The dry room at Solid Power’s Louisville, Colorado, facility is abrasively bright, and yet the low, encompassing hum of the fans and chillers is oddly soothing. It’s here in the humidity- and contaminant-free production area where Solid Power produced their first full-size solid-state lithium-metal battery cells. The cells, a shining silver contrast to their surroundings, were a moonshot.
The technology, in theory, sounded too good to be true: a 10x jump in power (or 10x drop in size) from traditional lithium-ion cells. Solid Power was aiming for more modest gains in its first prototypes, but could still see an 80 percent improvement in the near future. Then on August 7, 2021, three engineers donned protective Tyvek “bunny suits,” entered the dry room, and drew voltage from the largest prototype lithium-metal battery to date.
Josh Buettner-Garrett, Solid Power’s chief technology officer, monitored from his office. He felt confident, but a little apprehensive: “We knew we could make something that looked like a battery cell, but there was still a chance we’d have a brick.”
The lithium-ion battery that Solid Power hopes to make obsolete is already a modern marvel that earned its key researchers a Nobel Prize. And the preceding lithium-iodine cells of the 1970s lasted years longer than existing alkaline-based AA, AAA, or D batteries, thanks to the material’s unmatched energy density. They were, for example, an immediate boon for pacemaker patients, who could now rely on a battery for 10 years instead of two. But lithium’s greatest impact on batteries came with the rechargeable lithium-ion batteries in the 1990s for portable electronics and electric cars.
Lithium has been the focus of battery research for decades because it’s an excellent conductor. Like its fellow alkali metals on the far left of the periodic table, lithium has a single outer electron that it easily gives up, says Jeff Sakamoto, Ph.D., a mechanical engineering professor at University of Michigan who specializes in solid-state battery research. “That creates a really high voltage,” he explains. And compared with other alkalis, such as potassium or sodium, lithium has the smallest ion size—and third-lowest atomic weight on the periodic table—meaning more electrons and charge for a given battery size.
The energy density of lithium-ion cells is as much as four times greater than that of the nickel-cadmium batteries they’ve largely replaced. Current lithium-ion batteries use a liquid electrolyte where ions flow back and forth between the anode and cathode, recharging and discharging electrons (see How Lithium-Ion Batteries Work, below). The cathode (positive electrode) is a lithium compound, and the anode (negative electrode)—which determines total storage—is made of graphite. This material is plentiful, conducts well, and is easy to work with. However, lithium metal’s capacity is 10 times that of graphite.
“Lithium metal is the highest-capacity material we know of,” says Jun Liu, Ph.D., a director at Pacific Northwest National Laboratory in Richland, Washington. There, Liu leads a consortium searching for the electric-vehicle battery holy grail: light, fast charging, and resistant to corrosion. He believes they’ve found that in recent lithium-metal advancements.
To tap lithium’s potential, researchers have spent decades working through the metal’s numerous roadblocks. Chief among them, says Liu, is its reactivity. “The difficulty is, lithium metal is too reactive. You can think of it as corrosion—if you get it in contact with anything, it corrodes everything.”
The main form of lithium corrosion in batteries are dendrites, which are branched lithium structures that grow out from the anode. Dendrites, which are also a problem for lithium-ion batteries, can puncture battery parts and short-circuit the cell. In a traditional lithium-ion battery with a liquid electrolyte, that can lead to a fire. The liquid electrolyte is a flammable solvent just waiting to be ignited—it’s the fuel behind the battery fires on airplanes that have made recent headlines.
Scientists eventually landed on a solution that prevented the growth of dendrites and eliminated the risk of fire: a solid electrolyte—often made of a ceramic similar to a semiconductor—that replaced the flammable liquid electrolyte and physically blocked the growth of dendrites. And if dendrites still manage to push through the ceramic electrolyte, there’s no flammable reactivity.
Solid electrolytes present additional challenges. They must match the relatively easy seal between a liquid electrolyte and the cathode and anode—the liquid simply forms around them. Lithium is at least malleable at room temperature and can be pressed into the craggy surfaces of a material, but there's still the connection to the cathode. And the brittle nature of ceramics—which leads to dendrite-friendly cracks—poses additional manufacturing difficulties that companies like Solid Power have had to solve.
The next fundamental hurdle is rechargeability, says Neil Dasgupta, Ph.D., a mechanical engineering professor at the University of Michigan who studies solid-state lithium-metal batteries with Sakamoto. Lithium-ion batteries meet an industry standard of charging more than 1,000 times before they significantly degrade, he says. “If you’re plugging your phone in five times a week for four years, you’ve already charged it over a thousand times.” Solid Power won’t share how many cycles its current prototypes can reach, but Will McKenna, the company’s communications director, says they’re still pushing to surpass the 1,000-cycle bar.
Much of the emerging research on lithium-metal batteries focuses on how many charge cycles research batteries can sustain. A team at Harvard University made news in May 2021 when they published findings that their lithium-metal cell held its charge over an astonishing 10,000 cycles.
At 10,000 cycles, we could reset our expectations for battery life, says Xin Li, Ph.D., one of the Harvard researchers behind the battery. “[It] could be as long as 25 years or even half a century.”
However, Harvard’s battery is a paper-thin version of a coin cell—like a watch or hearing aid battery. And these proportions are likely not the same ones for most commercial applications down the road, where batteries will be much larger and thicker, and have different ratios of materials.
The Harvard findings, however, still get more impressive. Their lithium-metal battery cell was able to recharge in just three minutes. If this technology can reach electric vehicles, that would mean being able to recharge a car in the same time (or less) required to fill a gas tank. Most EVs currently need at least three hours to recharge.
The world got its first look at a solid-state-battery electric vehicle at the Tokyo Olympics, where Toyota, working with Panasonic, outfitted a fleet of its LQ concept cars. The bubble-shaped LQs could be seen following the men’s and women’s marathons and even starred in commercials for the rescheduled Olympic Games.
These demonstrations are exciting—despite Toyota releasing no further details on the LQ’s batteries—but we’re still years from seeing a lithium-metal battery reach a showroom. Solid Power CEO Doug Campbell says the company is five years out from putting their batteries into consumer vehicles—BMW and Ford have signed on as partners. The company’s current target is an OEM battery that’s almost twice the energy density of today’s auto cells and that charges to 90 percent in just 10 minutes. The company, he adds, is years ahead of most rivals, thanks to its research on adapting existing lithium-ion manufacturing technology.
“Most other groups, with the exception of a few behemoths based in Asia, are still entrenched in that research and development phase,” Campbell says. Toyota, for example, says their solid-state battery is likely to come in 2025—no car included. Sakamoto runs a solid-state-battery startup, in addition to his work at the University of Michigan, and says the recent push to develop lithium-metal batteries arose after electric vehicles became viable and in-demand. “I’m surprised how quickly a light went on and at this outpouring of financial support and interest in solid-state batteries,” he says. “There’s no commercial product yet, but there’s all this investment.”
The push for solid-state batteries can give us a world in which electric vehicles recharge in minutes and pacemaker batteries last half a century. There’s only the question of when we’ll get there.