Degradation Factors and Durability of Large Scale Ni-metal Hydride Batteries

Abstract

The lifetime of a nickel-metal hydride battery power system (BPS) used in railway systems is investigated. Frequent acceleration and deceleration are performed in normal railway operation, so the narrow range of SOC of the corresponding BPS is discussed. Since the lifetime of the battery used in that BPS should be estimated in accordance with the operation pattern, the operation pattern was analyzed by Fourier transform, and battery lifetime is evaluated in the frequent discharge/charge with a current change every 6 seconds within a 3% depth of discharge (DOD) as the main pattern and the float charging at a constant voltage. Major factors of the battery lifetime are operation voltage and the internal cell temperature caused by an internal resistance. The lifetime of the battery do not depend on the operation pattern such as frequent discharge/charge and float charging. Furthermore, it was almost the same as the lifetime at rest potential in the open circuit state. Applying electrochemical reaction kinetics equations to this system, calculation results indicate a good correlation with the experimental data.