Continuous composite fibers have been obtained by online modifying the direct-spun carbon nanotube (CNT) fibers with active materials (LiFePO 4 or LiTi 2 PO 4 ) through dipping and twisting. The composite fibers exhibit high specific capacity and good rate performance for an aqueous lithium-ion battery with 1 M Li 2 SO 4 electrolyte, due to the fast electron transport arising from the close contact between the active materials and CNTs. A flexible fiber-shaped aqueous lithium-ion battery fabricated from the composites can deliver a high specific capacity of 29.1 mAh g −1 at a current density of 0.25 A g −1 and a high energy density of 30.12 Wh kg −1 , showing the great potential of the composite fibers for applications in flexible energy storage devices
