Visualizing the failure of solid electrolyte under GPa-level interface stress induced by lithium eruption

Solid electrolytes hold the promise for enabling high-performance lithium (Li) metal batteries, but suffer from Li-filament penetration issues. The mechanism of this rate-dependent failure, especially the impact of the electrochemo-mechanical attack from Li deposition, remains elusive. Herein, we reveal the Li deposition dynamics and associated failure mechanism of solid electrolyte by visualizing the Li|Li7La3Zr2O12 (LLZO) interface evolution via in situ transmission electron microscopy (TEM). Under a strong mechanical constraint and low charging rate, the Li-deposition-induced stress enables the single-crystal Li to laterally expand on LLZO. However, upon Li eruption, the rapidly built-up local stress, reaching at least GPa level, can even crack single-crystal LLZO particles without apparent defects. In comparison, Li vertical growth by weakening the mechanical constraint can boost the local current density up to A center dot cm(-2) level without damaging LLZO. Our results demonstrate that the crack initiation at the Li|LLZO interface depends strongly on not only the local current density but also the way and efficiency of mass/stress release. Finally, potential strategies enabling fast Li transport and stress relaxation at the interface are proposed for promoting the rate capability of solid electrolytes. The mechanism of lithium dendrites penetrating solid electrolytes remains elusive. Herein, the authors reveal the Li deposition dynamics and the associated failure mechanism of solid electrolyte by visualizing the Li|LLZO interface evolution via in situ transmission electron microscopy.

Automated summary

In this study, the authors visualize the evolution of the Li|LLZO interface via in-situ transmission electron microscopy, revealing the dynamics of Li deposition and the associated failure mechanism of solid electrolytes. The results show that under a strong mechanical constraint and low charging rate, Li deposition can cause lateral expansion of single-crystal Li on LLZO. However, upon Li eruption, rapidly built-up local stress can crack single-crystal LLZO particles. In comparison, vertical growth of Li by weakening the mechanical constraint can increase the local current density without damaging LLZO.