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

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/Li₃N-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|LiFePO₄ (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.