Modified porous silicon negative electrode material, preparation method and application thereof
By forming a three-dimensional conformal coating of crystalline Li2SiF6 and amorphous Li3AlF6 on the surface of porous silicon anode material, the volume expansion problem of silicon anode material during lithium insertion/extraction process is solved, and the cycle stability and rate performance of the battery are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2026-03-10
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, silicon anode materials suffer from structural collapse and repeated SEI film rupture due to volume expansion during lithium insertion/extraction, which consumes active lithium and electrolyte, increases interfacial impedance, and has poor conductivity, making it difficult to improve the cycle life and rate performance of the battery.
A three-dimensional conformal coating of porous silicon substrate is formed by using crystalline Li2SiF6 and amorphous Li3AlF6 to form a crystalline-amorphous composite structure. A stable fluoride coating layer is formed on the surface of porous silicon through in-situ chemical reaction, which provides lithium-ion diffusion channels and interfacial inertness, and enhances toughness and ion conduction performance.
It significantly improves the electrochemical performance of lithium-ion batteries, optimizes the stability and rate performance of the electrode/electrolyte interface, and enhances the cycle performance and electrochemical performance of porous silicon anode materials.
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Figure CN122117864A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of secondary battery materials technology, specifically relating to modified porous silicon anode materials, their preparation methods, and applications. Background Technology
[0002] As the global energy structure accelerates its transition to a low-carbon model, the development of efficient and sustainable energy storage technologies is of strategic significance. Lithium-ion batteries, currently the most widely used electrochemical energy storage device, have seen their energy density and cycle life improvements become a focus of social attention. Silicon anodes, due to their theoretical specific capacity far exceeding that of traditional graphite anodes, high crustal abundance, and suitable lithium intercalation potential, are considered one of the key materials for next-generation high-performance lithium-ion batteries.
[0003] However, the dramatic volume expansion (>300%) of silicon during lithium insertion / extraction not only causes particle breakage and electrode structure collapse, but also leads to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film. This process continuously consumes active lithium and electrolyte, and significantly increases interfacial impedance, ultimately causing rapid capacity decay. Furthermore, silicon's inherently poor conductivity further limits its rate performance.
[0004] Nanostructuring is a common strategy to improve the volume effect of silicon anode materials, such as using nanoparticles, nanowires, porous structures, or composite materials. However, while nanostructures improve structural stability, their large specific surface area can also exacerbate interfacial side reactions, making it difficult to effectively suppress negative effects during cycling. Interface modification has been proven to effectively alleviate these problems and improve the lithium storage performance of silicon anodes. Existing technologies have reported the use of fluoride-coated silicon-based materials; for example, patent application CN117476913A uses ordinary nano-silicon as a substrate to prepare a Li2SiF6 coating layer. However, such methods typically use commercial silicon powder with a single surface composition, and the coating layer structure has limited impact on improving interfacial kinetics and long-term cycling stability. Therefore, this invention provides a simple, low-cost, and high-yield crystalline-amorphous composite fluoride-coated porous silicon anode material, its preparation method, and its applications. Summary of the Invention
[0005] The present invention aims to solve the above-mentioned problems of the prior art, and its purpose is to provide modified porous silicon anode materials, their preparation methods and applications.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, a modified porous silicon anode material is provided, comprising a porous silicon substrate and a three-dimensional composite fluoride coating layer conformally coated on the surface of the porous silicon substrate, wherein the composite fluoride coating layer comprises crystalline Li2SiF6 and amorphous Li3AlF6.
[0007] In some preferred embodiments, the amorphous Li3AlF6 is dispersed within the crystalline Li2SiF6 phase, forming a crystalline-amorphous composite structure.
[0008] In some preferred embodiments, the mass percentage of crystalline Li2SiF6 is 1-20% based on the total mass of the modified porous silicon anode material.
[0009] In some preferred embodiments, the ratio of the molar amount of Al to the molar amount of Si in the composite fluoride coating is 1:10~25.
[0010] In some preferred embodiments, the composite fluoride coating is formed through an in-situ chemical reaction and chemically bonded to the surface of the porous silicon substrate.
