Mechanistic Insights into Interactions of Polysulfides at VS2 Interfaces in Na-S Batteries: A DFT Study

Rahul Jayan; Md Mahbubul Islam

doi:10.1021/acsami.1c10868

Mechanistic Insights into Interactions of Polysulfides at VS₂ Interfaces in Na-S Batteries: A DFT Study

ACS Appl Mater Interfaces. 2021 Aug 4;13(30):35848-35855. doi: 10.1021/acsami.1c10868. Epub 2021 Jul 20.

Authors

Rahul Jayan¹, Md Mahbubul Islam¹

Affiliation

¹ Department of Mechanical Engineering, Wayne State University, Detroit, Michigan 48202, United States.

PMID: 34284574
DOI: 10.1021/acsami.1c10868

Abstract

Room temperature sodium-sulfur (Na-S) batteries, because of their high theoretical energy density and low cost, are considered as a promising candidate for next-generation energy storage devices. However, the practical utilization of the Na-S batteries is greatly hindered by various deleterious factors such as dissolution of sodium polysulfides (Na₂S_n) into the electrolyte commonly termed as "shuttle effect," sluggish decomposition of solid Na₂S, and poor electronic conductivity of sulfur. To overcome the challenges, we introduced single-layer vanadium disulfide (VS₂) as an anchoring material (AM) to immobilize higher-order polysulfides from the dissolution and also to accelerate the otherwise sluggish kinetics of insoluble short-chain polysulfides. We employ density functional theory (DFT) calculations to elucidate the Na₂S_n interactions at the VS₂ interfaces. We show that the adsorption strengths of various Na₂S_n species on the VS₂ basal plane are adequate (1.21-4.3 eV) to suppress the shuttle effect, and the structure of Na₂S_n are maintained without any decomposition, which is necessary to mitigate capacity fading. The calculated projected density of states (PDOS) reveals that the metallic character of the pristine VS₂ is retained even after Na₂S_n adsorption. The calculated Gibbs free energy of each elementary sulfur reduction reaction indicates a significant decrement in the free energy barrier due to the catalytic activity of the VS₂ surface. Furthermore, VS₂ is found to be an excellent catalyst to significantly reduce the oxidative decomposition barrier of Na₂S, which facilitates accelerated electrode kinetics and higher utilization of sulfur. Overall, VS₂ with strong adsorption behavior, enhanced electronic conductivity, and improved oxidative decomposition kinetics of polysulfides can be considered as an effective AM to prevent the shuttle effect and to improve the performance of Na-S batteries.

Keywords: density functional theory; electrocatalysis; shuttle effect; sodium−sulfur batteries; vanadium disulfide.