The effect of free-moving zincate ions on the MnO2 cathode is studied by both potential dynamic and galvanostatic techniques. Strategies to immobilize zincate ions are provided. We demonstrate that the use of a free standing zincate-absorbing interlayer fabricated of Ca(OH)2 is effective in localizing and trapping the zincate ions, while not affecting the transport of OH- ions. It successfully prevents short-circuit of the battery by suppressing zinc dendrites, and inhibits the formation of zinc manganese spinel phase at high depth of discharge (DOD). Separator featuring selective transport of OH- and [Zn(OH)4]2- ions are investigated as well. We fabricate a graphene oxide/ poly(vinyl alcohol) (GO/PVA) composite membrane with a layered structure. The nanocapillaries formed within the stacked and overlapped GO monolayers as well as the oxygen functional groups which repel the bulky [Zn(OH)4]2- anions are responsible for its ion sieving properties. PVA is impregnated to provide a conductive pathway for OH- ions and to improve the mechanical stability. Here we successfully demonstrate the superiority of the GO/PVA composite membrane in suppressing zincate ion crossover, while minimally impairing OH- conduction. Modification of electrolytes also provides a solution for reducing zincate ion mobility. Additives such as zinc complexing agents are investigated, and gel electrolytes are designed to restrain the movement of zincate ions.
Scaling up of a Zn/MnO2 battery is made possible based on the above technologies. Batteries each has 118 Ah full capacity are tested. We report more than 200 cycles at 20% DOD with no capacity fade, and demonstrate that with the combination of electrolyte modification and interlayer application, the lifetime and energy density of a scaled-up rechargeable Zn/MnO2 battery is significantly improved.