Fluoride Ion Conductivity of Rb Doped KSbF4

Abstract

All solid-state fluoride ion batteries are considered to be high energy density and safe energy storages. However, the F– ion conductivities of solid electrolytes at room temperature are significantly low (<10−6 S cm−1), which requires the higher operating temperature of fluoride ion battery such as 420 K or higher. Therefore, the faster F– ion conductors is strongly desired to operate fluoride ion battery at lower or even room temperature. KSbF4 is one of the promising candidates to have a faster F– ion conductivity. To expand F– ion conduction pathways, we doped Rb in KSbF4 and further investigated the compositional dependence of ionic conductivity in K1−x Rb x SbF4 system. We found that ionic conductivity strongly depends on the chemical composition and conductivity was maximized at x = 0.15. At room temperature, the F– ion conductivity in the bulk and at the grain boundary of K0.85Rb0.15SbF4 were σ bulk = 1.01 × 10−4 S cm−1 and σ GB = 4.80 × 10−5 S cm−1, respectively.