Double-coating-layer modified silicon-based negative electrode material and preparation method thereof, negative electrode and lithium ion battery

Abstract

The invention provides a double-coating-layer modified silicon-based negative electrode material and a preparation method thereof, a negative electrode and a lithium ion battery. The double-coating-layer modified silicon-based negative electrode material comprises a porous silicon core, a carbon coating layer and a lithiated vulcanized polyacrylonitrile coating layer, pores of the porous silicon core are filled with the carbon coating layer, the outer surface of the porous silicon core is coated with the carbon coating layer, and the surface of the carbon coating layer is coated with the lithiated vulcanized polyacrylonitrile coating layer. The lithiated sulfurized polyacrylonitrile coating layer can promote uniform lithiation of the porous silicon core in the charging process while inhibiting volume expansion of the porous silicon core in the charging process. Besides, the carbon coating layer and the lithiated sulfurized polyacrylonitrile coating layer can synergistically prevent the porous silicon core from being in contact with an electrolyte, so that continuous consumption of lithium ions is avoided, coulombic efficiency is improved, and the technical problems of huge volume expansion of the silicon-based negative electrode in the charge-discharge cycle process and serious side reaction with the electrolyte are solved.

Description

Double-coated modified silicon-based anode material and its preparation method, anode and lithium-ion battery Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a double-coated modified silicon-based anode material, its preparation method, the anode, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, low self-discharge, and no memory effect, leading to their widespread application in electric vehicles, 3C electronic products, and grid energy storage. In lithium-ion batteries, the performance of the anode material is a crucial factor determining the overall battery performance. Currently, commercially available lithium-ion batteries primarily use graphite as the anode material, with a theoretical specific capacity of only 372 mAh / g. With the increasing demand for high-energy-density batteries, graphite anodes are increasingly unable to meet the future development requirements of lithium-ion batteries. Compared to graphite anodes, silicon boasts an extremely high theoretical specific capacity (when lithium is lithiated to Li). 15 Si (with a capacity of up to 3579 mAh / g) is a highly promising candidate for next-generation lithium-ion battery anode materials. However, silicon undergoes severe volume expansion and contraction during charge-discharge cycles, with volume fluctuations reaching 300-400%. This not only leads to silicon particle breakage and pulverization and damage to the anode structure, but also causes the solid electrolyte interphase (SEI) film on the surface of silicon particles to frequently rupture and regenerate during cycling, as the SEI film cannot withstand the significant mechanical stress generated by repeated volume expansion and contraction. This continuously consumes Li in the electrolyte. + This leads to a significant decrease in coulombic efficiency during cycling. Furthermore, repeated rupture and regeneration of the SEI film cause a continuous increase in its thickness, resulting in increased internal resistance and intensified polarization, ultimately leading to a significant decline in battery performance.

[0003] Currently, various methods have been used to improve the performance of silicon-based anode materials, such as preparing nanomaterials, constructing porous structures, designing surface coatings and yolk-shell structures, etc. Among them, nano-silicon materials such as zero-dimensional nanoparticles, one-dimensional nanowires and nanotubes, and two-dimensional nanosheets (such as the nano-silicon-MXene composite anode material published in Chinese patent application CN109346681 A) and porous silicon materials (such as the porous silicon-carbon composite anode material published in Chinese patent application CN 115241440 A) can effectively buffer the volume expansion of silicon-based anode materials. However, these materials all have a large specific surface area, which will cause a high degree of side reaction with the electrolyte during the first lithiation process, resulting in a low initial coulombic efficiency. Surface coating design (such as the silicon-carbon anode material coated with a highly elastic polymer published in Chinese patent application CN 119050291 A) can avoid direct contact between silicon and electrolyte, but such materials have limited effect on inhibiting the volume expansion during silicon lithiation. Eggshell-structured silicon-based anode materials (such as the silicon-carbon composite anode material with a yolk shell structure published in Chinese patent application CN 115117328 A) are also available. x Silicon-based anode materials with a yolk-shell structure (comprising a Si core, a LiF-Ti shell, and the voids between the core and shell) can effectively accommodate the volume expansion generated during lithiation. However, the manufacturing process for such materials is typically complex, and the shell often contains defects, making it difficult to completely prevent direct contact between the silicon core and the electrolyte. This leads to continuous electrolyte consumption, sustained SEI film growth, and rapid capacity decay during cycling. Therefore, there is an urgent need to develop a silicon-based anode material with low expansion rate, low side reaction degree, simple manufacturing process, and good cycle performance.

[0004] In summary, existing technologies suffer from the technical problems of significant volume expansion of silicon-based anodes during charge-discharge cycles and severe side reactions with the electrolyte.

[0005] There is currently no good solution to the above problems. Summary of the Invention

[0006] This application provides a double-coated modified silicon-based anode material and its preparation method, as well as an anode and a lithium-ion battery, to at least solve the technical problems of huge volume expansion of silicon-based anodes during charge-discharge cycles and serious side reactions with electrolytes in the prior art.

[0007] According to one aspect of the embodiments of this application, a dual-coating modified silicon-based anode material is provided. The dual-coating modified silicon-based anode material includes a porous silicon core, a carbon coating layer, and a lithium-sulfurized polyacrylonitrile coating layer, wherein the carbon coating layer fills the pores of the porous silicon core and coats the outer surface of the porous silicon core, and the lithium-sulfurized polyacrylonitrile coating layer coats the surface of the carbon coating layer.

