Full Charge: The eVTOL Revolution Will Need Batteries

Professor Martin Winter says powerful, but small, lightweight, batteries are essential to eVTOL success.

“Battery development is triggered by the stakeholders,” says battery technology expert Professor Martin Winter. Winter is founder and scientific director of the MEET Battery Research Center at Münster University (about 340 miles west of Berlin).

But, so far, most of the work that’s been done regarding batteries for motion has been focused on automobiles, he explains. Unlike cars, the energy generated per battery weight, will be critical to aviation.

Germany-based eVTOL manufacturer Lilium claims to have a solution but they only had two prototypes and one of them caught fire. While lithium ion batteries are under consideration, lithium metal batteries are “the holy grail,” Winter says.

At first, Winter predicts that all eVTOLs will be compromises in one way or another, a means to demonstrate a prototype that will someday be able to propel the aircraft and their passengers (or cargo) 400 to 500 miles.

What we have currently is good enough for drones but not for manned vehicles. With the possible exception of Boeing and Airbus, which have their own battery development projects underway, it seems the eVTOL industry is largely relying on the auto industry to take the lead.

There are many research activities on lithium metal batteries. Some examples are the Pacific Northwest National Laboratory, a division of the U.S. Department of Energy located in Richland, Washington, and MEET in Münster.

To meet the needs of manned vehicles, Winter explains, the batteries will need to produce 600 kWh/kg. If drones using batteries with up to 450 Wh/kg presently are successful, the question will then become how to scale up capacity while maintaining safety and life.

Batteries: I’ll Swap You

Given the time needed to recharge a lithium battery, it’s likely commercial, passenger eVTOLS will need to swap spent batteries for freshly charged batteries. It’s unclear how this critical component of the flying car market will develop.

Will there be ‘battery swapping stations’? How will they know how many fresh batteries to keep in stock for the various vehicles in service? Will you need 50 in Colorado and 50 in Idaho? Or will you have 200 in stock and no one uses them for a week? Winter suggests a fleet approach will be necessary.

A lithium ion battery has a different design than a lithium metal battery. Winter explains you can get eight to 10 years of life out of a lithium ion battery in your car. For lithium metal, that usable lifespan might only be a few years at first. If scientists can devise a new solid-state battery with solid electrolytes—nothing liquid or flammable—that  that would advance safety.

My Battery Has Acrophobia

Yes, batteries are inanimate. But if they could talk, they might tell you they’re not especially fond of heights.

With altitude, Professor Winter says, comes a reduction in temperature. And lithium ion and lithium metal batteries don’t take well to extreme temperatures.

Some battery designs also don’t do well with changes in air pressure, another consideration eVTOL manufacturers need to take into account.

“As the pressure changes, the plastic housing can balloon or bulge, it can lose its dimension. That can be a problem,” Winter says.

Electric-powered vehicles, land-based or airborne, are a good idea; they’re good for the environment, they’re sustainable. But while many of the technological challenges of car-sized, city-smart, smart-city helicopters are getting most of the attention – lift, noise, infrastructure – the ‘e’ in eVTOLs is still a work in progress.

“Progress,” President Theodore Roosevelt said, “is accomplished by the man who does things.” People are doing things. The batteries we need will come.

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