Idemitsu Begins Construction on Solid Electrolyte Plant for Toyota

Idemitsu Kosan began construction on a mass-scale pilot plant for solid-state battery materials on January 29, Reuters reported. The facility is located within the company’s Chiba Complex in Ichihara City, and it is intended to produce sulfide solid electrolytes.

The company has described the project as part of a staged plan with Toyota Motor Corporation. Idemitsu has said it already operates a smaller pilot line at the same site, and the new plant is meant to scale output toward the hundreds of tons per year range.

Toyota has publicly described sulfide-based solid electrolytes as part of its approach to solid-state batteries, citing their performance potential and manufacturability. In Toyota’s description, solid electrolytes replace the liquid electrolyte used in today’s lithium-ion cells, which changes both safety characteristics and possible operating voltages.

Toyota has also said it is aiming for a 2027 to 2028 introduction window for vehicles using next-generation batteries, with initial volumes limited. The company has framed that period as a commercialization step rather than immediate mass production.

For Japan, the project also sits inside a broader industrial policy goal of domestic battery supply chain capability. Reuters reported that the program is eligible for government support, and it cited Idemitsu’s planned investment for pilot infrastructure.

What remains unknown is the pace of scale beyond the pilot phase. Idemitsu and Toyota have outlined ambition, but the gap between a pilot plant and a stable, high-volume electrolyte supply chain is where most solid-state timelines have historically slipped.