Studies of the structure of vacuum deposited silicon films on metal substrates as anode materials for Li-ion batteries

Our prepared vacuum deposited silicon films on Ni and Cu substrates show excellent cycle performance opposing to the conventional silicon film having short cycle life. In this paper, the reasons for this long cycle behavior were studied by the measurements of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electronic microscopy (TEM) and selected area electron diffraction (SAED). At first glance, it seemed that the vacuum deposited silicon films were amorphous from XRD. However, we found that the films consisted of nano-particles with polycrystalline structure. Large surface energy and specific volume of the nano-crystals kept the structure stable against collapsing during the expansion and shrinkage process under lithium insertion and extraction. Consequently, the vacuum deposited silicon films presented good cycling performance.