[0011] Secondly, a method for preparing modified porous silicon anode materials is provided, including: Aluminum-silicon alloy powder was added to hydrochloric acid solution for etching, and then washed and dried to obtain a porous silicon substrate with residual aluminum on the surface. A porous silicon substrate was added to a lithium hydroxide solution and stirred to obtain a suspension. A mixed suspension and a fluoride solution were reacted, followed by solid-liquid separation and drying to obtain a modified porous silicon anode material.
[0012] Thirdly, a lithium-ion battery is provided, comprising the modified porous silicon anode material described in the first aspect or the modified porous silicon anode material prepared by the preparation method described in the second aspect.
[0013] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: This invention provides a modified porous silicon anode material. It employs a three-dimensional conformal coating of porous silicon crystals with crystalline Li₂SiF₆ and amorphous Li₃AlF₆. The porous structure provides space to accommodate the dramatic volume expansion of silicon. The surface crystalline Li₂SiF₆ serves as the structural framework of the coating layer, providing stable lithium-ion diffusion channels and interfacial chemical inertness. Amorphous Li₃AlF₆ is dispersed within the crystalline Li₂SiF₆, enhancing interfacial toughness (providing a flexible buffer) and optimizing stress distribution. The synergistic effect of these two materials establishes a physical-chemical barrier during cycling, improving electrode / electrolyte interface stability and optimizing electrode mechanical properties. Furthermore, the excellent ion conduction properties of both crystalline and amorphous Li₂SiF₆ contribute to the construction of a superior three-dimensional ion transport network, which is beneficial for improving the rate performance of the porous silicon anode material. This synergistic effect of structural design and interface engineering significantly enhances the electrochemical performance of the battery.
[0014] This invention obtains a porous silicon substrate with residual aluminum on the surface through acid etching, and then activates the porous silicon surface with LiOH solution. The surface oxides are then converted in situ into crystalline-amorphous composite fluorides through the combined action of Li and F elements in the solution, resulting in a porous silicon anode material coated with crystalline-amorphous composite fluorides. This preparation method can produce modified porous silicon anode materials with good structural stability, three-dimensional ion and electron transport capabilities, strong electrolyte wetting ability, and good surface stability, which is beneficial for improving the cycle performance, rate performance, and capacity of porous silicon anode materials.
[0015] The preparation method provided by this invention has a short process, low cost, and high yield, and can be promoted on a large scale. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 SEM images of the silicon-based anode materials prepared in Examples 1-3 and Comparative Example 1; Figure 2 The images show the XRD patterns of the silicon-based anode materials in Examples 1-3 and Comparative Example 2. Figure 3 The TG curves are for the silicon-based anode materials in Examples 1-3; Figure 4 XPS images of Example 2 after different Ar+ etching times; Figure 5 Example 2 in different Ar + The atomic molar percentage of each element obtained by XPS detection after etching time; Figure 6 The graphs show the cycle performance of silicon-based anode materials in Examples 1-3, Comparative Examples 1 and 3. Detailed Implementation
[0018] Some embodiments of the present invention provide a modified porous silicon anode material, comprising a porous silicon substrate and a three-dimensional composite fluoride coating layer conformally coated on the surface of the porous silicon substrate, wherein the composite fluoride coating layer comprises crystalline Li2SiF6 and amorphous Li3AlF6.
[0019] It is worth noting that the three-dimensional composite fluoride coating layer conformally covering the surface of the porous silicon substrate specifically refers to the contour of the coating layer conforming to the contour of the porous silicon substrate. That is, the composite fluoride coating layer covers the outer surface and the inner surface of the pores of the porous silicon substrate. Since the porous structure is a three-dimensional porous skeleton structure, the coating layer also has a three-dimensional structure.
[0020] By coating porous silicon crystals with crystalline Li₂SiF₆ and amorphous Li₃AlF₆, the porous structure provides space for the dramatic volume expansion of silicon. The surface crystalline Li₂SiF₆ serves as the framework of the three-dimensional coating structure, providing stable lithium-ion diffusion channels and interfacial chemical inertness. Amorphous Li₃AlF₆ is dispersed within the crystalline Li₂SiF₆, enhancing interfacial toughness (amorphous Li₃AlF₆ provides a flexible buffer for crystalline Li₂SiF₆) and optimizing stress distribution. Furthermore, since amorphous Li₃AlF₆ has a higher ionic conductivity than crystalline Li₂SiF₆, it further improves ion transport performance. The synergy between the two can establish a physical-chemical barrier during cycling, improve the stability of the electrode / electrolyte interface, optimize lithium-ion transport kinetics, and the excellent ion transport performance of both crystalline and amorphous Li₂SiF₆, combined with the construction of an excellent three-dimensional ion transport network, is beneficial for improving the rate performance of porous silicon anode materials.
