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 Mg 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. 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 LiFePO/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.