Mesoporous layered hexagonal platelets of CoO nanoparticles with (111) facets for battery applications: high performance and ultra-high rate capability.

The thermally stable and crystalline 2D layered mesoporous hexagonal platelets of cobalt oxide (CoO) with (111) facets were prepared by using the template-free wet chemical synthesis approach. The high surface energy (111) facets known for a highly electroactive surface are expected to enhance the electrochemical properties, especially the rate capability. The highly crystalline CoO with an average particle size of 25 nm formed a 2D mesoporous layered structure, with an average thickness of ∼40 nm, a pore size of 8-10 nm, and a specific surface area of 45.68 m g promoting large surface confined electrochemical reaction. The 2D layered mesoporous CoO exhibits a maximum specific capacity of 305 mA h g at a scan rate of 5 mV s and 137.6 mA h g at a current density of 434.8 mA g. The maximum energy and power densities of 32.03 W h kg and 9.36 kW kg, respectively, are achieved from the 2D hexagonal platelets of mesoporous CoO nanoparticles with (111) facets. An excellent ultra-high rate capability of ∼62% capacity retention was observed after increasing the discharge current density from ∼434.8 mA g to 43 480 mA g. Furthermore, a cycling stability of 81.25% was achieved even after 2020 charge-discharge cycles at a current density of 12 170 mA g. This high performance and ultra-high rate capability could be attributed to the (111) facets 'crystal plane' effect of CoO. Our results presented here confirm that the 2D mesoporous layered hexagonal platelets of CoO exhibit "battery-mimic" behaviour in an aqueous electrolyte of KOH.