Unlocking Na-Storage Potential: Hierarchical NASICON Na₄MnV(PO₄)₃ Cathode with Precise V(III)/Mn(II) Integration through the Citric Acid-Derived Carbon Layer

The inherent low electronic conductivity of NASICON-type Na 4 MnV(PO 4 ) 3 (NMVP) impedes its use in advanced energy storage. Herein, we address this challenge by introducing a citric acid-derived carbon coating to elevate the material’s conductivity and electrochemical performance. By precisely tailoring the configuration of the carbon layer, we fabricated Na 4 MnV(PO 4 ) 3 encapsulated by a carbon coating (NMVP@C) and constructed a 3D hierarchical architecture with incorporated V(III) and Mn(II) states, which prompts the reversible redox reaction, augments Na + storage capability, and mitigates volume expansion during cycling. The optimal cathode manifests superior rate capability and a long life span with 107.5 mA h g –1 at 1 C and 82.5% capacity retention over 5000 cycles at 20 C. The hard carbon//NMVP@C full cell confirms practical applicability with good electrochemical performance. This work underscores the pivotal interplay among the carbon layer, Na + mobility, and structural integrity in NASICON cathodes, offering a pathway to develop high-performance and cost-effective cathode materials for sodium-ion batteries.