Donut Lab's Test 2 - I Didn't Expect This!

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.

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.