Air-metal hydride battery construction and evaluation

An air-metal hydride battery (32 Ah) using a noble metal-free air electrode (300 cm(2)) was constructed and tested. The battery was charged with a third nickel mesh electrode and discharged using oxygen, with discharge voltages of 0.87 V at 3 A and 0.58 V at 30 A. The peak power was 25 W (83 mW/cm(2)) with oxygen and 15 W (50 mW/cm(2)) with air. Energy density and power density per total electrode weight were 120 Wh/kg at 3 A and 75 W/kg at 30 A, respectively. A low initial Wh efficiency (41%) due to a high charging voltage (1.95 V at 6 A) was raised to 58% by replacing the Ni mesh with a sintered nickel electrode (capacity 7.5 Ah). The new battery design (air-MH-Ni hybrid) allows two discharge possibilities, the air-MH couple for low voltage and low rate and the NiMH couple for high voltage and high rate discharges.