Free-standing fluorine and nitrogen co-doped graphene paper as a high-performance electrode for flexible sodium-ion batteries

Free-standing fluorine and nitrogen co-doped graphene paper (FNGP) electrodes were synthesized by a solvothermal process as potential anodes for flexible sodium-ion batteries (SIBs). F and N co-doping in the graphene frameworks simultaneously increases structural defects, provides active sites, and enlarges the graphene interlayer distance; these properties are favourable for improving Na+ storage capabilities. In particular, the semi-ionic C-F bonds in FNGP, prepared at a solvothermal temperature of 120 degrees C, enhance electrical conductivity and hence facilitate electron transport in the electrode. Therefore, this FNGP anode delivers a reversible capacity of 203 mAh g(-1) (114.9 mAh cm(-3)) at 50 mA g(-1) after 100 cycles and exhibits superb long-cycling stability with a reversible capacity of 56.3 mAh g(-1) at 1 A g(-1) after 5000 cycles. In addition, the excellent tensile strength (43.5 +/- 1.8 MPa) and maintained electrochemical performance of the FNGP anode in the bent state demonstrate the promise of this electrode for applications in flexible, wearable and rolled-up devices. (C) 2017 Elsevier Ltd. All rights reserved.