A Thiol Branched 3D Network Quasi Solid‐State Polymer Electrolyte Reinforced by Covalent Organic Frameworks for Lithium Metal Batteries

Abstract Quasi solid‐state polymer electrolytes (QSPEs) are particularly attractive due to their high ionic conductivity and excellent safety for lithium metal batteries (LMBs). However, it is still a great challenge for QSPEs to achieve strong mechanical strength and high electrochemical performance simultaneously. Herein, a QSPE (SCOF‐PEP‐PEA) using a covalent organic framework (COF) containing abundant allyl groups (SCOF) as a rigid porous filler as well as a cross‐linker to reinforce the polymer network is reported. Benefitting from the unique 3D nanonetwork structure and abundant lithiophilic functional groups, SCOF‐PEP‐PEA QSPE exhibits high ionic conductivity (4.0 × 10 −4 S cm −1 ) and high lithium‐ion transference number (0.82) at room temperature. Moreover, SCOF‐PEP‐PEA QSPE displays much improved mechanical strength compared to PEP‐PEA QSPE (AFM Young's modulus: 453 vs 36 MPa). As a result, the Li/LFP full cell with SCOF‐PEP‐PEA QSPE shows great rate performance of 141 mAh g −1 at 1C and delivers a high specific capacity retention of 92% after 220 cycles at 0.5 C (60 °C). This work provides a new strategy to design and prepare high‐performance QSPEs with COFs as porous organic filler, and further expand the application of COFs for energy storage applications.