Is the ‘Holy Grail of batteries’ about to make its long-awaited debut?

Earlier this year, a little-known startup from Finland made waves with a bold claim: it had cracked the code for solid-state batteries. Donut Lab, a spinoff from Verge Motorcycles, announced that its solid-state battery—often dubbed the “Holy Grail of batteries” for its high energy density, durability, and rapid charging capabilities—was set to enter production later this year.

Naturally, battery experts were skeptical. Solid-state batteries have long been touted as the future, alongside concepts like artificial general intelligence and the hyperloop, yet they always seem to be just out of reach. Most credible efforts in this arena, whether from academia or industry, come with a trail of published research or established names. In contrast, Donut Lab appeared seemingly out of nowhere, raising questions about its legitimacy.

“I can’t say they didn’t do it,” remarked Eric Wachsman, director of the Maryland Energy Innovation Institute and a solid-state battery expert. “All I can say is they haven’t demonstrated that they have.”

The skepticism is understandable, especially considering the many players who have been pursuing the solid-state dream. Could this obscure startup really have outpaced giants like Toyota, Stellantis, and the entire nation of China? The odds seemed stacked against them.

Anticipating doubt, Donut Lab launched a website called idonutbelieve.com to share independent tests validating its claims about the solid-state battery. Over several weeks, the startup released third-party results from the VTT Technical Research Centre of Finland, asserting that its battery was indeed a fast-charging, high-energy-density solid-state battery—not just a supercapacitor in disguise.

“The resistance won’t disappear when we present the proof,” said Donut Lab CEO Marko Lehtimäki in a video. “It will just intensify because this new technology poses a threat to established industry players.”

However, Donut Lab has yet to disclose some critical information. At CES in January, the startup claimed its solid-state battery boasts an energy density of 400Wh per kilogram—about double that of standard lithium iron phosphate (LFP) batteries. It also claimed the battery could fully charge in five minutes, endure 100,000 charging cycles, operate in extreme temperatures (from -30°C to 100°C), and contain no rare earth elements, precious metals, or flammable liquid electrolytes.

Much of this remains unverified. Despite sharing five independent test reports from VTT, the startup has not yet substantiated three key metrics: chemistry, density, and cycle-life claims.

The potential impact is enormous. Imagine an electric vehicle capable of traveling 700–800 miles on a single charge, without the risk of catching fire due to flammable electrolytes being replaced with solid materials.

In lithium-ion batteries, the movement of liquid electrolytes generates heat, which can lead to a dangerous “thermal runaway” situation. Solid-state batteries could allow for safer, faster charging, reducing the need for extensive temperature control and potentially enabling more battery cells to fit into the same space.

After reviewing the tests of the Donut battery, Wachsman expressed ongoing concerns. For instance, during extreme heat tests, the pouch surrounding Donut’s battery lost its vacuum seal. Gas generation within batteries—due to electrolyte decomposition or oxygen release—can cause swelling and rupture. Without knowing the exact chemistry of the cell, it’s hard to assess the significance of this failure.

Turning to the broader landscape, solid-state batteries have faced challenges transitioning from lab to production due to well-known issues. One major hurdle is the formation of metallic cracks called dendrites, which can short-circuit the battery. These are akin to cracks in a sidewalk caused by tree roots growing underneath.

Dendrites have plagued battery developers since the 1970s. Lithium-ion batteries have become the standard partly because their graphite anodes are less prone to dendrite formation. However, recent research from MIT suggests that high electrical currents weaken electrolytes, making them more susceptible to dendrite growth. This indicates that simply developing stronger electrolytes isn’t enough; more chemically stable materials are needed to realize the potential of solid-state batteries.

Meanwhile, progress is being made in China. Recently, CATL, which holds nearly 40% of the global battery market, filed a patent for solid-state batteries with a reported energy density of 500Wh. The company is already planning small-scale production by 2027, though automotive-grade cells may not be ready until the end of the decade.

Other Chinese firms are also advancing. Automaker FAW recently announced its “liquid-solid-state” lithium-rich manganese cell with a density of 500Wh/kg, ready for vehicle integration.

China is positioning itself for mass production by the decade’s end, aiming for mature technology by then. This country has been serious about EVs and battery development for years, allowing it to dominate much of the global supply.

Different companies are exploring various approaches. Honda is focusing on sulfur-based electrolytes, while Toyota announced plans for the “world’s first practical use of all-solid-state batteries in BEVs” by 2027 or 2028. Mercedes, using a prototype from startup Factorial, achieved a real-world range of 749 miles for its electric EQS sedan.

“The 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. “There’s no comparison between what’s happening in China and what’s happening here in the US.”

Despite the skepticism surrounding its claims, Donut Lab remains undeterred. On April 1st, Lehtimäki released a video addressing some of the controversy and revealed that the company had developed a second, more production-ready version of its battery, set to ship to customers later this year.

In a crucial admission, he clarified that the much-discussed “100,000 cycles” figure was a design target rather than an experimentally verified result. Actual testing has been conducted over shorter cycles, with projections based on known variables like charge rate, temperature, and usage conditions.

He then shifted focus to a more immediate project: Donut Lab’s latest merchandise drop, featuring a “tin-foil”-covered bucket hat.