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

Abstract

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 LiNi_0.5Mn_1.5O₄ 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.