Surface-modified Si thin film electrode for Li ion batteries (LiFePO4/Si) by cluster-structured Ni under layer

Abstract

An amorphous Si film with thickness of 350 nm was fabricated on both Cu substrate and Ni film (under layer)/Cu substrate by direct current (DC) and radio frequency (RF) magnetron sputtering. The surface morphology, crystallographic structure and electrochemical properties were investigated. Flat surface was formed in Si/Cu film, whereas in Si/Ni/Cu film a rough surface was formed consisting of Si clusters. In a Si/Li half-cell test with current densities of 210 (0.05 C-rate), 810 (0.2 C-rate) and 4200 mA g(-1) (1 C-rate), the surface-modified Si film electrode exhibited a significantly improved cycle performance compared to the Si film deposited on only Cu substrate. LiFePO4/Si full cell tested at current density 85 mA g(-1) of (0.5 C-rate) displayed the first charge capacity of 154.0 mAh g(-1), corresponding to 90.5% of theoretical capacity of LiFePO4 and the capacity retention of 79.4% at 20th cycle. (C) 2008 Elsevier B.V. All rights reserved.