Ultrastable and High-Rate Sodium Storage Enabled by High-Entropy Doping in HE-Fe₃Se₄/Se/MXene Composites

The development of high-performance sodium-selenium (Na-Se) batteries is hindered by the shuttle effect of polyselenides and sluggish reaction kinetics. To address these challenges, we engineered a high-performance composite cathode by confining selenium within a catalytic host of high-entropy iron selenide and MXene (HE-Fe₃Se₄/Se/MX). This material was synthesized through the in situ growth of a high-entropy Prussian blue analogue on MXene followed by selenization. The resulting architecture exhibits a powerful synergy: the high-entropy doping enhances intrinsic conductivity and creates active sites that boost reaction kinetics and immobilize polyselenides via chemical adsorption, while the MXene matrix provides a conductive scaffold and mitigates volume strain. When evaluated in Na-Se batteries, the HE-Fe₃Se₄/Se/MX composite demonstrates exceptional rate capability, delivering a high specific capacity of 512 mAh g^{- 1} at 0.1 A g^{- 1} and retaining 330 mAh g^{- 1} at 30 A g^{- 1}. This corresponds to a 64.4% capacity retention despite a 300-fold current increase. Furthermore, it exhibits remarkable long-term stability, maintaining 337 mAh g^{- 1} after 1000 cycles at 10 A g^{- 1} with an ultralow decay rate of 0.0106% per cycle. This work demonstrates that the rational integration of high-entropy engineering with conductive scaffolding is a highly promising strategy for constructing durable, high-rate cathodes for advanced energy storage systems.