Anode-Protective Covalent Organic Framework Layer with Synergistic Cation–Anion Regulation for Dendrite-Free Lithium Metal Batteries

Lithium (Li) dendrite formation in Li metal batteries intrinsically challenges Coulombic efficiency (CE) and safety. While constructing an anode protective layer offers a potential solution for dendrite suppression, existing approaches are limited by insufficient molecular-level control over both Li+ and anion dynamics simultaneously. Herein, we construct a binary cooperative magnesium porphyrin-based covalent organic framework (Mg-Por-COF) protective layer designed for synergetic cation-anion regulation at the anode-electrolyte interface. This design spatially separates lithiophilic and anionophilic sites within the pore walls and framework. Specifically, Mg-Por-COF promotes Li+ desolvation through strong interactions and immobilizes TFSI- anions via Mg2+ coordination. This dual action prevents space charge accumulation caused by local anion depletion, enabling smooth and compact Li deposition, even under a demanding areal current of 10 mA cm-2. Consequently, the Li/Mg-Por-COF-Cu cell achieves an extended cycle life of 400 cycles with a high average CE of 98.3%, outperforming the bare Cu counterpart by ∼400%. Furthermore, the LiFePO4/Mg-Por-COF-Li full cell demonstrates remarkable cycling stability with an average CE of 99.1% over 324 cycles. Simulations corroborate the dual role of Mg-Por-COF in modulating Li+ transport and immobilizing TFSI- anions, providing unique atomic control for Li uniform deposition. These findings highlight the potential of structurally designed COFs as superior protective layers for high-performance energy storage, offering high chemical designability and sustainability.