Recent Developments of Planar Micro-Supercapacitors: Fabrication, Properties, and Applications

The increasing development of wearable, portable, implantable, and highly integrated electronic devices has led to an increasing demand for miniaturization of energy storage devices. In recent years, supercapacitors, as an energy storage device, have received enormous attention owing to their excellent properties of quick charge and discharge, high power density, and long life cycle with minimal maintenance. Micro-supercapacitors (MSCs) as a promising candidate for miniaturized energy storage components have undergone considerable theoretical and experimental investigations. Particularly, planar MSCs with a 2D architecture design have more attractive application prospects due to their flexible design and excellent electrochemical performance. However, the major drawbacks of MSCs are their intrinsically low energy density. For this reason, researchers have conducted much investigation to improve their energy density in order to promote their practical application. Herein, the recent development and progress of planar MSCs from the scope of the substrates, electrode materials, fabrication methods, electrochemical properties, and applications are discussed. Finally, the currently existing challenges and developments associated with planar MSCs are also discussed. All in all, planar MSCs have great application potential in various fields of electrochemical energy storage, self-powered wireless sensors, and stimuli-responsive and photoresponsive, alternating current line filtering.