RESUMO
Printing of ultrathin layers of polymeric and colloidal inks is critical for the manufacturing of electronics on nonconventional substrates such as paper and polymer films. Recently, we found that nanoporous stamps overcome key limitations of traditional polymer stamps in flexographic printing, namely, enabling the printing of ultrathin nanoparticle films with micron-scale lateral precision. Here, we study the dynamics of liquid transfer between nanoporous stamps and solid substrates. The stamps comprise forests of polymer-coated carbon nanotubes, and the surface mechanics and wettability of the stamps are engineered to imbibe colloidal inks and transfer the ink upon contact with the target substrate. By high-speed imaging during printing, we observe the dynamics of liquid spreading, which is mediated by progressing contact between the nanostructured stamp surface and by the substrate and imbibition within the stamp-substrate gap. From the final contact area, the volume of ink transfer is mediated by rupture of a capillary bridge; and, after rupture, liquid spreads to fill the area defined by a precursor film matching the stamp geometry with high precision. Via modeling of the liquid dynamics, and comparison with data, we elucidate the scale- and rate-limiting aspects of the process. Specifically, we find that the printed ink volume and resulting layer thickness are independent of contact pressure; and that printed layer thickness decreases with retraction speed. Under these conditions, nanoparticle films with controlled thickness in the <100 nm regime can be printed using nanoporous stamp flexography, at speeds commensurate with industrial printing equipment.
RESUMO
The ability to store energy on the electric grid would greatly improve its efficiency and reliability while enabling the integration of intermittent renewable energy technologies (such as wind and solar) into baseload supply. Batteries have long been considered strong candidate solutions owing to their small spatial footprint, mechanical simplicity and flexibility in siting. However, the barrier to widespread adoption of batteries is their high cost. Here we describe a lithium-antimony-lead liquid metal battery that potentially meets the performance specifications for stationary energy storage applications. This Li||Sb-Pb battery comprises a liquid lithium negative electrode, a molten salt electrolyte, and a liquid antimony-lead alloy positive electrode, which self-segregate by density into three distinct layers owing to the immiscibility of the contiguous salt and metal phases. The all-liquid construction confers the advantages of higher current density, longer cycle life and simpler manufacturing of large-scale storage systems (because no membranes or separators are involved) relative to those of conventional batteries. At charge-discharge current densities of 275 milliamperes per square centimetre, the cells cycled at 450 degrees Celsius with 98 per cent Coulombic efficiency and 73 per cent round-trip energy efficiency. To provide evidence of their high power capability, the cells were discharged and charged at current densities as high as 1,000 milliamperes per square centimetre. Measured capacity loss after operation for 1,800 hours (more than 450 charge-discharge cycles at 100 per cent depth of discharge) projects retention of over 85 per cent of initial capacity after ten years of daily cycling. Our results demonstrate that alloying a high-melting-point, high-voltage metal (antimony) with a low-melting-point, low-cost metal (lead) advantageously decreases the operating temperature while maintaining a high cell voltage. Apart from the fact that this finding puts us on a desirable cost trajectory, this approach may well be more broadly applicable to other battery chemistries.
RESUMO
Nickel oxide-gadolinia-doped ceria thin films with a ceria composition of 80 at% Ce and 20 at% Gd were grown by pulsed laser deposition on sapphire and SiO2/Si wafers as well as on yttria stabilized zirconia polycrystalline substrates. Upon reduction of the NiO phase in a H2/N2 atmosphere at 600 degrees C, a stable three-phase, 3-D interconnecting microstructure was obtained of metallic Ni, ceramic, and pores. Coarsening and segregation of the Ni to the surface of the film was observed at higher temperatures. The kinetics of this process depend strongly on the microstructures that can be developed in situ during deposition or post-deposition heat treatments. In situ minimization of Ni-coarsening can be achieved at temperatures as low as 500 degrees C when the deposition pressure does not exceed 0.02 mbar. For films deposited at higher pressure and at temperatures below 800 degrees C, coarsening can be minimized post deposition by annealing in air at 1000 degrees C. The films showed very good metallic conductivity and stability upon thermal cycling in a reducing atmosphere. Redox cycles performed at 600 degrees C between air and H2 induced a loss of connectivity of the metallic phase and consequent degradation of the conductivity. After 16 cycles, corresponding to 65 hrs, the conductivity is reduced by one order of magnitude.
