Toyota, the maker of the bZ4X electric crossover, has partnered with Japanese petroleum company Idemitsu to make a mass-market solid-state battery that will be used in upcoming electric vehicles starting in 2027 or 2028, the two entities announced today.

Leaving the obvious irony of a petroleum company that operates oil platforms making EV batteries aside, it’s worth noting that Idemitsu has been working on sulfide solid electrolytes since 2001 and already has a small pilot facility that has been steadily increasing its output since its announcement in June.

Toyota’s recently announced battery technology roadmap showed that the first generation of solid-state batteries to be fitted in its EVs will come around 2027-2028 and will enable a driving range of over 621 miles (1,000 kilometers) on a full charge, while a top-up from 10 percent State of Charge (SoC) to 80 percent will take approximately 10 minutes from a DC fast charger.

Some of the advantages of solid-state batteries over traditional lithium-ion batteries with liquid electrolytes are higher stability at extreme temperatures, faster energy transfer, and a smaller footprint.

The collaboration between the two companies will have three phases, with the first one being the development of better sulfide solid electrolytes with attention to quality, cost, and lead times.

The second phase will involve the construction of a large pilot facility where Idemitsu will try to achieve mass production for solid electrolyte-based batteries, while Toyota will handle the integration of the all-solid-state batteries into its next-gen battery electric vehicles (BEVs), ensuring they’ll be ready for a 2027-2028 market launch.

The third and final phase will see both companies searching for solutions for future full-scale production and sales of EVs with solid-state batteries.

A timeline for the three-phase plan was not provided, but Toyota President and CEO Koji Sato said that a longstanding technical issue for solid-state batteries has been that repeatedly charging and discharging the battery causes cracks between the anodes, cathodes, and solid electrolytes, degrading battery performance.

“Through repeated trial and error and by combining the material technologies of both companies, we have been able to develop a crack-resistant material that demonstrates high performance,” he added.

“By combining this new solid electrolyte with the Toyota Group’s cathode and anode materials and battery technologies, we are now on the path toward achieving both performance and durability in solid-state batteries.”

At the same time, Idemitsu Kosan President and CEO Shunichi Kito said that sulfide-based solid electrolytes, which are byproducts of improving petroleum products, are the most promising solution for EV battery issues like cruising range and charging times.

“Idemitsu discovered the usefulness of sulfur components in the mid-1990s, and through our research and technological capabilities cultivated over many years, we have succeeded in creating a solid electrolyte,” said Idemitsu’s CEO. “This solid electrolyte is about to open up a new future for mobility.”