Polysulfide-incompatible additive suppresses reaction of Li-S batteries

초록

CONTEXT & SCALE The ineffective electrolyte wetting and sluggish ion transport in thick tortuous S cathode dramatically hinder lithium-sulfur (Li-S) cell performance, especially under practical high S loading and lean electrolyte conditions. Meanwhile, the insufficient understanding of the relationship between solid/cathodeelectrolyte properties and cell-level behavior further limits practical Li-S battery development. To subsequently enhance the electrolyte wetting/ion transportation inside a thick S cathode and deepen the mechanism understanding, in this work, we reveal that the polysulfide-incompatible Lewis acid additive (LAA), which has long been considered unsuitable for Li-S batteries due to the chemical compatibility, can induce the in situ homogeneous interphase layer formation within the tortuous S cathode to promote ion transportation. Our conception is validated by a suite of fundamental investigations, including advanced synchrotron characterization and computational simulations. SUMMARY Rational electrolyte engineering for practical pouch cells remains elusive because the correlation between the cathode/solid-electrolyte interphase layer and cell-level reaction behavior is poorly understood. Here, by combining multiscale characterization and computational modeling, we show that-counter to the conventional perception of polysulfide-incompatible additives-the spontaneous reaction of sparingly solvated polysulfides with Lewis acid additives (LAAs) can induce in situ formation of a homogeneous interphase on thick and tortuous S cathode. Multiscale synchrotron X-ray characterization consistently affirms that such interface design could effectively eliminate the notorious problems of polysulfide shuttle and lithium corrosion and, more importantly, provide an interconnected "ion transport highway"to alleviate the uneven ion transport within the tortuous S cathode. Hence, this design dramatically reduces the reaction heterogeneity of lithium-sulfur (Li-S) pouch cells under lean electrolyte conditions. This work resolves controversy around the role of polysulfide-incompatible additives in high-energy Li-S pouch cells and highlights the importance of suppressing reaction heterogeneity for practical batteries.

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