A non-confined gamma monoclinic sulfur cathode in carbonate electrolyte based room temperature K-S batteries

Potassium-sulfur cells have garnered a lot of interest in grid storage chemistry due to the high abundance of both elements and hence their low cost. However, their development is hindered by the polysulfide shuttle effect and their dependency on electrolytes with limited commercial viability. The inability to use carbonate electrolytes is due to the irreversible reaction between it and PS, rendering the cell useless in the first few cycles. Here we expand our use of monoclinic γ-sulfur in carbon nanofibers (γS-CNFs) to the potassium-sulfur, K-S, chemistry. Herein we show that using γ-S enables the cells to run for 500 cycles at ∼900 mA h g −1 in commercial carbonate electrolytes. We further attempt to understand the role of γS-CNFs in K-S cells with electrochemical characterization and postmortem spectroscopy. As far as we are aware this is the first application of γ-S in K-S cells. Its outstanding performance should lead to new avenues for the development of this promising chemistry. This work extends our novel monoclinic γ-sulfur approach of polysulfide mitigation to the K-S chemistry. The lack of soluble polysulfides enable extremely stable cycling to 500 cycles in carbonate electrolyte.