Amorphous FeSnOxNanosheets with Hierarchical Vacancies for Room-Temperature Sodium-Sulfur Batteries.

Abstract

Room-temperature sodium-sulfur (RT Na-S) batteries, noted for their low material costs and high energy density, are emerging as a promising alternative to LIBs in various applications including power grids and standalone renewable energy systems. These batteries are commonly assembled with glass fiber membranes, which face significant challenges like the dissolution of polysulfides, sluggish sulfur conversion kinetics, and the dendrites growth. Here, we develop an amorphous FeSnOx nanosheet with hierarchical vacancies, including abundant oxygen vacancies (Ovs) and nano-sized perforations, that can be assembled into a multifunctional layer overlaying commercial separators for RT Na-S batteries. The Ovs offer strong adsorption and abundant catalytic sites for polysulfides, while the defect concentration is finely tuned to elucidate the polysulfides conversion mechanisms. The nano-sized perforations aid in regulating Na ions transport, resulting in uniform Na deposition. Moreover, the strategic addition of trace amounts of Ti3C2 forms an amorphous/crystalline interface that significantly improves the mechanical properties of the separator and suppresses dendrite growth. As a result, the task-specific layer achieves ultra-light (~0.1mg cm-2), ultra-thin (~200nm), and ultra-robust (modulus = 4.9GPa) characteristics. Consequently, the RT Na-S battery maintained a high capacity of 610.3mAh g-1 and an average Coulombic efficiency of 99.9% after 400 cycles at 0.5C.