Rechargeable Aluminum-Air Batteries Based on Aqueous Solid-State Electrolytes

The feasibility to recharge aluminum-air cells realized with a dual water-based electrolyte without separator is demonstrated. The dual electrolyte, made of polyvinyl alcohol and Xanthan gum, has a different water content, lower at the anodic interface, where parasitic reactions involving hydrogen production play a crucial role in hindering metal re-deposition, and higher at the cathode side, where water, depending on the pH, allows an efficient reduction of oxygen during discharge or the oxygen evolution during cell charging. The galvanostatic cycles show in the first discharge and charge cycles, the characteristic plateau trends of secondary batteries. By electrochemical impedance spectroscopy analysis effected after each discharge/charge phase and by measuring anode and cathode potentials during cycling, it is demonstrated that, during the first cycles, the re-deposition of aluminum is possible by adopting adequate water management in the electrolyte, while the cell malfunctioning in the subsequent cycles is mainly due to the damage of the cathode.