Composite-coated modified silicon-carbon negative electrode material, preparation method thereof and battery
By encapsulating a matrix polymer and metal oxide grafted with a fluorinated silane coupling agent onto a silicon-carbon composite material to form a buffer layer, the volume expansion and SEI instability issues of the silicon-carbon composite material during charge and discharge processes are solved, improving the initial coulombic efficiency and cycle stability, and achieving high energy density lithium-ion battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LANXI ZHIDE ADVANCED MATERIALS CO LTD
- Filing Date
- 2026-04-13
- Publication Date
- 2026-06-05
AI Technical Summary
Existing silicon-carbon composite materials suffer from problems such as particle breakage and pulverization due to volume expansion during charge and discharge, unstable SEI film, low initial coulombic efficiency, and poor cycle life. Furthermore, their conductivity is insufficient, making it difficult to meet the application requirements of lithium-ion batteries.
A composite coating modification method is used to coat a matrix polymer grafted with a fluorinated silane coupling agent to form a buffer layer on the outside of a silicon-carbon composite core, and load metal oxides to form a multi-level stable interface structure, thereby improving electronic conductivity and interfacial compatibility.
It significantly improves the initial coulombic efficiency and long-term cycle stability. The material is uniformly dispersed, has consistent performance, and has high tap density and volumetric energy density, meeting the high energy density requirements of lithium-ion batteries.
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Figure CN122158546A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon-carbon anode material technology, and more specifically, to composite-coated modified silicon-carbon anode materials, their preparation methods, and batteries. Background Technology
[0002] In the high-end consumer electronics sector, including smartphones, tablets, and wearable devices, consumers' pursuit of longer battery life, faster charging speeds, and slimmer designs is endless. This directly drives the extreme demands on the energy density, power density, and volumetric energy density of lithium-ion batteries. Most lithium-ion batteries use carbon materials as the anode. Compared to hard carbon and artificial graphite, natural graphite has become the preferred anode material for lithium-ion batteries due to its superior performance and lower cost. Currently, the carbon materials used as anodes in the market are approaching the upper limit of their lithium storage capacity. In particular, commercially available graphite has achieved a practical discharge capacity close to its theoretical maximum of 372 mAh g⁻¹. -1 This makes it extremely challenging to further increase its energy storage capacity.
[0003] Silicon anode materials stand out due to their superior theoretical specific capacity; at room temperature, their theoretical maximum charge storage capacity can reach 3579 mAh g⁻¹. -1 However, this value can increase to 4200 mAh g as the temperature rises. -1 Silicon anodes far surpass the energy storage capacity of commonly used graphite anode materials and are renowned for their low lithium insertion / extraction potential, environmental friendliness, and abundant crustal reserves, making them the preferred anode material for lithium-ion batteries. However, silicon anodes face the problem of significant volume changes (approximately 300%) in practical applications. The expansion / contraction stress generated during lithium insertion / extraction causes severe cracking of the silicon, leading to the formation of an unstable SEI film on the silicon surface and a large consumption of active lithium ions, resulting in rapid capacity loss and low initial coulombic efficiency.
[0004] To overcome the shortcomings of carbon and silicon materials, existing technologies typically combine them to form silicon-carbon negative materials. Specifically, silicon nanoparticles are atomized, dried, and carbonized with a carbon source (such as pitch, phenolic resin, biomass carbon, etc.) slurry using a spray drying process to form micron-sized silicon-carbon composite microspheres with a core-shell or porous structure. Simultaneously, an elastic polymer binder (such as CMC / SBR, PAA / SF, etc.) is incorporated to construct a stable electrode system that can adapt to volume expansion. The carbon coating layer enhances conductivity, buffers silicon volume expansion, and reduces direct contact between silicon and the electrolyte, thereby improving the material's cycle stability and interfacial compatibility.
[0005] However, the following defects exist in the preparation of silicon-carbon anode materials using the above process: (1) High intrinsic resistivity of the material: The high resistivity leads to insufficient electronic conductivity of silicon-carbon composite materials. This high resistance characteristic will cause severe ohmic polarization, reduce the rate performance and charge-discharge efficiency of the battery, and increase energy loss, making it difficult to meet the application requirements of lithium-ion batteries in various scenarios.
[0006] (2) The process control is complex and the performance uniformity is challenging: There will be significant differences between small-batch laboratory samples and scale-up (pilot-scale) products in terms of silicon particle dispersion uniformity and carbon coating consistency.
