A Double-Layer Artificial SEI Film Fabricated by Controlled Electrochemical Reduction of LiODFB-FEC Based Electrolyte for Dendrite-Free Lithium Meal Anode

The commercial application of lithium (Li) metal anode has long been hindered by low coulombic efficiency (CE) and Li dendrites, which are closely correlated with the quality of solid electrolyte interphase (SEI) film. Naturally formed SEI films are usually unsatisfactory due to their non-ideal structures and components caused by in situ reactions of electrolyte with Li metal anode. Herein, a double-layer artificial SEI (ASEI) film is prepared by controlled electrochemical reduction of lithium difluoro(oxalato)borate (LiODFB) and fluoroethylene carbonate (FEC) based electrolyte on Cu substrate. The thickness of the optimized ASEI film is about 67.2 nm, with boron (B) -containing oligomers and CF x compounds existing in the outer part of the layer, and the inner part of the layer is mainly composed of inorganic species (LiF, Li 2 CO 3 , Li 2 O). Such a specific structure enables the ASEI film with enough flexibility, high mechanical modulus, desirable Li + conductivity and homogeneous Li + flux, thus leading to uniform deposition of Li. ASEI@Cu∣Li cell achieves stable CE of ∼98% and ∼3 times lifespan compared to bare Cu. The much improved electrochemical performance of LiNi 0.5 Co 0.2 Mn 0.3 O 2 ∣ASEI@Cu(Li) full cell also demonstrates its potential in practical applications.