Key findings
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Finland’s state-backed VTT independently tested a Donut Labs solid-state cell and recorded 0–80% in about 4.5 minutes and a full charge in just over 7 minutes.
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The observed performance corresponds to an approximate 11C charge rate, far beyond typical lithium‑ion norms.
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At 5C, the cell reached 80% in ~9.5 minutes and full in a little over 12 minutes, matching C‑rate expectations.
Test setup
VTT evaluated the cell at three charge rates: 1C, 5C, and 11C. Tests used two passive cooling configurations:
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The cell lightly compressed between two aluminum cooling plates.
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The cell attached to a single bottom aluminum plate.
Donut Labs emphasized that the cell sustained high charging speeds with passive cooling, without pumps or liquid chillers.
Cooling and thermal management
The results suggest the chemistry tolerated aggressive fast charging without active temperature control in the tested setups. Detailed temperature traces were not provided, but the implication is that reduced cooling overhead could enable simpler, lighter pack architectures.
Pack-level caveats
These findings describe a single cell, not a full pack. Real packs integrate many cells plus electronics, structural elements, and thermal systems; current distribution, thermal gradients, and mechanical constraints can limit pack-level charge speeds. The report did not specify the tested cell’s capacity or format, which would clarify absolute current and heat loads.
Comparisons to conventional lithium-ion
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Most conventional Li‑ion cells typically accept ~1C to 3C with active cooling.
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The reported ~11C behavior highlights why high-rate solid-state chemistries are attracting interest: they could cut plug-in time and reduce thermal hardware requirements if validated at pack scale.
Mechanical and chemistry claims
Donut Labs says its cells do not require high compressive pressures and avoid the 15–20% volume changes seen in some solid‑state designs. If borne out over many cycles, that could simplify pack mechanics and reduce cost, while improving energy and power density.
Interpreting the C-rate numbers
A 1C rate implies a one-hour full charge; at 5C it’s roughly 12 minutes. The “~11C” figure here is an equivalency inferred from the just-over‑7‑minute full charge, indicating very high current acceptance with only modest taper near 100% state of charge.
What’s missing and what’s next
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No data were provided on cycle life, operating temperature range, or energy density.
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Further disclosures are expected, potentially covering repeated fast‑charge durability, alternative test configurations, and pack‑integration data.
Bottom line: Independent single‑cell tests corroborate ultra‑fast charging claims (80% in ~4.5 minutes; full just over 7) under passive cooling, but pack‑level validation, durability, and detailed thermal data will determine practical viability for EVs.
