Mapping the Nanoscopic Filament Growth Kinetics in Lithium Solid Electrolytes

Ceramic lithium conductors such as Li7La3Zr2O12 (LLZO) are promising solid electrolytes for solid-state batteries. However, the lithium filaments can penetrate the electrolytes at high current densities, leading to cell failure. Due to the limited spatial resolution of macroscopic electrochemical measurement techniques, the nanoscopic growth kinetics of lithium filaments and its physical origin remain unrevealed. Here, we report in-situ nanoscale electrochemical characterizations of the filament growth kinetics in LLZO using conductive-atomic force microscope (c-AFM). Significant local inhomogeneity is observed with a hundredfold decrease in the filament triggering bias at the grain boundaries compared with the grain interiors. The origin of the local weakening is assigned to the nanoscopic variation of elastic modulus and surface potential. Further reverse cycles lead to the discovery of the memristive behavior of lithium filament in LLZO based on which a model memristor is designed and demonstrated. A high on/off ratio of ~1E5 is achieved consistently for over 200 cycles. This work provides insights into the nanoscale electrochemical deposition stability in solid-state batteries and opens up opportunities for novel designs of memristive devices.