Pre-Treatment of Li-Metal Anode with Hydrohalic-Acid for Stable Cycling of Li-Metal Batteries Under Practical Conditions

Abstract

Lithium (Li) metal anodes (LMAs) are considered as an ultimate choice for beyond Li-ion batteries because of their high capacity (3860 mAh g–1) and low working potential (–3.04 V vs. SHE). However, due to extremely high surface reactivity, uncontrollable dendritic plating, and infinite volume expansion, making Li-metal batteries (LMBs) has long encountered fatal challenges. Heterogeneous solid-electrolyte interphase (SEI) can be the main reason for Li dendrite growth, stemming from the electrolyte byproducts and native LMA surface. In this regard, uniform passivation of LMAs and homogenous SEI at the initial stage is necessary which can occur uniform Li+ ion flux. Furthermore, halogenated SEI is considered as promising component for achieving superior mechanical strength, insulating properties and thermodynamic stability.In this study, we present a simple LMA treatment using hydrohalic acids (HXs, X = F, Cl, Br, and I) to regenerate native passivation layer (NPL) of as-manufactured LMAs and evenly nourish halogenated compounds. The water molecules of aqueous HXs can dissolve the existing inorganic Li-compounds in the NPL, e.g., Li2O, LiOH, and Li2CO3, rendering the chemical reactions of HXs with pure Li, enriching the LiX compounds within the NPL. A comparative study was done to reveal which LiX compounds is beneficial to stabilize the LMA surface and to enhance the cycling stability of LMBs. Furthermore, it is elucidated that the pivotal role of LiX compounds was proved in the interfacial reaction when using localized high concentration electrolyte (LHCE) as an advanced electrolyte in LMBs. Through comparative study, building LiCl-rich SEI at the initial stage effectively reduces the energy barrier of Li nucleation and interfacial resistances, thereby enhancing the cycling performances in LMBs even under practical conditions.