> ## Content Index > Fetch the complete content index at: https://www.insidedeeptech.com/llms.txt > Use this file to discover other available public pages before exploring further. # Toyota and Idemitsu: A Full Guide to Sulfide All-Solid-State Batteries When the Factory Is the Hard Part - URL: https://www.insidedeeptech.com/toyota-idemitsu-sulfide-all-solid-state-batteries-full-guide/ - Published: 2026-09-29T06:06:00.000Z - Updated: 2026-09-29T06:06:00.000Z - Description: Toyota Idemitsu sulfide solid-state full guide (Sept 2026): 2027-28 ASSB BEV target, Chiba Li2S (~21.3B yen, 3 GWh/year equiv.) and several-hundred-ton electrolyte pilot, METI certification, and honest factory limits. - Author: Austin Heaton - Tags: Energy, Hardware, Deep Tech Commercialization calendars are easy. Factories are not. On January 29, 2026, **Idemitsu Kosan** took a final investment decision and started construction of a large pilot plant for sulfide solid electrolytes at its Chiba Complex, the material backbone for **Toyota**'s all-solid-state battery plan. The target window is still **2027-2028**. The hard part is whether those plants ship powder at the quality, cost, and rate a production BEV needs. This guide covers the Toyota/Idemitsu sulfide all-solid-state path as of September 2026: what the October 2023 cooperation agreement actually locked in, how the June 2023 Technical Workshop performance claims are framed, what METI certification does and does not prove, how the Li2S and solid-electrolyte plants stack as of early 2026, and the honest limits that still sit between a pilot line and a production car. For ceramic-separator licensing, see Inside Deep Tech's [QuantumScape QSE-5 full guide](https://www.insidedeeptech.com/quantumscape-qse-5-licensing-model-2029-full-guide/). For quasi-solid and sulfide OEM paths into Mercedes and Stellantis, see the [Factorial Energy FEST and Solstice full guide](https://www.insidedeeptech.com/factorial-energy-fest-solstice-cells-full-guide/). For ceramic Logithium cells with Mercedes priority testing, see the [ProLogium Gen4 full guide](https://www.insidedeeptech.com/prologium-gen4-ceramic-electrolyte-cells-full-guide/). Numbers below come from Toyota and Idemitsu primary releases plus electrive and Electrek reporting on those releases, not invented datasheets. ## Key Takeaways - Toyota and Idemitsu target ASSB BEV **commercialization in 2027-28**, then full-scale mass production ([Toyota](https://www.automotiveworld.com/news-releases/idemitsu-and-toyota-announce-beginning-of-cooperation-toward-mass-production-of-all-solid-state-batteries-for-bevs/?ref=insidedeeptech.com)). - Jan 29, 2026: Idemitsu FID + construction of large SE pilot, **several hundred tons/year**, complete **2027** at Chiba ([Idemitsu](https://www.idemitsu.com/jp/news/2025/260129%5Fen.pdf?ref=insidedeeptech.com)). - Li2S plant: \~**21.3 billion yen** project, \~**7.1 billion yen** max grant, **3 GWh/year** equivalent, June 2027 ([Idemitsu](https://www.idemitsu.com/jp/news/2024/250227%5Fen.pdf?ref=insidedeeptech.com)). - Workshop target band: \~**1,200 km** range path and **10-80% charge in 10 min** or less ([Green Car Reports](https://www.greencarreports.com/news/1139929%5Ftoyota-10-minute-ev-charging-solid-state-battery-due-in-2027?ref=insidedeeptech.com)). - METI certified Toyota ASSB R&D/production under the Supply Assurance Plan; performance liquid cells **9 GWh/year** from 2026 ([Toyota](https://www.automotiveworld.com/news/toyotas-next-generation-bev-battery-development-and-production-plan-certified-by-meti/?ref=insidedeeptech.com)). 