熔盐电化学合成TiSi2/Si复合材料及其储锂性能的研究

Silicon based composite materials have been deemed as the anode candidate by replacing graphite anode materials for the next generation of lithium ion batteries owing to its higher theoretical specific capacity of lithium and natural abundance. In order to solve the problems existing during the lithiation/delithiation process of silicon anode, such as weak conductivity, fast capacity fade, poor cycling performance, and to realize the research-oriented nanocrystallization and recombination of silicon based materials, this project will extract silicon-titanium directly from silica and titanium dioxide raw materials by the use of molten salt electrolysis to explore a controllable process applying to the synthesis of TiSi2/Si nanocomposite with enhanced electrochemical performance. The major research contents include: the reaction mechanism and morphology evolution rule during the electrochemical reduction of mixed oxides; to clarify the rate capacity and cycling stability of TiSi2/Si composite under various discharge regime and the corresponding dependence of controllable electrolytic conditions such as raw material proportion, cell voltage, electrolytic temperature et. al during the electrochemical synthesis on the above indexes of anode; to establish the new technology for molten salt electrolytic preparation of silicon-titanium nanocomposite for lithium ion batteries and to offer a new solution for preparing silicon based anode materials.

硅基复合材料由于具有储锂比容量高、来源丰富等优点，是能够替代商业化石墨类碳材料的下一代锂离子电池负极。本项目针对硅负极在锂化/去锂化过程中存在的导电性差、容量衰减快、循环性能不理想问题，以实现硅基材料纳米化、复合化为研究导向，以SiO2/TiO2为原料，用熔盐作为电解质提取硅钛，开发电化学性能提升的TiSi2/Si纳米复合材料可控合成新技术。主要研究混合氧化物的电化学还原反应机理和形貌演变规律；厘清TiSi2/Si复合材料在不同放电制度下的倍率性能及循环稳定性等指标与电化学合成过程中物料配比、槽电压、电解温度等可控参数之间的对应关系；建立熔盐电解制备锂离子电池硅钛纳米复合材料技术路线，为硅基负极材料的制备提供新的思路。

项目针对硅负极在锂化/去锂化过程中存在的导电性差、容量衰减快、循环性能不理想问题，以实现硅基材料纳米化、复合化为研究导向，以SiO2为原料，用熔融盐作为电解质制备获得单质硅，微观结构为1~3 μm长、100~200 nm宽的弯曲线状；以不同硅钛摩尔比TiO2/SiO2混合物为原料，制备获得了Si/TiSi2复合材料，实现了储锂性能的提升。项目取得的结果主要有：.（1）以预烧结的多孔块体SiO2为阴极，电解后得到1~3 μm长、100~200 nm宽的弯曲线状单质硅。硅负极在200 mA·g-1放电电流密度下，尽管硅活性材料的首次放电比容量高达2250 mAh·g-1，但是首次库伦效率仅有67.8%，经过100次充放电循环后，硅活性物质放电比容量仅有405.7 mAh·g-1，容量保持率为18 %。.（2）以预烧结的多孔块体TiO2/SiO2为阴极，控制TiO2/SiO2摩尔比为1:1时，电解产物为Si/Ti5Si3，控制TiO2/SiO2摩尔比为1:20、1:25和1:50时，电解产物为Si/TiSi2复合物。在200 mA·g-1放电电流密度下，当硅钛摩尔比为1:1时，首次嵌锂比容量仅有1410.5 mAh·g-1，首次库伦效率为80.72 %；当硅钛摩尔比为1:20时，首次嵌锂比容量增加到2107.02 mAh·g-1，首次库伦效率为89.95 %；当硅钛摩尔比增加到1:25时，首次嵌锂比容量为2303.38 mAh·g-1，首次库伦效率为81.99 %；当硅钛摩尔比增加到1：50时，首次嵌锂比容量为2498.60 mAh·g-1，首次脱锂比容量为1753.68 mAh·g-1，首次库伦效率仅有70.69 %。控制硅钛摩尔比为1:20时，可以获得最好的储锂性能。项目执行期内发表论文8篇，授权发明专利1篇。