Idemitsu Kosan Holds Groundbreaking Ceremony for Large-Scale Pilot Plant for Solid Electrolyte (Solid-State Battery Material)

## Idemitsu Kosan Holds Groundbreaking Ceremony for Large-Scale Pilot Plant for Solid Electrolyte (Solid-State Battery Material)

Idemitsu Kosan Co., Ltd. (Headquarters: Chiyoda-ku, Tokyo; President: Norio Sakai; hereinafter "the Company") is constructing a large-scale pilot plant (hereinafter "the Plant") at its Chiba Complex (Ichihara City, Chiba Prefecture) to manufacture solid electrolytes, a material for all-solid-state lithium-ion secondary batteries (hereinafter "solid-state batteries"). On May 13, 2026, a groundbreaking ceremony was held at the construction site. Following the successful completion of the foundation work, construction has now begun in earnest, with completion scheduled for 2027.

* Solid-state batteries: Unlike conventional liquid electrolyte batteries, these use solid electrolytes, which facilitate ion movement, enable faster charging, and provide higher power output for electric vehicles. They are also resistant to high voltage and heat, holding promise for higher energy density and longer battery life.

The Company is collaborating with Toyota Motor Corporation (hereinafter "Toyota") to achieve the commercialization of solid-state batteries between 2027 and 2028. Attendees at the ceremony included representatives from Chiyoda Corporation, which is in charge of constructing the Plant, and Toyota.

Through this Plant, the Company will further accelerate the performance improvement of solid electrolytes and the development of mass production technology, while steadily building a consistent supply chain from raw materials to finished products, thereby supporting the social implementation of solid-state batteries from the material perspective.

### Reference

- Position of Solid Electrolyte Development at Idemitsu
In its mid-term management plan (FY2026–FY2030), the Company has identified the expansion of material solutions—a key to the development of the electrification and ICT integration field—as part of its "creation of growth businesses." Specifically, it is promoting the creation and expansion of businesses such as organic EL materials, next-generation display materials, and photoelectric conversion materials for high-speed data communications. Among these, solid electrolytes, a key material for solid-state batteries, are being positioned as a core business to support the Company's growth strategy, and the Company is advancing technical development and efforts toward mass production.

- Solid Electrolytes Developed by Idemitsu
The raw material uses sulfur components produced as a byproduct in the petroleum refining process. Idemitsu identified the utility of sulfur components as early as the mid-1990s and has successfully developed solid electrolytes by leveraging the technological capabilities it has cultivated over many years.

- Technical Development for Mass Production of Solid Electrolytes
This project has been adopted as part of the Green Innovation Fund Project: Development of Next-Generation Storage Batteries and Next-Generation Motors by the New Energy and Industrial Technology Development Organization (NEDO).

- Employee Interview (Lithium Battery Materials Department)
An interview with staff members from the Lithium Battery Materials Department, who are taking on the challenge of developing and mass-producing "solid electrolytes," a key material for solid-state batteries that does not yet exist in the market.

- Press Release: Final Investment Decision and Commencement of Construction for Large-Scale Pilot Plant for Solid Electrolyte (Solid-State Battery Material) (January 29, 2026)