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

Abstract

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 0.172 mWcm−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.