Revitalising sodium–sulfur batteries for non-high-temperature operation: a crucial review†
Rechargeable sodium–sulfur (Na–S) batteries are regarded as a promising energy storage technology due to their high energy density and low cost. High-temperature sodium–sulfur (HT Na–S) batteries with molten sodium and sulfur as cathode materials were proposed in 1966, and later successfully commercialised for utility-scale stationary energy storage. However, their high working temperature (300–350 °C) causes some detrimental problems such as high operating costs, difficulties of maintenance (corrosion), and severe safety issues. In particular, HT Na–S batteries with Na polysulfides as the final discharge product only deliver about a third of the sulfur's theoretical capacity. These drawbacks greatly limited the broader applications of HT Na–S batteries. In recent years, extensive efforts have been devoted to developing next-generation intermediate-temperature sodium–sulfur batteries (IMT Na–S, operating at 120–300 °C) and room-temperature sodium–sulfur batteries (RT Na–S) with higher capacity, lower maintenance cost and enhanced safety. Herein, we provide a comprehensive review of the latest progress on IMT Na–S and RT Na–S batteries. We elucidate the working principles, opportunities and challenges of these non-high-temperature Na–S battery systems, and summarise the advances in the battery components including cathodes, anodes, electrolytes, and other battery constituents. In particular, the applications of solid-state electrolytes in IMT Na–S and RT Na–S chemistry are emphasised. The remaining challenges and clear perspectives are outlined for the future development of novel high-performance Na–S batteries.