Donut Lab's DL6 Cell Hits 409 Wh/kg in Independent VTT Test
The battery startup reports breakthrough energy density in lab settings, but the path to mass production remains unproven.
Donut Lab has released independent test results for its latest battery cell, claiming a leap in energy density that could theoretically transform electric vehicle range. The results, verified by a third party, mark the first time the company has placed specific performance figures on the public record.
According to a report from the VTT Technical Research Centre of Finland, the "Donut Battery V1.5" (cell DL6) achieved a gravimetric energy density of 409.3 Wh/kg and a volumetric energy density of 804.7 Wh/L. These measurements were recorded under specific laboratory conditions, including an ambient temperature of +25 °C and a 0.1C discharge rate, with a voltage range spanning 2.3V to 4.25V.
The Path to V1.5
Donut Lab has spent several months promoting its solid-state battery technology, though it previously lacked documented performance data. The DL6 cell is an energy-optimized iteration of the company's earlier V1 cell. By refining the chemistry and structure of the V1 prototype, the company aimed to maximize the amount of energy stored relative to the cell's weight and size, resulting in the figures now confirmed by VTT.
The Lab-to-Road Gap
While a density of 409.3 Wh/kg represents a potential breakthrough for EV efficiency and weight reduction, the industry views these results with caution. A vast technical divide exists between a single, lab-tested cell and a mass-producible battery pack capable of powering a vehicle. Achieving high density in a controlled environment does not guarantee that the chemistry can be stabilized, cooled, or manufactured at scale without prohibitive costs or safety risks.
Scaling Challenges
For the automotive industry, the primary concern is not the peak performance of a prototype, but the ability to demonstrate a scalable production path. Donut Lab has yet to showcase a working prototype integrated into a vehicle or provide a roadmap for how the DL6 cell can be transitioned from a research environment to a factory floor. Until the company moves beyond isolated cell tests, the practical utility of these figures remains speculative.
What to Watch
Industry observers are now looking for evidence of multi-cell modules or a functional battery pack that maintains these density figures under real-world driving cycles. The next critical milestone for Donut Lab will be demonstrating that the V1.5 technology can survive the rigors of automotive testing—such as rapid charging and extreme temperature fluctuations—while remaining economically viable for mass production.