Solid-state battery road tests start

A “slightly modified” Mercedes-Benz EQS is road testing a new solid-state battery pack.

“Safer, lighter, more efficient and 25% longer range in the first vehicle: the solid-state cell chemistry means higher energy density and weight reduction, with improved driving efficiency and cell safety,” says Mercedes-Benz which, with Mercedes AMG High Performance Powertrains (HPP) based in Brixworth, United Kingdom, developed and patented a new solid-state battery pack.

Mercedes-Benz integrated the solid-state battery with cells from US based Factorial Energy into the “1000km” EQS.

It’s the first car powered by a lithium-metal solid-state battery on the road, says Mercedes-Benz.

After intensive testing on various test benches, the prototype solid-state battery was integrated into an EQS at the end of 2024, the brand says.

“The all-electric car from Mercedes-Benz was slightly modified to fit the solid-state battery and was equipped with all accessories to operate it.

“The first laboratory vehicle tests were already conducted in Stuttgart at the end of 2024 to prepare for the road tests that started in February 2025.

“We will gain crucial insights into possible series integration of this cutting-edge battery technology,” says Mercedes-Benz Group AG management board member and development and procurement chief technology officer Markus Schäfer.

Solid-state batteries use a solid electrolyte instead of a liquid one, which enhances cell safety and allows for the use of new anodes like lithium metal, thus significantly outperforming conventional lithium-ion cells, says Mercedes-Benz.

“They also enable next-level energy densities, in combination with a lithium-metal anode. The solid-state technology has the potential to increase the gravimetric energy density for vehicle batteries up to 450Wh/kg at the cell level and thereby increasing the driving range.

“Gravimetric energy density refers to the amount of energy stored in a battery cell per unit mass. This metric is crucial for evaluating the efficiency and performance of battery cells, especially in applications where weight is a critical factor, such as in electric vehicles.

“Solid-state battery technology reduces the battery weight while improving cell safety.

“Being the first to successfully integrate lithium metal solid-state batteries into a production vehicle platform marks a historic achievement in electric mobility,” says Factorial Energy chief executive and co-founder Siyu Huang.

“This breakthrough demonstrates that solid-state battery technology has moved beyond the laboratory and into real-world application, setting a new benchmark for the entire automotive industry.

“Our collaboration with Mercedes-Benz proves that the future of electric vehicles is not just a vision, but a reality we’re delivering today.”

The solid-state battery features an innovative floating cell carrier, for which a patent has been granted.

When the battery charges, the materials expand, and when it discharges, it contracts. To support the cells during these volume changes, the Mercedes-Benz solid-state battery is equipped with pneumatic actuators that interact with the cell volume change during charging and discharging, which affects the battery’s performance and lifespan, says the brand.

During the next few months, Mercedes-Benz will further test the solid-state battery and its overall performance.