carbon nanotubes, 30g of ammonium lignosulfonate solid obtained in Preparation Example 1, and 8g of water-soluble ammonium polyphosphate were added in sequence. The mixer was turned on, and the revolution speed was set to 30rpm and the rotation speed to 400rpm. The top exhaust valve was opened at the same time. A 5wt% ammonia solution was slowly added dropwise to the slurry to adjust the pH value of the system to 10.5 and maintain it stable. The mixture was stirred and dispersed for 2 hours at a temperature of 25°C and the above pH conditions.

[0056] (2) Addition of polyethyleneimine: Keep the mixer temperature at 25°C, add the aqueous solution containing 6g net weight of polyethyleneimine obtained in Preparation Example 2 to the above slurry at a uniform rate, and continue stirring for 1 hour.

[0057] (3) Two-step dynamic induced coagulation: A 5 wt% glacial acetic acid solution was added dropwise to the slurry surface using a metering pump, and the pH decrease rate was controlled at 0.15 pH / min. In the first stage, the system temperature was maintained at 25°C, and the glacial acetic acid solution was added dropwise at a uniform rate. When the pH value of the system dropped to 8.0, the second stage was started. In the second stage, the jacket temperature control system was adjusted to make the slurry system heat linearly at a heating rate of 1.0°C / min, and the glacial acetic acid solution was added dropwise during the heating process to keep the pH decrease rate of the system at 0.15 pH / min. When the pH value of the system dropped to 5.0, the addition of glacial acetic acid solution was stopped, and then the temperature was continued to rise to 65°C at the above heating rate. After the system temperature reached 65°C, the system was kept stirred and aged for 1 hour to obtain a gel.

[0058] (4) Dehydration, drying and pulverization: The obtained gel was transferred to a centrifuge and centrifuged at 3000 rpm for 15 minutes to remove the supernatant; the wet gel was placed in a vacuum drying oven and baked for 12 hours at 120℃ and -0.09 MPa; the dried material was mechanically ground and pulverized, and the precursor particles with D50 of 12 μm were collected by sieving.

[0059] (5) High-temperature pyrolysis: The precursor particles are placed in a tube furnace and nitrogen gas with a flow rate of 1.0 L / min is introduced for atmosphere protection; the temperature is raised to 800℃ at a heating rate of 3℃ / min and kept at a constant temperature for 4 hours; after calcination, the furnace is naturally cooled to room temperature and the composite electrode material is obtained by sieving.

[0060] Comparative Example 1: The difference from Example 1 is that water-soluble ammonium polyphosphate is not added in step one, but all other steps are the same.

[0061] Comparative Example 2: Compared with Example 1, the difference is that in step three, instead of using a two-step dynamic induced coagulation reaction, the system temperature is maintained at 25°C, and a 5wt% glacial acetic acid solution is added in one go to instantly lower the pH of the system to 5.0. Then, the system is directly aged for 1 hour. The rest are the same.

[0062] Comparative Example 3: Compared with Example 1, the difference is that in step one, ammonium lignosulfonate is replaced with an equal mass of sodium lignosulfonate, and water-soluble ammonium polyphosphate is replaced with an equal mass of sodium tripolyphosphate, while the rest are the same.

[0063] Comparative Example 4: Compared with Example 1, the difference is that: polyethyleneimine is not added, nor is glacial acetic acid added to induce coagulation. The dispersed homogeneous slurry is directly subjected to conventional spray drying treatment, and then directly subjected to high-temperature in-situ pyrolysis treatment under nitrogen atmosphere. All other aspects are the same.

[0064] Test Example 1: This test case is used to examine the rheological changes of the slurry system during the gelation process under different acidification induction methods.

[0065] (1) Take the co-solubilized slurry obtained after step (2) of Example 1 and the co-solubilized slurry obtained at the corresponding stage in Comparative Example 2 as test objects for rheological analysis.

[0066] (2) A rotational rheometer equipped with a Peltier temperature control module was used for testing. During the test, a parallel plate test rotor with a diameter of 40 mm was installed, the test distance between the upper and lower plates was set to 1.0 mm, the test mode was small amplitude oscillation shear mode, the strain was set to 1%, and the test angular frequency was fixed at 10 rad / s.

[0067] (3) The test object of Example 1 was loaded onto the rheometer test platform, and the initial system temperature was set to 25°C. After starting the measurement program, a 5wt% glacial acetic acid solution was slowly added to the edge of the sample liquid film using a micro-injection pump, and the pump speed and temperature control program were adjusted to make the sample test environment simulate the two-step dynamic induced coagulation process in step (3) of Example 1 as much as possible. That is, the pH was slowly reduced at 25°C, and then the temperature was increased at a rate of 1.0°C / min, and the acid was continuously reduced to pH 5.0. After stopping the acid dripping, the temperature was increased to 65°C. During the test, the changes in the system's storage modulus G' and loss modulus G'' over time were recorded.

