High electrochemical energy storage in self-assembled nest-like CoO nanofibers with long cycle life

Developing efficient electrode material is essential to keep pace with the demand for high energy density together with high power density and long cycle life in next generation energy storage devices. Herein, we report the electrochemical properties of hydrothermally synthesized CoO nanofibers of diameter 30–80 nm assembled in a nest-like morphology which showed a very high reversible lithium storage capacity of 2000 mA h g−1 after 600 cycles at 0.1 mA cm−2 as lithium-ion battery anode. Systematic investigation by ex situ transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and impedance spectroscopy at different cycling stages indicated that the extraordinary performance could be related to an enhancement in the Co2+↔Co x+ (2 < x ≤ 3) redox process in addition to the commonly believed structural and morphological evolution during cycling favoring generation of large number of accessible active sites for lithium insertion. Further, when examined as a supercapacitor electrode in 1.0 M KOH, a capacitance of 1167 F g−1 is achieved from these 1D CoO nanofibers after 10,000 charge discharge cycles at a high current density of 5 A g−1 demonstrating good application potential. Nest-like CoO nanofibers showed a reversible lithium storage capacity of 2000 mA h g−1 after 600 cycles as LIB anode and a capacitance of 1167 F g−1 after 10,000 cycles as electrochemical supercapacitor.