A phenol-formaldehyde resin-based multi-shape silicon-carbon negative electrode material and a preparation method thereof

Abstract

The application provides a phenolic resin-based multi-shape silicon-carbon negative electrode material and a preparation method thereof, and the steps of the preparation method comprise the following steps: mixing a formaldehyde solution, a phenol solution and an acidic catalyst, introducing a boron-based modifier to obtain a boron-modified phenolic resin precursor, and performing hot-pressing treatment on the phenolic resin precursor to obtain a multi-shape phenolic resin, wherein the multi-shape phenolic resin comprises at least one of a spherical almond-like phenolic resin, a polyhedral phenolic resin and a dice-like phenolic resin; the multi-shape phenolic resin is subjected to high-temperature carbonization in an inert atmosphere, is mixed with magnesium powder and is subjected to magnesium hot reduction to obtain a porous hard carbon with nanopores; the porous hard carbon is subjected to deposition by introducing a silicon source gas, is coated with a nitrogen source and a soft carbon source and is subjected to sintering treatment to obtain the phenolic resin-based multi-shape silicon-carbon negative electrode material. The material has excellent cycle stability and rate performance while maintaining high energy density.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a multi-shaped silicon-carbon anode material based on phenolic resin and its preparation method. Background Technology

[0002] Porous silicon-carbon anode materials utilize porous carbon as a carrier, depositing a silicon source into the pores of the porous carbon under specific temperature and pressure conditions. Porous carbon primarily consists of micropores and small mesopores. The deposited silicon is separated by these micropores and mesopores, resulting in the absence of large silicon particles and low expansion stress. Furthermore, the porous structure of the carbon provides space for silicon expansion. Therefore, porous silicon-carbon anode materials exhibit excellent anti-expansion properties and long cycle performance, and are widely considered one of the most promising battery anode materials for the future. Porous carbon is the core material of porous silicon-carbon anode materials, and its morphology and composition significantly influence the performance of these products.

[0003] Currently, most porous carbon is irregular block or spherical porous carbon, which has several problems: (1) Block porous carbon has sharp corners, which will be crushed or punctured during the compaction process, resulting in internal micro-short circuits and affecting the voltage and capacity of the battery cell; (2) Perfect spherical porous carbon has point-to-point lithium ion conduction, poor rate performance, and the arc surface will cause the glue to detach during the cyclic expansion and contraction process, resulting in serious cycle drop phenomenon; (3) Ellipsoidal porous carbon conducts lithium ions line-to-line, which improves the rate performance compared with perfect spherical porous carbon, but still has a high degree of curvature. During the cyclic expansion and contraction process, there is still a risk of glue debonding, and the preparation method is significantly more expensive than that of perfect spherical porous carbon; (4) Fiber or strip-shaped porous carbon, compared with the above three morphologies, has more sufficient interface contact, but the existing melt spinning preparation technology is difficult to reduce the diameter of phenolic resin fiber to less than 10um, resulting in a larger overall particle size, which is not suitable for high energy density lithium-ion battery anode materials, and it is difficult to crush to a uniform particle size, with more long filaments, debris and sharp corners, which pose a safety risk of puncturing the separator during the cycle. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a multi-shaped silicon-carbon anode material based on phenolic resin and its preparation method, aiming to solve the problem that the existing morphology of porous carbon materials cannot simultaneously meet the requirements of safety, electrochemical performance and high energy density applications.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: The present invention proposes a method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin for manufacturing lithium-ion batteries, the steps of which include:

[0006] S1. Formaldehyde solution, phenol solution and acidic catalyst are mixed and boron modifier is introduced to obtain boron modified phenolic resin precursor. The phenolic resin precursor is subjected to hot pressing to obtain polymorphic phenolic resin. The polymorphic phenolic resin includes at least one of spherical almond-shaped phenolic resin, polyhedral phenolic resin and dice-shaped phenolic resin.

[0007] S2. The multi-shaped phenolic resin is carbonized at high temperature under an inert atmosphere, and then mixed with magnesium powder and subjected to magnesothermic reduction to obtain porous hard carbon with nanopores.

[0008] S3. Porous hard carbon is deposited by introducing silicon source gas, and then coated with nitrogen source and soft carbon source for sintering treatment to obtain multi-shaped silicon-carbon anode material based on phenolic resin.

[0009] In some embodiments, step S1 includes:

[0010] S1.1 Mix formaldehyde solution, acidic catalyst and deionized water in proportion, then add boron modifier and dispersant. The amount of boron modifier added is 1.5~5.5% of formaldehyde solution. Stir at high speed at 30~45°C for 60~180 minutes, then add phenol solution to obtain boron modified phenolic resin precursor.

[0011] S1.2. Turn on the cooling system of the reactor to lower the system temperature to 10~25°C. Use a high shear emulsifier to perform emulsification at a speed of 800~1500 rpm. Then raise the temperature to 55~75°C and maintain it for 30~90 minutes to perform preliminary crosslinking and obtain phenolic resin particles.

[0012] S1.3 After filtration and washing, the phenolic resin particles are laid on a hot press with a Teflon liner, and a longitudinal high pressure of 80~100MPa is applied. The temperature is maintained at 80~120°C for 0.5~4 hours to induce an asymmetric deformation reaction and obtain polymorphic phenolic resin.

[0013] S1.4 Disperse the polymorphic phenolic resin in a crosslinking agent solution with a mass fraction of 5%~15%, and perform post-curing treatment at a temperature of 75~95°C for 2~6 hours using a circulating water bath heating device.

[0014] In some embodiments, in step S1, the acidic catalyst includes at least one of acetic acid, oxalic acid, hydrochloric acid, phosphoric acid, and sulfuric acid; the boron modifier includes at least one of boric acid, trimethyl borate, tributyl borate, boron oxide, and borate; the dispersant includes at least one of sodium carboxymethyl cellulose, polyvinyl alcohol, xanthan gum, and guar gum; and the crosslinking agent includes at least one of hexamethylenetetramine, hydrochloric acid, formaldehyde, and para-oxygenated formaldehyde.

[0015] In some embodiments, step S2 includes:

[0016] S2.1 Place the polymorphic phenolic resin in a tube furnace, introduce argon as a protective gas to maintain an inert atmosphere, heat to 800~1100°C at a heating rate of 1~5°C / min and hold at the temperature for 2~5 hours to obtain polymorphic hard carbon.

[0017] S2.2 Mix the multi-shaped hard carbon particles, metallic magnesium powder and heat scavenger at a preset mass ratio at a speed of 800~1500 rpm for 20~60 minutes, then transfer them to a reactor under an argon atmosphere and heat them to 650~800°C and maintain the temperature for 2~6 hours to carry out the magnesium thermal reduction reaction.

[0018] S2.3 After the reaction is complete and the product has cooled to room temperature naturally, it is transferred to a chemical reaction vessel, a hydrochloric acid solution with a concentration of 1~2 mol / L is added and the mixture is stirred continuously for 4~12 hours. After repeated filtration and washing with deionized water until the filtrate is neutral, it is vacuum dried at 80~120°C to obtain porous hard carbon with nanopores.

[0019] In some embodiments, the heat scavenger includes at least one of sodium chloride, potassium chloride, magnesium chloride, and magnesium oxide, and the mass ratio of polymorphic hard carbon particles: metallic magnesium powder: heat scavenger ranges from 1:(0.5~1.5):(1~5).

[0020] In some embodiments, step S3 includes:

[0021] S3.1. The porous hard carbon is placed in the constant temperature zone of the chemical vapor deposition furnace, and silicon source gas diluted with high-purity argon is introduced. The dilution ratio is 10~30%. The temperature is maintained at 500~700°C for 2~10 hours to obtain silicon-loaded composite material.

[0022] S3.2 Transfer the silicon-based composite material to a mixer, add a soft carbon source and a nitrogen source. The mass ratio of the soft carbon source to the silicon-based material is 5%~20%, and the mass ratio of the nitrogen source to the silicon-based material is 2%~8%. Stir in anhydrous ethanol solvent at a speed of 500~1200 rpm and sonicate at 40~60°C for 2~5 hours. After the solvent evaporates naturally, precursor particles with a nitrogen-carbon mixed layer on the surface are obtained.

[0023] S3.3. The precursor particles are placed in a tube furnace and heated to 900-1100°C at a rate of 2-8°C / min under the protection of flowing argon gas. The mixture is then sintered at a constant temperature for 2-6 hours and cooled to obtain a multi-shaped silicon-carbon anode material based on phenolic resin.