[0008] In several embodiments, the mass ratio of the porous silicon core to the carbon coating layer is 1:1 to 4:1; and / or, the total mass ratio of the porous silicon core and the carbon coating layer to the mass ratio of the polyacrylonitrile in the lithium-cured polyacrylonitrile coating layer is 5:1 to 20:1.

[0009] In several embodiments, the mass ratio of polyacrylonitrile to sulfur in the lithium-cured polyacrylonitrile coating layer is 3:1 to 5:1; and / or, the porous silicon core is a primary spherical particle with a median particle size of 0.2 μm to 5 μm; and / or, the porosity of the porous silicon core is 40% to 60%; and / or, the pores of the porous silicon core are open pores with a pore size of 20 nm to 500 nm; and / or, the volume of open pores with a pore size of 50 nm to 250 nm in the porous silicon core accounts for 50% to 80% of the total open pore volume.

[0010] According to another aspect of the embodiments of this application, a method for preparing a double-coated modified silicon-based anode material is also provided. The preparation method includes: step S1, in an inert atmosphere, a carbon source is deposited on porous silicon by chemical vapor deposition to obtain a precursor; step S2, raw materials including polyacrylonitrile, elemental sulfur, the precursor and a first organic solvent are mixed to obtain a mixed slurry; step S3, the mixed slurry is sequentially spray-dried and calcined to obtain an intermediate; step S4, raw materials including lithium metal, an aromatic hydrocarbon compound and a second organic solvent are mixed to obtain an aromatic hydrocarbon compound-lithium solution; step S5, the intermediate is added to the aromatic hydrocarbon compound-lithium solution for a lithiation reaction, followed by filtration, washing with the second organic solvent and vacuum drying to obtain a double-coated modified silicon-based anode material, wherein the precursor includes porous silicon and a carbon coating layer, the carbon coating layer fills the pores of the porous silicon and coats the outer surface of the porous silicon; the aromatic hydrocarbon compound is C 6~ C 12 Aromatic hydrocarbons.

[0011] In several embodiments, in step S1, the carbon source is selected from any one or more of methane, ethane, and propane; and / or, the temperature of chemical vapor deposition is 500°C to 900°C, and the time of chemical vapor deposition is 4h to 12h; and / or, the inert atmosphere is selected from any one or more of helium, nitrogen, and argon.

[0012] In several embodiments, in step S2, the first organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; and / or, the mass ratio of the precursor to polyacrylonitrile in the mixed slurry is 5:1 to 20:1; and / or, the mass ratio of polyacrylonitrile to elemental sulfur in the mixed slurry is 3:1 to 5:1; and / or, the solid content of the mixed slurry is 35% to 75%.

[0013] In several embodiments, in step S3, the inlet air temperature for spray drying is 120°C to 200°C, and the feed rate is 2L / h to 6L / h; and / or, the calcination temperature is 250°C to 350°C, and the calcination time is 4h to 8h.

[0014] In several embodiments, in step S4, the aromatic hydrocarbon compound is selected from any one or more of biphenyl, 4,4'-dimethylbiphenyl, 2,3'-dimethylbiphenyl, and 4,4'-dimethoxybiphenyl; and / or, the second organic solvent is selected from any one or more of anhydrous tetrahydrofuran, N-methylpyrrolidone, and dioxane; and / or, the mass concentration of metallic lithium in the aromatic hydrocarbon compound-lithium solution is 5 g / L to 20 g / L; and / or, the concentration of aromatic hydrocarbon compound in the aromatic hydrocarbon compound-lithium solution is 50 g / L to 300 g / L; and / or, step S5 includes: stirring and mixing the intermediate with the aromatic hydrocarbon compound-lithium solution for a certain period of time, followed by filtration, washing, and vacuum drying to obtain a double-coated modified silicon-based anode material; wherein, the stirring and mixing temperature is 60℃ to 100℃, and the stirring and mixing time is 4 h to 12 h; the vacuum drying temperature is 60℃ to 100℃, and the vacuum drying time is 6 h to 12 h.

[0015] According to another aspect of the embodiments of this application, a negative electrode is also provided, including a negative electrode material, wherein the negative electrode material is the aforementioned double-coated modified silicon-based negative electrode material or is prepared by the aforementioned preparation method.

[0016] According to another aspect of the embodiments of this application, a lithium-ion battery is also provided, including a positive electrode, a negative electrode and a separator, wherein the negative electrode is the aforementioned negative electrode.

[0017] In this embodiment, the porous silicon core serves as the main active material, providing the primary capacity for the anode material. The carbon coating layer fills the pores of the porous silicon core and coats its outer surface, providing uniform and rapid lithium-ion / electron transport channels for both the inner and outer surfaces of the porous silicon core. This promotes uniform lithiation and expansion of the porous silicon core during charging and also buffers the volume expansion / contraction of the porous silicon core during charge-discharge cycles. The lithiated and sulfidated polyacrylonitrile coating layer possesses excellent lithium-ion / electron transport capabilities and toughness. While providing lithium-ion / electron transport channels for the carbon-coated porous silicon core, it further restricts the volume expansion of the porous silicon core during charging. Furthermore, the carbon coating layer and the lithiated and sulfidated polyacrylonitrile coating layer can synergistically prevent the porous silicon core from contacting the electrolyte, thereby avoiding continuous lithium-ion consumption and improving coulombic efficiency. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0019] Figure 1 is a schematic diagram of a double-coated modified silicon-based anode material according to an embodiment of this application;

[0020] Figure 2 is a schematic diagram of the preparation process of an optional double-coated modified silicon-based anode material according to an embodiment of this application;

[0021] Figure 3 is an example diagram illustrating the preparation steps of an optional double-coated modified silicon-based anode material according to Embodiment 1 of this application.

