Ultrathin honeycomb-like MnO2 on hollow carbon nanofiber networks as binder-free electrode for flexible symmetric all-solid-state supercapacitors

Carbon nanofiber-based supercapacitors hold great promise for powering wearable electronics due to their high specific density, fast charge/discharge rate and ultralong cycling life. However, the most common polyacrylonitrile-based carbon nanofiber (CNF) is fragile and easy to break, which limits their practical application. Herein, a poly(acrylonitrile-co-p-methylhydrogen itaconate) copolymer is synthesized and used as precursor to prepare flexible hollow carbon nanofiber (HCNF) by coaxial electrospinning, which can be bended freely without breaking. Then, the ultrathin honeycomb-like MnO2 is coated uniformly on the inner and outer surface of HCNF by in-situ reduction method to prepare freestanding flexible 3D HCNF/MnO2 networks. The HCNF/MnO2 electrode exhibits high capacity 587.5 F-1 at 0.5 A g(-1) and good cycling stability 78.96% retention after 5000 cycles. The HCNF/MnO2 composite is directly utilized to fabricate symmetric all-solid-state symmetric supercapacitors (ASSCs) without using any current collector or binders. The ASSC exhibits a maximum specific energy of 59.15 Wh kg(-1) at a specific power of 1575 W kg(-1). Four ASSC in series can power a 'DHU' Logo consisted of 36 light emitting diodes, confirming the lightweight flexible HCNF/MnO2 based flexible ASSCs have great potential application in wearable and portable electronics.