LITHIUM INSERTION IN SPUTTERED VANADIUM-OXIDE FILM

Vanadium oxide films have been prepared by RF-sputtering using an oxygen containing sputter ps and a V2O5 target. The main component of these films is orthorhombic V2O5 with poor crystallinity and a tendency for ordering of the crystallites with the c-direction parallel to the substrate. All films were oxygen deficient compared to V2O5. Films prepared in pure argon were reduced to V(4) or lower. The vanadium oxide films were tested in solid-state lithium cells. Films sputtered in oxygen showed electrochemical properties similar to crystalline V2O5. The main differences are a decreased capacity above 3.0 V, showing that V is partially reduced, and a broadening of the capacity peaks, showing that the crystallinity of these films is rather low. The film sputtered in argon behaved differently, discharging at a very low potential, 1.9 V versus Li, in the first cycle. In subsequent cycles the average insertion potential was increased due to a structural distortion of the host.