Effects of Scandium substitution on the electrochemical performance of Na₄MnV(PO₄)₃ cathode material for sodium-ion batteries

The sodium superionic conductor (NASICON)-type Na₄VMn(PO₄)₃ (NMVP) cathode material is regarded as a promising candidate for sodium-ion batteries due to its open and stable three-dimensional framework. However, its development is limited by low electronic conductivity and the Jahn-Teller effect of Mn3+.In this work, NASICON-structured cathode materials Na_4-xMn_1−xSc_xV(PO₄)₃ (x = 0-0.5) were synthesized via a solid-state ball milling method. XRD characterization confirms that Sc3+ has been successfully substituted into the crystal structure. EIS and GITT results show that an appropriate amount of Sc substitution effectively reduces the charge transfer resistance and enhances the Na ion migration ability. The 20%Sc-NMVP sample exhibits the optimal comprehensive performance. At a current density of 0.2C, the sample delivers an initial discharge specific capacity of 94.24 mAh·g−1, with a capacity retention rate of 89.42% after 100 cycles. At 1 C, its initial discharge specific capacity reaches 85.33 mAh·g−1. The sample exhibits the minimum charge transfer resistance of 62.92 Ω. Calculated via the GITT method, the Na ion diffusion coefficient falls within the range of 10−12∼10−11 cm2 s−1. Furthermore, in tests with an extended voltage window (2.0-4.3 V), Sc substitution effectively mitigates the structural degradation induced by irreversible V4+/V5+ redox reactions under high voltage, significantly improving the cycling stability of the NMVP cathode material. In conclusion, Sc substitution is an effective strategy to enhance the electrochemical performance of the NMVP material. It provides theoretical and experimental support for its application in high-performance sodium-ion batteries.