Surface engineering toward stable lithium metal anodes

Abstract

The lithium (Li) metal anode (LMA) is susceptible to failure due to the growth of Li dendrites caused by an unsatisfied solid electrolyte interface (SEI). With this regard, the design of artificial SEIs with improved physicochemical and mechanical properties has been demonstrated to be important to stabilize the LMAs. This review comprehensively summarizes current efficient strategies and key progresses in surface engineering for constructing protective layers to serve as the artificial SEIs, including pretreating the LMAs with the reagents situated in different primary states of matter (solid, liquid, and gas) or using some peculiar pathways (plasma, for example). The fundamental characterization tools for studying the protective layers on the LMAs are also briefly introduced. Last, strategic guidance for the deliberate design of surface engineering is provided, and the current challenges, opportunities, and possible future directions of these strategies for the development of LMAs in practical applications are discussed.

Fig. 1.. Schematic illustration of the current surface engineering strategies for stabilizing LMAs.

Fig. 2.. Schematic illustration of surface pretreatment using solid-phase pathways.

(A) The stamp modified process on Li metal. (B) Fabrication of the LBASEI Li via a roll-press process. (C) The glass fiber cloth is directly coated on copper foil to render the dendrite-free Li deposits. (D) The schematic diagram for the fabrication of the Li-Sr anode via a high-temperature alloying process. (E) Schematic illustration of GF-LiF-Li preparation and its protective effect for LMAs.

Fig. 3.. Schematic illustration of surface pretreatment using liquid-phase pathways.

(A) Surface processing strategies via various solution casting methods, including slurry casting, immersion, dripping, and spray casting. (B) High-polarity DMSO was selected to dissolve sufficient metal fluorides (e.g., SnF₂, InF₃, and ZnF₂), which is crucial to forming the uniform and robust BSLs on Li metal. (C) Design of a polymer-inorganic SEI using the RPC precursor rather than the electrolyte to trigger a chemical reaction with Li. (D) Potentiostatic stripping and galvanostatic plating for polishing of and formation of SEI on metal anode (MA) surface. (E) Ex situ SEI construction on the Li plate by electrochemical methods in 1.0 M LiTFSI-DOL/DME electrolyte with 0.02 M Li₂S₅–5.0 wt % LiNO₃ hybrid additives.

Fig. 4.. Schematic illustration of surface pretreatment using gas-phase pathways.

(A) The preparation process of Li_xSi-modified lithium foil. (B) The fabrication method for a MoS₂-coated LMA via sputtering and subsequent lithiation. (C) The fabrication of zwitterionic polymeric interphases. Step 1: iCVD precursor polymer film. Step 2: derivatization. (D) The fabrication process of the dual protective layer by ALD and MLD. (E) The surface processing strategies via chemical reactions with various gases.

Fig. 5.. Schematic illustration of surface pretreatment using some peculiar pathways.

(A) A desired Li₃N film can be formed on the Li metal as the protective layer by a plasma activation in a short time. (B) The design of silly putty modified LMA. (C) A designed “spansule” can sustainably supply functional ingredients that effectively guide dendrite-free Li deposition. (D) A self-assembled monolayer of electrochemically active 1,3-benzenedisulfonyl fluoride on Cu can lead to uniform seeding of Li with a stable LiF-rich SEI layer.

Fig. 6.. Schematic illustration of the current characterization techniques for the artificial SEIs on Li metal.

Fig. 7.. Summary and comparison of various surface pretreatment strategies for LMAs.

(A) Roadmap of major achievements in the field of surface engineering. (B to D) The panels on the upper row are the cycling performance of Li symmetric cell (current density and capacity is 1 mA cm⁻² and 1 mAh cm⁻², respectively) using the modified LMAs pretreated by different methods. The solid symbols represent using the ether-based electrolytes, while the hollow ones mean using the carbonate-based electrolytes. The panels on the nether row are the evaluation of these methods from five practical application metrics: protective efficiency, volume energy density, processing simplicity, cost effectiveness, and scalability.