Unraveling the Fast Na Diffusion Kinetics of NASICON at High Voltage via High Entropy for Sodium‐Ion Battery

Abstract Vanadium based sodium superionic conductors (NASICON) have attracted unpreceded attention owing to their high structural stability and excellent Na + ion diffusion. However, Na 4 VM(PO 4 ) 3 suffer from low‐rate capability and capacity decay at high voltage (≈4.0 V) due to low electronic conductivity and irreversible phase transition of V 4+ /V 5+ . Herein, a high entropy Na 4 VFe 0.6 Mn 0.2 Cr 0.1 (CoMgAl) 0.1 (PO 4 ) 3 (NVFP‐HE) NASICON material is designed, which allows the intrinsic effect of multi‐metal to achieve the excellent rate capability at high voltage, good ionic as well as electronic conductivity. This NVFP‐HE cathode not only delivers a high discharge capacity of 141.98 mAh g −1 at 1C, but also presents an exceptional capacity of 85.77 mAh g −1 at as high as 50C current rate. Additionally, NVFP‐HE can also retain 66.7% of initial capacity after 10 000 charge–discharge cycles at 50C. It is important to highlight that the high entropy mitigates the performance decay that arises from the irreversible phase change at 4 V. Interestingly, NVFP‐HE//HC full cell delivers 81 mAh g −1 at 0.2C. This high entropy effect and its proof of concept can allow to look for unique combinations and rationally designed advanced cathode materials for wide applications.