First-Principles Investigation on Multi-Sodium Sulfide and Sodium Sulfide Clusters in Sodium-Sulfide Batteries

Abstract

Room temperature sodium-sulfur batteries are expected to be widely used in large energy storage and power batteries due to their high energy density, abundant resources, and low price. However, shuttle effect of polysulfide, low reactivity of the end product, low activity of sodium sulfide, and electrode swelling are the main challenges. In order to improve the low sodium sulfide reaction performance and electrode swelling, the volume swelling of the final product sodium sulfide can be well controlled by using sodium sulfide directly as the cathode, and a special cathode structure was developed to overcome the “inert” problem of Na2S. Nevertheless, the structure, relative stability and electronic properties of (Na2S)n clusters are still uncertain so far, which is a necessary prerequisite for optimizing their properties and understanding their partitioning processes. In this paper, theoretical calculations of (Na2S)n clusters were performed to investigate the catalytic decomposition of sodium sulfide by mono-atomic catalysts, giving the energy distribution of sodium ions diffusing over FeN4 and FeN2. Together, these calculations confirm the high coordination design of mono-atomic Fe–N–C catalysts with high sulfur affinity and catalytic activity. Our work is an important step toward understanding (Na2S)n clusters and improving the performance of Na–S cells.