High capacity and long cycle life silicon anode for Li-ion battery

A silicon film was deposited on a Ni or Cu foil in vacuum up to a thickness of 4 μm and the Li insertion/extraction behaviour was evaluated under constant current charge/discharge in an electrolyte solution of propylene carbonate containing 1 M LiClO4. The surface of a 30 μm thick Ni foil was roughened by etching with FeCl3. The Li insertion/extraction performance was strongly dependent on the roughness factor. A thick silicon film is necessary for practical application. However, the cycle performance as well as the Li accommodation capacity was markedly depressed when the film thickness was increased. We found that the roughening of the substrate surface was a key factor for attaining good performance with a thick film. Surface roughening was found to be very effective, but the best performance was obtained by the use of an electrolytically deposited Cu foil on which a silicon film was vacuum-deposited rapidly.