Comparison of Lithium-Ion Battery Chemistries in the Hybridization of Ultralight Aircraft

Many research centers and companies in general aviation have been devoting efforts to the electrification of propulsive plants to reduce environmental impact and/or increase safety. Even if the final goal is the total elimination of fossil fuels, the limitations of today's battery in terms of energy and power densities suggest the adoption of hybrid-electric solutions. These systems combine the advantages of conventional and electric propulsive systems, namely reduced fuel consumption, high peak power, and increased safety deriving from redundancy. Today, lithium-ion batteries are the best commercial option for the electrification of all means of transportation. However, lithium batteries are a family of technologies that presents a variety of specifications in terms of gravimetric and volumetric energy density, discharge and charge currents, safety, and cost. This work presents a series/parallel hybrid electric powertrain derived from automotive applications (Honda i-MMD) tailored to ultralight aircraft and discusses the sizing of the battery, which is performed based on a normal operation mission and an electric backup operation after engine failure. The normal operation mission is assumed to be performed under different hybridization modes (series, parallel, and all-electric). In this investigation, seven lithium battery chemistries are compared, quantitatively (in terms of mass and volume required to satisfy the proposed missions and hybridization modes) and, qualitatively (contrasting lifespan and runaway temperature). The results of the investigation prove the importance of including the tradeoff between power density and energy density in the sizing of the battery. From this point of view Nickel-Manganese-Cobalt chemistry, thanks to an energy density of 230Wh/kg and a maximum discharge current of 10C presents the best results. The investigation considers also the combination of the hybridization modes used for the sizing to develop an energy management strategy that allows a compromise between fuel economy and reliability to be obtained