Idemitsu Kosan — Solid-State Electrolyte Program
Table of Contents

⚠ Disclaimer: This entry may be incomplete, out of date, or inaccurate. It is AI-maintained on a best-effort basis. Do not rely on it as a sole source — verify claims independently using the sources listed below.

Summary

Idemitsu Kosan is a Japanese petroleum and chemicals company that has researched sulfide solid electrolytes since the mid-1990s and is Toyota’s partner in mass-producing them. It is building a lithium sulfide (Li₂S) plant at its Chiba Complex for about ¥21.3 billion, due in June 2027, and began construction of a larger solid electrolyte pilot plant in January 2026. Whether Toyota reaches its 2027–2028 all-solid-state EV target depends in part on Idemitsu’s materials scale-up.

Key Facts

  • Type: Public Japanese petroleum and chemicals company (pivoting part of its business to battery materials)
  • Solid electrolyte R&D history: Idemitsu researched all-solid-state battery elemental technologies from 2001; CEO Shunichi Kito says it discovered the usefulness of sulfur components in the mid-1990s; Toyota says Idemitsu has been its partner on the battery cracking issue since 2013 (Toyota, Electrek)
  • Toyota cooperation: announced 12 October 2023, covering sulfide solid electrolyte mass-production technology and supply chain; the announcement does not mention exclusivity (Toyota)
  • Lithium sulfide plant (Chiba Complex): about ¥21.3 billion with a ¥7.1 billion METI grant; about 1,000 t per year (equivalent to about 3 GWh per year of batteries); operational June 2027 (Electrive)
  • Solid electrolyte pilot plant (Chiba): construction began in early 2026; several hundred t per year; completion scheduled for end of 2027, with operation in early 2028 (Battery-News)
  • Partners named for the Chiba pilot plant: Toyota, Chiyoda Corporation and Sumitomo Metal (Battery-Tech Network)
  • Intended customer: Toyota; Idemitsu says the plant’s materials are intended for Toyota’s all-solid-state batteries
  • Commercialization target: 2027 or 2028, aligned with Toyota’s all-solid-state EV launch

What It Is / How It Works

Sulfide solid electrolytes are the leading candidate for high-performance all-solid-state batteries because their ionic conductivity approaches that of liquid electrolytes. They are chemically sensitive, reacting with moisture and oxygen, which makes large-scale manufacturing hard.

Idemitsu is a materials producer, not a cell maker. Lithium sulfide is the key precursor from which sulfide electrolytes such as argyrodite-type compounds are synthesized, and Idemitsu makes it from sulfur recovered in petroleum refining (see Sulfur). In the Toyota cooperation, Idemitsu manufactures and mass-produces the solid electrolyte while Toyota develops the batteries and vehicles. The work runs in three phases: joint development and preparation of a large pilot facility, mass production at that facility, then study of full-scale commercialization (Toyota).

The Chiba solid electrolyte pilot plant is the step after the lithium sulfide plant: it converts Li₂S into finished electrolyte in a controlled, large-format process. Mass-production process development is supported by Japan’s NEDO agency under a green innovation program (Battery-News).

Notable Developments

  • 2026-02 to 2026-10: No newer Idemitsu or Toyota milestone (completion, capacity change, customer or financing) was found in searches through October 2026; a September 2026 article repeating the 2027–2028 target cites no primary source and is not relied on.
  • 2026-02: Idemitsu starts construction of the Chiba solid electrolyte pilot plant (several hundred t per year, completion end of 2027); CEO Kito says the electrolyte will open a new future for mobility. (Battery-News, Electrek)
  • 2025-10: Toyota, Sumitomo Metal Mining and Idemitsu detail their path to a first all-solid-state EV in 2027 or 2028; Toyota received METI certification to manufacture the batteries in Japan. (Electrek)
  • 2025-03: Idemitsu announces the ¥21.3 billion lithium sulfide plant at Chiba. (Electrive)
  • 2023-10-12: Toyota and Idemitsu announce cooperation on sulfide solid electrolyte mass production. (Toyota)

Key People / Key Organizations

Shunichi Kito — CEO

  • LinkedIn: not found
  • Role: CEO of Idemitsu Kosan; publicly leads the solid electrolyte message (Electrek)
  • Career (reverse-chronological): prior roles not available in the sources reviewed

Tetsuji Mishina — Executive Officer; Manager, Lithium Battery Material Department

  • LinkedIn: not found
  • Role: Executive Officer; leads the Lithium Battery Material Department; primary external spokesperson for Idemitsu’s solid electrolyte commercialization program; publicly announced the ¥21.3B Li₂S plant capacity (1,000 MT/year) and final investment decisions for the solid electrolyte pilot facility
  • Background: Long-tenure Idemitsu career through the petroleum/chemicals division into battery materials; no external employment history available from public sources. His public statements indicate deep technical familiarity with the sulfide electrolyte manufacturing challenges, suggesting direct R&D involvement over multiple years.

Nakata — Development Leader, Solid Electrolyte Program

  • LinkedIn: not found
  • Role: Development leader for solid electrolyte project within Idemitsu’s Battery Material Development Center; named in Idemitsu’s published accounts of the solid electrolyte program history
  • Background: Idemitsu career spanning the early R&D phase of the solid electrolyte program; part of the team that worked on sulfide electrolytes starting in the 1990s, over 30 years before the current industry spotlight

Key Partner Organizations

  • Toyota Motor Corporation — Cooperation partner since October 2023 (collaboration since 2013 on cracking issues per Toyota); 2027–2028 all-solid-state EV target
  • Sumitomo Metal Mining — Secondary materials supply agreement with Toyota for cathode materials (separate from Idemitsu’s electrolyte role)

Roles of Mishina and Nakata are as of the previous review and were not re-verified; verify current status.

People — Last Reviewed: 2026-10-20

Claim Verification

Claim: Lithium sulfide plant operational in June 2027

Status: Unverified (construction-stage schedule)

Supporting sources:

  • Electrive — company announcement of the June 2027 target, ¥7.1 billion METI grant
  • Battery-News — repeats the June 2027 date

Refuting / questioning sources:

  • None found; the date has not yet been tested by completion.

Summary: A funded, government-supported project on schedule as of early 2026; no completion evidence yet.

Claim: Toyota will launch all-solid-state BEVs in 2027–2028 using this supply chain

Status: Unverified (target)

Supporting sources:

  • Toyota and Electrek — Toyota and Idemitsu both state 2027–2028 targets

Refuting / questioning sources:

  • Electrek — notes Toyota has promised this technology for years; the Chiba solid electrolyte pilot plant is not scheduled to complete until end of 2027, close to the stated vehicle window.

Summary: Targets are stated by the partners; the electrolyte pilot plant timing leaves little margin for a 2027 launch.

Supply Chain Position

Idemitsu operates at the Precursor Chemicals → Electrolyte/Active Materials layers as a raw material and electrolyte producer, not a cell maker. It is vertically integrated from petroleum refining (which produces sulfur as a by-product) through lithium sulfide to finished sulfide electrolyte; lithium inputs come via lithium commodity markets. The downstream customer named in sources is Toyota; no supply relationship with other sulfide developers such as Solid Power or QuantumScape is disclosed in the sources reviewed.

⚑ Key bottleneck: the Chiba lithium sulfide plant (about 1,000 t per year, about 3 GWh equivalent) is the only large dedicated Li₂S investment documented in this knowledge base and its first intended customer is Toyota. Additional Li₂S producers will be needed as sulfide programs scale. Sulfur price volatility since 2025 (see Sulfur) is a cost risk for any producer outside a refinery-integrated position.

Sources

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