Cyano‐Functionalized Hybrid Electrode‐Electrolyte Interphases Enabled by Cyano‐Substituted Tetrafluorobenzene Derivatives Additives for High‐Voltage Lithium Metal Batteries

Abstract Lithium metal batteries (LMBs) operating at high voltages are attractive for their energy storage capacity but suffer from challenges: cathode instability, electrolyte consumption, and lithium dendrite growth. Modulating the electrode/electrolyte interphase (EEI) with functional additives is a practical strategy. Herein, a cyano (‐CN)‐functionalized hybrid EEI strategy is proposed to develop electrolytes for high‐voltage Li||LiNi_0.8Co_0.1Mn_0.1O₂ (Li||NCM811) battery with ‐CN‐substituted tetrafluorobenzene derivatives (tetrafluorophthalonitrile (o‐TFPN), tetrafluoroisophthalonitrile (m‐TFPN)), and tetrafluoroterephthalonitrile (p‐TFPN)) as additives. The results demonstrate that the electrolyte‐containing additives, particularly o‐TFPN‐contained electrolyte, can derive a robust, and thermally stable cathode electrolyte interphase (CEI) enriched with LiF and ‐CN groups. Furthermore, the o‐TFPN‐contained electrolyte forms a stable solid electrolyte interface (SEI) with Li₂O, LiF, and ‐CN. The ‐CN group generates electrostatic attraction, guiding Li⁺ flux, while LiF and Li₂O with high ionic conductivity facilitate rapid Li⁺ deposition. The excellent EEI suppresses cathode degradation, electrolyte consumption, and dendrite formation. Therefore, the Li||NCM811 battery achieves stable performance over 200 cycles at 4.6 V, while the Li||Li symmetric cell stably cycles for over 350 h at a current density of 1 mA cm⁻².