Long-Life Polysulfide-Polyhalide Batteries with a Mediator-Ion Solid Electrolyte

Polysulfide-polybromide and polysulfide-polyiodide batteries are promising redox-flow systems due to their use of low-cost and abundant active materials. However, these systems have traditionally suffered from substantial crossover of redox active materials, causing loss of active material and the necessity of reconditioning their electrolytes, which has the overall effect of lowering battery lifetimes and adding system level costs. This work demonstrates how using a solid electrolyte instead of the traditional Nafion separator completely prevents crossover of redox active species, enabling long cycle life batteries. To achieve this, a mediator-ion strategy is employed, in which Li+ or Na+ ions transfer ionic charge through the solid electrolyte to achieve charge balance without active participation in the anode and cathode reactions. This is demonstrated with both polysulfide-polybromide (PSB) and polysulfide-polyiodide (PSI) batteries. The effect of the solid electrolyte on battery rate performance, as well as the long-term stability of the ceramic electrolyte in the corrosive polybromide and polyiodide catholytes, is examined.