Fully Conjugated Phthalocyanine Copper Metal–Organic Frameworks for Sodium–Iodine Batteries with Long‐Time‐Cycling Durability

Abstract Rechargeable sodium–iodine (Na–I 2 ) batteries are attracting growing attention for grid‐scale energy storage due to their abundant resources, low cost, environmental friendliness, high theoretical capacity (211 mAh g −1 ), and excellent electrochemical reversibility. Nevertheless, the practical application of Na–I 2 batteries is severely hindered by their poor cycle stability owing to the serious dissolution of polyiodide in the electrolyte during charge/discharge processes. Herein, the atomic modulation of metal–bis(dihydroxy) species in a fully conjugated phthalocyanine copper metal–organic framework (MOF) for suppression of polyiodide dissolution toward long‐time cycling Na–I 2 batteries is demonstrated. The Fe 2 [(2,3,9,10,16,17,23,24‐octahydroxy phthalocyaninato)Cu] MOF composited with I 2 (Fe 2 –O 8 –PcCu/I 2 ) serves as a cathode for a Na–I 2 battery exhibiting a stable specific capacity of 150 mAh g −1 after 3200 cycles and outperforming the state‐of‐the‐art cathodes for Na–I 2 batteries. Operando spectroelectrochemical and electrochemical kinetics analyses together with density functional theory calculations reveal that the square planar iron–bis(dihydroxy) (Fe–O 4 ) species in Fe 2 –O 8 –PcCu are responsible for the binding of polyiodide to restrain its dissolution into electrolyte. Besides the monovalent Na–I 2 batteries in organic electrolytes, the Fe 2 –O 8 –PcCu/I 2 cathode also operates stably in other metal–I 2 batteries like aqueous multivalent Zn–I 2 batteries. Thus, this work offers a new strategy for designing stable cathode materials toward high‐performance metal–iodine batteries.