Cooperative Effect of Multiple Active Sites and Hierarchical Chemical Bonds in Metal–Organic Compounds for Improving Cathode Performance

Metal–organic cathode compounds with low solubility and more viable eco-efficient production still suffer from relatively low voltage and limited discharge capacity because their redox reactions solely rely on active organic functional groups or metal clusters. Here, a metal–organic compound Cu2(p-O2NC6H4CO2)4(EtO)2 was demonstrated to have high capacity of 243 mA h g–1 and high-voltage plateaus of 3.66, 3.15, 2.25, and 2.08 V vs Li+/Li through first-principles calculations. Electronic structure analysis reveals Cu2+ ↔ Cux+ (1 < x < 2) and Oy– (1 < y < 2) ↔ O2– in a metal–ligand moiety and N5+ ↔ Nx+ (4 < x < 5) and O2– ↔ Oz– (1 < z < 2) in −NO2 groups, achieving high voltage and capacity by operating cooperative cationic–anionic redox reactions based on multiple active sites and hierarchical chemical bonds. Furthermore, the Cu2(p-O2NC6H4CO2)4(EtO)2 is also predicted to have good electrochemical reversibility because the cationic conversion reaction is inhibited by a higher-voltage anionic reaction and hierarchical chemical bonds of [MO5]n−. The present study provides a strategy to design metal–organic cathode compounds with high performance.