Scandium-Substituted Na₃Zr₂(SiO₄)₂(PO₄) Prepared by a Solution-Assisted Solid-State Reaction Method as Sodium-Ion Conductors

Abstract

As possible electrolyte materials for all-solid-state Na-ion batteries (NIBs), scandium-substituted Na 3 Zr 2 (SiO 4 ) 2 (PO 4 ) in the structure of NASICONs (Na superionic conductors) has received hardly any attention so far, although among all the trivalent cations, Sc 3+ might be the most suitable substitution ion for Na 3 Zr 2 (SiO 4 ) 2 (PO 4 ) because the ionic radius of Sc 3+ (74.5 pm) is the closest to that of Zr 4+ (72.0 pm). In this study, a solution-assisted solid-state reaction (SASSR) method is described, and a series of scandium-substituted Na 3 Zr 2 (SiO 4 ) 2 (PO 4 ) with the formula of Na 3+ x Sc x Zr 2- x (SiO 4 ) 2 (PO 4 ) (NSZSP x, 0 ≤ x ≤ 0.6) have been prepared. This synthesis route can be applied for powder preparation on a large scale and at low cost. With increasing degrees of scandium substitution, the total conductivity of the samples also increases. An optimum total Na-ion conductivity of 4.0 × 10 –3 S cm –1 at 25 °C is achieved by Na 3.4 Sc 0.4 Zr 1.6 (SiO 4 ) 2 (PO 4 ) (NSZSP0.4), which is the best value of all reported polycrystalline Na-ion conductors. The possible reasons for such high conductivity are discussed.