Evaluation of Si based composite nanorods used as anodes in LIB

Films with nanorods made of various Cu-Si atomic ratios (10-90%, 20-80%, 30-70%) were fabricated by an ion-assisted oblique angle co-deposition technique. The effect of Cu/Si atomic ratios on the morphologies andthe structures were studied by SEM and XRD. The use of those nanorods as anode materials in lithium ion batteries were evaluated by galvanostatic test results. The SEM analyses demonstrate that during the co-evaporation an increase in Cu/Si atomic ratio decreases the nanorod width and height but increases the nanorod tilting angle. The galvanostatic tests show that the Sample 1 (film having 70% at. Si) performs 900 mAh/g as the first discharge capacity with a higher initial coulombic efficiency (80%) and it retains 40% of its first discharge capacity after 100 cycles due to higher amount of Cu, which improves its geometry and increases the electrical conductivity as well as the mechanical tolerance of the electrode. The samples 2 and 3 (films with 80% and 90%at. Si contents) deliver higher capacities with lower coulombic efficiencies (1720 and 2550 mAh/g with 68% and 54% coulombic efficiencies) compared to Sample 1 because of their amorphous structures and high Si contents. They only retain 30% and 20% of their first capacities after 100 cycles due to limited amount of Cu presence. The results show that an optimization is always required to perform high capacity with a good capacity retention for longcycle life.