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.