Optimization of carbon nanotube ultracapacitor for cell design

Abstract

We report a methodology to optimize vertically grown carbon nanotube (CNT) ultracapacitor (CNU) geometrical features such as CNT length, electrode-to-electrode separation, and CNT packing density. The electric field and electrolyte ionic motion within the CNU are critical in determining the device performance. Using a particle-based model (PBM) based on the molecular dynamics techniques we developed and reported previously, we compute the electric field in the device, keep track of the electrolyte ionic motion in the device volume, and evaluate the CNU electrical performance as a function of the aforementioned geometrical features. We show that the PBM predicts an optimal CNT density. Electrolyte ionic trapping occurs in the high CNT density regime, which limits the electrolyte ions from forming a double layer capacitance. In this regime, the CNU capacitance does not increase with the CNT packing density as expected, but dramatically decreases. Our results compare well with existing experimental data and the PBM methodology can be applied to an ultracapacitor built from any metallic electrode materials, as well as the vertical CNTs studied here.

Aligned carbon nanotube/zinc oxide nanowire hybrids as high performance electrodes for supercapacitor applications

“…High performance, cost-effective, and environmentally friendly renewable energy storage devices are crucial in order to mitigate the present energy challenge. [1][2][3][4] Among various energy storage devices, electrochemical capacitors (ECs) or supercapacitors (SCs) are considered as one of the suitable options in order to develop energy efficient, robust, sustainable energy storage systems. 5,6 This is largely due to the fact that SCs exhibit longer life cycles and faster charge/discharge capability than conventional batteries.…”

Modeling of nanohole silicon pin/nip photodetectors: Steady state and transient characteristics

“…All elements p-, i-, and n-layers are connected in series, and we study the steady state current. All current is conduction current [17][18][19] related to physical movement of charged particles, and there should be no displacement current [17][18][19][20] related to time dependence of the electric field. In developing an equivalent circuit for our PDs, it must be created by resistors only, and there should be no capacitors, as long as steady state properties are concerned, which is the entire purpose of this manuscript.…”

“…Now, / ¶ ¶ n P is a quantity indicating the density of electrons and holes in cm −3 generated per 1 mW, and is experimentally determined by 1×10 19 cm −3 from figure 1 for a PD with a round PD with a diameter of 25 μm. Our p and n doping is in the neighborhood of 5×10 19 cm −3 .…”