The unique operating profiles and requirements of electric vertical takeoff and landing (eVTOL) aircraft—also known as flying cars—present formidable challenges to batteries. In a paper in the journal Joule, a team from Penn State University has analyzed the primary performance metrics required for eVTOL batteries compared with electric vehicle (EV) batteries.

EVTOL requirements on battery specific power and energy.

1. Schematic illustration of a typical eVTOL trip.
2. Representative battery power profile during an eVTOL trip.
3. Required battery specific power in hover versus in cruise for the aircraft configurations being pursued by the industry.
4. Trip distance versus consumed specific energy for three representative aircraft configurations.

5. Battery energy breakdown for eVTOL trips with design-C and a 200Wh/kg battery pack.

Further, eVTOL batteries should continue functioning even after a safety incident occurs until a safe landing.

Notably, we highlight the importance of fast charging, which is essential for downsizing aircraft and batteries to reduce cost while achieving high vehicle use rates to maximize revenues. We stress that any fast-charging technology should fulfill three metrics simultaneously—charge time less than passenger swapping (5–10 min), charged energy sufficient for the next trip, and a long cycle life.

We experimentally demonstrate two energy-dense Li-ion battery designs that can recharge adequate energy for 80 km eVTOL trips in 5–10 min and sustain over 2,000 fast-charge cycles. We hope that these initial designs will spur exciting development of eVTOL batteries.

—Yang et al.

Battery requirements for eVTOLs versus for EVs. Note: EV batteries could have even lower C-rate (C/10) in city driving. Yang et al.

Resources

• Yang et al. (2021) “Challenges and key requirements of batteries for electric vertical takeoff and landing aircraft”, Joule doi: 10.1016/j.joule.2021.05.001