📌 Scope note: This is a named-thing Full Guide to Toyota and Idemitsu's sulfide all-solid-state battery path as of September 2026, not a glossary of "what is a solid-state battery," not investment advice, and not a claim that sulfide ASSB BEVs are already in series production. Range, charge-time, plant-capacity, and cost figures come from Toyota and Idemitsu press materials and secondary reports cited inline. Inside Deep Tech has not audited cell performance in an independent lab. ## What the partnership actually is On October 12, 2023, [Toyota and Idemitsu](https://www.automotiveworld.com/news-releases/idemitsu-and-toyota-announce-beginning-of-cooperation-toward-mass-production-of-all-solid-state-batteries-for-bevs/?ref=insidedeeptech.com) announced an agreement to develop mass-production technology for **sulfide solid electrolytes**, improve productivity, and establish a supply chain for all-solid-state batteries in BEVs. The stated goal is commercialization in **2027-28** (the window Toyota set at its June 2023 Technical Workshop), **followed by full-scale mass production**. The chemistry choice is deliberate. Sulfide solid electrolytes are soft and adhesive to other materials, which both companies frame as suited to battery mass production. Idemitsu has worked on elemental technologies since **2001**; Toyota since **2006**. CEO Koji Sato said Idemitsu has been a partner on the durability problem since **2013**: repeated charge and discharge can crack interfaces between cathodes, anodes, and solid electrolytes. The joint answer is a more flexible, adhesive, crack-resistant electrolyte combined with Toyota Group cathode and anode know-how. The cooperation is staged in three phases. Phase 1 develops better sulfide electrolytes on quality, cost, and lead time, and prepares a large pilot. Phase 2 builds and runs that pilot so Idemitsu can manufacture sulfide electrolyte at scale while Toyota develops ASSB cells and the BEVs that use them for a **2027-28** market launch. Phase 3 studies future full-scale mass production based on Phase 2 results. That sequence matters: the press cycle is not the factory cycle. | Phase | Who leads what | What success looks like | | ------------------------------------ | ---------------------------------------------------- | ------------------------------------------ | | 1\. Develop SE + prep large pilot | Joint SE quality/cost/lead time; Idemitsu pilot prep | Mass-production demonstration path ready | | 2\. Mass production via large pilot | Idemitsu manufactures SE; Toyota builds ASSB + BEV | Market launch of ASSB BEVs in 2027-28 | | 3\. Study full-scale mass production | Both, based on Phase 2 results | Decision path beyond limited early volumes | Source: [Toyota / Idemitsu cooperation release (Oct 12, 2023)](https://www.automotiveworld.com/news-releases/idemitsu-and-toyota-announce-beginning-of-cooperation-toward-mass-production-of-all-solid-state-batteries-for-bevs/?ref=insidedeeptech.com). ## The Workshop numbers: relative targets, not a datasheet Treat Toyota's June 13, 2023 Technical Workshop battery slide as a relative roadmap, not a certified cell datasheet. Per Toyota's June 2023 battery briefing, as reported by [Green Car Reports](https://www.greencarreports.com/news/1139929%5Ftoyota-10-minute-ev-charging-solid-state-battery-due-in-2027?ref=insidedeeptech.com), the company said it was aiming to commercialize solid-state batteries for EVs in the **2027-2028** timeframe, with fast charging from **10% to 80% in 10 minutes or less**. The same reporting maps Toyota's relative range claims to about **1,200 km** (746 miles) initially and up to roughly **1,500 km** (932 miles) on a higher-spec path, including a potential **50%** improvement in future solid-state versions. [electrive](https://www.electrive.com/2026/02/02/toyota-partner-idemitsu-kosan-builds-pilot-plant-for-solid-electrolytes/?ref=insidedeeptech.com) likewise cites initially **1,200 km** and up to **1,500 km** at peak performance for the Toyota ASSB roadmap. Those kilometer figures sit on company relative claims and optimistic test cycles, not independent lab certificates. [Green Car Reports](https://www.greencarreports.com/news/1139929%5Ftoyota-10-minute-ev-charging-solid-state-battery-due-in-2027?ref=insidedeeptech.com) notes the 1,200 / 1,500 km framing is often tied to China's CLTC cycle, which runs high versus real-world EPA results. Treat them as Toyota's public ambition band, not a production datasheet. 