Synergistic regulation engineering of interfacial charge by N-Zn-F coordinated triazine-based COF for dendrite-free lithium metal anodes

The disorganized lithium dendrites and unstable solid electrolyte interphase (SEI) severely impede the practical application of lithium metal batteries (LMBs). Herein, the N-Zn-F coordinated triazine-based covalent organic framework (TTA-COF-ZnF2) is fabricated for the first time as an artificial SEI layer on the surface of lithium metal anodes (LMAs) to handle these issues. Zn–N coordination in one-dimensional (1D) ordered COF can increase lithiophilic sites, reduce the Li-nucleation barrier, and regulate the Li+ local coordination environment by optimizing surface charge density around the Zn metal. The electron-rich state induced by strong electron-withdrawing F-groups constructs electronegative nanochannels, which trigger efficient Li+ desolvation. These beneficial attributes boost Li+ transfer, and homogenize Li+ flux, leading to uniform Li deposition. Besides, the lithiophilic triazine ring polar groups in TTA-COF-ZnF2 further facilitate the Li+ migration. The latent working mechanism of adjusting Li deposition behaviors and stabilizing LMAs for TTA-COF-ZnF2 is illustrated by detailed in-situ/ex-situ characterizations and density functional theory (DFT) calculations. As expected, TTA-COF-ZnF2-modified Li|Cu half cells deliver a higher Coulombic efficiency (CE) of 98.4% over 250 cycles and lower nucleation overpotential (11 mV) at 1 mA cm−2, while TTA-COF-ZnF2@Li symmetric cells display a long lifespan over 3785 h at 2 mA cm−2. The TTA-COF-ZnF2@Li|S full cells exert ultrahigh capacity retention of 81% (837 mA h g−1) after 600 cycles at 1C. Besides, the TTA-COF-ZnF2@Li|LFP full cells with a high loading of 7.1 mg cm−2 exert ultrahigh capacity retention of 89% (108 mAh g−1) after 700 cycles at 5C. This synergistic strategy in N-Zn-F coordinated triazine-based COF provides a new insight to regulate the uniform plating/stripping behaviors for developing ultra-stable and dendrite-free LMBs.