High-Voltage Honeycomb Layered Oxide Positive Electrodes for Rechargeable Sodium Batteries
Abstract
Natural abundance, impressive chemical characteristics and economic feasibility have rekindled the appeal for rechargeable sodium (Na) batteries as a practical solution for the growing energy demand, environmental sustainability and energy independence. However, the scarcity of viable positive electrode materials remains a huge impediment to the actualization of this technology. In this paper, we explore honeycomb layered oxides adopting the composition Na2Ni2-xCoxTeO6 (x = 0, 0.25 and 0.50) as feasible positive electrode (cathode) materials for rechargeable sodium batteries at both room- and elevated temperatures using ionic liquids. Through standard galvanostatic assessments and analyses we demonstrate that substitution of nickel with cobalt in Na2Ni2TeO6 leads to an increase in the discharge voltage to nearly 4 V (versus Na+ / Na) for the Na2Ni2-xCoxTeO6 family of honeycomb layered oxide materials, which surpasses the attained average voltages for most layered oxide positive electrode materials that facilitate Na-ion desertion. We also verify the increased kinetics within the Na2Ni2-xCoxTeO6 honeycomb layered oxides during operations at elevated temperatures which lead to an increase in reversible capacity of the rechargeable Na battery. This study underpins the doping of congener transition metal atoms to the honeycomb structure of Na2Ni2TeO6 in addition to elevated-temperature operation as a judicious route to enhance the electrochemical performance of analogous layered oxides.