Regulating Li+ Transport and Interfacial Stability with Zwitterionic COF Protective Layer Towards High-Performance Lithium Metal Batteries

Abstract The sluggish Li + migration kinetics and unstable electrode/electrolyte interface severely hinder the commercial application of high-performance lithium metal batteries (LMBs). Herein, an artificial protective layer is constructed using zwitterionic covalent organic framework (Z-COF) simultaneously containing sulfonate and ethidium groups, aiming to facilitate rapid, uniform Li + transport and stabilize anode interface. The sulfonate groups with high lithiophilicity provide abundant hopping sites for fast Li + diffusion. The ethidium cations immobilize TFSI − and solvent molecules by ion–dipole interactions, which accelerate the dissociation of LiTFSI and Li + desolvation. Moreover, the monodispersed zwitterionic units coupling with ordered micropore structures in Z-COF create exclusive Li + migration channels, modulate homogeneous space charge distribution, kinetically facilitating uniform Li + deposition. Experiments and theoretical calculations indicate that C–F and S–N bonds of TFSI − exhibit enhanced cleavage susceptibility driven by electrostatic attraction, realizing a LiF/Li 3 N-rich electrolyte/electrode interface. The designed Z-COF protection layer enables Li|Li symmetrical cells stable cycling over 6300 h at 2 mA cm −2 /2 mAh cm −2 . The Z-COF@Li|LiFePO 4 (LFP) full cells deliver high-capacity retention of 85.2% after 1000 cycles at 8 C. The assembled Z-COF@Li|LFP pouch cells demonstrate a lifespan of more than 240 cycles. This work provides fresh insights into the practical application of zwitterionic COF in next-generation LMBs.