Mercedes bets on Solstice solid-state battery for 1,000 km range

Mercedes-Benz is betting on solid-state batteries, co-developed with US-based Factorial, for its future electric car range. The companies promise a high energy density of 450 Watt-hours per kilogram that can extend the EV range up to 80%, which, at the same time, is safer, more compact, and cost-efficient to produce.

The new battery—Solstice—should be ready to be used in production EVs by the decade’s end. It offers ranges of up to 1,000 km on one charge while being 33% smaller and 40% lighter than current lithium-ion battery packs. Using a sulfide-based all-solid-state electrolyte instead of the flammable liquids today makes these batteries less hazardous.

Quasi-solid-state samples

Factorial Energy is an American developer of solid-state battery cells supported by Mercedes-Benz in the first place and by Stellantis and Hyundai-Kia. Mercedes’ Head of Battery Development, Uwe Keller, is part of Factorial’s Board of Directors, and another familiar Mercedes face, former CEO Dieter Zetsche, is still prominently presented as an ‘Investor and Senior Advisor.’

Factorial opened its first development and production facility near Boston in the autumn of 2023. It started by developing a ‘quasi-solid-state’ battery that Mercedes has been testing for use in EVs from 2026 onward.

The US cell maker delivered B-samples to Mercedes-Benz in June of this year. Utilizing Factorial’s FEST platform, these batteries have an energy density of 391 Wh/kg. The German carmaker is integrating these into modules and battery packs before extensively testing them.

Setting the bar higher

The following generation Factorial presented now sets the bar much higher, at 450 kWh or a 40% improvement in energy density over the most performant battery packs a carmaker like Mercedes uses today.

That would allow the extension of current EV ranges by 80% to over 1,000 km, addressing once and for all the ‘range anxiety’ that prevents most people today from going electric. However, more advantages exist, such as the sulfide-based solid-state electrolyte maintaining stability at operating temperatures over 90°C.

Lowering the EV’s cost

It’s safer, but this also has the potential to reduce the cooling system requirements within the battery pack, lowering the overall vehicle cost. It also adds a novel dry cathode design for more efficient and sustainable production.

The technology also bypasses the so-called ‘formation process,’ the most energy-consuming stage of lithium-ion battery manufacturing, which takes hours today. In that process, the battery is slow-charged for the first time after production to stabilize the materials inside. That process greatly determines the battery’s lifespan. Recently, fast charging at high currents made a breakthrough, extending the battery’s lifespan by 70%.

By being more compact and 40% lighter, the next-generation batteries from Factorial would allow Mercedes to make smaller battery packs and use steel for EV bodies instead of far more expensive and carbon-intensive high-strength aluminum, Mercedes CTO Markus Schaefer told Reuters. The benefit for the user would be more range and ‘cheaper’ EVs.