| dc.description.abstract | Activated carbon is an essential component for the supercapacitor′s electrodes preparation, whose properties and interactions greatly affect the performances of supercapacitors. Pore structure, electronic properties, and chemical and electrochemical properties of carbon material have been identified as the main factor on reliability problem and self-discharge of supercapacitors, which need to be solved by industrially practical methods.
The first part of this dissertation reported the molecular level manipulation of nitrogen groups configuration on carbon surface that was conducted via post-heat treatment some precursors; melamine, ammonia, and nitrogen monoxide gas. XPS spectral confirmed that NO gas prefers to form higher N-Q formation through nitrogen substitution reaction in carbon bulk, which increased electronic and ionic conductivity. Compared with other electrodes, AC-NO electrode exhibited excellent electrochemical performance and cycle life stability at potential ranges of 2.5 V−3.0 V, due to higher concentration N-Q+N-O groups without much losses of surface area and pore volume. The galvanostatic charge-discharge curve confirmed that the charge storage of AC electrodes is controlled by electrical double layer formation. It also found that the charge leakage and gas evolution of the AC electrode depended on the type of N group, which N-Q being more favorable than N-5 and N-6 to suppress unwanted faradic side reactions. Another advantage, AC-NO with higher N-Q concentration allowed to increased electrode thickness and enlarging cell voltage up to 3.0 V without much reducing the electrochemical performances and electrode structure integrity.
From active material modification to electrode fabrication, this dissertation also describes the effects of various pore structures of binder-modified carbon electrodes on self-discharge behavior and reliability of supercapacitors. The use of CMC+SBR binder preserved specific surface area, pore volume and create more mesopore than PVDF and PTFE binder, leading to higher charge-storage capacity, high retention rate, and better cycle life stability for 3000 cycles. AC+CMC+SBR electrode also showed lower interfacial resistance (Rinter), higher electronic conductivity (σ), and apparent diffusion coefficient (Da) than other AC electrodes. Further investigation on reliability study showed that AC+CMC+SBR electrode had lower leakage current at voltage ranges of 2.4−3.5 V which indicated less parasitic faradic side reactions in organic electrolyte. Dual-phases of SDs were AC+CMC+SBR electrode, charge redistribution, and unwanted faradic side reaction, with the lowest total voltage decay for 50 h which could be attributed to the higher electronic conductivity, high mesopore ratio, and high stability of CMC+SBR. Moreover, employing CMC+SBR binder allowed applying the carbon electrode in severe environments, high voltage, and/or high temperature. SDs post-mortem analysis confirmed that AC+CMC+SBR electrode had the lowest interfacial resistance, better diffusion coefficient, and no impurity diffraction peaks which indicated CMC+SBR binder facilitates preferable charge distribution and prevent undesired parasitic faradic side reactions during severe operation. | en_US |