[0024] In some embodiments, in step S3, the silicon source gas includes at least one of silane, silane, dichlorosilane, trichlorosilane, and silicon tetrachloride; the soft carbon source includes at least one of medium-temperature pitch, high-temperature pitch, coal tar, petroleum pitch, and mesophase pitch; and the nitrogen source includes at least one of urea, melamine, polyacrylonitrile, polyaniline, and dicyandiamide.

[0025] This invention proposes a polymorphic silicon-carbon anode material based on phenolic resin, which is prepared by the preparation method of polymorphic silicon-carbon anode material based on phenolic resin as described above. The polymorphic silicon-carbon anode material based on phenolic resin includes porous hard carbon made of polymorphic phenolic resin, and the polymorphic phenolic resin includes at least one of spherical almond-shaped phenolic resin, polyhedral phenolic resin, and dice-shaped phenolic resin.

[0026] The spherical almond-shaped phenolic resin includes almond-shaped phenolic resin and perfectly spherical phenolic resin. The ratio of the shortest diameter to the longest diameter of the almond-shaped phenolic resin is less than 0.95, while the ratio of the shortest diameter to the longest diameter of the perfectly spherical phenolic resin is greater than or equal to 0.95. The surface of the spherical almond-shaped phenolic resin is covered with a disordered network of wrinkles; the included angle formed by adjacent network wrinkles is between 5 degrees and 89 degrees, and the area enclosed by adjacent network wrinkles is less than 1 nm. 2 ~10um 2 Between these ranges, the height of the mesh folds is between 1 nm and 1 μm, and the length of the mesh folds is between 10 nm and 500 μm.

[0027] The polyhedral phenolic resin surface has clear edges and included angles formed by these edges, with angles ranging from 15 to 178 degrees. The surfaces formed by the edges are flat. A flat surface is defined as one where, under a scanning electron microscope at 100,000x or higher magnification, the polyhedral surface shows no inward depressions. The number of flat surfaces is greater than or equal to 4 and less than or equal to 80. Flat surfaces are triangular or polygonal, with polygons having less than or equal to 20 and greater than or equal to 4 sides. The area of ​​a flat surface is greater than or equal to 1 nm. 2 And less than or equal to 100um 2 ;

[0028] The die-shaped phenolic resin surface has clear edges and the included angles formed by these edges. The surfaces formed by the edges are concave inwards. These concave surfaces, observed with a scanning electron microscope at 100,000 magnification, are curved surfaces formed by the edges and corners of the die-shaped phenolic resin surface. The central region of this curved surface is not on the same plane as the edges and is concave inwards. The distance between the deepest point of the concavity and the plane formed by the edges is less than or equal to 10 μm and greater than or equal to 20 nm. The number of surfaces formed by the surface edges is greater than or equal to 4 and less than or equal to 80. The concave surfaces are triangular or polygonal, with polygons having less than or equal to 20 and greater than or equal to 4 sides. The area of ​​the concave surfaces is greater than or equal to 1 nm. 2 And less than or equal to 100um2 .

[0029] Compared with existing technologies, the multi-shaped silicon-carbon anode material based on phenolic resin and its preparation method disclosed in this invention have the following advantages:

[0030] This invention employs a hot-pressing process in step S1 to transform boron-modified phenolic resin precursors into polyhedral, near-spherical almond-shaped, or dice-shaped structures. This geometric change elevates the particle-particle contact from unstable point-to-point or line-to-line interactions to stable surface contact. This significantly increases the mechanical interlocking force between the particles and the binder, completely eliminating adhesive detachment and water leakage caused by cyclic expansion and contraction of high-curvature surfaces. Furthermore, compared to irregular blocks, this controlled multi-shaped structure avoids sharp corners, and compared to fibrous structures, it exhibits more uniform particle size and is free of long filaments and debris, fundamentally preventing the risk of internal micro-short circuits caused by puncturing the separator, thus ensuring the safety and capacity of the battery cell. Regarding internal structure and interface stability, step S2 utilizes magnesium powder for magnesothermic reduction, in-situ etching rich nanopores within the multi-shaped hard carbon framework. This porous structure provides an ideal volume buffer for the active silicon introduced through silicon source gas deposition in step S3, effectively absorbing the expansion stress of silicon during lithium intercalation and preventing structural collapse. Finally, by coating with a nitrogen source and a soft carbon source and sintering, a protective layer with excellent conductivity and flexibility is constructed on the material surface. This step not only locks in the special morphology formed in S1, but also reduces charge transfer impedance through the synergistic effect of nitrogen and boron, solving the problem of poor rate performance of spherical particles. This allows the material to maintain high energy density while possessing excellent cycle stability and rate performance. Attached Figure Description

[0031] Figure 1 This is an optical microscope image of the spherical almond-shaped phenolic resin of Example 1;

[0032] Figure 2 This is an optical microscope image of the polyhedral phenolic resin from Example 2.

[0033] Figure 3 This is an optical microscope image of the dice-shaped phenolic resin from Example 3.

[0034] Figure 4 This is an optical microscope image of the spherical almond-shaped phenolic resin of Example 4.

[0035] Figure 5 This is a scanning electron microscope image of the polyhedral phenolic resin from Example 5.

[0036] Figure 6 This is an optical microscope image of the dice-shaped phenolic resin from Example 6.

[0037] Figure 7 This is an optical microscope image of the perfect spherical phenolic resin of Comparative Example 1.

[0038] Figure 8 This is an optical microscope image of the random phenolic resin in Comparative Example 2.

[0039] Figure 9 This is an optical microscope image of the fused spherical phenolic resin in Comparative Example 3.

[0040] Figure 10 This is a scanning electron microscope image of the polyhedral phenolic resin in Comparative Example 5, which contains a relatively large number of ultra-large particles. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] This invention provides a method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin, used in the fabrication of lithium-ion batteries, comprising the following steps:

[0043] S1. Formaldehyde solution, phenol solution and acidic catalyst are mixed, and then boron modifier is introduced to obtain boron-modified phenolic resin precursor. The phenolic resin precursor is subjected to hot pressing treatment to obtain polymorphic phenolic resin, wherein the polymorphic phenolic resin includes at least one of spherical almond-shaped phenolic resin, polyhedral phenolic resin and dice-shaped phenolic resin.

[0044] Step S1 includes:

[0045] S1.1 Mix formaldehyde solution, acidic catalyst and deionized water in a certain proportion, then add boron modifier and dispersant. The amount of boron modifier added is 1.5~5.5% of the formaldehyde solution. Stir at high speed at 30~45°C for 60~180 minutes, then add phenol solution to obtain boron-modified phenolic resin precursor. The acidic catalyst includes at least one of acetic acid, oxalic acid, hydrochloric acid, phosphoric acid and sulfuric acid. The boron modifier includes at least one of boric acid, trimethyl borate, tributyl borate, boron oxide and borate. The dispersant includes at least one of sodium carboxymethyl cellulose, polyvinyl alcohol, xanthan gum and guar gum.

[0046] By adding boron-based modifiers such as boric acid and borate esters, boron atoms participate in the molecular chain construction in the early stages of phenolic resin polymerization, achieving a uniform molecular-level distribution of boron within the resin. This distribution provides a stable basis for conductive modification in the subsequent carbonization process, helping to improve the charge-discharge performance of the material in cold environments. Simultaneously, using catalysts such as acetic acid and oxalic acid to control the reaction rate, combined with the wetting and spacer effects of dispersants such as sodium carboxymethyl cellulose, effectively prevents material agglomeration, ensuring that the resulting resin precursor has an ideal initial particle size profile.

[0047] S1.2. Turn on the cooling system of the reactor to lower the system temperature to 10~25°C. Use a high-shear emulsifier to perform emulsification at a speed of 800~1500 rpm. Then raise the temperature to 55~75°C and maintain it for 30~90 minutes to perform preliminary crosslinking and obtain phenolic resin particles.

[0048] By using a refrigeration system to lower the temperature to 10-25°C, the curing rate of the resin can be significantly slowed down. This allows the mechanical force of a high-shear emulsifier to break down the viscous prepolymer into tiny droplets. Subsequently, the temperature is raised to 55-75°C for initial cross-linking, causing these droplets to solidify into spherical particles with a certain degree of hardness while retaining elasticity and plasticity. This step effectively reduces particle size variation, ensuring good flowability of the precursor and providing raw materials with consistent dimensions for subsequent deformation processing.

[0049] S1.3 After filtering and washing the phenolic resin particles, they are laid on a hot press with a Teflon liner and subjected to a longitudinal high pressure of 80~100MPa. The mixture is then maintained at a temperature of 80~120°C for 0.5~4 hours to induce an asymmetric deformation reaction, thereby obtaining polymorphic phenolic resin.

