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Critical understanding of why and how solid-state batteries

Researchers from the Faraday Institution’s SOLBAT project have made a significant step in understanding how and why solid-state batteries (SSBs) fail. A paper, published in Nature Materials on 22 April, provides answers to one important piece of the scientific puzzle.

To make step changes in electric vehicle (EV) battery range and safety at a lower cost, new battery chemistries that are “beyond lithium ion” must be developed. SSBs are one such promising technology, but mass market adoption has been held back by several key technical challenges that cause the battery to fail when charged and discharged.

SSBs can short circuit after repeating charging and discharging. One well-recognised cause of battery failure is the growth of dendrites, branching networks of lithium that grow through the solid electrolyte during charging of a battery. Solving these two challenges could potentially usher in a new era of SSB-powered electric vehicles.

Researchers in the Materials, Chemistry and Engineering Science Departments at the University of Oxford, collaborating with Diamond Light Source and the Paul Scherrer Institut in Switzerland have generated strong evidence supporting one of two competing theories regarding the mechanism by which lithium metal dendrites grow through ceramic electrolytes leading to short circulates at high rates of charge.

Researchers used an imaging technique similar to that used in medical CAT scanners – X-ray computed tomography – coupled with spatially mapped X-ray diffraction, to visualise and characterise the growth of cracks and dendrites deep within an operating solid-state battery.

Conical pothole-like cracks first form in the electrolyte adjacent to the plated lithium anode. The crack propagates along a path where the porosity is above the average value of the ceramic. Metallic lithium is then deposited along the crack and this ingress drives the propagation of the cracks by widening the crack from the rear. The crack front propagates ahead of the lithium deposition, and lithium is not present at the crack tip. Only later, when lithium plates along the entire crack, does the cell finally short circuit.

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