【作者】 陈立宝；

【导师】 解晶莹；

【作者基本信息】 中国科学院研究生院（上海微系统与信息技术研究所） ， 材料物理与化学， 2007， 博士

【摘要】 硅因具有很高的嵌锂比容量，被认为是最具应用潜力的新一代高能锂离子电池负极材料。论文研究了磁控溅射法制备的硅薄膜负极材料的结构特征和电化学性能，为进一步提高硅薄膜的电化学性能，采用共溅射法制备了硅—铝和硅—镍复合薄膜。论文制备的硅薄膜负极材料是非晶态的结构，具有良好的电化学性能。300nm硅薄膜的可逆比容量高达3134.4mAh／g，首次库仑效率为87.1％；0.5C倍率下充放电，硅薄膜500次循环的容量保持率为61.3％；而且具有较好的倍率性能，10.0C放电容量为0.5C放电容量的41.4％。论文重点研究了硅薄膜负极材料表面SEI膜的形成机制。硅薄膜SEI膜的主要成分是电解液的还原产物ROCO₂Li、Li₂CO₃、LiF和有机聚合物，同时在硅薄膜的SEI膜中发现了少量的SiO_x。SiO_x是由Li_xSi与渗透SEI膜的电解液反应形成的。详细研究了电解液添加剂VC对硅薄膜SEI膜性能的改善作用。在含有VC添加剂的功能电解液中，首次循环后硅薄膜表面形成了稳定的SEI膜，SEI膜表面没有出现结晶的LiF；随着循环次数的增加，SEI膜的阻抗基本保持不变。VC添加剂大大提高了硅薄膜的循环性能，硅薄膜的200次循环容量保持率在常规电解液中为25.6％，在功能电解液中提高到78.5％。研究了薄膜厚度、集流体表面粗糙度和热处理对硅薄膜负极材料电化学性能的影响。随着薄膜厚度的增加，硅薄膜的比容量下降，倍率性能逐渐恶化；集流体表面粗糙度增大对硅薄膜负极材料的循环性能具有积极的影响；热处理改善了硅薄膜的循环性能。为提高薄膜电极的导电性和减小薄膜的体积效应，论文采用共溅射法制备了硅—铝和硅—镍复合薄膜。硅—铝复合薄膜的比容量略低于相近厚度的硅薄膜，但循环性能和倍率性能明显优于硅薄膜；硅—镍复合薄膜的比容量和循环性能都低于相近厚度的硅薄膜，但具有良好的倍率性能。硅基薄膜负极材料的锂离子扩散系数是决定其电化学动力学性能的主要因素，采用循环伏安法测定了硅基薄膜负极材料的锂离子扩算系数。硅薄膜的锂离子扩散系数为1.815×10^-9cm²／s，硅—铝复合薄膜的锂离子扩散系数为2.38×10^-7cm²／s，硅—镍复合薄膜的锂离子扩散系数为1.79×10^-8cm²／s。更多还原

【Abstract】 Si has been proposed as a promising anode material for the next generation high energy lithium ion batteries due to its highest specific capacity. We investigated the structure characteristics and electrochemical performance of Si film anode prepared by magnetron sputtering. To further improve the electrochemical performance of Si film, the Si-Al and Si-Ni films were fabricated by co-sputtering technique.Si film was amorphous and exhibited excellent electrochemical performance. The 300 ran Si film showed a reversible capacity of 3134.4 mAh/g and the initial coulomb efficiency of 87.1%. The capacity retention of Si film was 61.3% after 500 cycles at 0.5C rate. Si film exhibited good rate performance. The discharge capacity at 10C rate was 41.4% of the discharge capacity at 0.5C rate.The formation mechanism of SEI layer on the surface of Si film anode was studied. The major components of SEI layer of Si film anode were ROCO₂Li, Li₂CO₃, LiF and polycarbonate. It was also found that a small quantity of silicon oxide was formed in the SEI layer due to the reaction of lithiated silicon with permeated electrolyte. The effect of electrolyte additive of vinylene carbonate （VC） on the SEI layer properties was investigated in details. The perfect SEI layer was formed in VC-containing electrolyte and no LiF crystals appeared on the SEI layer after the first cycle. And the impedance of SEI layer kept almost invariant upon cycling. Especially, the cycling performance of Si film was greatly improved by the presence of VC in electrolyte. The capacity retention of Si film increased from 25.6% in VC-free electrolyte to 78.5% in VC-containing electrolyte after 200 cycles.To enhance the conductivity and decrease volumetric change of Si film, Si-Al and Si-Ni films were prepared by co-sputtering technique. The capacity of Si-Al film was lower than that of Si film with the similar thickness, but the cycling performance and rate performance were better than that of Si film. The capacity and cycling performance of Si-Ni film were lower than that of Si film. However, the Si-Ni film showed excellent rate performance. The diffusion coefficient of lithium ion is a key factor to decide the electrochemical kinetic property of Si-based film. The lithium ion diffusion coefficient of Si-based film was measured by cyclic voltammetry. The diffusion coefficient of lithium ion is 1.815×10^-9 cm/s in Si film, 2.38×10^-7 cm/s in Si-Al film and 1.79×10^-8 cm/s in Si-Ni film.更多还原