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Researchers used a high-resolution imaging method at the I13-2 beamline of Diamond Light Source to visualise batteries in unprecedented detail during charging.
The new insights could help overcome the technical issues with solid-state batteries, unlocking a game-changing technology for electric vehicles.
Significantly improved electric vehicle (EV) batteries could be a step closer thanks to a new study led by University of Oxford researchers, published today in Nature. Using advanced imaging techniques, this 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.
One of the co-lead authors of the study Dominic Melvin, a PhD student in the University of Oxford’s Department of Materials, said:
Progressing solid-state batteries with lithium metal anodes is one of the most important challenges facing the advancement of battery technologies. While lithium-ion batteries of today will continue to improve, research into solid-state batteries has the potential to be high-reward and a gamechanger technology.
Li-SSBs are distinct from other batteries because they replace the flammable liquid electrolyte in conventional batteries with a solid electrolyte and use lithium metal as the anode (negative electrode). The use of the solid electrolyte improves the safety, and the use of lithium metal 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, which Diamond is a partner, researchers have led a series of in-depth investigations to understand more about how this short-circuiting happens.
In this latest study, the group used an advanced imaging technique called X-ray Computed Tomography (X-ray CT) at the I13-2 beamline of 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. Dominic Melvin 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.
Paul Quinn, Science group leader of the Imaging and Microscopy Science at Diamond Light Source, said:
This study has provided an important insight into the failure mechanisms in Li-SSB’s and demonstrates the real impact our advanced imaging and characterization techniques and expert beamline scientists have in providing new details and insights into key materials processes.
To find out more about the I13-2 beamline or discuss potential applications, please contact Principal Beamline Scientist Christoph Rau: christoph.rau@diamond.ac.uk.
Ning, Z., Li, G., Melvin, D.L.R. et al. Dendrite initiation and propagation in lithium metal solid-state batteries. Nature 618, 287–293 (2023). https://doi.org/10.1038/s41586-023-05970-4
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