An amorphous Si thin film anode with high capacity and long cycling life for lithium ion batteries

A Si thin film of thickness 275 nm was deposited on rough Cu foil by magnetron sputtering for use as lithium ion battery anode material. X-ray diffraction (XRD) and TEM analysis revealed that the Si thin film was completely of amorphous structure. The electrochemical performance of the Si thin film was investigated by cyclic voltammetry and constant current charge/discharge test. The film exhibited a high capacity of 3,134 mAh g⁻¹ at 0.025 C rate. The capacity retention was 61.3% at 0.5 C rate for 500 cycles. An island structure formed on the Cu foil substrate after cycling adhered to the substrate firmly and provided electrical connection. This is the possible reason for the long cycling life of Si thin film anode. Moreover, the cycling performance was further improved by annealing at 300 °C. The Li⁺ diffusion coefficients (D ₀) of Si thin film, measured by cyclic voltammetry, are 1.47 × 10⁻⁹ cm² s⁻¹ and 2.16 × 10⁻⁹ cm² s⁻¹ for different reduced peaks.