3D imaging shows how lithium batteries degrade over time

How disposable lithium batteries degrade during normal use has been tracked in real time by a UCL-led team using sophisticated 3D imaging, giving a new way to non-invasively monitor performance loss and guide the development of more effective commercial battery designs.

The team recently used the same technique to show how rechargeable lithium-ion batteries fail when they are exposed to extreme levels of heat, but this is the first time the extent of day-to-day damage of disposable lithium batteries has been shown.

The study follows calls from investigators in August 2015 for a safety review of all lithium battery-powered equipment on planes after a fire onboard a grounded Boeing 787 Dreamliner at Heathrow Airport in 2013.

The fire was caused by the plane’s disposable lithium battery-powered emergency locator transmitter which sends out a radar signal to locate missing aircraft. The system is designed to work indefinitely until the aircraft is found but the results show the batteries may not be as resilient as they seem.

The study by UCL, Lund University, The European Synchrotron (ESRF), University of Manchester, Harwell Oxford, Oregon State University and the National Physical Laboratory, published in Advanced Science, shows the internal structural damage caused to batteries working under normal conditions in real time.

Using cutting-edge X-ray imaging techniques at ESRF, the team tracked different types of wear and tear which cause performance loss and linked this wear to design features of the commercial battery.

“On the outside, the batteries look like they are doing their job normally, but inside we saw the structure was undergoing great change. Electrical activity was high in some areas of the cell, whereas it was low in others; layers of electrode material separated and cracked. All of these changes in structure affect the flow of electricity and reduce the performance of the cell,” UCL PhD student Donal Finegan (UCL Chemical Engineering) said.

Real-time 3D images of active commercial Li/MnO₂ disposable batteries were captured using X-ray computed tomography (CT) and advanced digital volume correlation software. The images formed cross-section time-lapse videos showing the damage occurring on the electrodes inside the battery in real time. Dr Paul Shearing (UCL Chemical Engineering) said: “Lithium disposable batteries are used for mission-critical systems where recharging is impractical, so understanding the safety and reliability of them is important, particularly given recent high-profile cases where batteries on aircraft have failed. We gained valuable insights that apply to a variety of commercial batteries using this system, showing an effective, non-invasive way for industry to monitor performance and improvements in commercial battery design.”

Finegan added: “We effectively mapped the activity and strain on the material inside the battery, which will help manufacturers predict how a particular battery will perform during operation and over time. We see this is a valuable tool for optimising the material used in commercial batteries, which will improve their resilience.”