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, Na4VM(PO4)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 V4+/V5+. Herein, a high entropy Na4VFe0.6Mn0.2Cr0.1(CoMgAl)0.1(PO4)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.