In-Situ Formation of Ternary Sulfide-rich Interphases for Stabilizing Lithium Deposition in Lithium-sulfur Batteries

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Energy storage at an affordable cost has emerged as one of the challenging issues for the energy sector, being critical for a wide range of applications ranging from electric vehicles to grid storage of renewable energies. Lithium-sulfur batteries are one the most promising next-generation battery technologies, as lithium and sulfur exhibit charge-storage capacity ten times higher than that of the electrode materials used in current lithium-ion batteries. Also, sulfur is environmentally benign, inexpensive, and widely available with secure domestic supply chains. Despite these advantages, the commercial adoption of lithium-sulfur batteries is hobbled by their poor cycle life. This project focuses on developing an effective strategy for improving the cycle life of lithium-sulfur batteries by systematically tuning the surface composition and properties of the anode. The effect of the modified interface material anode layer on the cycle life will be investigated with various computational, electrochemical, and materials characterization techniques. This will be a crucial step towards realizing practically relevant lithium-sulfur batteries with high energy density and extended cycle life. This work is also expected to yield new insights into the unique chemistry of sulfur compounds, which find applications in diverse areas, including photovoltaics, catalysis, and organic semiconductors. The project will also provide a broad interdisciplinary training to graduate and undergraduate students as well as historically underrepresented community college students and teachers in the globally important area of clean energy, encompassing inorganic chemistry, solid-state physics, electrochemical systems, and materials science and engineering.The unique chemistry of sulfur and its tendency to form polysulfide intermediates that are soluble in the liquid electrolyte profoundly impact the solid-electrolyte interphase (SEI) layer formed on lithium-metal surface in Li-S batteries. This project focuses on developing a systematic and effective strategy for tailoring the composition of the SEI layer to improve the reversibility of lithium plating and stripping in Li-S batteries. Electrolyte and cathode additives will be identified that work in tandem with the generated polysulfide intermediates to form a stabilizing SEI layer on lithium-metal surface. Specifically, high Li-ion conductivity LiXS ternary sulfides will be investigated as in-situ engineered SEI components, where X is a high-oxidation state cation of an element less electronegative than sulfur. It is hypothesized that the nature of X-S bond would play a critical role in determining the properties of the modified SEI layer, and consequently, the measured lithium cycling efficiency. The impact of the in-situ modified SEI layers on electrochemical performance will be assessed with practically relevant anode-free full cells (limited lithium inventory) and pouch cells (limited electrolyte supply) by determining the lithium inventory loss rates. With the in-situ engineering of a sulfide-rich lithium SEI and careful application of computational and materials characterization techniques, the project aims to (i) identify stabilizing SEI components in Li-S batteries and methods of fabricating them, (ii) establish a fundamental understanding of the composition-structure-property relationships that underlie the effect of SEI layer on the reversibility of lithium plating and stripping, and (iii) demonstrate the impact of SEI modification on electrochemical performance under realistic cell design and testing conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.