[0022] The above figures include the following reference numerals:

[0023] 1. Porous silicon; 2. Carbon coating; 3. Lithium-cured polyacrylonitrile coating. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0025] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0026] This embodiment provides a dual-coating modified silicon-based anode material, as shown in Figure 1. The dual-coating modified silicon-based anode material includes a porous silicon core 1, a carbon coating layer 2, and a lithium-sulfurized polyacrylonitrile coating layer 3. The carbon coating layer 2 fills the pores of the porous silicon core and coats the outer surface of the porous silicon core, while the lithium-sulfurized polyacrylonitrile coating layer 3 coats the surface of the carbon coating layer 2.

[0027] The porous silicon core 1 serves as the main active material, providing the primary capacity for the anode material. The carbon coating layer 2 completely fills the pores of the porous silicon core and coats its inner and outer surfaces, providing uniform and rapid lithium-ion / electron transport channels, thereby promoting uniform lithiation and expansion of the porous silicon core during charging. Simultaneously, the carbon coating layer buffers the volume expansion / contraction of the porous silicon core during charge-discharge cycles, reducing the risk of material structural damage. The lithiated and sulfidated polyacrylonitrile coating layer 3 possesses excellent lithium-ion / electron transport capabilities and toughness, further limiting the volume expansion of the porous silicon core during charging. Furthermore, the carbon coating layer 2 and the lithiated and sulfidated polyacrylonitrile coating layer 3 synergistically prevent the porous silicon core 1 from contacting the electrolyte, thus avoiding continuous lithium-ion consumption and improving coulombic efficiency.

[0028] In several embodiments, the mass ratio of the porous silicon core to the carbon coating layer is 1:1 to 4:1; and / or, the total mass ratio of the porous silicon core and the carbon coating layer to the mass ratio of the polyacrylonitrile in the lithium-cured polyacrylonitrile coating layer is 5:1 to 20:1.

[0029] Preferably setting the mass ratio of the two components within the aforementioned range can better promote the synergistic effect among the porous silicon core, the carbon coating layer, and the lithium-sulfurized polyacrylonitrile coating layer, thereby maximizing the balance between the specific capacity and cycle stability of the dual-coating modified silicon-based anode material.

[0030] It should be noted that the above scope is only the preferred scope provided by the present invention and does not constitute a limitation on all embodiments of the present invention.

[0031] In several embodiments, the mass ratio of polyacrylonitrile to sulfur in the lithium-cured polyacrylonitrile coating layer is 3:1 to 5:1; and / or, the porous silicon core is a primary spherical particle with a median particle size of 0.2 μm to 5 μm; and / or, the porosity of the porous silicon core is 40% to 60%; and / or, the pores of the porous silicon core are open pores with a pore size of 20 nm to 500 nm; and / or, the volume of open pores with a pore size of 50 nm to 250 nm in the porous silicon core accounts for 50% to 80% of the total open pore volume.

[0032] In the preferred lithium-cured polyacrylonitrile coating layer, the mass ratio of polyacrylonitrile to sulfur is within the above range, which helps to promote the appropriate amount of Li. x The formation of sulfur (S) enables the lithium-cured polyacrylonitrile coating to possess both excellent lithium-ion and electron transport capabilities.

[0033] The term "spherical particles" refers to the morphological characteristics of porous silicon cores, where particles are formed in a single process, exhibiting a regular spherical structure. This morphological characteristic facilitates uniform material distribution, improving the stability and consistency of lithium-ion battery anode materials during electrochemical cycling. A median particle size of 0.2 μm to 5 μm for the porous silicon cores indicates that the particle size of the double-coated modified silicon-based anode material is moderate, providing sufficient surface area to promote lithium-ion insertion and extraction while avoiding the problems of excessive specific surface area and excessive side reactions during initial lithiation caused by excessively fine particles.

[0034] The porosity of the porous silicon core, limited to the above range, provides a buffer against the volume expansion of silicon during lithiation, effectively reducing the risk of particle breakage and electrode structure damage, and improving the cycle performance of the material. Simultaneously, the openness of the pores further enhances the mechanical stability of the porous silicon core. The open pore volume with a diameter of 50nm~250nm accounts for 50%~80% of the total open pore volume in the porous silicon core, ensuring that most pores have optimal size, which is beneficial to improving the mechanical stability of the anode material. In summary, the precise control of the median particle size, porosity, and pore size collectively promotes the mechanical stability of the anode material, thereby extending the cycle life of lithium-ion batteries.

[0035] It should be noted that the above scope is only the preferred scope provided by the present invention and does not constitute a limitation on all embodiments of the present invention.

[0036] According to an embodiment of this application, a method for preparing a double-coated modified silicon-based anode material is provided, as shown in Figures 2 and 3. The preparation method includes: Step S1, in an inert atmosphere, a carbon source is deposited on porous silicon by chemical vapor deposition to obtain a precursor; Step S2, raw materials including polyacrylonitrile, elemental sulfur, the precursor, and a first organic solvent are mixed to obtain a mixed slurry; Step S3, the mixed slurry is sequentially spray-dried and calcined to obtain an intermediate; Step S4, raw materials including lithium metal, an aromatic hydrocarbon compound, and a second organic solvent are mixed to obtain an aromatic hydrocarbon compound-lithium solution; Step S5, the intermediate is added to the aromatic hydrocarbon compound-lithium solution for a lithiation reaction, followed by filtration, washing with the second organic solvent, and vacuum drying to obtain a double-coated modified silicon-based anode material; wherein, the precursor includes porous silicon and a carbon coating layer, the carbon coating layer fills the pores of the porous silicon and coats the outer surface of the porous silicon; the aromatic hydrocarbon compound is C 6~ C 12 Aromatic hydrocarbons.

