Modeling discharge and charge characteristics of nickel–metal hydride batteries

A combined numerical and experimental study of the discharge and charge of nickel–metal hydride (Ni–MH) batteries has been performed. Numerical simulations were based on a previously developed micro–macroscopic coupled model which includes both the proton diffusion in the nickel active material and the hydrogen diffusion in metal-hydride particles. Oxygen generation and recombination, a principal mechanism to ensure safe operation of Ni–MH cells during overcharge, is also accounted for. A sealed Ni–MH cell (AA size, 1 Ah capacity) was prepared and discharge experiments were conducted at various rates. These experimental data along with other discharge and charge data available in the literature were used to validate the present model. Numerical results were presented to show the effects of oxygen evolution on battery performance, particularly on the charge acceptance, cell pressure build-up and self-discharge. This combined experimental and numerical study yields a computer-aided tool for the design and optimization of Ni–MH batteries.