[0068] (4) Load the test object of Comparative Example 2 onto the same cleaned test bench, and set the initial system temperature to 25°C. After starting the measurement program, at the 5th minute, use a pipette to inject a set volume of 5wt% glacial acetic acid solution into the periphery of the sample liquid film in one go, to simulate the operation of rapidly reducing the acidity to pH 5.0 in Comparative Example 2. Maintain the temperature at 25°C throughout the entire test cycle, and record the changes in the system's storage modulus G' and loss modulus G'' over time.

[0069] Table 1. Rheological characteristics of the slurry systems in Example 1 and Comparative Example 2 during the gelation process:

[0070] Based on the data in Table 1 and Figure 1 The rheological evolution trajectory of Example 1 and Comparative Example 2 shows a significant difference in the rheological change trend during the gelation process.

[0071] For Example 1, during the 0-30 minute stage, the loss modulus G'' of the system was higher than the storage modulus G', indicating that the slurry system still exhibited predominantly viscous flow characteristics during this stage, and no obvious rapid gelation or sudden flocculation was observed. With the gradual introduction of glacial acetic acid and the subsequent heating process, the storage modulus G' gradually increased, and after intersecting with the loss modulus G'' in the 55-60 minute interval, it exceeded G''. This trend suggests that under slow pH reduction and programmed temperature increase conditions, the slurry system may have undergone a gradual transition from a fluid dispersion state to a gel network state, which is beneficial for reducing the impact of localized rapid aggregation on the system's uniformity.

[0072] For Comparative Example 2, after a one-time rapid acid reduction operation at the 5th minute, the storage modulus G' increased significantly within a short period and quickly exceeded the loss modulus G'', subsequently maintaining a high level. This phenomenon indicates that the slurry system may have undergone a rapid structural transformation under rapid acid reduction conditions, making it easier for local aggregation or non-uniform coagulation structures to form within the system. Compared to Example 1, Comparative Example 2 lacked a slow pH reduction and programmed temperature increase process, and the moderating effect of water-soluble ammonium polyphosphate on the interaction between polyethyleneimine and ammonium lignosulfonate may not have been fully realized, thus making the system more prone to local structural differences during coagulation.

[0073] The above results show that the two-step dynamic induced coagulation method used in Example 1 is beneficial for the slurry system to gradually form a gel structure under relatively mild conditions, thereby providing conditions for the formation of a more uniform composite structure during subsequent drying and pyrolysis processes.

[0074] Test Example 2: This test case is used to examine the changes in the surface elemental composition and nitrogen and phosphorus-related chemical states of different samples.

[0075] (1) The composite electrode material powders prepared in Example 1, Comparative Example 1 and Comparative Example 3 were used as test objects. Before the test, each sample was placed in a vacuum drying oven and dehydrated at 80°C for 4 hours to reduce the influence of surface adsorbed moisture on the test results.

[0076] (2) Surface elemental composition and chemical state analysis of the sample was performed using X-ray photoelectron spectroscopy. During the test, the background pressure in the vacuum chamber was below 2 × 10⁻⁶. -7 mbar, the X-ray source uses monochromatic AlKα rays, photon energy hν=1486.6eV; the pass energy of the narrow scan test is set to 30.0eV, and the energy step is set to 0.05eV.

[0077] (3) Data processing of the obtained XPS spectra. Charge correction was performed using the C1s characteristic peak of contaminated carbon, i.e., the binding energy of 284.8 eV, as a benchmark. The Shirley method was used to subtract the background, and the Gaussian-Lorentz mixture function was used to perform peak fitting on the N1s and P2p high-resolution spectra, with the GL ratio set to 20% to 30%. Based on the fitting results, the peak areas corresponding to pyridine nitrogen, pyrrole nitrogen, and graphitized nitrogen were separated, and the relative percentage of each nitrogen-containing configuration in the total nitrogen was calculated. Simultaneously, based on the characteristic peak area attributable to the POP bond in the P2p spectrum, its relative percentage of the total peak area of ​​P element was recorded. The test results are shown in Table 2.

[0078] Table 2. Elemental composition and chemical structure parameters of XPS surfaces of Example 1 and comparative samples:

[0079] According to Table 2 and the appendix Figure 2 According to the data, the total nitrogen content of the composite electrode material obtained in Example 1 is 7.13 at%, of which the relative contents of pyridine nitrogen and pyrrole nitrogen are 43.21% and 36.52%, respectively; at the same time, the peak area attributable to POP bonds in the P2p spectrum accounts for 81.35% of the total peak area of ​​P element. The above results indicate that the surface of the material obtained in Example 1 has a high proportion of nitrogen-containing functional structures and forms obvious POP bond structure features.

[0080] Based on the analysis of the raw material composition and heat treatment process in Example 1, ammonium lignosulfonate, water-soluble ammonium polyphosphate, and polyethyleneimine may collectively participate in the formation of the carbon-based framework and the regulation of surface chemical states during pyrolysis. Specifically, the nitrogen-containing atmosphere generated by the decomposition of the ammonium salt components during heat treatment may facilitate the entry of nitrogen elements into the edges or defect sites of the carbon framework, thereby forming a certain proportion of pyridine nitrogen and pyrrole nitrogen structures. The aforementioned nitrogen-containing configuration generally helps to increase the number of active sites on the material surface and improve interfacial ion transport characteristics. Simultaneously, ammonium polyphosphate undergoes deamination, dehydration, and polycondensation reactions during heat treatment, potentially forming an amorphous polyphosphate structure characterized by POP bonds. This structure facilitates the formation of a buffer phase between the carbon matrix and porous silicon particles.

