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 µWh 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 m² 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.