(139c) Self-Discharge Evaluation of Ni-MH Battery Using Metal Hydride Alloy for Energy Storage Applications

Hydrogen storage alloys have been successfully applied in the nickel-metal hydride batteries for different energy storage applications such as in hybrid-electric vehicles (HEVs) and portable electronics. The advantages of this battery system are its high-rate charge/ discharge capability, good specific energy, and high reliability. Ni-MH batteries, as an alternative solution to nickel-cadmium batteries, rapidly become the most popular rechargeable batteries for consumer appliances because the nickel-metal hydride chemistry system has fewer environmental concerns and no memory effect in comparison with nickel-cadmium chemistry. Although the Ni-MH battery system is relative expensive, it is currently a realistic resource for rapid storage of mechanical energy into chemical energy because the lithium-ion battery system is still expensive, the innovations and breakthroughs for the conventional Pb-acid battery are under development efforts to serve consumers for cost considerations. This work uses ac impedance spectroscopy to collect impedance data for the nickel-metal battery at different of state-of-charge (SoC). After the battery was charged to a level of SoC, the battery system's self-discharge process was evaluated upon measurement of battery voltage drop at open circuit and analysis of its impedance data as a function of time. Using this impedance tool, the interfacial process, variation in the internal resistance, state-of-charge, and the residual capacity can be obtained using a proper equivalent circuit for simulating of the Ni-MH battery chemistry and physical processes. Energy efficiency is potentially improved upon understanding of self-discharge mechanism and electing of a proper operating range.