Enabling high-performance and high-rate-capability Na4MnV(PO4)3 sodium-ion battery cathodes through tuning the NASICON framework

Abstract

Na₄MnV(PO₄)₃ (NMVP) has emerged as a cost-effective alternative to Na₃V₂(PO₄)₃, which is considered a promising cathode material for sodium-ion batteries. However, challenges such as low electronic conductivity, fast capacity fading resulting from the dissolution of Mn and polarization due to irreversible structural transformation impede the widespread application of NMVP. In this study, a facile sol–gel method is employed to dope NMVP with Mo, aiming to address these limitations. Synchrotron extended X-ray absorption fine structure data, neutron powder diffraction results, and density functional theory (DFT) calculations indicate a preferential occupation of the P site by Mo. Mo-doped NMVP demonstrates an outstanding discharge capacity of 97.5 mA h g⁻¹ at 0.2C and 46.4 mA h g⁻¹ at 20C, along with impressive long-term stability, retaining 78.8% capacity after 300 cycles at 1C. DFT calculations reveal a significant reduction in the band gap of Mo-doped NMVP, enhancing electronic conductivity and thereby improving rate capability retention. In operando X-ray absorption spectroscopy reveals changes in the valence of V, Mn, and Mo in the material during charge/discharge, confirming the complete reversibility of redox reactions. The outstanding performance of the novel Mo-doped NMVP cathode highlights its promising potential for application in large-scale energy storage systems.