[0081] In Comparative Example 1, without the addition of water-soluble ammonium polyphosphate, the total nitrogen content decreased to 3.41 at%, and no valid signal attributable to POP bonds was detected in the P2p spectrum. These results indicate that in the absence of ammonium polyphosphate, it is difficult to form a significant POP bond structure in the sample, and the nitrogen configuration distribution also changes, with the relative content of graphitized nitrogen increasing to 46.03%.

[0082] Comparative Example 3 used a sodium salt system instead of an ammonium salt system, and its total nitrogen content was 1.87 at%, lower than that of Example 1 and Comparative Example 1; at the same time, its relative POP bond content was 12.68%, significantly lower than that of Example 1. These results indicate that the sodium salt system may have an adverse effect on nitrogen retention and the formation of phosphate condensation structures. It is speculated that this is because the presence of sodium ions alters the condensation behavior of phosphate components during heat treatment, making them more prone to forming relatively discrete sodium salt-type phosphate structures, thus hindering the formation of continuous POP network structures.

[0083] Based on the XPS test results above, it can be seen that the ammonium salt system used in Example 1 is more conducive to obtaining a higher surface nitrogen content and a more obvious POP bond structure feature, which is basically consistent with its subsequent design idea of ​​forming a nitrogen-containing carbon-based framework and a polyphosphate buffer phase.

[0084] Test Example 3: This test case is used to examine the pore structure parameters and sodium ion residue of different samples.

[0085] (1) The composite electrode material powders prepared in Example 1, Comparative Example 3 and Comparative Example 4 were used as test objects.

[0086] (2) Weigh 1.0 g of the powder to be tested and place it in the glass sample tube of the fully automatic specific surface area and porosity analyzer. Heat it at 150 °C and under vacuum for 6 hours to degas it, so as to reduce the influence of adsorbed moisture and impurity gases in the material pores on the test results. Transfer the degassed sample tube to the analysis station and perform nitrogen adsorption-desorption test at liquid nitrogen temperature of 77 K using high-purity nitrogen as the adsorbate. Based on the adsorption-desorption isotherms obtained from the test, calculate the specific surface area of ​​the material using the BET multi-point method, and calculate the total pore volume and mesopore size distribution based on the desorption branch data using the BJH model.

[0087] (3) Weigh 0.1g of the powder to be tested and place it in a microwave digestion vessel. Add a mixed acid solution of nitric acid, hydrofluoric acid, and hydrogen peroxide. Set the temperature program of the microwave digester and digest the sample at 200℃ for 2 hours to ensure the powder is fully dissolved. After cooling, dilute to a 50mL volumetric flask. Use inductively coupled plasma atomic emission spectrometry to test the sodium ion concentration in the digestion solution and calculate the mass fraction of sodium ions in the powder according to the dilution factor. The test results are shown in Table 3.

[0088] Table 3. Pore structure parameters and sodium ion residue test results of Example 1 and comparative sample:

[0089] Based on the data in Table 3 and Figure 3 The distribution pattern of the composite electrode material obtained in Example 1 shows that its BET specific surface area is 145.28 m². 2 / g, BJH total pore volume is 0.287cm³. 3 / g, the mesopores are concentrated with a pore size of 8.35 nm, and the sodium ion residual concentration is 41 ppm. The above results indicate that the material obtained in Example 1 has a high specific surface area and pore volume, exhibits obvious mesoporous structure characteristics, and has a low sodium ion residual level.

[0090] Based on the analysis of the preparation process in Example 1, ammonium lignosulfonate and water-soluble ammonium polyphosphate may generate volatile components such as nitrogen-containing gases and moisture during heat treatment. These volatile components, during their escape, are beneficial for forming a certain porous structure within the carbon-based framework. Furthermore, the initial dynamic induced aggregation process may help stabilize the distribution between the polymer components and the porous silicon and carbon nanotubes, thereby resulting in a more uniform mesoporous structure in the material obtained after subsequent heat treatment. The low residual sodium ion concentration also indicates that the low-sodium treatment in Example 1 helps reduce the introduction of alkali metal impurities.

[0091] Comparative Example 3 used a sodium salt system instead of an ammonium salt system, and its BET specific surface area was 36.51 m². 2 / g, BJH total pore volume is 0.058cm³. 3 The mesoporous pore size was 2.14 nm, and the sodium ion residual concentration was 19524 ppm. Compared with Example 1, Comparative Example 3 showed a significant decrease in specific surface area and pore volume, a pore size distribution biased towards the lower limit of the mesoporous region, and a significant increase in sodium ion residual concentration. These results indicate that sodium salt systems may not be conducive to the formation of a well-developed mesoporous structure and may introduce a higher level of inorganic sodium residue.

