Electrochemical study of NiO nanosheets: toward the understanding of capacity fading

NiO nanosheets are prepared by calcination of nickel hydroxide nanosheets, obtained by the hydrolysis of trans-bis(acetato-κO)bis(2-aminoethanol-κ2 N,O)nickel(II) complex. BET analysis reveals the presence of a high specific surface area of 48 m2g−1 and a pore volume of 0.26 cm3g−1 after calcination at 400 °C. The two-dimensional NiO nanostructure undergoes a reversible lithium ion uptake and release revealing an initial unexpectedly high capacity of ~1100 mAhg−1 at a cycling current of 400 mAg−1, exceeding the theoretical capacity of NiO (718 mAhg−1). We attribute this high storage capacity to the advantageous two-dimensional morphology of the sample, namely to the presence of agglomerates composed of NiO nanosheets, allowing a pronounced Li-ion storage through the insertion mechanism and by the formation of a polymer-like layer at the samples internal surfaces. However, after 20 cycles the recovered capacity diminishes rapidly due to the onset of Li-ion intercalation into NiO, which is found less reversible. In addition, an increase in the charge transfer resistance and increase in the electrode polarization, measured by differential capacity, contribute to the analyzed capacity decay upon continuous cycling.