High-Entropy NASICON Phosphates (Na3M2(PO4)3 and NaMPO4Ox, M = Ti, V, Mn, Cr, and Zr) for Sodium Electrochemistry

High-entropy materials, with complex compositions and unique cocktail characteristics, have recently drawn significant attention. Additionally, a family of sodium super ion conductors (NASICONs)-structured phosphates in energy storage areas shows a comprehensive application for traditional alkaline ion batteries and, in particular, solid-state electrolytes. However, there is no precedent in fabricating this kind of NASICON-type high-entropy phase. Here, we report the successful fabrication of two well-crystallized high-entropy phosphates, namely, Na₃(Ti_0.2V_0.2Mn_0.2Cr_0.2Zr_0.2)₂(PO₄)₃ (HE-N₃M₂P₃) and Na(Ti_0.2V_0.2Mn_0.2Cr_0.2Zr_0.2)₂PO₄O_x (HE-NMP). The prepared materials in which the transition metals (TMs) of Ti, V, Mn, Cr, and Zr occupy the same 12c Wykoff position can form a structure analogous to R3̅c Na₃V₂(PO₄)₃ that is carefully determined by X-ray diffraction, neutron diffraction, and transmission electron microscopy. Further, their performance for sodium ion batteries and sodium-based solid-state electrolytes was evaluated. The HE-N₃M₂P₃ might exhibit a promising electrochemical performance for sodium storage in terms of its structure resembling that of Na₃V₂(PO₄)₃. Meanwhile, the HE-NMP shows considerable electrochemical activity with numerous broad redox ranges during extraction and insertion of Na⁺, related to the coexistence of several TM elements. The evaluated temperature-dependent ionic conductivity for HE-NMP solid electrolyte varies from 10^-6 to 10^-5 S cm^-1 from room temperature to 398.15 K, offering high potential for energy storage applications as a new high-entropy system.