[0050] Under thermal induction at 80-120°C, a pressure of 80-100 MPa is applied, causing the originally smooth spherical particles to undergo physical deformation in a softened state. Thanks to the use of a Teflon liner, the pressure is transmitted smoothly, causing the particles to compress each other into polyhedral, spherical, almond-shaped, or dice-shaped structures. This multi-shaped structure changes the point contact between particles to surface contact, significantly increasing the density of the compacted electrode and enabling the particles to support each other under high external pressure. This greatly improves the material's resistance to pulverization and prevents rapid performance degradation due to particle breakage.

[0051] S1.4. Disperse the polymorphic phenolic resin in a crosslinking agent solution with a mass fraction of 5% to 15%, and perform post-curing treatment at a temperature of 75 to 95°C for 2 to 6 hours using a circulating water bath heating device. The crosslinking agent includes at least one of hexamethylenetetramine, hydrochloric acid, formaldehyde, and para-oxygenated formaldehyde.

[0052] The molded resin is dispersed in a crosslinking agent solution such as hexamethylenetetramine, hydrochloric acid, or formaldehyde, and a secondary deep crosslinking process is induced within the resin using heat at 75–95°C. When heated, the crosslinking agents such as hexamethylenetetramine release active groups, firmly welding the resin molecular chains together to form a robust three-dimensional network structure. This treatment not only locks in the various non-spherical shapes formed in S1.3, preventing shrinkage and springback during subsequent high-temperature carbonization, but also further stabilizes the initially incorporated boron atoms, ensuring the material maintains structural integrity and stable electrical properties during long-term cycling.

[0053] S2. The multi-shaped phenolic resin is carbonized at high temperature under an inert atmosphere, and then mixed with magnesium powder and subjected to magnesium thermothermal reduction to obtain porous hard carbon with nanopores.

[0054] Step S2 includes:

[0055] S2.1 Place the polymorphic phenolic resin in a tube furnace, introduce argon gas as a protective gas to maintain an inert atmosphere, heat to 800-1100°C at a heating rate of 1-5°C / min and hold at the temperature for 2-5 hours to obtain polymorphic hard carbon.

[0056] Argon gas is introduced into the tube furnace as a protective gas to effectively isolate oxygen and prevent the phenolic resin from oxidizing and burning at high temperatures, ensuring that the carbonization process proceeds smoothly in an inert environment. By controlling the slow heating rate of 1–5°C / min, the volatiles inside the resin can be uniformly discharged, avoiding particle cracking caused by severe dehydration and shrinkage, thus fully preserving the special morphologies such as polyhedral, spherical almond-shaped, or dice-shaped forms formed in step S1. The resulting hard carbon exhibits good structural stability, and the distributed 3D ion channels provide pathways for the rapid migration of lithium ions, laying the foundation for the material's conductivity at extremely low temperatures.

[0057] S2.2 Mix the multi-shaped hard carbon particles, metallic magnesium powder and heat scavenger at a preset mass ratio at a speed of 800~1500 rpm for 20~60 minutes, then transfer to a reactor under an argon atmosphere and heat to 650~800°C and maintain for 2~6 hours to carry out the magnesium thermal reduction reaction; the heat scavenger includes at least one of sodium chloride, potassium chloride, magnesium chloride and magnesium oxide, and the mass ratio of multi-shaped hard carbon particles: metallic magnesium powder: heat scavenger is 1:(0.5~1.5):(1~5).

[0058] Magnesium vapor generated by magnesium powder at 650–800°C possesses strong reducing properties, enabling it to act on a carbon matrix and induce porosity. Since magnesium thermal reduction is a violently exothermic reaction, the addition of heat-clearing agents such as sodium chloride and potassium chloride is crucial. These compounds absorb excess heat released during the reaction, acting as a thermal buffer to prevent localized high temperatures from causing the hard carbon particles to melt or deform. By strictly controlling the mass ratio to 1:0.5–1.5:1–5, efficient and uniform pore formation can be achieved without compromising the "surface contact" characteristics of multi-shaped particles (crucial for compressive strength), thus reserving sufficient volumetric buffer space for subsequent silicon embedding.

[0059] S2.3 After the reaction is complete and the product has cooled to room temperature naturally, it is transferred to a chemical reaction vessel, a hydrochloric acid solution with a concentration of 1~2 mol / L is added and the mixture is stirred continuously for 4~12 hours. After repeated filtration and washing with deionized water until the filtrate is neutral, it is vacuum dried at 80~120°C to obtain porous hard carbon with nanopores.

[0060] Using a 1–2 mol / L hydrochloric acid solution, the reaction byproduct magnesium oxide (MgO) and residual sodium chloride, among other heat-removing agents, can be neutralized or dissolved, completely removing them from the framework. This process is equivalent to removing the template, transforming the previously occupied spaces within the hard carbon into interconnected nanopores, forming a hierarchical pore network. Washing to neutrality and vacuum drying ensure the cleanliness of the hard carbon surface, eliminating interference from impurities in the electrochemical reaction. The resulting porous hard carbon retains a robust polyhedral shell to withstand the high pressure of the deep sea while possessing abundant internal pores to alleviate the expansion stress of silicon, greatly improving the material's cycling stability.

[0061] S3. Porous hard carbon is deposited by introducing silicon source gas, and then coated with nitrogen source and soft carbon source for sintering treatment to obtain multi-shaped silicon-carbon anode material based on phenolic resin.

[0062] Step S3 includes:

[0063] S3.1. Place porous hard carbon in the constant temperature zone of a chemical vapor deposition furnace, introduce silicon source gas diluted with high-purity argon gas at a dilution ratio of 10-30%, and maintain the temperature at 500-700°C for 2-10 hours to obtain silicon-loaded composite material.

[0064] By introducing silicon source gases such as silane, disilane, or silicon tetrachloride, and thermally decomposing them using chemical vapor deposition (CVD) at a constant temperature of 500–700°C, the resulting nanoscale silicon particles can penetrate deeply through the micropores constructed in the S2 stage and be uniformly deposited on the inner wall of the hard carbon framework. Due to the use of high-strength hard carbon with polyhedral, spherical, almond-shaped, or dice-shaped morphologies as support, this structure provides ample expansion buffer space for silicon at the microscopic level. When the battery is charged and discharged, the internal pores can effectively absorb the volume change stress of the silicon, while the multi-shaped hard carbon shell can resist external pressure, preventing the particles from cracking or the structure from collapsing.

[0065] S3.2 Transfer the silicon-supported composite material to a mixer, add a soft carbon source and a nitrogen source. The mass ratio of the soft carbon source to the silicon-supported material is 5%~20%, and the mass ratio of the nitrogen source to the silicon-supported material is 2%~8%. Stir in anhydrous ethanol solvent at a speed of 500~1200 rpm and sonicate at 40~60°C for 2~5 hours. After the solvent evaporates naturally, precursor particles with a nitrogen-carbon mixed layer on the surface are obtained.

[0066] By utilizing the solubility and dispersion properties of soft carbon sources such as medium-temperature and high-temperature asphalt, and nitrogen sources such as urea, melamine, or polyacrylonitrile in anhydrous ethanol, combined with high-speed stirring and ultrasonic oscillation at 500-1200 rpm, these substances can be tightly and uniformly adhered to the surface of irregularly shaped particles (such as dice-shaped depressions). This coating method not only lays the foundation for the subsequent formation of a continuous protective shell, but more importantly, it tightly bonds the externally introduced nitrogen source with the boron atoms pre-doped into the hard carbon framework in step S1 at the interface. This atomic-level spatial proximity creates a prerequisite for the formation of an efficient electronic conduction network in the next sintering process.

[0067] S3.3. The precursor particles are placed in a tube furnace and heated to 900-1100°C at a rate of 2-8°C / min under the protection of flowing argon gas. The mixture is then sintered at a constant temperature for 2-6 hours and cooled to obtain a multi-shaped silicon-carbon anode material based on phenolic resin.

[0068] During the high-temperature sintering process at 900–1100°C, the coated pitch undergoes pyrolysis and transforms into an amorphous soft carbon layer with good flexibility and conductivity. This flexible shell, like elastic skin, restricts the outward expansion of silicon and effectively isolates the electrolyte to reduce side reactions. Simultaneously, nitrogen atoms in the shell and boron atoms in the framework exhibit a synergistic electronic effect, forming a B / N co-doped interface that significantly reduces charge transfer impedance. Even at extremely low temperatures of -40°C, this structure can still establish a fast conductive pathway for ion migration, ensuring that the material can withstand both high physical pressure and extreme polar conditions, achieving long-life stable cycling under extreme environments.

[0069] In step S3, the silicon source gas includes at least one of silane, silane, dichlorosilane, trichlorosilane, and silicon tetrachloride; the soft carbon source includes at least one of medium-temperature pitch, high-temperature pitch, coal tar, petroleum pitch, and mesophase pitch; and the nitrogen source includes at least one of urea, melamine, polyacrylonitrile, polyaniline, and dicyandiamide.

