With the urgent need for cleaner transport – be it in the air, on the street or anywhere else – a central path pursued is the transition from fossil fuels towards electrification. Using electricity from renewable energy sources to power airplanes can cut overall greenhouse gas emissions drastically. But state-of-the-art batteries are still relatively heavy, posing a serious obstacle for the breakthrough of electrically propelled aviation.
This is where the EU-funded Clean Sky 2 project LiBAT took off. The LiBAT team designed and prototyped an outstanding lithium battery. The target was to reach superior overall energy and power density based on an intelligent pack concept rather than new cell technology. The battery system consists of two parts of elongated shape to be placed in the two wings of an electrified glider, each powering one of the two motors of the glider. The combination of energy, power and weight targets posed an ambitious challenge: The maximum weight of the battery pack was to be kept below 55 kg and an energy density of 200 Wh/kg or more at 1C discharge while 10 kW of power should be provided continuously per motor, with even higher values at peak. With further applications in mind, connection of the battery to AC aircraft networks was to be considered. Special attention was to be placed on a clear definition of the interfaces to current aircraft architectures. The thermal conditions of the battery system were to be considered to ensure a safe and efficient operation.
The potentially game-changing LiBAT battery system addresses the weight problem by an extraordinary level of integration and a combination of advanced technologies. By integrating multi-level-inverter technology into the battery, the LiBAT team created a unique, tuneable AC battery system that eliminates the need for additional charging or motoring power electronics and saves extra weight. Combined with a powerful immersive thermal management and a suitable cell choice, both excellent energy and power performance are realized, given the low weight and volume of the pack. The modular design guarantees a scalable system. Connected to an electric propulsion unit, the prototype battery that was built in LiBAT demonstrated powers of up to 3,25 kW in a lab setting – enough to maintain level flight for the targeted application, an electrified glider. With the identified design improvements, take-off will be feasible as well. Due to an exceptional commitment of the partners, LiBAT succeeded even though it faced extraordinary circumstances with the COVID-19 pandemic.
For future developments, a reasonable next objective would be to implement identified improvements and implement the battery in an actual glider prototype. On the other hand, the design could be advanced to a new level by integrating the battery structurally into aircraft architectures. Furthermore, new battery cell technologies could be considered.
