Recognition of V3+/V4+/V5+ Multielectron Reactions in Na3V(PO4)2: A Potential High Energy Density Cathode for Sodium-Ion Batteries

Na3V(PO4)2was reported recently as a novel cathode material with high theoretical energy density for Sodium-ion batteries (SIBs). However, whether V3+/V4+/V5+multielectron reactions can be realized during the charging process is still an open question. In this work, Na3V(PO4)2is 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 Na3V(PO4)2is evaluated in two different voltage windows, namely 2.5–3.8 and 2.5–4.3 V.51V solid-state NMR (ssNMR) results disclose the presence of V5+in Na2−xV(PO4)2when charging Na3V(PO4)2to 4.3 V, confirming Na3V(PO4)2is a potential high energy density cathode through realization of V3+/V4+/V5+multielectron reactions.Keywords:polyanion;energy density;multielectron reaction;solid-state NMR