Tesla has agreed to purchase a company that could help the electric plane take to the skies. The company announced Monday its plans to acquire Maxwell Technologies for $218 million, an energy storage firm that’s working on exotic technologies like ultracapacitors and dry electrodes.

The move could help Elon Musk achieve some of his biggest ideas. The Tesla CEO has floated his idea for an electric jet as early as 2009, even pitching the idea to Tony Stark in an Iron Man 2 cameo. The main hurdle has been energy density: Where Tesla’s electric car batteries store around 250 watt-hours per kilogram, a jet would need somewhere around 400 watt-hours per kilogram to fly properly, with 500 being a more ideal figure.

“The interesting thing about an electric plane is you want to go as high as possible, so you need a certain energy density in the battery pack, because you have to overcome gravitational potential energy,” Musk told Joe Rogan when he appeared on his podcast in September 2018. “The energy you use in cruise is very low, and then you can recapture a large amount of your gravitational potential energy on the way down. So you really don’t need any kind of reserve fuel if you will, because you have…the energy of height.”

Elon Musk on Joe Rogan. PowerfulJRE/YouTube

Maxwell Technologies can help reach these density goals. During a January presentation at the New York City-based Needham Growth Conference, the company outlined the benefits of its proprietary dry battery electrode compared to the traditional wet coating manufacturing process. The technology does not use solvents, enables the elimination of controversial cobalt materials, and reduces costs by up to 20 percent while boosting production capacity by a multiple of 16. The cells also offer double the battery life. Most importantly, the firm has demonstrated densities of 300 watt-hours per kilogram, with a “path” to 500 watt-hours identified.

The breakthrough would be a big boost versus analyst predictions, which claim that batteries could reach such a density in five to 10 years. With Tesla tied up sending out the Model 3 to more markets, though, it’s unclear if Musk will rush at the chance to produce a plane.

“I have a lot on my plate,” he told Joe Rogan. “The electric airplane isn’t necessary right now. Electric cars are important. Solar energy is important. Stationary storage of energy is important. These things are much more important than creating an electric supersonic VTOL.”