Rolls-Royce Claims Its Latest Electric Airplane Battery Has The World’s Highest Energy Density

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Making electric airplanes is hard. You need a lot of batteries to make an electric airplane fly. Batteries tend to be heavy and bulky — exactly the opposite of what aircraft designers want. No wonder electric airplanes have a much shorter range than conventional aircraft.

But just because a problem is hard doesn’t mean it is impossible to solve. Engineers at Rolls-Royce are hard at work designing the fastest single seat electric airplane in the world, according toIEEE Spectrum. The current record is 210 mph (338 km/h). Rolls-Royce has a new airplane that is expected to take to the skies this spring that could crack the 300 mph (483 kph) barrier and be able to fly up to 200 miles (322 km) — the distance between London and Paris — on a single charge.

That’s thanks to “the world’s most energy-dense flying battery pack,” according to Rolls-Royce. The aircraft has three 72 kWh batteries, each with 6,000 lithium-ion battery cells and weighing 450 kilograms (992 lbs.). That’s more than a ton and half of batteries — quite a lot for a small plane.

Getting all this power on board wasn’t easy, says Matheu Parr, project manager of the ACCEL project at Rolls-Royce. That’s short for Accelerating the Electrification of Flight. Every aspect of the electrification program had to be carefully considered. Lithium-ion battery cells come in many shapes, but after careful analysis, cylindrical cells were found to be best for holding a lot of energy and discharging it quickly at high power, Parr says.

Making all those cells into battery packs was another challenge. For that, Rolls-Royce turned to Electroflight, a startup specializing in aviation batteries. It began by analyzing innovations happening in electric racing series like Formula E. By using ultra lightweight materials — and as little of them as possible — Formula E has slashed the ratio of packaging to battery cell weight in half compared to normal electric vehicle battery packs.

Packing cells so close together produces lots of heat, so the Rolls-Royce engineers have devised a water and glycol cooling system that directly contacts each individual cell. Finally, they built an ultra strong exterior shell for the battery pack to reduce the risk of fire in the event of a crash landing. The battery management system can shut down any cells that experience a failure and the airplane can land even if one of its battery packs is inoperable.

The ACCEL battery has a specific energy of 165 watt-hours per kilogram, which is about the same as the battery in the Tesla Model 3. Future planes will need 500 watt-hours per kilogram to compete with jet powered airplanes, something that may take another decade to accomplish. For now, Rolls-Royce and other electric airplane companies think electric power will be reserved for small aircraft while hybrid propulsion systems will power larger planes, at least until battery technology catches up with its fossil fuel competitors. Rolls-Royce has partnered with Airbus and Siemens to develop hybrid airplanes.

With its high speed racing aircraft, Rolls-Royce wants to pioneer the transition to the “third age of aviation, from propeller aircraft to jet aircraft to electric,” says Parr. The project will also provide know-how that will shape future designs. “We’re learning an awful lot that we want to see packed into a future aircraft. Innovations in the battery and system integration, packaging and management will all help us shape any future electric product, be it all-electric or hybrid.”