Rocksalt high entropy oxide–enabled enhancement of redox kinetics in room-temperature sodium–sulfur batteries

Abstract

As a next-generation energy storage technology, room temperature sodium sulfur (RT-NaS) batteries offer higher energy density, lower cost and raw material abundance compared to lithium-ion batteries. However, major challenges impeding practical applications are polysulfide shuttling and sluggish redox kinetics. High entropy oxides exhibit a complex atomic distribution with multiple cations in a sublattice. This unique structural arrangement contributes to improved chemical stability and multiple active sites, which facilitate the effective trapping of sodium polysulfides (Na-PS). Herein, we study a rocksalt high entropy oxide, (Co,Cu,Mg,Ni,Zn)O (R-HEO) as a functional interlayer in a RT-NaS battery. The R-HEO interlayer facilitates adsorption of Na-PS and electrocatalytically promotes polysulfide conversion. Consequently, the cell featuring R-HEO interlayer demonstrates an initial reversible specific capacity of 998 mAh g −1 at 0.1 C, with a remarkable capacity retention of 93.2% after 200 cycles at 0.2 C. XPS, FTIR spectroscopy and density functional theory (DFT) calculations are used to study the nature of interactions between R-HEO and Na-PS. The enhanced electrochemical performance can be ascribed to the efficient confinement of Na-PS and the formation of polythionate complexes. These factors contribute to strong binding with soluble species and facilitate accelerated reaction kinetics, leading to superior electrochemical properties.