On chip, all solid-state and flexible micro-supercapacitors with high performance based on MnOx/Au multilayers

In this work, we introduce a new concept to fabricate on chip, all solid-state and flexible micro-supercapacitors based on MnOx/Au multilayers, which are compatible with current microelectronics. The micro-supercapacitor exhibits a maximum energy density of 1.75 mW h cm(-3) and a maximum power density of 3.44 W cm(-3), which are both much higher than the values obtained for other solidstate supercapacitors. At a scan rate of 1 V s(-1), a volumetric capacitance of 32.8 F cm(-3) is obtained for MnOx/Au multilayer electrodes, which is much higher than the bare MnOx electrode. Electrochemical impedance spectroscopy (EIS) and evolution complex capacitance confirm that the electrical conductivity of MnOx is improved due to the incorporation of gold, and a lowrelaxation time constant around 5 ms is observed. The MnOx/Au multilayer micro-supercapacitor also shows good long-term cycling stability, with a capacitance retention rate of 74.1% after a large cycling number of 15 000 times. Compared with other supercapacitors, which are not portable and are relatively bulky, the device demonstrated here allows fast and reliable applications in a portable and smart fashion. Furthermore, the nature of the process allows the micro-supercapacitor to be integrated with other micro-devices, to meet the need for microscale energy storage.