To make a workable hybrid locomotive that could harvest energy from braking, GE engineers have developed an alternative to the lithium and metal-hydride batteries commonly found in hybrid passenger vehicles. The company needed batteries with higher energy densities that can also withstand day-to-day operations on a long-haul locomotive. Further, the new batteries must tolerate cell failures and still operate safely and effectively. The result: a high-temperature sodium metal-chloride battery.
GE engineers relied on Comsol Multiphysics software to develop the battery. The software can model and simulate electrochemical reactions and the material and energy transport that takes place in a sodium metal-chloride battery. The model had to include electrochemical reaction kinetics as described by the Butler-Volmer equation, which must be solved at the electrodes. The model must also account for ion transport to the electrodes through migration, diffusion, and convection.
In addition, some materials change phase as the battery charges or discharges, and the corresponding kinetics must also be factored in. Further, temperature plays a crucial role in many of the battery’s physical properties such as ionic mobility, so it’s necessary to hold the operational temperatures within a narrow range. Comsol can couple these domains and solve them simultaneously, a key benefit.
The models uncovered some useful information. For example, engineers could identify areas of high current densities and adjust manufacturing tolerances at critical regions to handle them. The model also provided additional insights concerning convective rows in the cathode. Modeling even helped define operating policies. For example, plotting cell resistance versus the extent to which the reacting materials in the battery get consumed helped determine when operators should start a recharging cycle. Engineers also intend to use Comsol to investigate other properties, such as the battery’s structural integrity under vibration.