Establishing a multifunctional solid electrolyte interphase on a 3D host by an ultra-fast double coating strategy for stable lithium metal batteries

Establishing a multifunctional solid electrolyte interphase (SEI), which can not only reduce the electrode–electrolyte side reactions, but also promote the mass transport behavior of Li, can promisingly stabilize the operation of lithium metal batteries (LMBs). Herein, we introduce a multifunctional SEI constructing Cu based three-dimensional host (MSEI@Cu), whose electrochemical and chemical SEIs are characterized by excellent ionic conductivity, Li diffusivity and mechanical stability. The fabrication of MSEI@Cu is realized by a novel ultra-fast double coating strategy, during which metallic Cu nanowires grown on Cu foam are covered by a double coating layer constituted by a dense surficial carbon layer and inner carbon matrices containing CuSO4 and In2S3. Through electrochemical or chemical reduction by Li, CuSO4 and In2S3 are converted to Li2S and LixIn, and the positively charged residual Cu atoms can promote the decomposition of TFSi− anions, contributing to abundant formation of LiF. As a result, the inner SEI formed on MSEI@Cu is enriched by Li2S, LixIn and LiF, all of which synergistically improve electrical resistivity, mechanical strength and mass transport kinetics of Li. Meanwhile, the amorphous carbon matrices evenly distributing the above compounds further enhance the mechanical integrity of the as-formed SEI by successfully accommodating volume changes. Importantly, all the above components are densely covered by an outmost surficial carbon layer, which prevents the direct exposure of conductive metallic Cu nanowires to the electrolyte, thereby reducing excessive electrolyte decomposition. Benefiting from the sophistically engineered advanced SEI, MSEI@Cu exhibited substantial improvements in electrochemical performance: when paired with a LiFePO4 cathode, MSEI@Cu delivered a specific capacity of 125.9 mA h g−1 at 1C with an impressive capacity retention of 80% for 500 cycles.