[0037] In the double-coated silicon-based anode material provided by this invention, the carbon deposits filling the pores of the porous silicon core can buffer the volume expansion / contraction of the porous silicon core during charge-discharge cycles, thereby effectively mitigating the electrode structure damage caused by volume changes in the anode material. The carbon coating layer can provide uniform and rapid lithium-ion / electron transport channels for the inner and outer surfaces of the porous silicon core, thereby promoting uniform lithiation and expansion of the porous silicon core during charge-discharge cycles. During sulfidation, polyacrylonitrile (PAI) incorporates short-chain sulfur molecules onto the carbon skeleton and undergoes cyclization. After cyclization, PAI undergoes lithiation in an aromatic hydrocarbon-lithium solution. After lithiation, the short-chain sulfur molecules of the sulfided PAI are converted into Li. x The S-coating allows the lithium-sulfurized polyacrylonitrile coating to possess excellent lithium-ion / electron transport capabilities, providing a lithium-ion / electron transport channel for the precursor (carbon@porous silicon). The cyclized polyacrylonitrile exhibits good toughness, limiting the volume expansion of the porous silicon core during charging and maintaining the integrity of the negative electrode particles. This results in excellent cycle stability for the negative electrode material. Simultaneously, the carbon coating and the lithium-sulfurized polyacrylonitrile coating synergistically prevent the porous silicon core from contacting the electrolyte, thus avoiding continuous lithium-ion consumption and improving the coulombic efficiency of the negative electrode material during cycling. Furthermore, the preparation method provided by this invention is simple to operate and easy to industrialize. The prepared negative electrode material exhibits low expansion rate, high coulombic efficiency, and excellent long-term cycle stability, demonstrating high application value and broad development prospects in the field of lithium-ion batteries.

[0038] In several embodiments, in step S1, the carbon source is selected from any one or more of methane, ethane, and propane; and / or, the temperature of chemical vapor deposition is 500°C to 900°C, and the time of chemical vapor deposition is 4h to 12h; and / or, the inert atmosphere is selected from any one or more of helium, nitrogen, and argon.

[0039] Step S1 involves placing porous silicon in a chemical vapor deposition (CVD) apparatus. In an inert atmosphere, carbon source gas is deposited in the pores of the porous silicon core and on its outer surface using CVD technology, forming a carbon coating layer. Cooling then yields the precursor. The CVD method and the preferred deposition conditions described above help promote uniform carbon source coverage of the pores and outer surface of the porous silicon, thus providing a continuous and efficient channel for lithium-ion transport. The cooling process improves the stability of the carbon coating layer, reducing the risk of structural changes due to thermal stress. The preferred carbon source facilitates its decomposition at high temperatures, releasing carbon atoms.

[0040] In several embodiments, in step S2, the first organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; and / or, the mass ratio of the precursor to polyacrylonitrile in the mixed slurry is 5:1 to 20:1; and / or, the mass ratio of polyacrylonitrile to elemental sulfur in the mixed slurry is 3:1 to 5:1; and / or, the solid content of the mixed slurry is 35% to 75%.

[0041] The preferred first organic solvent helps promote the dispersion of polyacrylonitrile, elemental sulfur, and the precursor, resulting in a homogeneous slurry. Furthermore, it rapidly evaporates without leaving residue during subsequent spray drying and calcination, ensuring the purity of the material. The mass ratio of precursor to polyacrylonitrile in the slurry is limited to 5:1 to 20:1, reflecting a balance between material homogeneity and reaction efficiency. The mass ratio of polyacrylonitrile to elemental sulfur in the slurry is set to 3:1 to 5:1. Elemental sulfur is a crucial component of the vulcanized polyacrylonitrile coating layer, and its proportion in the slurry directly determines the sulfur content and degree of vulcanization in the final material. Vulcanized polyacrylonitrile can form a structure that is both stable and possesses highly efficient lithium-ion transport capabilities. Excessively high or low sulfur concentrations will affect the electrochemical performance of the material, including ion transport efficiency and cycle stability. The solid content in the mixed slurry is 35%~75%, ensuring that the precursor can be uniformly dispersed in the organic solvent and fully contacted with polyacrylonitrile and elemental sulfur, thereby forming a uniform and dense lithium-sulfurized polyacrylonitrile coating layer during spray drying and calcination. The proportion of the precursor directly affects the structure and performance of the final anode material. Too high a solvent ratio may result in a thin slurry, affecting the granulation effect, while too low a ratio will make the slurry too viscous and difficult to mix evenly.

[0042] In several embodiments, in step S3, the inlet air temperature for spray drying is 120°C to 200°C, and the feed rate is 2L / h to 6L / h; and / or, the calcination temperature is 250°C to 350°C, and the calcination time is 4h to 8h.

