First Test of Donut Lab's Solid State Battery!

Quick Overview

Donut Lab's solid-state battery test executed by VTT revealed a voltage profile and internal resistance squarely matching standard NMC lithium-ion batteries, challenging the claim that the cell contains no lithium, despite showing excellent fast-charging performance where performance improved with higher temperatures and less cooling.

Key Points: The VTT testing confirmed the cell's capacity at 26.1 amp hours and 91 Wh, exactly on Donut Lab's specification. At an 11C rate (286 amps) with minimal cooling, the cell achieved 0 to 80% charge in 4 minutes and 36 seconds, peaking at 89°C, just under VTT's 90°C cutoff. Performance improved with less cooling; the cell charged faster with one heat sink because higher temperatures lowered the cell's internal resistance. Calculated roundtrip efficiency was 90% at 1C, dropping to 82% at 11C, which challenges the pseudo-capacitor theory and is on the low end for regular lithium-ion (typically 92-95%). The measured internal resistance values (1.3 to 1.9 milliohms) align with liquid electrolyte NMC batteries, not typically expected from solid-state electrolytes which usually show higher resistance. The primary purpose of the test was to signal to OEMs that implementation challenges like needing 20 to 50 atmospheres of external pressure for contact are not an issue with this battery.

Context: The video analyzes the first independent fast-charging test results for a solid-state battery developed by Donut Lab, conducted by VTT, Finland's state-owned research organization. The testing focused on fast charging capabilities and thermal management, specifically addressing major engineering hurdles for solid-state batteries like pressure requirements and swelling, which Donut Lab claims their design circumvents.

Detailed Analysis

The analysis of Donut Lab's solid-state battery test data, executed by VTT using an industry-standard PEC ATC0550 cycler, yields complex results. The voltage profile during constant current charging climbed from 2.9V through a plateau at 3.6V to 3.8V, finally reaching 4.3V, which the presenter identifies as 'textbook for an NMC lithium-ion battery.' The test protocol involved charging at up to 11C (286 amps), reaching full charge in as little as 8 minutes under optimal cooling (two aluminum heat sinks) and showing 99.6% capacity recovery. Intriguingly, subsequent tests with only one heat sink—less cooling and more representative of a pack structure—resulted in faster charging times (e.g., full charge in 7 minutes and 18 seconds at 11C) because the elevated temperatures reduced internal resistance, a characteristic opposite to conventional lithium-ion cells which degrade with heat. Calculated roundtrip efficiency at 11C was 82%, and internal resistance measurements (1.3 to 1.9 milliohms) strongly correlated with liquid electrolyte NMC batteries, conflicting with Donut Lab's assertion that the cell contains no lithium. The presenter concludes that while the battery performs very well regarding fast charging and thermal management—meeting the goal of showing OEMs easy implementation—the fingerprint suggests standard lithium-ion chemistry, not a revolutionary solid-state breakthrough, although it remains a 'great battery' if other claims hold true.