  A rechargeable lithium metal battery (LMB), which uses metallic lithium at
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 carbon dioxide. Practical LMBs in any of these designs
remain elusive due to multiple stubborn 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 interface (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
additive, Li metal, and aprotic liquid electrolytes. We find that these SEI
films impart exceptional interfacial stability to a Li metal anode. We further
show that the improvements come from at least three processes: (i) in-situ
formation of Li-Al alloy, (ii) formation of a LiI salt layer on Li, and (iii)
creation of a stable polymer thin film on the lithium metal anode.