[0070] This invention proposes a polymorphic silicon-carbon anode material based on phenolic resin, which is prepared by a method for producing such a material. The polymorphic silicon-carbon anode material based on phenolic resin includes porous hard carbon made of polymorphic phenolic resin, wherein the polymorphic phenolic resin includes at least one of spherical almond-shaped phenolic resin, polyhedral phenolic resin, and dice-shaped phenolic resin.

[0071] The spherical almond-shaped phenolic resin includes almond-shaped phenolic resin and perfectly spherical phenolic resin. The ratio of the shortest diameter to the longest diameter of the almond-shaped phenolic resin is less than 0.95, while the ratio of the shortest diameter to the longest diameter of the perfectly spherical phenolic resin is greater than or equal to 0.95. The surface of the spherical almond-shaped phenolic resin is covered with a disordered network of wrinkles; the included angle formed by adjacent network wrinkles is between 5 degrees and 89 degrees, and the area enclosed by adjacent network wrinkles is less than 1 nm. 2 ~10um 2 Between these ranges, the height of the mesh folds is between 1 nm and 1 μm, and the length of the mesh folds is between 10 nm and 500 μm.

[0072] The polyhedral phenolic resin surface has clear edges and included angles formed by these edges, with angles ranging from 15 to 178 degrees. The surfaces formed by the edges are flat. A flat surface is defined as one where, under a scanning electron microscope at 100,000x or higher magnification, the polyhedral surface shows no inward depressions. The number of flat surfaces is greater than or equal to 4 and less than or equal to 80. Flat surfaces are triangular or polygonal, with polygons having less than or equal to 20 and greater than or equal to 4 sides. The area of ​​a flat surface is greater than or equal to 1 nm. 2 And less than or equal to 100um 2 ;

[0073] The die-shaped phenolic resin surface has clear edges and the included angles formed by these edges. The surfaces formed by the edges are concave inwards. These concave surfaces, observed with a scanning electron microscope at 100,000 magnification, are curved surfaces formed by the edges and corners of the die-shaped phenolic resin surface. The central region of this curved surface is not on the same plane as the edges and is concave inwards. The distance between the deepest point of the concavity and the plane formed by the edges is less than or equal to 10 μm and greater than or equal to 20 nm. The number of surfaces formed by the surface edges is greater than or equal to 4 and less than or equal to 80. The concave surfaces are triangular or polygonal, with polygons having less than or equal to 20 and greater than or equal to 4 sides. The area of ​​the concave surfaces is greater than or equal to 1 nm. 2And less than or equal to 100um 2 .

[0074] Example 1:

[0075] S1. Preparation of spherical, almond-shaped polymorphic phenolic resin: 13244g formaldehyde, 21188g acetic acid, and 14568g water were added to a reaction vessel and mixed thoroughly. Then, 364g sodium carboxymethyl cellulose and 397g boric acid (3% of the formaldehyde mass) were added. The mixture was heated to 35°C and stirred for 120 minutes until the dispersant was completely dissolved. The temperature was then lowered to 15°C. 10535g of 90% phenol aqueous solution was added, and emulsification was performed using a high-shear emulsifier at 1000rpm. The temperature was slowly raised to 60°C and reacted for 40 minutes. Then, 30000g of water was added for dilution. After filtration and washing, the mixture was extruded at 90MPa for 1 hour in a hot press to induce a spherical, almond-shaped morphology. The resin was then dispersed in a 10% hexamethylenetetramine solution and cured at 85°C for 4 hours. After washing and drying, the spherical, almond-shaped phenolic resin was obtained.

[0076] S2. Preparation of spherical almond-shaped porous hard carbon: The aforementioned resin was placed in a tube furnace, argon gas was introduced, and the temperature was increased to 1000 degrees Celsius at a rate of 2 degrees Celsius / min and held at this temperature for 3 hours to obtain spherical almond-shaped hard carbon. This hard carbon, magnesium powder, and sodium chloride were mixed at a mass ratio of 1:0.8:3 and mixed at 1000 rpm for 30 minutes. Subsequently, the mixture was heated to 700 degrees Celsius under argon gas and held for 4 hours for magnesothermic reduction. After cooling, 1.5 mol / L hydrochloric acid was added and stirred for 8 hours. After washing and vacuum drying at 100 degrees Celsius, spherical almond-shaped porous hard carbon with nanopores was obtained.

[0077] S3. Preparation of spherical almond-shaped silicon-carbon anode material based on phenolic resin: SiH4 diluted with argon (28% by volume) was introduced into the above porous hard carbon, and nano-silicon was loaded by vapor deposition at 600°C for 5 hours. The material was then transferred to a mixer, and medium-temperature pitch and urea were added in a mass ratio of silicon-supporting material: pitch: urea = 100:15:5. The mixture was ultrasonically stirred in anhydrous ethanol for 3 hours. After solvent evaporation, argon gas was introduced into a tube furnace, and the temperature was increased to 1000°C at 5°C / min, and sintered at this temperature for 3 hours. After cooling, a spherical almond-shaped silicon-carbon anode material with a B / N co-doped gradient core-shell structure was obtained.

[0078] Example 2:

[0079] S1. 13244g of formaldehyde, 21188g of acetic acid, and 14568g of water were added to a reactor and mixed thoroughly. Then, a composite dispersion system consisting of 364g of sodium carboxymethyl cellulose and 91g of polyvinyl alcohol (PVA) was added. 397g of boric acid was added and the mixture was heated to 35°C and stirred for 120 minutes to completely dissolve the polyol. The temperature was then lowered to 15°C. 10535g of 90% phenol solution was added, and emulsification was performed using a high-shear emulsifier at 1000rpm. The stable protective film formed by the composite dispersant on the droplet surface ensured the high monodispersity of the prepolymer. The mixture was slowly heated to 60°C and reacted for 40 minutes before dilution and discharge. The mixture was then extruded at 90MPa for 2 hours in a hot press to induce the formation of a polyhedral structure. After removal, the mixture was cured in a 10% hexamethylenetetramine solution at 85°C for 4 hours and dried to obtain a polyhedral phenolic resin. S2. The steps are the same as in Example 1. Hard carbon, magnesium powder, and sodium chloride were mixed in a ratio of 1:0.8:3 and subjected to magnesothermic reduction to construct a hierarchical pore structure with a total pore volume of 0.96 cc / g and a pore size of 2-4 nm accounting for 37%. After silicon loading in step S3, petroleum asphalt and melamine were added in step S3.2 for coating.

[0080] Example 3:

[0081] S1. The steps are the same as in Example 1, except that the hot pressing time in stage S1.3 is extended to 3 hours. S2. The steps are the same as in Example 1, except that the heat scavenger is replaced with potassium chloride, with a mass ratio controlled at 1:1:4, achieving a total pore volume of 0.89 cc / g, of which micropores smaller than 2 nm account for as much as 66%. S3. In the coating step of S3.2, polyaniline is introduced as a nitrogen source. During sintering, polyaniline is transformed into a nitrogen-carbon layer with high electrochemical activity, forming a strong BN synergistic interface with boron atoms in the framework.

[0082] Example 4:

[0083] S1. 13244g of formaldehyde, 21188g of acetic acid, and 14568g of water were added to the reactor at a phenol-formaldehyde molar ratio of 1:5.47. After adding 364g of sodium carboxymethyl cellulose, 520g of tributyl borate was introduced. The mixture was heated to 35°C to dissolve and then cooled to 15°C. Phenol solution was added for emulsification, followed by heating and dilution. The mixture was then extruded at 90MPa for 40min in a hot press to obtain a highly cross-linked, spherical, almond-shaped morphology. S2 and S3: Subsequent carbonization, magnesothermic reduction, and silicon-loaded coating steps were the same as in Example 1.

[0084] Example 5:

[0085] S1. 13244g of formaldehyde, 21188g of acetic acid, and 14568g of water were added to the reactor at a high formaldehyde molar ratio of 1:5.47. In addition to 364g of sodium carboxymethyl cellulose, 182g of sodium dodecylbenzenesulfonate (SDBS) was introduced as a surface-active stabilizer. Since the high formaldehyde ratio increases the viscosity of the resin droplets, the addition of SDBS effectively reduces interfacial tension and prevents uncontrolled coalescence of droplets during high-temperature polycondensation. The mixture was emulsified at 1000rpm at 15°C and then extruded at 90MPa for 1 hour in a hot press. Post-curing, washing, and drying followed. S2. The above large-particle-size polyhedral resin was carbonized at 1000°C. In the magnesothermic reduction stage, magnesium powder was reacted with sodium chloride (1:0.8:3). Thanks to the well-defined polyhedral structure of the precursor, the reduction reaction created highly uniform nanopores within the particles, with a total pore volume of 0.90 cc / g. Micropores smaller than 2 nm accounted for 54%, while mesopores of 4-7 nm accounted for 18%. S3: Nano-silicon (57.5% silicon content) was loaded using SiH4 vapor deposition and coated with petroleum asphalt and melamine according to the process described in Example 2.

