Donut Lab’s “miracle” solid‑state battery failed independent verification.
In April 2026, the Fraunhofer Institute for Solar Energy Systems (ISE) and the U.S. Department of Energy’s Argonne National Laboratory examined two of Donut Lab’s production‑ready cells. Both labs reported an energy density of 260 Wh/kg, well below the 370 Wh/kg the startup advertised. Cycle‑life testing showed capacity dropping to 80 % after just 300 cycles, versus the claimed 1,000‑plus cycles. The labs also detected liquid electrolyte residues, confirming the cells rely on conventional lithium‑ion chemistry rather than a true solid‑state design.
The findings matter because Donut Lab recently closed a $25 million Series A round and is now valued at $1.25 billion on the basis of those same claims. Investors and partners had anticipated a breakthrough that could reshape EV range and safety; the test results suggest the company’s valuation rests on overstated performance.
While the startup has not yet responded, the episode underscores the risk of betting on unverified battery hype, especially when billions of dollars hang on a single material claim.