Amorphous Silicon-Coated Carbon Nanofibers Composite as Anode Material for Lithium-Ion Batteries

Silicon can be considered one of the most promising anode materials for lithium ion batteries (LIBs) as it has a low charge/discharge voltage at room temperature and exhibits the highest known theoretical lithiation capacity in combination with good safety characteristics. However, the silicon anode experiences enormous volume changes during repeated lithium insertion/extraction processes in every charge/discharge cycle. This leads to severe particle pulverization and results in a quick electrode structure failure. Moreover, the Si has to be amorphous, as crystallized Si can hardly alloy with lithium at room temperature. Amorphous Si thin films are currently manufactured by techniques such as chemical vapor deposition, that usually, are quite expensive, have complex equipment design and have slow rate of deposition. Electrodeposition of Si can offer a suitable alternative method of producing a thin film of amorphous Si by much easier and lower cost means. In this study electrodeposited amorphous silicon on carbon nanofibers (CNFs) have been investigated as the anode material for LIBs. Electrically conductive CNFs are produced by electrospinning and later heat treating of polyacrylonitrile (PAN) precursor. It is shown that the macromorphology of electrospinning-derived CNFs template provides enough space to accommodate the silicon volume expansions. By controlling electrodeposition parameters, cycle-ability of the anode material was optimized. It is envisaged that exceptional characteristics of CNFs and the electrodeposited Si will make the composite material an ideal candidate for the anode material of high-power LIBs.