Sodium storage properties of Fe, Ni-bimetallic doped carbon-modified NaTi2(PO4)3

Abstract: NaTi2(PO4)3 (NTP), possessing a sodium superionic conductor (NASICON) structure, is considered an attractive anode material for aqueous sodium ion batteries (ASIBs) due to its three-dimensional open framework and appropriate negative voltage window. However, the intrinsically poor electrical conductivity of NTP hampers its application in ASIBs. Herein, bimetallic doped carbon material was designed and combined with the sol-gel method to synthesize NaTi2(PO4)3-C-FeNi (NTP-C-FeNi) composite materials. This bimetallic doped carbon composite NTP material not only effectively improves conductivity, but also enlarges the contact area with the electrolyte, facilitating the rapid migration of Na+. Following the rate performance test, NTP-C-FeNi retained a reversible capacity of 116.75 mAhg-1 at a small current density of 0.1 Ag-1, representing 95.9% of the initial capacity. After 500 cycles at a high current density of 1.5 Ag-1, the cycle stability was 85.3%. The improvement in electrochemical performance may be attributed to the widening of pathways and acceleration of Na+ insertion/extraction facilitated by FeNi-C doping, while the carbon coating effectively promotes electrode charge transfer. The results indicate that the bimetallic doped carbon composite NaTi2(PO4)3 holds potential for practical applications in novel aqueous sodium ion battery systems.