Electric vertical takeoff and landing (eVTOL) aircraft are one of the hottest segments of the aerospace industry, with legacy manufacturers and startups scrambling to develop a variety of urban air taxis and delivery drones. The new breed of vehicles are designed to rise into the air like a helicopter and fly using wing-borne lift like an airplane.

Compared with helicopters, eVTOLs generally use more rotors spinning at a lower speed, making them both safer and quieter. However, developing lightweight, yet powerful batteries is a big challenge.

According to engineers tackling the issue at Oak Ridge National Laboratory (ORNL), eVTOL batteries can’t just be adapted from electric car batteries, as some people think. So, they are evaluating how lithium-ion batteries fare under extremely high power draw, and developing new energy-dense materials and control systems.

“eVTOLs present a unique opportunity for creating a brand new type of battery with very different requirements and capabilities than what we have seen before," says Ilias Belharouak, Ph.D., head of the electrification section at ORNL. “This requires us to answer questions about the interplay of battery safety, cycle life and stability at high temperatures, while balancing the need for short bursts of high power with energy reserves for longer-range flight.”

According to Belharouak, the power and performance demands for eVTOL batteries can significantly reduce their longevity and durability. Unlike electric car batteries, which typically drain at a steady rate, eVTOL batteries need varying amounts of power for flight stages such as climbing, hovering and descent, with some phases requiring high bursts of power.

Belharouak and his colleagues recently made lithium-ion batteries at ORNL’s Battery Manufacturing Facility and ran them through simulated climb stages of eVTOL aircraft. They studied what happens inside the battery during cycling, including how much energy is rapidly accessible during the demanding takeoff phase. Afterwards, they tested the battery materials for corrosion and other chemical or structural changes.

As they push the limits for battery power, payload and safety, the engineers are also working on further improvements to the electrolyte and other battery components. Recent experiments involved collecting real-world data from drone flights over the lab’s campus, then using that information to develop a customized profile of the load and draw on the battery. Batteries made at ORNL were then run through the same cycles.