Stable Artificial Solid Electrolyte Interphases for Lithium Batteries

A rechargeable lithium metal battery (LMB), which uses metallic lithium as the anode, is among the most promising technologies for next generation electrochemical energy storage devices due to its high energy density, particularly when Li is paired with energetic conversion cathodes such as sulfur, oxygen/air, and oxygen–carbon dioxide mixtures. Practical LMBs in any of these designs remain elusive due to multiple problems, including parasitic reactions of Li metal with liquid electrolytes, unstable/dendritic electrodeposition at the anode during cell recharge, and chemical reaction of dissolved cathode conversion products with the Li anode. The solid electrolyte interphase (SEI) formed between lithium metal and liquid electrolytes plays a critical role in all of these processes. We report on the chemistry and interfacial properties of artificial SEI films created by in situ reaction of a strong Lewis acid AlI3, Li metal, and aprotic liquid electrolytes. The study takes advantage of the strong surface affinity of I– ions to initiate polymerization of dioxolane at the Li metal surface and to localize beneficial halide salts in the formed polymeric SEI thin film. We find that these SEI films impart chemical and electrochemical stability to a Li metal anode. We further show that the improvements come from at least three processes: (i) creation of a stable oligomer thin film on the Li anode, (ii) formation of a LiI salt layer at the interface, and (iii) in situ formation of a Li–Al alloy.