[0092] Comparative Example 4 did not undergo polyethyleneimine addition or acetic acid-induced coagulation treatment; instead, the dispersion slurry was directly dried and heat-treated. Its BET specific surface area was 68.74 m². 2 / g, BJH total pore volume is 0.113cm³. 3 / g, the mesopores are concentrated with a pore size of 19.82 nm. Compared with Example 1, Comparative Example 4 shows a decrease in both specific surface area and pore volume, and a shift in pore size distribution towards larger pore sizes. This result indicates that in the absence of pre-concentrated network fixation, the uniformity of the material's pore structure may decrease during drying and heat treatment, and some pore structures may coalesce or collapse.

[0093] The results in Table 3 show that the ammonium salt system and dynamic induced coagulation process used in Example 1 are beneficial for obtaining composite electrode materials with higher specific surface area, higher pore volume, moderate mesopore distribution, and lower sodium ion residue.

[0094] Test Example 4: This test case is used to examine the first charge-discharge performance of different composite electrode materials when used as negative electrode active materials in lithium-ion batteries.

[0095] (1) The composite electrode material powders prepared in Example 1, Example 2, Comparative Example 3 and Comparative Example 4 were used as active materials.

[0096] (2) The active material, conductive carbon black and polyacrylic acid binder are mixed in a mass ratio of 8:1:1, deionized water is added as a solvent, and the mixture is mixed evenly in a planetary mixer to obtain an electrode slurry with a solid content of 35wt%.

[0097] (3) The electrode paste is uniformly coated onto the surface of a copper foil current collector with a thickness of 10 μm using a coating machine, and the surface density of the active material is controlled to be 1.5 mg / cm³. 2 After coating, the electrode sheets are baked at a constant temperature of 110℃ in a vacuum drying oven for 10 hours, and then cut into circular electrode sheets with a diameter of 14mm using a punching machine.

[0098] (4) Assemble CR2032 button cell half-cells in an argon atmosphere glove box with both water and oxygen content below 0.1 ppm. A lithium metal sheet serves as the counter electrode, a polyethylene microporous membrane as the separator, and the electrolyte is a mixed solution of ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate containing 1.0 mol / L lithium hexafluorophosphate, with a volume ratio of ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate of 3:6:1.

[0099] (5) After assembling the coin cells, let them stand for 12 hours, then connect them to the battery testing system. Set the charge / discharge voltage window to 0.01V to 1.5V, and conduct the first constant current charge / discharge test at a current density of 0.1C, where the current density corresponding to 0.1C is 200mA / g. Record the initial lithium insertion specific capacity and the initial lithium extraction specific capacity of the sample, and calculate the initial coulombic efficiency. The specific capacity is calculated based on the mass of the active material of the composite electrode material in the electrode sheet.

[0100] Each test sample was prepared and tested in at least 3 parallel sets of batteries. The data in the table are the average values ​​of the test results of the parallel samples.

[0101] Table 4. Initial charge-discharge performance test results of the composite electrode materials in the examples and comparative examples:

[0102] According to the data in Table 4, the composite electrode materials obtained in Examples 1 and 2 both exhibited high initial delithiation specific capacity and initial coulombic efficiency. Specifically, Example 1 had an initial lithium insertion specific capacity of 2135.4 mAh / g, an initial delithiation specific capacity of 1887.6 mAh / g, and an initial coulombic efficiency of 88.40%; Example 2 had an initial lithium insertion specific capacity of 2087.1 mAh / g, an initial delithiation specific capacity of 1819.5 mAh / g, and an initial coulombic efficiency of 87.18%.

[0103] Based on the aforementioned structural characterization results, the high proportion of nitrogen-containing carbon structures, the prominent POP bond structure, and the low sodium ion residual level in the example samples may contribute to improving the interfacial stability and ion transport properties of the material. The buffer phase formed by the polyphosphate amorphous structure between the porous silicon particles and the carbon matrix may help mitigate the volume change during the initial lithium insertion process; simultaneously, carbon nanotubes and pyrolytic carbon frameworks can provide continuous electron transport pathways for the material. These structural factors may collectively contribute to the high initial lithium extraction specific capacity and initial coulombic efficiency of the example samples.

[0104] Comparative Example 3 used a sodium salt system instead of an ammonium salt system, and its initial delithiation specific capacity was 1431.1 mAh / g, with an initial coulombic efficiency of 73.70%. Compared with Example 1, the initial coulombic efficiency of Comparative Example 3 was significantly reduced. Based on the analysis of the results in Table 3, which showed higher sodium ion residual concentration, lower specific surface area, and lower pore volume, it is possible that residual sodium salt and insufficient pore structure development may increase interfacial side reactions and reduce lithium ion transport efficiency, thereby leading to an increase in irreversible capacity.

[0105] Comparative Example 4, without the addition of polyethyleneimine and acetic acid-induced agglomeration treatment, exhibited an initial delithiation specific capacity of 1572.8 mAh / g and an initial coulombic efficiency of 76.49%. These results indicate that in the absence of a pre-crosslinking agglomeration process, the uniformity of the coating and pore structure of the resulting material may decrease, making it easier to generate new interfacial contact regions during the initial lithium insertion process, thereby increasing irreversible capacity loss.