[0007] (3) The contradiction between initial coulombic efficiency and long-term cycling stability still exists: Although carbon coating and binder optimization improve cycling performance, the initial coulombic efficiency of high specific capacity silicon-carbon materials (especially when silicon content is high) is usually low, mainly due to the formation of irreversible SEI film on the silicon surface and lithium loss. At the same time, under long-term cycling conditions, repeated expansion of silicon particles may still lead to the cracking of carbon coating layer and continuous thickening of SEI film, making it difficult to predict long-term cycling performance.
[0008] In summary, in traditional silicon-carbon composite materials, the silicon component undergoes dramatic volume expansion during charge and discharge, leading to the cracking and pulverization of active material particles, which then detach from the current collector, resulting in rapid capacity decay. Simultaneously, expansion and contraction continuously damage and regenerate the solid electrolyte interphase (SEI) film, constantly consuming electrolyte and lithium source, resulting in low initial coulombic efficiency and poor cycle life. Furthermore, silicon itself has poor conductivity, and its highly active surface sites are prone to side reactions with the electrolyte, further deteriorating battery performance. Single additive coating may cause the coating layer to crack during volume changes and may introduce significant interfacial impedance. Therefore, it is necessary to construct a multi-layered stable interfacial structure that combines flexible buffering, high-strength protection, high ionic conductivity, and good electronic conductivity to synergistically address issues such as volume expansion, SEI instability, and numerous side reactions.
[0009] In view of this, the present invention is proposed. Summary of the Invention
[0010] The purpose of this invention is to provide a composite-coated modified silicon-carbon anode material, its preparation method, and a battery. The composite-coated modified silicon-carbon anode material provided in this invention has the characteristics of flexible buffering, high ionic conductivity, and electronic conductivity, solving problems such as volume expansion, SEI instability, and side reactions.
[0011] This invention is implemented as follows: In a first aspect, the present invention provides a composite-coated modified silicon-carbon anode material, comprising a silicon-carbon composite core and a buffer layer wrapped around the silicon-carbon composite core, wherein the buffer layer is a coating layer formed by grafting a matrix polymer with a fluorinated silane coupling agent, and a metal oxide is loaded on the buffer layer.
[0012] In an optional embodiment, the silicon-carbon composite core is silicon-carbon particles formed by filling porous carbon with silicon nanoparticles; Preferably, the silicon nanoparticles fill the pores of the porous carbon; Preferably, the silicon nanoparticles are chemically deposited to fill the pores of the porous carbon. Preferably, the particle size D of the silicon-carbon composite core is... 50 Its thickness is 5-10 μm, and its resistivity is 200-300 Ω·cm.
[0013] In an optional implementation, the buffer layer satisfies at least one of the following requirements: (1) The matrix polymer is selected from one or more of polyimide, polyacrylic acid, polyurethane and sodium carboxymethyl cellulose; preferably polyimide; (2) The mass of the buffer layer accounts for 0.1-1% of the mass of the silicon-carbon composite core; the mass of the buffer layer here is only the mass of the matrix polymer; (3) The thickness of the buffer layer is 10-80 nm.
[0014] In an optional embodiment, the metal oxide satisfies at least one of the following requirements: (1) The metal oxide includes any one of aluminum oxide, zirconium oxide, titanium oxide, magnesium oxide, zinc oxide, niobium oxide, tantalum oxide, hafnium oxide and yttrium oxide, preferably aluminum oxide; preferably, the aluminum oxide is composed of aluminum oxide particles with a length of 1-50 nm and a width of 1-10 nm; (2) The mass of the metal oxide accounts for 0.1-1% of the mass of the silicon-carbon composite core.
[0015] In an optional embodiment, the mass difference between the buffer layer and the metal oxide is 0.1-0.9%; Preferably, the grafting process includes: the fluorinated silane coupling agent undergoing a condensation reaction with the functional groups on the surface of the matrix polymer and the silicon-carbon composite core to form chemical bonds.
[0016] In an optional embodiment, the fluorinated silane coupling agent includes at least one of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, tridecafluorooctyltriethoxysilane, and trifluoropropyltrimethoxysilane; preferably 1H,1H,2H,2H-perfluorooctyltriethoxysilane. Preferably, the mass of the fluorinated silane coupling agent is 0.2-2% of the mass of the silicon-carbon composite core.
