Si film electrodes with surface-modified Cu current collectors for micro Li batteries

Si film electrodes were fabricated on surface-modified Cu current collectors using an oxidation-reduction process. Flower-like nanostructures (FLNSs) with diameters of 2–3 μm and plate-like nanostructures (PLNSs) with lengths of 1 μm were formed on the Cu foil oxidized at 423 K for 0.5 h, but only the PLNSs remained after sonication. Reduction of the preoxidized Cu foil at 673 K resulted in the formation of plate-like and coral-like nanostructures on the Cu foils reduced for 1 and 3 h and a smooth surface without specific structures on the Cu foil reduced for 6 h. The best electrochemical properties in terms of the first columbic efficiency (85.4%) and the cycle performance (67.3% at 50 cycles) were obtained from the Si film electrode fabricated on the Cu foil that had been reduced for 3 h because the coral-like nanostructures on the Cu foil enhanced the adhesion of the Si film and improved the structural stability of the Si film electrode during the electrochemical reactions.