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  1. Transition metal dichalcogenides (TMDs) such as the WS2 have been widely studied as potential electrode materials for lithium-ion batteries (LIB) owing to TMDs’ layered morphology and reversible conversion reaction with the alkali metals between 0 to 2 V (v/s Li/Li+) potentials. However, works involving TMD materials as electrodes for sodium- (NIBs) and potassium-ion batteries (KIBs) are relatively few, mainly due to poor electrode performance arising from significant volume changes and pulverization by the larger size alkali-metal ions. Here, we show that Na+ and K+ cyclability in WS2 TMD is improved by introducing WS2 nanosheets in a chemically and mechanically robust matrix comprising precursor-derived ceramic (PDC) silicon oxycarbide (SiOC) material. The WS2/SiOC composite in fibermat morphology was achieved via electrospinning followed by thermolysis of a polymer solution consisting of a polysiloxane (precursor to SiOC) dispersed with exfoliated WS2 nanosheets. The composite electrode was successfully tested in Na-ion and K-ion half-cells as a working electrode, which rendered the first cycle charge capacity of 474.88 mAh g−1 and 218.91 mAh g−1, respectively. The synergistic effect of the composite electrode leads to higher capacity and improved coulombic efficiency compared to the neat WS2 and neat SiOC materials in these cells.
    Free, publicly-accessible full text available December 1, 2023
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  5. Transition metal dichalcogenides (TMDs) such as MoSe2 have continued to generate interest in the engineering community because of their unique layered morphology—the strong in-plane chemical bonding between transition metal atoms sandwiched between two chalcogen atoms and the weak physical attraction between adjacent TMD layers provides them with not only chemical versatility but also a range of electronic, optical, and chemical properties that can be unlocked upon exfoliation into individual TMD layers. Such a layered morphology is particularly suitable for ion intercalation as well as for conversion chemistry with alkali metal ions for electrochemical energy storage applications. Nonetheless, host of issues including fast capacity decay arising due to volume changes and from TMD’s degradation reaction with electrolyte at low discharge potentials have restricted use in commercial batteries. One approach to overcome barriers associated with TMDs’ chemical stability functionalization of TMD surfaces by chemically robust precursor-derived ceramics or PDC materials, such as silicon oxycarbide (SiOC). SiOC-functionalized TMDs have shown to curb capacity degradation in TMD and improve long term cycling as Li-ion battery (LIBs) electrodes. Herein, we report synthesis of such a composite in which MoSe2 nanosheets are in SiOC matrix in a self-standing fiber mat configuration. This was achieved via electrospinningmore »of TMD nanosheets suspended in pre-ceramic polymer followed by high temperature pyrolysis. Morphology and chemical composition of synthesized material was established by use of electron microscopy and spectroscopic technique. When tested as LIB electrode, the SiOC/MoSe2 fiber mats showed improved cycling stability over neat MoSe2 and neat SiOC electrodes. The freestanding composite electrode delivered a high charge capacity of 586 mAh g−1electrode with an initial coulombic efficiency of 58%. The composite electrode also showed good cycling stability over SiOC fiber mat electrode for over 100 cycles.« less
    Free, publicly-accessible full text available February 1, 2023
  6. Micro-computed tomography (µCT) is a valuable tool for visualizing microstructures and damage in fiber-reinforced composites. However, the large sets of data generated by µCT present a barrier to extracting quantitative information. Deep learning models have shown promise for overcoming this barrier by enabling automated segmentation of features of interest from the images. However, robust validation methods have not yet been used to quantify the success rate of the models and the ability to extract accurate measurements from the segmented image. In this paper, we evaluate the detection rate for segmenting fibers in low-contrast CT images using a deep learning model with three different approaches for defining the reference (ground-truth) image. The feasibility of measuring sub-pixel feature dimensions from the µCT image, in certain cases where the µCT image intensity is dependent on the feature dimensions, is assessed and calibrated using a higher-resolution image from a polished cross-section of the test specimen in the same location as the µCT image.
    Free, publicly-accessible full text available February 1, 2023
  7. Ceramics derived from organic polymer precursors, which have exceptional mechanical and chemical properties that are stable up to temperatures slightly below 2000 °C, are referred to as polymer-derived ceramics (PDCs). These molecularly designed amorphous ceramics have the same high mechanical and chemical properties as conventional powder-based ceramics, but they also demonstrate improved oxidation resistance and creep resistance and low pyrolysis temperature. Since the early 1970s, PDCs have attracted widespread attention due to their unique microstructures, and the benefits of polymeric precursors for advanced manufacturing techniques. Depending on various doping elements, molecular configurations, and microstructures, PDCs may also be beneficial for electrochemical applications at elevated temperatures that exceed the applicability of other materials. However, the microstructural evolution, or the conversion, segregation, and decomposition of amorphous nanodomain structures, decreases the reliability of PDC products at temperatures above 1400 °C. This review investigates structure-related properties of PDC products at elevated temperatures close to or higher than 1000 °C, including manufacturing production, and challenges of high-temperature PDCs. Analysis and future outlook of high-temperature structural and electrical applications, such as fibers, ceramic matrix composites (CMCs), microelectromechanical systems (MEMSs), and sensors, within high-temperature regimes are also discussed.