Stellantis plans 2026 demo fleet with solid-state battery models

Stellantis claims it has taken a significant step forward in electric vehicle battery technology. It has cleared internal validation tests for its next-generation solid-state cells and is now paving the way for a demonstration fleet by 2026. But the revolution might be a bit less victorious than the press clippings suggest.

The 77 Ah cells, developed with the American startup Factorial Energy, deliver an energy density of 375 watt-hours per kilogram—around 50% higher than today’s top-tier lithium-ion batteries. Charging performance is equally striking: they can jump from 15% to 90% charge in just 18 minutes at room temperature.

This milestone strengthens Stellantis’ € 66 million partnership with Factorial, first announced in 2021. Mercedes is also using these cells, but whereas the Germans chose for the limo eQS, Stellantis will debut the battery packs in prototype Dodge Charger Daytona EVs before expanding across the group’s brands. 

The electric muscle car will serve as the platform for the solid-state battery demonstration fleet, underscoring Stellantis’ intent to blend high-performance heritage with cutting-edge EV technology. Sports cars like these are portrayed as the gateway to solid-state battery adoption.

Semi-solid today, solid-state tomorrow

But these aren’t fully solid-state batteries—yet. The Factorial Electrolyte System Technology (FEST) cells are semi-solid-state, retaining a small fraction (5–10% by weight) of liquid solvent within the electrolyte. This helps maintain fast ion transport while significantly reducing flammability, a crucial safety feature.

In contrast, true solid-state batteries replace all liquid components with solid materials like ceramics or sulfides. They promise even higher energy densities—450 to 550 Wh/kg—and intrinsic fire resistance, but their manufacturing remains complex and expensive. Full solid-state cells require specialist environments, such as dry-room sintering, and still face technical hurdles like dendrite formation at scale.

China’s headstart

Though the validation bears big significance, Stellantis isn’t the first manufacturer offering these types of solid-state batteries. Chinese automakers, however, are already proving that semi-solid-state technology works in the real world. NIO has been offering 150 kWh semi-solid packs through its battery swap stations since mid-2024, delivering up to 1,000 km of range. Zeekr sold 1,000 limited-edition 001 models with a 140 kWh semi-solid battery pack, while IM Motors’ L6 launched with a 133 kWh semi-solid battery capable of adding 400 kilometers of range in just 12 minutes on a high-voltage platform.

Though these early models come with hefty price tags and limited production runs, they demonstrate that semi-solid manufacturing can scale faster and more cheaply than full solid-state designs—something Stellantis is keen to replicate, particularly for its heavier SUVs and pickup trucks, where battery weight can exceed 900 kilograms.

The road ahead

Cost remains the biggest barrier. Factorial’s pilot cells are currently up to 30 times more expensive than conventional lithium-ion equivalents. However, Stellantis expects economies of scale to cut costs rapidly, halving prices with every tenfold increase in production.

For Factorial CEO Siyu Huang, the validation marks a turning point in bringing solid-state batteries from research to reality. She acknowledges that the path hasn’t been easy. The journey involved significant production hurdles and material challenges. “It took us a long time, with a lot of scrap,” Huang admitted in an interview. The group will now focus on packaging, crash-testing, and validating these battery packs through 2025.

The competition isn’t standing still. At the Shanghai Auto Show, China’s CATL has hinted at a five-minute, 520 km charge on megawatt-scale hardware, while Toyota continues to push ahead with its own solid-state prototype, targeting a 20% to 80% charge in just ten minutes.