A thin film silicon anode for Li-ion batteries having a very large specific capacity and long cycle life

A thin film of Si was vacuum-deposited onto a 30 μm thick Ni foil from a source of n-type of Si, the film thickness examined being 200–1500 Å. Li insertion/extraction evaluation was performed mainly with cyclic voltammetry (CV) and constant current charge/discharge cycling in propylene carbonate (PC) containing 1 M LiClO4 at ambient temperature. The cycleability and the Li accommodation capacity were found to depend on the film thickness. Thinner films gave larger accommodation capacity. A 500 Å thick Si film gave a charge capacity over 3500 mAh g−1 being maintained during 200 cycles under 2 C charge/discharge rate, while a 1500 Å film revealed around 2200 mAh g−1 during 200 cycles under 1 C rate. The initial charge loss could not be ignored but it could be reduced by controlling the deposition conditions.