Thermal behavior of nickel metal hydride battery during rapid charge and discharge cycles

Abstract

The secondary batteries for an electric vehicle (EV) generate much heat during rapid charge and discharge cycles, when the EV quickly starts consuming the battery power and suddenly stops recovering the inertia energy. The generated heat significantly increases the cell temperature and possibly leads to negative effects on the battery performance and the safety requirement. We have studied the thermal behavior of nickel/metal hydride (Ni/MH) batteries during rapid charge and discharge cycles, applying our previous battery thermal model, and found agreement with the experimental results at smaller charge current than the rated current. The heat sources by the entropy change, the hydrogen occlusion and the side reaction have been referred to the published data, and the overpotential resistance and the current efficiency, the ratio of main reaction current to charge current, have been measured experimentally through the rapid charge and discharge characteristics with constant current. By using these data our thermal model for the Ni/MH battery has estimated its temperature increase, which agrees well with the measured temperature rise, with a root mean square error of 1.5 and 2.1°C for charge and discharge cycles, respectively. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 30–39, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20284