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

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/Li₃N-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.