Regenerating native surface of lithium-metal electrodes via hydrohalic acid-assisted pre-halogenation

Building a uniform and homogeneous solid-electrolyte interphase (SEI) at the initial stage is critical for achieving a long, stable cycling performance in lithium (Li) metal batteries (LMBs). Typically, the majority of Li metal anodes (LMAs) are pre-passivated by inherently heterogeneous native oxide layers, which adversely induce spatially irregular Li⁺ ion fluxes and sporadic Li dendrite growth, thereby resulting in uncontrollable SEI evolution and poor cycling stability. Although halogenated SEI can offer superior mechanical strength, insulation, and thermodynamic stability, the most suitable Li halides for the halogenation of the LMA surface remain in ongoing debates. This study presents the pre-halogenation of an LMA surface via a simple chemical reaction using hydrohalic acids (HXs, X = F, Cl, Br, and I) dissolved in aprotic solutions. With different halide anions (X⁻), LiX compounds can be selectively enriched and homogenized on the entire LMA surface. Among the pre-halogenated LMAs (HX-Li), it is experimentally revealed that LiCl-enriched pre-passivation (HCl-Li) can enhance Li electroplating kinetics, facilitating uniform Li nucleation and leading to dendrite-less compact Li plating. HCl-Li effectively mitigates the volume expansion of the reacted Li/SEI layer, leading to longer cycling of the LMBs.