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When Donut Lab first announced its solid-state battery earlier this year, There has been some speculation On whether the Finnish startup has already produced a supercapacitor, a short-term form of electricity storage. The supercapacitors can charge and discharge quickly, similar to the solid-state battery claimed by Donut Lab. But supercapacitors are very different from batteries in terms of energy storage capacity and long-term use. Was the Donut Lab battery actually just a supercapacitor in disguise?
The startup says no, and it does Independent testing Results prove it. The test, again conducted by Finland’s state-owned technical research center VTT, “evaluates charge retention over an extended idle period.” This is the third test in series to Independent examinations Asked by Donut Lab to evaluate its claims about its new battery.
“Many have said that the donut battery specifications can only be achieved with a supercapacitor,” Marco Lehmäki, the company’s CEO, said in a video. “Well, today we prove that’s not the case.”
Essentially, VTT connected the Donut Lab to a battery tester and left it idle for 10 days, measuring the voltage every 10 seconds. According to the results, the cell showed high stability, retaining 97.7 percent of its energy during the 10-day inactivity period.
Some minor fluctuations were detected, with VTT reporting a drop in voltage from the initial 3861 mV to 3722 mV (a change of -128 mV) during the first hour due to chemical fixation. But otherwise, the cell retained most of its energy, which Donut Lab says disproves theories that its battery is actually a supercapacitor.
During a similar idle period, supercapacitors will lose a significant portion of their stored energy through self-discharge. This is because supercapacitors are not designed to store energy long-term, and unlike batteries, they will see their voltage drop significantly over a few days or weeks. The test confirms “the normal charge retention of the battery type – not the rapid linear discharge characteristic of supercapacitors,” the laboratory says.
Donut Lab says it’s important to refute these claims to clear the air around its solid-state battery. The reason for this is that most of what the startup claims seems implausible to many battery experts. Solid-state batteries are often considered the “holy grail” of battery technology, allowing electric vehicles to travel farther and charge faster without any of the issues that current electric vehicle batteries have around fires and thermal runaway.
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.
There’s still a lot we don’t know about the Donut Lab battery. There was no independent testing to confirm the chemistry of the package. And we still haven’t seen any explanation of how the startup addresses the “dendrite problem,” where microscopic stalagmites growing from anode to cathode through a solid-state electrolyte can cause a short circuit. Perhaps Donut Labs will address this in subsequent independent testing results, which are part of its findings “I Don’t Believe” series..