Regulating the Crystallinity of the Bimetallic Metal–Organic Frameworks for Supercapacitors with High Energy Density

Supercapacitors often face the challenge of narrow charging voltage windows, which lead to limited energy density and limit their practical applications. Using neutral aqueous electrolytes is an efficient approach to expand the voltage window, but this kind of electrolyte is detrimental to the specific capacity of electrode materials. In this study, we propose a crystallinity-control engineering (termed CCE) strategy to overcome the challenge. The bimetallic MOF was chosen as the electrode material for its high capacity. By using the CCE method proposed in this work, the modified MOF with low crystallinity was prepared, which delivered fast charge transfer capability, abundant oxidatively active sites, and excellent hydrophilicity. The modified material demonstrates exceptional electrochemical performance, exhibiting a stable 0.78 V voltage window in 1 M Na2SO4 aqueous electrolyte. The material achieves an excellent specific capacitance of 835.5 F g–1 at 1 A g–1, surpassing the capacity of the pristine MOF by almost 400%. Furthermore, in asymmetric supercapacitor applications, this material enables outstanding energy storage characteristics, delivering a 103.1 W h·kg–1 energy density at an 859.1 W·kg–1 power density. When subjected to extended cycling tests (10,000 cycles at 10 mA·cm– 2), the material maintained 93.9% of its initial charge storage capacity, performing long cycle stability.