Why solid-state batteries present so many rewards, with risks

A current Mercedes-Benz EQS has an energy density of 550 Wh/liter, Mercedes CTO Sajjid Khan noted in July at a Daimler EV strategy event. Solid state batteries “will double the energy capacity and reduce the weight in the same packaging space,” he said, as well as allow for more charging cycles. 

“With solid state, we have the opportunity to rethink the design of battery systems as a whole,” Khan added.

Daimler is currently producing a test series of electric buses with solid-state batteries, the eCitaro G, using cells produced by the French company BlueSolutions. But the batteries need to be pre-heated, which is not practical for private passenger cars.

Solid-state batteries also have advantages in terms of charging time. Volkswagen estimates that an ID4 electric SUV with a 77 KWh battery now takes 25 minutes to add 280 miles of range (going from 10 percent charge to 80 percent) — but solid-state batteries can cut that time to 12 minutes.

Another critical benefit is safety. Battery recalls linked to fires have cost automakers and suppliers billions of euros in recent years. In the most recent case, Chevrolet recalled all 141,000 Bolt EVs it had built since the car was launched, at an estimated cost of $2 billion — and LG Chem, the battery supplier, agreed to pay Chevrolet $1.9 billion to cover the cost.

In 2020, Ford recalled 69,000 Kuga plug-in hybrids at a cost of $800 million. And in February 2021 Hyundai said it would spend $900 million to replace battery systems in 82,000 EVs.

Solid-state batteries can mitigate much of this risk, because they do not use a flammable electrolyte and because a solid electrolyte should act as a shield against the growth of dendrites — spiky, algae-like lithium deposits that can form on the anode, move through the electrolyte and puncture the separator, causing short circuits that can lead to fires. 

“A reduction in dendrites results in a longer-lived cell that can take more load with less fire risk, especially as a flammable liquid electrolyte is no longer required,” Petschenyk said.

Agarwal and Rosina, the Yole analysts, say the risk of dendritic formation is less, but still very real because even solid electrolytes have grains or faults than can allow them to grow.

Finally, there are some benefits that will appear only when solid-state cells are assembled into battery packs and integrated into electric cars, experts say.

If solid-state batteries are indeed much safer, that means electric vehicles will need less robust (and cheaper) components to ensure safe functioning. They could also require less cooling, Rosina said, meaning less energy would be drawn from the battery that could be used for range.