Origin of Lithium Dendrite Formation in Sulfide-Based Electrolyte

The Li dendrite growth during battery cycles is a well-known obstacle to the practical application of sulfide-based electrolytes (SEs), notably Li₃PS₄ (LPS), in lithium metal batteries. However, there remains a significant gap in understanding the mechanism for Li dendrite penetration through SEs exhibiting high shear modulus. Herein, we investigate the optimum deposition sites for Li⁰ atoms within typical LPS configurations, encompassing crystalline, lithiated, and degraded structures, with their ionization levels employed as descriptors to determine the preferential state (Li⁰/Li⁺) of the interstitial Li. Our results suggest that both bulk LPS and solid electrolyte interphase (SEI) layer are predicted to be electrochemically resistive upon Li⁰ deposition. Conversely, the defect configurations, including cracks and grain boundaries (GBs), exhibit a marked propensity to promote the electrochemical deposition of Li⁰ atoms. Once Li dendrites initiate, the electronic conductivities of those defects undergo a significant surge, catalyzing electron transport and facilitating Li dendrite penetration through the SEs, ultimately driving dendrite growth. Furthermore, we underscore the synergistic interaction between Li dendrite propagation and crack formation within SEs, offering deeper insights into the electrochemical-mechanical degradation mechanism in SEs. These findings present novel methodologies for predicting Li dendrite growth and open up alternative perspectives in SE engineering.