Amorphous Si film anode coupled with LiCoO2 cathode in Li-ion cell

An amorphous silicon film with an average thickness of up to 2 μm was deposited on copper foil by direct-circuit (dc) magnetron sputtering and coupled with commercial LiCoO2 cathode to fabricate cells. Their cycle performance and high rate capability at room temperature have been investigated. In the voltage range 2.5–3.9 V at the current density of 0.2C (0.11 mA cm−2), the lithiation and delithiation capacity of this cell was first increased to 0.55 mAh cm−2 within 80 cycles and maintained stable during the following cycles. After 300 cycles its capacity still retained 0.54 mAh cm−2. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) image indicated that the sputtered film could keep an amorphous structure although the volume expansion ratio during the lithiation and delithiation was still up to 300% after 300 cycles observed from scanning electron microscopy (SEM) image. This recovered amorphous structure was believed to be beneficial for the improvement of the cycle life of the cell. Rate performance showed that the cells had a promising high rate capability. At 30C, its lithiation/delithiation capacity remained 25% of that at 0.2C.