If electric vehicles are ever going to fully supplant gas guzzlers on the world’s roads, they’re going to need an entirely new type of battery. Despite steady improvements over the past decade in the energy density and lifetimes of lithium-ion batteries, the cells in new EVs still lag behind internal combustion engines on pretty much every performance metric. Most EVs have a range of less than 300 miles, it takes more than an hour to recharge their battery packs, the cells lose nearly a third of their capacity within a decade, and they pose a serious safety risk because of their flammable materials.
The solution to these problems has been known for decades: It’s called a solid-state battery, and it’s based on a deceptively simple idea. Instead of a conventional liquid electrolyte—the stuff that ferries lithium ions between electrodes—it uses a solid eloctrolyte. Also, the battery’s negative terminal, called its anode, is made from pure lithium metal. This combination would send its energy density through the roof, enable ultra-fast charging, and would eliminate the risk of battery fires. But for the past 40 years, no one has been able to make a solid-state battery that delivers on this promise—until earlier this year, when a secretive startup called QuantumScape claimed to have solved the problem. Now it has the data to prove it.
On Tuesday, for the first time, QuantumScape’s cofounder and CEO, Jagdeep Singh, publicly revealed test results for the company’s solid-state battery. Singh says the battery resolved all of the core challenges that have plagued solid-state batteries in the past, such as incredibly short lifetimes and slow charging rate. According to QuantumScape’s data, its cell can charge to 80 percent of capacity in 15 minutes, it retains more than 80 percent of its capacity after 800 charging cycles, it’s noncombustible, and it has a volumetric energy density of more than 1,000 watt-hours per liter at the cell level, which is nearly double the energy density of top-shelf commercial lithium-ion cells.
“We think that we're the first to solve solid-state,” Singh told WIRED ahead of the announcement. “No other solid-state systems come close to this.”
QuantumScape’s battery cell is about the size and thickness of a playing card. Its cathode, or positive terminal, is made of nickel manganese cobalt oxide, or NMC, a common chemistry in EV batteries today. Its negative electrode, or anode, is made from pure lithium metal—but it's more accurate to say that it doesn’t have an anode at all, since it’s manufactured without one. When the battery discharges during use, all of the lithium flows from the anode to the cathode. The vacancy left on the anode side—thinner than a human hair—is temporarily compressed like an accordion. The process reverses when the battery is charged, and the lithium ions flood into the anode space again.
“This anode-free design is important because it’s probably the only way that lithium-metal batteries can be manufactured today with current manufacturing facilities,” says Venkat Viswanathan, a mechanical engineer working on lithium-metal batteries at Carnegie Mellon University and a technical adviser to QuantumScape. “Anode-free has been a big challenge for the community.”
But the key to QuantumScape’s solid-state breakthrough is the flexible ceramic separator that sits between the cathode and the anode. This is the material that puts the “solid” in solid-state. Like the liquid electrolyte that sits between the electrodes in a conventional cell, its main function is to ferry lithium ions from one terminal to the other when the battery charges and discharges. The difference is that the solid separator also acts as a barrier that keeps lithium dendrites—metallic tendrils that form on lithium metal anodes during charge cycles—from snaking between the electrodes and causing a short circuit.
Venkat Srinivasan, the director of the Argonne Collaborative Center for Energy Storage Science, has spent nearly a decade researching solid-state batteries at the national lab outside Chicago. He says that finding a separator material that allows lithium ions to flow freely between electrodes while blocking dendrites has been far and away the biggest challenge. Typically, researchers have used either a plasticky polymer or a hard ceramic. Although polymers are the separator material of choice in liquid electrolyte batteries, they’re inadequate for solid-state cells because they don’t block dendrites. And most ceramics used for experimental solid-state batteries have been too brittle to last more than a few dozen charging cycles.
“These dendrites are like the root of a tree,” says Srinivasan, who was not involved in the QuantumScape work. “The problem that we’re trying to solve is, how do you mechanically stop this root system from growing with something solid? You can’t just put anything you want, because you have to feed ions back and forth. If you don’t do that, there is no battery.”
Lithium-ion batteries are complex systems, and the reason for their plodding improvement over the years is that tweaking one part of a cell often has cascading effects that alter its performance in unforeseen ways. To build a better battery, researchers have to systematically investigate different materials until they find something that works, which can be an incredibly time-consuming task. Singh says it took QuantumScape 10 years and $300 million in R&D before the company dialed in on a solid-state separator that fit the bill. He wouldn’t disclose what it's made of—that’s the company’s secret sauce—but he says the material is cheap and readily available. “We didn't have some divine revelation that said, ‘This material is going to work, go build it,’” says Singh. “We had to go through a lot of dead ends. But nature did provide a material that meets the requirements, and luckily, through our systematic search process, we were able to find it.”
