The arrival of electric planes that can carry hundreds of people thousands of miles hinges on developing a new generation of batteries, motors and other technologies beyond what's powering today's electric cars.

Why it matters: Electric planes lead to cleaner flying, but plenty of R&D work remains before takeoff.

State of play: Smaller, shorter-range electric planes and electric air taxis could become commercially available as early as 2025, with others in development.

• Many are electric vertical-takeoff-and-landing (eVTOL) aircraft that resemble helicopters and carry a handful of people a short distance — say, between downtown and the airport.
• The moonshot, though, is to electrify larger planes that can take off and land like conventional airplanes that run on jet fuel.

How it works: "To fly an airplane you need two big things: power to propel them forward and energy to keep them flying for a long duration," says Kiruba Haran, a professor at the University of Illinois at Urbana-Champaign.

For electric aircraft, the energy part of that equation centers on batteries and fuel cells.

• Electric aviation presents unique challenges, Alex Kosyakov, co-founder and CEO of Illinois-based battery materials startup Natrion, tells Axios.
• Batteries for eVTOLS and electric planes require higher energy density than those for electric cars because it takes so much power to get off the ground.
• And they must last for the duration of longer flights connecting cities.

What they're saying: "It's a far more resilient and robust solution that's required than is needed for an EV," says Halle Cheeseman, a program director at the Department of Energy's Advanced Research Projects Agency-Energy (ARPA-E).

• The necessary energy density intersects with other important considerations for aircraft, including batteries' weight and heat tolerance.

Driving the news: The Department of Energy (DOE) this week announced that 12 teams will receive a total of $15 million through Cheeseman's program to try to develop batteries and energy storage systems with about four times as much energy density as current technologies.

• The goal is to electrify a plane that could carry up to 100 people for 1,000 miles.

Zoom in: The winning teams are taking a range of approaches, including new battery chemistries, optimizing electrode materials, rethinking the packaging of hydrogen that powers fuel cells and developing hybrid fuel-cell battery systems.

• Natrion, NASA, and others are developing solid-state batteries that can tolerate much higher temperatures, potentially making them safer than traditional lithium-ion batteries — and useful for aviation. They also charge faster.

For power, electric aircraft need motors that convert electricity — possibly generated by batteries and fuel cells, though there are hybrid scenarios as well — into mechanical work for propulsion.

• Haran and others, including Toshiba and Airbus, are focusing on superconducting motors that can generate megawatts of power to propel jets. Superconducting materials have no resistance, minimal heat loss and can carry more current, meaning less material — and less weight.
• Superconducting materials hold the promise of being "very efficient, very lightweight, power dense," says Haran.

Yes, but: Existing superconducting materials have to be cooled to extremely low temperatures.

• One possible design uses the energy generated from vaporizing liquid hydrogen into fuel to cool the superconductor.
• There are also a variety of non-superconducting machines in development, plus hybrid turboelectric planes that use gas turbines to drive electric motors.

The bottom line: For the last 50 years, people were making electric machines "incrementally better," Haran says. Now they have a "clean sheet" for designing "a really efficient propulsion system."

• "We're trying to reinvent the electric machine," he says.