以四氯化矽透過鋁還原反應製備奈米矽之研究

Abstract

太陽能 (PV) 在 2020 年實現了 138 GWh的全球年安裝量，每年矽的使用量超過 40,000 噸。四氯化矽是在處理冶金級矽形成多晶矽過程中產生的廢液。每生產一噸多晶矽，將生產近三到四噸四氯化矽。因此，四氯化矽作為潛在矽源的回收再利用方法是促進工業循環經濟的關鍵問題。因此，本研究將通過在更溫和的反應條件以及更低的排放過程中還原四氯化矽來生產奈米矽薄片。由於矽的高電池容量和奈米矽薄片克服體積膨脹和粉化問題所需的性能，所生產的奈米矽薄片將用作鋰離子電池應用的陽極材料。本研究用3微米球狀鋁粉為起始原料並通過研磨技術和特製研磨漿料配方來把球狀鋁打薄成約10多奈米銀鋁粉。本文中奈米矽薄片的生產將通過將自製奈米片狀銀鋁粉與化學計量比為10%過量的四氯化矽在 225 oC 下反應來完成。還原過程將生成氯化鋁和奈米矽薄片，經清洗便可獲得用於電化學測試的厚度約10納米的高純度片狀矽。因片狀物的堆叠對電池的循環表現影響巨大，本文將通過噴塗方式備製極片用於電池測試，並分別在2.1A/g和4.2A/g高電流100圈充放電條件下有2327 mAh/g和1687mAh/g比電容表現。本文的奈米矽薄片與傳統的奈米矽薄片製備方法相比，所提出的合成方法具有可擴展性和環境友好性，因為所使用的合成溫度低，不涉及複雜的原料製備和副產物去除過程，減少產生的廢水和廢氣。

The photovoltaic sector has achieved 138 GW global annual installations in 2020 and the use of silicon is more than 40,000 tonnes annually. Silicon tetrachloride is an undesired waste generated during the treatment of metallurgical grade silicon to form polysilicon. There are almost three to four tonnes of silicon tetrachloride will be produced for each tonne of polysilicon generation. Thus, the method of recycling and reusing silicon tetrachloride as a potential silicon source is a critical issue for promoting the circulatory economy for industries. Therefore, this paper aims to produce silicon nanosheets through the reduction of silicon tetrachloride in a milder reaction condition as well as a lower emission procedure. Due to the high galvanic capacity of the silicon and the desired properties of the nano-silicon sheet to overcome the volumetric expansion and pulverization problem, the nano-silicon sheet produced will be used as anode material for LIB application. The production of the nano-silicon sheet in this paper will be done by reacting the aluminum leafing powder and 10 % stoichiometric ratio excess silicon tetrachloride at 225 oC. This paper will use the 3 um spherical aluminum powder as the starting material and use the high-speed milling process to reduce the thickness of the aluminum leafing with the aid of milling aid. Aluminum chloride and silicon nanosheet will be generated as the product of the reduction process and the high purity silicon nanosheet is obtained for electrochemical testing after the washing procedure. Due to the stacking of the silicon nanosheet affecting cyclability to a certain extent, the electrode in this work is prepared using the spray coating method to ensure layer-by-layer stacking. For 100-cycle electrochemical testing, the spray-coated electrode is still able to retain a high specific capacity of 2327 mAh/g and 1687 mAh/g under the high current rate of 2.1A/g and 4.2 A/g respectively. The proposed synthesis method is scalable as well as environmentally friendly compared to the conventional preparation methods of the silicon nanosheet due to the low synthesis temperature used, no complicated process involved, and minimal wastewater and waste gas generated.