Strain Self‐Adaptive Iron Selenides Toward Stable Na+‐Ion Batteries with Impressive Initial Coulombic Efficiency

Abstract High tap density electrodes play a vital role in developing rechargeable batteries with high volumetric capacities, however, developing advanced electrodes with satisfied capacity, excellent structural stability, and achieving the resulted batteries with a high initial Coulombic efficiency (ICE) and good rate capability with long lifespan simultaneously, are still an intractable challenge. Herein, an ultrahigh ICE of 94.1% and stable cycling of carbon‐free iron selenides anode is enabled with a high tap density of 2.57 g cm −3 up to 4000 cycles at 5 A g −1 through strain‐modulating by constructing a homologous heterostructure. Systematical characterization and theoretical calculation show that the self‐adaptive homologous heterointerface alleviates the stress of the iron selenide anodes during cycling processes and subsequently improves the stability of the assembled batteries. Additionally, the well‐formed homologous heterostructure also contributes to the rapid Na + diffusion kinetic, increased charge transfer, and good reversibility of the transformation reactions, endowing the appealing rate capability of carbon‐free iron selenides. The proposed design strategy provides new insight and inspiration to aid in the ongoing quest for advanced electrode materials with high tap densities and excellent stability.