High-Performance Wearable Micro-Supercapacitors Based on Microfluidic-Directed Nitrogen-Doped Graphene Fiber Electrodes

Fiber-shaped micro-supercapacitors (micro-SCs) have attracted enormous interest in wearable electronics due to high flexibility and weavability. However, they usually present a low energy density because of inhomogeneity and less pores. Here, we demonstrate a microfluidic-directed strategy to synthesize homogeneous nitrogen-doped porous graphene fibers. The porous fibers-based micro-SCs utilize solid-state phosphoric acid/polyvinyl alcohol (H3PO4/PVA) and 1-ethyl-3-methylimidazolium tetrafluoroborate/ poly(vinylidenefluoride-co-hexafluoropropylene) (EMIBF4/PVDF-HFP) electrolytes, which show significant improvements in electrochemical performances. Ultralarge capacitance (1132 mF cm(-2)), high cycling-stability, and long-term bending-durability are achieved based on H3PO4/PVA. Additionally, high energy densities of 95.7-46.9 mu Wh cm(-2) at power densities of 1.5-15 W cm(-2) are obtained in EMIBF4/PVDF-HFP. The key to higher performances stems from microfluidic-controlled fibers with a uniformly porous network, large specific surface area (388.6 m(2) g(-1)), optimal pyridinic nitrogen (2.44%), and high electric conductivity (30785 S m(-1)) for faster ion diffusion and flooding accommodation. By taking advantage of these remarkable merits, this study integrates micro-SCs into flexible and fabric substrates to power audio-visual electronics. The main aim is to clarify the important role of microfluidic techniques toward the architecture of electrodes and promote development of wearable electronics.