Characterization of electrolytic Co3O4 thin films as anodes for lithium-ion batteries

The electrolytic deposition of Co3O4 thin films on stainless steel was conducted in Co(NO3)2 aqueous solution for anodes in lithium-ion thin film batteries. Three major electrochemical reactions during the deposition were discussed. The coated specimens and the coating films carried out at −1.0 V (saturated KCl Ag/AgCl) were subjected to annealing treatments and further characterized by XRD, TGA/DTA, FE-SEM, Raman spectroscopy, cyclic voltammetry (CV) and discharge/charge cyclic tests. The as-coated film was β-Co(OH)2, condensed into CoO and subsequently oxidized into nano-sized Co3O4 particles. The nano-sized Co3O4, CoO, Li2O and Co particles revealed their own characteristics different from micro-sized ones, such as more interfacial effects on chemical bonding and crystallinity. The initial maximum capacity of Co3O4 coated specimen was 1930 mAh g−1 which much more than its theoretical value 890 mAh g−1, since the nano-sized particles offered more interfacial bondings for extra sites of Li+ insertion. However, a large ratio of them was trapped, resulting in a great part of irreversible capacity during the first charging. Still, it revealed a capacity 500 mAh g−1 after 50 discharged-charged cycles.