Factorial Logo Credit: Factorial Factorial Energy has signed a joint development agreement with Japan’s Mitsui Kinzoku for solid electrolytes, the latest in a run of partnerships its chief executive says are necessary because no single company can bring all-solid-state batteries to market. ProLogium, which is building Europe’s solid-state gigafactory at Dunkirk, is already mass-producing all-solid-state cells in Taiwan. Factorial Energy has signed a joint development agreement with Japan’s Mitsui Kinzoku to industrialise its all-solid-state platform, the latest in a run of partnerships, InsideEVs reported. “Battery innovation can’t be done by one single company,” chief executive Siyu Huang said. The company listed on Nasdaq in June.
That is an unusual thing for a battery startup to say out loud. The coalition splits the problem up. Posco Future M handles anodes and cathodes, Korea’s Phil Energy covers manufacturing tools, and Factorial is exploring how to scale with SK On. Factorial says it holds foundational intellectual property for all-solid electrolytes.
Two of its partners are European. It has joint development agreements with Volkswagen’s PowerCo battery division and with Hyundai, and Mercedes ran a modified EQS 1,200km on its cells in September 2025. Huang said the company is “very well settled for both North American and European volumes“. Mercedes is a backer as well as a test partner, and Stellantis supplied the Dodge demonstrator.
None of it is in a production car yet. The semi-solid FEST cell is rated up to 375 watt-hours per kilogram and sits in prototype Mercedes and Dodge vehicles. The all-solid Solstice targets 450 Wh/kg, roughly double a current lithium-ion cell, and uses a sulfide electrolyte Mitsui makes at a dedicated plant in Saitama. Karma Automotive is due to be the first to ship, in 2028.
The all-solid half is further off than the announcements suggest. It is also not unclaimed territory. ProLogium is already mass-producing all-solid-state cells at 381 Wh/kg in Taiwan, about 6,000 packs a year, and broke ground on its French gigafactory in February. Dunkirk is still a building site.
It is due to start at 0.8 GWh in 2028 and reach 12 GWh by 2032, subsidised by France and sited beside the Gravelines nuclear plant. It is also Taiwanese-owned, which is what a European solid-state champion looks like after Northvolt. The continent’s own champion did not get there. The other view is that none of this reaches cars soon.
LG Energy Solution’s North America president said last month that the technology will arrive in phones “probably a decade“ before it reaches electric cars, because large formats are where companies struggle. Factorial’s answer is to stop trying to do it alone.