[0086] Example 6:

[0087] S1. A phenolic resin molar ratio of 1:5.47 was used, and the hot-pressing shaping time was set to 2 hours. S2. In the S2.2 magnesium thermal reduction step, a composite heat scavenging agent system was composed of sodium chloride and magnesium oxide (MgO) in a mass ratio of 3:1. Magnesium oxide acts as a physical template in the reaction, and after being completely removed in the S2.3 acid washing stage, more open channels are released inside the particles. S3. Subsequent silicon loading and sintering steps are the same as in Example 1.

[0088] Comparative Example 1: Step S1 is the same as in Example 2, but the 90MPa extrusion shaping process in stage S1.3 is omitted, while the remaining steps remain unchanged. Perfectly spherical phenolic resin and subsequent silicon-carbon materials are finally obtained.

[0089] Comparative Example 2: S1: The steps are the same as in Example 2. In S2, after the polyhedral resin is directly carbonized at 1000 degrees to obtain hard carbon, the S2.2 magnesium thermal reduction pore-forming step is skipped, and silicon loading in the S3 stage is carried out directly.

[0090] Comparative Example 3: Step S1 is the same as in Example 2, but boric acid modifier is not added. Step S2 is the same as in Example 2. Step S3 is the same as in Example 2, but nitrogen sources such as urea are not added; only asphalt is coated.

[0091] Comparative Example 4: Step S1 is the same as in Example 2, but in stage S1.3, it is compressed at 120 MPa for 8 hours.

[0092] Comparative Example 5: Step S1 is the same as in Example 1, but the amount of boron modifier added is adjusted to 10% of the formaldehyde mass.

[0093] Methods for manufacturing lithium batteries:

[0094] (1) Preparation of the positive electrode

[0095] Lithium cobalt oxide (LiCoO2), conductive carbon black, and polyvinylidene fluoride binder were mixed in a weight ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil. The aluminum foil was dried, and then cold-pressed, cut, and slit before being dried under vacuum to obtain the positive electrode sheet.

[0096] (2) Preparation of negative electrode

[0097] The negative electrode material, graphite, conductive agent (conductive carbon black, SuperP), and binder PAA of the above embodiments and comparative examples were mixed in a weight ratio of 70:15:5:10, deionized water was added, and a negative electrode slurry was obtained under vacuum stirring.

[0098] The negative electrode slurry is evenly coated onto the negative electrode current collector copper foil; the copper foil is dried, and then cold-pressed, cut, and slit.

[0099] The negative electrode is obtained by drying under vacuum conditions.

[0100] (3) Electrolyte

[0101] In a dry argon atmosphere glove box, LiPF6 is added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of approximately 1:1:1, and mixed thoroughly. The concentration of LiPF6 is approximately 1.15 mol / L. The electrolyte is obtained by mixing thoroughly.

[0102] (4) Separating membrane

[0103] Polyethylene porous polymer film is used as the separator.

[0104] (5) Assembly of pouch batteries

[0105] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode sheets. Then, they are wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0106] Lithium-ion battery cycle performance test: The lithium-ion battery was placed in a 45℃ (25℃) constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 0.7C to a voltage of 4.4V, followed by constant voltage charging at 4.4V to a current of 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to a voltage of 3.0V. The capacity obtained from this process was taken as the initial capacity. Cycling tests were performed using 0.7C charging / 0.5C discharging. The capacity decay curve was obtained by comparing the capacity at each step with the initial capacity. The number of cycles at 25℃ until 90% capacity retention was recorded as the room temperature cycle performance, and the number of cycles at 45℃ until 80% capacity retention was recorded as the high temperature cycle performance. The cycle performance of the material was compared by comparing the number of cycles under these two conditions.

[0107] Discharge rate test: The lithium-ion battery was placed in a 25℃ constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then discharged at a constant current of 0.2C to a voltage of 3.0V, left to stand for 5 minutes, charged at a constant current of 0.5C to a voltage of 4.45V, and then charged at a constant voltage of 4.45V to a current of 0.05C, left to stand for 5 minutes. The discharge rate was then adjusted, and discharge tests were conducted at 0.2C, 0.5C, 1C, 1.5C, and 2.0C. The discharge capacity was obtained at each rate, and the capacity obtained at 2C was compared with the capacity obtained at 0.2C. The rate performance was compared by comparing the ratio of the 2C to 0.2C values.

[0108] Battery full charge expansion rate test: Use a spiral micrometer to measure the thickness of the fresh battery when it is half-charged (50% SOC). After 400 cycles, the battery is in a fully charged (100% SOC) state. Use a spiral micrometer to measure the thickness of the battery at this time. Compare it with the thickness of the fresh battery when it is initially half-charged (50% SOC) to obtain the expansion rate of the battery at the full charge (100% SOC).

[0109] Particle size testing process: The microstructure and particle size of the material are observed using a scanning electron microscope (SEM). First, a small amount of negative electrode material particles are prepared as powder samples or dispersed in solvents such as anhydrous ethanol using ultrasonic dispersion. These are then uniformly coated onto conductive tape or copper mesh and sputter-coated with gold to enhance conductivity. Under vacuum conditions, high-resolution SEM equipment is used to image the particles at multiple magnifications, recording the true physical dimensions of spherical, almond-shaped, polyhedral, or dice-shaped particles. Finally, statistical analysis of a large number of representative images is performed using professional image processing software to calculate the average diameter and distribution range of the particles. Alternatively, a laser particle size analysis procedure can be used. First, 0.1g of sample is ultrasonically dispersed in anhydrous ethanol for 5 minutes, then injected into the test area of ​​a laser particle size analyzer. The Dv50 and Span values ​​are automatically calculated and output using Mie scattering theory.

[0110] Pore ​​volume performance testing process: First, a certain mass of multi-shaped porous hard carbon or silicon-carbon anode material is placed in a quartz test tube of the sample. The test tube is then installed on the degassing station of the physical adsorption instrument. Under vacuum or flowing inert gas conditions, the heating temperature (typically 150~300°C) is set according to the material's thermal stability and heated continuously for several hours to thoroughly remove adsorbed moisture, oil, and other impurities from the sample pores. After degassing, the test tube and sample are accurately weighed, and the net weight of the dried sample is obtained by subtracting the mass of the empty tube. The processed sample tube is transferred to the instrument's analysis station and immersed in a Dewar flask containing liquid nitrogen to ensure the test is conducted at a constant low temperature of approximately 77K. The instrument automatically and gradually introduces a known volume of nitrogen into the test tube, recording the amount of nitrogen adsorbed by the sample under different relative pressures. As the pressure increases, nitrogen molecules evolve from monolayer adsorption to multilayer adsorption, and eventually undergo capillary condensation within the pores, forming a complete adsorption-desorption isotherm. Total pore volume is typically calculated using nitrogen adsorption at a relative pressure close to 1 (usually around 0.99). Based on Michaelis-Menten theory or relevant physical constants, the volume of adsorbed nitrogen at this pressure is converted to the volume of liquid nitrogen, and then divided by the sample mass to obtain the total pore volume in cc / g. This value represents the total space capacity within the material, from micropores to macropores, that can accommodate active materials or electrolytes. Based on experimentally measured adsorption-desorption curves, different theoretical models are used for data fitting analysis. For materials containing mesopores (2–50 nm), the Barrett-Joyner-Halenda (BJH) model is commonly used; while for hard carbon materials containing a large number of micropores (less than 2 nm), the nonlocal density functional theory (NLDFT) model is preferred to obtain more accurate pore size distribution data. The calculation software can output the pore volume percentage for pores of different diameters.

[0111] The particle size and pore volume performance data are shown in Table 1.

