Micro-electrochemical capacitors: Progress and future status

Self-powered energy autonomy drives the sustainable operation of miniaturized electronics and wireless sensor networks in the current era of emerging internet of things (IoTs). Development and integration of on-chip energy storage with the harvesting modules enables autonomous functioning of microsensors for health tracking and environmental monitoring among many other micro-world requirements. By the virtue of high-power density, ultrahigh rate capabilities and longevity, microsupercapacitors (MSCs) turn out to be the maintenance-free micro-power sources. In this review, we discuss major breakthroughs in the field of MSCs over the past decade in terms of fabrication techniques, processing of electrode materials towards achieving optimal electrochemical performance metrics. The essence of moving from two-dimensional (2D) to three-dimensional (3D) electrode designs, symmetric to asymmetric devices and hybrid metal-ion capacitors is emphasized. Energy harvesting by solar, vibrational, and wireless charging show promise in developing self-powered MSCs in compatible manner. The design of MSCs for alternating current line-filtering applications, which potentially replace bulky low energy density electrolytic capacitors is highlighted. Scalable manufacturing of MSCs, ease of integration and packaging open the avenues for the maintenance-free operation of remote sensors, biomedical implantable chips, and wearable electronic gadgets in a self-sufficient manner.