Entropy Driving “Quasi‐Zero Strain” Stepwise Multicationic Redox Chemistry Toward a High‐Performance NASICON‐Cathode for Na‐Ion Batteries

Abstract Achieving multicationic redox reactions with low lattice strain accumulation upon repeated sodiation/desodiation processes is pivotal for developing high‐energy and long‐durability Na superionic conductor (NASICON)‐type cathodes but still a formidable task. Herein, a novel NASICON‐structured high‐entropy Na 3.4 VMn 0.2 Fe 0.2 Al 0.3 Cr 0.3 (PO 4 ) 3 (HE‐NVMFACP) cathode is delicately devised, where the entropy‐driving stepwise Fe 2+ /Fe 3+ , V 3+ /V 4+ /V 5+ , Mn 2+ /Mn 3+ /Mn 4+ , and Cr 3+ /Cr 4+ redox couples not only trigger the multielectron transfer chemistry, but also alleviate the lattice strain accumulation. Consequently, the HE‐NVMFACP cathode exhibits a high reversible capacity of 151.3 mAh g −1 with an admirable energy density of 520.5 Wh kg −1 , and an impressive “quasi‐zero strain” behavior (1.33% cell volume change) during the whole charge‐discharge process. Meanwhile, an excellent rate capability of 90.4 mAh g −1 at 50 C and an ultralong cycling life of 91.9% capacity retention after 5000 cycles are demonstrated. Advanced in situ/ex situ techniques reveal the complete solid‐solution behavior and highly reversible stepwise multicationic redox mechanism of HE‐NVMFACP upon Na + uptake/release, and the rapid electrode process kinetics of HE‐NVMFACP are confirmed by systematic electrochemical measurements and theoretical computations. Furthermore, the HE‐NVMFACP||hard carbon Na‐ion full batteries are assembled in both coin and pouch configurations, manifesting bright application prospects. The present high‐entropy strategy provides invaluable perspectives for designing high‐energy and long‐life NASICON‐cathodes for sodium‐ion batteries.