ALL SOLID-STATE FLEXIBLE SUPERCAPACITORS WITH VERTICALLY ALIGNED MULTIWALLED CARBON NANOTUBES (MWCNT) SYNTHESIZED DIRECTLY ON METAL FOIL

Author

Gardiyawasam L Thushani Thilanjani De Silva, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2019

Degree Name

Master of Science

Department

Physics

First Advisor

Talapatra, Saikat

Abstract

This work is mainly focused on the investigation on all solid-sate flexible supercapacitors using MWCNT directly grown on Inconel foil. Detail physical characterization of the as grown MWCNTs were performed using Scanning Electron Microscopy (SEM), Raman and Specific surface area measurement (SSA). SSA evaluated using volumetric adsorption isotherm measurements show that such MWCNTs have effective surface area of ~ 30m2/g. These as grown MWCNT on metals foils were used to fabricate the Electrochemical Double Layer Capacitors (EDLC) or Supercapacitors. A poly(vinyl alcohol)/phosphoric acid (PVA/H3PO4) polymer gel has been used as both the electrolyte and the separator. The capacitors were fabricated by dipping the as synthesized Inconel stripes in PVA/H3PO4 gel polymer and then combining two such stripes together. Several electrochemical measurements such as Cyclic Voltammetry (CV), Galvanic Charge Discharge (GCD) cycling and Electrochemical Impedance Spectroscopy (EIS) were performed on multiple devices in order to establish these structures as viable energy storage systems. Key device parameters measured and analyzed along with standard electrochemical circuit modeling indicates that these devices have Specific Capacitances (CSP) in the mF range with a low internal resistance. The low internal resistance could be a consequence of growing the MWCNTs directly on metal foils. The highest areal capacitance measured was 19.6 mF/cm2 at 1mVs-1. The flexibility and robustness of the devices were tested by performing the aforementioned measurements at different bending angles. Our measurements indicate that these devices can withstand a large number of such bending cycles (~ 2000) without losing any functionality. It was however observed that these capacitors sustain physical damage for bending cycles > 2000 cycles and loose ~50% of their capacitance values. A detailed energy density and power density analysis confirmed that the performance of these devices is in the rage of Supercapacitors. The device parameters can be further improved by thermal annealing of the as grown electrodes in air. A summary of the comparison with other work is also presented.