Characterizing mechanical and electrochemical degradation in solid-state battery electrolytes using x-ray tomography
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Transformations at unstable interfaces between solid-state electrolytes (SSEs) and the lithium metal electrode can lead to high impedance and capacity decay during cycling of solid-state batteries (SSBs), but the links between structural/chemical/mechanical evolution of interfaces and electrochemical behavior are not well understood. Here, we use in-situ micro X-ray computed tomography (CT) to reveal the evolution of mechanical damage within a LAGP SSE caused by the growth of a lithiated interphase between lithium and LAGP during electrochemical cycling. The growth of an interphase with expanded volume drives mechanical fracture in this material, and the extent of fracture within the ceramic during cycling is found to be the primary factor causing the increase in impedance, as opposed to the resistance of the interphase itself. Cracks are observed to initiate near the edge of the lithium/LAGP interface, which agrees with finite element analysis simulations that predict stress concentrations at these locations. This work provides quantitative links between chemo-mechanical degradation and interphase growth, and it is thus an important step towards controlling interfaces in a wide variety of solid electrolyte materials for improved longevity in batteries.