China's battery maker CATL has passed a key safety test for an aviation battery to be installed in passenger electric vertical takeoff and landing aircraft, or eVTOLs. Thermal runaway did not spread to other cells even when abnormalities were intentionally induced in two adjacent cells, in what was seen as a step forward in battery safety and certification competition needed to commercialise eVTOLs.

On Aug. 10 local time, electric vehicle outlet CleanTechnica reported that CATL conducted a test on an aviation battery system to check thermal runaway and thermal propagation under conditions where two adjacent cells were intentionally activated.

The test was conducted at the centre and at the corner of the battery pack. In both locations, a cell in which an abnormality occurred did not spread its impact to nearby cells, and there was no sign of heat being transferred across the entire battery pack.

Thermal runaway is seen as a key safety issue in aviation batteries. If an abnormality in one cell spreads rapidly to surrounding cells, it can lead to damage to the entire battery pack, which is directly linked to passenger safety. The test was meaningful in that it checked whether risk can be prevented from expanding to the overall system even if a problem occurs in a specific cell.

CATL said a representative designated by the Civil Aviation Administration of China, or CAAC, observed the entire process from cell production to inspection and testing. The company said the procedure could provide a basis for future eVTOL aircraft to meet civil aviation safety standards. CATL in particular claimed the battery was the first case among aviation battery systems based on prismatic cells with an energy density of 350 watt-hours per kilogram to pass the safety test.

Energy density is also an important factor in electric aviation. In eVTOLs, battery weight directly affects flight range, payload and operating efficiency, so batteries that can store more energy at the same weight are advantageous in the race to commercialise.

CATL said it has moved beyond technology development into preparation for mass production. The company said it has completed preparations to mass-produce batteries for eVTOLs and named eVTOL developer Autoflight as the first application target.

With the battery maker disclosing the intended installation target, commercialisation moves aimed at the eVTOL market also appear to be taking shape. However, the announcement did not disclose a timeline for actual commercial operations, additional customers or an aircraft certification schedule.

The eVTOL market has grown around aircraft development and test flights, but for commercial operations it must clear separate tasks of battery safety and aviation certification. In aircraft carrying passengers in particular, technology to prevent battery fires or thermal runaway from spreading to the entire airframe is likely to act as a key certification requirement.

CATL's suppression of thermal propagation at both the centre and corner of the battery pack in the test could become an important technical foundation in such certification processes. It means the company is advancing technology beyond simply raising energy density toward meeting safety standards required for aviation batteries.

The move is also drawing attention because it shows CATL's battery business is expanding beyond electric vehicles into electric aviation. As the eVTOL market moves closer to the stage of actual passenger transport, battery makers are also accelerating development of aviation products differentiated from automotive batteries.

The key going forward is how quickly the safety test results lead to actual aircraft certification and commercial operations. If the 350 watt-hours per kilogram energy density and thermal runaway suppression technology presented by CATL are applied to real aircraft and linked to Autoflight's eVTOL certification and operations, it is expected to affect the pace of commercialisation in the electric aviation battery market.