Browsing by Author "Salpekar, Devashish"

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    Fluorinated Multi-Walled Carbon Nanotubes Coated Separator Mitigates Polysulfide Shuttle in Lithium-Sulfur Batteries
    (MDPI, 2023) Salpekar, Devashish; Dong, Changxin; Oliveira, Eliezer F.; Khabashesku, Valery N.; Gao, Guanhui; Ojha, Ved; Vajtai, Robert; Galvao, Douglas S.; Babu, Ganguli; Ajayan, Pulickel M.
    Li-S batteries still suffer from two of the major challenges: polysulfide shuttle and low inherent conductivity of sulfur. Here, we report a facile way to develop a bifunctional separator coated with fluorinated multiwalled carbon nanotubes. Mild fluorination does not affect the inherent graphitic structure of carbon nanotubes as shown by transmission electron microscopy. Fluorinated carbon nanotubes show an improved capacity retention by trapping/repelling lithium polysulfides at the cathode, while simultaneously acting as the “second current collector”. Moreover, reduced charge-transfer resistance and enhanced electrochemical performance at the cathode-separator interface result in a high gravimetric capacity of around 670 mAh g−1 at 4C. Unique chemical interactions between fluorine and carbon at the separator and the polysulfides, studied using DFT calculations, establish a new direction of utilizing highly electronegative fluorine moieties and absorption-based porous carbons for mitigation of polysulfide shuttle in Li-S batteries.
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    Generation of intense phase-stable femtosecond hard X-ray pulse pairs
    (National Academy of Sciences, 2022) Zhang, Yu; Kroll, Thomas; Weninger, Clemens; Michine, Yurina; Fuller, Franklin D.; Zhu, Diling; Alonso-Mori, Roberto; Sokaras, Dimosthenis; Lutman, Alberto A.; Halavanau, Aliaksei; Pellegrini, Claudio; Benediktovitch, Andrei; Yabashi, Makina; Inoue, Ichiro; Inubushi, Yuichi; Osaka, Taito; Yamada, Jumpei; Babu, Ganguli; Salpekar, Devashish; Sayed, Farheen N.; Ajayan, Pulickel M.; Kern, Jan; Yano, Junko; Yachandra, Vittal K.; Yoneda, Hitoki; Rohringer, Nina; Bergmann, Uwe
    Coherent nonlinear spectroscopies and imaging in the X-ray domain provide direct insight into the coupled motions of electrons and nuclei with resolution on the electronic length scale and timescale. The experimental realization of such techniques will strongly benefit from access to intense, coherent pairs of femtosecond X-ray pulses. We have observed phase-stable X-ray pulse pairs containing more than 3 × 107 photons at 5.9 keV (2.1 Å) with ∼1 fs duration and 2 to 5 fs separation. The highly directional pulse pairs are manifested by interference fringes in the superfluorescent and seeded stimulated manganese Kα emission induced by an X-ray free-electron laser. The fringes constitute the time-frequency X-ray analog of Young’s double-slit interference, allowing for frequency domain X-ray measurements with attosecond time resolution.
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    Novel Pathways in Materials Engineering for Energy Storage, Conversion, and Structural Applications
    (2022-04-22) Salpekar, Devashish; Pulickel , Ajayan M; Vajtai, Robert; Biswal , Sibani Lisa; Boul, Peter J
    Advancements in Materials Science and Nanotechnology have led to breakthroughs in several disciplines, including energy storage devices, portable electronics, and sustainable electrocatalysis. Despite the huge success, several roadblocks limit the development of advanced materials for several practical applications. Therefore, modifications of these materials and a rigorous understanding of the entire system are essential to make them viable alternatives. The thesis is split into three major sections with each part discussing the chemistries of the synthesized materials, their properties, and their influence in respective applications. In the first part of this thesis, an electrolyte formulation was studied for higher temperatures Li-ion batteries. In addition, bifunctional material additives were introduced for alternate high energy density cathodes. The second part of the thesis discusses a technique to fluorinate layered hexagonal boron nitride. Fluorination of hBN leads to major structural and electronic changes, suggesting an effective thermal transport medium for future electronics. In the third section, defect-rich functional materials are derived using atomic layer deposition for electro. Finally, facile synthesis methods are suggested to develop smart and sustainable composites for specific applications. Overall, this thesis presents several processing techniques to derive advanced high-performance materials, their careful investigation, and their utilization in energy storage, electronics, & structural applications.