Development of a Liquid Immersion-Type Nickel-Metal Hydride Battery Under High-Pressure

A nickel-metal hydride (Ni–MH) prototype battery completely immersed in an aqueous electrolyte solution of KOH under high-pressure was fabricated to examine the effects of high-pressure on the quality of Ni–MH batteries. The small battery cell comprised positive and negative electrode materials, as used in electric vehicles, and an Ag/AgO reference electrode. The electric capacity of the Ni–MH battery was measured at different temperatures and pressures with small currents and charge/discharge voltages of 1.6–1.0 V. High-pressure was found to clearly and effectively enhance the electric capacity of the Ni–MH battery at larger currents. The considerable effect of high-pressure on the Ni–MH battery was elucidated by the change in internal resistance during the charge/discharge cycle life experiment, indicating that the voltage of the positive electrode did not appreciably change under high-pressure compared to that of the negative electrode. Moreover, the use of large currents in rapid charge/discharge cycle tests at high pressures of up to 30 MPa resulted in charge/discharge cycles that were five times faster and a quick recovery of capacity was achieved in the 0.5–2.1 V range.