Defect-Triggered\nReversible Phase Transformation for\nBoosting Electrochemical Performance of Coordination Polymers

Coordination polymers (CPs) hold promise for reliable\nand powerful\nsupercapacitors (SCs) to overcome the energy crisis. However, CP-SCs\nface the daunting challenge of maintaining high pseudocapacitance\nafter long-term charge/discharge cycling. Generally, if introducing\ndefects exerted a positive effect on the property, eliminating defects\nwould show a negative effect, and vice versa. Contrary to this common\nsense, here we demonstrate that both implanting defects and eliminating\ndefects can significantly boost the specific capacitance of the defect-engineered\nCPs (DECPs), which are about 1.23 and 1.62 times that of the pristine\nCP, respectively, without loss of rate capability even after 10,000\ncharge–discharge cycles. The aqueous (A-ASC) and solid-state\nasymmetric supercapacitor (SS-ASC) devices based on DECPs deliver\nhigh energy densities of 80.3 and 61.5 Wh kg<sup>–1</sup>,\nsuperb power densities of 8471.0 and 8430.6 W kg<sup>–1</sup>, and long cycling lifespan of up to 2000 cycles with 92.0 and 80.0%\ncapacity retention, respectively. Moreover, the SS-ASC exhibits excellent\nflexibility, verified by 99.0% maintenance of its initial capacitance\nwhen it is twisted and bent at 180°. Importantly, this work has\ncertified that stepwise increasing/decreasing the concentration of\nordered defects gradually triggered reversible phase transformation\nof CP from nonporous to microporous by charge–discharge cycling,\nin situ addition of the modulator, and postsynthetic treatment. The\nmechanism of forming/eliminating defects and their effects on supercapacitive\nperformances of CP-SCs have been unprecedentedly clarified. These\nfindings offer insight into the relationship between defective structure\nand electrochemical behavior for developing efficient long-cycling\nCP-SCs.