Yes, it’s fast: Donut Lab’s solid-state battery gets its first test result

Since announcing earlier this year that it was on On the cusp of a major battery boomFinnish startup Donut Lab has faced a lot of questions and a lot of skepticism about its production-ready solid-state battery. Can the company really make a fast-charging battery at scale while avoiding some of the theoretical production problems that have hampered previous efforts? Today, Donut Lab sought to dispel some doubts by releasing the first independent test of its battery, evaluating the charging speed and “thermal behavior” of its pack.

Testingconducted by Finland’s state-owned technical research center VTT, concluded that the battery can be charged much faster than a conventional lithium-ion battery. In several tests, the battery was able to charge from 0 to 80 percent in about 9.5 minutes, while maintaining 100 percent of its capacity. In other tests, 0-80 percent was achieved in about 4.5 minutes with 99 percent power retention.

Solid-state batteries, often referred to as the “holy grail” of batteries, have eluded researchers for decades. Most electric vehicle companies use “wet” lithium-ion batteries, which use liquid electrolytes to move power. But these batteries can be slow to charge, can freeze at subzero temperatures, and contain flammable materials that could be dangerous in the event of an accident. Solid-state packs are made of a “dry” conductive material that can hold more power without any of the thermal runaway problems of a traditional battery.

Normally, if you top up a battery that quickly, the chemistry degrades immediately and you lose capacity. According to these tests, the Donut Lab battery retained approximately 100 percent of its power potential even after being powered off. This could transform an electric vehicle charging session from a 30-40 minute stay into a 5-minute visit, similar to refueling at a gas station.

Most electric car batteries, like Tesla or Hyundai, have active cooling systems that keep the battery cool while charging. In this test, VTT stripped it all away, using a passive cooling system to prove that the battery wouldn’t require a heavy and expensive liquid cooling system to charge safely. They did this in two different ways, firstly by placing the battery between two pieces of aluminum, and secondly by placing the battery on only one piece of metal, all while monitoring the temperature.

VTT used “C-rate” metrics to describe how quickly a battery charges relative to its capacity, with 1C representing a charge from empty to full in one hour. Conventional lithium-ion batteries are typically charged at a temperature of 1°C to 3°C with active cooling, while in this measurement the charging energy rises to much higher rates without active cooling. VTT began with standard discharge capacity testing at 1°C, followed by fast charging tests at 5°C and 11°C with both cooling configurations.

Under these conditions, the Donut Lab battery was successfully charged at 5°C for more than nine minutes. At this charging power, the battery cell reached an 80 percent charge state in about 9.5 minutes and a full 100 percent charge state in just over 12 minutes. When discharged after charging, 100 percent of the charged capacity was available from the cell.

There were some hiccups. During one test with just one cooling pad, the battery became so hot that it reached the safety limit of 90°C, and the device automatically shuts down to prevent any damage. The researchers realized that the battery wasn’t touching the cooling plate tightly enough, so they bonded it to improve thermal contact and heat could escape into the metal more efficiently.

“Unlike other solid-state batteries that require high compression pressures and are subject to volume changes of up to 15-20% during recharging cycles, the Donut battery does not require special compression or more extensive cooling,” Donut Lab CTO Ville Piippo said in a statement. “This greatly simplifies the structure of battery packs and enables solutions that are cost-effective, robust and better than conventional lithium-ion batteries in terms of energy and energy density.”

Donut Lab claimed that its battery delivers 400 watt-hours per kilogram. In comparison, most lithium-ion batteries today range from 200 to 300 watt-hours per kilogram. The company also says the battery can be charged in less than 10 minutes and lasts for 100,000 cycles. Current lithium-ion batteries typically last between 1,500 and 3,000 cycles. According to the institute, the “V1 solid-state battery” tested by VTT has 26A and 94Wh of nominal power.

But before you start popping open the champagne, keep in mind that the report doesn’t address some basic questions about Donut Lab’s solid-state battery. First, VTT does not confirm the chemistry of the packaging, but simply takes it seriously. Second, the test did not address what edge Contributor Tim Stevens points to the “dendrite problem,” where microscopic stalagmites growing from the anode to the cathode across the solid-state electrolyte can cause a short circuit. Perhaps Donut Labs will address this in subsequent independent test results, which are part of its findings “I Don’t Believe” series..