💡 Inside Deep Tech's take: Believe the calendar and the factory CAPEX as industrial evidence. Treat the \~1,200 / 1,500 km range band and 10-minute 10-80% charge as company targets on optimistic cycles until a named model, cycle protocol, and production cell publish. The factory is the hard part because sulfide powder quality, interface durability, and cost have to land together. ## METI certification: what it buys On September 6, 2024, [Toyota](https://www.automotiveworld.com/news/toyotas-next-generation-bev-battery-development-and-production-plan-certified-by-meti/?ref=insidedeeptech.com) said METI certified its next-generation battery and all-solid-state plans under Japan's **Supply Assurance Plan for Batteries** (Economic Security Promotion Act). Certification covered three items: | Item | Applicant | Start / scale (as disclosed) | | ------------------------------ | ---------------------------------- | --------------------------------------------------------------- | | Next-gen battery (performance) | PPES + Toyota | From 2026, gradually; 9 GWh/year | | Next-gen battery (performance) | PEVE (now TOYOTA BATTERY) + Toyota | Same program umbrella | | All-solid-state battery | Toyota | R&D and production certified; start year / scale blank in table | Source: [Toyota METI certification release (Sep 6, 2024)](https://www.automotiveworld.com/news/toyotas-next-generation-bev-battery-development-and-production-plan-certified-by-meti/?ref=insidedeeptech.com). Here's why that matters. METI certification unlocks policy support for an equipment-heavy industry Japan has labeled critical. It is not a vehicle SOP date, not a Wh/kg third-party certificate, and not proof that ASSB capacity equals the **9 GWh/year** disclosed for the performance liquid program. The ASSB row lists Toyota as applicant for R&D and production without filling production start year or scale in the published table. ## Factories: Li2S first, then several hundred tons of electrolyte The industrial story in 2025-2026 is two Chiba plants, not a finished BEV line. On February 27, 2025, [Idemitsu](https://www.idemitsu.com/jp/news/2024/250227%5Fen.pdf?ref=insidedeeptech.com) decided to build a large-scale **lithium sulfide (Li2S)** production facility at the Chiba Complex (Ichihara City), scheduled for completion in **June 2027**. The company frames capacity as world top-class, **equivalent to 3 GWh/year of storage batteries**. Total project cost is about **21.3 billion yen**, with about **7.1 billion yen** planned as the maximum grant under METI's storage-battery supply-assurance plan. Li2S is the intermediate raw material for Idemitsu's sulfide solid electrolytes, produced from sulfur by-products of petroleum refining. Idemitsu says it established Li2S mass-production technology in **1994**. On January 29, 2026, [Idemitsu](https://www.idemitsu.com/jp/news/2025/260129%5Fen.pdf?ref=insidedeeptech.com) announced the final investment decision and construction start for the **large pilot facility for solid electrolytes**. Production capacity is expected to reach **several hundred tons per year**. Construction completion is aimed for **2027** at the same Chiba Complex, with Chiyoda Corporation as contractor. Two small-scale verification plants already run: Plant 1 develops electrolytes primarily for Toyota; Plant 2 develops other types. The large pilot is the next scale-up based on Plant 1 results. The solid electrolytes from