[0106] The results above show that the ammonium salt system and dynamic induced agglomeration process used in Examples 1 and 2 are beneficial to improving the first delithiation specific capacity and first coulombic efficiency of the composite electrode material.

[0107] Test Example 5: This test case is used to examine the long-cycle performance of different composite electrode materials under high-rate conditions.

[0108] (1) Take the composite electrode material powder prepared in Example 1, Comparative Example 2 and Comparative Example 4, prepare the electrode sheet according to the method in Test Example 4 and assemble the CR2032 coin cell, and use the obtained coin cell as the long cycle performance test object.

[0109] (2) Connect the button cell to be tested to the multi-channel battery testing system and place it in a temperature-controlled constant temperature chamber, maintaining the test environment temperature at 25°C.

[0110] (3) Set the charge and discharge voltage range to 0.01V to 1.5V. Before testing, perform three charge and discharge cycles on the battery at a current density of 0.1C to stabilize the electrode interface state.

[0111] (4) After formation, the charge / discharge current density was adjusted to 1C, and 500 constant current charge / discharge cycles were continuously performed, where the current density corresponding to 1C was 2000 mA / g. The test system continuously and automatically collected capacity data for each cycle during the cycle process, and extracted the continuous delithiation specific capacity data from the 1st to the 500th cycle under 1C conditions to plot the long cycle performance curve (see Figure 4This reflects the actual continuous decay process; and specifically extracts the delithiation specific capacity of the 1st, 100th, 300th, and 500th cycles for comparison calculation of tabular data. The delithiation specific capacity is calculated based on the mass of the active material of the composite electrode material in the electrode sheet, and the capacity retention rate after 500 cycles is calculated according to the ratio of the delithiation specific capacity of the 500th cycle to the delithiation specific capacity of the 1st cycle.

[0112] Each test sample was prepared and tested in at least 3 parallel sets of batteries. The data in the table are the average values ​​of the test results of the parallel samples.

[0113] Table 5. Test results of long-cycle capacity decay and retention rate of the composite electrode materials in the examples and comparative examples:

[0114] According to Table 5 and Appendix Figure 4 The results, shown in the continuous long-cycle curves, indicate that after 500 cycles at a 1C current density in Example 1, the delithiation specific capacity decreased from 1724.8 mAh / g in the first cycle to 1481.5 mAh / g in the 500th cycle, corresponding to a capacity retention of 85.89%. Figure 4 The continuous curves clearly show that Example 1 exhibits a gradual capacity decay throughout the entire 500-cycle process, without any significant interruption or drop in capacity; while Comparative Examples 2 and 4 show continuous and severe capacity declines in the later stages of cycling. These complete and continuous long-cycle test results demonstrate that the composite electrode material obtained in Example 1 possesses good capacity retention and excellent long-cycle mechanical structural stability under high-rate cycling conditions.

[0115] Based on the aforementioned structural characterization results, the nitrogen-containing carbon-based framework, carbon nanotube conductive network, and polyphosphate amorphous structure formed in Example 1 may help maintain the structural integrity and electron transport continuity of the electrode material during cycling. The POP bond-related structure formed by water-soluble ammonium polyphosphate during heat treatment may act as a buffer between the porous silicon and the carbon matrix, thereby reducing the impact of volume changes in porous silicon during repeated lithium insertion / extraction processes on the overall electrode structure. Simultaneously, the two-step dynamic induced aggregation process is beneficial for improving the uniformity of component distribution in the precursor, which may be one of the reasons why Example 1 exhibits a high cycling capacity retention rate.

[0116] Comparative Example 2 exhibited a delithiation specific capacity of 1681.3 mAh / g during the first cycle, which decreased to 618.9 mAh / g after 500 cycles, with a capacity retention of 36.81%. Compared to Example 1, Comparative Example 2 showed a more significant capacity decay. Analysis of its preparation process suggests that Comparative Example 2 employed a one-time rapid acid reduction method, lacking a slow pH reduction and programmed temperature increase process. This may have resulted in the water-soluble ammonium polyphosphate's modulating effect on the interaction between polyethyleneimine and ammonium lignosulfonate. Consequently, its aggregated structure uniformity may be lower than that of Example 1, thus affecting the stability of the carbon-based network and silicon particle coating structure after pyrolysis.

[0117] Comparative Example 4, without the addition of polyethyleneimine and acetic acid-induced agglomeration treatment, exhibited a lithium delithiation specific capacity of 345.2 mAh / g after 500 cycles, with a capacity retention of 21.68%. This result indicates that the material obtained without a pre-crosslinking agglomeration process has weaker capacity retention during long-term cycling. It is speculated that this may be due to insufficient continuity and uniformity of the carbon-based structure obtained through direct drying and heat treatment, making the electrode more susceptible to increased interfacial side reactions, conductive network degradation, or decreased utilization of active materials during cycling.

[0118] The results above show that the two-step dynamic induced agglomeration process and ammonium salt system used in Example 1 are beneficial to improving the capacity retention of composite electrode materials in long-cycle testing.