[0017] In a second aspect, the present invention provides a method for preparing the composite-coated modified silicon-carbon anode material described in the foregoing embodiments, comprising: sequentially forming an intermediate with a polymer-metal oxide primary coating layer by combining a silicon-carbon composite core with a matrix polymer and a metal oxide; A condensation reaction is carried out by mixing a fluorinated silane coupling agent and the intermediate, which grafts the matrix polymer and the silicon-carbon composite core together to form a buffer layer.
[0018] In an optional embodiment, the intermediate is dispersed in a solvent containing a fluorosilane coupling agent and reacted at 30-80°C for 1-6 hours. Preferably, the solvent includes water and C1-C3 alcohol solvents; more preferably, the volume ratio of the C1-C3 alcohol solvent to water is 1:(8-10).
[0019] In an optional embodiment, the method includes: mixing and dispersing a silicon-carbon composite core and a matrix polymer to form a primary slurry, and then mixing the primary slurry with the metal oxide to form a mixed slurry; Next, the mixed slurry is subjected to solid-liquid separation to form an intermediate, or the mixed slurry is spray-dried to form an intermediate; Preferably, the inlet temperature of the spray dryer is 150-200℃ and the outlet temperature is 100-130℃.
[0020] Thirdly, the present invention provides a battery comprising the composite-coated modified silicon-carbon anode material described in the foregoing embodiments.
[0021] The present invention has the following beneficial effects: (1) Excellent first coulombic efficiency and long-term cycle stability: The embodiments of the present invention can significantly improve the first coulombic efficiency by wrapping a buffer layer around the silicon-carbon composite core and loading metal oxides on the buffer layer, and can ensure the stability of SEI, thereby improving the long-term cycle stability.
[0022] (2) The process is simple and the silicon-carbon anode material formed has uniform performance: The composite coated modified silicon-carbon anode material provided in the embodiments of the present invention is uniformly dispersed and uniformly coated.
[0023] (3) High tap density and volumetric energy density of silicon-carbon anode material: The composite coating modification provided in the embodiments of the present invention not only has high specific capacity, but also high tap density and high volumetric energy density. Attached Figure Description
[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0025] Figure 1 This is a SEM image of the silicon-carbon anode material provided in Embodiment 2 of the present invention; Figure 2 This is a SEM image of the silicon-carbon anode material coated with a buffer layer provided in Embodiment 2 of the present invention. Figure 3 This is a SEM image of the composite-coated modified silicon-carbon anode material provided in Embodiment 2 of the present invention; Figure 4 This is a TEM image of the composite-coated modified silicon-carbon anode material provided in Embodiment 2 of the present invention. Detailed Implementation
[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0027] In traditional silicon-carbon composite materials, the silicon component undergoes dramatic volume expansion during charge and discharge, leading to the cracking and pulverization of active material particles and their detachment from the current collector, resulting in rapid capacity decay. Simultaneously, expansion and contraction continuously damage and regenerate the solid electrolyte interphase (SEI) film, constantly consuming electrolyte and lithium source, resulting in low initial coulombic efficiency and poor cycle life. Furthermore, silicon itself has poor conductivity, and its highly active surface sites are prone to side reactions with the electrolyte, further deteriorating battery performance. Single additive coating may cause the coating layer to crack during volume changes and may introduce significant interfacial impedance. Therefore, this invention provides a composite-coated modified silicon-carbon anode material that overcomes the aforementioned technical problems.
[0028] Specifically, the composite-coated modified silicon-carbon anode material includes a silicon-carbon composite core, which is silicon-carbon particles formed by filling porous carbon with silicon nanoparticles; specifically, filling the pores of the porous carbon. The filling method includes deposition, such as chemical deposition or physical deposition. The particle size D of the silicon-carbon composite core... 50The micrometer size is 5-10 μm, for example, any value between 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.; the resistivity is 200-300 Ω·cm, for example, any value between 200 Ω·cm, 210 Ω·cm, 220 Ω·cm, 230 Ω·cm, 240 Ω·cm, 250 Ω·cm, 260 Ω·cm, 270 Ω·cm, 280 Ω·cm, 290 Ω·cm, 300 Ω·cm, etc. The silicon-carbon composite core is either commercially available silicon-carbon particles or silicon-carbon particles prepared using existing methods.
