A Medium‐Entropy NASICON Cathode for Sodium‐Ion Batteries Achieving High Energy Density Through Dual Enhancement of Voltage and Capacity

Abstract Na 3 V 2 (PO 4 ) 3 (NVP) is recognized for its promising commercialization potential as a sodium‐ion battery (SIB) cathode, due to its thermodynamic stability and open structure. However, the limited energy density remains a major obstacle to further advancement of NVP. Herein, a medium‐entropy NASICON Na 3.3 V 1.4 Al 0.3 (MgCoNiCuZn) 0.06 (PO 4 ) 3 (NVAMP‐0.3) is designed by introducing Al 3+ , Mg 2+ , Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ to regulate configurational entropy. These NVAMP‐0.3 achieve an elevated average operating voltage (3.33 V) and high capacity (138.1 mAh g −1 , based on 2.3 Na + ) through V 3+ /V 4+ /V 5+ multi‐electron reactions. By simultaneously enhancing capacity and voltage, NVAMP‐0.3 exhibits an impressive energy density of 460 Wh kg −1 . Furthermore, NVAMP‐0.3 demonstrates excellent low‐temperature tolerance with a capacity retention rate of 94.6% after 300 cycles at −40 °C. In situ XRD unveils the underlying cause of the unique phenomenon where the solid‐solution reaction accounts for the faster electrochemical reaction kinetics of the V 4+ /V 5+ compared to the V 3+ /V 4+ redox. DFT calculations indicate that NVAMP‐0.3 possesses superior electronic conductivity and reduced Na + migration energy barriers. A pouch cell assembled with the NVAMP‐0.3 cathode and hard carbon anode exhibits highly stable cycling (89.3% after 200 cycles at 1 C). This study provides valuable insights into developing NASICON‐type cathodes with high energy densities for SIBs.