Singh says that QuantumScape’s battery is the kind of step change in performance that will push EVs into the mainstream. He’s not the only one who thinks so. The company counts Bill Gates and Vinod Khosla among its investors, and several battery barons, such as Tesla cofounder J. B. Straubel, sit on its board of directors. One of the company’s biggest backers is Volkswagen, the world’s largest car manufacturer, which has plowed more than $300 million into QuantumScape and plans to start using the solid-state cells in some of its own EVs as soon as 2025.
QuantumScape and VW aren’t the only companies in the solid-state battery game, of course. Toyota is also developing a solid-state cell, which company officials planned to unveil at the Tokyo Olympics this year before it was postponed due to the pandemic. Like VW, Toyota plans to have its solid-state batteries on the road by 2025. But earlier this year, Keiji Kaita, vice president of Toyota’s powertrain division, told the industry publication Automotive News that the company still needed to improve the battery’s limited life span. Toyota representatives did not return WIRED’s request for comment.
A six-year-old startup called Solid Power has also made a functioning solid-state cell and begun producing prototype batteries with 10 stacked layers at a pilot plant in Colorado. Like QuantumScape, these cells have a lithium-metal anode and a ceramic solid-state electrolyte. Solid Power’s electrolyte is sulfide-based, a chemistry that is desirable for solid-state batteries because of its high conductivity and compatibility with existing manufacturing processes. The company has partnerships with a number of auto manufacturers, including Ford, BMW, and Hyundai, although its executives don’t expect to see their cells on the road before 2026 because of the lengthy automotive qualification process. Solid Power hasn’t released data on its cell yet, but the company is expected to unveil a larger cell and publish its performance data for the first time this Thursday.
“The solid-state battery competitive landscape is becoming increasingly crowded due to the huge potential that solid-state batteries have in enabling vehicle electrification,” says Doug Campbell, Solid Power’s CEO. “This ultimately leads to EVs with greater range, greater reliability, and lower cost.”
QuantumScape’s performance data is impressive, but it comes with an important caveat. All of the test data was generated in individual cells that, technically speaking, aren’t complete batteries. The thin cell unveiled by QuantumScape is destined to be stacked together with about 100 others to form a full cell that is about the size of a deck of cards. Powering an EV will require hundreds of those stacked batteries, but so far the company hasn’t tested a fully stacked cell.
Scaling a battery from a subunit of a single cell to a full cell and eventually to a full battery pack can create a lot of problems, says Srinivasan. When batteries are made in small batches, he says, it’s easier to eliminate defects that crop up during the production process. But once you start manufacturing batteries at scale, it can be difficult to control defects, which can quickly sap a battery’s performance. “Even though a material may look really promising at the small scale, in the scale-up these defects could become a bigger problem,” says Srinivasan. “Real-world operation is very different from lab-scale operation.”
Jeff Sakamoto, a mechanical engineer focused on energy storage at the University of Michigan who was not involved with QuantumScape, agrees. He says there are still significant knowledge gaps about the fundamental mechanical properties of lithium-metal solid-state batteries, which could create problems when it comes to commercializing the technology. He points to the world’s first commercial passenger jet, the ill-fated De Havilland Comet, as an example of the consequences of launching a technology before its material properties are completely understood. Shortly after the Comet took to the skies, it experienced several catastrophic midair breakups because engineers didn’t fully understand the degradation process of the metals used in its hull. While the stakes are somewhat lower for solid-state cells than for commercial jets—the batteries are, after all, designed to be ultrasafe—a battery that goes to market and experiences unexpected performance problems could slow the electrification of transportation.
“I am astonished at how little is known about the mechanical behavior of lithium metal and how the physics of lithium affects the feasibility of solid-state batteries,” says Sakamoto. “I don't know to what extent these knowledge gaps will affect the widespread adoption of lithium-metal solid-state batteries. But the more we know about the fundamental behavior, the better the transition to wide-scale adoption.”
Singh is unfazed by the challenges that QuantumScape must address before its batteries make it out of the lab and into a car. As far as he’s concerned, the company has solved the hard basic-science problems that have stymied the commercialization of a solid-state battery. “I don’t want to trivialize the work that remains,” says Singh. “But it’s not a question of whether this will work or not. It’s a question of engineering.”
Earlier this year, QuantumScape went public through a special acquisition company and added around $700 million to its already sizable balance sheet. Singh says the company now has more than $1 billion in its war chest, which is more than enough to carry it into production. It seems impossible that the company could fail, but that’s also what investors thought about A123 Systems and Envia Systems, two companies that raised huge amounts of money from legacy automakers with the promise of a game-changing EV battery—only to come crashing down when the performance of their cells didn’t match expectations. QuantumScape may very well become the first startup to deliver a commercial solid-state battery, but the company still has a long road ahead.