Chapter 13 - Summary and future perspectives

Abstract

The high aspect ratio and mechanical flexibility of these atomically 2D nanosheets provides a unique environment for the assembly of thin film structures required for the fabrication of flexible supercapacitors. Self-stacking of these 2D nanosheets, owing to the strong van der Waals interaction between adjacent nanosheets, can be effectively alleviated by creating new compositions with other nanomaterials or by forming novel three-dimensional (3D) porous structures. Currently significant advances have been made for the fabrication of flexible and lightweight supercapacitors using 2D materials. However, some challenges still remain if we are to produce flexible robust supercapacitors with high energy density, high power density, excellent cycling stability, and low cost. For example, control of the quality of 2D nanosheets produced via wet-chemistry approaches remains a challenge. Strong and stable interaction between electrolyte and electrode, in particular during the long-term deformation process, is critical to high-performance flexible supercapacitors. With the creation of 3D porous structures to enable high energy and power density, the volumetric capacitance and mechanical flexibility are often compromised. Apart from novel electrode materials, safe electrolytes with a wide electrochemical window such as ionic liquid are highly desirable for achieving high energy density. In addition, to achieve energy autonomy (i.e., self-powered integrated circuits or microelectromechanical systems) the integration of supercapacitors with solar, thermal, or mechanical energy harvesting systems is to be pursued. A supercapacitor is an energy storage component to compensate for the intermittency generated by those renewable sources, and provide consistent power to deployed devices. The downscaling of electronic devices and power sources to microscale is the current direction, which may be achieved by 3D printing, a layer-by-layer technology. It has emerged as an innovative approach to fabricate energy storage devices from the macroscale down to the nanoscale. It provides freedom and accurate control over the device geometry and architecture, which will greatly promote the development of microscaled supercapacitors and their integration with energy generators. We must continue to consider the whole pipeline from source to processing of 2D materials, fabrication approaches to final products if practical devices are to be realized.