is transportation editor with 10+ years of experience who covers EVs, public transportation, and aviation. His work has appeared in The New York Daily News and City & State.
Since announcing earlier this year that it was on the cusp of a major battery breakthrough, Finnish startup Donut Lab has faced a lot of questions, and plenty of skepticism, about its production-ready, solid-state battery. Could the company really make a fast-charging battery at scale while avoiding some of the theoretical production headaches that have stymied past efforts? Today, Donut Lab sought to dispel some of the doubts with the release of the first independent test of its battery, evaluating its charging speed and the “thermal behavior” of its pack.
The test, which was conducted by state-owned VTT Technical Research Centre of Finland, concludes that the battery is able to be charged significantly faster than a traditional lithium-ion battery. In several tests, the battery was able to charge from 0–80 percent in around 9.5 minutes, while retaining 100 percent of its capacity. In other tests, 0–80 percent was achieved in about 4.5 minutes while retaining 99 percent capacity.
Donut Lab’s solid-state battery in VTT’s test. Image: Donut Labs
Solid-state batteries, which are often referred to as the “holy grail” of batteries, have eluded researchers for decades. Most EV companies use “wet” lithium-ion batteries, which use liquid electrolytes to move energy around. But these batteries can be slow to charge, can freeze up in subzero temperatures, and contain flammable material that can be hazardous in the event of a crash. Solid-state packs are made of “dry” conductive material that can hold more energy without any of the thermal runaway problems of a traditional battery.
Usually, if you force-feed a battery that fast, the chemistry degrades instantly and you lose capacity. According to these tests, Donut Lab’s battery kept almost 100 percent of its energy potential even after being blasted with power. That could transform an EV charging session from a 30–40 minute sojourn into a 5–minute visit, akin to a gas station refuel.
That could transform an EV charging session from a 30–40 minute sojourn into a 5–minute visit, akin to a gas station refuel.
Most EV batteries, like Tesla or Hyundai, have active cooling systems that keep the battery cool while charging. In this test, VTT stripped all that away, using a passive cooling system in order to prove that the battery wouldn’t require a heavy, expensive liquid cooling system to charge safely. They did this two different ways, first by sandwiching the battery between two pieces of aluminum, and second by placing the battery on just one piece of metal — all while monitoring the temperature.
VTT used “C-rate” measures to describe how fast a battery charges relative to its capacity, where 1C represents charging from empty to full in one hour. Traditional lithium-ion batteries typically charge at 1C to 3C with active cooling, whereas in this measurement the charging power rises to significantly higher rates without active cooling. VTT started with a standard discharge capacity test at 1C, followed by rapid charging tests at 5C and 11C with both cooling configurations.
Under these conditions, Donut Lab’s battery was successfully charged at 5C for over nine minutes. At this charging power, the battery cell reached an 80 percent state of charge in about 9.5 minutes and a full 100 percent state of charge in just over 12 minutes. When discharged after charging, 100 percent of the charged capacity was available from the cell.
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