A German startup believes it has the recipe for electric vehicle battery cells that are cheaper, more energy dense, and less problematic for the environment than current lithium-ion cells. But commercialization seems a long way off.

Theion announced Thursday in a press release that it is close to completing a 15 million euro (approximately $16.2 million at current exchange rates) Series A round to development of its sulfur-crystal battery chemistry. It’s based on proprietary anode technology that Theion hopes will extend battery life—one of the main obstacles to sulfur-based chemistries.

With this chemistry, Theion is aiming for energy density of 1,000 Wh/kg, which is about triple that of leading-edge nickel manganese cobalt (NMC) cells today, including the 4680 cells used in the Tesla Cybertruck. Such energy density would allow for much lighter cells without sacrificing range, or increased range from the same volume.

Theion claims it can achieve this without using nickel or cobalt, addressing environmental and human-rights concerns associated with the mining of those metals. Overall, Theion claims its cells could have a one-third lower carbon footprint—and cost—compared to conventional cells. That’s because, as the firm notes in its release, sulfur is the 16th most abundant element on Earth, and costs much less than the raw materials of NMC cells.

Stellantis STLA Medium platform

But as Theion emphasizes, longevity in cycle life will be the challenge for sulfur-crystal batteries. The startup believes its batteries need to maintain performance over 1,000 charge/discharge cycles to be commercially viable, a target it aims to build up to, after initial testing of 500 Wh/kg cells at 500 cycles, before starting production.

Research into lithium-sulfur batteries for EVs goes back at least a decade, and we’ve seen impressive claims about their ability to boost EV range before. Stellantis has even partnered with not one, but two startups—Lyten and Zeta Energy—that aim to commercialize the tech, perhaps by the end of the decade. But it remains to be seen if any of these efforts—Theion’s included—will overcome the hurdles and get sulfur batteries into production EVs.