[0119] Test Example 6: This test case is used to evaluate the change in electrode thickness of different composite electrode materials during the lithium insertion / extraction process.

[0120] (1) The composite electrode materials prepared in Example 1, Comparative Example 1, and Comparative Example 4 were mixed with conductive agent SuperP and polyacrylic acid binder at a mass ratio of 85:5:10, and an appropriate amount of deionized water was added to form a uniform slurry. The resulting slurry was then coated onto the surface of a copper foil with a thickness of 10 μm. After vacuum drying at 110 °C, the coated electrode was rolled to 2.5 g / cm³ using a roller press. 3 The compaction density was measured. The initial absolute thickness of the electrode sheet after roll forming was measured using a high-precision micrometer, and the thickness of the copper foil was deducted.

[0121] (2) The prepared electrodes were assembled into a coin cell with a quartz window for in-situ expansion testing in an argon glove box. A lithium metal sheet was used as the counter electrode, and glass fiber filter paper was used as the separator. An electrolyte with the same composition as in Test Example 4 was added. The electrolyte was a mixed electrolyte containing 1.0 mol / L LiPF6 of ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate, wherein the volume ratio of ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate was 3:6:1.

[0122] (3) The assembled battery was placed in a 25°C constant temperature test chamber and connected to the displacement sensor of the in-situ expansion tester. During the test, it was first discharged to 0.01V at a current density of 0.1C, where the current density corresponding to 0.1C is 200mA / g, so that the electrode was in the first full lithium insertion state, and the corresponding displacement data was recorded to calculate the thickness of the first full lithium insertion electrode; then the current density was adjusted to 0.5C, where the current density corresponding to 0.5C is 1000mA / g, and charge-discharge cycles were continuously performed, and the displacement data at the end of the 50th cycle discharge, i.e., the full lithium insertion state, was recorded to calculate the thickness of the 50th full lithium insertion electrode.

[0123] (4) Based on the measured thickness data, calculate the percentage increase of electrode thickness at each stage relative to the initial absolute thickness to obtain the corresponding thickness expansion rate.

[0124] Each test sample was prepared and tested in at least three parallel sets of batteries. The data shown in Table 6 are the average values ​​of the test results of the parallel samples.

[0125] Table 6. Thickness and expansion rate test data of the electrode sheets of the examples and comparative examples at different cycling stages:

[0126] According to Table 6 and Appendix Figure 5 The results show that the initial thickness of the electrode in Example 1 was 42.15 μm, and the corresponding thickness in the first fully lithium-intercalated state was 51.64 μm, with an initial thickness expansion rate of 22.51%. In the 50th fully lithium-intercalated state, the electrode thickness was 55.48 μm, with a thickness expansion rate of 31.63%. The above results indicate that under the test conditions, the thickness change of the electrode in Example 1 during the first lithium-intercalation and subsequent cycles was relatively small.

[0127] Based on the aforementioned structural and compositional analysis, the POP-bonded amorphous structure formed by the heat treatment of water-soluble ammonium polyphosphate in Example 1, along with the carbon coating layer and mesoporous structure, may play a certain buffering role in the volume change of porous silicon particles during lithium insertion / extraction. Meanwhile, the precursor structure obtained by the dynamic induced agglomeration process in Example 1 exhibits relatively good structural uniformity, suggesting that the composite network structure formed after pyrolysis may help mitigate the overall thickness increase of the electrode during cycling.

[0128] The initial thickness of the electrode in Comparative Example 1 was 41.83 μm, increasing to 66.45 μm under the first fully lithium-intercalated state, with an initial thickness expansion rate of 58.86%. By the 50th cycle under the fully lithium-intercalated state, the thickness further increased to 88.54 μm, with a thickness expansion rate of 111.67% after the 50th cycle. Compared with Example 1, the electrode thickness increase of Comparative Example 1 was more significant. This result indicates that, without the addition of water-soluble ammonium polyphosphate, the dimensional stability of the material during cycling is relatively weak. This may be related to the lack of relevant phosphate amorphous buffer structures in the system, thus making the volume change of porous silicon particles more significant on the overall electrode structure.

[0129] The initial thickness of the Comparative Example 4 electrode was 42.41 μm, and it reached 74.32 μm in the first fully lithium-intercalated state, with an initial thickness expansion rate of 75.24%. By the 50th cycle in the fully lithium-intercalated state, the thickness further increased to 108.19 μm, with a thickness expansion rate of 155.10% after the 50th cycle. These results indicate that the Comparative Example 4 electrode exhibited the most significant thickness expansion during cycling. Analysis of its fabrication process suggests that the absence of polyethyleneimine addition and acetic acid-induced agglomeration treatment may have hindered the formation of a continuous and stable composite coating structure in the precursor during subsequent heat treatment. This, in turn, makes the resulting electrode more prone to exhibiting loose structure, changes in particle contact state, and a continuous increase in electrode thickness during cycling.

[0130] The results in Table 6 show that Example 1 exhibits relatively good electrode thickness stability under the test conditions, indicating that the raw material system and precursor construction method used may help to mitigate the volume expansion effect of silicon-based composite electrodes during cycling.

