First exploration of ultrafine Na7V3(P2O7)4 as a high-potential cathode material for sodium-ion battery

The development of sodium ion battery demands high-performance materials, especially the polyanion compounds with rich crystal chemistry and competent electrochemical properties. Herein, for the first time, we report the sodium vanadium pyrophosphate of Na7V3(P2O7)(4) as a new high-potential cathode material for sodium ion battery. A facile synthetic strategy assisted by the molten-salt mechanism is developed to prepare high-pure single-phase Na7V3(P2O7)(4). The prepared material has ultrafine nano particles and surface carbon decoration, which facilitates its fast electron/ion transport and results in superior kinetics. The quasi-2D framework with well-defined ion-conducting planes enables it to have good electrochemical activities, which delivers a high average potential of 4.0 V on the basis of one electron reaction. The high efficiency in sodium-intercalation capability is demonstrated by the superior high-rate capability and long-term cycling property. As a new electroactive sodium vanadium pyrophosphate for sodium ion battery, the high operating voltage and superior high-rate capability of Na7V3(P2O7)(4) are among the best of state-of-art polyanion-based sodium hosts. Therefore, the discovery of Na7V3(P2O7)(4) opens a new opportunity for the development of the cathode materials for sodium ion batteries. (C) 2016 Elsevier B.V. All rights reserved.