The development of flexible display, wearable electronics and foldable phones has attracted more and more attention. To date, it is not only a concept but also a real commercial product in the market. The development of these lightweight and flexible smart electronics urgently calls for the adaptive new-concept energy storage devices.

Flexible micro-supercapacitors (MSCs) exhibit the properties of short ion diffusion distance, high power density, superior cycling lifetime, robust mechanical flexibility and high safety. They are considered as one of the most promising power sources candidates for full integration into the manufacturing process of electronics.

Scientists WU Zhongshuai, BAO Xinhe and et al. from Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), collaborated with REN Wencai and CHENG Huiming from Institute of Metal Research of CAS, developed a simple approach to fabricate flexible MSCs. Such devices can be used as the new-concept energy storage system and can accelerate the development of flexible electronics.

Ilustration of simplified fabrication of phosphorene/graphene planar MSCs and the demonstration of serially interconnected MSCs (Image by XIAO Han and ZHAO Xuejun)

These new-developed interdigital patterned MSCs were based on stacking high-qualified few-layer phosphorene nanosheets and electrochemically exfoliated graphene in ionic liquid electrolyte, which exhibited a high-energy density and excellent flexibility. Moreover, these flexible MSCs showed good stability without capacitance fluctuation even under highly folded states.

The fabrication method of these obtained MSCs was much simple compared with previous MSCs fabrication process: The interdigital electrode patterns can be obtained by only one-step-mask assistance filtration. The hybrid phosphorene and graphene films with interdigital patterns were manufactured by layer-by-layer deposition of phosphorene and graphene nanosheets. A customized interdigital mask assistance is needed during this process. Then the films were directly transferred onto a flexible substrate.

Scientists found that these patterned phosphorene and graphene films present good properties of uniformity, flexibility, conductivity (319 s/cm) and structural integration. The energy density of this MSCs can reach to as high as 11.6 mWh cm^-3 in ionic liquid electrolyte.

In addition, the fabrication method of MSCs is not only very simple, but also highly flexible for simplified production of parallel and serial interconnected modular power sources, without need of conventional metal-based interconnects and contacts, for designable integrated circuits with high output current and voltage.

The above work was published online in ACS Nano（DOI: 10.1021/acsnano.7b03288). It was funded by Thousand Youth Talents Plan of China, Ministry of Science and Technology of China, National Natural Science Foundation of China, Natural Science Foundation of Liaoning Province and DICP, and China Postdoctoral Science Foundation.