Mn doped NaV 3 (PO 4 ) 3 /C anode with high-rate and long cycle-life for sodium ion batteries

Abstract Mn-doped NaV 3 (PO 4 ) 3 /C (NaV 3-3x Mn 3x (PO 4 ) 3 /C) has been synthesized by a facile sol-gel method and evaluated as a promising anode candidate for sodium-ion batteries (SIBs). An effective investigation combining in-situ XRD and ex-situ TEM is conducted to reveal the structure transformation of NaV 3-x Mn x (PO 4 ) 3 /C, confirming that Mn substitution can effectively suppresses the unfavorable phase transition and improve the highly structural reversibility. Furthermore, electrochemical measurements indicate that the Na-ion mobility and reaction kinetic of NaV 3-3x Mn 3x (PO 4 ) 3 /C electrode are significantly enhanced, resulting in enhanced electrochemical performance. Especially, the NaV 2.91 Mn 0.09 (PO 4 ) 3 /C composite displays remarkable rate capability and long cycling stability (a capacity retention of 71.2% after 5000 cycles at an ultrahigh rate of 10C). The strategy with appropriate metal ion substitution is suitable for the electrochemical enhancement of polyanion materials, which provides a new insight to optimal design for SIB anodes.