Na_1+xMn_x/2Zr_2–x/2(PO₄)₃ as a Li⁺ and Na⁺ Super Ion Conductor for Solid-State Batteries

Here we report dual ion conduction capability of Na-based NASICON type super ion conductor materials using Na_1+xMn_x/2Zr_2–x/2(PO₄)₃ (NMZP) as a candidate system. This method enables the use of Na-based NASICON material family in both Na as well as Li all solid-state batteries (SSBs). NZMPs with x = 1.5 and x = 2 showed the highest room-temperature conductivities of 2.86 × 10^–5 and 2.82 × 10^–5 S cm^–1, respectively. Crystallographic analysis using neutron diffraction revealed that conductivities observed in these materials are related to the variations in the Na–O bond length and the concentration of mobile sodium content. Using galvanostatic plating and stripping tests, we show that these NMZPs boast good cycling stability against both Na and Li metals, which also reveals dual ion conduction. Mechanistic investigations through post-mortem SEM/EDS and XPS characterizations of the alkali metal and the cycled NMZPs confirm that the Na–Li ion-exchange occurs readily in these materials when electrochemically cycled.