Improved Electrochemical Performance of Zinc Anodes by EDTA in Near-Neutral Zinc-Air Batteries

The influence of ethylenediaminetetraacetic acid (EDTA) electrolyte additive on the performance of Zn-air batteries with near-neutral chloride-based electrolytes was examined for primary and secondary batteries. The electrochemical measurements indicated that Zn is not completely active in neat 2 M NaCl, but still could be discharged up to 1 mA cm(-2) around -1.0 V-Ag/AgCl. The characterization of the Zn surfaces revealed the existence of a passive film consisting of Simonkolleite, Zn(OH)(2), and/or ZnO. The EDTA additive enhanced the discharge voltages by 200 mV to -1.2 V-Ag/AgCl indicating an active Zn surface. The effect of EDTA is explained by its chelation abilities with Zn2+ before formation of hydroxide or oxide species. The Zn-air cells with EDTA were operated up to 930 h with specific energies up to 840 Wh kg(Zn)(-1). The cells could also be cycled up to 70 cycles while providing enhanced discharge voltages at 1.15 V over 50 cycles. The positive effect of EDTA is dependent on the amount of free EDTA molecules. Nevertheless, the Zn-air cells showed better performance in terms of higher discharge voltage, discharge energies, and lower overpotentials in presence of EDTA.