Investigation of failure processes in porous battery substrates: Part II - Simulation results and comparisons

Models are presented for the evolution of transport and mechanical properties of nickel-metal hydride (NiMH) battery substrates. In the first paper in this series (Wang et al., 1999), conductive losses and enhancement of mechanical properties in these materials were quantified experimentally. These were qualitatively shown to be related to observed morphological changes in the substrate materials. Here, an evolution hypothesis for changes in these structures is presented, along with a simplified approximation of the real material microstructure (porous fiber/powder nickel network) with a tractable simulation geometry (porous fiber networks). Transport and mechanics models are then compared with experimental results, with stochastically-arranged fibers approximated as conductive beams connected by elastic torsion springs. Both quantitative and qualitative agreement are found with the models. Limitations of the approaches proposed are also discussed, along with the consequences of the simplifications of geometry for analysis.