[0043] A nitrogen-based closed-loop spray dryer is preferred for spray drying the mixed slurry, which helps reduce the risk of oxidation and other adverse reactions. The inlet air temperature is a crucial control variable in the spray drying process, referring to the temperature of the drying air entering the drying tower. In this embodiment, it is limited to between 120°C and 200°C. This temperature range effectively balances the drying rate and changes in material properties, ensuring rapid evaporation of organic solvents in the mixed slurry while avoiding structural deformation or performance degradation due to overheating. At lower temperatures, the drying rate may be slow, leading to solvent residue and affecting the electrochemical performance of the material; while at higher temperatures, thermal decomposition of certain sensitive components in the mixed slurry may occur, similarly impairing material performance. The feed rate refers to the amount of slurry entering the spray drying tower per unit time. In this embodiment, it is controlled within the range of 2L / h to 6L / h. An appropriate feed rate is also crucial for the drying effect. Too high a rate may result in incompletely dried slurry droplets being discharged, leading to excessive residual solvent; too slow a rate may increase the time the material is exposed to high temperatures due to prolonged drying time, affecting its properties. The limitation on the feeding speed in this embodiment ensures uniform drying of the slurry, resulting in an ideal particle morphology and creating favorable conditions for subsequent low-temperature calcination.

[0044] The purpose of calcination is twofold: firstly, to further promote the chemical reaction between polyacrylonitrile and elemental sulfur, forming a lithium-cured polyacrylonitrile coating layer; and secondly, to solidify the material structure and eliminate any potentially residual volatile substances. Preferred calcination temperatures and times are beneficial for forming a structurally stable and high-performance lithium-cured polyacrylonitrile coating layer.

[0045] In several embodiments, in step S4, the aromatic hydrocarbon compound is selected from any one or more of biphenyl, 4,4'-dimethylbiphenyl, 2,3'-dimethylbiphenyl, and 4,4'-dimethoxybiphenyl; and / or, the second organic solvent is selected from any one or more of anhydrous tetrahydrofuran, N-methylpyrrolidone, and dioxane; and / or, the mass concentration of metallic lithium in the aromatic hydrocarbon compound-lithium solution is 5 g / L to 20 g / L; and / or, the concentration of aromatic hydrocarbon compound in the aromatic hydrocarbon compound-lithium solution is 50 g / L to 300 g / L; and / or, step S5 includes: stirring and mixing the intermediate with the aromatic hydrocarbon compound-lithium solution for a certain period of time, followed by filtration, washing, and vacuum drying to obtain a double-coated modified silicon-based anode material; wherein, the stirring and mixing temperature is 60℃ to 100℃, and the stirring and mixing time is 4 h to 12 h; the vacuum drying temperature is 60℃ to 100℃, and the vacuum drying time is 6 h to 12 h.

[0046] The preferred second organic solvent helps promote the dispersion of aromatic hydrocarbons and lithium therein. The aromatic hydrocarbon-lithium solution is highly reactive, with the concentration of metallic lithium limited to 5 g / L to 20 g / L. This characteristic ensures that the lithium ion concentration in the solution is maintained within a suitable range that promotes the lithiation reaction without causing excessively vigorous reactions that could affect the material structure. The concentration of the aromatic hydrocarbons is set between 50 g / L and 300 g / L. The aromatic hydrocarbons in the solution act as a medium to promote the reaction between lithium and polyacrylonitrile, thereby achieving the sulfidation and lithiation of polyacrylonitrile. The concentration control has a direct impact on the reaction rate and material properties. Too high a concentration may lead to over-lithiation of the material surface, while too low a concentration may prevent sufficient reaction, resulting in an incomplete lithiation-sulfurized polyacrylonitrile coating. Therefore, this concentration range ensures optimal reaction conditions during the lithiation process, providing a foundation for forming a negative electrode material with excellent electrochemical performance. After adding the intermediate from step S3, stirring and mixing ensures sufficient contact and reaction between the two, forming a lithiation-sulfurized polyacrylonitrile coating. Optimal filtration, washing, and vacuum drying conditions within the above ranges help to remove excess aromatic hydrocarbon compounds and lithium solution residues more efficiently, thereby further purifying and stabilizing the material structure.

[0047] This embodiment provides a negative electrode, including a negative electrode material, which is the aforementioned double-coated modified silicon-based negative electrode material or prepared by the aforementioned preparation method.

[0048] The anode material, including the double-coated modified silicon-based anode material, has both excellent capacity retention and coulombic efficiency.

[0049] This embodiment provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator, wherein the negative electrode is the aforementioned negative electrode.

[0050] Lithium-ion batteries with the aforementioned negative electrode have higher electrical performance and longer lifespan.

[0051] In some optional embodiments of the present invention, exemplary implementations are as follows:

[0052] Example 1

[0053] Step S1: Porous silicon (median particle size 5μm, porosity 60%, pore size 50nm~250nm open pore ratio 80%) is placed in a chemical vapor deposition apparatus, and methane gas is decomposed and deposited on the inner and outer surfaces of the porous silicon for 6 hours at 900℃ in a helium atmosphere to form a carbon coating layer. Then it is cooled to room temperature in a helium atmosphere to obtain carbon@porous silicon precursor.

[0054] Step S2: Add 10g of polyacrylonitrile to 37.5g of N,N-dimethylformamide. After the polyacrylonitrile dissolves, add 2.5g of elemental sulfur to N,N-dimethylformamide and mix evenly. Then add 100g of the carbon@porous silica precursor obtained in step S1 to N,N-dimethylformamide and mix evenly to obtain a mixed slurry.

[0055] Step S3: The mixed slurry obtained in step S2 is spray-dried using a nitrogen-type closed-loop spray dryer at an inlet air temperature of 120℃ and a feed rate of 6L / h. The resulting material is then calcined at 250℃ in a helium atmosphere for 4 hours. After calcination, it is cooled to room temperature in a helium atmosphere to obtain a vulcanized polyacrylonitrile@carbon@porous silicon intermediate.

