Cobalt oxide thin film prepared by an electrochemical route for Li-ion battery

Cobalt oxide (CoO) thin film was prepared by the calcination of its precursor (Co(OH)2) electrodeposited in the Co(NO3)2 and NaNO3 aqueous solution. The characteristics of Co(OH)2 and CoO were analyzed by SEM, FTIR and XRD, respectively. The FTIR analysis revealed that the cobalt hydroxide was of the form α-Co(OH)2, which could be converted to β-type by immersing in KOH solution. The pure CoO could be obtained by calcining α-Co(OH)2 at a temperature greater than 500 °C in high purity N2 atmosphere. Increasing the run number for electrodepositing α-Co(OH)2 from 2 to 6, the weight of α-Co(OH)2 and CoO decreased from 0.913 and 0.700 mg to 0.750 and 0.525 mg due to the decrease in the pH of the electrolyte with the run number. The grain size of CoO decreased from 12.88 to 6.98 nm by decreasing the pH for preparing α-type precursor from 3.30–3.14 to 2.82–2.71. The morphologies of CoO and α-type precursor found from the SEM images were to be nano-fibrillar structures. Using CoO synthesized by calcining α-Co(OH)2 electrodeposited at pH 3.30–3.14 as the cathode, the maximum discharge capacity of Li/CoO coin cell was obtained to be 1589.4 mAh g−1. The irreversible discharge capacity of the Li/CoO coin cells at the first cycle could be recovered in the following activation cycles.