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Creators/Authors contains: "Thangavel, Naresh Kumar"

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  1. Deducing the electrochemical activity of intermediates and providing materials solution to alter their reaction pathways holds the key for developing advanced energy storage systems such as lithium-sulfur (Li-S) batteries. Herein, we provide mechanistic perspectives of the substrate guided reaction pathways of intermediate polysulfides and their correlation to the redox activity of discharge end products using In Situ atomic force microscopy-based scanning electrochemical microscopy (AFM-SECM) coupled Raman spectroscopy at nanoscale spatiotemporal resolution. In Situ SECM intermediate detection along with Raman analysis at the electrode/electrolyte interface reveals that the precipitation of Li 2 S can occur via an electrochemically active lithium disulfide (Li 2 S 2 ) intermediate step. With a detailed spectro-electrochemical and morphological mapping, we decipher that the substrate-dependent Li 2 S 2 formation adversely affects the Li 2 S oxidation in the subsequent cycles, thereby reducing the round-trip efficiency and overall performance of the cell. The present study provides nanoscale-resolved information regarding the polysulfide reaction pathways in Li-S batteries with respect to the electrode structure and its properties. 
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  2. Lithium metal as an anode has been widely accepted due to its higher negative electrochemical potential and theoretical capacity. Nevertheless, the existing safety and cyclability issues limit lithium metal anodes from practical use in high-energy density batteries. Repeated Li deposition and dissolution processes upon cycling lead to the formation of dendrites at the interface which results in reduced Li availability for electrochemical reactions, disruption in Li transport through the interface and increased safety concerns due to short circuiting. Here, we demonstrate a novel strategy using Ionic Liquid Crystals (ILCs) as the electrolyte cum pseudo-separator to suppress dendrite growth with their anisotropic properties controlling Li-ion mass transport. A thermotropic ILC with two-dimensional Li-ion conducting pathways was synthesized and characterized. Microscopic and spectroscopic analyses elucidate that the ILC formed with a smectic A phase, which can be utilized for wide temperature window operation. The results of electrochemical studies corroborate the efficacy of ILC electrolytes in mitigating dendrite formation even after 850 hours and it is further substantiated by numerical simulation and the mechanism involved in dendritic suppression was deduced. 
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    The lithium-sulfur (Li-S) redox battery system is considered to be the most promising next-generation energy storage technology due to its high theoretical specific capacity (1673 mAh g−1), high energy density (2600 Wh kg−1), low cost, and the environmentally friendly nature of sulfur. Though this system is deemed to be the next-generation energy storage device for portable electronics and electric vehicles, its poor cycle life, low coulombic efficiency and low rate capability limit it from practical applications. These performance barriers were linked to several issues like polysulfide (LiPS) shuttle, inherent low conductivity of charge/discharge end products, and poor redox kinetics. Here, we review the recent developments made to alleviate these problems through an electrocatalysis approach, which is considered to be an effective strategy not only to trap the LiPS but also to accelerate their conversion reactions kinetics. Herein, the influence of different chemical interactions between the LiPS and the catalyst surfaces and their effect on the conversion of liquid LiPS to solid end products are reviewed. Finally, we also discussed the challenges and perspectives for designing cathode architectures to enable high sulfur loading along with the capability to rapidly convert the LiPS. 
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