[0029] A buffer layer is wrapped around the silicon-carbon composite core. This buffer layer is formed by grafting a matrix polymer with a fluorinated silane coupling agent. Specifically, the fluorinated silane coupling agent undergoes a condensation reaction with functional groups on the surface of both the matrix polymer and the silicon-carbon composite core to form chemical bonds. The silanol groups (-Si-OH) generated by the pre-hydrolysis of the fluorinated silane coupling agent undergo a condensation reaction with the Si-OH groups on the surface of the silicon-carbon core and / or the active groups such as -NH in the polymer to form Si-O-Si or Si-NC covalent bonds.
[0030] Furthermore, the thickness of the buffer layer is 10-80 nm; for example, any value between 10-80 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, etc.
[0031] The matrix polymer forming the above buffer layer is selected from one or more of polyimide, polyacrylic acid, polyurethane and sodium carboxymethyl cellulose; preferably polyimide (PI).
[0032] Furthermore, the mass of the buffer layer accounts for 0.1-1% of the mass of the silicon-carbon composite core; that is, the mass of the matrix polymer accounts for 0.1-1% of the mass of the silicon-carbon composite core. For example, it can be any value between 0.1-1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.
[0033] Furthermore, the fluorinated silane coupling agent includes at least one of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, tridecafluorooctyltriethoxysilane, and trifluoropropyltrimethoxysilane; preferably 1H,1H,2H,2H-perfluorooctyltriethoxysilane.
[0034] The mass of the fluorinated silane coupling agent is 0.2-2% of the mass of the silicon-carbon composite core. For example, it is 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, or 2.0%.
[0035] Furthermore, a metal oxide is loaded onto the aforementioned buffer layer. The metal oxide includes any one of aluminum oxide, zirconium oxide, titanium oxide, magnesium oxide, zinc oxide, niobium oxide, tantalum oxide, hafnium oxide, and yttrium oxide, preferably aluminum oxide. For example, the aluminum oxide is composed of aluminum oxide particles with a length of 1-50 nm and a width of 1-10 nm.
[0036] Furthermore, the mass of the metal oxide accounts for 0.1-1% of the mass of the silicon-carbon composite core. For example, it is any value between 0.1-1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.
[0037] Furthermore, the mass of the buffer layer differs from the mass of the metal oxide by 0.1-0.9%; that is, the mass difference between the matrix polymer and the metal oxide can be any value between 0.1% and 0.9%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or 0.9%. In other words, the amount of the group polymer is higher than that of the metal oxide.
[0038] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned composite-coated modified silicon-carbon anode material, comprising: A silicon-carbon composite core is sequentially combined with a matrix polymer and a metal oxide to form an intermediate polymer-metal oxide primary coating layer. Specifically, the silicon-carbon composite core, the matrix polymer, and a solvent are mixed and dispersed to form a primary slurry, and then the primary slurry is mixed with the metal oxide to form a mixed slurry.
[0039] The mixed slurry is then subjected to solid-liquid separation, such as filtration, to form an intermediate. Alternatively, the mixed slurry can be spray-dried to form an intermediate; wherein the inlet temperature of the spray dryer is 150-200℃ and the outlet temperature is 100-130℃. Both solid-liquid separation and spray drying can yield a solid intermediate.
[0040] A condensation reaction is carried out by mixing a fluorinated silane coupling agent and the intermediate, thereby grafting the matrix polymer and the silicon-carbon composite core and forming a buffer layer. Specifically, the intermediate is dispersed in a solvent containing the fluorinated silane coupling agent and reacted at 30-80°C for 1-6 hours; for example, any value between 30-80°C, such as 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C. The reaction time is any value between 1-6 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours. The solvent includes water and C1-C3 alcohol solvents (e.g., methanol, ethanol, etc.); more preferably, the volume ratio of the C1-C3 alcohol solvent to water is 1:(8-10).
[0041] Thirdly, embodiments of the present invention provide a battery comprising a composite-coated modified silicon-carbon anode material.
[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0043] Example 1 This invention provides a method for preparing a composite-coated modified silicon-carbon anode material, comprising: Step 1, take 100g of silicon-carbon anode material particles (D 50 =8μm, powder resistivity =214Ω·cm), 1g PI was dispersed in 500g deionized water and stirred at 400rpm for 30 minutes to form a uniform primary slurry. This silicon-carbon anode material is produced by introducing silane gas into the pores of porous carbon particles, followed by high-temperature pyrolysis to deposit the gas and form silicon nanoparticles. These silicon nanoparticles are dispersed within the pores of the porous carbon, forming a uniform and dense silicon-carbon composite material.