[0131] Test Example 7: (1) Take an appropriate amount of the composite electrode material powder prepared in Example 1 and Comparative Example 2 respectively, disperse it and embed it in epoxy resin, and obtain resin-embedded block after curing at room temperature.

[0132] (2) The resin-embedded block was cut and thinned using a focused ion beam system to prepare ultrathin slices of single-particle cross-section with a thickness of 80 to 100 nanometers.

[0133] (3) The sliced ​​samples were tested in a high-resolution transmission electron microscope equipped with an X-ray energy dispersive spectrometer. The electron beam acceleration voltage was set to 200 kV. After selecting a representative single-particle cross-sectional area, a radial straight scanning path was set along the direction from the inner region of the porous silicon core to the outer carbon coating layer, and the selected starting point located in the inner region of the silicon core was taken as the 0 nm position. At the same time, the scanning path was confirmed to not penetrate the particle boundary into the epoxy resin embedded matrix region by combining bright field images or high-angle annular dark field images.

[0134] (4) Start the energy spectrum line scanning program, collect the characteristic X-ray signals of each detection point on the path according to the preset sampling points, and appropriately densify the sampling in the region near the silicon / carbon transition interface, calculate the relative atomic percentage content of silicon, carbon and phosphorus elements at the detection point, and record the data from the starting position (0nm) inside the silicon core to different radial depths in the outer carbon coating layer region.

[0135] The relative elemental content distribution at each detection point is shown in Table 7.

[0136] Table 7. Test results of relative elemental content distribution at different radial depths of the cross-section of a single particle of the composite electrode material of Example 1 and Comparative Example 2: Note: The relative atomic percentages listed in Table 7 are calculated based on all elements detected in the test area. Only the data for the three main elements, Si, C, and P, are listed in the table. O, N, and other trace elements that are not listed are not listed separately in the table.

[0137]

[0138] According to Table 7 and Appendix Figure 6 Appendix Figure 7 and attached Figure 8 As shown in the results, the composite electrode material obtained in Example 1 maintains a relative Si content of over 90 at% in the radial distance range of 0 nm to 30 nm, while the relative contents of C and P are relatively low. This region can be considered to mainly correspond to the porous silicon core region. In the radial distance range of 55 nm to 65 nm, the relative C content increases to over 93 at%, while the relative Si content decreases to a low level, indicating that there is a carbon-dominated coating region on the outside of the porous silicon particles.

[0139] Within a radial distance of 42 nm to 48 nm, the relative content of Si in the sample of Example 1 showed a decreasing trend, while the relative content of C showed an increasing trend. This region corresponds to the transition region between the porous silicon core and the external carbon coating layer. Furthermore, the relative content of P was relatively enriched within this transition region, reaching 7.68 at% at a radial distance of 45 nm and maintaining a high level within the 45 nm to 48 nm range. Combined with the analysis results of the POP bond structure in the aforementioned XPS test, it can be considered that this P-enriched region is related to the phosphorus-containing amorphous phase structure formed during pyrolysis, which may mainly exist in the form of polyphosphate structures.

[0140] In contrast, in Comparative Example 2, the relative content of carbon element was generally higher near the silicon core and transition region, and the variation range of Si and C elements was relatively dispersed, suggesting that the uniformity of carbon phase distribution was relatively weak, and there may be a non-uniform distribution of carbon components towards the core region. Although the P element in Comparative Example 2 also showed some fluctuations near the silicon / carbon transition region, its highest relative content was 1.95 at%, which was lower than the relative content of P element at the corresponding position in Example 1, and the enrichment degree and concentration were relatively low, indicating that no P element enrichment characteristics comparable to those in Example 1 were observed at its interface.

[0141] Based on the differences in the preparation processes between Example 1 and Comparative Example 2, it can be concluded that the two-step dynamic induced agglomeration process used in Example 1 is beneficial for the relatively uniform agglomeration and distribution of water-soluble ammonium polyphosphate, polyethyleneimine, and ammonium lignin sulfonate on or near the surface of porous silicon particles under conditions of gradually decreasing pH and gradually increasing temperature. After subsequent pyrolysis treatment, the phosphorus-containing components can form a relatively concentrated phosphorus-containing amorphous phase region between the porous silicon and the carbon coating layer. This phosphorus-containing amorphous phase region at the interface may play a certain role in buffering or dispersing local deformation stress during the lithium insertion / extraction process of silicon-based particles, thereby helping to improve the interfacial structural stability of the composite electrode material during cycling.

[0142] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A carbon nanotube porous silicon composite electrode material, characterized in that, It is made from raw materials containing the following parts by weight through high-temperature pyrolysis: 100 parts of porous silica powder; 2-8 parts of multi-walled carbon nanotubes; Ammonium lignosulfonate, 30-50 parts; the sodium ion content of the ammonium lignosulfonate is less than 100 ppm on a dry basis; 5-8 parts of water-soluble ammonium polyphosphate; Polyethyleneimine 4.5–10 parts; The composite electrode material includes a porous silicon core, a carbon matrix coating layer with a mesoporous structure located outside the porous silicon core, and a phosphorus-containing interface phase located between the porous silicon core and the carbon matrix coating layer. The multi-walled carbon nanotubes are at least partially dispersed and interspersed within the carbon matrix coating layer; The phosphorus-containing interface phase is a phosphorus-containing amorphous phase containing a POP bond structure.

