Designing a 2D Calcium Coordination Polymer Interconnected with Carbon as a High-Performance Cathode for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) as a new generation of environmentally friendly, high-security, and low-cost energy storage devices have received extensive attention from researchers. Coordination polymers (CPs) show great potential as cathode materials for AZIBs due to their tunable composition, diverse functional groups, highly ordered porous channels, and easily controllable structure. Nevertheless, the inherent limitations of CPs including poor electrical conductivity and low chemical stability severely constrain the cycling stability and rate property of AZIBs. Herein, a highly crystalline calcium-based CP (Ca-ddmb/Ca₂L(H₂O)₂) with a 2D-layered structure was directly successfully grown on nanocarbon black via a simple solvothermal method. The resulting Ca-ddmb@C composite with high electrical conductivity was designed as a cathode to construct high-performance AZIBs. Profiting from the synergistic effect of abundant active sites of Ca-ddmb and conductive nanocarbon, Ca-ddmb@C exhibited a high reversible capacity of 346.75 mAh g^–1 at 100 mA g^–1 and demonstrated a superb rate performance of 53.34 mAh g^–1 at 2000 mA g^–1. An in-depth study of the zinc storage mechanism through a series of characterization techniques revealed the redox-active sites of Ca-ddmb. This study provides new insights into the design of a desirable-performance CP-based cathode for AZIBs.