[0021] In some preferred embodiments, the amorphous Li3AlF6 is dispersed in the crystalline Li2SiF6 phase, forming a crystalline-amorphous composite structure.
[0022] In some preferred embodiments, the porous silicon substrate is porous micron-sized spherical or near-spherical secondary particles; the porous micron-sized spherical or near-spherical secondary particles are formed by the interlacing and stacking of nanosheet-like or fibrous primary particles to form a continuous three-dimensional network framework; the spherical or near-spherical particles have macropores and / or mesopores inside, wherein the macropores are distributed in a honeycomb or cavity shape inside the microspheres, and the mesopores are formed between the nanosheet-like or fibrous primary particles, and the nanosheet-like or fibrous primary particles constitute the pore walls of the porous network. In this structure, the macropores (honeycomb / cavitary) and mesopores inside the microspheres provide ample free space. When the silicon volume expands, these pores can accommodate the expanded portion, thus significantly mitigating the overall macroscopic volume change of the particles, preventing electrode cracking, and maintaining structural integrity. The framework consists of nanosheet-like or fibrous primary particles. The nanoscale structure greatly shortens the diffusion path of lithium ions in the solid phase, improving the high-rate performance of the material. The three-dimensional network framework and hierarchical porosity allow the electrolyte to penetrate more easily into the particle interior, promoting electrolyte wetting and increasing the interface for electrochemical reactions, thereby increasing the utilization rate of silicon and improving the utilization rate of active materials. Furthermore, the three-dimensional framework not only provides mechanical support but also constructs a continuous conductive network, improving ionized electron conductivity and reducing internal resistance. Based on this structure, crystalline Li₂SiF₆ and amorphous Li₃AlF₆ constitute a three-dimensional ion conduction network, further improving ion conductivity and enhancing the rate performance of porous silicon composite materials.
[0023] In some preferred embodiments, based on the total mass of the modified porous silicon anode material, the mass percentage of the crystalline Li2SiF6 is 1-20%, for example 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., preferably 2-10%.
[0024] In some preferred embodiments, the ratio of the molar amount of Al to the molar amount of Si in the composite fluoride coating layer is 1:10 to 25, for example, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, etc.
[0025] In some preferred embodiments, the composite fluoride coating layer is formed through an in-situ chemical reaction and chemically bonded to the surface of the porous silicon substrate. The in-situ reaction and chemical bonding result in a strong interfacial bond and excellent peel resistance between the coating layer and the porous silicon substrate surface. Even under the severe volume expansion and contraction of silicon particles, the coating layer is not easily detached or peeled off, ensuring the durability and stability of substrate protection. Furthermore, due to the tight chemical bond, when the internal silicon particles expand, this strong bonding force effectively transfers stress to the flexible amorphous Li3AlF6. The coating layer can undergo a certain degree of elastic deformation with the expansion of the core, remaining tightly attached to the silicon surface, achieving an "adaptive" capability to volume contraction and expansion. Simultaneously, the chemical bonding creates a gradually changing transition layer between the coating layer and the silicon substrate, rather than a completely separate interface, reducing lattice mismatch and interface defects, lowering the interfacial resistance of lithium ions entering the silicon substrate from the coating layer, and eliminating the loss of active material caused by side reactions at the interface.
[0026] Some embodiments of the present invention provide a method for preparing modified porous silicon anode materials, comprising: Aluminum-silicon alloy powder was added to hydrochloric acid solution for etching, and then washed and dried to obtain a porous silicon substrate with residual aluminum on the surface. A porous silicon substrate is added to a lithium hydroxide solution and stirred to obtain a suspension; this process achieves the oxidation of silicon on the surface of the porous silicon substrate and further reaction between silicon / aluminum oxide and lithium hydroxide. A mixed suspension and a fluoride solution were reacted, followed by solid-liquid separation and drying to obtain a modified porous silicon anode material.
