High‐Performance Alluaudite‐Type Na2.54(Fe0.97Mg0.03)1.73(SO4)3 Microspheres Cathode for Sodium‐Ion Batteries with an Ultrahigh Rate Capability and 9000 Cycle Life

diffusion kinetics and low ionic-migration energy barrier. This work provides an effective strategy and a fundamental understanding to enhance the electrochemical performance of cathode materials for SIBs.