Li_3–2xNb_xCr_2–x(PO₄)₃ Complex Phosphates with the NASICON Structure: Synthesis and Ionic Conductivity

One of the main trends in the development of metal-ion batteries concerns the transition to lithium anodes, the safe use of which is impossible without replacing liquid membranes with solid ones, primarily inorganic membranes. Lithium–niobium–chromium phosphates with calculated compositions Li_3–2xNb_xCr_2–x(PO₄)₃ (х = 0.95, 1.00, 1.05) were obtained by solid-state synthesis and characterized by XRD analysis and impedance spectroscopy. The obtained complex lithium-niobium-chromium phosphates with the NASICON structure crystallize in hexagonal modification. The unit cell parameters of crystal lattice of the synthesized materials decrease with increasing chromium content. The highest ionic conductivity and the lowest activation energy are exhibited by the material of composition Li_1.1Nb_0.95Cr_1.05(PO₄)₃ (3 × 10^–5 S/cm at 25°С), which indicates a greater mobility of lithium ions by the interstitial mechanism even in the region of its own disorderliness.