Factorial CEO Says Cells with 375Wh/kg Energy Density a ‘Milestone’ for Stellantis

October 1, 2025

Sebastian Blanco

The standout claims from Factorial and Stellantis and the cells resulting from their partnership. (Factorial/Stellantis)

In April, Stellantis and Factorial Energy announced that the two companies validated automotive-sized solid-state battery cells with an energy density of 375Wh/kg. The companies called this “a major step toward commercial use.” Factorial’s cells can charge from 15% to over 90% in 18 minutes at room temperature and have discharge rates up to 4C. Stellantis invested $75 million in Factorial in 2021. SAE Media recently spoke with Factorial CEO Siyu Huang about the partnership.

The Factorial Electrolyte System Technology (FEST) cells that Stellantis will use have a claimed energy density of 375Wh/kg. How are these different from the B-samples sent to Mercedes-Benz last year, which had a rating of over 106Ah while the Stellantis ones are 77Ah?

We’re not releasing technical spec sheets or comparing across programs, but what we can confirm is that the validated 77Ah FEST cells for Stellantis are large-format, automotive-sized solid-state batteries with an energy density of 375Wh/kg. The Ah rating relates to cell capacity. In general, differences like 77Ah vs. 106Ah reflect tailoring cells for specific vehicle platforms and performance requirements. For Stellantis, this validation is a milestone because it's the first time a solid-state lithium-metal battery of this size has demonstrated both high energy density and durability over 600 charge cycles.

Stellantis will test these batteries in Dodge Charger Daytonas by 2026, and the companies are “closely collaborating on pack design” and on reducing weight and improving overall system efficiency. What challenges did the engineering teams face and find solutions for?

Stellantis and Factorial’s collaboration goes beyond cell development to jointly optimizing pack architecture, vehicle integration and system-level efficiency. This includes reducing weight to extend range and improve performance. While we’re not sharing specific engineering workflows, the integration of solid-state batteries into a demonstration fleet by 2026 reflects progress on joint development milestones and real-world readiness.

Can you share any technical details about how the collaboration goes “beyond cell development to optimizing pack architecture, improving vehicle integration, and enhancing overall range and cost efficiency”?

Factorial’s FEST technology offers higher energy density and the potential for smaller, lighter packs, giving OEMs more flexibility in vehicle design. The collaboration with Stellantis includes refining pack design and integration approaches to take full advantage of these benefits, with the goal of reducing overall system weight and improving both range and cost efficiency. This work is ongoing and tied directly to the demonstration fleet planned for 2026.

Tell me about Factorial’s “AI-driven tools.” How was AI used in the development of the cells, and how did AI change the process?

Factorial’s AI-driven tools played a key role in developing the latest FEST electrolyte formulation, which supports high-performance operation from -30 C to 45 C (-22 F to 113 F), helping to overcome traditional temperature limitations in solid-state batteries. AI accelerated electrolyte optimization and it enabled faster iteration to balance safety, energy density and fast-charging capability in large-format cells. We also use a digital twin to make more informed decisions about which physical experiments – such as electrolyte formulations – to run. In addition, we used it to forecast the cycle life of cell designs, which was later validated through physical testing.