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

ABSTRACT 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.