Effect of compaction pressure on the behaviour of metal hydride pellet electrodes: New modelling

J. E. THOMAS; E. B. CASTRO; A, VISINTIN

Foz de Iguaçú

Congreso; ISE 2008 Spring Meeting; 2008

International Society of Electrochemistry

Metal hydride alloys are commercially used in electrodes for rechargeable batteries. AB5-type alloys show high capacity and good kinetics in the hydriding/dehydriding reactions. These reactions occur on the metal particle surfaces, but the influence of the structural properties of the electrode such as porosity, active area and electrode length, affect the response of these electrodes.In previous works  the constant current discharge response of these electrodes was simulated in terms of a physicochemical model based on the classical theory of flooded porous electrodes. In this work the effect of structural parameters, determined by the compaction pressure during electrode preparation, on the discharge potential /time curves is analysed.Working electrodes were prepared with Carbon Vulcan, PTFE and AB5-type alloy. Using a Helyum Pycnometry method the dependence of the electrode porosity and volume with pressure was derived . The dependence of the active area per unit volume with pressure was calculated in terms of a model taking into account plastic deformation and fragmentation effects . This analysis predicts a maximum in active area and porosity at low pressures, leading to an improvement in discharge performance and rate capability with diminishment of the compaction pressure. Experimental data show these effects too, but these electrodes have a limiting low pressure when a disaggregation effect appears.