Scientists have long seen lithium-metal batteries as an ideal technology for energy storage, leveraging the lightest metal on the periodic table to deliver cells jam-packed with energy.
But researchers and companies have tried and failed for decades to produce affordable, rechargeable versions that didn’t have a nasty habit of catching on fire.
Then earlier this year Jagdeep Singh, the chief executive of QuantumScape, claimed in an interview with The Mobilist that the heavily funded, stealth Silicon Valley company had cracked the key technical challenges. He added that VW expects to have the batteries in its cars and trucks by 2025, promising to slash the cost and boost the range of its electric vehicles.
After going public in November, QuantumScape is now valued at around $20 billion, despite having no product or revenue as yet (and no expectation that it will until 2024). VW has invested more than $300 million in the company and has created a joint venture with QuantumScape to manufacture the batteries. The company has also raised hundreds of millions from other major investors.
Still, until now Singh had revealed few details about the battery, prompting researchers, rivals and journalists to scour patent filings, investor documents and other sources for clues as to what precisely the company had achieved—and how.
In a press announcement on Tuesday, December 8, QuantumScape finally provided technical results from lab tests. Its technology is a partially solid-state battery, meaning that it uses a solid electrolyte instead of the liquid that most batteries rely on to promote the movement of charged atoms through the device.
Numerous researchers and companies are exploring solid-state technology for a variety of battery chemistries because this approach has the potential to improve safety and energy density, though developing a practical version has proved difficult.
The company, based in San Jose, California, is still withholding certain details about its battery, including some of the key materials and processes it's using to make it work. And some experts remain skeptical that QuantumScape has truly addressed the tricky technical challenges that would make a lithium-metal battery possible in commercial vehicles in the next five years.
In an interview with MIT Technology Review, Singh says the company has shown that its batteries will effectively deliver on five key consumer needs that have thus far prevented electric vehicles from surpassing 2% of new US auto sales: lower costs, greater range, shorter charging times, longer total lifetime on the road, and improved safety.
“Any battery that can meet these requirements can really open up the 98% of the market in a way you can’t do today,” he says.
Indeed, QuantumScape’s performance results are notable.
The batteries can charge to 80% capacity in less than 15 minutes. (MotorTrend found that Tesla’s V3 Supercharger took a Model 3 from 5% to 90% in 37 minutes, in a test last year.) And they retain more than 80% of their capacity over 800 charging cycles, which is the rough equivalent of driving 240,000 miles. In fact, the battery shows little degradation even when subjected to aggressive charge and discharge cycles.
Finally, the company says that the battery is designed to achieve driving ranges that could exceed those of electric vehicles with standard lithium-ion batteries by more than 80%—though this hasn’t been directly tested yet.
“The data from QuantumScape is quite impressive,” says Paul Albertus, an assistant professor of chemical and biomolecular engineering at the University of Maryland and previously the program director of ARPA-E’s solid-state-focused IONICS program, who has no affiliation or financial relationship with the company.
The company has “gone much further than other things I’ve seen” in lithium-metal batteries, he adds: “They’ve run a marathon while everyone else has done a 5K.”
How it works
So how’d they achieve all this?
In a standard lithium-ion battery in an electric car today, one of the two electrodes (the anode) is mostly made from graphite, which easily stores the lithium ions that shuttle back and forth through the battery. In a lithium-metal battery, that anode is made from lithium itself. That means that nearly every electron can be put to work storing energy, which is what accounts for the greater energy density potential.
But it creates a couple of big challenges. The first is that the metal is highly reactive, so if it comes into contact with a liquid, including the electrolyte that supports the movement of those ions in most batteries, it can trigger side reactions that degrade the battery or cause it to combust. The second is that the flow of lithium ions can form needle-like formations known as dendrites, which can puncture the separator in the middle of the battery, short-circuiting the cell.
Over the years, those issues have led researchers to try to develop solid-state electrolytes that aren’t reactive with lithium metal, using ceramics, polymers, and other materials.
One of QuantumScape’s key innovations was developing a solid-state ceramic electrolyte that also serves as the separator. Just a few tens of micrometers thick, it suppresses the formation of dendrites while still allowing lithium ions to pass easily back and forth. (The electrolyte on the other end of the battery, the cathode side, is a gel of some form, so it’s not a fully solid-state battery.)
Singh declines to specify the material they’re using, saying it’s one of their most closely guarded trade secrets. (Some battery experts suspect, on the basis of patent filings, that it’s an oxide known as LLZO.) Finding it took five years; developing the right composition and manufacturing process to prevent defects and dendrites took another five.
The company believes that the move to solid-state technology will make the batteries safer than the lithium-ion variety on the market today, which still occasionally catch on fire themselves under extreme circumstances.
The other big advance is that the battery is manufactured without a distinct anode. (See QuantumScape’s video here to get a better sense of its “anode free” design.)
As the battery charges, the lithium ions in the cathode side travel through the separator and form a perfectly flat layer between it and the electrical contact on the end of the battery. Nearly all of that lithium then returns to the cathode during the discharge cycle. This eliminates the need for any “host” anode material that’s not directly contributing to the job of storing energy or carrying current, further reducing the necessary weight and volume. It also should cut manufacturing costs, the company says.
There is a catch, however: QuantumScape’s results are from lab tests performed on single-layer cells. An actual automotive battery would need to have dozens of layers all working together. Getting from the pilot line to commercial manufacturing is a significant challenge in energy storage, and the point at which plenty of once promising battery startups have failed.
Albertus notes that there’s a rich history of premature claims of battery breakthroughs, so any new ones are met with skepticism. He’d like to see QuantumScape submit the company’s cells to the sorts of independent testing that national labs perform, under standardized conditions.
Other industry observers have expressed doubts that the company could achieve the scale-up and safety tests required to put batteries into vehicles on the road by 2025, if the company has only rigorously tested single-layer cells so far.
Sila Nanotechnologies, a rival battery startup developing a different sort of energy dense anode materials for lithium-ion batteries, released a white paper a day before the Mobilist story that highlights a litany of technical challenges for solid-state lithium-metal batteries. It notes that many of the theoretical advantages of lithium-metal narrow as companies work toward commercial batteries, given all the additional measures required to make them work.
But the paper stresses that the hardest part will be meeting the market challenge: competing with the massive global infrastructure already in place to source, produce, ship, and install lithium-ion batteries.
Other observers, however, say that the recent advances in the field indicate both that lithium-metal batteries will significantly surpass the energy density of lithium-ion technology and that the problems holding up the field can be resolved.
“It used to be whether we’ll have lithium-metal batteries; now it’s a question of when we’ll have them,” says Venkat Viswanathan, an associate professor at Carnegie Mellon who has researched lithium-metal batteries (and has done consulting work for QuantumScape).
Singh acknowledged that the company still face challenges, but he insists they relate to engineering and scaling up manufacturing. He doesn’t think any additional breakthroughs in the chemistry are required.
He also noted the company now has more $1 billion, providing it considerable runway to get to commercial production.
Asked why journalists should have confidence in the company’s results without the benefit of independent findings, Singh stressed that he’s sharing as much of the data as he can to be transparent. But he adds that QuantumScape isn’t “in the business of academic research.”
“No offense, but we don’t really care what you think,” he says. “The people we care about are our customers. They’ve seen the data, they’ve run the tests in their own lab, they’ve seen it works, and as a result they’re putting in massive bets on this company. VW has gone all in.”
In other words, the real test of whether QuantumScape has solved the problems as fully as it claims is whether the German auto giant puts cars equipped with the batteries on the road by 2025.