[0112] Table 1:

[0113]

[0114] Experimental data show that the particle size distribution index (Span) of Examples 1 to 4 remained stable between 1.0 and 1.2, exhibiting excellent monodispersity. However, in Comparative Example 5, due to insufficient dispersant, the Span value soared to 10.029, resulting in a severe bimodal particle size distribution, with an excessively high proportion of large particles larger than 20 micrometers. This non-uniform particle size distribution not only causes instability in the internal structure of the particles but also leads to significant yield losses in subsequent carbonization and silicon loading processes, demonstrating the necessity of precisely controlling the precursor polymerization conditions to ensure the quality of the finished product. In the examples, the total pore volume was maintained between 0.89 and 0.98 cc / g, with micropores and small mesopores smaller than 4 nm accounting for over 90%. This highly concentrated pore size distribution confines the nano-silicon regions generated by vapor deposition to below 20 nm, effectively suppressing the agglomeration of silicon particles. Simultaneously, the abundant microporous structure acts as a natural stress buffer, absorbing the volumetric stress generated during silicon lithium intercalation expansion, ensuring the hard carbon framework maintains structural integrity even under extreme pressure conditions. The phenomena of "explosive polymerization" caused by an excessively high phenol-formaldehyde ratio (Comparative Example 4) and "particle size runaway" caused by insufficient dispersant (Comparative Example 5) clarified the scientific basis for prepolymerization at a specific ratio between 30 and 45°C. These data collectively demonstrate that only through the synergistic effect of specific morphology, particle size, and pore size parameters can silicon-carbon anode materials simultaneously possess anti-expansion, high-pressure resistance, and excellent conductivity under low-temperature conditions while ensuring high compaction density.

[0115] Figure 1The image shows an optical microscope image of the spherical almond-shaped phenolic resin from Example 1. Morphologically, the particles exhibit a distinctly asymmetrical elongated ellipse shape, resembling a spherical almond, with clear boundaries and good monodispersity. This unique geometry is induced by applying a directional longitudinal high pressure of 90 MPa during the preparation process, breaking the isotropy of traditional phenolic resin microspheres. Observation reveals a relatively uniform particle size distribution, smooth surfaces, and flattened regions formed by restricted extrusion, demonstrating the precise morphological control achieved through low-temperature emulsification and high-pressure shaping processes. In terms of technical effects, this spherical almond-shaped morphology changes the contact method between particles from the traditional point contact of spheres to a stable surface contact. After being fabricated into battery electrodes, the flat contact surfaces significantly enhance the mechanical interlocking force between the particles and the binder and conductive agent, greatly improving the overall stability of the electrode structure. This structure exhibits extremely strong physical pressure resistance under deep-sea high-pressure environments, mitigating external pressure stress through mutual support between particles and preventing physical pulverization or structural collapse of the negative electrode material during high-pressure cycling. In addition, the spherical almond-shaped structure optimizes the particle packing density in the electrode, effectively buffering the volume expansion stress of the internal nano-silicon during charging and discharging while ensuring the electrolyte permeation channel, thus ensuring the long cycle life of the battery.

[0116] Figure 2 In Example 2, the morphology analysis of the polyhedral phenolic resin clearly shows that the particles have completely departed from the traditional spherical shape, evolving into a polyhedral structure with multiple clear edges and flat crystal faces. These particles exhibit excellent monodispersity and a uniform particle size distribution, with the particle size marked in the figure mainly concentrated between 4 μm and 11 μm. This regular geometry was induced by continuous extrusion under a longitudinal high pressure of 90 MPa for 2 hours. During this process, the softened resin particles are compressed against each other in a confined space, transforming from initial spherical deformation into a closely packed crystalline polyhedral morphology. During electrode compaction, the flat surfaces of the polyhedra can form a larger area of ​​physical interlocking with adjacent particles, conductive agents, and binders, significantly improving the mechanical cohesion within the electrode. This structure exhibits excellent anti-pulverization capabilities in deep-sea high-pressure applications, and the mutual support between particles can effectively share external loads, preventing structural stress collapse of the material during high-pressure cycling. Furthermore, this tight geometric stacking not only increases the compaction density of the electrodes, but also provides a stable framework to support the expansion of the internal nano-silicon, ensuring that the active material does not debond or break during long-term cycling, thereby maintaining the stability of the highly efficient conductive network.

[0117] Figure 3This is an optical microscope image of the dice-shaped phenolic resin from Example 3. In terms of morphological characteristics, the microscopic image shows that the particles exhibit a regular polyhedral shape, with the most significant feature being the inwardly concave center of the particle surface, resembling a miniature die. These particles have extremely clear boundaries and sharp edges, and exhibit excellent monodispersity in the solvent, without obvious agglomeration. This morphology was formed by continuous extrusion at 90 MPa for 3 hours, utilizing the asymmetric deformation reaction induced by thermo-pressurization. In the preparation of lithium-ion battery electrodes, this structure can form a denser mechanical bond with the binder and conductive agent, significantly improving the structural integrity of the electrode material during charge-discharge cycles. Furthermore, this complex geometry, under the high pressure of deep-sea conditions, can form a stable microstructure through the interlacing support of multiple flat surfaces, effectively preventing physical pulverization of the particles. Meanwhile, experimental data show that its total pore volume is 0.89cc / g, and the proportion of micropores smaller than 2nm is as high as 66%. This rich internal pore structure provides sufficient volume expansion buffer for the loaded nano-silicon, thereby ensuring that the material still has extremely high cycle stability and compressive strength under extreme working conditions.

[0118] Figure 4 This is an optical microscope image of the spherical almond-shaped phenolic resin from Example 4. In terms of morphology, the microscopic images show that the particles exhibit a clear elliptical, almond-shaped appearance, with an extremely sparse distribution, demonstrating excellent monodispersity. Compared to spherical particles, these almond-shaped particles have a distinct difference between their major and minor axes and a relatively flat surface. Combined with the experimental data table, this indicates that by precisely controlling the dispersant ratio in S1.1 and the emulsification speed in S1.2, a highly regular and narrowly distributed asymmetric precursor was successfully prepared. This morphology was induced by longitudinal high-pressure extrusion at 90 MPa for 40 minutes, retaining the unique flattened characteristics of the almond-shaped particles. After being prepared into a negative electrode sheet, the flat surface of the almond-shaped particles can form a stronger physical anchoring force with the binder, preventing the material from debonding due to the volume expansion of silicon during charge-discharge cycles. Furthermore, Example 4 exhibits a high total pore volume of 0.92 cc / g, with pore sizes entirely concentrated below 4 nm (of which micropores smaller than 2 nm account for 59%). This fine pore structure provides an ideal confined growth space and stress buffer for the subsequent deposition of nano-silicon. Combined with the high boron content modifier introduced in S1.1, efficient electron conduction dynamics are maintained under extremely low temperature conditions, ensuring long-life operation of the battery in extreme environments.

[0119] Figure 5This is a scanning electron microscope (SEM) image of the polyhedral phenolic resin from Example 5. In terms of morphology, the SEM image shows that the particles exhibit a highly regular polyhedral structure with clear edges and multiple flat geometric crystal faces. Although the particle size is relatively large, the particles still maintain a good monodisperse state, with a particle size distribution index (Span) of 1.297, which is within a reasonable and controlled range. This morphology is due to the deep physical compression and mutual shaping of the resin particles within a confined space during the high-pressure heat treatment at 90 MPa in step S1.3, thus transforming them from spheres into a close-packed polyhedral morphology. During battery charging and discharging, the flat surfaces of the polyhedra provide greater friction and anchoring force, preventing the particles from slipping or debonding under the stress generated by the expansion of silicon volume. Furthermore, Example 5 has a total pore volume of 0.90 cc / g, of which 54% of the pores are micropores smaller than 2 nm. This hierarchical pore structure effectively confines the deposited nano-silicon in situ, providing it with sufficient volume buffer space.

[0120] Figure 6 This is an optical microscope image of the dice-shaped phenolic resin from Example 6. The microscopic image shows that the particles exhibit regular polyhedral features, with each facet having a distinct inward indentation at its center, resembling a miniature "dice." As observed from the scale bar in the image, the physical size of a single particle is approximately 10 micrometers. Although the particle size is larger than in previous examples, the particle edges still maintain clear edges and an extremely narrow particle size distribution (Span=1.123), demonstrating excellent morphological regularity. This unique surface indentation feature is formed through the combined effect of precisely controlled drying time and hot-pressed induced asymmetric deformation reaction. This special dice-shaped structure, when used to prepare electrode sheets, generates stronger physical and mechanical bonding forces with the binder and conductive agent, significantly improving the material's resistance to debonding during charge-discharge cycles in the face of silicon expansion. Furthermore, Example 6 possesses a total pore volume as high as 0.98 cc / g, with the pore size distribution mainly concentrated below 4 nm (of which micropores smaller than 2 nm account for 53%). This highly developed pore network provides excellent volumetric buffer space for the loaded active silicon.

