Nitrogen-doped CNT on CNT hybrid fiber as a current collector for high-performance Li-ion capacitors

In this work, we describe a scalable synthesis process of binder-free, nitrogen-doped carbon nanotubes (CNTs) on CNT fibers combining a solvothermal process with chemical vapor deposition (CVD). Li4Ti5O12 was selected as an example active material to evaluate the performance of the obtained current collector electrode, which achieved 100% capacity retention after 1000 cycles at a 15C rate and a stable specific capacity of 144 mAhg(-1) at 5C. We also report here the fabrication of an asymmetrical hybrid capacitor that exhibited a maximum specific energy of 0.296 mWhcm(-2)/0.019 Whcm(-3)/68 Whkg(-1) at a specific power of 0.172mWcm(-2)/0.011 Wcm(-3)/126 Wkg(-1). It maintained specific capacitance of 0.0779 mWhcm(-2)/0.005 Whcm(-3)/17 Whkg (-1) at a high specific power of 57.05 mWcm(-2)/3.719 Wcm(-3)/12,500 Wkg(-1). The device exhibited a very stable cycling performance, retaining 100% of its specific energy after 2000 cycles at 4 Ag-1 current density. The increase in specific power, energy and cycling performance was attributed to the porous network afforded by the nitrogen-doped CNTs and their strong binding with the active material Li4Ti5O12. The porous network enabled fast Li-ion diffusion paths while the pristine CNT allowed for fast electron transfer all in a fiber format, making it attractive as an electrode for wearable energy storage devices. (C) 2019 Elsevier Ltd. All rights reserved.