Weakly solvating fluoroether enables nitrile-mediated dual-interface passivation in high-voltage lithium batteries

Li-rich Mn-based layered oxides (LRMO) provide high capacity, but operation above 4.5 V is constrained by a transport-stability conflict: carbonate-rich Li⁺ coordination supports ion conduction while delivering reactive solvent molecules to an oxygen-redox-active cathode and a Li-metal anode. Here, a carbonate electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), 1,3,6-hexanetricarbonitrile (HTCN), and trace LiNO₃ is used to regulate how Li⁺-containing species pass through the outer and inner Helmholtz layers. Molecular dynamics, Raman/NMR spectroscopy, in situ Raman tracking, and interfacial electrochemical measurements show that HFE weakens Li⁺-carbonate coordination and enriches fluorinated species near electrified surfaces. This environment allows HTCN to remain transiently associated with incoming Li⁺ clusters through the outer Helmholtz plane (OHP) and to become available near LRMO during partial desolvation, where nitrile-derived species participate in cathode electrolyte interphase (CEI) formation. At Li metal, reduced carbonate competition allows trace nitrate to enter the earliest reduction events in the inner Helmholtz plane (IHP). The resulting N/F-rich CEI and Li₃N/LiF-rich solid electrolyte interphase (SEI) suppress gas evolution, transition-metal dissolution, and nonuniform Li growth. LRMO cells cycled to 4.8 V deliver 276.9 mAh·g^–1 and retain 85.43% after 200 cycles at 0.1 C, demonstrating coordinated dual-interface regulation for high-voltage lithium batteries.