High-Entropy Strategy Enables Low Volume Strain and High Energy Density through Suppressing the Phase Separation in NASICON Cathodes

NASICON-type Na 3 V 2 (PO 4 ) 3 material features an open three-dimensional framework structure, which has garnered extensive attention due to its high ionic conductivity and structural stability. However, poor electronic conductivity, harmful phase transitions, and inadequate rate performance hinder their practical applications. Herein, a high-entropy Na 3.185 V 1.725 Mn 0.055 Co 0.05 Cu 0.045 Cr 0.045 Al 0.045 Ni 0.035 (PO 4 ) 3 (HE-NVTMP) cathode is elaborately crafted by multielement doping strategy. The cathode renders a high initial specific capacity of 197.7 mAh g –1 and a large energy density of 552 Wh kg –1 at 0.2 C. Additionally, the cathode maintains stable long-term cycling durability and minimal capacity fade under high 10 C-rate conditions (1100 cycles with 80.95% capacity retention). The synergistic high-entropy doping activates the V 4+ /V 5+ redox couple, enhancing Na + diffusion kinetics and achieving high reversibility. In situ XRD analysis reveals that the high-entropy effect optimizes the crystal structure and achieves a low volumetric strain (3.4%) by suppressing the two-phase reaction (Na 3 V 2 (PO 4 ) 3 → Na 3-x V 2 (PO 4 ) 3 → NaV 2 (PO 4 ) 3 ). The multielement synergy promotes the occurrence of single-phase reaction and inhibits phase separation. The full cell of HE-NVTMP//hard carbon delivers a high initial capacity of 107.7 mAh g –1 at 0.5 C and an excellent rate performance (79.1 mAh g –1 at 15 C).