【作者】 张杰；

【导师】 韩冬梅；

【作者基本信息】 北京化工大学 ， 材料与化工（专业学位）， 2025， 硕士

【摘要】 硅基负极因其超高的理论比容量和低脱/嵌锂电位而在锂离子电池领域受到广泛关注。但是,硅在嵌/脱锂过程中体积变化会导致电极结构破坏和SEI膜增厚,其自身较低的本征电导率和锂离子扩散系数也严重制约了实际应用。多孔结构设计可通过内部孔隙缓冲硅的体积膨胀、缩短锂离子传输路径,从而提升硅负极的循环稳定性。本论文针对多孔硅首次库伦效率低,动力学性能不足的问题,从材料设计与合成策略出发,分别开展了Ge掺杂和碳包覆多孔硅研究,并对合成负极材料的储锂机制及性能进行了系统研究,主要内容如下:（1）针对多孔硅首次库伦效率低及锂离子扩散动力学慢的问题,通过Ge掺杂与三维多孔结构协同优化策略,以微米级Mg₂Si与Mg₂Ge为前驱体,通过高温合金化与脱合金化法构建Ge掺杂三维多孔硅材料。通过对原料、各阶段产物样品和不同Ge掺杂量样品的结构、形貌、表面状态及孔结构分析,揭示了Ge掺杂多孔材料提高硅负极的锂离子扩散动力学性能的机制。得益于以上优势,锗掺杂的多孔硅基负极首次库伦效率达85.3%,在1.0 A g^-1下循环200次后仍保持961.6 mAh g^-1的稳定放电比容量。（2）针对多孔硅其动力学性能不足的问题,以廉价的光伏硅废料为原料,通过合金化与CO₂热氧化法,制备多孔Si@C纳米片。基于硅废料的二维纳米片结构,采用同步体相孔隙工程和原位碳包覆策略,调查了原料、各阶段产物及碳包覆所得样品的晶体结构、形貌、表面状态及孔结构的变化。实验发现,孔隙结构为硅在嵌锂/脱锂过程所产生的体积变化提供缓冲空间,碳层可构建高效的离子/电子传输通道。这一结构优势使得制备的多孔Si@C纳米片在1.0 A g^-1电流密度下循环750次后保持786.4mAh g^-1可逆容量,在5.0 A g^-1高倍率下容量达879.0 mAh g^-1。更多还原

【Abstract】 Silicon-based anode have attracted widespread attention in the field of lithium-ion batteries due to their ultra-high theoretical specific capacity and low lithium insertion/extraction potential.However,the severe volume changes during the charging and discharging process of silicon will lead to electrode structure fracture and instability of the SEI（Solid-Electrolyte Interphase）membrane.Additionally,the low electrical conductivity and diffusion coefficient of lithium-ion significantly hinder its practical application.The porous structures could buffer volume expansion through internal voids and shorten the lithium-ion transport pathways,thereby improving the cyclic stability of silicon anodes.This thesis addresses the issues of low initial coulombic efficiency and insufficient dynamic performance of porous silicon.Based on the material design and synthesis strategies,Ge-doped and carbon-coated porous silicon was prepared to enhance the initial coulombic efficiency and the dynamic performance of silicon anode material.The lithium storage mechanisms and performance of anode materials were systematically examined.The detailed contents are as follows:（1）Ge-doped silicon anode material with three-dimensional porous structure was synthesized via high-temperature alloying and dealloying methods using Mg₂Si and Mg₂Ge as the precursors.The relationship between the structural,morphological,surface state,and pore structure of the raw materials,intermediate products,and as-prepared samples with varying Ge doping concentration were investigated by XRD,SEM,TEM,XPS and BET method.The mechanisms by which Ge-doped porous materials enhance the lithium-ion diffusion dynamic performance of silicon anodes were also revealed.Benefiting from these advantages,Ge-doped porous silicon-based anode achieved an initial coulombic efficiency of 85.3%.After 200 cycles at 1 A g^-1,the specific capacity of 961.6mAh g^-1 was maintained.（2）Porous Si@C nanosheets were prepared via alloying and CO₂ thermal oxidation methods,utilizing photovoltaic silicon waste as the raw material.Based on the 2D nanosheet structure of silicon waste,we employed in-situ carbon coating and synchronous solid-phase pore engineering strategies.Through comparative analysis of the crystal structure,morphology,surface state,and pore structure of the raw materials,intermediate products,and carbon-coated samples,it was found that the porous structure offered a buffering effect for silicon’s volume expansion during lithium insertion/extraction,while the carbon layer constructed efficient ion/electron transport channels.These structural advantages enable the prepared porous Si@C nanosheets to maintain capacity of 786.4 mAh g^-1 after 750 cycles at 1 A g^-1 and deliver a capacity of879 mAh g^-1 at a high rate of 5 A g^-1.更多还原