Cobalt-Nickel Double Hydroxide toward Mild Aqueous Zinc-Ion Batteries

Transition metal layered double hydroxides (LDHs) are widely used as high-performance cathode materials for aqueous alkaline zinc (Zn) batteries. Yet, the strongly alkaline electrolytes may lead to undesirable rechargeability of the alkaline devices and environmental issues. Herein, as a research prototype, CoNi LDH material is designed with abundant H vacancies using electrochemical methods (denoted as CoNi LDH(v)). As a Zn-ion battery cathode, CoNi LDH(v) exhibits promising electrochemical performances in mild ZnSO4 electrolyte, such as a good specific capacity of 185 mAh g(-1) at the current density of 1.2 A g(-1), a high average discharge potential of 1.6 V versus Zn2+/Zn, and a large energy density of 296.2 Wh kg(-1) at the power density of 1894 W kg(-1), outperforming most of the cathode materials for aqueous Zn-ion batteries. Experimental and computational results indicate that the introduced H vacancies in the double hydroxide matrix induce the improved electronic conductivity and cation adsorption thermodynamics, endowing the double hydroxides with good electrochemical activity for reversible cation insertion. Structural and spectroscopy studies identify that CoNi LDH(v) experiences reversible H+/Zn2+ co-intercalation mechanism in an aqueous ZnSO4 electrolyte. As far as it is known, it is the first report on transition-metal-based double hydroxides used for mild aqueous Zn-ion batteries.