Yes—but the result is a comparison of measured discharge capacity under specific test conditions, not evidence that the cell permanently gained rated capacity. In a VTT test of one Donut Lab-supplied cell, the cell delivered 27.481 Ah at 80°C, or 110.5% of its initial 20°C result at the same 24 A discharge current. At 100°C it delivered 107.1% of a separate 20°C reference, but the pouch lost vacuum after that test.
What VTT tested
VTT Technical Research Centre of Finland Ltd’s customer report, Donut Lab Solid-State Battery V1 High Temperature Performance Test (VTT-CR-00124-26), is dated 27 February 2026 and was approved by VTT on 2 March 2026. The customer supplied three visually identical cells for parallel tests and identified them as solid-state battery cells. The high-temperature results in this report are for one cell, DL2, and followed the customer’s test plan. VTT report
The setup used a climate chamber, a heat sink under the cell and a 2.4 kg steel plate on top to apply mechanical pressure. Before each high-temperature discharge, the cell spent two hours stabilising at the test temperature. Charging was done at 20°C. VTT report
What the capacity figures mean
Ampere-hours (Ah) measure the charge delivered during a discharge. VTT compared each high-temperature result with a 20°C measurement made at the same discharge current; the percentages are ratios between those measured results.
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| Test | 20°C reference | High-temperature result | Observed condition |
|---|---|---|---|
| 80°C, 24 A | 24.872 Ah at 24 A | 27.481 Ah; 110.5% of the 20°C result | No visible change was observed through the 80°C cycle. |
| 100°C, 12 A | 25.770 Ah at 12 A | 27.610 Ah; 107.1% of the 20°C result | The pouch had lost vacuum after the test; the cell charged normally afterward. |
All measurements and observations in the table are from VTT’s report. VTT report VTT test data
The 80°C result
At 20°C and 24 A, the initial discharge measured 24.872 Ah. After recharge and temperature stabilisation, DL2 delivered 27.481 Ah at 80°C and the same 24 A. VTT calculated the latter as 110.5% of the initial capacity. The matching current makes this the clearest basis for the headline figure.
The 100°C result
At 12 A, the 20°C reference measurement was 25.770 Ah. The cell delivered 27.610 Ah at 100°C, which VTT calculated as 107.1% of that reference. This is a different comparison from the 80°C test: it uses a different current and its own 20°C reference, so the two percentages should not be read as a like-for-like temperature comparison.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the test does—and does not—show
VTT’s report supports a limited finding: under the specified test conditions, this cell discharged successfully at 80°C and 100°C and delivered more measured Ah than its corresponding 20°C reference. The result does not mean the cell’s permanent rated capacity increased; it describes the amount measured in those particular discharges.
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Donut Lab says lower internal resistance at higher temperatures explains the higher usable capacity. That is the company’s interpretation, not a separate conclusion established by VTT’s report. Donut Lab’s announcement
- The report covers one cell’s high-temperature discharge tests, not pack-level performance or performance in a vehicle.
- It does not establish repeatability across production cells, long-term cycle life or a general safety conclusion.
- The 100°C test ended with the pouch having lost vacuum. Although the cell charged normally afterward, that observation is material context for the result.
VTT’s report also says that using VTT’s name in advertising or publishing part of the report requires written authorisation. VTT report
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