Fast Ion‐Transport and Stable Interface Enabled by a Phthalocyanine Covalent Organic Framework Protective Layer for High‐Performance Magnesium Metal Anode

ABSTRACT Copper tetraaminophthalocyanine (CuPc) with magnesiophilic sites can serve as an interfacial layer to adsorb Mg 2+ and benefit for compatibility between the Mg anode and electrolytes in rechargeable magnesium batteries (RMBs). However, the disordered stacking of phthalocyanine molecules and the absence of efficient Mg 2+ transport pathways within interfacial layer limit the cycling performance of RMBs. Here, we propose a phthalocyanine‐based covalent organic framework (COF) with magnesiophilic sites and an ordered porous network, which can enhance the interfacial durability and guarantee the rapid Mg 2+ transport. When employed as a protective interfacial layer, the COF‐coated Mg anode (COF@Mg) enables the symmetric cell to display stable cycling for 1600 h at 1.0 mA cm −2 in Mg[B(hfip) 4 ] 2 electrolyte (bare Mg and CuPc‐modified Mg suffer from short circuit at 300, 670 h). After cycling, less decomposition byproducts of electrolytes and integral structure of COF are confirmed by time‐of‐flight secondary ion mass spectrometry and X‐ray absorption fine structure, demonstrating the stability of the COF protective layer. Moreover, the COF@Mg||S full cell achieves an energy density of 468.3 Wh kg −1 after 150 cycles. This work offers a new insight into the design of stable protective layers strategy for high‐performance RMBs.