Multi-layered Cu/Si nanorods and its use for lithium ion batteries
Abstract An ion assisted oblique angle (80°) electron beam deposition method was used to form well-aligned nanorods of a multi-layered Cu/Si film. For comparison, a flat multilayered Cu/Si film was coated at 0° angle using the same electron beam deposition system. The galvanostatic test results demonstrated that both electrodes performed better cycleability compared to bulk Si anode because the multilayer structure of the films enhanced the degree of atomic interactions between Cu and Si to form nano-sized intermetallics. Moreover, Cu buffered the mechanical stresses caused by lithiation and improved the electrical conductivity of the whole film which also affected the cycle life of the multilayered thin film anodes. Galvanostatic half-cell measurements showed that the Cu/Si film made of well aligned nanorods exhibited 1700 mA h g −1 as initial discharge capacity then it decreased to 500 mA h g −1 after 1st cycle (with 99% coulombic efficiency) and became stable for 100 cycles. The remarkable high coulombic efficiency, capacity retention and stable performance of the electrode are related to its unique structural morphology: the high surface area of nanorods increased the contact area of the anode with Li, decreased polarizations and enhanced mechanical resistance against volumetric changes due to the homogenously distributed nano-sized interspaces among them.