[0056] Step S4: Add 1g of lithium metal and 30g of biphenyl to 100mL of anhydrous tetrahydrofuran solution. After the lithium metal and biphenyl are completely dissolved, a biphenyl-lithium solution is obtained.

[0057] Step S5: Subsequently, 5g of the sulfurized polyacrylonitrile@carbon@porous silicon intermediate obtained in step S3 is added to the biphenyl-lithium solution, mixed evenly, and stirred at 60°C for 12h. Then, it is filtered, washed with anhydrous tetrahydrofuran, and vacuum dried at 60°C for 12h to obtain lithium-ionized sulfurized polyacrylonitrile@carbon@porous silicon, which is a double-coated modified silicon-based anode material.

[0058] Example 2

[0059] Step S1: Porous silicon (median particle size 0.2 μm, porosity 40%, pore size 50 nm ~ 250 nm open pore ratio 60%) is placed in a chemical vapor deposition apparatus, and ethane gas is decomposed and deposited on the inner and outer surfaces of the porous silicon at 700 °C and in a nitrogen atmosphere for 4 h to form a carbon coating layer. Then it is cooled to room temperature in a nitrogen atmosphere to obtain carbon@porous silicon precursor.

[0060] Step S2: Add 5g of polyacrylonitrile to 57.6g of N,N-dimethylacetamide. After the polyacrylonitrile dissolves, add 1g of elemental sulfur to N,N-dimethylacetamide and mix evenly. Then add 25g of the carbon@porous silicon precursor obtained in step S1 to N,N-dimethylacetamide and mix evenly to obtain a mixed slurry.

[0061] Step S3: The mixed slurry obtained in step S2 is spray-dried and granulated using a nitrogen-type closed-loop spray dryer at an inlet air temperature of 200℃ and a feed rate of 2L / h. The resulting material is then calcined at 300℃ in a nitrogen atmosphere for 6 hours. After calcination, it is cooled to room temperature in a nitrogen atmosphere to obtain a vulcanized polyacrylonitrile@carbon@porous silicon intermediate.

[0062] Step S4: Add 0.5g of lithium metal and 5g of 4,4'-dimethylbiphenyl to 100mL of N-methylpyrrolidone solution. After the lithium metal and biphenyl are completely dissolved, a biphenyl-lithium solution is obtained.

[0063] Step S5: Then, 5g of the sulfurized polyacrylonitrile@carbon@porous silicon intermediate obtained in step S3 is added to the biphenyl-lithium solution, mixed evenly, and stirred at 100°C for 4h. After filtration and washing with anhydrous tetrahydrofuran, the double-coated modified silicon-based anode material is obtained after vacuum drying at 100°C for 6h.

[0064] Example 3

[0065] Step S1: Porous silicon (median particle size 2 μm, porosity 50%, pore size 50 nm ~ 250 nm open pore ratio 50%) is placed in a chemical vapor deposition apparatus, and propane gas is decomposed and deposited on the inner and outer surfaces of the porous silicon for 12 h at 500 °C in an argon atmosphere to form a carbon coating layer. Then, it is cooled to room temperature in an argon atmosphere to obtain a carbon@porous silicon precursor.

[0066] Step S2: Add 10g of polyacrylonitrile to 62g of N-methylpyrrolidone. After the polyacrylonitrile dissolves, add 3g of elemental sulfur to N-methylpyrrolidone and mix evenly. Then add 80g of the carbon@porous silicon precursor obtained in step S1 to N-methylpyrrolidone and mix evenly to obtain a mixed slurry.

[0067] Step S3: The mixed slurry obtained in step S2 is spray-dried and granulated using a nitrogen-type closed-loop spray dryer at an inlet air temperature of 150℃ and a feed rate of 3L / h. The resulting material is then calcined at 350℃ in an argon atmosphere for 6 hours. After calcination, it is cooled to room temperature in an argon atmosphere to obtain a vulcanized polyacrylonitrile@carbon@porous silicon intermediate.

[0068] Step S4: Add 0.8g of lithium metal and 20g of 2,3'-dimethylbiphenyl to 100mL of dioxane. After the lithium metal and biphenyl are completely dissolved, a biphenyl-lithium solution is obtained.

[0069] Step S5: Then, 5g of the sulfurized polyacrylonitrile@carbon@porous silicon intermediate obtained in step S3 is added to the biphenyl-lithium solution, mixed evenly, and stirred at 80°C for 8h. After filtration and washing with anhydrous tetrahydrofuran, the double-coated modified silicon-based anode material is obtained after vacuum drying at 80°C for 8h.

[0070] Example 4

[0071] Step S1: Porous silicon (median particle size 3.5 μm, porosity 55%, pore size 50 nm ~ 250 nm open pore ratio 60%) is placed in a chemical vapor deposition apparatus, and ethane gas is decomposed and deposited on the inner and outer surfaces of the porous silicon for 5 h at 800 °C and in an argon atmosphere to form a carbon coating layer. Then it is cooled to room temperature in an argon atmosphere to obtain a carbon@porous silicon precursor.

[0072] Step S2: Add 15g of polyacrylonitrile to 320g of N,N-dimethylformamide. After the polyacrylonitrile dissolves, add 5g of elemental sulfur to N,N-dimethylformamide and mix evenly. Then add 300g of carbon@porous silica precursor obtained in step S1 to N,N-dimethylformamide and mix evenly to obtain a mixed slurry.

