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De Novo Nanostructures and Their Applications in Energy Storage

  • Author(s): Wang, Wei
  • Advisor(s): Ozkan, Cengiz S
  • et al.
Abstract

Nanostructured synthetic carbon allotropes are considered good candidates for applications in electronics and energy storage devices due to the unique combination of their physical and chemical properties. In this thesis, synthesis of nanostructured carbon materials including pillared CNT and graphene nanostructures (PGN), cone-shape CNT clusters (CCC), and graphene and CNT (GM) hybrid foam have been developed. Potential applications in electrochemical energy storage devices including supercapacitors (SCs) and lithium ion batteries (LIBs) have been demonstrated.

The seamlessly connected graphene and CNT pillars in PGN provide a relatively strong active material-current collector connection integrity, which facilitates conduction of electrons in the system. LIB based PGN electrode shows a reversible capacity of 900 mAh g-1. Moreover, with a subsequent inductively coupled plasma (ICP) treatment on PGN, an CCC structure is achieved. The cone-shape nature can be advantageous due to a decrease in homogeneity and in surface area of the array which provides interpenetrating channels and minimizes the effects of solid electrolyte interface (SEI) formation during lithiation and delithiation. LIBs based on Si-CCC architecture demonstrates high reversible capacity of 1954 mAh g-1.

Furthermore, a three-dimensional (3D) GM foam is grown on industrial grade metal foam foils and applied as electrodes for SCs. SC based on GM foam demonstrates a high specific capacitance of 286 F g-1 which leads to an energy density of 39.72 Wh kg-1 and a superior power density of up to 154.67 kW kg-1. Improved functionality of carbon materials via a non-invasive, high-throughput, and inexpensive UV generated ozone (UV-ozone) treatment has been developed and systematically studied. This process allows precise and continous tuning of the transition of GM foam from ultrahydrophobic to hydrophilicwithin 60 sec. Hydrothermally synthesized α-MnO2 nanowires are integrated onto the GM foam by a simple bath deposition which yields a monographical graphene foam conformally covered with intertwined, densely packed CNT/MnO2 nanowire nanocomposite network. SC based on GMM show an extended operational voltage window of 1.6 V in aqueous electrolyte. A high specific capacitance (1108.79 F g-1) is also achieved. The SC based 3D chrysanthemum-like carbon nanofiber (CNF) foam architecture demonstrates a high areal capacitance of 1.37 F/cm2 (gravimetric specific capacitance: 23.83 Fg-1), which leads to superior values for per-area energy density (0.19 Wh cm-2) and power density (141.77 W cm-2).

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