Synergistic Mn‐Cr Co‐doping in Na 3 V 2 (PO 4 ) 2 O 2 F Promising Cathode: Unlocking Superior Performance for Next‐Generation Sodium‐Ion Batteries

Abstract Sodium vanadium fluorophosphate (Na 3 V 2 O 2 (PO 4 ) 2 F, NVOPF), with a NASICON framework, is a promising cathode material due to its robust 3D structure, high operating potential (∼3.8 V), and theoretical energy density (≈494 Wh kg −1 ). However, its commercial viability is limited by low electronic conductivity and a reduced practical energy density. To address these limitations, vanadium in NVOPF is partially substituted with cost‐effective Mn and Cr via a one‐pot solvothermal method. This co‐doping induces lattice distortion, enhances Na⁺ diffusion kinetics, and improves ionic/electronic conductivity, as confirmed by DFT calculations. The optimized Na 3 V 1.9 Mn 0.095 Cr 0.005 O 2 (PO 4 ) 2 F (NVMC‐95) cathode delivers an initial discharge capacity of 120 mAh g −1 at 0.1 C and 87 mAh g −1 at 20 C, with 94% capacity retention after 500 cycles at 1 C and 76% after 2000 cycles at 5 C. The co‐doped NVOPF exhibits excellent thermal stability at 40 °C, retaining 91% of its capacity over 400 cycles at 2 C. In a full‐cell configuration (NVMC‐95//hard carbon), the system delivers 110 mAh g⁻¹ at 3.75 V, retaining 97% capacity over 100 cycles at 0.2 C. Mn/Cr co‐doping synergy in Na 3 V 2 O 2 (PO 4 ) 2 F enhances Na⁺ transport, reduces impedance, accelerates diffusion kinetics, and stabilizes cycling, enabling durable NASICON‐type cathodes with extended cycle life for practical applications.