鋰離子電池多孔性矽負極材料製備與分析

Abstract

在過去的十年當中，由於矽相較於石墨而言，具有有絕佳的比電容量（~3500 mAh/g），而受到重視。然而矽在充放電的過程當中，伴隨劇烈的體積膨脹收縮與本身所具有的低導電度特性，使得矽負極材料在商業化應用上受到了阻礙。 本論文之目的在於開發以矽為主體的鋰離子二次電子負極材料。根據前人的研究，我們可以知道矽碳複合材料的應用，可以改善上述矽應用在鋰離子電池所遭遇到的問題。本研究試圖進一步從矽本身作改善為出發點，藉由提高矽的表面積，在材料本身預留孔洞的方式，來緩衝矽在充放電過程時，所造成的體積劇烈變化。 我們應用半導體製成中蝕刻的技術，利用氧化劑以及氫氟酸水溶液來製備多孔矽，實驗結果顯示，此方法確實可以在矽表面上產生許多的孔洞。並且在定電容(1000mAh/g)充放電初步測試中，相較於矽(<8cycles)或碳矽複合材料(~80cycles)所組裝的電池，有碳層匹覆的多孔矽材料具有100圈以上的循環壽命，此結果對於理離子二次電池負極材料的開發，有明顯的進展。

In the last decade, silicon has attracted much attention because it has a high specific capacity (~3600 mAh/g) compared to graphite (372 mAh/g). However, silicon is known for its intrinsic low conductivity while possessing a dramatic volumetric variation during cycling, which results in structural instability and poor cyclability that hinders its commercial application. The main objective of this research is to explore new materials based on silicon for the lithium-ion battery. According to past investigations, Si-C composite materials are developed to overcome the inherent problems of silicon. But now, intrinsic silicon is further improved, increasing the surface area on the silicon surface. The preset intra-particle voids have been shown to help in accommodating volume expansion arising from the Si. The preparation of porous silicon applies etching technology used typically in semiconductor manufacturing as well as the use of an oxidizing agent and hydrofluoric acid solution. Results showed that this method produces many pores on the Silicon surface, and gave an outstanding performance of more than 100 cycles without fading under constant capacity (1000mAh/g) charge-discharge. This performance is a significant improvement over intrinsic Silicon and Carbon-coated intrinsic silicon in electrodes which only sustain less than 8 cycles and 80 cycles, respectively.