Development of polysulfide battery systems with low-cost active materials and solid electrolytes
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Effective utilization of renewable, intermittent energy sources will require cost-effective, long-life energy storage systems. Sulfur is a low-cost, benign, and widely abundant material that has attracted substantial attention as a battery material due to its promise of a high energy density (1,675 mA h g⁻¹). Dissolved sulfur in the form of aqueous polysulfide promises to overcome the limitations associated with solid sulfur, such as its low conductivity and poor electrochemical utilization. However, batteries with aqueous polysulfide as a redox material often suffer from degradation due to chemical crossover of the polysulfide. Aqueous polysulfide also suffers from sluggish redox kinetics, requiring the use of a catalyst. This work aims to demonstrate novel aqueous polysulfide battery couples and improve the lifetime and performance of aqueous polysulfide batteries enabled by the development of novel catalysts and the use of a solid electrolyte separator to confine the aqueous polysulfide. First, a zinc-aqueous polysulfide battery with a mediator-ion solid electrolyte is demonstrated with both a Li⁺ and Na⁺ mediator ion. The CoS electrocatalyst developed for improved aqueous polysulfide redox kinetics presents improved stability when synthesized on a stable stainless-steel substrate. Overall, the battery exhibits good energy density and capacity retention, and the choice of mediator ion is determined to have substantial impact on the battery performance. A long-life polysulfide-air battery is developed with a highly active CuS polysulfide catalyst, mediator-ion solid electrolyte, and decoupled air electrodes for oxygen reduction and evolution reactions. The redox activity of the CuS in the absence of polysulfide at the intermediate voltages of a polysulfide-air battery are shown to have minimal effect on its long-term cycling stability. Next two polysulfide-polyhalide battery systems, polysulfide-polybromide and polysulfide-polyiodide, are demonstrated with a mediator-ion solid electrolyte to eliminate chemical crossover of the redox-active materials and enable excellent long-term cyclability. The polyiodide catholyte proves to be substantially less corrosive to the Na⁺-conducting solid electrolyte than the polybromide catholyte, and a Li⁺-conducting solid electrolyte is shown to have remarkable stability in both the polybromide and polyiodide catholytes. Lastly, a novel sodium-aqueous polysulfide hybrid battery is developed in which a sodium metal anode and nonaqueous anolyte are protected from the aqueous polysulfide catholyte with a solid electrolyte. The hybrid system is shown to have remarkable long-term cycling performance compared to fully nonaqueous room-temperature sodium-sulfur batteries. A novel freestanding CuS-CNT electrode is developed and it demonstrates excellent catalytic activity towards polysulfide redox.