A researcher from the James Watt School of Engineering is a co-author of a new study which could significantly improve future generations of electric vehicle (EV) batteries.
Dr Guanchen Li contributed to the research, which is led by the University of Oxford and published in Nature .
Using advanced imaging techniques, the researchers revealed mechanisms which cause lithium metal solid-state batteries (Li-SSBs) to fail. If these can be overcome, solid-state batteries using lithium metal anodes could deliver a step-change improvement in EV battery range, safety and performance, and help advance electrically powered aviation.
Dr Li, a co-lead author of the paper, helped to develop the computer modelling which underpins the study. He said: "Solid-state batteries have the potential to deliver transformative improvements over the current generation of lithium-ion batteries - a solid-state battery of the same size could potentially store twice as much energy, helping electric cars or electric planes to travel further. Until now, however, they have suffered from some fundamental chemo-mechanical issues which prevent them from working at commercial scale. This research may help to solve that problem in solid-state batteries going forward."
Li-SSBs are distinct from other batteries because they replace the flammable liquid electrolyte in conventional batteries with a solid electrolyte and enable lithium metal as the anode (negative electrode). The use of solid electrolyte makes the battery safer and means more energy can be stored.
A critical challenge with Li-SSBs, however, is that they are prone to short circuit when charging due to the growth of ’dendrites’: filaments of lithium metal that crack through the ceramic electrolyte. As part of the Faraday Institution’s SOLBAT project, researchers from the University of Oxford’s Departments of Materials, Chemistry and Engineering Science, have led a series of in-depth investigations to understand more about how this short-circuiting happens.
X-ray computed tomography images showing the progressive growth of a lithium dendrite crack within a solid-state battery during the charging process. Image credit: Dominic Melvin, Nature, 2023.
In this latest study, the group used an advanced imaging technique called X-ray computed tomography at Diamond Light Source to visualise dendrite failure in unprecedented detail during the charging process. The new imaging study revealed that the initiation and propagation of the dendrite cracks are separate processes, driven by distinct underlying mechanisms. Dendrite cracks initiate when lithium accumulates in sub-surface pores. When the pores become full, further charging of the battery increases the pressure, leading to cracking. In contrast, propagation occurs with lithium only partially filling the crack, through a wedge-opening mechanism which drives the crack open from the rear.
This new understanding points the way forward to overcoming the technological challenges of Li-SSBs. Another co-lead author of the study, Dominic Melvin, a PhD candidate in the University of Oxford’s Department of Materials, said: "For instance, while pressure at the lithium anode can be good to avoid gaps developing at the interface with the solid electrolyte on discharge, our results demonstrate that too much pressure can be detrimental, making dendrite propagation and short-circuit on charging more likely."
Sir Peter Bruce, Wolfson Chair, Professor of Materials at the University of Oxford, Chief Scientist of the Faraday Institution, and corresponding author of the study, said: "The process by which a soft metal such as lithium can penetrate a highly dense hard ceramic electrolyte has proved challenging to understand with many important contributions by excellent scientists around the world. We hope the additional insights we have gained will help the progress of solid-state battery research towards a practical device."
According to a recent report by the Faraday Institution, SSBs may satisfy 50% of global demand for batteries in consumer electronics, 30% in transportation, and over 10% in aircraft by 2040.
Professor Pam Thomas, CEO, Faraday Institution, said: "SOLBAT researchers continue to develop a mechanistic understanding of solid-state battery failure - one hurdle that needs to be overcome before high-power batteries with commercially relevant performance could be realised for automotive applications. The project is informing strategies that cell manufacturers might use to avoid cell failure for this technology. This application-inspired research is a prime example of the type of scientific advances that the Faraday Institution was set up to drive."
The researchers’ paper, titled ’Dendrite initiation and propagation in lithium metal solid-state batteries’, is published in Nature.