Defect-Triggered Reversible Phase Transformation for Boosting Electrochemical Performance of Coordination Polymers

Coordination polymers (CPs) hold promise for reliable and powerful supercapacitors (SCs) to overcome the energy crisis. However, CP-SCs face the daunting challenge of maintaining high pseudocapacitance after long-term charge/discharge cycling. Generally, if introducing defects exerted a positive effect on the property, eliminating defects would show a negative effect, and vice versa. Contrary to this common sense, here we demonstrate that both implanting defects and eliminating defects can significantly boost the specific capacitance of the defect-engineered CPs (DECPs), which are about 1.23 and 1.62 times that of the pristine CP, respectively, without loss of rate capability even after 10,000 charge-discharge cycles. The aqueous (A-ASC) and solid-state asymmetric supercapacitor (SS-ASC) devices based on DECPs deliver high energy densities of 80.3 and 61.5 Wh kg^-1, superb power densities of 8471.0 and 8430.6 W kg^-1, and long cycling lifespan of up to 2000 cycles with 92.0 and 80.0% capacity retention, respectively. Moreover, the SS-ASC exhibits excellent flexibility, verified by 99.0% maintenance of its initial capacitance when it is twisted and bent at 180°. Importantly, this work has certified that stepwise increasing/decreasing the concentration of ordered defects gradually triggered reversible phase transformation of CP from nonporous to microporous by charge-discharge cycling, in situ addition of the modulator, and postsynthetic treatment. The mechanism of forming/eliminating defects and their effects on supercapacitive performances of CP-SCs have been unprecedentedly clarified. These findings offer insight into the relationship between defective structure and electrochemical behavior for developing efficient long-cycling CP-SCs.