The unprecedented boom of portable and wearable electronics has stimulated the demand for microscale energy storage devices with various properties, especially flexibility, tailored performance according to actual situations and seamless integration with existing electronics industry systems.

Planar micro-supercapacitors (MSCs), consisting of two adjacent electrodes separated by a separator-free interspace on a single substrate, could substantially simplify integration process and avoid possibility of multilayer delamination under bending states in comparison with conventional stacked geometry. However, cost-effective and scalable fabrication of integrated MSCs is still unsolved.

A research group led by WU Zhongshuai and BAO Xinhe from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (CAS), in collaboration with researchers from the Institute of Metal Research, CAS, developed rapid and scalable fabrication of ultrahigh-voltage integrated micro-supercapacitors (IMSCs) with designable shapes and superior flexibility.

Schematic of screen-printing fabrication of IMSCs; Photographs of IMSCs with various geometries and diverse integration; Photograph of letter-shaped IMSCs powering 3 liquid crystal displays. (Image by SHI Xiaoyu and HOU Xiaocheng)

Through elaborated selection and optimization of active material, conducting additive and polymer binder, the scientists prepared highly stable and conducting graphene-based ink with outstanding rheological, electrical and electrochemical properties.

With assistance of a universal, cost-effective, industrially applicable screen-printing strategy, they demonstrated fast and scalable fabrication of graphene-based planar IMSCs, with shape diversity, aesthetic versatility, and outstanding flexibility.

More importantly, by using the highly conductive ink as current collectors, microelectrodes and interconnects simultaneously, they directly screen-printed IMSCs consisting of hundreds of individual MSCs on arbitrary substrates in several seconds.

The resulting IMSCs are free of metal current collectors and interconnects as well as separators, and exhibit exceptional electrical double-layer capacitive behaviors and remarkable flexibility.

Notably, the output voltage and capacitance of IMSCs are readily adjustable through connection in well-defined arrangements of MSCs. As a proof of concept, a tandem energy storage pack of IMSCs with 130 MSCs can output a recorded voltage exceeding 100 V, demonstrative of superior modularization and performance uniformity.

This work exhibits great potential for scalable fabrication and integration of other planar energy storage devices, such as hybrid capacitors and batteries.

The work published in Energy & Environmental Science was supported by the National Natural Science Foundation of China, the National Key R&D Program of China, the Natural Science Foundation of Liaoning Province.