Low-Temperature Sodium-Sulfur Battery

Room temperature sodium-sulfur (RT-Na/S) batteries have emerged as a highly promising candidate for stationary energy storage systems, driven by their high energy density, resource abundance, and environmental sustainability. Leveraging sodium’s natural abundance (2.3 wt.% in earth’s crust) and low raw material expenses compared to lithium (0.0017 wt.%), they offer a compelling alternative to lithium-based technologies for large-scale applications such as renewable energy integration, grid peak shaving, and electric vehicles. Despite these advantages, RT Na-S batteries remain in their early stages, facing formidable challenges that hinder their practical implementation. This chapter mainly introduces the basic working principle of RT-Na/S batteries, key challenges, the type of electrolytes, separators, cathode and anode materials. In addition, the related research progress and current strategies to solve these problems are also summarized. Finally, the application prospects and directions of RT-Na/S batteries are discussed. The RT-Na/S mainly uses metal sodium as the anode and sulfur as the cathode. During discharge, sodium ions migrate through the electrolyte from the anode to the sulfur-based cathode, while electrons travel externally through the circuit to maintain charge balance. At the cathode, sodium ions sequentially react with sulfur to form intermediate polysulfide species (Na₂Sₓ, 2< × ≤8), ultimately generating sodium sulfide (Na₂S) while releasing stored chemical energy. The charging process reverses this reaction: under external voltage, electrons flow back to the anode, enabling sodium metal plating through the reduction of sodium ions that return via the electrolyte. Concurrently, polysulfide intermediates at the cathode dissociate into sulfur and sodium ions. However, solid polysulfide arises from sluggish reaction kinetics, leading to incomplete sulfur utilization and irreversible polysulfide dissolution in the electrolyte, collectively manifesting as capacity fading over cycles. Addressing these interfacial reaction dynamics and phase transformation inefficiencies remains a fundamental challenge in enhancing the cyclability and energy density of RT-Na/S battery systems. RT-Na/S batteries employing sodium metal (or sodium alloys/composite anodes) as the sodium-supplying anode face challenges, such as parasitic reactions with electrolytes and dendrite-induced short-circuit risks. The sulfur-based cathode, while offering high theoretical capacity, suffers from intrinsic insulation that severely restricts reaction kinetics and sulfur utilization. Conventional electrolytes require careful optimization through additives or structural modifications to balance ionic conductivity with the mechanical stability of separators, particularly to mitigate polysulfide shuttling. Recent advancements in material engineering (e.g., nanostructured sulfur hosts, artificial solid-electrolyte interphases) and system architecture innovations are addressing these limitations. With growing research emphasis on polysulfide confinement strategies, sodium anode stabilization techniques, and advanced electrolyte formulations, RT-Na/S batteries demonstrate emerging potential for grid-scale energy storage. Current research highlights the systematic integration by achieving polysulfide regulation, sodium anode protection, and electrolyte optimization.