Benzonitrile‐Based Electrolyte with Tighter Aggregate Solvation Structure Enables Ultralong Cycling and High‐Rate 4.5 V Lithium Metal Batteries

Nitrile-based electrolytes offer exceptional oxidative stability for high-voltage cathodes but suffer from reductive instability at lithium metal anodes (LMAs) and poor rate capability. Herein, we report a molecular engineering strategy to overcome these limitations by introducing a benzonitrile-based electrolyte (BNE) to realize long-cycling, high-voltage, and high-rate LMBs. We leverage the unique molecular features of benzonitrile (BN), where the cyano groups dynamically coordinate lithium ions (Li⁺), the electron-deficient phenyl groups interact weakly with anions, and crucially, the bulky BN molecules compress the Li⁺ solvation sheath through a spatial site-blocking effect. The steric demand imposed by BN during Li⁺ solvation, coupled with its ability to simultaneously coordinate Li⁺ and interact with anions, induces a tighter aggregate (t-AGG) solvation structure, which is confirmed by various spectroscopic techniques and molecular dynamics simulations. Mechanistically, the t-AGG solvation structure eliminates most free BN molecules for enhanced stability at LMAs, accelerates Li⁺ transport kinetics via increased hopping frequency, and promotes an anion-derived solid-electrolyte interphase. Consequently, BNE enables a 4.5 V NCM811||Li cell to achieve 500 cycles with 80% capacity retention at 5C, setting a benchmark for nitrile-based LMBs. This work provides fundamental insights for designing high-performance nitrile-based electrolytes via precise solvation structure engineering for LMBs.