Silicon oxide thin films featuring different stoichiometries (SiOx, x = 0.72, 1.23, and 1.58) are prepared using radio frequency sputtering, and the electrochemical behaviors of these films as anode materials for lithium ion batteries are investigated. X-ray photoelectron spectroscopy and glazing incidence X-ray diffraction measurements are conducted at different discharge/charge potentials. The results reveal that the main lithium silicates phases observed during lithiation/delithiation processes are Li2Si2O5, Li6Si2O7, and Li4SiO4. Films featuring high O stoichiometries tend to form silicate phases exhibiting high O stoichiometries, which present high redox potentials. The Li2Si2O5 phase is a kinetically favorable phase and primary reversible product of the lithiation process, while the Li6Si2O7 and Li4SiO4 phases appear to be the irreversible products of films presenting high O stoichiometries during the early lithiation/delithiation cycles within the redox potential range of 0.01–1.5 V. However, if the delithiation potential is increased to 3 V, the LiSi2O5 and Li6Si2O7 phases appear to be reversible during the early lithiation/delithiation cycles. The Li4SiO4 phase, which is the main silicate phase of SiO1.58, remains irreversible. The SiO1.58 film presents the specific capacities of 1129, 1044, 854, and 828 mAh/g at the charge/discharge rates of 0.1, 0.5, 1, and 5 C, respectively, after 200 cycles.