A high theoretical energy density makes lithium-sulfur (Li−S) batteries promising candidates for energy storage systems of the post-lithium-ion generation. As the performance of Li−S cells with liquid electrolytes is impaired by the solubility of reaction intermediates, solid-state cell concepts represent an auspicious approach for future electrochemical energy storage. However, the kinetics of Li−S solid-state batteries and high charge/discharge rate still remain major challenges, and in-depth knowledge of the charge carrier transport in solid-state composite sulfur cathodes is still missing. In this work, the charge transport and cyclability of composite cathodes consisting of sulfur, Li6PS5Cl and carbon, with varying volume fractions of ion- and electron-conducting phases is investigated. The limiting thresholds of charge transport are elucidated by comparing the battery performance with effective transport properties of the cathode composite. Although both the effective electronic and ionic conductivities indicate high tortuosity factors, ionic transport is identified as a critical bottleneck. This work underscores the importance of quantitative transport analysis as a tool for cathode optimization.
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