Air-metal hydride secondary battery with long cycle life

We report the evaluation of a novel air-metal hydride rechargeable battery. A copper plated MmNi(3.5)Co(0.7)Al(0.7)Mn(0.1) alloy was used as the active material in the metal hydride electrode. The metal hydride electrode was charged and discharged via a gas diffusion electrode based on a La0.6Ca0.4CoO3 perovskite (supported on carbon) as the catalyst for both oxygen reduction (discharge) and oxygen evolution (charge). In a laboratory cell, measurements on a 2.5X2.5 cm metal hydride electrode sandwiched between two air-electrodes of the same size were performed in a 6 M KOH electrolyte at 25degreesC with oxygen or air supply. A very long cycle life of 250 cycles at I C charge and discharge (1 h charge and 1 h discharge) was achieved. After 250 cycles, the capacity of the metal hydride electrode had decreased by about 10%, from 268 mAh g(-1) to 242 mAh g(-1). After more than 220 cycles, the discharge voltage of the cell was 0.64 V for oxygen and 0.55 V for air. At 10 mA cm(-2) (approx. 2 h charge and 2 h discharge) the cell voltage was 1.57 V for charge and 0.77 V for discharge (using oxygen), measured after more than 100 cycles. Peak power was 51.0 mW cm(-2) for oxygen and 34.8 MW cm(-2) for air. These values were measured at currents of 150 mA cm(-2) for oxygen and at 100 mA cm(-2) for air. (C) 2002 Elsevier Science BY. All rights reserved.