Ultrafine Nb₂O₅ Nanocrystal Coating on Reduced Graphene Oxide as Anode Material for High Performance Sodium Ion Battery

Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb₂O₅ NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb₂O₅ NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb₂O₅ NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb₂O₅ NCs existed. The architecture of ultrafine Nb₂O₅ NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. Ex situ XPS analysis revealed that the sodium ion storage mechanism in Nb₂O₅ could be accompanied by Nb⁵⁺/Nb⁴⁺ redox reaction and the ultrafine Nb₂O₅ NCs provide more surface area to accomplish the redox reaction.