[0027] In some preferred embodiments, the concentration of the hydrochloric acid solution is 0.5~5M, for example 0.5M, 1M, 1.5M, 2M, 2.5M, 3M, 3.5M, 4M, 4.5M, 5M, etc., preferably 0.5~2.5M; the etching treatment time is 6~24h, for example 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc.; the etching treatment temperature is 10~60℃, for example 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, etc., preferably 20~40℃. The etching process using hydrochloric acid affects the morphology of porous silicon substrates. High acid concentrations and excessively rapid etching rates can generate large amounts of hydrogen, leading to the fragmentation of the spherical structure and releasing significant heat. This increases the oxidation of Si, consequently reducing the initial charge-discharge efficiency, capacity, and cycle stability of the porous silicon material. By controlling the etching conditions, the residual Al content in the porous silicon after etching can be controlled, thereby controlling the Al content in the subsequent coating layer, and ultimately controlling the composition of the coating layer. This allows for performance control of the modified porous silicon anode material.
[0028] In some preferred embodiments, the concentration of the lithium hydroxide solution is 0.01~0.05M, such as 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, etc.; the molar ratio of Li element in the lithium hydroxide solution to Si element in the porous silicon substrate is 1:5~25, such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, etc., preferably 1:8~1:24.
[0029] In some preferred embodiments, the solvent of the lithium hydroxide solution is a mixture of water and ethanol, preferably with a volume ratio of water to ethanol of 1:4 to 100, such as 1:4, 1:5, 1:8, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, etc.
[0030] In some preferred embodiments, the stirring time is 1 to 12 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc.; the stirring temperature is 20 to 60 degrees Celsius, for example, 20 degrees Celsius, 30 degrees Celsius, 40 degrees Celsius, 50 degrees Celsius, 60 degrees Celsius, etc.
[0031] In some preferred embodiments, the fluoride solution is one or a mixture of hydrofluoric acid solution and ammonium fluoride solution; the concentration of the fluoride solution is 0.3~3M, for example 0.3M, 0.5M, 0.8M, 1M, 1.2M, 1.5M, 1.8M, 2M, 2.2M, 2.5M, 2.8M, 3M, etc.
[0032] In some preferred embodiments, the molar ratio of Li element in the lithium hydroxide solution to F element in the fluoride solution is 1:30~130, for example 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, 1:105, 1:110, 1:115, 1:120, 1:125, 1:130, etc.
[0033] In some preferred embodiments, the reaction time is 6 to 24 hours, such as 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc.; the reaction temperature is 20 to 60 degrees Celsius, such as 20 degrees Celsius, 30 degrees Celsius, 40 degrees Celsius, 50 degrees Celsius, 60 degrees Celsius, etc.
[0034] In some preferred embodiments, the drying process is any one of vacuum drying, water bath drying, or freeze drying.
[0035] Some embodiments provide a lithium-ion battery, characterized in that it includes the aforementioned modified porous silicon anode material or includes a modified porous silicon anode material prepared by the aforementioned preparation method.
[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.
[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0039] The silicon alloy raw material used in the following embodiments of the present invention has a particle size of 0.5~20μm.
[0040] When testing the electrochemical performance of the following examples and comparative examples, the target materials were first assembled into coin cells as follows: Anode material, sodium alginate, and Super P were mixed in a mass ratio of 7:2:1, and then an appropriate ethanol-water mixture was added to prepare a uniform slurry. The slurry was then coated onto copper foil using a coating machine to a thickness of 100 μm. The electrode was dried in an 80 °C vacuum oven for 12 h to ensure complete solvent evaporation. The electrode was then cut into small circular pieces with a diameter of 12 mm to serve as the working electrode.
[0041] A 16mm diameter lithium metal sheet was used as the counter electrode, a 19mm diameter Celgard 2325 separator, and an organic solution of LiPF6 / EC+DEC (volume ratio 1:1) / FEC (mass fraction 10%) as the electrolyte. The battery assembly was completed in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). The positive electrode shell, electrode, separator, electrolyte, lithium sheet, gasket, spring, and negative electrode shell were placed in the following order from bottom to top. The assembled battery was then sealed using a button cell sealing machine.
