# Donut Lab's Test 2 - I Didn't Expect This! Source: https://www.youtube.com/watch?v=AzIpgYi4rjM Recap page: https://rapidrecap.app/video/AzIpgYi4rjM Generated: 2026-03-03T05:04:14.973+00:00 --- ## Quick Overview Donut Lab's analysis of their solid-state battery cell (DL2) revealed that while it maintained high coulombic efficiency (99.18%) after high-temperature cycling (80°C), the energy density claim of 400 Wh/kg was not substantiated by the initial testing, and the cell failed catastrophically when subjected to 100°C stress testing, losing its vacuum and venting, although it surprisingly continued to function afterward. **Key Points:** - The DL2 cell demonstrated high coulombic efficiency (99.18%) after one cycle at 80°C, recovering to 99.88% efficiency when returned to room temperature, suggesting the solid-state components were not permanently damaged by thermal stress. - The claimed energy density of 400 Wh/kg was not verified; the best commercial NVPF cell (Tiamat) achieves 105 Wh/kg, meaning Donut's claim is over 2x higher than the current record. - The cell's discharge voltage profile at room temperature closely matched the expected profile for NMC Lithium-Ion, not the expected smooth curve of layered oxide sodium-ion, suggesting the cell contained lithium. - The Na-ion architecture components claimed by Nordic Nano (TiO2 anode, CNT network, Na-ion electrolyte) align with sodium chemistry, but the voltage profile contradicts this. - The cell failed the 100°C stress test by losing its seal and venting after two hours, though it surprisingly continued to function, unlike conventional NMC cells which degrade ~40% in two cycles at that temperature. - The thermal runaway threshold for the Na-ion layered oxide is 135–165°C, significantly higher than the ~150°C threshold for NMC Lithium-Ion, indicating superior thermal stability if the cell were truly Na-ion. ![Screenshot at 00:08: The initial comparison graph shows the DL2 cell discharged 27.5 Ah \(+11.0%\) at 80°C compared to its 24.9 Ah baseline at 20°C, indicating capacity gain at elevated temperatures, which contradicts the expected performance trend for lithium-ion cells.](https://ss.rapidrecap.app/screens/AzIpgYi4rjM/00-00-08.jpg) **Context:** This video, presented by Ricky Roy, details the second phase of testing (Test 2: High Temps) performed by the independent lab VTT on a solid-state battery cell (DL2) provided by Donut Lab. The testing aimed to verify Donut Lab's claims regarding energy density (400 Wh/kg), high-temperature performance, and the absence of lithium, contrasting the cell's performance against published data for both sodium-ion and conventional NMC lithium-ion chemistries. ## Detailed Analysis Donut Lab sent three cells (DL1, DL2, DL3) to the VTT testing lab in Finland. Test 1 (DL1) on charging characteristics is complete, showing a baseline capacity of 24.9 Ah at 20°C and a capacity gain of 11.0% (27.5 Ah) when tested at 80°C after a 2-hour soak. Test 2 (DL2) involved elevated temperature stress testing at 80°C and 100°C. The coulombic efficiency remained high (99.18% at 80°C) and recovered to 99.88% at room temperature after the high-temp exposure, suggesting the core chemistry survived the heat without significant degradation. However, the 100°C test caused the pouch to lose its vacuum and vent, though the cell surprisingly continued to function. The cell's voltage discharge curve at room temperature closely matched NMC Lithium-Ion reference data (3.5V average) rather than the expected two-plateau curve for layered oxide sodium-ion, strongly suggesting the presence of lithium. Furthermore, Donut Lab's energy density claim of 400 Wh/kg is more than double the current best reported NVPF sodium-ion cell at 175 Wh/kg (CATL NaxTra). Finally, the thermal runaway threshold for true Na-ion layered oxide is 135–165°C, much higher than NMC's ~150°C, but the Donut cell failed catastrophically (seal loss) at 100°C, indicating it was not as thermally stable as claimed for a solid-state sodium-ion battery. ### High-Temperature Performance (DL2 Test 2) - Cell delivered 27.5 Ah at 80°C (110% of baseline) and 27.6 Ah at 100°C (107% of baseline); The cell lost its seal and vented during the 100°C test but continued to function afterward, which is unprecedented for commercial cells. ### Internal Resistance Change - The Donut cell showed an 18% drop in internal resistance when moving from 20°C to 80°C, significantly less than the typical 40% drop seen in conventional NMC liquid electrolyte cells over the same temperature range. ### Chemistry Fingerprinting (Voltage vs. SOC) - The Donut cell's discharge curve closely matched the NMC Lithium-Ion reference curve (3.5V average), failing to show the distinct two-plateau signature expected from NVPF sodium-ion chemistry. ### Energy Density Comparison - Donut's 400 Wh/kg claim is more than double the best published sodium-ion record of 175 Wh/kg (CATL NaxTra), highlighting the massive performance gap claimed. ### Thermal Stability Comparison - Published research indicates Na-ion layered oxide has a thermal runaway threshold of 135–165°C, significantly higher than NMC's ~150°C, but the Donut cell failed structurally (seal loss) at 100°C. ### Supply Chain Investigation - Nordic Nano, described as the battery materials supplier, explicitly mentions using Carbon Nanotubes coated with Titanium Oxide (TiO2) and a sodium electrolyte, suggesting a sodium-ion architecture, though the test data contradicts the sodium claim. ![Screenshot at 00:04: Bar graph comparing discharge capacity showing 27.5 Ah \(+11.0%\) at 80°C versus 24.8 Ah baseline at 20°C.](https://ss.rapidrecap.app/screens/AzIpgYi4rjM/00-00-04.jpg) ![Screenshot at 01:04: The voltage fingerprint chart shows the Donut Lab Cell \(red line\) voltage curve closely tracking the NMC Lithium-Ion reference \(purple line\) rather than the expected sodium-ion profiles.](https://ss.rapidrecap.app/screens/AzIpgYi4rjM/00-01-04.jpg) ![Screenshot at 01:11: A slide highlighting the 80°C and 100°C tests performed on cell DL2, which involved high-temperature stress cycling.](https://ss.rapidrecap.app/screens/AzIpgYi4rjM/00-01-11.jpg) ![Screenshot at 02:29: A summary bar chart showing the capacity results: 24.9 Ah baseline, 27.5 Ah at 80°C, and 27.6 Ah at 100°C.](https://ss.rapidrecap.app/screens/AzIpgYi4rjM/00-02-29.jpg) ![Screenshot at 09:54: A slide from Nordic Nano's technology page explicitly listing Carbon Nanotubes, Titanium Oxide \(TiO2\), and a sodium electrolyte, confirming the claimed materials align with sodium chemistry.](https://ss.rapidrecap.app/screens/AzIpgYi4rjM/00-09-54.jpg)