Synergetic impact of nitrate-based additives for enhanced solid electrolyte interphase performance†

Practical application of high-energy-density lithium (Li) metal batteries is hindered by instability of the solid electrolyte interphase (SEI) that grows as a passivation layer on the anode surface. Attempts to address SEI degradation often involve a rational modification of its composition, through the introduction of appropriate electrolytic additives. Notably, amalgamation of a fluorine (F) source and a nitrate (NO₃⁻) source as additives for growing a fluorinated-nitrided SEI in situ has been previously reported to enhance battery performance and longevity. However, the intrinsic structure and properties of such mixed SEI phases remain poorly understood. Herein, using atomistic simulations, we present the synergetic chemistry of nitrate-based additives with lithium fluoride (LiF), with potentially transformative impact on SEI performance. Our studies demonstrate that spontaneous Li-induced decomposition of NO₃⁻ leads to dispersion of lithiophilic impurities with a stabilizing influence on desirable amorphous SEI phases. Furthermore, detailed analyses showcase mixed LiF(NO₃) phases to be capable of being electronically insulating super Li-ionic conductors with exceptional ductility over a wide lithiation window. Such atomic level findings may be essential for in situ SEI design strategies that can help improve interfacial stability in rechargeable batteries.