Examinando por Autor "Mikhalchan, Anastasiia"

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Composite Fabrics of Conformal MoS2 Grown on CNT Fibers: Tough Battery Anodes without Metals or Binders
(ACS, 2021-06-28) Rana, Moumita; Boaretto, Nicola; Mikhalchan, Anastasiia; Vila, María; Marcilla, Rebeca; Vilatela, Juan José
In the quest to increase battery performance, nanostructuring battery electrodes gives access to architectures with electrical conductivity and solid-state diffusion regimes not accessible with traditional electrodes based on aggregated spherical microparticles while often also contributing to the cyclability of otherwise unstable active materials. This work describes electrodes where the active material and current collector are formed as a single nanostructured composite network, consisting of macroscopic fabrics of carbon nanotube fibers covered with conformal MoS2 grown preferentially aligned over the graphitic layers, without a metallic current collector or any conductive or polymeric additives. The composite fabrics of CNTF/MoS2 retain high toughness and show out-of-plane electrical conductivity as high as 1.2 S/m, above the threshold to avoid electrical transport-limited performance of electrodes (1 S/m) and above that of control nanocomposite lithium-ion battery electrodes (0.1 S/m) produced from dispersed nanocarbons. Cycled against Li, they show specific capacity as high as 0.7 A h/g along with an appreciable rate capability and cycling stability in low (108% capacity retention after 50 cycles at 0.1 A/g) as well as high current density (89% capacity retention after 250 cycles at 1 A/g). The composite fabrics are flexible, with high tensile toughness up to 0.7 J/g, over two orders of magnitude higher than conventional electrodes or regular MoS2 materials, and full-electrode capacity above state-of-the-art at different current densities.
Simultaneous improvements in conversion and properties of molecularly controlled CNT fibres
(Elsevier, 2021-07) Mikhalchan, Anastasiia; Vila, María; Arévalo, Luis; Vilatela, Juan José
Fibres of ultralong and aligned carbon nanotubes (CNT) have axial properties above reference engineering materials, proving to be exceptional materials for application in structural composites, energy storage and other devices. For CNT fibres produced by direct spinning from floating catalyst chemical vapor deposition (FCCVD), a scaled-up method, the challenge is to simultaneously achieve high process conversion and high-performance properties. This work presents a parametric study of the CNT fibre spinning process by establishing the relation between synthesis conditions, molecular composition (i.e. CNT type), fibre mechanical and electrical properties, and conversion. It demonstrates tensile properties (strength 2.1 ± 0.13 N/tex, modulus 107 ± 7 N/tex) above some carbon fibres, combined with carbon conversion about 5%, significantly above literature on similar materials. The combined improvement in conversion and properties is obtained by conducing the reaction at high temperature (1300 °C), using toluene as a carbon source, and through adjustment of the promotor to carbon ratio (S/C) to favor formation of few-layer, collapsed CNTs that maximize packing at relatively high conversions. Lower S/C ratios produce low-defect single-wall CNT, but weaker fibres. An increase in electrical conductivity to 3 × 105 S/m is also observed, with the data suggesting a correlation with longitudinal modulus.