Low-cost micro-supercapacitors using porous Ni/MnO2 entangled pillars and Na-based ionic liquids

The enhanced areal energy of three-dimensional (3D) micro-supercapacitors has made these miniaturized energy-storage components increasingly important at the dawn of the Internet of Things. Although ultrahighcapacitances have been obtained with Ru-based pseudocapacitive materials, their substitution with abundant non-noble transition metals is a key requirement to reduce the price of electrochemical micro-storage systems and enable long-term sustainability. Here we report a cost-effective and industrially feasible approach to realize 3D micro-supercapacitors based on highly porous scaffolds of Ni/MnO2. These low-price electrodes exhibit a huge areal capacitance exceeding 4 F cm-2 and excellent cycling stability. In addition, extended cell voltages up to 2.6 V with areal energy of 1159 mJ cm-2 (i.e. 0.3 mWh cm-2) and high power of 11.1 mW cm-2 were achieved using innovative Na-based ionogel electrolytes. We also show a novel micro-supercapacitor design based on entangled porous Ni/MnO2 pillars, combining both energy and power ability on a small footprint area.