The effect of temperature and bias on the energy storage of a Ru/YSZ/Ru thin-film device

Abstract

The next generation of all-solid-state thin-film energy storage devices, such as supercapacitors and pseudocapacitors, requires a wide operating temperature range to work under demanding conditions. We have conducted an electrical study of the Ru/YSZ/Ru thin film device to better understand the nature of the ionic conduction processes during the transition from the super-to pseudocapacitive regime as a function of the temperature. Also, it was correlated the storage characteristics of the device to its electrical properties. The complex modulus analysis indicates increased ion mobility with temperature. A DC bias increased the mobility by three orders of magnitude. The activation energy for the ionic mobility without and with DC bias was 1.06 eV and 1.86 eV, respectively. The difference in energy is attributed to the electrostatic repulsion originated by the decomposition of YSZ, the accumulation of ions and vacancies at interfaces, and reactions at the electrode interfaces. Galvanostatic charge-discharge showed a maximum energy density of 200 mWh/cm3 @170 °C. The transition from a super-to a pseudocapacitive behavior occurs at the temperature where redox reactions initiate at electrodes interfaces, as determined by the equivalent circuits for impedance curves. At this point, the increase of energy density becomes steeper.