Eutectic‐Like Ion‐Conductive Phase‐Incorporated Zwitterionic Covalent Organic Framework Solid Electrolyte for All‐Solid‐State Li Metal Batteries

Abstract High energy‐density Li metal batteries with improved safety and cyclic performance can be achieved by adopting solid polymer electrolytes. However, current solid polymer electrolytes show inferior room‐temperature ionic conductivity and Li‐ion transference number (t Li+ ), impeding their practical applications. Herein, a 3‐(pyridinium)propane‐1‐sulfonate zwitterionic covalent organic framework (PSZ‐COF) incorporating a eutectic‐like ion‐conductive phase is prepared by making a complex with N ‐methyl‐ N ‐propylpyrrolidinium bis(fluorosulfonyl)imide (Pyrrol‐FSI) and Li salts in its channels as a solid electrolyte (eutectic PSZ‐COF). The eutectic PSZ‐COF possesses a zwitterionic Li‐salt‐dissociating mode, a Pyrrol‐FSI Li‐cation‐transporting carrier, and a pyridinium anion‐holding trap in the ordered channels, providing a high ionic conductivity (0.127 mS cm −1 ) and t Li+ (0.62) at room temperature. Moreover, the eutectic PSZ‐COF can suppress Li dendrites and drive a LiF/Li 3 N‐rich solid electrolyte interface layer on a Li anode. Computational simulations reveal that the time‐evolved average distance and hoping distance of Li + ions are significantly reduced in the eutectic PSZ‐COF, allowing their facile migration. The all‐solid‐state Li metal batteries bearing eutectic PSZ‐COF with a lithium iron phosphate(LFP) cathode (2.0 mg cm − 2 ) exhibit an initial capacity of 153.3 mAh g −1 , 99.9% Coulombic efficiency, and 100% capacity retention over 150 cycles at room temperature. This study offers an effective route to high‐performance solid electrolytes for all‐solid‐state Li batteries.