[0044] Step 2: Add 1g of Al2O3 to the above primary slurry and stir and disperse at 400rpm for 30 minutes to form the final mixed slurry.
[0045] Step 3: Spray dry the mixed slurry. The inlet temperature of the spray dryer is set to 180℃, and the outlet temperature is controlled at 120℃. After drying, an intermediate with a polymer-metal oxide primary coating layer is obtained.
[0046] Step 4, prepare the grafting reaction solution: Add 2g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane to a mixed solvent consisting of 90g of deionized water and 10g of ethanol, and stir for 10 minutes to pre-dissolve it.
[0047] Step 5: Disperse the intermediate obtained in step 3 in the above grafting reaction solution, place it in a constant temperature water bath at 60°C, and react for 4 hours to complete the fluorination grafting.
[0048] Step 6: After the reaction is complete, the product is washed three times with anhydrous ethanol by centrifugation and then dried in a vacuum drying oven at 80°C for 12 hours to finally obtain the composite-coated modified silicon-carbon anode material, wherein the thickness of the buffer layer is about 60 nm.
[0049] Example 2 This invention provides a method for preparing a composite-coated modified silicon-carbon anode material, comprising: Step 1, take 100g of silicon-carbon anode material particles (D 50=8μm, powder resistivity=214Ω·cm), 1g PI was dispersed in 500g deionized water and stirred at 400rpm for 30 minutes to form a uniform primary slurry.
[0050] Step 2: Add 0.8g Al2O3 to the above primary slurry and stir and disperse at 400rpm for 30 minutes to form the final mixed slurry.
[0051] Step 3: Spray dry the mixed slurry. The inlet temperature of the spray dryer is set to 180℃, and the outlet temperature is controlled at 120℃. After drying, an intermediate with a polymer-metal oxide primary coating layer is obtained.
[0052] Step 4, prepare the grafting reaction solution: Add 2g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane to a mixed solvent consisting of 90g of deionized water and 10g of ethanol, and stir for 10 minutes.
[0053] Step 5: Disperse the intermediate obtained in step 3 in the above grafting reaction solution, place it in a constant temperature water bath at 60°C, and react for 4 hours to complete the fluorination grafting.
[0054] Step 6: After the reaction is complete, the product is washed three times with anhydrous ethanol by centrifugation and then dried in a vacuum drying oven at 80°C for 12 hours to finally obtain the composite-coated modified silicon-carbon anode material, wherein the thickness of the buffer layer is about 45 nm.
[0055] Example 3 This invention provides a method for preparing a composite-coated modified silicon-carbon anode material, comprising: Step 1, take 100g of silicon-carbon anode material particles (D 50 =8μm, powder resistivity=214Ω·cm), 1g PI was dispersed in 500g deionized water and stirred at 400rpm for 30 minutes to form a uniform primary slurry.
[0056] Step 2: Add 0.5g Al2O3 to the above primary slurry and stir and disperse at 400rpm for 30 minutes to form the final mixed slurry.
[0057] Step 3: Spray dry the mixed slurry. The inlet temperature of the spray dryer is set to 180℃, and the outlet temperature is controlled at 120℃. After drying, an intermediate with a polymer-metal oxide primary coating layer is obtained.
[0058] Step 4, prepare the grafting reaction solution: Add 2g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane to a mixed solvent consisting of 90g of deionized water and 10g of ethanol, and stir for 10 minutes.
[0059] Step 5: Disperse the intermediate obtained in step 3 in the above grafting reaction solution, place it in a constant temperature water bath at 60°C, and react for 4 hours to complete the fluorination grafting.
[0060] Step 6: After the reaction is complete, the product is washed three times with anhydrous ethanol by centrifugation and then dried in a vacuum drying oven at 80°C for 12 hours to finally obtain the composite-coated modified silicon-carbon anode material, wherein the thickness of the buffer layer is about 40 nm.
[0061] Example 4 This invention provides a method for preparing a composite-coated modified silicon-carbon anode material, comprising: Step 1, take 100g of silicon-carbon anode material particles (D 50 =8μm, powder resistivity=214Ω·cm, 1g PI dispersed in 500g deionized water, stirred at 400rpm for 30 minutes to form a uniform primary slurry.
