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

Abstract

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 LiClO 4, 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 2 C. 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 2 C charge/discharge rate was over 750 cycles. One of the important issues to solve is to reduce the large initial charge loss.