[0121] Figure 7This is an optical microscope image of the perfectly spherical phenolic resin in Comparative Example 1. In terms of morphological characteristics, the microscopic image shows that the particles exhibit an extremely regular, symmetrical, perfectly spherical structure with a very smooth and continuous surface. The particle size is highly uniform, with almost no deformation or angular features. This indicates that without the high-pressure heat treatment shaping in step S1.3, the phenolic resin tends to maintain the lowest energy spherical state, exhibiting extremely high geometric symmetry. However, this perfectly spherical morphology has a significant drawback in the field of high-performance silicon-carbon anodes. Because the spheres can only achieve point contact, the mechanical interlocking force between the particles and the binder (glue) and conductive agent is weak after they are fabricated into electrode sheets. During the charging and discharging process of the battery, the spherical particles are prone to slipping from each other or falling off the conductive network due to the intense volume expansion stress of the internal nano-silicon. The perfect spherical structure lacks the mutual support of surface contact like a polyhedron or a spherical almond-shaped structure, and cannot effectively disperse physical stress. This makes the material very prone to pulverization and collapse, resulting in the battery's cycle stability and compressive strength being significantly inferior to the shaped embodiment.

[0122] Figure 8 The image shows an optical microscope image of the irregular phenolic resin in Comparative Example 2. In terms of morphology, the microscopic images reveal an extremely chaotic and non-uniform appearance, completely lacking any geometric symmetry. Numerous broken lumps, sharp edges, and randomly fused agglomerates are clearly visible in the images, with a lack of clear boundaries and consistent size between particles. Analysis of the experimental data shows that the particle size distribution index (Span) of Comparative Example 2 is as high as 1.424, significantly higher than the approximately 1.0 level in other examples. This indicates that during the preparation process, excessively high pressure (e.g., 96 MPa) or excessively long extrusion time, exceeding process limits, physically broke down the original resin structure, leading to a complete loss of control over the particle morphology. Due to the sharp and asymmetrical shape of the particles, their stacking pattern in the electrode is extremely chaotic, unable to achieve the ordered surface contact and mutual support of a polyhedral structure, resulting in a significant decrease in the electrode's compaction density and mechanical stability. During charge-discharge cycles, the volume expansion of the internal active silicon will generate severe stress concentration at the sharp edges or structurally weak points of these irregular particles, easily inducing further particle pulverization and electrical contact failure. Furthermore, this disordered morphology causes uneven penetration of electrolyte within the pores, increasing charge transfer resistance. Consequently, the material's cycle life, compressive strength, and reliability under extreme conditions are far inferior to those of shaped almond-shaped, polyhedral, or dice-shaped structures.

[0123] Figure 9This is an optical microscope image of the partially fused spherical phenolic resin in Comparative Example 3. In terms of morphology, the microscopic images show that the particles exhibit a non-independent aggregated state. A large number of particles that should have been spherical have fused and merged at the interface, resulting in extremely blurred physical boundaries between particles, forming clusters resembling "honeycombs" or "fused blocks." As observed in the images, except for a few scattered near-spherical particles at the edges, the main body has completely lost its monodispersity. Analysis of the experimental data shows that the particle size distribution index (Span) of Comparative Example 3 is as high as 1.505, reflecting that during the polymerization stage, improper temperature control (such as excessively high temperature or localized overheating) caused physical cross-fusion of the resin particles before they were fully cured and shaped. Because the particles are mutually adhered and have unclear boundaries, they cannot achieve regular surface contact and mutual support after being prepared into electrodes, resulting in a large number of structural dead zones inside the electrodes, severely hindering the effective penetration of the electrolyte and ion transport kinetics. Furthermore, the data shows that the pore size distribution of this sample has deteriorated significantly, with a significant increase in the proportion of medium and large pores (4-7 nm and larger than 7 nm) (totaling 16%), far exceeding the levels of other embodiments. This coarse pore structure not only fails to effectively constrain and alleviate the volume expansion stress of nano-silicon, but also makes the fusion points structurally fragile, easily becoming the initiation points of stress cracks, thereby triggering large-area physical pulverization and electrochemical cycle failure.

[0124] Figure 10 The image shown in Comparative Example 5 is a scanning electron microscope (SEM) image. In terms of morphology, the SEM image clearly shows that the product is in an extremely heterogeneous mixed state. Although some basic particles still have polyhedral outlines, the system contains a large number of enormous ultra-large particles, whose physical size far exceeds normal process requirements. According to the measurements in the image, the diameters of these giant particles are generally between 30 μm and 43 μm, with some even showing fragments approaching 60 μm. This perfectly matches the particle size distribution index (Span) of 10.029 recorded in the experimental data table, indicating that the material has lost its monodispersity and exhibits an extremely wide particle size distribution range. Regarding technical defects, this severe loss of particle size control directly led to the failure of subsequent pore-forming and composite processes. Due to the severely insufficient addition of dispersant (CMC) in the S1.1 stage, the surface energy of the droplets could not be maintained stably during the polymerization reaction, resulting in large-scale uncontrolled coalescence. Because of their huge volume ratio, in the subsequent magnesothermic reduction reaction, the reducing gas and thermal scavenging agent could not penetrate uniformly into the particle core, preventing the formation of effective nanopores inside. This extreme structural inhomogeneity prevented Comparative Example 5 from producing qualified porous hard carbon. Its total pore volume and pore volume distribution data were recorded as "none," and it completely lost its significance as a high-capacity silicon-carbon anode material in terms of electrochemical performance.

[0125] Single-particle strength test: A 50μm diameter planar diamond indenter is used to aim at a particle with a particle size near Dv50. A load is applied to the particle, and the test force and compressive displacement are measured in real time until the compressive displacement no longer changes with the load. The ratio of the load to the indentation area is the compressive strength, and the ratio of the compressive displacement to Dv50 is the crush strain. 50 particles are selected for each test, and the average compressive strength is taken. The equipment used is a microhardness tester.

[0126] Test method for silicon content in negative electrode materials: Weigh 0.05 to 0.1 g of sample and add 1.2 to 1.5 g of dry potassium hydroxide. Place the sample in a muffle furnace at 400°C. After cooling, add boiling water to wet the sample. Wash and dry the sample repeatedly. Filter the sample solution into a 100 mL PP bottle using medium-speed filter paper and make up to volume. Then dilute the solution 100 times and test the diluted solution using ICP-OES. Calculate the silicon content of the sample.

[0127] Method for testing the specific surface area of ​​negative electrode materials: Under constant temperature and low temperature, the amount of gas adsorbed on the solid surface at different relative pressures is measured. Based on the Brownauer-Etter-Taylor adsorption theory and its formula (BET formula), the amount of monolayer adsorption of the sample is calculated, thereby calculating the specific surface area of ​​the solid. Approximately 1.5g to 3.5g of powder sample is weighed and placed into the test sample tube of a TriStarII3020, degassed at approximately 200℃ for 120min, and then tested.

[0128] The method for testing the true density of negative electrode materials is as follows: Weigh a sample of a certain mass (1g to 5g), place it in a true density tester, seal the test system, and introduce helium or nitrogen gas according to the procedure. By testing the pressure of the gas in the sample chamber and the expansion chamber, and then calculating the true volume according to Bohr's Law (PV=nRT), the true density can be calculated.

[0129] The experimental data are shown in Table 2.

[0130] Table 2:

[0131]

[0132] Experimental data show that the expansion rate after 100 cycles in all embodiments was generally controlled between 3.9% and 5.9%, significantly lower than 9.1% in Comparative Example 1 and 8.0% in Comparative Example 2. This excellent ability to suppress volume expansion directly translates into superior cycling performance. For example, Example 2 achieved a room temperature cycle life of 1643 cycles and maintained 1323 cycles at high temperatures, while Comparative Example 1, lacking morphology control, only achieved 832 cycles. This demonstrates that by constructing polyhedral, almond-shaped, and other surface contact morphologies, combined with abundant internal nanoporous buffer zones, the enormous volume stress of silicon during charging and discharging can be effectively absorbed, preventing the active material from debonding and failing, thus achieving long-life stable cycling. Secondly, the material exhibits extremely high physical and mechanical strength, capable of withstanding extreme high-pressure environments. The data table shows that the compressive strength of all embodiments ranges from 879 MPa to 982 MPa, with Example 4 exhibiting the highest strength at 982 MPa. In contrast, Comparative Example 3, with its fused morphology and disordered pore structure, has a compressive strength of only 732 MPa. This high-strength technical effect is attributed to the close-packed framework formed by the phenolic resin precursor during hot pressing. This allows the particles to support each other through flat contact surfaces during deep-sea high-pressure or high-pressure electrode processing, effectively preventing physical pulverization and ensuring the structural integrity of the electrode under extreme physical loads. Furthermore, the material maintains high capacity while also exhibiting excellent kinetic performance. Although Comparative Example 2 showed a high initial specific capacity, its rate performance and cycle stability were poor. In contrast, all examples maintained a high capacity of approximately 1900 mAh / g while generally achieving a rate performance better than 87%, with Example 2 reaching as high as 94.3%. This demonstrates that the present invention, through intrinsic doping with boron and nitrogen and a specific pore structure, significantly reduces charge transfer impedance, allowing lithium ions to migrate rapidly within the porous hard carbon framework even at large charge and discharge currents. This technical effect ensures that the material can not only serve as a high-energy-density energy storage medium but also meet the kinetic requirements of fast charging and discharging and low-temperature environments.