[0062] Step 2: Add 0.3g Al2O3 to the above primary slurry and stir and disperse at 400rpm for 30 minutes to form the final mixed slurry.
[0063] Step 3: Spray dry the mixed slurry. The inlet temperature of the spray dryer is set to 180℃, and the outlet temperature is controlled at 120℃. After drying, an intermediate with a polymer-metal oxide primary coating layer is obtained.
[0064] Step 4, prepare the grafting reaction solution: Add 2g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane to a mixed solvent consisting of 90g of deionized water and 10g of ethanol, and stir for 10 minutes.
[0065] Step 5: Disperse the intermediate obtained in step 3 in the above grafting reaction solution, place it in a constant temperature water bath at 60°C, and react for 4 hours to complete the fluorination grafting.
[0066] Step 6: After the reaction is complete, the product is washed three times with anhydrous ethanol by centrifugation and then dried in a vacuum drying oven at 80°C for 12 hours to finally obtain a composite coated silicon-carbon anode material modified by grafting with a fluorinated silane coupling agent, wherein the coating thickness is about 40 nm.
[0067] Comparative Example 1 This comparative example provides a method for preparing a composite-coated modified silicon-carbon anode material. This preparation method is basically the same as the preparation method provided in Example 1, except that the amount of PI is changed to 1.5%, that is, 1.5g PI. All other operations and conditions are the same as in Example 1.
[0068] Comparative Example 2 This comparative example provides a method for preparing a composite-coated modified silicon-carbon anode material. This preparation method is basically the same as the preparation method provided in Example 1, except that steps 4, 5 and 6 of Example 1 are not performed. That is, only PI and Al2O3 are physically coated on the surface of the silicon-carbon anode material particles, which means that only the mixed slurry is spray-dried. The specific operation is the same as in Example 1.
[0069] Comparative Example 3 This comparative example provides a method for preparing a composite-coated modified silicon-carbon anode material. This method is basically the same as the method provided in Example 1, except that step 2 of Example 1 is not performed, which involves spray drying the primary slurry and then mixing it with the grafting reaction solution to carry out the grafting reaction. The remaining operations are the same as in Example 1.
[0070] Comparative Example 4 This comparative example provides a method for preparing a composite-coated modified silicon-carbon anode material. This method is essentially the same as the method provided in Example 1, except for step 4 of Example 1, where the amount of 1H,1H,2H,2H-perfluorooctyltriethoxysilane added is changed to 1g, and then mixed with the grafting reaction solution to carry out the grafting reaction. The remaining operations are the same as in Example 1.
[0071] Comparative Example 5 This comparative example provides a method for preparing a composite-coated modified silicon-carbon anode material. This method is basically the same as the method provided in Example 1, except that in step 1 of Example 1, PI is replaced with polyacrylic acid (PAA), and then mixed with the grafting reaction solution to carry out the grafting reaction. The remaining operations are the same as in Example 1.
[0072] Comparative Example 6 Select silicon-carbon anode material particles (D) from Example 1 50 =8μm, powder resistivity =214Ω·m) as the finished product.
[0073] Detection example Using the composite-coated modified silicon-carbon anode materials from Examples 1-4 and Comparative Examples 1-6 as the anode active materials, anode sheets were prepared respectively. CR2032 coin cells were fabricated using conventional methods, and the electrical performance of the cells was tested. The specific testing methods are as follows: (1) Half-cell assembly: Assemble CR2032 button cells in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), wherein the concentration of LiPF6 is 1mol / L.
[0074] The battery was tested for charge and discharge using the LAND battery testing system.
[0075] (2) Cyclic specific capacity, initial efficiency test and rate performance: After the CR2032 button cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V and the capacity was recorded as Q1; then it was discharged at a constant voltage of 0.005V to the current cutoff of 0.02C and the capacity was recorded as Q2; after standing for 5 minutes, it was charged at a constant current of 0.1C to 0.8V and the capacity was recorded as Q3; after standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V and the capacity was recorded as Q4; after standing for 5 minutes, it was discharged at a constant current of 1C to 0.05V and the capacity was recorded as Q5; the initial delithiation specific capacity is the specific capacity (or mass specific capacity) of the electrode material, and the ratio of the initial delithiation capacity to the initial lithium insertion capacity is the initial coulombic efficiency of the battery.
