Fabrication of novel power sources for portable and wearable devices

Abstract

Practical applications of portable and wearable electronics is linked with the development of power sources that address the physical requirements of these electronic devices, such as flexibility and a small footprint. In this work, we report on the development of several promising power sources for microdevices and flexible electronics. We fabricate microbattery on a glass substrate because this is a well-defined material and very similar to silicon, a standard material for micro-electro-mechanical systems. However, the miniaturization of a nickel/metal hydride cell requires a different method of fabrication than that of macroscale batteries. Microfabrication techniques including electrodeposition, e-beam evaporation, and magnetron sputtering can be used to fabricate the electrodes of a microbattery. Thus, we introduce a process for the deposition of intermetallic thin-film alloy on a glass substrate. We use this technique for the fabrication of a coplanar thin-film Nickel-Metal hydride microbattery with a gel electrolyte. The performance of the electrodes and the device is evaluated using electrochemical methods, including cyclic voltammetry and galvanostatic charge-discharge and electrochemical impedance spectroscopy. This work also presents the fabrication of a supercapacitor made by printing and reduction of graphene oxide inks. A leavening agent is added to enhance the capacity of the electrodes. The effect of the leavening agent electrode capacitance of the electrodes is investigated in terms of material characterization and electrochemical performance. Finally, we introduce a novel hybrid battery supercapacitor based on the combination of a self-assembled graphene hydrogel that encapsulates a vanadium solution. The electrochemical characterization of device shows that the hydrogel combines the high specific surface area of the reduced graphene oxide and the redox activity of the vanadium ions, leading to a specific capacity of 200 mAh/g. This power source can be operated as a supercapacitor, as a battery, or as a hybrid, depending on the operating conditions. Its unique power-handling capabilities depend on the rate of discharge which makes it suitable for a wide range of applications. Additionally, this device offers further significant advantages, including fast charging capability (10 minutes), high durability, and mechanical flexibility.