Super-Flexible Carbon Nanofiber Networks Containing PAN/PVP and Composites Coated with NiCo2O4 Nanosheets as Self-Supporting Electrodes for Supercapacitors and Sodium-Ion Batteries**

The rapid development of wearable electronics requests a higher energy-storage-device flexibility. Nevertheless, the fabrication of high-performance electrodes for achieving the goal of super-flexibility remains challenging. In this work, novel super-flexible PAN/PVP carbon nanofiber networks (PAN/PVP CNFs, PCF) are prepared by electrospinning followed by in situ carbonisation, whose micro-mesoporous structure could disperse stress during folding and super-flexible PCF/NCONS self-supporting electrodes are fabricated through the electrodeposition of NiCo2O4 nanosheets (NCONS) with three-dimensional membrane structure on the PCF firmly. The obtained PCF/NCONS cannot only achieve 8000 times folding, but also show high electrochemical performance for both supercapacitors and sodium-ion batteries (SIBs). For supercapacitor, the specific capacitance of the PCF/NCONS reaches 1403.5 F/g at 1 A/g and it could maintain at 95.7 % after 2000 cycles. The PCF/NCONS electrodes are also used to fabricate an asymmetric supercapacitor device. The device exhibit high energy density (26.96 Wh/kg), high power density (3870.69 W/kg at 14.52 Wh/kg) and outstanding cycling stability (96.8 % retention after 3000 cycles). For SIBs, the PCF/NCONS electrodes show a high reversible capacity of 227.68 mAh/g after 100 cycles at a current density of 0.1 A/g. The super-flexible PCF/NCONS electrodes have a wide application prospect for flexible electronics.