High-Entropy NASICON Phosphates (Na 3 M 2 (PO 4 ) 3 and NaMPO 4 O x , 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, Na 3 (Ti 0.2 V 0.2 Mn 0.2 Cr 0.2 Zr 0.2 ) 2 (PO 4 ) 3 (HE-N 3 M 2 P 3 ) and Na(Ti 0.2 V 0.2 Mn 0.2 Cr 0.2 Zr 0.2 ) 2 PO 4 O 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 R 3̅ c Na 3 V 2 (PO 4 ) 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-N 3 M 2 P 3 might exhibit a promising electrochemical performance for sodium storage in terms of its structure resembling that of Na 3 V 2 (PO 4 ) 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.