[0042] During the battery cycle performance test, the first three cycles were activated at a current density of 200 mA / g, and then the battery was charged and discharged 300 times at a current density of 2000 mA / g, with a voltage range of 0.01V to 2V.
[0043] Example 1 A method for preparing a porous silicon anode material coated with a crystalline-amorphous composite fluoride includes the following steps: S1: Prepare 300 mL of 2 M hydrochloric acid solution.
[0044] S2: Add 5g of AlSi 12 Alloy powder was added to hydrochloric acid solution to obtain a uniform suspension. The suspension was stirred for 24 hours and then etched to remove metal elements from the material. After drying, porous silicon material was obtained.
[0045] S3: Mix 0.5 mmol of LiOH, 5 mL of deionized water and 45 mL of ethanol to obtain a uniform alkaline solution. Add 0.3 g of porous silica particles to 30 mL of ethanol and stir with ultrasound and mechanical stirring to obtain a uniform suspension. Add 2 mL of 50% hydrofluoric acid to 20 mL of ethanol and stir to obtain a fluoride solution.
[0046] S4: Add the above alkaline solution to the suspension and mechanically stir at room temperature for 4 hours to perform surface oxidation treatment, thereby obtaining a uniform suspension.
[0047] S5: Add a fluoride solution to the above suspension and continue stirring for 4 hours. After stirring, filter and freeze-dry to obtain a porous silicon anode material coated with a crystalline-amorphous composite fluoride.
[0048] Example 2 A method for preparing a porous silicon anode material coated with a crystalline-amorphous composite fluoride includes the following steps: Steps S1 and S2: Same as in Example 1; S3: Mix 1 mmol of LiOH, 5 mL of deionized water and 45 mL of ethanol to obtain a uniform alkaline solution. Add 0.3 g of porous silica particles to 30 mL of ethanol and stir with ultrasound and mechanical stirring to obtain a uniform suspension. Add 2 mL of 50% hydrofluoric acid to 20 mL of ethanol and stir to obtain a fluoride solution.
[0049] Steps S4 and S5: Same as in Example 1.
[0050] Example 3 A method for preparing a porous silicon anode material coated with a crystalline-amorphous composite fluoride includes the following steps: Steps S1 and S2: Same as in Example 1; S3: Mix 1.5 mmol of LiOH, 5 mL of deionized water and 45 mL of ethanol to obtain a uniform alkaline solution. Add 0.3 g of porous silica particles to 30 mL of ethanol and stir with ultrasound and mechanical stirring to obtain a uniform suspension. Add 2 mL of 50% hydrofluoric acid to 20 mL of ethanol and stir to obtain a fluoride solution.
[0051] Steps S4 and S5: Same as in Example 1.
[0052] Comparative Example 1 A method for preparing a porous silicon anode material includes the following steps: S1: Prepare 300 mL of 2 M hydrochloric acid solution.
[0053] S2: Add 5g of AlSi 12 Alloy powder was added to hydrochloric acid solution to obtain a uniform suspension. The suspension was stirred for 24 hours and then etched to remove metal elements from the material. After drying, porous silicon anode material was obtained.
[0054] Comparative Example 2 A method for preparing a porous silicon anode material coated with a composite fluoride includes the following steps: Steps S1-S5: Same as in Example 2; S6: Under an argon atmosphere, porous silicon anode material coated with crystalline-amorphous composite fluoride is heated at 350°C for 2 hours to obtain the sintered material.
[0055] Comparative Example 3 This comparative example provides commercial nano-silicon material that has not undergone any treatment.
[0056] Figure 1 The images show SEM images of the silicon anode materials prepared in Examples 1-3 and Comparative Example 1. In Comparative Example 1, the particles exhibit a spherical porous structure; the particles in Examples 1-3 further break down, transforming into a flower-like structure. That is, the silicon anode materials have spherical or near-spherical outlines. The microspheres have an interconnected hierarchical pore structure and an open porous network with both surface and internal morphology. The hierarchical pore structure includes both macropores and mesopores. The macropores are distributed in a honeycomb or cavity-like pattern inside the microspheres, while the mesopores are formed between nanosheets. The nanosheets cross-link to form a three-dimensional framework, constituting the pore walls of the porous network. The pore walls of the three-dimensional framework are sheet-like, and the surface of the microspheres exhibits flower-like protrusions or a honeycomb-like hollow morphology. The particle size of the microspheres is submicron, and the macropore diameter of the hierarchical pore structure is 50 nm to 500 nm. The macropores facilitate electrolyte wetting and reduce the material's specific surface area to an appropriate level, which helps reduce interfacial side reactions.
