Review of Battery-type Transition Metal (Cu, Co, and Ni) Oxide Based Electrodes: From Fundamental Science to Fabrication of a Hybrid Supercapacitor Device

Energy storage (electrochemical) devices such as batteries and supercapacitors present crucial components of alternate energy sources which can cater to the high energy requirements around the globe. Enhancing the energy density of supercapacitor electrodes on par with the batteries is yet another challenging target. A way to resolve the issue is the incorporation of battery-like electrodes in the supercapacitor device. Battery-like electrodes rely on the reversible Faradaic reactions happening throughout the electroactive surface area of the electrode for the storage and accumulation of charge. Battery-like electrodes are sometimes misunderstood as pseudocapacitor-type electrodes with Faradaic redox properties, which creates a lot of confusion. Hence the motivation behind this review is first to provide a pristine picture of the fundamentals of battery-type electrodes; second, to differentiate battery-type electrodes from pseudocapacitor electrodes; and finally, to describe some recent trends in the fabrication of hybrid supercapacitor devices (HSCs) taking battery-type transition metal (Cu, Co, and Ni) oxide-based electrodes.