The nitrogen-doped carbon coated Na₄MnV(PO₄)₃ as a high electrochemical performance cathode material for sodium-ion batteries

As a promising cathode material for sodium-ion batteries, the NASICON-structured Na₄MnV(PO₄)₃ (NMVP) possesses a high working voltage with two discharge potential plateaus located at ∼3.4 V and 3.6 V from the V⁴⁺/V³⁺ and Mn³⁺/Mn²⁺ redox couples, respectively. However, the rate capability and cycling stability of NMVP is unsatisfactory because of the low electronic conductivity and dissolution of manganese. In this work, a series of NMVP@C-xN (x = 10, 20 and 30) was synthesized using a sol-gel method with the generation of a nitrogen-doped carbon on the surface of NMVP particles to reveal the effect of heteroatom-doped carbon coating on improving the electrochemical performance of the cathode material. Among the prepared samples, NMVP@C–20N exhibited a high initial reversible capacity of 103.8 mAh g⁻¹ at 0.1 C and an excellent cycling stability with a capacity retention of 86.1 % after 2000 cycles at 5 C. The excellent performance of the cathode material should be ascribed to the generation of defects and active sites of the nitrogen-doped carbon coating, leading to increased electronic conductivity and diffusion rate of sodium ions.