Considerations for the sizing and structure of the battery pack for a direct-hybrid-electric aircraft

The development of hydrogen fuel-cell-based aircraft has received a lot of attention recently. Components like the battery need to be carefully designed to meet power and safety requirements while minimizing weight to enable longer flight ranges. Experimental data from three different commercially available lithium-ion batteries with different cathode materials and housing was used to parameterize an equivalent circuit battery model. The model with the three datasets was integrated into a system model for the powertrain of a direct hybrid and used to find the required battery configuration for an exemplary flight profile with cells connected in series and parallel for all three battery types. The resulting battery configurations were compared with respect to flight reserve and weight. It was found that due to current and voltage restraints, the most suitable and lightest configuration was the one based on lithium nickel cobalt aluminum oxide (NCA) cylindrical cells despite the fact that they were not the type of battery with the highest specific energy on cell level. The NCA had a specific energy on cell level of 126 Wh/kg at 23 °C with a 1 C-discharge, compared to the lithium nickel manganese cobalt oxide (NMC) battery with 232 Wh/kg and lithium iron phosphate (LFP) with 79 Wh/kg. The battery systems that met all voltage and flight reserve requirements however resulted in a system weight of 200 kg for the NMC cell, while the system using NCA cells was only 183 kg. • Equivalent circuit model experimentally validated for 3 types of Li-ion batteries • Aviation powertrain model to find system configurations for different battery types • Best battery set-up determined for a hybrid aircraft with exemplary flight profile • Evaluation with respect to flight reserve and weight • NCA cylindrical cells identified as the most suitable and lightest configuration