PROTON DIFFUSION IN NICKEL-HYDROXIDE - PREDICTION OF ACTIVE MATERIAL UTILIZATION

Galvanostatic charge and discharge experiments reveal that the active material in nickel electrodes cannot be fully accessed at high current s or for thick films. It has been proposed that the utilization of the active material is controlled by the diffusion rate of protons throug h the film. This hypothesis is supported by the good agreement between mathematical simulations of material utilization and experimental dat a over a range of charge and discharge currents and film thicknesses. Furthermore, the fraction of material utilized is larger on charge tha n on discharge. The asymmetry on charge and discharge is due to a diff usion coefficient that is a function of the state-of-charge of the act ive material. The mathematical model is used to perform a parametric s tudy of material utilization as a function of charge and discharge cur rents, and material loading (i.e., film thickness, concentration of ni ckel sites) in order to improve battery design and operation.