Operando Characterizations of Lithium Penetration-Induced Fracture in Solid Electrolytes

Lithium penetration-induced fracture within solid electrolytes (SEs) is a major issue hindering the commercialization of solid-state lithium-ion batteries (SS-LIBs). Such fracture has been frequently observed during electrochemical plating of lithium (Li)-metal anodes, but its mechanistic origin is still largely unclear.

We present the first quantitative operando analysis of the fracture characteristics of a model SE material under battery-relevant electrochemical cycling conditions.

Full-field deformation during Li deposition-induced cracking of garnet-type LLZTO was measured using the digital image correlation (DIC) method. The obtained displacement data were denoised via equilibrium smoothing, and then fitted to the linear elastic asymptotic crack-tip field to extract the electrochemical fracture toughness values under different current densities.

The physics-based equilibrium smoothing method demonstrated effectiveness in enhancing the accuracy of DIC measurements. The electrochemical fracture toughness obtained was substantially lower than the mechanical fracture toughness of the same material determined through indentation, attributed to combined effects of electrochemical embrittlement and a transition in fracture mode from intergranular to transgranular.

The discrepancy between the two types of fracture toughness suggests that electrochemical cycling could have a significant impact on the fracture mode and resistance of a solid electrolyte.