Carbon based nano-composite materials for energy storage applications.

摘要

Energy storage systems and devices are an integral part of advanced electronic technology. Electronic technology is ever-advancing, but in order to do so, it must be supported by all its systems. The energy storage system is one key system that may dictate the performance and limitation of such electronics. Thus, research emphasis on energy storage devices has been on improving the performance of energy storage devices, such as: improved energy and power density, increased stability and cycle life, as well as reduced costs. Lithium-ion-batteries, and supercapacitors offer the potential to meet energy storage demands and to be improved further upon. Herein, novel hybrid electrode materials utilizing high surface area carbon structures and transition metal oxide nanomaterial are implemented to improve the energy storage performance in lithium-ion-battery and supercapacitor applications. Initial characterization methods for all the electrode materials include: scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction (XRD). Supercapacitor performance is improved by utilizing porous-carbon/cerium-oxide nanoparticle (PC-CON) hybrid electrode material synthesized via a low temperature hydrothermal method and using tretraethyl ammonium tetrafluroborate in acetonitrile as the organic electrolyte. This electrode material allows for a hybrid capacitance mechanism that utilizes both, electric-double-layer capacitance and pseudocapacitance. Additionally, the excellent electrode-electrolyte interaction due to the electronchemical properties of the ionic electrolyte provides a better voltage window. Electrochemical measurements performed using a potentio-galvanostat revealed that the specific capacitance was improved by 30% using PC-CON electrode material compared with pure porous carbon. Lithium-ion-battery performance is improved over porous carbon by implementing two different hybrid anode materials: one utilizing porous-carbon/cerium-oxide nanoparticles (PC-CON) and the other utilizing microwave-reduced (exfoliated) graphene-oxide/titanium-oxide nanowires (MEGO-TON). High surface area carbon structures such as porous carbon and microwave-reduced graphene oxide alone provide high lithiation and excellent cycling capability by shortening the transport length for Li+ ions with the large electrode/ electrolyte interface. Addition of a transition metal oxide structure such as cerium oxide nanoparticles, which offer a high redox potential, can enhance surface electrochemical reactivity and increase capacity retention capability for a higher number of cycles, while the addition of titanium oxide nanowires, which offer high specific surface area, serve to improve lithium-ion electrode/electrolyte intercalation. Battery performance was measured using a battery analyzer. It was determined that the PC-CON hybrid anode material showed significantly higher specific capacity and better capacity retention, while the MEGO-TON hybrid showed even better results with a specific capacity improvement of 80% over porous carbon, as well as an improved charge-discharge rate.