Designing superhydrophobic surfaces using fluorosilsesquioxane-urethane hybrid and porous silicon gradients

Bellingham, Washingto

Fusion of carbon nanotubes for fabrication of field emission cathodes

Consolidated carbonaceous samples prepared by spark plasma sintering of multi-walled carbon nanotubes are analyzed, and the effect of the heating regime on their morphology, density, thermal stability, electron field emission and adhesive behavior studied. The trend in the field emission properties of these samples is explained by the changes in the mobility of the nanotube tips. The effect of such changes in the number of free nanotube tips is also deduced from micro-adhesion data, obtained from pull-off tests using atomic force microscopy

A high power density electrode with ultralow carbon via direct growth of particles on graphene sheets

The application of lithium ion batteries in high power applications such as hybrid electric vehicles and electric grid systems critically requires drastic improvement in the electronic conductivity using effective materials design and strategies. Here, we demonstrate that the growth of a multi-component structure of composition LiTi2(PO4)(3) [LTP] on a reduced graphene oxide (rGO) surface via a facile synthetic strategy could achieve an ultrahigh rate capability with the total carbon content as low as 1.79 wt%. The rGO-LTP hybrid material has been prepared using a two-step approach, where the growth of TiO2 nanoparticles on the graphene oxide surface is followed by the high temperature growth of LTP on graphene sheets and simultaneous thermal reduction of graphene oxide. The LTP particles are densely packed within the ripples of rGO and form a compact, well-connected graphene network requiring no additional conductive carbon to facilitate fast electron transport from active materials to the current collector. Here, graphene not only acts as a stable conductive substrate but also helps to control the size of the formed particles. The rGO-LTP hybrid as a cathode in lithium ion batteries achieves an ultrahigh specific power of 10 000 W kg(-1) at a specific energy of 210 W h kg(-1), which corresponds to a charge and discharge time of 36 s and also retains 92% of the initial capacity after 100 cycles at a 10 C charge-discharge rate. Such an excellent performance is attributed to the multifunctional roles performed by rGO such as controlling the particle size, enhancing the electronic conductivity through a highly conductive network and rendering stability during cycling. This provides an effective design strategy for growing complex hybrid materials on graphene and engineering graphene nanosheets for advanced energy storage applications.close8

Diffusion behavior of sodium ions in Na0.44MnO2 in aqueous and non-aqueous electrolytes

The slow kinetics of bigger-sized sodium ions in intercalation compounds restricts the practical applications of sodium batteries. In this work, sodium ion intercalation/de-intercalation behavior of Na0.44MnO2 (NMO), which is one of the promising cathode materials for sodium batteries, is presented in both aqueous and non-aqueous electrolyte systems. The NMO samples synthesized using modified Pechini method shows better rate capability in 0.5 M sodium sulfate aqueous electrolyte system than the 1 M sodium perchlorate non-aqueous system. The difference in the rate performance is extensively investigated using electrochemical impedance spectroscopy (EIS) measurements and the apparent diffusion coefficients of sodium in NMO are determined to be in the range of 1.08 ?? 10-13 to 9.15 ?? 10 -12 cm2 s-1 in aqueous system and in the range of 5.75 ?? 10-16 to 2.14 ?? 10-14 cm2 s-1 in non-aqueous systems. The differences in the evaluated rate capability are mainly attributed to nearly two to three orders of magnitude difference in the apparent diffusion coefficient along with the charge transfer resistance and the resistance from the formed SEI layer.close292

Improvement of the Cycling Performance and Thermal Stability of Lithium-Ion Cells by Double-Layer Coating of Cathode Materials with Al₂O₃ Nanoparticles and Conductive Polymer

We demonstrate the effectiveness of dual-layer coating of cathode active materials for improving the cycling performance and thermal stability of lithium-ion cells. Layered nickel-rich LiNi_0.6Co_0.2Mn_0.2O₂ cathode material was synthesized and double-layer coated with alumina nanoparticles and poly­(3,4-ethylenedioxythiophene)-<i>co</i>-poly­(ethylene glycol). The lithium-ion cells assembled with a graphite negative electrode and a double-layer-coated LiNi_0.6Co_0.2Mn_0.2O₂ positive electrode exhibited high discharge capacity, good cycling stability, and improved rate capability. The protective double layer formed on the surface of LiNi_0.6Co_0.2Mn_0.2O₂ materials effectively inhibited the dissolution of Ni, Co, and Mn metals from cathode active materials and improved thermal stability by suppressing direct contact between electrolyte solution and delithiated Li_1–<i>x</i>Ni_0.6Co_0.2Mn_0.2O₂ materials. This effective design strategy can be adopted to enhance the cycling performance and thermal stability of other layered nickel-rich cathode materials used in lithium-ion batteries

Surface enriched graphene hollow spheres towards building ultra-high power sodium-ion capacitor with long durability

We report the synthesis and fabrication of all carbonaceous electrode based high-energy and high-power- sodiumion capacitors (NICs) which are anticipated to bridge the gap between rechargeable batteries and double layer capacitors. Unfortunately, the kinetic imbalance between battery type electrode and capacitive cathodes severely restricts the energy-power capabilities of NICs. To circumvent the kinetic mismatch and boost the efficiency of NICs, we are utilizing the rationally designed graphene hollow nanospheres (GHNS) as a bi-functional electrode in which nitrogen and sulfur atoms are infiltrated through the carbonaceous matrix. This eventually results in enhanced Na-ion storage capacity of GHNS which is paralleled by density functional theory calculations owing to the binding ability. All GHNS based NIC displays a high operating voltage, high energy density, and high power density, for example, the energy densities of 121 Wh kg(-1) at the power density of 100 W kg(-1). Further, the NIC can render remarkable cycling stability of similar to 85% retention after 10,000 cycles (similar to 0.0015% energy decay per cycle) and emphasized to be used as a potential candidate for hybrid charge storage systems in the near future.

Effective Trapping of Lithium Polysulfides Using a Functionalized Carbon Nanotube-Coated Separator for Lithium–Sulfur Cells with Enhanced Cycling Stability

The critical issues that hinder the practical applications of lithium–sulfur batteries, such as dissolution and migration of lithium polysulfides, poor electronic conductivity of sulfur and its discharge products, and low loading of sulfur, have been addressed by designing a functional separator modified using hydroxyl-functionalized carbon nanotubes (CNTOH). Density functional theory calculations and experimental results demonstrate that the hydroxyl groups in the CNTOH provoked strong interaction with lithium polysulfides and resulted in effective trapping of lithium polysulfides within the sulfur cathode side. The reduction in migration of lithium polysulfides to the lithium anode resulted in enhanced stability of the lithium electrode. The conductive nature of CNTOH also aided to efficiently reutilize the adsorbed reaction intermediates for subsequent cycling. As a result, the lithium–sulfur cell assembled with a functional separator exhibited a high initial discharge capacity of 1056 mAh g^–1 (corresponding to an areal capacity of 3.2 mAh cm^–2) with a capacity fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate

Gold-Decorated Block Copolymer Microspheres with Controlled Surface Nanostructures

Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-<i>b</i>-poly(4-vinylpyridine) (PS-<i>b</i>-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-<i>b</i>-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV–vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres can be extended to other NP systems such as iron-oxide or platinum NPs. These precursors can also be selectively incorporated into P4VP domains and induce the formation of hybrid BCP-microspheres with controlled surface nanostructures