Electrochemical Synthesis of Lithium Dicobalt Tetraoxide for Thin Film Lithium-Ion Batteries

Abstract

Lithium cobalt oxide coatings on 304 stainless steel substrates have been carried out by using cathodic electrochemical synthesis in LiNO3 and Co(NO3)2 aqueous solution and subsequent annealing for thin film lithium-ion batteries. The as-deposited film is composed of the mixture of Co(OH)2·H2O and LiOH, condensed into lithium di-cobalt tetraoxide (LiCo2O4) at 310°C, and transformed into lithium cobalt dioxide (LiCoO2) and Co3O4 at 500°C, identified by X-ray diffraction (XRD) and thermal gravitational/differential thermal analysis (TGA/DTA). The two-layer structured film is observed by field emission scanning electron microscopy (FE-SEM). Cyclic voltammetry (CV) reveals the oxidation peaks at 3.75 V and 3.98 V, and the reduction peaks at 3.43 V and 3.89 V (vs. Li/Li+) for LiCo2O4 and LiCoO2, respectively. The charge/discharge test of LiCo2O4 reveals the greater reversibility and capacity at 10 μAcm−2 between 3.8 and 3.2 V (vs. Li/Li+), compared with that between 4.2 and 2.5 V. LiCo2O4, not successfully synthesized by solid state reaction at moderate temperature before, has been originally prepared by electrochemical synthesis and subsequent annealing at low temperatures (≦310°C) which could provide a suitable choice for preparing thin film lithium ion batteries applied to flexible 3C electronic products of low-cost.