Flexible electrode materials with excellent cycle performance and high capacity for lithium ion batteries remain elusive. In this study, we first annealed polypyrrole coatings electrodeposited onto carbon fibre (CF) in nitrogen to obtain N-doped CF (NCF) with a high specific area (84 m(2) g(-1)). The NCF was treated in sodium azide solution at a hydrothermal environment to obtain a dual N-doped NCF (NNCF) with enhanced conductivity. The NNCF electrode delivered high reversible areal capacity (up to 4.55 mAh cm(-2)) and excellent cycle performance (97.32% retention after 200 cycles). A flexible lithium ion battery with structural flexibility was then assembled by employing the NNCF as anode electrode and NNCF-LiCoO2 as cathode electrode. The device exhibited a high discharge capacity of 0.2 mAh cm(-2) at 0.2 mA cm(-2) with a working voltage of 2.6 V. The excellent performance was attributed to the excellent conductivity and high specific area of the NCF, which facilitated the insertion of Li+ ion.