Donut Lab’s solid-state battery struggles to retain charge after sustaining damage.

Donut Lab is determined to showcase the authenticity of its solid-state battery through a series of independent tests. We’ve witnessed speed charging trials, extreme heat evaluations, and assessments to confirm it’s not just a supercapacitor. The latest test focuses on how the battery performs when subjected to damage. The outcome? While it struggled to maintain a charge, it didn’t ignite, which Donut Lab considers a win.

Previously, during the extreme heat tests, the pouch encasing Donut’s battery lost its vacuum seal. This prompted researchers from Finland’s VTT Technical Research Centre, who have conducted all prior tests, to investigate whether the cell could still operate under such high-stress, high-temperature scenarios. Donut highlighted that damage like this, which occurred during the heat test, can lead to fires or thermal runaway in traditional lithium-ion batteries. The startup aimed to determine if its solid-state battery could sidestep similar disasters.

Researchers carried out three tests: a baseline test of five cycles at 1C (26 amps), a high-stress test of 50 cycles at 5C (130 amps), and a concluding baseline test of five cycles at 1C to assess degradation. Post-testing, the team noted a significant drop in energy capacity, plummeting from 24.7 amp-hours to 11.2 Ah, equating to a loss of about 55 percent. Efficiency also dipped from 89.6 percent to 83 percent, and the pack’s thickness increased by 17 percent.

Considering the damage the pack endured, these results aren’t entirely unexpected. The loss of the vacuum seal certainly sped up the battery’s degradation and contributed to its swollen state after testing. Nevertheless, Donut Lab views this as further evidence that its battery can avoid some of the most severe consequences associated with damaged lithium-ion batteries.

“No temperature spikes, no fire risk,” the company stated on its site. “In this scenario, the Donut Battery fails gracefully when damaged, continuing to operate safely at reduced capacity rather than posing danger to the user.”

However, these tests also mark the closest Donut Lab’s battery has come to a cycle test, and it was under compromised conditions. The startup has yet to demonstrate how its pack performs under an accelerated aging process that repeatedly charges and discharges the cells to assess their long-term performance and safety. Donut has previously claimed its solid-state battery can endure 100,000 cycles, which would translate to roughly 270 years of charging and discharging—far exceeding the 1,000-2,000 cycles typical for standard EV batteries before capacity begins to decline.

Moreover, Donut has not yet sought independent verification for its asserted energy density of 400 watt-hours per kilogram. This seems like a straightforward test—just weigh the cell and measure its output—and it’s puzzling why Donut Lab hasn’t pursued it yet.

Stay tuned for more insights on Donut Lab’s tests and the perspectives of independent experts regarding the startup in the coming weeks.