New Interpretation of the Performance of Nickel-Based Air Electrodes for Rechargeable Zinc-Air Batteries

Rechargeable zinc-air batteries with high energy density, cycle life, and calendar life require corrosion-resistant support materials in the air electrode. Nickel-based air electrodes have shown promise in this regard as a substitute for conventional carbon-based air electrodes, but their performance in zinc-air batteries has not been studied in-depth. Specifically, the effect of the nickel (oxy)hydroxide passivating film on the electrode's catalytic performance and durability requires investigation. To fill this research gap, a method involving electrochemical estimation of the nickel (oxy)hydroxide film capacity was used to link the growth of the film to performance losses experienced on the air electrode after battery cycling. The main cause of voltage loss was the nickel (oxy)hydroxide film growing overtop of and inside the catalyst-coated nickel aggregates. This resulted in significant activation and mass transfer losses, where the latter losses were caused by the film growing overtop of the catalyst and accounted for at least 65% of the total voltage degradation at 10 mA cm(-2). Potential modifications to the electrode structure which could mitigate these voltage losses are discussed, including reducing the nickel particle aggregate size, using high-aspect ratio catalysts, and physically separating the catalyst and nickel particles with nonfilm-forming conductive additives.