Stabilizing Dual Interphases for High-Voltage Li Metal Batteries via Trace Dinitrile-Ether Additives in Localized High-Concentration Electrolytes

The integration of lithium metal anodes with high-voltage LiMn x Fe γ PO 4 (LMFP) cathodes is critical for advancing battery energy density, yet it is hindered by severe interfacial instability, particularly at elevated temperatures. This study presents dinitrile-ether (EGBE) as a molecularly engineered multifunctional additive that synergizes with a concentrated ether electrolyte to stabilize both electrode interfaces. Theoretical and experimental evidence confirms that EGBE promotes preferential anion decomposition, forming robust, inorganic-rich interphases on the cathode and anode. These interphases enable uniform lithium plating-stripping and enhance high-voltage resilience. Mechanistically, electron-withdrawing cyano groups (−CN), augmented by an adjacent ether oxygen, simultaneously elevate the reductive stability of nitrile moieties and fortify oxidative resistance via retained lone-pair electrons. This dual functionality addresses the inherent limitations of conventional nitriles and ethers. Furthermore, EGBE effectively chelates dissolved Mn 3+ ions, reducing dissolution by 60%. The resultant interphases support highly reversible lithium deposition, with a Coulombic efficiency of 99.3%. In a 4.5 V Li||LMFP full cell, the EGBE-modulated electrolyte achieves 96% capacity retention after 800 cycles and sustains stable operation over 320 cycles at 70 °C, demonstrating exceptional thermoelectrochemical robustness. This work establishes a rational electrolyte design paradigm using tailored additives to enable high-performance lithium metal batteries under extreme conditions.