A-Site Vacancy Engineering in KNbO₃ Perovskite for Enhanced Lithium Storage

Design of tailored materials using innovative approaches that allow faster charging/discharging processes could be the key for improvement of electric mobility. In this work, a strategy is developed to modify KNbO3 perovskite structure by partially substituting K+ with La3+ at the A-site of the structure, creating two cation vacancies per substitution in the lattice. Materials with the general formula K1–3xLax□2xNbO3 (with 0 ≤ x ≤ 0.15; □ is an A-site vacancy) have been synthesized by the sol–gel method. With La substitution and creation of artificial vacancies in the structure, KNbO3 became activated for Li+ insertion. The highly substituted K0.55La0.15□0.30NbO3 (30% atomic A-site vacancies) exhibited 164 mAh g–1 at 0.02 A g–1 in the 0.05–3.0 V vs Li+/Li potential window. Ex situ 7Li and 93Nb MAS NMR confirmed an increased Li+ insertion in relation to vacancies and corresponding changes in Nb5+ local environment, respectively. In situ X-ray diffraction (XRD) analysis revealed a solid-solution-type storage mechanism with a maximum volume change of only 1.3% upon Li+ insertion for highly substituted material. This accounts for the remarkable capacity retention obtained after 900 cycles at 0.1 A·g–1. Diverged from the classical design of insertion materials, this study presents an alternative approach of creating vacancies without sacrificing the pristine phase, with a possibility to use the not so common class of ABO3-type perovskites as the battery electrode.