Recognition of V(3+)/V(4+)/V(5+) Multielectron Reactions in Na(3)V(PO(4))(2): A Potential High Energy Density Cathode for Sodium-Ion Batteries

Na(3)V(PO(4))(2) was reported recently as a novel cathode material with high theoretical energy density for Sodium-ion batteries (SIBs). However, whether V(3+)/V(4+)/V(5+) multielectron reactions can be realized during the charging process is still an open question. In this work, Na(3)V(PO(4))(2) is synthesized by using a solid-state method. Its atomic composition and crystal structure are verified by X-ray diffraction (XRD) and neutron diffraction (ND) joint refinement. The electrochemical performance of Na(3)V(PO(4))(2) is evaluated in two different voltage windows, namely 2.5–3.8 and 2.5–4.3 V. (51)V solid-state NMR (ssNMR) results disclose the presence of V(5+) in Na(2−x)V(PO(4))(2) when charging Na(3)V(PO(4))(2) to 4.3 V, confirming Na(3)V(PO(4))(2) is a potential high energy density cathode through realization of V(3+)/V(4+)/V(5+) multielectron reactions.