Novel halloysite based nanoionic Na2ZnSiO4 solid electrolyte: Structural and electrical properties

Abstract

Halloysite clay was acid-treated to obtain SiO2 nanoparticles that were used as one of the starting reagents to synthesise clay-based Na2ZnSiO4 (Clay-NZS) through sol-gel method. XRD and FESEM results showed that the Clay-NZS produced a nanocrystalline structure, with grain sizes of 50–70 nm, in comparison to its synthetic counterpart (Synth-NZS) that had grain sizes of ~200 nm. BET measurements showed that Clay-NZS pellets pressed and sintered at the same condition as Synth-NZS were denser, allowing for a better grain-grain contact. Conductivity studies using EIS demonstrated superior conductivity of Clay-NZS in contrast to Synth-NZS due to the exponential reduction in grain boundary resistance, with calculated conductivity values of σClay(500)=2.95×10−5Scm−1 and σSynth(500)=3.25×10−6Scm−1 at 500 °C. Activation energy required for ionic conduction was also found to be lower in Clay-NZS, ΔEA(Clay)=0.67±0.01eV compared to ΔEA(Synth)=0.71±0.02eV, testifying that nanostructured ionic materials (nanoionics) provided easier diffusion pathway for ionic conduction in Clay-NZS.