Fabrication of microspheres with oxygen vacancy via conformal conversion strategy for hybrid supercapacitor

The main challenge for high-performance hybrid supercapacitor (HSC) development is the design of electrode materials possessing both ideal microstructures and adjustable defect properties. In this study, CoNi layered double hydroxide with oxygen vacancy (O_V-CoNi-LDH) microspheres were successfully synthesized as cathode materials through a conformal transformation strategy. Attributed to the unique hierarchical porous framework of the material, which facilitates efficient electrolyte ion diffusion and rapid charge transfer, the electrochemical specific capacitance is significantly boosted to 1169 F g^-1 (1 A g^-1). Theoretical calculations based on density functional theory (DFT) further reveal a synergistic effect between the heterointerface and defect structure in optimizing the electronic structure. This electronic structure optimization significantly enhances the adsorption affinity of O_V-CoNi-LDH for OH^- ions and improves the reaction kinetics of the electrode process. A high energy density of 45.51 to 24.89 Wh kg^-1 was delivered by the O_V-CoNi-LDH//activated carbon (AC) HSC, with corresponding power densities between 800 and 8000 W kg^-1. By integrating the OH^- adsorption energy in DFT calculations with the density of states (DOS) analysis, this study reveals the fundamental mechanism through which oxygen vacancies enhance reaction kinetics. This enhancement occurs by reducing the OH^- adsorption energy barrier and increasing electron density near the Fermi level. These findings provide valuable theoretical guidance for the design of high-performance electrode materials for hybrid supercapacitors.