Earlier this year, a relatively unknown startup from Finland made a surprise announcement: It had finally solved the solid-state battery.
Not only that, but Verge Motorcycles spinoff Donut Lab said its solid-state battery – long considered the “Holy Grail of batteries” for its high-density, durable, fast-charging capabilities – will go into production later this year.
Battery experts were naturally skeptical. After all, solid-state batteries along with artificial general intelligence and hyperloop are one of those technologies that always seem to be two years away. And while most legitimate efforts in this area – whether academic or commercial – have some level of published research or recognizable names attached, Donut Lab seems to have emerged out of nowhere, with no known researchers or prior presence in the field. This lack of traceability immediately raised concerns about the startup’s credibility.
“I can’t say they didn’t do it,” said Eric Wachsman, director of the Maryland Energy Innovation Institute and an expert on solid-state batteries and solid oxide fuel cells. “All I can say is that they have not demonstrated that they did.”
Skepticism seems justified, especially when you consider how many other people are chasing the solid-state dream. Were we really to believe that this obscure startup had outcompeted Toyota, Stellantis, and all of China? The circumstances were against it.
Donut Lab, anticipating the skepticism, launched a website last February called idonutbelieve.com that would serve as a platform to publish independent tests that would verify that its solid-state batteries were, in fact, real and great. Over the course of several weeks, the startup posted third-party results from Finland’s state-owned VTT Technical Research Center that it said proved that its battery was what it said it was: a fast-charging, high-energy-density solid-state battery that was not actually a supercapacitor in disguise.
“The resistance will not disappear when we present the evidence,” Donut Lab CEO and co-founder Marko Lehtimäki said in a video. “This will accelerate as this new technology threatens established players in the industry.”
But Donut Lab is still hiding some important information. At CES in January, the startup said its solid-state battery has an energy density of 400Wh per kilogram — nearly twice that of typical lithium iron phosphate (LFP) batteries in production. Not only that, but it can be fully charged in five minutes, has a practically unlimited lifespan of 100,000 charging cycles, is unaffected by heat and cold (negative 30°C and 100C), and contains no rare earth elements, precious metals, or flammable liquid electrolytes.
Much of this is unproven. Even after posting five independent test reports from VTT, the startup has yet to demonstrate the three most important metrics: chemistry, density, and cycle-life claims.
The stakes are incredibly high. Imagine an electric vehicle that could travel 700-800 miles on a single charge, and that was not a fire hazard because the flammable electrolytes were replaced with a solid material.
In lithium-ion batteries, the movement of liquid electrolytes generates heat, and in some situations, this can result in a “thermal runaway” effect that can result in fire. By comparison, solid-state batteries make it safer to quickly draw power from the battery (or add it back in), meaning you can theoretically charge an EV faster. It could also mean that, structurally, less space would have to be devoted to temperature control, allowing companies to squeeze more battery cells into the same size pack.
After reviewing tests of the donut battery, Wachsman said there were still significant concerns. For example, during extreme heat tests, the bag surrounding the donut’s battery lost its vacuum seal. Gas production inside the battery – caused by processes such as electrolyte decomposition or oxygen release – can cause swelling and rupture of the battery pouch. But without knowing the exact chemistry of the cell, it is difficult to say how significant this failure is in the donut battery.
Putting aside the donut battery for a moment, solid-state batteries have struggled to get from the laboratory to the assembly line due to well-documented problems. These batteries often suffer from the formation of metal cracks called dendrites that cause short circuits in them. Think of them like the cracks that form on the sidewalk when the roots of a tree grow below.
Dendrites have been a thorn in the side of battery developers since the 1970s. One reason why lithium-ion batteries have become ubiquitous while other approaches have stalled is that their commonly used graphite anodes are less sensitive to dendrite formation.
But new discoveries may eventually help engineers overcome these obstacles. A research team from MIT recently published a study Nature It found that chemical reactions caused by high electrical currents, which weaken the electrolyte, make dendrites more susceptible to growth. This is why developing stronger electrolytes alone has not solved the decades-old dendrite problem. And it may ultimately point to the importance of developing more chemically stable materials to fulfill the promise of solid-state batteries.
Progress is already being made – where else? – in China. Last month, CATL, which controls about 40 percent of the global battery market, filed a patent application for a solid-state battery with 500Wh energy density. according to carnewschinaThe battery maker is already planning small-scale production in 2027. But automotive-grade cells won’t be ready until the end of the decade.
Other Chinese companies are moving forward. Automaker FAW recently said its 500Wh/kg “liquid-solid-state” lithium-rich manganese cell was ready for vehicle integration.
China is already laying the groundwork for mass production by the end of the decade, expecting the technology to be mature by that point. And why wouldn’t that happen? This is a country that has taken EV and battery development seriously for years, allowing it to capture the market on most of the world’s supply.
Different companies are taking different approaches. For example, Honda remains committed to sulfur-based electrolytes despite emerging alternatives. Last October, Toyota announced “the world’s first practical use of all-solid-state batteries in BEVs” by 2027 or 2028. And Mercedes, using a prototype battery from startup Factorial, was able to get an electric EQS sedan with a real-world range of 749 miles.
“Companies probably have a ways to go,” said Alevtina Smirnova, director of the NSF Industry-University Cooperative Research Center for Solid-State Electric Power Storage. “Because what’s happening in China now is no comparison to what’s happening in America.”
For its part, Donut Lab isn’t bothered by skepticism over its claims. On April 1, Lehtimaki posted a new video addressing some of the controversies surrounding its solid-state batteries. He also revealed that Donut Lab has created a second, more production-ready version of its battery that will begin shipping to customers later this year.
There was an important admission: The widely discussed “100,000 cycles” figure was a design goal, he said, not an experimentally verified result. Actual testing has been conducted in short cycles, with estimates based on known variables such as charge rate, temperature and usage conditions.
He then turned to a more near-term project: Donut Lab’s latest merchandise drop, which also included a “tin-foil” covered bucket hat.
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