An Efficient Evaluation of F-doped Polyanion Cathode Materials with Long Cycle Life for Na-Ion Batteries Applications

Abstract A series of Na 3− x V 2 (PO 4− x F x ) 3 ( x = 0, 0.1, 0.15 and 0.3) polyanion cathode materials are synthesized via a sol-gel method. The optimal doping concentration of F in Na 3 V 2 (PO 4 ) 3 is 0.15 mol %. By neutron powder diffraction data, the chemical composition of as-synthesized material is Na 2.85 V 2 (PO 3.95 F 0.05 ) 3 . The half-cell of Na 2.85 V 2 (PO 3.95 F 0.05 ) 3 cathode exhibits a stable discharge capacity of 103 mAh g −1 and 93% of capacity retention over 250 cycles without decay at 0.1 A g −1 , which is higher than that of bare Na 3 V 2 (PO 4 ) 3 (98 mAh g −1 ). The high rate capability of Na 2.85 V 2 (PO 3.95 F 0.05 ) 3 is also dramatically enhanced via increase the conductivity of host material by F-doping. Moreover, the symmetrical Na-ion full-cell is fabricated using Na 2.85 V 2 (PO 3.95 F 0.05 ) 3 as cathode and anode materials. It is achieved that the good reversibility and superior cycling stability about 98% of capacity retention with ~100% of coulombic efficiency at 1.0 A g −1 throughout 1000 cycles. These results demonstrate that the optimal amount of Na 2.85 V 2 (PO 3.95 F 0.05 ) 3 is a distinctive potential candidate for excellent long-term cyclic stability with high rate low-cost energy storage applications.