Super-capacitor and thin film battery hybrid energy storage for energy harvesting applications

This paper presents the design of hybrid energy storage unit (HESU) for energy harvesting applications using super-capacitor and thin film battery (TFB). The power management circuits of this hybrid energy storage unit are proposed to perform "smart" charge/discharge control in order to optimize the HESU from the perspectives of energy loss due to leakage current and equivalent series resistance (ESR). This paper shows the characterizations of ESUs for energy harvesting powered wireless sensor networks (WSN) applications. A new design of power management circuits is proposed in order to utilize the low ESR characteristics of super-capacitor and the low leakage current characteristics of the TFB in the hybrid energy storage. The average power loss due to leakage current is measured at 38μW in the proposed system. When Compared to the super-capacitor energy storage with the similar capacity, the proposed hybrid energy storage unit reduces the leakage power by approximately 45% whilst maintains a similar (<100 mΩ) ESR.