Structural Heterogeneity Induced Li Dendrite Growth in Li_0.33La_0.56TiO₃ Solid-State Electrolytes

Solid-state electrolytes (SSEs) are driving next-generation Li-ion batteries (LIBs) with higher energy density and improved safety compared with organic liquid electrolytes. However, the gradual Li dendrite growth during cycling is still a critical issue limiting the long-term service of SSEs, the mechanism of which remains largely unclear. Here, we investigate the Li dendrite growth-induced short circuiting of Li0.33La0.56TiO3 (LLTO) ceramic pellets through detailed electron microscopy and spectroscopy analysis. Under both electrochemical cycling and thermal chemical reaction between Li and LLTO, we find that the Li dendrites prefer to nucleate at the voids in the LLTO pellet, followed by vertical growth along the grain boundaries, and finally result in the buildup of internal stress and the cracking of LLTO. In addition, Li dendrite growth accompanies the decomposition of Li0.33La0.56TiO3 because of the reduction of Ti4+ to Ti3+, which inevitably alters the bulk diffusion of Li ions.