Sulfur-anchored oxygen vacancies boost ion storage in supercapacitor electrodes

Nickel-cobalt oxide exhibits synergistic redox activity and high theoretical specific capacity, but it also faces challenges such as low conductivity and low energy density. This study proposes a new strategy to introduce oxygen vacancies into nickel-cobalt oxide (NCO) doped with non-metallic ions (S2−) to construct a modified electrode with dual anion active sites. The size disparity between S2− and O2− anions effectively tunes the electronic and chemical environment of the material, facilitating accelerated ion diffusion kinetics and improved charge storage performance. The electrochemical performance of sulfur-anchored NiCo2O4 (S2−/NCO) is significantly enhanced, achieving an impressive specific capacity of 1468.0 C g−1 and a capacitance retention rate of 85 % after 10,000 cycles. Meanwhile, hybrid supercapacitors made from S2−/NCO have an energy density of 104.3 Wh kg−1 and an impressive power density of 853 W kg−1. Density-functional theory (DFT) simulations confirm the presence of oxygen vacancies creates an in-built electric field and facilitates charge distribution, whereas the S2− doping leads to the emergence of an impurity energy level in the forbidden band that is below the Fermi energy level, which efficiently modulates the energy band structure. The proposed anion anchoring vacancy strategy provides new ideas for the efficient storage and conversion of renewable energy.