Next-generation Li1.3+xAl0.3AsxTi1.7-x(PO4)3 NASICON electrolytes with outstanding ionic conductivity performance

Abstract

NASICON-type solid electrolytes feature prominently in the improved safety and energy density of solid-state lithium batteries (ASSLBs). Achieving high ionic conductivity in these electrolytes is key to optimizing their performance. In this study, we introduced a new class of NASICON-type materials by doping arsenic into the Li_1.3Al_0.3Ti_1.7(PO₄)₃ framework, creating a series of Li_1.3+xAl_0.3As_xTi_1.7-x(PO₄)₃ phases with varying arsenic content (x = 0, 0.1, 0.2, 0.3), synthesized using the standard solid-state reaction method. X-ray diffraction confirmed the successful formation of the Li_1.3+xAl_0.3As_xTi_1.7-x(PO₄)₃ phases, which was further validated by Rietveld refinement. Structural analyses through FT-IR, Raman spectroscopy, NMR, and ICP-AES studies validate the effective incorporation of arsenic into the lattice. Among the different compositions, Li_1.5As_0.2Al_0.3Ti_1.5(PO₄)₃ phase stood out due to its high relative density of 89 % and its pore-free microstructure, as observed through scanning electron microscopy results, revealing the largest grain and crystallite size. Notably, doping with arsenic resulted in a significant enhancement in ionic conductivity, increasing from 5.34 × 10⁻⁵ Ω⁻¹ cm⁻¹ for Li_1.3Al_0.3Ti_1.7(PO₄)₃ to 8.57 × 10⁻⁴ Ω⁻¹ cm⁻¹ for the Li_1.5As_0.2Al_0.3Ti_1.5(PO₄)₃ at 25 °C. With a lithium transference number of 0.99, and a conduction mechanism largely unaffected by changes in temperature or composition, demonstrating its suitability as a promising candidate for solid electrolyte applications.