Cells with advanced chemistry pose adoption challenges but can be safer and more energy-dense than lithium-ion versions.
US electric-aviation development project Helios Horizon has completed what it calls the first “human-piloted” flight of an aircraft powered by solid-state batteries.
Such batteries usually have greater energy density than the lithium-ion batteries typically used to power electric aircraft, including in-development air taxis. They also tend to be safer, but pose technical challenges that have so far kept them in the development phase.
Founded by Miguel Iturmendi – a veteran of well-known aerospace test programmes like the Perlan Project and Solar Impulse – Helios completed the flights using its modified Pipistrel Taurus Electro motor-glider on 5 June from Zephyrhills airport in Florida.
Solid-state batteries “can more than double the range of electric vehicles and recharge in a fraction to the time of traditional EV batteries”, Helios says.
“For the first time, we have a battery technology that yields the range and charging times necessary to make commercial electric aviation viable, while providing the safety the flying public will demand,” adds Iturmendi, who piloted the Taurus during the test flights.
Helios has for several years been completing high-altitude electric-propulsion demonstration flights using its modified Taurus Electro. For those prior flights, the team had replaced the aircraft’s stock electric propulsion system with custom lithium-ion batteries and other components.
Lithium-ion batteries use a liquid electrolyte to separate an anode and cathode, while solid-state types use a solid electrolyte.
NASA, under a programme called SABERS, and several aviation companies have been studying solid-state batteries recently. Such batteries generally hold more energy than their lithium-ion equivalents, and tend to be less likely to combust, more resilient to damage, smaller and lighter, due partly to not needing complex packaging and cooling features.
But solid-state batteries come with manufacturing challenges and tend to be expensive, and traditional designs can degrade faster due to repeated cycling causing defects on the lithium anode.
Chinese air taxi developer EHang several years ago flew an air taxi prototype using solid-state batteries.
Helios says solid-state batteries can “offer 60-80% greater energy density and can be charged from almost empty to 80% in less than 15 minutes”.
The Taurus Electro’s prior lithium-ion set-up had 260Wh/kg energy density, while the solid-state batteries have 410Wh/kg density.
“Expense and availability are certainly challenges currently, but the solid-state batteries have significantly better longevity than their traditional [lithium-ion] batteries, not worse,” says Helios. “Longevity has to do with cell degradation based on temperature. Since solid-state cells handle a wider range of temperatures, they are lasting longer.”
The 5 June flights in Florida lasted “a few minutes” each and followed “tethered ground runs of the aircraft running at full power until battery depletion”, Helios says. “These first test flights were primarily just to assess changes to weight and balance with the new batteries installed.”
The tests will inform a plan by Helios to equip the Taurus Electro with a new battery system and fly it into the stratosphere – 40,000ft is the target. It aims to start that test programme this autumn.
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