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.