this facility are planned for Toyota's ASSB BEVs targeting **2027-2028** commercialization. Technical development sits under NEDO's **Green Innovation Fund** for next-generation storage batteries and motors. [electrive](https://www.electrive.com/2026/02/02/toyota-partner-idemitsu-kosan-builds-pilot-plant-for-solid-electrolytes/?ref=insidedeeptech.com) and [Electrek](https://electrek.co/2026/01/30/toyota-partner-breaks-ground-on-all-solid-state-ev-battery-plant/?ref=insidedeeptech.com) both note the early volumes will be limited as the program scales. That matches Phase 2 language from 2023: start producing for BEVs in 2027-28, then lay the foundation for mass production. A several-hundred-ton electrolyte pilot is not a multi-GWh cell gigafactory. It is the powder bottleneck Toyota cannot skip. | Milestone | Date / status | What it proves | | ----------------------------------- | ----------------------------------- | --------------------------------------------------------------- | | ASSB commercialization target set | Jun 2023 Workshop (via trade press) | 2027-28 window; \~1,200/1,500 km band; 10-min 10-80% | | Toyota-Idemitsu cooperation | Oct 12, 2023 | Sulfide SE mass-production partnership + 3 phases | | METI Supply Assurance certification | Sep 6, 2024 | Policy support for ASSB R&D/production + 9 GWh liquid path | | Li2S large facility decision | Feb 27, 2025 | \~21.3B yen; \~7.1B yen max grant; 3 GWh/year equiv.; June 2027 | | Large SE pilot FID + construction | Jan 29, 2026 | Several hundred tons/year; complete 2027; Plant 1 for Toyota | | ASSB BEV market launch (target) | 2027-28 | Company target; not yet a named model SOP | Source: [Toyota Workshop](https://www.greencarreports.com/news/1139929%5Ftoyota-10-minute-ev-charging-solid-state-battery-due-in-2027?ref=insidedeeptech.com); [cooperation release](https://www.automotiveworld.com/news-releases/idemitsu-and-toyota-announce-beginning-of-cooperation-toward-mass-production-of-all-solid-state-batteries-for-bevs/?ref=insidedeeptech.com); [METI certification](https://www.automotiveworld.com/news/toyotas-next-generation-bev-battery-development-and-production-plan-certified-by-meti/?ref=insidedeeptech.com); [Idemitsu Li2S](https://www.idemitsu.com/jp/news/2024/250227%5Fen.pdf?ref=insidedeeptech.com); [Idemitsu large pilot](https://www.idemitsu.com/jp/news/2025/260129%5Fen.pdf?ref=insidedeeptech.com). ## How Toyota/Idemitsu sits next to QS, Factorial, and ProLogium Solid-state coverage only helps if you keep the chemistries and industrial models apart. | Company / platform | Electrolyte class | OEM / industrial signal | Model | | ------------------------- | -------------------------------------- | ---------------------------------------------- | ------------------------------------------------ | | Toyota + Idemitsu | Sulfide solid electrolyte | 2027-28 ASSB BEV target; Chiba Li2S + SE pilot | OEM + materials partner; Japan METI/NEDO support | | QuantumScape QSE-5 | Ceramic separator, anode-free Li-metal | PowerCo licensing path into 2029 | Licensing-heavy; see QSE-5 guide | | Factorial FEST / Solstice | Quasi-solid polymer; sulfide all-solid | Mercedes EQS road test + Stellantis | Public (FAC); SK On / Mitsui | | ProLogium Gen4 | Inorganic ceramic / SF-Ceramion | Mercedes priority testing (Sep 2026) | Own gigafactories (Taiwan + Dunkirk design) | Source: company materials summarized in Inside Deep Tech's [QuantumScape](https://www.insidedeeptech.com/quantumscape-qse-5-licensing-model-2029-full-guide/), [Factorial](https://www.insidedeeptech.com/factorial-energy-fest-solstice-cells-full-guide/), and [ProLogium](https://www.insidedeeptech.com/prologium-gen4-ceramic-electrolyte-cells-full-guide/) guides, plus Toyota/Idemitsu primary releases above. Toyota/Idemitsu's differentiator is vertical Japanese industrialization: sulfur by-product to Li2S to sulfide electrolyte to OEM cell, with METI and NEDO money on the materials side. QuantumScape's differentiator is anode-free ceramic separator licensing into Volkswagen Group's PowerCo. Factorial's is quasi-solid FEST that can ride existing lithium-ion equipment while Solstice waits for sulfide scale. ProLogium's is ceramic Logithium lines that already claim Gen 3.5 mass production. Different bets. Same unfinished category. ## Honest limits Name the downside before the FAQ. - 2027-28 is a commercialization **window**, not a named model SOP or disclosed annual GWh for ASSB cells ([Toyota](https://www.automotiveworld.com/news-releases/idemitsu-and-toyota-announce-beginning-of-cooperation-toward-mass-production-of-all-solid-state-batteries-for-bevs/?ref=insidedeeptech.com)). - Workshop range (\~1,200 / 1,500 km) and 10-minute charge figures are company targets on optimistic cycles ([Green Car Reports](https://www.greencarreports.com/news/1139929%5Ftoyota-10-minute-ev-charging-solid-state-battery-due-in-2027?ref=insidedeeptech.com); [electrive](https://www.electrive.com/2026/02/02/toyota-partner-idemitsu-kosan-builds-pilot-plant-for-solid-electrolytes/?ref=insidedeeptech.com)). - The large SE pilot is **several hundred tons/year** of electrolyte powder, not multi-GWh cell output ([Idemitsu](https://www.idemitsu.com/jp/news/2025/260129%5Fen.pdf?ref=insidedeeptech.com)). - Li2S capacity is disclosed as **3 GWh/year equivalent**, not as finished pack volume ([Idemitsu](https://www.idemitsu.com/jp/news/2024/250227%5Fen.pdf?ref=insidedeeptech.com)). - METI's ASSB row certifies R&D and production plans without publishing start year or scale in the table ([Toyota](https://www.automotiveworld.com/news/toyotas-next-generation-bev-battery-development-and-production-plan-certified-by-meti/?ref=insidedeeptech.com)). - Sulfide handling, moisture sensitivity, and interface durability remain the classic scale risks every OEM will re-test under its own protocols. ## Who this is for (and who should wait) If you are an OEM materials or cell-program lead, Toyota/Idemitsu belongs on the sulfide shortlist because the powder plants are funded and under construction, not just sketched. If you are a deep-tech investor mapping Japanese industrials, treat the **21.3 billion yen** Li2S CAPEX and the several-hundred-ton electrolyte pilot as the evidence, and the 2027-28 BEV window as the open question. If you need a 2026 production car with sulfide ASSB cells, this program does not give you that calendar. If you are comparing power bets beyond EV cells, keep the series next to Inside Deep Tech's [800 VDC power distribution guide for AI data centers](https://www.insidedeeptech.com/800-vdc-power-distribution-ai-data-centers-full-guide/) and the companies tracked in the [Top 100 deep tech companies list](https://www.insidedeeptech.com/top-100-companies-in-the-deep-tech-industry-2026-list/). --- [Read the ProLogium Gen4 guide](https://www.insidedeeptech.com/prologium-gen4-ceramic-electrolyte-cells-full-guide/) [Read the Factorial FEST / Solstice guide](https://www.insidedeeptech.com/factorial-energy-fest-solstice-cells-full-guide/) [ProLogium Gen4: A Full Guide to Ceramic-Electrolyte Cells When Mercedes Gets First AccessCeramic SF-Ceramion cells, Mercedes priority testing, Gen 3.5 TÜV numbers, Dunkirk design capacity, and honest limits.![](https://www.insidedeeptech.com/favicon.ico)Inside Deep Tech](https://www.insidedeeptech.com/prologium-gen4-ceramic-electrolyte-cells-full-guide/) ## FAQ #### What is the Toyota and Idemitsu solid-state partnership? It is a October 12, 2023 agreement to co-develop mass-production technology for **sulfide solid electrolytes**, improve productivity, and build a supply chain so Toyota can commercialize all-solid-state battery BEVs in **2027-28**, then