Dendrite-free reversible Li plating/stripping in adiponitrile-based electrolytes for high-voltage Li metal batteries

The energy densities (EDs) of lithium-ion batteries have improved remarkably mostly via increases in the capacity of cathode materials, which suggests that the next quantum leap will require the simultaneous implementation of high-voltage cathodes and Li metal anodes for high-voltage operations. Herein, we describe for the first time that the compatibility of Li metal in adiponitrile (ADN) is ensured via the utilization of porous Li2O-coated Li (Li/Li2O). The optimal Li2O layer is constructed simply by immersing Li metal in ADN containing nitronium tetrafluoroborate (NO2BF4). When cycled in LiBF4/ADN, porous Li2O facilitates the formation of a stable LiF-enriched interfacial layer, which enables reversible Li plating/stripping during extended cycles with no dendrite formation. The sequential formation of LiF within the pores of Li2O is crucial, because massive formation of LiF precipitates is unavoidable without Li2O. Li/Li2O is also operable in LiTFSI/ADN (TFSI = bis(trifluoromethane)sulfonimide) with the addition of LiBF4. Finally, as a proof-of-concept experiment, we show the charge/discharge behaviors of LiNi0.5Mn1.5O4 when coupled with Li/Li2O in LiBF4:LiTFSI/ADN, which proves that a Li metal cell can be charged to 6.0 V. We hope that this work will expedite the development of Li metal batteries with a high level of ED in the dinitrile family.