Insight into Highly Reversible Multielectron V/V/V Reaction of High-Entropy Doped NASICON Cathode for Sodium Ion Batteries.

High-entropy doping has been demonstrated to be an effective method for enhancing the electrochemical performance of NASICON cathode materials, yet the underlying mechanisms remain unclear. In this study, we employ V-based sodium superionic conductor (NASICON) cathode materials as a model system to investigate the impact of various substituting elements (Al, Cr, Fe, Ga, and In) on the local structure of the material. This strategy is proven to effectively suppress V-ion migration and, as a consequence, enhance the reversibility of multielectron reactions. By combining electrochemical analysis and spectroscopic techniques (in situ XRD, STEM, and XAFS), we investigated the changes in the composition, structural evolution, and distortion of the VO octahedral before and after cycling. Under a 1 C rate, the capacity retention after 500 cycles is increased from 52.3% to 85.7%, with significant suppression of voltage hysteresis and capacity fading. This work elucidates the mechanism of improved multielectron reaction reversibility and provides guidance for the design of high-performance polyanion electrodes.