[0076] 1.5V initial coulombic efficiency: Q4 / (Q1+Q2)*100%; 0.8V Initial coulombic efficiency: Q3 / (Q1+Q2)*100%; 1C / 0.1C charging rate: Q5 / Q4*100%.
[0077] (3) Capacity retention rate test: After standing for 5 minutes, repeat the above charge and discharge steps twice; select 3 coin cells and discharge them to 0.05V at 0.1C, and after standing for 2 hours, disassemble them one by one to measure the thickness of the negative electrode sheet, and record the average value as h1. Then discharge the remaining 3 coin cells to 0.005V at 0.1C; after standing for 5 minutes, charge them to 1.5V at a constant current of 0.1C, and cycle 50 times. Calculate the specific capacity retention rate by dividing the specific capacity of the 50th cycle by the charging capacity of the 1st cycle by 100%.
[0078] The results are shown in Table 1.
[0079] Table 1 Test Results
[0080] As shown in Table 1, the composite-coated modified silicon-carbon anode materials obtained in Examples 1-4 exhibit higher capacity retention and better resistivity. In the lithium-ion battery test system, the initial reversible capacity can reach over 1950 mA·h / g, and the initial coulombic efficiency is over 90%. The metal oxides and binders added in Examples 1-4, through surface fluorination coating with a fluorinated silane coupling agent, can significantly influence the initial efficiency and initial expansion rate of the silicon-carbon anode materials. After fluorination treatment, the direct contact between the surface nano-silicon and the electrolyte is isolated, which helps to reduce side reactions during charging and avoid repeated SEI formation, thereby reducing the volume expansion changes during the lithium intercalation process of the anode material. The initial efficiency and capacity retention indicate that the optimal coating amounts of alumina and polyimide are 0.8 g, 0.5 g, 1 g, and 1 g.
[0081] Comparing Examples 1-4 with Comparative Example 2, it can be seen that the unfluorinated sample has better powder resistivity, but poorer cycling performance; fluorination constructs a stable surface coating layer, which enhances the interfacial stability.
[0082] Comparing Comparative Example 1 and Comparative Example 6, it can be seen that the polyimide coating brings better conductivity to silicon-carbon, which can significantly reduce battery internal resistance, reduce energy loss, and improve cycle life and fast charging performance.
[0083] Comparing Example 1 and Comparative Example 4, it can be seen that reducing the amount of fluorinated silane coupling agent worsens the cycle performance. When the amount is insufficient, the density of fluorinated functional groups grafted at the interface decreases, making it impossible to form a complete and dense fluorinated passivation layer. This leads to instability of the SEI film, increased side reactions, continuous consumption of active lithium, increased interfacial impedance, and ultimately a significant decrease in cycle life.
[0084] Comparing Examples 1-4 with Comparative Example 5, it can be seen that when polyacrylic acid is coated, its good flexibility can effectively buffer the volume expansion of silicon, while the carboxyl groups help to form a stable SEI film, reduce side reactions, and thus improve first-efficiency and cycle stability.
[0085] Comparing Examples 1-4 with Comparative Example 1, it can be seen that when the polyimide coating content is too low, the coating will be incomplete, and the improvement of first efficiency and cycle stability will be limited; while an excessively thick coating layer will increase the interfacial impedance, hinder lithium-ion diffusion, and lead to a decrease in cycle performance, and excessive insulating material will reduce the overall specific capacity.
[0086] Characterization The silicon-carbon anode materials used in Examples 1-4 and Comparative Examples 1-6 were characterized by SEM. The results are shown in [reference needed]. Figures 1-4 .
[0087] according to Figure 1It can be seen that the silicon-carbon anode material has a smooth surface, the particles are regularly spherical, and no coating layer is visible, indicating that it is an unmodified original silicon-carbon anode material.
[0088] The silicon-carbon anode material of Example 2, which only added a fluorinated silane coupling agent and a polymer, was characterized by SEM. The results are shown in [link to SEM]. Figure 2 .
[0089] according to Figure 2 It can be seen that the material surface exhibits a uniform thin layer coating with clear outlines and no obvious agglomeration, indicating that the adhesive and fluorinated silane coupling agent have successfully grafted to form a dense buffer layer.
[0090] SEM and TEM images of the composite-coated modified silicon-carbon anode material prepared in Example 2 are shown in the attached images. Figure 3 and Figure 4 .
