ABSTRACT
The corrosion and dendritic growth of the Zn anode limit its electrochemical performance in aqueous Zn batteries. Here, we present an amphoteric betaine additive for 5 m ZnCl2 aqueous electrolyte. The carboxyl group on betaine forms hydrogen bonds with water and reduces the water activity. The molecule also experiences preferential adsorption on the Zn surface and separates the interactions between Zn and water. Side reactions at the Zn electrode are thus inhibited. The regulated interface also ensures uniform Zn deposition. As a result, the electrolyte with betaine additive allows reversible Zn plating/stripping for over 1400 h at 0.5 mA cm-2. A capacity retention of 94% is obtained after 3000 cycles for a VO2 cathode.
ABSTRACT
The transformation of polyanion cathodes into oxides in aqueous Zn batteries results in voltage decay. Herein, we uncover a polyanion dissolution and oxide re-electrodeposition process for this transformation. Accordingly, the dissolution is inhibited by reducing the water activity in the electrolyte with the hydrogen bond regulator of glucose (Glu). In the 4 m Zn(OTf)2/5.5 m Glu electrolyte, the VOPO4·2H2O cathode maintains the redox reactions at a high voltage of 1.6 V/1.5 V with stable capacity retention during cycling at different rates. It also shows promising electrochemical activity and stability at temperatures down to -20 °C.
