(159bc) The low-maintenance application of hydrogel electrolytes to Zn|MnO2 rechargeable batteries

Zinc-manganese dioxide (Zn|MnO₂) alkaline batteries have been studied because of the high theoretical capacities of active materials, inherent safety, low cost, and environmentally friendliness. Liquid alkaline electrolytes, such as potassium hydroxide (KOH), are generally used, however, some issues with liquid electrolytes are commonly reported. Their high pH level easily causes corrosion when leaking, and evaporation requires extra maintenance. In the fundamental view, Zn ions can be redistributed, and therefore passivation of Zn anodes occurs. It is also widely known that active Mn³⁺ ions are poisoned by zincate ions, leading to the formation of hetaerolite, ZnMn₂O₄. In addition, at high utilization, MnO₂ undergoes crystal structure breakdown, and inactive spinel Mn₃O₄ is formed. For these reasons, alternative electrolytes are commonly studied to mitigate the issues in Zn|MnO₂ rechargeable batteries.

Our approach is to use a gelled potassium hydroxide electrolyte under the 1^st electron reaction capacity of MnO₂. The gelled electrolyte is based on radical polymerization reaction, and the electrolyte in the Zn|MnO₂ cells was gelled in-situ. Control cells were tested with liquid alkaline electrolytes with the same concentration as the gelled electrolyte. It was observed that the gelled electrolyte cells showed better capacity achievement and cycle life than the control cells. Cyclic voltammetry experiments were conducted with the cell voltage range between 1.75 – 1 V at 0.01 mV/sec, which showed the gelled electrolyte cell achieved ~30% utilization of the 1^st electron MnO₂ capacity at the 10^th cycle, while the control cell achieved only ~6% utilization. Moreover, after galvanostatic cycling, the dissected cell with the gelled electrolyte showed no sign of Zn penetration from the anode to the MnO₂ cathode through the separators compared the control cell, which reduces hetaerolite formation. The results suggest that the gelled electrolyte could resolve the failure causes, improving cell performance for long-term energy storage.