熔盐电化学低温合成微/纳米SiC及其机理研究

Silicon carbides have wide application in many fields due to its thermal stability, high thermal conductivity, wide bandgap and excellent chemical stability,etc. However, the present methods for producing SiC have some disadvantages such as high synthesis temperature resulting large energy consummation, complicated technology, big equipment investment and high operating cost. On basis of technology that electrochemical reduction of SiO2 in molten salt at low temperature, and according to our preliminary results on the synthesis of SiC by molten salt electrochemistry method, we will explore the synthesis technology of micro/nano scale SiC by electrochemical reduction of the composite of C/SiO2.The effects of temperature of molten salt, electrode potential and composition of reactants on electrocehmical behavior of C/SiO2 composite will be studied in order to analyze thermodynamic route and dynamic process of SiC formation and then clear and understand the mechanism of electrochemical synthesis of SiC in molten salt at low temperature. Furthermore, by optimizing the thermodynamic and dynamic factors affecting the formation of SiC, the synthesis method of SiC by electrochemical reduction of C/SiO2 composite in molten salt at low temperature will be set up. The results will have not only important significance on the theoretical and technological development of low-temperature synthesis of SiC and energy conservation for producing SiC, but also supply the experimental and theoretical supports for synthesizing a variety of metal carbides by molten salt electrochemistry method.

SiC具有高温稳定性、高热导率和宽带间隙及好的化学稳定性等优异特性，使其在诸多领域有着广泛的应用，而目前制备SiC的方法存在温度高、能耗大，或工艺复杂、设备投资和运行成本高等不足。本项目借鉴熔盐低温电解SiO2技术，并基于对SiC的熔盐电化学合成的初期研究结果，拟以C/SiO2复合物为原料，研究开发熔盐电化学低温合成微/纳米SiC方法，通过研究熔盐温度、电极电势、反应物组成等因素对C/SiO2复合物的熔盐电化学行为的影响及机制，分析SiC形成的热力学途径和动力学过程，从而明晰熔盐电化学低温合成SiC机理，进而通过优化影响SiC形成热力学和动力学因素，建立熔盐电化学低温合成微/纳米SiC方法,相关研究结果不仅对SiC的低温合成科学技术的发展和SiC生产的节能降耗和减排具有重要意义，而且也将为进一步开拓广泛种类的金属炭化物的熔盐电化学低温合成技术提供实验和理论基础。

SiC具有高温稳定性、高热导率和宽带间隙及好的化学稳定性等优异特性，使其在诸多领域有着广泛的应用，目前制备SiC的方法存在温度高、能耗大，或工艺复杂、设备投资和运行成本高等不足。基于目前碳化硅合成技术的不足，项目开展了以C/SiO2复合物为原料，熔盐电化学低温合成微/纳米SiC热力学和动力学研究，建立了熔盐电化学合成SiC实验装置方法，确立了合成熔盐温度、电极电势热力学参数，及大量合成纳米SiC的动力学电势与温度，提出了C和SiO2基于界面的固相电化学反应机理。此外，项目研发了以分子筛为模板，采用镁热还原技术和CVD 方法，在700℃制备具有双有序介孔和双相（碳、碳化硅）界面的多孔C@SiC复合材料，其作为超级电容器电极材料，展现了良好的比容量、倍率和循环稳定性。项目研究结果相关对SiC的低温合成科学技术、SiC结构调控和SiC生产的节能降耗和减排具有重要意义。.随着新能源汽车行业的发展，对动力锂离子电池能量密度提升需求迫切。硅作为负极理论能量密度高达3570 mAh g-1，是当前应用的石墨的十倍左右。然而，硅在充放电过程中存在严重的体积效应,导致电极材料的粉化,严重影响硅基负极循环稳定性。尽管采用核-壳结构、纳米复合等路线能有效改善其稳定性，但因原料、工艺等导致的高成本，使它们难以商业化。本项目利用镁热还原技术，开展了以硅藻土为原料和自模板硅碳负极材料制备研究，成功制备了具有分级孔结构的硅碳负极，其比容量在0.5A g-1电流密度下循环200次以后仍可达990 mAh g-1, 达到行业要求，且成本远低于目前商业硅基负极材料，具有良好商业应用前景。