Single-layer molybdenum disulfide (MoS) has attracted significant attention due to its electronic and physical properties, with much effort invested toward obtaining large-area high-quality monolayer MoS films. In this work, we demonstrate a reactive-barrier-based approach to achieve growth of highly homogeneous single-layer MoS on sapphire by the use of a nickel oxide foam barrier during chemical vapor deposition. Due to the reactivity of the NiO barrier with MoO, the concentration of precursors reaching the substrate and thus nucleation density is effectively reduced, allowing grain sizes of up to 170 μm and continuous monolayers on the centimeter length scale being obtained. The quality of the monolayer is further revealed by angle-resolved photoemission spectroscopy measurement by observation of a very well resolved electronic band structure and spin-orbit splitting of the bands at room temperature with only two major domain orientations, indicating the successful growth of a highly crystalline and well-oriented MoS monolayer.
Silicon (Si) is the most promising anode candidate for the next generation of lithium-ion batteries but difficult to cycle due to its poor electronic conductivity and large volume change during cycling. Nanostructured Si-based materials allow high loading and cycling stability but remain a challenge for process and engineering. We prepare a Si nanowires-grown-on-graphite one-pot composite (Gt-SiNW) via a simple and scalable route. The uniform distribution of SiNW and the graphite flakes alignment prevent electrode pulverization and accommodate volume expansion during cycling, resulting in very low electrode swelling. Our designed nano-architecture delivers outstanding electrochemical performance with a capacity retention of 87% after 250 cycles at 2C rate with an industrial electrode density of 1.6 g cm -3 . Full cells with NMC-622 cathode display a capacity retention of 70% over 300 cycles. This work provides insights into the fruitful engineering of active composites at the nanoand microscales to design efficient Si-rich anodes.
The best p-type skutterudites so far are didymium filled, Fe/Co substituted, Sb-based skutterudites. Substitution at the Sb-sites influences the electronic structure, deforms the Sb 4 -rings, enhances the scattering of phonons on electrons and impurities and this way reduces the lattice thermal conductivity.In this paper we study structural and transport properties of p-type skutterudites with the nominal composition DD 0.7 Fe 2.7 Co 1.3 Sb 11.7 {Ge/Sn} 0.3 , which were prepared by a rather fast reaction-annealing-melting technique. The Ge-doped sample showed impurities, which did not anneal out completely and even with ZT > 1 the result was
The development of low cost supercapacitor cells with unique capacitive properties is essential for many domestic and industrial purposes. Here we report the first ever application of SnS-reduced graphene oxide (SnS/RGO) layered nanocomposite as a superior electrode material for symmetric aqueous hybrid supercapacitors. We synthesized SnS/RGO nanocomposite comprised of nanosheets of SnS and graphene oxide via a one-pot hydrothermal approach. in situ as-synthesized SnS/RGO is devised for the first time to give high specific capacitance 500 Fg, energy density 16.67 Wh kg and power density 488 W kg. The cell retains 95% charge/discharge cycle stability up to 1000 cycles. In-short, the SnS/RGO nanosheet composite presented is a novel and advanced material for application in high stability moderate value hybrid supercapacitors. All the currently available surveys in literature state the potential applicability of SnS as the anode material for reversible lithium/sodium ion batteries (LIBs/NIBs) but there is a lack of equivalent studies on electrochemical capacitors. We filled up this knowledge gap by the use of the same material in a cost-effective, highly active hybrid supercapacitor application by utilizing its pseudocapacitance property combined with the layered capacitance property of graphene sheets.
The (de)lithiation process and resulting atomic and nanoscale morphological changes of an a-Si/ c-FeSi 2 /graphite composite negative electrode are investigated within a Li-ion full cell at several current rates (Crates) and after prolonged cycling by simultaneous operando synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS). WAXS allows the probing of the local crystalline structure. In particular, the observation of the graphite (de)lithiation process, revealed by the Li x C 6 Bragg reflections, enables access to the respective capacities of both graphite and active silicon. Simultaneously and independently, information on the silicon state of (de)lithiation and nanoscale morphology (1 to 60 nm) is obtained through SAXS. During lithiation, the SAXS intensity in the region corresponding to characteristic distances within the a-Si/c-FeSi 2 domains increases. The combination of the SAXS/WAXS measurements over the course of several charge/ discharge cycles, in pristine and aged electrodes, provides a complete picture of the C-rate-dependent sequential (de)lithiation mechanism of the a-Si/c-FeSi 2 /graphite anode. Our results indicate that, within the composite electrode, the active silicon volume does not increase linearly with lithium insertion and point toward the important role of the electrode morphology to accommodate the nanoscale silicon expansion, an effect that remains beneficial after cell aging and most probably explains the excellent performance of the composite material.
Failure mechanisms associated with silicon‐based anodes are limiting the implementation of high‐capacity lithium‐ion batteries. Understanding the aging mechanism that deteriorates the anode performance and introducing novel‐architectured composites offer new possibilities for improving the functionality of the electrodes. Here, the characterization of nano‐architectured composite anode composed of active amorphous silicon domains (a‐Si, 20 nm) and crystalline iron disilicide (c‐FeSi2, 5–15 nm) alloyed particles dispersed in a graphite matrix is reported. This unique hierarchical architecture yields long‐term mechanical, structural, and cycling stability. Using advanced electron microscopy techniques, the nanoscale morphology and chemical evolution of the active particles upon lithiation/delithiation are investigated. Due to the volumetric variations of Si during lithiation/delithiation, the morphology of the a‐Si/c‐FeSi2 alloy evolves from a core‐shell to a tree‐branch type structure, wherein the continuous network of the active a‐Si remains intact yielding capacity retention of 70% after 700 cycles. The root cause of electrode polarization, initial capacity fading, and electrode swelling is discussed and has profound implications for the development of stable lithium‐ion batteries.
Advanced anode material designs utilizing dual phase alloy systems like Si/FeSi2 nano-composites show great potential to decrease the capacity degrading and improve the cycling capability for Lithium (Li)-ion batteries. Here, we present a multi-scale characterization approach to understand the (de-)lithiation and irreversible volumetric changes of the amorphous silicon (a-Si)/crystalline iron-silicide (c-FeSi2) nanoscale phase and its evolution due to cycling, as well as their impact on the proximate pore network. Scattering and 2D/3D imaging techniques are applied to probe the anode structural ageing from nm to μm length scales, after up to 300 charge-discharge cycles, and combined with modeling using the collected image data as an input. We obtain a quantified insight into the inhomogeneous lithiation of the active material induced by the morphology changes due to cycling. The electrochemical performance of Li-ion batteries does not only depend on the active material used, but also on the architecture of its proximity.
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