Size controlling and surface engineering enable NaTi2(PO4)3/C outstanding sodium storage properties

NaTi2(PO4)3 with open and stable frameworks shows great potential for sodium ion batteries (SIBs), while it is suffering from the intrinsic low electronic conductivity, causing poor active material utilization and inferior rate capability. Herein, a facile solvothermal reaction with size controlling and in-situ carbon coating process is developed to synthesize NaTi2(PO4)3/C nanocomposites, in which the well-dispersed NaTi2(PO4)3 nanoparticles with size of 20-40 nm are well coated by carbon shell with uniform thickness of ∼4 nm. The uniform carbon coating layer and small nanoparticles enable the high utilization ratio of carbon and active material, thus nanostructured NaTi2(PO4)3/C with 3.82% carbon content can deliver outstanding sodium ion storage properties in multiple occasions including organic/aqueous electrolyte and half/full cell. In organic electrolyte system, the electrode presents remarkable rate capability with reversible capacity of 92 and 66 mAh g−1 at 20 C and 50C (1C = 150 mA g−1), respectively. Moreover, a NaTi2(PO4)3/C//Na3V2(PO4)2F3 sodium ion full cell with excellent rate capability up to 20C and cycling stability is also demonstrated. In aqueous electrolyte, after the optimization of current collector and electrolyte, the aqueous NaTi2(PO4)3/C//sodium Prussian blue (PB) full cell also demonstrates excellent cycling life up to 500 times with a capacity retention of 86.5% at 1C.