Explore Electrocatalysis to Improve the Cathode Performance in Li-S Batteries

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Lithium-ion batteries are leading technologies for electric vehicles and large-scale renewable energy storage. Lithium-sulfur battery technology, in particular, is a forerunner of next-generation lithium-ion batteries due to their material availability and their high energy density. The project will investigate a new electrocatalytic concept for improving the performance of lithium sulfide batteries. Specifically, the goal is to enhance charge/discharge rates and suppress battery deactivation, both of which are limiting the performance of current Li-S batteries. Beyond the technical aspects, the project includes educational and outreach activities, focusing on underrepresented students from middle- and high-school to graduate level. Advances in LiS battery technology are hindered by several critical barriers, including the low electrical conductivity of elemental S and discharged product Li2S at the cathode, high overpotentials, and the rapid capacity fading of the S cathode due to diffusion of soluble lithium polysulfide (LiPS) intermediates from the cathode to react with the Li anode, notoriously known as the “shuttle effect”. Transition metal sulfide electrocatalysts with strong adsorption of LiPS intermediates will be explored to accelerate the conversion between S and Li2S, the two insoluble end products. The project focuses on improving the cathode performance based on the new electrocatalytic concept using two types of hybrid materials as the electrocatalysts, i.e. the two-dimensional (2D) atomic layered MoS2 and the quasi-1D chain-like VS4, both strongly attached on highly conductive reduced graphene oxide (rGO) nanosheets. The specific objectives include (1) catalyst synthesis and characterization (including their ability for LiPS adsorption and electrocatalytic conversion); (2) electrocatalytic LiPS trapping and conversion (via hybrid materials incorporation in the interlayer and the S/C cathode, respectively), and (3) electrocatalytic conversion of Li2S to S. The MoS2/rGO and VS4/rGO catalysts will be incorporated in the lithium-loaded Li2S/C cathode to reduce the activation energy of the initial delithiation of Li2S and enable a stable and reversible Li2S/C cathode. Electrochemical characterizations will be correlated with both ex-situ and operando micro-Raman spectroscopy studies to provide a good understanding of the dynamic charge/discharge processes and render mechanistic insights of the electrocatalysis. These studies will provide solutions to realize the full potentials of the Li-S batteries, an important sustainable energy technology. In addition to the technical objectives, this project provides cross-disciplinary training in nanomaterials synthesis/characterization, electrochemistry, catalysis and energy storage technologies to two graduate students and one undergraduate student. The project team will participate in summer STEM camps to engage with high/middle school students (particularly girls in Kansas) and provide hands-on workshops using the materials developed in this project. An outreach effort will be made through a strong collaboration with Xavier University of Louisiana (XULA), a Historically Black Colleges and Universities (HBCU), to host visiting undergraduate students from XULA for summer research on electrical energy storage in Kansas State University.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.