High-Entropy Spinel Oxide Nanofibers as Catalytic Sulfur Hosts Promise the High Gravimetric and Volumetric Capacities for Lithium–Sulfur Batteries

Abstract

The exploration of new catalytic hosts is highly important to tackle the sluggish electrochemical kinetics of sulfur redox for achieving high energy density of lithium–sulfur batteries. Herein, for the first time, we present high-entropy oxide (HEO, (Mg0.2Mn0.2Ni0.2Co0.2Zn0.2)Fe2O4) nanofibers as catalytic host of sulfur. The HEO nanofibers show a synergistic effect among multiple metal cations in spinel structure that enables strong chemical confinement of soluble polysulfides and fast kinetics for polysulfide conversion. Consequently, the S/HEO composite displays the high gravimetric capacity of 1368.7 mAh g−1 at 0.1 C rate, excellent rate capability with the discharge capacity of 632.1 mAh g−1 at 5 C rate, and desirable cycle stability. Furthermore, the S/HEO composite shows desirable sulfur utilization and good cycle stability under a harsh operating condition of high sulfur loading (4.6 mg cm−2) or low electrolyte/sulfur ratio (5 μL mg−1). More impressively, the high volumetric capacity of 2627.9 mAh cm−3 is achieved simultaneously for the S/HEO composite due to the high tap density of 1.92 g cm−3, nearly 2.5 times of the conventional sulfur/carbon composite. Therefore, based on high-entropy oxide materials, this work affords a fresh concept of elevating the gravimetric/volumetric capacities of sulfur cathodes for lithium–sulfur batteries.