MSE PhD Defense - Wentian Gu

Committee members: 

Prof. Gleb Yushin (MSE, Advisor)

Prof. Faisal Alamgir (MSE)

Prof. Ting Zhu (MSE)

Prof. Alexander Alexeev (ME)

Prof. Thomas Fuller (ChBE)

Date/Time: Thursday, July 2, 9-11 am

Location: Love Building, Room 295

Title: Application of Highly Porous Carbons for Electrochemical Energy Storage Devices

Abstract: 

Highly porous carbon plays an important role in the fabrication of electrode materials, both for high-power supercapacitors and Li-ion batteries. It qualifies as suitable electrodes for high-power supercapacitors, thanks to its large surface area and high electrical conductivity. To further increase the specific capacitance of porous carbons, researchers have proposed heavy surface functionalization on carbon materials for additional pseudocapacitance. However, the potential negative effects caused by the surface functionalizations, including promoted self-discharge, shrinkage of electrochemical window of electrolyte and more sluggish rate performance, have been long-overlooked. The first part of this work discuss the effect of oxygen-containing functional groups (including hydroxyl, carbonyl and carboxyl groups) on the self-discharge behavior of carbon-based electrical double layer supercapacitors (EDLCs). The effects of carbon pore size and pore size distribution, pore alignment, electrolyte solvent and conducting ion are also studied. Based on the understandings of these multiple factors which have impact on the performance of carbon-based EDLCs, a novel S-doped activated carbon synthesized by carbonization and simultaneous activation of S-based polymers, which is almost free of  bottle-neck pores and performs excellent capacitance and capacitance retention, is developed.
Besides their essential role in carbon-based EDLCs, highly porous carbon materials have also been intensively studied as structural scaffold and conductive additives to assist the highly capacitive but poorly conductive active electrode materials for Li-ion batteries. The second part of this work discuss the application of mesoporous activated carbon spheres as structural matrix and conductive network which enables higher capacity, better rate retention and longer cycle life of transition metal fluoride-based cathode materials, compared to the simple mixture of non-porous conductive carbon filler and the active material.

As a whole, this dissertation expands our understandings of key parameters influencing the application of highly porous carbon materials for multiple energy storage devices, and demonstrates the possibility of improving the performance of carbon-based energy storage devices via optimizing these parameters.