Engineering topics
Le Thai, Mya
Publications and source records attributed to Le Thai, Mya.
Supercharging a MnO 2 Nanowire: An Amine-Altered Morphology Retains Capacity at High Rates and Mass Loadings
The influence of hexamethylenetetraamine (HMTA) on the morphology of $δ$-MnO 2 and its properties for electrical energy storage are investigated—specifically for ultrathick $δ$-MnO 2 layers in the micron scale. Planar arrays of gold@$δ$-MnO 2 , core@shell nanowires, were prepared by electrodeposition with and without the HMTA and their electrochemical properties were evaluated. HMTA alters the MnO 2 in three ways: First, it creates a more open morphology for the MnO 2 coating, characterized by “petals” with a thickness of 6 to 9 nm, rather than much thinner $δ$-MnO 2 sheets seen in the absence of HMTA. Second, the electronic conductivity of the $δ$-MnO 2 is increased by an order of magnitude. Third, $δ$-MnO 2 prepared in HMTA shows a (001) interlayer spacing that is expanded by ≈30% possibly accelerating Li transport. The net effect of “HTMA doping” is to dramatically improve high rate performance, culminating in an increase in the specific capacity for the thickest MnO 2 shells examined here by a factor of 15 at 100 mV/s.
Collateral Advantages of a Gel Electrolyte for MnO 2 Nanowire Capacitors: Higher Voltage and Reduced Volume
Recently we demonstrated that symmetric, all Au@δ-MnO 2 core@shell nanowire capacitors can achieve cycle stability to 100 000 cycles and beyond in a poly(methyl methacrylate) (PMMA) gel electrolyte. Here we examine the limits of the PMMA gel to confer this extraordinary stability, in terms of the accessible maximum voltage, Vmax, and the thickness of the PMMA gel electrolyte layer. Two conclusions are (1) the PMMA gel permits the Vmax to be increased by 50% from 1.2 V to 1.8 V, allowing the specific energy to be increased 5–6 fold, and (2) the PMMA gel layer thickness can be reduced from 180 μm (previously) to 2 μm while simultaneously utilizing two layers of nanowires and patterning nanowires in each layer at 5× higher density. For this nanowire “sandwich” architecture, a net increase in volumetric capacity of 600× up to 500 mF/cm3 can be achieved while retaining cycle stability to 100 000 cycles.
Solid-State Ionic Diodes Demonstrated in Conical Nanopores
Not Available
100k Cycles and Beyond: Extraordinary Cycle Stability for MnO 2 Nanowires Imparted by a Gel Electrolyte
Explore the source record for details and available documents.