[0073] Step S3: The mixed slurry obtained in step S2 is spray-dried and granulated using a nitrogen-type closed-loop spray dryer at an inlet air temperature of 180℃ and a feed rate of 4L / h. The resulting material is then calcined at 300℃ in an argon atmosphere for 8 hours. After calcination, it is cooled to room temperature in an argon atmosphere to obtain a vulcanized polyacrylonitrile@carbon@porous silicon intermediate.

[0074] Step S4: Add 2g of lithium metal and 25g of 4,4'-dimethoxybiphenyl to 100mL of anhydrous tetrahydrofuran solution. After the lithium metal and biphenyl are completely dissolved, a biphenyl-lithium solution is obtained.

[0075] In step S5, 5g of the sulfurized polyacrylonitrile@carbon@porous silicon intermediate obtained in step S3 is added to the biphenyl-lithium solution, mixed evenly, and stirred at 150°C for 6 hours. Then, it is filtered, washed with anhydrous tetrahydrofuran, and vacuum dried at 100°C for 12 hours to obtain the double-coated modified silicon-based anode material.

[0076] Comparative Example 1

[0077] The only difference from Example 2 is that step S1, which constructs the carbon coating layer, was not performed.

[0078] Comparative Example 2

[0079] The only difference from Example 2 is that step S4, which involves lithium treatment of the vulcanized polyacrylonitrile coating, was not performed.

[0080] Comparative Example 3

[0081] The only difference from Example 2 is that steps S2, S3, S4 and S5 are not performed, and a carbon coating layer is only constructed on the porous silicon surface.

[0082] Comparative Example 4

[0083] The only difference from Example 2 is that steps S1, S2, S3, S4 and S5 are not performed, and only porous silicon material is used as the negative electrode material.

[0084] Performance testing:

[0085] The ratio of the mass of the porous silicon core to the mass of the carbon coating layer: Using the porous silicon core as a control, thermogravimetric analysis was performed on the precursor, and the ratio of the mass of the porous silicon core to the mass of the carbon coating layer was analyzed based on the thermogravimetric analysis results.

[0086] The test results are listed in Table 1.

[0087] The silicon-based anode materials of the examples and comparative examples were assembled into coin half-cells and their electrochemical performance was tested using the LAND BT battery testing system. The test results are shown in Table 2. The specific test scheme is as follows:

[0088] Button half-cell assembly:

[0089] 1. Weigh out silicon-based anode material and carbon black at a mass ratio of 80:10 and mix them evenly. Add an appropriate amount of the mixture to a pre-prepared binder solution. The solvent of the binder solution is deionized water, and the binder is polyacrylic acid. The mass ratio of polyacrylic acid in the binder solution to the mass of the mixture is 1:9. Stir with a magnetic stirrer for 12 hours to form a uniform slurry.

[0090] 2. The well-stirred slurry was poured onto the surface of a copper foil with a thickness of 9 μm, coated with an automatic coating machine, and the coating thickness was set to 110 μm. Then, it was vacuum dried at 80℃ for 6 hours to obtain the negative electrode sheet.

[0091] 3. The dried negative electrode sheet was rolled to a thickness of 100μm using an electric roller mill, and then punched into a disc with a diameter of 8mm using a punching machine. After vacuum drying at 80℃ for 12h, the negative electrode disc was weighed and the mass of active material was calculated.

[0092] 4. Using elemental lithium foil as the counter electrode, Celgard 2250 membrane as the battery separator, and 1.0M LiPF6 EC / DEC solution with a volume ratio of 1:1 (with 5wt.% FEC added) as the electrolyte, CR2032 button half-cells were assembled for electrochemical performance testing.

[0093] Electrochemical performance testing:

[0094] 1. Initial specific capacity: After assembling the button half-cell, let it stand for 2 hours, then discharge it to 0.005V with a constant current of 0.05C, and then discharge it to 0.005V with a constant current of 0.01C; after standing for 5 minutes, charge it to 1.5V with a constant current of 0.05C. The charging specific capacity obtained is the initial specific capacity of the negative electrode material.

[0095] 2. Initial Coulomb Efficiency: After assembling the button half-cell, an initial specific capacity test is performed. The ratio of the charging specific capacity to the discharging specific capacity of the negative electrode material is its initial coulomb efficiency.

[0096] 3. Initial Full-Charge Expansion Rate: After assembling the button cell, let it stand for 2 hours, then discharge it at a constant current of 0.05C to 0.005V, and then discharge it at a constant current of 0.01C to 0.005V. Disassemble the button cell in a glove box and measure the electrode thickness. The electrode expansion rate is calculated as follows: Electrode Expansion Rate = (Electrode Thickness After Cycles - Original Electrode Thickness) / Original Electrode Thickness × 100%.

[0097] 4. Cycle performance: After assembling the button half-cell, let it stand for 2 hours, then discharge it to 0.005V with a constant current of 0.05C, then discharge it to 0.005V with a constant current of 0.01C, let it stand for 5 minutes, then charge it to 1.5V with a constant current of 0.05C; after standing for 5 minutes, repeat the above steps 3 times to activate the button half-cell; then discharge it to 0.005V with a constant current of 0.5C, then charge it to 1.5V with a constant current of 0.5C; repeat the above steps until the set value (capacity retention rate of 80%) is reached.

