Lithium offers other kinds of trouble. Over time, and especially when the battery is forced to charge up fast, lithium ions can form dendrites — tendrils of metal that wind their way between the electrodes and eventually cause the battery to shorten. It sounds scary — and in an old-school lithium-ion battery it could be a recipe for a fire. But in lab tests of solid-state batteries, it hasn’t proven dangerous because the solid electrolyte isn’t flammable. Mostly, it’s just inconvenient, because it affects how many times the battery can be charged.
A few years ago, Solid Power set aside lithium in favor of an anode that’s mostly made of silicon. It was a practical move, Campbell says. No more messy foil, no more short circuits. Luckily for Solid Power, the sulfide that they chose starts off in a powder form too. For battery makers, it’s familiar stuff.
Those choices have trade-offs. Swapping out the lithium anode for silicon means adding more weight to the battery, putting a limit on how much energy it can pack. The design is still poised to be a big improvement over lithium-ion. But, well… it could be better. Campbell says the company is still working on a lithium design, though it will lag a year or two behind the silicon version. In the meantime, lithium metal manufacturing can catch up.
That kind of incremental approach is likely a smart idea, says Shirley Meng, a battery scientist at the University of Chicago. Large battery makers have gotten immensely better at making lithium-ion batteries over the past 30 years, she points out, designing massive factories and better automation that has driven down costs. “We don’t want to reinvent all the machines,” she says. “We want to drop in the solid-state and only make small tweaks. That’s the most ideal situation. ”
But there’s a risk of being leap-frogged. Solid State’s archrival, QuantumScape, uses a different kind of proprietary ceramic and a lithium-based design that requires a distinct set of manufacturing processes. The company has suggested it plans to build its own factories, rather than try to retool or replicate ones already out there. The company, which is currently building out a pre-pilot production line in California, told investors in an earnings call last month that it hopes to deliver batteries to automakers for road testing sometime next year.
Both companies — and a slew of competitors — are still likely years away from putting their batteries in vehicles that are for sale. As the size of the batteries increases — measured in layers — tiny imperfections compound, which poses a particular problem for scaling up. A lithium-ion battery maker that’s really good at what it does might find that only 80 to 90 percent of its cells are actually usable. They’re constantly fighting to inch that number upwards. For solid-state batteries, expect that number to start off way lower. “This is probably the biggest challenge that everybody will be dealing with,” Srinivasan says.
For Solid Power, the current EV-size cells do not do as well as they should in cold temperatures, and battery life declines too fast when the cells are repeatedly fast-charged. But Campbell says that working out the kinks in smaller versions of the battery gives him optimism. “It gives us the confidence that the chemistry is right,” he says. “This is not a chemistry problem. This is an engineering problem. ”
Updated June 6, 2022 at 6:20 pm ET to clarify the timeline of QuantumScape’s plans for automotive testing.