Fundamental Studies of Lithium Sulfur Batteries for Electric Aviation

Lithium sulfur (LiS) batteries have the potential to outperform lithium ion batteries and secure a space for both civilian and military electric vertical takeoff and landing (eVTOL) aircraft. The high theoretical capacity of sulfur promises high specific energy LiS batteries that would enable practical eVTOL aircraft. The drawbacks are low cycle count and uncertain behavior at high power. First, results from a conceptual eVTOL sizing code is used to demonstrate the benefits of advanced battery technology with increased specific energy for an intracity air taxi mission with an electric quadcopter. Next, small-scale LiS cells are fabricated with a polyacrylonitrile-sulfur cathode, lithium anode, and various liquid electrolytes. Electrochemical cycling data is analyzed, including tests at high C-Rates. The C- Rate test showed the ability of the LiS cell to recover initial capacity after experiencing high C-Rates of up to 6C. Microscopy analysis was performed on a cycled LiS cell to observe the cell mechanisms and cause of cell degradation. In conclusion, the advanced specific energy of LiS allows for a more effective quadcopter, with a weight, size, and payload suited for intracity travel. Additionally, characterization of small-scale LiS cells shows high specific capacity and good cycle life of over 600 cycles. Finally, understanding the behavior of larger, scaled up LiS batteries is crucial for eVTOL, and is part of future work.