First Test Results of Donut Lab’s Solid-State Battery Released

2026-03-01 | Calvin

On February 24, according to The Verge, after Finnish startup Donut Lab announced earlier this year that it was on the verge of a major breakthrough in battery technology, its production-oriented all-solid-state battery faced widespread skepticism and numerous questions. Could the company truly mass-produce fast-charging batteries while overcoming the theoretical manufacturing challenges that have long hindered the industry? Recently, Donut Lab released its first independent third-party test report, evaluating the battery’s charging speed and the battery pack’s “thermal behavior,” in an effort to address these concerns.

The testing was conducted by Finland’s state-owned research organization VTT Technical Research Centre of Finland. The results indicate that the battery charges significantly faster than conventional lithium-ion batteries. In multiple tests, the battery was charged from 0% to 80% in approximately 9.5 minutes while maintaining 100% capacity retention. In another test, it reached 80% in about 4.5 minutes, with capacity retention still at 99%.

Solid-state batteries are often referred to as the “holy grail” of battery technology and have remained a challenge for researchers for decades. Most electric vehicles currently use “wet” lithium-ion batteries that rely on liquid electrolytes to transfer energy. However, these batteries charge slowly, can freeze at low temperatures, and contain flammable materials that pose safety risks in collisions. Solid-state battery packs, by contrast, use “dry” conductive materials, offer higher energy density, and eliminate the risk of thermal runaway associated with traditional batteries.

Typically, such high-intensity fast charging would rapidly degrade a battery’s chemical system, leading to significant capacity loss. However, the tests show that Donut Lab’s battery retained nearly 100% of its energy even after high-power fast charging. This suggests that electric vehicle charging times could potentially be reduced from 30–40 minutes to around 5 minutes—approaching the convenience of refueling at a gas station.

Electric vehicles from automakers such as Tesla and Hyundai generally use active cooling systems to keep battery temperatures under control during charging. In these tests, however, VTT removed all active cooling devices and relied solely on passive heat dissipation to demonstrate that the battery can safely fast-charge without bulky and expensive liquid cooling systems. Two test configurations were used: one with the battery clamped between two aluminum plates, and another with the battery placed on a single metal plate, while temperature changes were monitored throughout.

VTT used the “C-rate” to describe the charging speed relative to battery capacity: 1C means charging from empty to full in one hour. Traditional lithium-ion batteries typically operate at 1C–3C with active cooling. In contrast, this solid-state battery achieved higher C-rates without active cooling. VTT first conducted a standard discharge capacity test at 1C, then performed fast-charging tests at 5C and 11C under both cooling configurations.

Under the test conditions, the Donut Lab battery successfully fast-charged at 5C for over 9 minutes: it reached approximately 80% in 9.5 minutes and fully charged to 100% in just over 12 minutes, releasing its full charged capacity during discharge.

Some minor issues were observed during testing. In one single-plate cooling test, the battery temperature spiked to the 90°C safety limit, triggering an automatic shutdown for protection. Researchers determined that insufficient contact between the battery and the cooling plate was the cause. After reinforcing the pressure and improving thermal conductivity, heat was transferred more efficiently to the metal plate.

In a statement, Donut Lab’s Chief Technology Officer, Ville Piippo, said: “Unlike other solid-state batteries, our Donut battery does not require high-pressure fastening, nor does it experience 15%–20% volume changes during charge and discharge cycles. It does not need special pressurization or complex cooling. This greatly simplifies the battery pack structure, enabling a low-cost, high-performance solution that surpasses traditional lithium-ion batteries in both energy density and power density.”

Donut Lab claims its battery can achieve an energy density of 400 Wh/kg, compared to the current mainstream lithium-ion batteries at 200–300 Wh/kg. The company also states that the battery can be fully charged in 10 minutes and offers a cycle life of up to 100,000 cycles, whereas existing lithium-ion batteries typically last 1,500–3,000 cycles. According to VTT, the tested “Solid-State Battery V1” has a capacity of 26Ah and a nominal energy of 94Wh.

However, before celebrating, it is important to note that the report does not address several key questions regarding Donut Lab’s solid-state battery. First, VTT did not verify the battery’s specific chemical composition and only tested the provided samples. Second, the tests did not examine the “dendrite issue”—the potential formation of microscopic crystal structures that can grow from the anode to the cathode within solid electrolytes, potentially causing short circuits. Donut Lab may address this issue in future independent tests, as the company has pledged to release a series of reports titled “I Donut Believe.”