On January 29, 2026, Idemitsu Kosan commenced construction of a large-scale pilot facility for sulfide-based solid electrolytes at its Chiba site, marking a significant advance after three decades of research and 13 years of collaboration with Toyota. Designed for an annual output of several hundred metric tons, the plant aims to resolve key engineering scale-up and cost-reduction challenges ahead of the mass production phase slated for 2027–2028. By transitioning solid-state electrolyte manufacturing from laboratory proofs to factory-level processes, the project underpins Toyota’s plan to launch all-solid-state battery-equipped vehicles in that timeframe.
Idemitsu’s core technology leverages sulfur by-products from its petroleum operations to produce lithium sulfide–based electrolytes. Using nanoscale composite methods, the company achieves uniform mixing of sulfur, lithium, and phosphorus to create highly flexible, crack-resistant electrolyte layers capable of withstanding tens of thousands of charge–discharge cycles. A continuous melting–cooling–crushing process, coupled with 3D printing, enables precise control of layer thickness at the micron scale, cutting production costs by roughly 50% while improving consistency and throughput.
In joint development with Toyota, these sulfide electrolytes support battery energy densities of 450–500 Wh/kg—about double that of conventional lithium-ion cells—while enabling fast charging to 80% in 10 minutes and driving ranges of 1,000–1,200 km. The solid-state design raises thermal runaway thresholds by 200 °C, eliminates leakage risks, and allows operation down to –30 °C. Cycle life exceeds 1,000 cycles, with projected battery lifespans up to 40 years.
To secure raw-material supply, Idemitsu is also building a 1,000 mt-per-year lithium sulfide production unit, scheduled for completion in mid-2027. The company has filed more lithium sulfide patents globally than any other organization and holds core intellectual property covering synthesis and mass-production processes. Supported by a ¥7.1 billion government subsidy and grants from the NEDO Green Innovation Fund, the investments total ¥21.3 billion for lithium sulfide and solid electrolyte capacity expansion. Key partners include Toyota, Chiyoda Corporation, and Sumitomo Metal.
Source: Metal.com
