All-Soft Supercapacitors Based on Liquid Metal Electrodes with Integrated Functionalized Carbon Nanotubes

Abstract

Soft energy storage devices, such as supercapacitors, are an essential component for powering integrated soft microsystems. However, conventional supercapacitors are mainly manufactured using hard/brittle materials that easily crack and eventually delaminate from the current collector by mechanical deformation. Therefore, to realize all-soft supercapacitors, the electrodes should be soft, stretchable, and highly conductive without compromising the electrochemical performance. This paper presents all-soft supercapacitors for integrated soft microsystems based on gallium–indium liquid metal (eutectic gallium–indium alloy, EGaIn) electrodes with integrated functionalized carbon nanotubes (CNTs). Oxygen functional groups on the surface of the CNTs ensure strong adhesion between the functionalized CNTs and the thin native oxide layer on the surface of EGaIn, which enables delamination-free soft and stretchable electrodes even under mechanical deformation. The electrochemical performances of fabricated all-soft supercapacitors in a parallel-plate arrangement were investigated without and with applied mechanical deformation. The fabricated supercapacitors exhibit areal capacitances as high as 12.4 mF cm–2 and show nearly unchanged performance under 30% applied strain. They maintain >95% of their original capacitance after >4200 charging and discharging cycles with a periodic applied strain of 30%. Finally, fabricated supercapacitors have been successfully integrated with a commercial light-emitting diode to demonstrate an integrated soft microsystem.

Nacre‐Inspired, Liquid Metal‐Based Ultrasensitive Electronic Skin by Spatially Regulated Cracking Strategy

“…[ 4,5 ] The realization of liquid metal‐based, integrated systems will be a significant milestone toward high‐performance, integrated electronic skin for applications such as tattoo electronics and human organs‐on‐chips. [ 6,7 ] In recent years, liquid metal has sparked revolutionary progress for many components in electronic skin, including wearable electrodes/circuits, [ 8,9 ] interconnects, [ 10 ] switches, [ 11 ] and actuators. [ 12,13 ] However, an essential “piece of the puzzle” for liquid metal‐based, integrated electronic skin is still missing, which is highly sensitive electromechanical sensors.…”

Recent advances in liquid-metal-based wearable electronics and materials

“… (B,ii) Voltammetry cycle respect to number of cells tested. (B,iii) Reproduced with Permission ( Kim et al., 2020e ). Copyright, American Chemical Society.…”

“…With an aid of LM alloy, Kim et have demonstrated that all soft supercapacitors can be constructed by synergistically combining it with an oxygen functionalized carbon nanotube (O-CNT) ( Kim et al., 2020e ). The EGaIn (≈1.5 μm) as an LM electrode is stamped onto paper-textured PDMS substrate layer first to serve as a support electrode for O-CNT electrode and form a strong bonding with its native oxide ( Figure 7 Bi) ( Kim et al., 2020e ). Thus, this proposed architecture can withstand applied strains without delamination between high conductive electrical pathways and 3D CNT network.…”

Recent Advances in Deformable Circuit Components with Liquid Metal

“…Liquid metal power sources have been demonstrated to achieve flexibility and stretchability while maintaining electrical performance stability and high sensitivity, which presents a better alternative for self‐powered and deformable devices than conventional power sources. These liquid metal‐based deformable power sources include using liquid metal electrodes for all‐soft supercapacitors that are electrochemically and mechanically stable, [ 147 ] liquid metal batteries that are operational at room temperature, [ 148 ] and energy storage batteries employing liquid metal electrodes. [ 149 ] State‐of‐the‐art liquid metal power sources generally take one of three forms: triboelectric generators, thermoelectric generators, and magnetic field harvesting devices.…”