Minimizing Shape Change at Zn Sponge Anodes in Rechargeable Ni–Zn Cells: Impact of Electrolyte Formulation

The historically poor electrochemical rechargeability of Zn in alkaline electrolyte has hindered the commercial viability of Ni–Zn batteries, a system otherwise of interest because of high specific energy (up to 140 Wh kg–1). We have redesigned the Zn anode as a three-dimensional (3D), monolithic porous architecture ("sponge") that exhibits unprecedented Zn specific capacity and dendrite-free cycling. Maintaining the integrity of the 3D Zn sponge architecture throughout charge–discharge is required to ultimately achieve technologically relevant performance in terms of cycle life and capacity. En route to this goal, we systematically evaluated a series of electrolyte and electrode additives used in conjunction with our Zn sponge anode in order to down-select formulations that minimize electrode shape change with cycling in prototype Ni–3D Zn cells. The classes of additives chosen for this study include those that either inhibit ZnO passivation during discharge (Type I: LiOH, K2SiO3) or promote it (Type II/III: KF, K2CO3, ZnO, Ca(OH)2), as well as combinations thereof. We find that the second class of additives effectively retains the cycled Zn sponge in its pre-cycled condition.