Silicon thin film anodes coated on micron carbon-fiber current collectors for lithium ion batteries

• Si thin films have been sputter deposited on vapor grown carbon-fibers.
• Micron carbon-fibers are used as the current collectors.
• The current collectors can ease the volume-change induced stress.

Si thin films have been sputter deposited on vapor grown carbon-fibers and used as the anode materials for lithium ion batteries. A common issue for the Si anodes is the volume expansion during charge–discharge, leading to severe capacity fading. In this study, micron carbon-fibers (MCFs) are used as the current collectors to ease the volume-change induced stress, and significantly improve the cycling stability. The MCFs were fabricated using thermal chemical vapor deposition on stainless steel substrates. The Si films can be coated on MCFs as characterized by field emission scanning electron microscopy. The electrochemical properties of Si thin film anodes with various Si/MCFs ratios were investigated. The larger quantity of MCFs, the higher specific capacities can be obtained after 200 cycles for a given amount of Si. The cycling stability is enhanced under low Si/MCFs ratios. After 200 charge–discharge cycles, the Si anode deposited on suitable amount of MCFs shows a well rounded surface with very few cracks. The results indicate that the combination of Si anodes and MCFs current collectors can effectively reduce the volume-change induced stress, and enhance the cycling stability.