Revitalizing Native Lithium-Metal Electrode Surfaces through Hydrohalic Acid-Assisted Pre-Halogenation

Lithium metal anodes (LMAs) represent the ultimate choice for advancing beyond traditional Li-ion batteries due to their remarkable attributes, including a high capacity of 3860 mAh g–1 and a low working potential of –3.04 V vs. SHE. However, the inherent challenges associated with LMA usage, such as their exceedingly high surface reactivity, uncontrollable dendritic plating, and unbounded volume expansion, have long hindered the development of practical lithium-metal batteries (LMBs). The primary culprit behind these issues is the formation of a non-uniform solid-electrolyte interphase (SEI) layer, arising from byproducts within the electrolyte and the inherent surface characteristics of LMAs. In light of these challenges, achieving uniform passivation of LMAs and the formation of a homogeneous SEI layer during the initial stages are imperative. Such uniformity is crucial to enable consistent Li⁺ ion flux. Additionally, the integration of halogenated SEI components holds great promise, offering enhanced mechanical strength, insulation properties, and thermodynamic stability.<br/>In this study, we introduce a straightforward LMA treatment technique utilizing hydrohalic acids (HXs, X = F, Cl, Br, and I) to rejuvenate the native passivation layer (NPL) found on as-manufactured LMAs. This treatment ensures an even distribution of halogenated compounds across the LMA surface. A key aspect of this process involves the dissolution of existing inorganic Li-compounds, such as Li₂O, LiOH, and Li₂CO₃, present in the NPL by water molecules from aqueous HXs. This results in chemical reactions between HXs and pure Li, ultimately enriching the NPL with LiX compounds. A comparative analysis was conducted to identify the most advantageous LiX compounds for stabilizing the LMA surface and enhancing the cycling stability of LMBs. Furthermore, we elucidated the critical role played by LiX compounds in interfacial reactions when employing localized high-concentration electrolyte (LHCE) as an advanced electrolyte in LMBs. Through this comparative study, it was demonstrated that the establishment of a LiCl-rich SEI layer during the initial stages effectively lowers the energy barrier for Li nucleation and reduces interfacial resistances. This leads to significant enhancements in cycling performance for LMBs, even under practical operating conditions.