[0098] Table 1

[0099]

[0100] Table 2

[0101]

[0102] The test results of the silicon anode materials prepared in each embodiment and comparative example are shown in Table 1. The difference between Examples 1, 2, 3, and 4 lies in the pore structure of the porous silicon core and the construction conditions of the carbon coating layer and the lithium-sulfurized polyacrylonitrile coating layer. The data of Examples 1, 2, 3, and 4 show that optimizing the pore structure of the porous silicon core and the construction conditions of the carbon coating layer and the lithium-sulfurized polyacrylonitrile coating layer can yield the anode material with the best performance. Comparing the data of Comparative Examples 1, 2, 3, and 4 with the data of Example 2, it can be seen that the construction of both the carbon coating layer and the lithium-sulfurized polyacrylonitrile coating layer is beneficial to improving the initial coulombic efficiency, reducing the initial full-charge expansion rate, and increasing the cycle life of the porous silicon-based anode material. The anode material provided in this application has low expansion rate, high coulombic efficiency, and excellent long-term cycle stability.

[0103] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0104] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A double-coated modified silicon-based anode material, characterized in that, The dual-coating modified silicon-based anode material includes a porous silicon core, a carbon coating layer, and a lithium-ionized sulfurized polyacrylonitrile coating layer. The carbon coating layer fills the pores of the porous silicon core and coats the outer surface of the porous silicon core, while the lithium-ionized sulfurized polyacrylonitrile coating layer coats the surface of the carbon coating layer.

2. The double-coated modified silicon-based anode material according to claim 1, characterized in that, The mass ratio of the porous silicon core to the carbon coating layer is 1:1 to 4:1; and / or, the total mass ratio of the porous silicon core and the carbon coating layer to the mass ratio of the polyacrylonitrile in the lithium-cured polyacrylonitrile coating layer is 5:1 to 20:

1.

3. The double-coated modified silicon-based anode material according to claim 1 or 2, characterized in that, The mass ratio of polyacrylonitrile to sulfur in the lithium-cured polyacrylonitrile coating layer is 3:1 to 5:1; and / or, the porous silicon core is a primary spherical particle with a median particle size of 0.2 μm to 5 μm; and / or, the porosity of the porous silicon core is 40% to 60%; and / or, the pores of the porous silicon core are open pores with a pore size of 20 nm to 500 nm; and / or, the volume of open pores with a pore size of 50 nm to 250 nm in the porous silicon core accounts for 50% to 80% of the total open pore volume.

4. A method for preparing the double-coated modified silicon-based anode material according to any one of claims 1 to 3, characterized in that, The preparation method includes: Step S1, in an inert atmosphere, a carbon source is deposited on porous silicon by chemical vapor deposition to obtain a precursor; Step S2, raw materials including polyacrylonitrile, elemental sulfur, the precursor, and a first organic solvent are mixed to obtain a mixed slurry; Step S3, the mixed slurry is sequentially spray-dried and calcined to obtain an intermediate; Step S4, raw materials including metallic lithium, aromatic hydrocarbons, and a second organic solvent are mixed to obtain an aromatic hydrocarbon-lithium solution; Step S5, the intermediate is added to the aromatic hydrocarbon-lithium solution for a lithiation reaction, followed by filtration, washing with the second organic solvent, and vacuum drying to obtain the double-coated modified silicon-based anode material; wherein, the precursor includes porous silicon and a carbon coating layer, the carbon coating layer fills the pores of the porous silicon and coats the outer surface of the porous silicon; the aromatic hydrocarbon is C 6~ C 12 Aromatic hydrocarbons.

5. The preparation method according to claim 4, characterized in that, In step S1, the carbon source is selected from any one or more of methane, ethane, and propane; and / or, the temperature of the chemical vapor deposition is 500℃~900℃; and / or, the time of the chemical vapor deposition is 4h~12h; and / or, the inert atmosphere is selected from any one or more of helium, nitrogen, and argon.

6. The preparation method according to claim 4, characterized in that, In step S2, the first organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; and / or, the mass ratio of the precursor to the polyacrylonitrile in the mixed slurry is 5:1 to 20:1; and / or, the mass ratio of the polyacrylonitrile to elemental sulfur in the mixed slurry is 3:1 to 5:1; and / or, the solid content of the mixed slurry is 35% to 75%.

7. The preparation method according to claim 4, characterized in that, In step S3, the inlet air temperature of the spray drying is 120℃~200℃, and the feeding rate is 2L / h~6L / h; and / or, the calcination temperature is 250℃~350℃, and the calcination time is 4h~8h.

8. The preparation method according to claim 4, characterized in that, In step S4, the aromatic hydrocarbon compound is selected from any one or more of biphenyl, 4,4'-dimethylbiphenyl, 2,3'-dimethylbiphenyl, and 4,4'-dimethoxybiphenyl; and / or, the second organic solvent is selected from any one or more of anhydrous tetrahydrofuran, N-methylpyrrolidone, and dioxane; and / or, the mass concentration of lithium metal in the aromatic hydrocarbon compound-lithium solution is 5 g / L to 20 g / L; and / or, the concentration of the aromatic hydrocarbon compound in the aromatic hydrocarbon compound-lithium solution is 50 g / L to 300 g / L. And / or, step S5 includes: stirring and mixing the intermediate with the aromatic hydrocarbon compound-lithium solution for a certain period of time, followed by filtration, washing, and vacuum drying to obtain the double-coated modified silicon-based anode material; wherein the stirring and mixing temperature is 60℃~100℃, and the stirring and mixing time is 4h~12h; the vacuum drying temperature is 60℃~100℃, and the vacuum drying time is 6h~12h.

9. A negative electrode, comprising a negative electrode material, characterized in that, The negative electrode material is the double-coated modified silicon-based negative electrode material according to any one of claims 1 to 3 or prepared by the preparation method according to any one of claims 4 to 8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The negative electrode is the negative electrode as described in claim 9.

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