Sub-zero and room-temperature sodium–sulfur battery cell operations: A rational current collector, catalyst and sulphur-host design and study

Abstract Minimizing polysulfide-shuttling while using a high-sulfur loaded cathode is vital in the effort to realize practical room-temperature sodium-sulfur (RT Na–S) batteries. Because of their inexpensive, highly abundant materials, these batteries have great potential as future, low-cost, stationary energy storage devices. The sluggish kinetics associated with the electrochemical conversion of electrolyte-soluble Na-polysulfides into insoluble final products causes a rapid accumulation of the intermediates in the electrolyte that escalates the polysulfide-shuttling. We report indium tin oxide nanoparticles decorated onto activated carbon cloth (ITO@ACC) as an electrocatalytic substrate that immobilizes the higher-order Na-polysulfides and also promotes their conversion into the insoluble end-discharge products and thus suppresses the accumulation of intermediate products in the electrolyte. The conversion into the insoluble end-discharge product is confirmed by electron paramagnetic resonance (EPR) spectroscopy to be via a free-radical coupling mechanism. At 20 °C, the ITO@ACC-catalyzed sodium-sulfur batteries (6.8 mg(S) cm–2) gave an early cycle capacity of 684 mA h g(S)–1 and after 1000 cycles the capacity was maintained at 445 mA h g(S)–1 at a 0.5C rate. Moreover, a subzero-temperature sodium-sulfur battery is also realized for the first time; operating at –10 °C, the initial specific capacity of the battery operating at 0.1C at this temperature was 342 mA h g(S)–1 and after 100 cycles, the capacity was maintained at 310 mA h g(S)–1.