[0057] Figure 2 The XRD patterns of the silicon anode materials in Examples 1-3 and Comparative Example 2 show that the anode materials in each example all exhibit Li2SiF6 crystal diffraction peaks, confirming the formation of the Li2SiF6 phase. The intensity of the Li2SiF6 diffraction peaks in the silicon anode materials of Examples 1-3 gradually increases, indicating that different lithium salt addition amounts affect the content and crystallinity of Li2SiF6. In contrast, after sintering, the diffraction peaks of Li2SiF6 in the material of Comparative Example 2 completely disappeared, indicating that the phase had been completely decomposed into LiF. Furthermore, diffraction peaks of Li3AlF6 appeared in the XRD pattern of Comparative Example 2, indicating that crystalline Li3AlF6 formed on its surface. It is noteworthy that no Li3AlF6 diffraction peaks were observed in the material before sintering, suggesting that Li3AlF6 may have existed in an amorphous form in the initial material of Example 2 and underwent a crystallization transformation during the subsequent high-temperature sintering process.
[0058] Figure 3The TG curves of the silicon-based anode materials in Examples 1-3 are shown. The porous silicon anode materials prepared in Examples 1-3 were subjected to thermogravimetric analysis (TGA) under the following conditions: heating rate of 10℃ / min, temperature range of 30-800℃, and argon atmosphere. The mass losses of the porous silicon anode materials prepared in Examples 1, 2, and 3 during the TGA process were measured to be 1.96%, 3.53%, and 12.93%, respectively, corresponding to the loss of gaseous SiF4, a decomposition product of Li₂SiF₆. Calculations showed that the mass percentages of Li₂SiF₆ in Examples 1, 2, and 3 were 3.01%, 5.43%, and 19.87%, respectively.
[0059] Figure 4 Example 2 in different Ar + XPS graph after etching time, with Ar + As etching proceeds, the Al2O3 peak on the material surface gradually intensifies, while the SiO2 peak... x The peak gradually weakens, with high-valence Si being the most prominent. 4+ The low-valence state of Si continues to weaken until it disappears. + and Si 2+ The peaks continuously strengthen. Furthermore, in the F 1s spectrum, the Si-F peaks continuously weaken, while the Al-F peaks slightly strengthen. This result reveals the chemical structural evolution from the surface to the bulk phase in Example 2. The surface layer of Example 2 is composed of high-valence SiO₂. x (Si) 4+ The main components are crystalline Li₂SiF₆, and the absence of silicon oxide diffraction peaks in the XRD pattern indicates that SiO₂ is composed of... x It is an amorphous phase with low content; with increasing depth, the Al2O3 signal increases, and SiO... x Chemical state shifts to lower valence state (Si) + / Si 2+ The transformation occurs, and at the same time, fluorides gradually transition from being dominated by Li2SiF6 to amorphous Li3AlF6.
[0060] In combination with the above Figure 2 and Figure 4 Analysis shows that the porous silicon material is coated with crystalline Li2SiF6 and amorphous Li3AlF6. Since Al and Si are derived from the etched porous silicon, it can be concluded that the amorphous Li3AlF6 is dispersed in the crystalline Li2SiF6 phase, forming a crystalline-amorphous composite structure.
[0061] Figure 5 Example 2 in different Ar + The atomic molar ratio of each element obtained by XPS detection after etching time was calculated to be between 1:13 and 1:24 at different etching stages.
