氟化咪唑基离子液体体系电沉积制备太阳能级硅薄膜

Based on the purpose of reducing the fabrication cost of solar grade silicon, high purity silicon oxide is chosen as raw material to produce solar grade silicon thin films by electrodeposition in ionic liquids. By measuring the dissolution behavior of SiO2 in the ionic liquids, the solubility which functions with temperature and the composition of the electrolyte are modeled. The ionic structures of silicon in ionic liquids are investigated using Spectrum methods, and the related physicochemical issues of SiO2 dissolution behaviors in ionic liquids are described. The diffusion and mass transfer, crystallization and nucleation of the electrochemical reactive species on both cathode and anode electrodes are investigated using the techniques of cyclic voltammetry, electrochemical impedance spectroscopy, electrochemical quartz crystal microbalance and scanning electrochemistry microscope. Meanwhile, the transfer and dissapation between the energy and mass in the system are concluded. The ionic structure of electrolyte located in several positions including the center of electrolyte, the vicinity of electrode, the interface between electrode and electrolyte, and the surface of electrode, are monitored and detected using electrochemical in-situ Raman spectroscopy, Resonance Raman spectoscopy and Convolution voltammetry techniques. The mechanism of conversion and transference process of the reactive species ions which converses starting from initial state to intermediate state, and to final product, are analyzed in the level of electron, ion and molecular according to the coupling orientation and style between the electrons and ions，which is used to describe and illustrate the mechanism and behaviors of silicon electro-deposition and oxygen absorption, desorption and evolution on anode surface. A completely explanation and description of the physicochemical issue on the whole process is anticipated. It will be used as a principle and practice guidance to produce solar grade silicon using silica as a solute and extract metal from ionic liquids using oxide as a solute.

基于大幅降低太阳能电池成本的目的，用SiO2为原料在离子液体中电沉积制备太阳能级硅薄膜。研究SiO2在离子液体中的溶解行为，建立溶解度与温度、组成关系的数学模型，用光谱技术研究硅在离子液体中的离子结构，阐明SiO2溶解过程的物理化学问题；采用电化学石英微晶天平、扫描电化学显微镜及循环伏安和电化学交流阻抗谱技术，揭示电极过程的质能转化及耗散规律，探明电极反应的扩散传质、结晶成核及吸/脱附等动力学问题；通过电化学原位及共振拉曼光谱和卷积伏安法，原位检测电极反应中电解质本体、电极近液层、电极界面上的离子结构和印迹，获得反应离子经由中间体到产物的转化迁移规律，从电子、离子、分子等微观层面分析、表征离子与电子键合的构型及取向，推演阴极电沉积硅薄膜和阳极析氧反应历程和机理，解析整个过程相关物理化学问题，为低成本制备太阳能级硅和在离子液体中氧化物的电化学冶金提供理论指导。

经济快速发展加速了化石能源的消耗速度，部分地区化石能源资源几近枯竭，需要开发太阳能等二次资源。光伏发电用的太阳能级硅，因制作流程长、副产物多、能耗高，使其成本很高，本研究用电解法电解氧化硅制备硅。研究结果发现氟化咪唑等氟化物离子液体可以溶解二氧化硅，电沉积得到Si，但溶解度较低，沉积效率慢。在氟化物熔盐中二氧化硅有较高溶解度，可以较高效的电沉积Si。同时，我们在研究离子液体电解硅的过程中，合成了一些能电解活泼金属的离子液体，研究了电沉积活泼金属过程的物理化学问题，具体结果如下：.首先，我们合成了吡啶、吡咯和咪唑氟化物，发现氟化咪唑可以溶解二氧化硅，并且在石墨基体上电沉积得到硅；氟化物-氯化铝离子液体可以溶解氧化亚铜、氧化锌和氧化铅等金属氧化物，且电沉积得到金属；合成了可溶解氧化锂、氯化锂和氯化钕的离子液体碳酸乙烯酯-氯化铝（EC-AlCl3）；合成了可以溶解氯化镧的离子液体咪唑啉酮-硝酸锂（DMI-LiNO3）。.其次，我们研究发现摩尔比6:4的氟化钠硅酸钠是电解二氧化硅较好的电解质组成，940℃时二氧化硅溶解度为5.35克。Si的还原为两步且不可逆，由扩散控制。Si(IV)的传递系数、扩散系数为2.51、2.5×10-5cm2/s。NaF-LiF熔盐体系添加二氧化硅和硅酸钠后，可在750℃电解硅。两种熔盐体系电沉积都得到纳米硅。将其与碳复合构成Si@C材料作为锂离子电池负极，充电比容量高达1260 毫安克，库伦效率接近100%。.最后，我们研究发现碳酸乙烯酯-氯化铝体系存强酸性离子团[AlCl2(EC)4]+，且有强的亲氧性，可以与Li2O通过桥式结构配位将氧化锂溶解，溶解度达到0.02mol%。氧化锂、氯化锂和氯化钕与[AlCl2(EC)4]+溶剂化反应分别生成 (Li2O)xAlCl2(EC)4–x+、（2Li+ + AlCl4– + 4EC）和（2Nd(III)complex + 3AlCl4– + 3nEC）。通过调整溶质LiCl和NdCl3与AlCl3的摩尔比，可消除体系中[AlCl2(EC)4]+物种，电解得到铝锂合金、金属锂和铝钕合金。咪唑啉酮-硝酸锂体系的阳离子为[Li(DMI)n]+，阴离子为[NO3]–，该体系可溶解氯化镧，XRD检测表明阴极铝基体上电沉积产物为金属镧。