Microfluidic-architected core–shell flower-like δ-MnO2@graphene fibers for high energy-storage wearable supercapacitors

Abstract Wire-shaped supercapacitor is an ideal candidate for wearable energy-storage devices in future. However, complex preparation process and poor capacitance of electrode materials seriously limit practical applications. Herein, we investigated a controllable method to synthesize core–shell MnO2/graphene fibers (MnGFs), where sheath flower-like δ-MnO2 were in situ growth wrapped on graphene core via microfluidic-spinning techniques. The MnGFs possess excellent mechanical flexibility and can be repeatedly bent without damage. Moreover, a flexible wire-shaped supercapacitors (MGSCs) assembled by MnGFs is successfully manufactured and display high capacitance (164.2 F cm−3), prominent energy density (4.3 mWh cm−3), and brilliant cycling stability (93.6% retention over 10,000 cycles). These comprehensive properties of MGSCs are obtained from MnGFs with porous and well-aligned core–sheath structure, resulting in abundant electron transport channels and rich ion pseudo-capacitance. Based on these achievements, the synthesized MGSCs can be employed to light up LEDs and electronic timers. This microfluidic strategy offers an extended design approach of electrochemically active electrode materials and guides the development of wearable fiber-shaped energy storage devices.