[0062] Figure 6 The graphs show the cycling performance of silicon anode materials in Examples 1-3 and Comparative Examples 1-3. Compared with Comparative Examples 1 and 3, the specific capacity of the first charge of Examples 1-3 decreased, but all showed significantly better cycling stability. Among them, Example 2 had the best performance, indicating that the introduction of crystalline-amorphous composite fluoride will reduce the specific capacity of the material, but can significantly improve the cycling stability of the material and optimize its electrochemical performance. Compared to Example 2, Comparative Example 2 exhibits a significantly reduced high-rate capacity and significantly worse cycling stability. This indicates that the conformal coating modification effect of crystalline Li2SiF6 and amorphous Li3AlF6 on porous silicon in Example 2 is significantly better than that in Comparative Example 2. Analysis shows that this is because the surface crystalline Li2SiF6, as the framework of the three-dimensional coating structure, provides stable lithium-ion diffusion channels and interfacial chemical inertness. Amorphous Li3AlF6 is dispersed within the crystalline Li2SiF6, enhancing interfacial toughness (amorphous Li3AlF6 can provide a flexible buffer for crystalline Li2SiF6) and optimizing stress distribution. Furthermore, the excellent ion conduction performance of both crystalline Li2SiF6 and amorphous Li3AlF6 further enhances ion conduction performance. The synergy between the two can establish a physical-chemical barrier during cycling, improve the stability of the electrode / electrolyte interface, and optimize the mechanical properties of the electrode.
[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A modified porous silicon anode material, characterized in that, It includes a porous silicon substrate and a three-dimensional composite fluoride coating layer conformally coated on the surface of the porous silicon substrate, wherein the composite fluoride coating layer includes crystalline Li2SiF6 and amorphous Li3AlF6.
2. The modified porous silicon anode material as described in claim 1, characterized in that, The amorphous Li3AlF6 is dispersed in the crystalline Li2SiF6 phase, forming a crystalline-amorphous composite structure; The porous silicon substrate consists of porous micron-sized spherical or near-spherical secondary particles; the porous micron-sized spherical or near-spherical secondary particles are formed by the interlacing and stacking of nanosheet-like or fibrous primary particles to create a continuous three-dimensional network framework; the spherical or near-spherical particles have macropores and / or mesopores inside, wherein the macropores are distributed in a honeycomb or cavity-like manner inside the microspheres, and the mesopores are formed between the nanosheet-like or fibrous primary particles, which constitute the pore walls of the porous network.
3. The modified porous silicon anode material as described in claim 1, characterized in that, Based on the total mass of the modified porous silicon anode material, the mass percentage of the crystalline Li2SiF6 is 1~20%.
4. The modified porous silicon anode material as described in claim 3, characterized in that, The ratio of the molar amount of Al to the molar amount of Si in the composite fluoride coating is 1:10~25.
5. The modified porous silicon anode material as described in claim 1, characterized in that, The composite fluoride coating is formed through an in-situ chemical reaction and chemically bonded to the surface of the porous silicon substrate.
6. A method for preparing modified porous silicon anode materials, characterized in that, include: Aluminum-silicon alloy powder was added to hydrochloric acid solution for etching, and then washed and dried to obtain a porous silicon substrate with residual aluminum on the surface. A porous silicon substrate was added to a lithium hydroxide solution and stirred to obtain a suspension. A mixed suspension and a fluoride solution were reacted, followed by solid-liquid separation and drying to obtain a modified porous silicon anode material.
7. The method for preparing the modified porous silicon anode material as described in claim 6, characterized in that, The concentration of the hydrochloric acid solution is 0.5~5M; the etching time is 6~24h; and the etching temperature is 10~60℃.
8. The method for preparing the modified porous silicon anode material as described in claim 6, characterized in that, The concentration of the lithium hydroxide solution is 0.01~0.05M; the molar ratio of Li to Si in the porous silicon substrate is 1:5~25; the solvent of the lithium hydroxide solution is a mixture of water and ethanol; the stirring time is 1~12h; and the stirring temperature is 20~60℃.
9. The method for preparing the modified porous silicon anode material as described in claim 6, characterized in that, The fluoride solution is one or a mixture of hydrofluoric acid solution and ammonium fluoride solution; the concentration of the fluoride solution is 0.3~3M; the molar ratio of Li element in the lithium hydroxide solution to F element in the fluoride solution is 1:30~130; the reaction time is 6~24h; the reaction temperature is 20~60℃; the drying is any one of vacuum drying, water bath drying, and freeze drying.
10. A lithium-ion battery, characterized in that, It includes the modified porous silicon anode material as described in any one of claims 1 to 5, or the modified porous silicon anode material prepared by the preparation method described in any one of claims 6 to 9.