Operando identification of anion effect on lithium nucleation and growth via in situ transmission electron microscopy

Lithium metal batteries are considered promising candidates for next-generation energy storage due to the high capacity and low redox potential of lithium negative electrodes. However, dendritic Li growth and unstable solid-electrolyte interphase formation remain critical bottlenecks for practical implementation. While electrolyte anion chemistry critically governs solid-electrolyte interphase formation, nanoscale observations of anion-regulated Li nucleation and growth mechanisms remain limited in tracking dynamic interfacial processes. Here, we employ in situ liquid-phase transmission electron microscopy combined with cryogenic spectroscopy and computational modelling to unravel anion-specific Li nucleation and growth in three distinct electrolytes: LiClO4, LiPF6, and LiTFSI-based electrolytes. Real-time tracking reveals that ClO4− drives dendritic Li growth with organic dominated solid-electrolyte interphase, whereas PF6− stabilizes moss-like Li nucleation through LiF-organic hybrid interphases. Notably, TFSI⁻ forms a bilayer SEI with LiF/Li2CO3-rich inner layers, enabling Li lateral growth and fusion. Molecular dynamics simulations correlate anion-induced interface architectures with Li+ transport and surface potential distributions, demonstrating that TFSI− suppresses dendrites via balanced mechanical confinement and ion-flux regulation. These anion-mediated interface engineering observations offers principles for electrolyte design toward stable lithium metal batteries. Lithium metal batteries face challenges with dendritic growth. Here, authors employ in situ TEM to reveal how specific electrolyte anions dictate lithium nucleation and interphase architecture, establishing design principles for suppressing dendrites and enabling stable lithium deposition.