Vanadium substituted Li+-NASICON systems: Tailoring electronic conductivity for electrode applications

Abstract

Mixed ionic-electronic NASICON structured systems namely, LiTi2(PO4)3-x(VO4)x and Li1.3Al0.3Ti1.7(PO4)3-x(VO4)x, for x = 0.1–0.4 have been prepared by partial substitution of V5+ in place of P5+ in LiTi2(PO4)3 (LTP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), respectively. A systematic investigation has been carried out to understand the mechanism of mixed electrical transport by varying the amount of Vanadium in subsequent steps. The structural features of these systems have been studied using XRD and FESEM that suggest Vanadium acceptability in the NASICON type network structure atleast up to x = 0.4 without any notable precipitation. High temperature in situ XRD studies suggest stability of the structure at least up to ∼500 °C. The electronic conductivity in these composites have been attributed to polaron hopping that could be tailored systematically as suggested by dc conductivity studies. The highest total conductivity and electronic conductivity values have been found to be 2 × 10−4 Ω−1cm−1 and 9 × 10−5 Ω−1cm−1, respectively for LTP with x = 0.4 at 100 °C. In order to test their potential as electrodes, symmetric cells of the type MIE|LiPF6/Li2SO4|MIE have been fabricated and charged/discharged at different current densities. These materials exhibit appreciable capacity and have been found to be suitable for EDLC/pseudo supercapacitor electrode applications.