The Mercedes-Benz EQS Claims 620 Miles of Range in Semi-Solid-State Battery Testing
The emerging battery technology promises longer range, faster charge speeds, and is production feasible.
Mercedes-Benz is testing a prototype EQS electric sedan fitted with a semi-solid-state battery pack co-developed with its Formula 1 powertrain subsidiary, Mercedes-AMG High Performance Powertrains (HPP), and US-based battery specialist Factorial Energy. The automaker says the prototype lithium-metal battery is expected to deliver at least 25 percent more range compared with the lithium-ion battery fitted to production EQS models. In fact, Mercedes-Benz engineers believe the EQS prototype will have a real-world driving range of more than 620 miles, compared with the 390 mile EPA-rated range of the EQS 450+ currently sold in the U.S.
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Solid-state batteries are regarded as the next key step in improving the range and usability of EVs. In simple terms they use a solid electrolyte rather than a liquid one, which makes them lighter and allows the use of more efficient anodes. They not only have a higher energy density than conventional lithium-ion EV batteries but can also be charged faster, and because they don’t have a flammable liquid electrolyte, they are less prone to fires.
The downsides? Solid-state batteries require more lithium than conventional lithium-ion packs and are prone to growing organic looking structures called lithium dendrites over multiple charge and discharge cycles. These dendrites can grow through the solid electrolyte, causing the battery to short out. Solid-state batteries also don’t achieve high conductivity at room temperature.
The EQS prototype’s battery has been built using Factorial Energy’s proprietary FEST cells. These cells have a quasi-solid electrolyte, a solid matrix infused with a liquid or gel-like electrolyte, which is why it’s technically correct to refer to the prototype battery as a semi-solid-state unit. A quasi-solid electrolyte combines the safety advantages of solid-state electrolytes with the improved performance and manufacturability of liquid electrolytes, says Factorial Energy’s vice-president of business development, Raimund Koerver. What’s more, quasi-solid-state cells can use lithium metal anodes, which are needed to obtain higher energy densities. “Quasi-solid electrolytes offer a promising middle ground,” Koerver says.
The Mercedes-Benz battery’s secret sauce is a patented floating cell carrier. When the battery charges, the cells expand, and when it discharges, they contract, and to support them during these volume changes, the battery is equipped with pneumatic actuators. “Solid-state cells need to be kept under constant pressure,” explains Adam Allsopp, who heads the Advanced Technology division at Mercedes-AMG HPP. “That reduces the dendrite formation in the cells.”
Mercedes has been working on solid-state battery technology with Factorial Energy since 2021, and the first sample cells were shipped to the automaker in 2024 – we got a sneak peek inside the prototype battery pack when we visited Mercedes-AMG HPP’s facility in Brixworth, England, late last year. Now the technology is about to hit the road as part of an extensive testing program. “We will gain crucial insights into possible series integration of this cutting-edge battery technology,” says Mercedes-Benz board member and chief technology officer Markus Schäfer.
And this is just the beginning. Mercedes, which in 2022 took an equity stake in Woburn, Massachusetts, based Factorial Energy, is also working with the cell developer on a new all-solid-state cell called Solstice. The highly energy dense Solstice cell, which features a sulfide-based electrolyte, promises an 80 percent increase in range compared with today’s lithium-ion batteries, and a significant reduction in the weight of battery packs.
Thanks to a new dry coating process, Solstice also eliminates the need for hazardous solvents and energy-intensive steps commonly used in traditional cathode production. The technology also bypasses the formation process, the most energy consuming stage of lithium-ion battery manufacturing that typically involves multiple charge and discharge cycles to activate the materials and establish protective layers at the electrochemically active interfaces that enable the stable operation of the cell.
Though other automakers are also working on solid-state battery technology – most notably Toyota, which first showed a prototype solid-state cell in 2010 – Mercedes and Factorial Energy may be the first to get a form of the technology into mass production. “Being the first to successfully integrate lithium-metal solid-state batteries into a production vehicle platform marks a historic achievement in electric mobility,” says Siyu Huang, CEO and co-founder of Factorial Energy. “This breakthrough demonstrates that solid-state battery technology has moved beyond the laboratory and into real world application.”
I can’t remember a time when I wasn’t fascinated by cars. My father was a mechanic, and some of my earliest memories are of handing him wrenches as he worked to turn a succession of down-at-heel secondhand cars into reliable family transportation. Later, when I was about 12, I’d be allowed to back the Valiant station wagon out onto the street and drive it around to the front of the house to wash it. We had the cleanest Valiant in the world.
I got my driver’s license exactly three months after my 16th birthday in a Series II Land Rover, ex-Australian Army with no synchro on first or second and about a million miles on the clock. “Pass your test in that,” said Dad, “and you’ll be able to drive anything.” He was right. Nearly four decades later I’ve driven everything from a Bugatti Veyron to a Volvo 18-wheeler, on roads and tracks all over the world. Very few people get the opportunity to parlay their passion into a career. I’m one of those fortunate few.
I started editing my local car club magazine, partly because no-one else would do it, and partly because I’d sold my rally car to get the deposit for my first house, and wanted to stay involved in the sport. Then one day someone handed me a free local sports paper and said they might want car stuff in it. I rang the editor and to my surprise she said yes. There was no pay, but I did get press passes, which meant I got into the races for free. And meet real automotive journalists in the pressroom. And watch and learn.
It’s been a helluva ride ever since. I’ve written about everything from Formula 1 to Sprint Car racing; from new cars and trucks to wild street machines and multi-million dollar classics; from global industry trends to secondhand car dealers. I’ve done automotive TV shows and radio shows, and helped create automotive websites, iMags and mobile apps. I’ve been the editor-in-chief of leading automotive media brands in Australia, Great Britain, and the United States. And I’ve enjoyed every minute of it. The longer I’m in this business the more astonished I am these fiendishly complicated devices we call automobiles get made at all, and how accomplished they have become at doing what they’re designed to do. I believe all new cars should be great, and I’m disappointed when they’re not. Over the years I’ve come to realize cars are the result of a complex interaction of people, politics and process, which is why they’re all different. And why they continue to fascinate me.Read More
