Sodium–sulfur (Na–S) batteries have emerged as a promising candidate for large-scale energy storage owing to the natural abundance and low cost of sodium and sulfur. However, their practical implementation remains severely hindered by intrinsic challenges associated with sulfur cathodes, including poor electronic conductivity, dissolution and shuttling of sodium polysulfides, sluggish redox kinetics, and severe interfacial instability with the sodium metal anode. These issues collectively result in rapid capacity fading, low Coulombic efficiency, and limited rate capability.

Sulfurized polyacrylonitrile (SPAN) represents a compelling alternative to conventional elemental sulfur cathodes. By covalently bonding sulfur within a carbon–nitrogen polymer backbone, SPAN effectively suppresses polysulfide dissolution and enables a predominantly solid-state sulfur redox pathway. Despite its demonstrated electrochemical stability in lithium-based systems, the sodium storage mechanism of SPAN remains far less understood. Fundamental questions persist regarding the nature of sulfur redox centers, Na⁺ coordination environments, charge compensation pathways, and the role of electrolyte chemistry in governing reaction reversibility and interfacial stability.

This project aims to establish a mechanistic understanding and rational design framework for SPAN-based cathodes in Na–S batteries, with a particular emphasis on electrolyte engineering. We hypothesize that the electrochemical behavior of SPAN is strongly coupled to electrolyte composition, including sodium salt chemistry, solvent coordination structure, and interfacial solvation dynamics. These factors critically influence Na⁺ transport, sulfur redox kinetics, and the formation of stable cathode–electrolyte interphases.

To test this hypothesis, the project will systematically investigate the interaction between SPAN cathodes and tailored electrolytes using a combination of electrochemical analysis and advanced spectroscopic characterization. Emphasis will be placed on identifying the dominant sulfur redox pathways, tracking the evolution of sulfur bonding configurations, and elucidating Na⁺–sulfur coordination during cycling. Insights gained from these mechanistic studies will guide the rational design of electrolytes that promote reversible sulfur redox, suppress parasitic side reactions, and stabilize both cathode and anode interfaces.

By integrating mechanistic investigation with electrolyte-driven materials design, this project seeks to overcome key limitations of Na–S batteries and unlock the full potential of organic sulfur cathodes. The outcomes are expected to provide fundamental insights into solid-state sulfur chemistry in sodium systems and establish design principles broadly applicable to next-generation sulfur-based energy storage technologies.