Li insertion/extraction reaction at a Si film evaporated on a Ni foil

In an attempt to provide a Si material having a long cycle life as an anode of Li-ion batteries, we prepared a metallic Si film on a Ni foil by a vacuum evaporation method. Due to the presence of a naturally formed compact passivation film on the Ni foil, a homogeneous, compact amorphous-like Si film strongly adhering to the Ni substrate could be obtained very easily. The Si film thus obtained on a Ni foil was evaluated electrochemically with cyclic voltammetry (CV) and constant current charge/discharge cycle test (CT) in two types of solvents containing 1 M LiClO4, i.e. propylene carbonate (PC), and a 1:1 (v/v) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). Two strong peaks were observed on the anodic branch of the CV at 300 mV (versus Li/Li+) and 500 mV and the constant current discharge curve of CT produced a wide plateau at around 400 mV in EC/DMC with a discharge capacity of 1700-2200 mAh/g at a discharge rate of 2C. Nearly the same performance was observed as well in PC, where no solvent decomposition was detected. The capacity depended on the preparation conditions and the film thickness. The cycleability at 2C charge/discharge rate was over 750 cycles. One of the important issues to solve is to reduce the large initial charge loss. (C) 2003 Elsevier Science B.V. All rights reserved.