[0133] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin, characterized in that the steps include... include: S1. Formaldehyde solution, phenol solution and acidic catalyst are mixed and boron modifier is introduced to obtain boron modified phenolic resin precursor. The phenolic resin precursor is subjected to hot pressing to obtain polymorphic phenolic resin. The polymorphic phenolic resin includes at least one of spherical almond-shaped phenolic resin, polyhedral phenolic resin and dice-shaped phenolic resin. Step S1 includes: S1.1 Mix formaldehyde solution, acidic catalyst and deionized water in proportion, then add boron modifier and dispersant. The amount of boron modifier added is 1.5~5.5% of formaldehyde solution. Stir at high speed at 30~45°C for 60~180 minutes, then add phenol solution to obtain boron modified phenolic resin precursor. S1.

2. Turn on the cooling system of the reactor to lower the system temperature to 10~25°C. Use a high shear emulsifier to perform emulsification at a speed of 800~1500 rpm. Then raise the temperature to 55~75°C and maintain it for 30~90 minutes to perform preliminary crosslinking and obtain phenolic resin particles. S1.3 After filtration and washing, the phenolic resin particles are laid on a hot press with a Teflon liner, and a longitudinal high pressure of 80~100MPa is applied. The temperature is maintained at 80~120°C for 0.5~4 hours to induce an asymmetric deformation reaction and obtain polymorphic phenolic resin. S1.4 Disperse the polymorphic phenolic resin in a crosslinking agent solution with a mass fraction of 5%~15%, and perform post-curing treatment at a temperature of 75~95°C for 2~6 hours using a circulating water bath heating device. S2. The multi-shaped phenolic resin is carbonized at high temperature under an inert atmosphere, and then mixed with magnesium powder and subjected to magnesothermic reduction to obtain porous hard carbon with nanopores. S3. Porous hard carbon is deposited by introducing silicon source gas, and then coated with nitrogen source and soft carbon source for sintering treatment to obtain multi-shaped silicon-carbon anode material based on phenolic resin.

2. The method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin according to claim 1, characterized in that, In step S1, the acidic catalyst includes at least one of acetic acid, oxalic acid, hydrochloric acid, phosphoric acid, and sulfuric acid; the boron modifier includes at least one of boric acid, trimethyl borate, tributyl borate, boron oxide, and borate; the dispersant includes at least one of sodium carboxymethyl cellulose, polyvinyl alcohol, xanthan gum, and guar gum; and the crosslinking agent includes at least one of hexamethylenetetramine, hydrochloric acid, formaldehyde, and para-oxygenated formaldehyde.

3. The method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin according to claim 1, characterized in that, Step S2 includes: S2.1 Place the polymorphic phenolic resin in a tube furnace, introduce argon as a protective gas to maintain an inert atmosphere, heat to 800~1100°C at a heating rate of 1~5°C / min and hold at the temperature for 2~5 hours to obtain polymorphic hard carbon. S2.2 Mix the multi-shaped hard carbon particles, metallic magnesium powder and heat scavenger at a preset mass ratio at a speed of 800~1500 rpm for 20~60 minutes, then transfer them to a reactor under an argon atmosphere and heat them to 650~800°C and maintain the temperature for 2~6 hours to carry out the magnesium thermal reduction reaction. S2.3 After the reaction is complete and the product has cooled to room temperature naturally, it is transferred to a chemical reaction vessel, a hydrochloric acid solution with a concentration of 1~2 mol / L is added and the mixture is stirred continuously for 4~12 hours. After repeated filtration and washing with deionized water until the filtrate is neutral, it is vacuum dried at 80~120°C to obtain porous hard carbon with nanopores.

4. The method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin according to claim 3, characterized in that, The heat scavenger includes at least one of sodium chloride, potassium chloride, magnesium chloride, and magnesium oxide, and the mass ratio of multi-shaped hard carbon particles: metallic magnesium powder: heat scavenger ranges from 1:(0.5~1.5):(1~5).

5. The method for preparing a multi-shaped silicon-carbon anode material based on phenolic resin according to claim 1, characterized in that, Step S3 includes: S3.

1. The porous hard carbon is placed in the constant temperature zone of the chemical vapor deposition furnace, and silicon source gas diluted with high-purity argon is introduced. The dilution ratio is 10~30%. The temperature is maintained at 500~700°C for 2~10 hours to obtain silicon-loaded composite material. S3.2 Transfer the silicon-based composite material to a mixer, add a soft carbon source and a nitrogen source. The mass ratio of the soft carbon source to the silicon-based material is 5%~20%, and the mass ratio of the nitrogen source to the silicon-based material is 2%~8%. Stir in anhydrous ethanol solvent at a speed of 500~1200 rpm and sonicate at 40~60°C for 2~5 hours. After the solvent evaporates naturally, precursor particles with a nitrogen-carbon mixed layer on the surface are obtained. S3.

3. The precursor particles are placed in a tube furnace and heated to 900-1100°C at a rate of 2-8°C / min under the protection of flowing argon gas. The mixture is then sintered at a constant temperature for 2-6 hours and cooled to obtain a multi-shaped silicon-carbon anode material based on phenolic resin.

6. A method for preparing a polymorphic silicon-carbon anode material based on phenolic resin according to claim 2 or 5, characterized in that, In step S3, the silicon source gas includes at least one of silane, silane, dichlorosilane, trichlorosilane, and silicon tetrachloride; the soft carbon source includes at least one of medium-temperature pitch, high-temperature pitch, coal tar, petroleum pitch, and mesophase pitch; and the nitrogen source includes at least one of urea, melamine, polyacrylonitrile, polyaniline, and dicyandiamide.

7. A polymorphic silicon-carbon anode material based on phenolic resin, characterized in that, The anode material is prepared by a method for preparing a polymorphic silicon-carbon anode material based on phenolic resin as described in any one of claims 1-6. The polymorphic silicon-carbon anode material based on phenolic resin includes porous hard carbon made of polymorphic phenolic resin. The polymorphic phenolic resin includes at least one of spherical almond-shaped phenolic resin, polyhedral phenolic resin, and dice-shaped phenolic resin. The spherical almond-shaped phenolic resin includes almond-shaped phenolic resin and perfectly spherical phenolic resin. The ratio of the shortest diameter to the longest diameter of the almond-shaped phenolic resin is less than 0.95, while the ratio of the shortest diameter to the longest diameter of the perfectly spherical phenolic resin is greater than or equal to 0.

95. The surface of the spherical almond-shaped phenolic resin is covered with a disordered network of wrinkles; the included angle formed by adjacent network wrinkles is between 5 degrees and 89 degrees, and the area enclosed by adjacent network wrinkles is less than 1 nm. 2 ~10um 2 Between these ranges, the height of the mesh folds is between 1 nm and 1 μm, and the length of the mesh folds is between 10 nm and 500 μm. The polyhedral phenolic resin surface has clear edges and included angles formed by these edges, with angles ranging from 15 to 178 degrees. The surfaces formed by the edges are flat. A flat surface is defined as one where, under a scanning electron microscope at 100,000x or higher magnification, the polyhedral surface shows no inward depressions. The number of flat surfaces is greater than or equal to 4 and less than or equal to 80. Flat surfaces are triangular or polygonal, with polygons having less than or equal to 20 and greater than or equal to 4 sides. The area of ​​a flat surface is greater than or equal to 1 nm. 2 And less than or equal to 100um 2 ; The die-shaped phenolic resin surface has clear edges and the included angles formed by these edges. The surfaces formed by the edges are concave inwards. These concave surfaces, observed with a scanning electron microscope at 100,000 magnification, are curved surfaces formed by the edges and corners of the die-shaped phenolic resin surface. The central region of this curved surface is not on the same plane as the edges and is concave inwards. The distance between the deepest point of the concavity and the plane formed by the edges is less than or equal to 10 μm and greater than or equal to 20 nm. The number of surfaces formed by the surface edges is greater than or equal to 4 and less than or equal to 80. The concave surfaces are triangular or polygonal, with polygons having less than or equal to 20 and greater than or equal to 4 sides. The area of ​​the concave surfaces is greater than or equal to 1 nm. 2 And less than or equal to 100um 2 .

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