高频热等离子体氢强化还原制备纳米硅粉及在锂离子电池负极的应用研究

Silicon stands out as the most promising material for the next generation LIBs due to its known highest theoretical capacity (4200 mA h g-1) and appropriate voltage platform. However, silicon as anode material is severely hindered by low electric conductivity and the huge volume changes during lithium insertion/extraction process, which cause the silicon particles dramatically pulverized and eventually lead to the capacity rapidly fading. Si nanopowders is known as one method to solve the above problems, however, the existing techniques with the disadvantages of high cost and wide distribution of particles size can not meet the requirement. In this research, SiCl4 as the starting materials are reduced with H2 in the RF thermal plasma, which develops the enhancement of hydrogen plasma reductive reaction. Considered it is easy to aggregate in the heat process, we add carbon in the Si slurry of washed HCl and get C/Si composite after spray granulation. This technique has the advantage of Si with fine particles size, and highly dispersive condition and low cost. The feature of hydrogen plasma will be characterized using optical emission spectroscopy diagnosis of radio frequency thermal plasma, dynamic process of SiCl4 reductive reaction and conversion of reactivity with hydrogen plasma. Enhancement of SiCl4 reductive reaction with hydrogen thermal plasma will be used to prepare the Si nanopowders with highly dispersive condition. The effects of concentration of hydrogen plasma, concentration of SiCl4, reaction temperature and reaction time on the conversion will be considered, and the parameters of preparation of Si nanopowders will be given. The study will give a new process for reductive reaction with hydrogen plasma and help to development of outfield intensification.

硅负极是未来最具潜力的锂离子电池负极材料，但硅负极电导性差且充放电过程中伴随着巨大的体积膨胀，纳米化是解决硅体积膨胀的重要途径之一，而已有的纳米化技术因成本、粒度控制等原因，难以满足锂离子电池硅负极商用化要求。本项目以SiCl4为原料，采用氢热等离子体强化还原制备纳米硅粉，结合水洗硅粉表面HCl过程形成的纳米硅浆料，加入碳形成硅碳复合浆料，经喷雾造粒形成硅碳复合负极材料。兼有粒度细、分散好和价格较低的综合优势。研究氢活性粒子强化SiCl4还原和硅转化率提高的机制，建立氢活性粒子影响转化率的规律；解析氢活性粒子对纳米硅颗粒生长的影响，探寻调控纳米硅大小和形貌的因素，构建扩散-反应竞争协调的介尺度结构与纳米硅粉结构性能之间关系；研究硅碳复合结构中纳米硅在充放电过程结构的演变，获得满足循环稳定的硅碳负极材料。氢活性粒子强化还原反应和调控颗粒生长的研究，能够为等离子体外场强化化工过程提供新的基础。

硅碳负极是极具潜力的锂离子电池负极材料，但由于硅的电导性差且充放电过程中伴随着巨大的体积膨胀，已成为制约硅碳负极工业化应用的关键难题，硅颗粒的超细化（纳米化）是解决硅体积膨胀的重要途径之一。本项目采用高频感应热等离子体制备超细纳米硅，充分挖掘了气相合成过程颗粒大小调控技术和氢等离子体强化还原反应的特点，把颗粒大小调控与氢还原SiCl4反应高转化率有机结合起来，实现了超细纳米硅的可控制备，制备的纳米硅表现出了优异的电化学性能。.采用热等离子体光谱诊断进行了氢热等离子体强化还原SiCl4反应过程中氢活性粒子的演变行为研究，结合硅生长过程的热力学和动力学研究了氢热等离子体还原过程纳米硅的生长调控机制，并进行了等离子体强化还原过程扩散-反应竞争协调的介尺度机制的解析，研究了表面吸附HCl对纳米硅性能的影响及脱出工艺，探讨了制备的纳米硅在锂离子电池负极充放电过程中的结构演变行为。研究表明，等离子体产生的氢活性粒子有助于促进SiCl4还原反应的进行，同时，热等离子体中氢也会影响硅颗粒的生长行为，反应物氢与SiCl4的比率依然是影响转化率的关键因素，提高氢的比例可显著提升转化率；通过调控等离子体参数、氢与SiCl4的比率等可有效调控硅颗粒的大小，硅颗粒可在30-100nm调控。水洗可有效脱除硅颗粒表面吸附的副产物氯和氯化氢，水洗与喷雾造粒有机结合可避免硅颗粒团聚，获得性能优良的硅碳负极材料。