Enhancement of electrical properties of NASICON-type solid electrolytes (LiSn2P3O12) via aluminium substitution

Abstract

Abstract NASICON-type electrolyte is one of the possible solid-state electrolytes to be employed in solid-state energy devices. The Li1+xAlxSn2-xP3O12 NASICON-based solid electrolyte materials were fabricated using a mechanochemical milling method at 650 °C for 8 h, where x is from 0 to 0.8. From the X-ray diffraction (XRD) analysis, the crystallographic phases of the parent material and the partial aluminium (Al) substituted one have been verified. Site occupancy factor (s.o.f) studies from the XRD data refinement illustrate that the material with x = 0.4 has a stoichiometry in good agreement with the nominal tin (Sn):aluminium (Al) ratio which is 8:2. Field emission scanning electron microscopy (FESEM) was conducted to study the surface morphological properties, revealing the homogenous single-crystalline structure in the sample with x = 0.4, which consists of particles of the smallest crystallite size of 3.77 nm among the samples investigated. The process of partial Al-substitution was further confirmed by the energy dispersive X-ray (EDX). The material with x = 0.4 possesses the maximum conductivity value of 7.57 × 10−6 S·cm−1, which was improved up to 3.79 × 10−5 S·cm−1 by a silver paint treatment. The correlation between the microstructure and the ionic conductivity has been explained via the EDX and impedance analysis results. Ions were found to be the main charge carriers from the transference number analysis (TNM). Variation of relaxation in the dielectric study verifies that Li1+xAlxSn2-xP3O12 obeys a non-Debye characteristic. Patterns of the dielectric results strengthened the trend of ionic conductivity.