2. The carbon nanotube porous silicon composite electrode material according to claim 1, characterized in that, The raw materials are in the following weight proportions: 100 parts porous silica powder, 5 parts multi-walled carbon nanotubes, 40 parts ammonium lignosulfonate, 6.5 parts water-soluble ammonium polyphosphate, and 7 parts polyethyleneimine.

3. The carbon nanotube porous silicon composite electrode material according to claim 1, characterized in that, The preparation method of the ammonium lignosulfonate is as follows: the aqueous solution of ammonium lignosulfonate is passed through a chromatography column packed with ammonium-type strong acid cation exchange resin for ion exchange treatment, the effluent is collected and spray-dried to obtain the ammonium lignosulfonate.

4. The carbon nanotube porous silicon composite electrode material according to claim 1, characterized in that, The composite electrode material has a BET specific surface area of ​​140-150 m². 2 / g, with mesopores concentrated in a pore size of 8.0–8.5 nm; and the nitrogen-containing configuration on the surface of the composite electrode material includes pyridine nitrogen and pyrrole nitrogen doped at the edges of the carbon lattice.

5. A method for preparing a carbon nanotube porous silicon composite electrode material as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Alkaline dispersion: Porous silica powder, multi-walled carbon nanotubes, ammonium lignosulfonate and water-soluble ammonium polyphosphate are added sequentially to a liquid medium. Ammonia solution is added to adjust the pH of the system to be alkaline. The mixture is stirred and dispersed at a constant temperature to obtain a homogeneous alkaline slurry. (2) Addition of polyethyleneimine: While maintaining a constant system temperature, add an aqueous solution of polyethyleneimine to the alkaline slurry and continue stirring to homogenize the reaction; (3) Two-step dynamic induced coagulation: In the first stage, the system temperature is kept constant and acid solution is added dropwise to the liquid surface of the system to reduce the pH of the system to the first set value; in the second stage, the system is linearly heated and the acid solution is added dropwise during the heating process until the pH of the system drops to the second set value and then the acid solution is stopped. Then the temperature is continued to rise to the target aging temperature and the gel is obtained by isothermal aging. (4) Dehydration, drying and pulverization: The obtained gel is centrifuged and vacuum dried in sequence, the dried material is mechanically ground and sieved, and the precursor particles are collected. (5) High-temperature pyrolysis: The precursor particles are calcined under inert gas protection by programmed heating. After the pyrolysis is completed, the material is cooled in the furnace and sieved to obtain the composite electrode material.

6. The method for preparing a carbon nanotube porous silicon composite electrode material according to claim 5, characterized in that, In step (1), the liquid medium is deionized water; the constant temperature during dispersion is set to 20-30℃; an ammonia solution with a mass concentration of 3-8wt% is added to adjust the pH value of the system to 10.2-10.8 and maintain it stable; the stirring and dispersion time is 1.5-2.5 hours.

7. The method for preparing a carbon nanotube porous silicon composite electrode material according to claim 5, characterized in that, The method for preparing the polyethyleneimine aqueous solution in step (2) is as follows: pure polyethyleneimine with a weight average molecular weight of 25,000 is dissolved in deionized water and stirred continuously at room temperature until completely dissolved to prepare a homogeneous polyethyleneimine aqueous solution with a mass fraction of 20 wt%; the stirring time after the polyethyleneimine aqueous solution is added in step (2) is 0.8 to 1.5 hours.

8. The method for preparing a carbon nanotube porous silicon composite electrode material according to claim 5, characterized in that, In step (3), the acid solution is a glacial acetic acid solution with a mass concentration of 3 to 8 wt%, and the pH decrease rate is controlled to be kept constant at 0.10 to 0.15 pH / min during the dropwise addition process; The first setting value is 7.8 to 8.2; the second setting value is 4.8 to 5.2; In the second stage, the linear heating rate of the system is controlled at 0.8–1.2 °C / min, the target aging temperature is 60–70 °C, and the isothermal aging time is 0.8–1.5 hours.

9. The method for preparing a carbon nanotube porous silicon composite electrode material according to claim 5, characterized in that, In step (4), the vacuum drying process is controlled at a temperature of 110 to 130°C, a vacuum degree of -0.08 MPa to -0.10 MPa, and a vacuum drying time of 10 to 14 hours; the D50 particle size of the collected precursor particles is controlled in the range of 10 to 15 μm.

10. The method for preparing a carbon nanotube porous silicon composite electrode material according to claim 5, characterized in that, The specific implementation method of step (5) is as follows: place the precursor particles in a tube furnace, introduce nitrogen gas with a flow rate of 0.5 to 1.5 L / min for atmosphere protection, heat to 750 to 850°C at a heating rate of 2 to 5°C / min, and keep at a constant temperature for calcination for 3 to 5 hours.

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