Direct Observation of the Growth of Lithium Dendrites on Graphite Anodes by Operando EC-AFM

Lithium dendrite growth is one of the most challenging problems affecting the safety performance of lithium-ion batteries (LIBs). It causes low Coulombic efficiency as well as safety hazards for LIBs. Understanding the evolution process of Li-dendrite growth at the nanoscale is critical for solving this problem. Herein, an in situ electrochemical atomic force microscopy (EC-AFM) investigation of the initial Li deposition in ethylene carbonate (EC)-based and fluoroethylene carbonate (FEC)-based electrolytes on graphite anodes is reported. These results show that the solid electrolyte interphase (SEI) formed from the FEC-based electrolyte can suppress Li-dendrite growth. The FEC-based electrolyte induces formation of LiF-rich SEI films, which are harder and denser than those formed in an EC-based electrolyte. Due to its better mechanical properties and larger resistance, the SEI layer formed from the FEC-based electrolyte is sufficient to prevent reduction of Li⁺ ions and deposition of Li⁺ ions on the anode surface. These results demonstrate that EC-AFM is a powerful in situ technique for the study of lithium-dendrite growth.