Electrochemically active binary anion compounds with tailored oxygen vacancy for energy storage system

The search for new materials that exhibit rapid Faradaic energy-storing behavior continues to be ever more important as they offer a promising alternative to battery technology because of their unrivalled ability to deliver large amounts of power along with large amounts of energy. Here, we present a reduced binary anion compound (r-BAC) as a first demonstration of redox-active materials, which are fabricated by a facile and direct activation synthetic method. The r-BAC exhibits excellent energy storage characteristics compared to non-reduced full binary anion compound (f-BAC). Based on the density functional theory (DFT) calculations and the ex-situ chemical study, it is found that the superior electrochemical performance is strongly attributed to not only the Ni cation sites (Ni²⁺/Ni³⁺ redox couple) that are energetically more activated by oxygen vacancies, but also to the additive electrochemical activity at the unsaturated sulfur sites (S⁴⁺/S⁶⁺ redox couple) in a binary anion. Thus, we expect that this study on the binary anion material and the corresponding anion-based charge transfer mechanisms may provide a new strategy for the efficient storage of charge in next-generation energy storage applications.