Lithium-Ion Capacitor Based on LiFePO4 and Nanostructured Carbon By Electrostatic Spray Deposition

Abstract

Many efforts have demonstrated the practicability of power units based on electrical double-layer capacitors (EDLCs) to replace or complement batteries, generally because of their ability to deliver higher power density, faster charge and discharge rate as wells as longer operational life cycle. However, EDLCs exhibit relatively poor energy density. This limitation is revealed in portable electronic systems whose functions demand high energy and power density at the same time. In order to overcome the low energy density limitation of EDLCs, lithium-ion capacitors have gained much interest. Lithium-ion capacitors are hybrid electrochemical charge storage devices that combine the high energy density capability of lithium-ion batteries and the high power density in EDLCs. This is typically achieved by using electrodes based on battery-type lithium intercalating material as the high energy density source, and a capacitor-type material as the high power density source, in a lithium-containing electrolyte. In this work, we evaluated the electrochemical performance of lithium-ion capacitor comprising lithium iron phosphate (LiFePO4) battery-type cathode and reduced graphene oxide-carbon nanotube (RGO-CNT) composite as capacitor-type anode for half and full cells. The electrodes were prepared via electrostatic spray deposition (ESD) method, a thin-film deposition method capable of operating in ambient conditions. The choice of LiFePO4 is mainly because it is relatively inexpensive and exhibit attractive electrochemical properties such as good cycling stability, high intercalating potential of ~3.5 V versus Li+/Li as well as flat voltage plateaus. On the other hand, among a variety of nanostructured carbon materials, RGO-CNT composite has been shown as a good double-layer electrode material in EDLCs with high power density capability. Material characterization of the electrodes was carried out using scanning electron microscopy (SEM) and X-Ray diffractometry (XRD) respectively. Detailed results will be presented at the meeting.