Abstract
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 K1-3x La x square 2x NbO3 (with 0 <= x <= 0.15; square 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 square 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 Ag-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.