Unique electrochemistry of Zn electrode in Zn-EDTA aqueous solutions and its application for high-voltage Zn-MnO2 cell

Abstract

• Strong chelation ability of EDTA brings about unique electrochemistry of Zn electrode in Zn-EDTA aqueous electrolyte. • Stripping potential of Zn anode in 0.1 M Zn-EDTA solution keeps unchanged with applied currents. • Nucleation over potential of Zn is much larger in 0.1 M Zn-EDTA than that in 0.1 M ZnCl 2 . • MnO 2 -Zn full cell using 0.1 M Zn-EDTA reveals 2.05 V voltage and 86.4 % capacity retention after 500 cycles. The poor reversibility of Zn anode in aqueous solution is ascribed to many parasitic reactions, such as passivation, dendrite growth, shape change, and hydrogen evolution. Here a simple strategy is reported that employs ethylene diamine tetraacetic acid disodium salt (Na 2 EDTA) as chelant to form Zn-EDTA coordination ion so as to increase the polarizability of zinc deposition, suppress dendrite generation and growth, and accordingly improve the reversibility of Zn anode. By this means, zinc anode displays good reversibility for 740 charge/discharge cycles at 8 mA cm −2 . In addition, the stripping potential of zinc anode keeps stable at −1.05 V vs SCE in the wide range of current density from 1 to 20 mA cm −2 , boosting a 2.05 V MnO 2 -Zn full cell which exhibits a discharge voltage retention rate of 83 % after 500 continuous charge/discharge cycles.