[0091] according to Figure 3 and Figure 4 It can be seen that the coating layer on the surface of the spherical silicon-carbon anode is denser, and the morphology of the metal oxide particles remains intact (see...). Figure 3 Metal oxide particles are uniformly dispersed outside the grafted layer (see...) Figure 4 This ultimately forms a multi-layered composite protective structure.
[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A composite-coated modified silicon-carbon anode material, characterized in that, It includes a silicon-carbon composite core and a buffer layer wrapped around the silicon-carbon composite core, wherein the buffer layer is a coating layer formed by grafting a matrix polymer with a fluorinated silane coupling agent, and the buffer layer is loaded with metal oxides.
2. The composite-coated modified silicon-carbon anode material according to claim 1, characterized in that, The silicon-carbon composite core is formed by silicon nanoparticles filling porous carbon to form silicon-carbon particles. Preferably, the silicon nanoparticles fill the pores of the porous carbon; Preferably, the silicon nanoparticles are chemically deposited to fill the pores of the porous carbon. Preferably, the particle size D of the silicon-carbon composite core is... 50 Its thickness is 5-10 μm, and its resistivity is 200-300 Ω·cm.
3. The composite-coated modified silicon-carbon anode material according to claim 1, characterized in that, The buffer layer meets at least one of the following requirements: (1) The matrix polymer is selected from one or more of polyimide, polyacrylic acid, polyurethane and sodium carboxymethyl cellulose; preferably polyimide; (2) The mass of the buffer layer accounts for 0.1-1% of the mass of the silicon-carbon composite core; (3) The thickness of the buffer layer is 10-80 nm.
4. The composite-coated modified silicon-carbon anode material according to claim 1, characterized in that, The metal oxide satisfies at least one of the following requirements: (1) The metal oxide includes any one of aluminum oxide, zirconium oxide, titanium oxide, magnesium oxide, zinc oxide, niobium oxide, tantalum oxide, hafnium oxide and yttrium oxide, preferably aluminum oxide; preferably, the aluminum oxide is composed of aluminum oxide particles with a length of 1-50 nm and a width of 1-10 nm; (2) The mass of the metal oxide accounts for 0.1-1% of the mass of the silicon-carbon composite core.
5. The composite-coated modified silicon-carbon anode material according to claim 1, characterized in that, The mass difference between the buffer layer and the metal oxide is 0.1-0.9%; Preferably, the grafting process includes: the fluorinated silane coupling agent undergoing a condensation reaction with the functional groups on the surface of the matrix polymer and the silicon-carbon composite core to form chemical bonds.
6. The composite-coated modified silicon-carbon anode material according to claim 1, characterized in that, The fluorinated silane coupling agent includes at least one of 1H,1H,2H,2H-perfluorooctyltriethoxysilane, tridecafluorooctyltriethoxysilane, and trifluoropropyltrimethoxysilane; preferably 1H,1H,2H,2H-perfluorooctyltriethoxysilane. Preferably, the mass of the fluorinated silane coupling agent is 0.2-2% of the mass of the silicon-carbon composite core.
7. A method for preparing the composite-coated modified silicon-carbon anode material according to claim 1, characterized in that, include: The silicon-carbon composite core is sequentially combined with a matrix polymer and a metal oxide to form an intermediate polymer-metal oxide primary coating layer; A condensation reaction is carried out by mixing a fluorinated silane coupling agent and the intermediate, which grafts the matrix polymer and the silicon-carbon composite core together to form a buffer layer.
8. The preparation method according to claim 7, characterized in that, include: The intermediate was dispersed in a solvent containing a fluorosilane coupling agent and reacted at 30-80°C for 1-6 hours; Preferably, the solvent includes water and C1-C3 alcohol solvents; more preferably, the volume ratio of the C1-C3 alcohol solvent to water is 1:(8-10).
9. The preparation method according to claim 7, characterized in that, include: A primary slurry is formed by mixing and dispersing a silicon-carbon composite core and a matrix polymer, and then the primary slurry is mixed with the metal oxide to form a mixed slurry. Next, the mixed slurry is subjected to solid-liquid separation to form an intermediate, or the mixed slurry is spray-dried to form an intermediate; Preferably, the inlet temperature of the spray dryer is 150-200℃ and the outlet temperature is 100-130℃.
10. A battery, characterized in that, It includes the composite-coated modified silicon-carbon anode material as described in claim 1.