move to full-scale mass production. See the [Toyota newsroom release](https://www.automotiveworld.com/news-releases/idemitsu-and-toyota-announce-beginning-of-cooperation-toward-mass-production-of-all-solid-state-batteries-for-bevs/?ref=insidedeeptech.com). #### When will Toyota launch solid-state battery EVs? Toyota's stated target remains **2027-2028**, first set at the June 2023 Technical Workshop and repeated in the Idemitsu cooperation and plant releases. That is a commercialization window, not a named model or disclosed ASSB GWh volume. #### What factories is Idemitsu building for Toyota? Two Chiba Complex projects: a **Li2S** intermediate plant (\~21.3 billion yen, \~7.1 billion yen max grant, capacity equivalent to 3 GWh/year, complete June 2027 per the [February 27, 2025 release](https://www.idemitsu.com/jp/news/2024/250227%5Fen.pdf?ref=insidedeeptech.com)) and a **large solid-electrolyte pilot** (several hundred tons/year, complete 2027, FID and construction start January 29, 2026 per the [Idemitsu PDF](https://www.idemitsu.com/jp/news/2025/260129%5Fen.pdf?ref=insidedeeptech.com)). #### What performance does Toyota claim for sulfide ASSB? Toyota's June 2023 briefing, as reported by [Green Car Reports](https://www.greencarreports.com/news/1139929%5Ftoyota-10-minute-ev-charging-solid-state-battery-due-in-2027?ref=insidedeeptech.com), framed ASSB commercialization for 2027-2028 with **10% to 80% charge in 10 minutes or less**, and trade press maps the range ambition to about **1,200 km** initially and up to about **1,500 km** on a higher-spec path (also [electrive](https://www.electrive.com/2026/02/02/toyota-partner-idemitsu-kosan-builds-pilot-plant-for-solid-electrolytes/?ref=insidedeeptech.com)). These are company targets on optimistic cycles, not third-party cell certificates. #### Did METI certify Toyota's solid-state plan? Yes. On September 6, 2024, [Toyota](https://www.automotiveworld.com/news/toyotas-next-generation-bev-battery-development-and-production-plan-certified-by-meti/?ref=insidedeeptech.com) said METI certified next-generation performance batteries (9 GWh/year from 2026 at PPES/PEVE) and R&D plus production of all-solid-state batteries under the Supply Assurance Plan for Batteries. The ASSB row does not publish start year or scale in the table. #### Is Toyota's chemistry the same as QuantumScape or ProLogium? No. Toyota/Idemitsu is a **sulfide** solid-electrolyte path. QuantumScape is ceramic-separator anode-free lithium-metal. ProLogium Gen4 is inorganic ceramic / SF-Ceramion. Factorial runs both quasi-solid FEST and sulfide Solstice. Keep the electrolyte class separate when you compare OEM programs. #### Why does Inside Deep Tech say the factory is the hard part? Because the public evidence in 2025-2026 is materials CAPEX and pilot scale (Li2S + several-hundred-ton electrolyte), while vehicle SOP, ASSB GWh, and independently measured cell metrics are still open. Sulfide softness helps manufacturability in principle; moisture sensitivity and interface durability still have to clear OEM protocols at rate. #### Should investors treat 1,200 km range slides as proven? No. Use funded Chiba plants, METI/NEDO support, and the repeated 2027-28 window as evidence of industrial intent. Treat Workshop range and charge-time marketing as relative company targets until a named production cell and protocol publish. This guide is not investment advice. --- Next on the solid-state watchlist: whether Idemitsu's 2027 Chiba completions hold, whether Toyota names a first ASSB BEV and volume band, and whether sulfide interface durability survives OEM cycle protocols at pilot rate. Until then, the factories under construction are the checked facts, and 2027-28 remains the open door. [Explore more Inside Deep Tech energy coverage](https://www.insidedeeptech.com/)