Thermal behavior of small nickel/metal hydride battery during rapid charge and discharge cycle

The nickel/metal hydride battery (Ni/MH) has been developed as a power source for the hybrid electric vehicle (HEV) and the pure electric vehicle (PEV). But the large battery with heavy duty cycle by more rapid charge and discharge than today's is desirable for the diffusion of HEV and PEV. Therefore the thermal behavior of Ni/MH battery must be understood precisely for the battery size enlargement and its performance improvement. In this report the thermal behavior of small Ni/MH battery during rapid charge and discharge cycle has been studied numerically and experimentally by considering the entropy changes by electrochemical reactions, the endothermic reaction by hydrogen occlusion to MH, the exothermic reaction by side reaction, the heat generation by overpotential and the heat transfer to the ambient air. The calculated cell temperature agrees well with the measured under both the charge and discharge cycles below the rated current, but the calculated is larger than the measured above the rated current.