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Matls 701/702: Wenjuan Yang, PhD Candidate

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ABB 163

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materials@mcmaster.ca

Advanced Supercapacitor Electrodes and Devices for Energy Storage

Overview

Supercapacitors are currently of significant interest for energy storage due to their high power, fast charge/discharge and good cycling stability. MnO2 is a promising electrode material for supercapacitor electrodes due to its high theoretical capacitance of 1380 F g-1 in a wide potential window and neutral electrolytes. However, it is challenging to achieve high capacitance at practically important high active mass loadings due to low electronic conductivity of MnO2 and poor electrolyte access to the material surface. This problem can be addressed by the development of composites containing non-agglomerated MnO2 nanoparticles mixed with carbon nanotubes as conductive additives.

However, the fabrication of non-agglomerated nanoparticles of small size presents difficulties due to the use of highly reactive permanganate precursors, which react with capping agents. This problem was addressed by the synthesis of Mn3O4 from Mn2+ solutions in the presence of new capping agents, which facilitated the formation of small non-agglomerated nanoparticles, acted as co-dispersants for Mn3O4 and carbon nanotubes and improved their mixing. Electrochemical oxidation allowed for in-situ conversion of the Mn3O4 particles to the electrochemically active MnO2 phase.

As a result, a record high capacitance of 8 F cm-2 was achieved for composite electrodes. The transformation kinetics was studied by different electrochemical and chemical techniques. The analysis of testing results for different capping agents provided an insight into the influence of the chemical structure of the capping agents on the material microstructure and performance.  The Mn3O4-carbon nanotube electrodes outperformed MnO2-carbon nanotube electrodes of the same mass. The new approach developed in this investigation paves the way for the fabrication of advanced electrodes for supercapacitors