Novel electrochemical ion-exchange of LixNa3-xZr2Si2PO12 (LNZSP): a Li-ion conducting solid electrolyte for battery applications

Abstract

As the demand for high-performance and safer batteries continues to grow, solid electrolytes are emerging as essential alternatives to conventional liquid electrolytes, which are prone to leakage, flammability, and thermal runaway. Among various candidates, NASICON-type materials have garnered significant attention because of their high ionic conductivity, low cost, and high chemical stability under ambient conditions. However, Li+ conducting NASICON-type solid electrolytes are limited by interfacial instability, primarily owing to reduction reactions at the interface. To address this issue, researchers have attempted to replace Ti with the more stable Zr-based frameworks. However, the direct synthesis of Li-based Zr-NASICON structures via traditional solid-state methods remains challenging and often results in poor phase purity or low ionic conductivity. In this study, we propose a novel "electrochemical ion-exchange" process to convert Na+ conducting NZSP (Na3Zr2Si2PO12) into Li+ conducting LNZSP (LixNa3-xZr2Si2PO12) at room temperature. Electrochemical and elemental analyses confirm the successful incorporation of Li+, and the resulting material exhibited enhanced ionic conductivity (approximate to 1.8 x 10-4 S cm-1 at room temperature) among oxide electrolytes that are stable in air and moisture. This straightforward electrochemical approach not only improves ionic transport in NASICON-type electrolytes, but also offers a scalable and energy-efficient pathway for next-generation solid-state electrolyte technologies.