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

Themorphology of Li deposition has a profound effect on the cyclingperformance of a Li-metal battery. However, in situ research studieson the targeted regulation of Li deposition behavior and explorationof the thermodynamic and kinetic factors affecting Li deposition morphologyare quite limited. Herein, we employ in situ atomic force microscopy(AFM) to investigate the effects of lithium iodide (LiI) additiveon 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 morphologyafter the addition of 10 mM LiI, leading to a combined 3D nucleationand quasi-two-dimensional (2D) growth behavior. Complemented by X-rayphotoelectron spectroscopy (XPS) profiling analysis and AFM nanomechanicalcharacterization, the composition, structure, and properties of solidelectrolyte interphases (SEIs) are comprehensively inspected. TheSEI formed in the LiI-containing electrolyte bears an inorganic-organichybrid structure with improved mechanical flexibility, compared withthe rigid and thick SEI formed in the basic electrolyte. Meanwhile,the possible interfacial adsorption of I (-) contributes to the uniform distribution of Li+ and rapiddiffusion of the Li atom. This work reveals the importance of an additivein regulating the Li deposition behavior, which is helpful in improvingthe Li-metal battery performance.