Ultrastable and High‐Rate Sodium Storage Enabled by High‐Entropy Doping in HE‐Fe ₃ Se ₄ /Se/MXene Composites

ABSTRACT 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‐Fe 3 Se 4 /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‐Fe 3 Se 4 /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.