Exploring the Role of LiI Additive in Regulating the Morphology of Lithium Deposition by In Situ AFM

The morphology of Li deposition has a profound effect on the cycling performance of a Li-metal battery. However, in situ research studies on the targeted regulation of Li deposition behavior and exploration of the thermodynamic and kinetic factors affecting Li deposition morphology are quite limited. Herein, we employ in situ atomic force microscopy (AFM) to investigate the effects of lithium iodide (LiI) additive on the evolution of Li deposition morphology in propylene carbonate (PC)-based electrolyte. The spherical Li deposits formed via three-dimensional (3D) nucleation and growth partially transform into planar morphology after the addition of 10 mM LiI, leading to a combined 3D nucleation and quasi-two-dimensional (2D) growth behavior. Complemented by X-ray photoelectron spectroscopy (XPS) profiling analysis and AFM nanomechanical characterization, the composition, structure, and properties of solid electrolyte interphases (SEIs) are comprehensively inspected. The SEI formed in the LiI-containing electrolyte bears an inorganic–organic hybrid structure with improved mechanical flexibility, compared with the rigid and thick SEI formed in the basic electrolyte. Meanwhile, the possible interfacial adsorption of Ĩ– contributes to the uniform distribution of Li+ and rapid diffusion of the Li atom. This work reveals the importance of an additive in regulating the Li deposition behavior, which is helpful in improving the Li-metal battery performance.