“Stressed Out” Drone Batteries Could Be Reassigned Less Demanding Jobs

The vertical take-offs performed by drones and other flying machines impart a huge amount of stress on their batteries, causing them to degrade at an accelerated rate. But what if these power sources – instead of being thrown away – could go on to live new lives powering other useful tech?

That’s the vision proposed by researchers from Oak Ridge National Laboratory. In a new study, published in ACS Energy Letters, the team manufactured and tested a set of lithium-ion batteries similar to those used in heavy-duty drones.

They found that under high-stress conditions similar to drone operation, the batteries began to show decreased performance very quickly. But when they were switched to more “normal” operating conditions, the batteries partially recovered.

Powering drone flight is a tough task

Lithium-ion batteries (LiBs) have become a cornerstone of the tech industry, thanks to their ability to pack large amounts of power into relatively small and lightweight units. But these batteries aren’t a perfect solution for everything, especially in high-stress situations.

Most hobby drones use a type of lithium-ion polymer battery. But for heavier-duty drones – such as those used to deliver cargo to remote conditions – a higher energy density is needed. These industrial drones are the ones that rely on LiBs to get the job done.

Powering a drone is a tough task for a battery. Vertical take-offs require an intense initial discharge pulse right at the start of the battery cycle to get the drone off the ground, followed by a much lower discharge rate during flying.

To better understand how high-strain events like lift-off affect LiB stability, the researchers created and “stressed out” a set of LiBs while tracking how their performance changed over time.

From drone fleets to the humble power pack

The set of manufactured LiB cells contained a specially made electrolyte designed to enable fast charging and discharging. During testing, the cells were drained at a rate 15 times greater than their rated battery capacity for 45 seconds. This intense discharge pulse was done to simulate the rapid, high-power draws needed during vertical drone take-offs. After the strong initial discharge, the cells were further drained at a more standard discharge rate, before being recharged.

None of the tested cells were able to last more than 100 cycles under these stressful conditions, with the majority of cells beginning to show signs of decreased performance after around 85 cycles.

Once the cells had been sufficiently “stressed out” the team continued to use the cells, but this time with a more normal (i.e. lower rate) initial power draw.

To their surprise, the cells were partially restored to their normal electrochemical capabilities under these typical operating conditions. They recovered to achieve their original capacities and showed good signs of charge retention. However, when returned to a high-stress discharge scheme, the cells quickly failed again.

Based on these observations, the research team suggests that heavy-duty drone batteries could be retired and sent off for use in other applications with less intense power demands, instead of being scrapped. Examples of more typical applications could include energy-grid storage or use as backup battery packs for power supplies.

The researchers acknowledge funding from the US Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory.

Reference: Dixit M, Bisht A, Essehli R, Amin R, Kweon CBM, Belharouak I. Lithium-ion battery power performance assessment for the climb step of an electric vertical takeoff and landing (eVTOL) application. ACS Energy Lett. 2024:934-940. doi: 10.1021/acsenergylett.3c02385

This article is a rework of a press release issued by the American Chemical Society. Material has been edited for length and content.