Nanotube-like hard carbon as high-performance anode material for sodium ion hybrid capacitors

Sodium ion hybrid capacitors (SIHCs) are of great concern in large-scale energy storage applications due to their good energy-and-power characteristic, as well as abundant reserves and low cost of sodium. However, the sluggish faradaic kinetics of anode materials severely limit the overall electrochemical performance of SIHC devices. Herein, we report an application of nanotube-like hard carbon (NTHC) anode material prepared by high-temperature carbonization (1150°C) of polyaniline (PANI) nanotubes for high-performance SIHCs. As a result, the assembled sodium ion half-cell with NTHC shows a high reversible capacity of 419.5 mA h g−1 at 0.05 A g−1 and a good rate performance of 74.6 mA h g−1 at 2.5 A g−1 in a potential window of 0–2 V (vs. Na/Na+). On this basic, a SIHC using such NTHC as anode and a high-capacity activated carbon (APDC) as cathode is fabricated, which exhibits a high energy density of 133.0 W h kg−1 at 2850 W kg−1 and still remains 100.9 W h kg−1 at 14,250 W kg−1. Within the potential range of 1.5–3.5 V, the SIHCs display an outstanding cycling stability tested at 2 A g−1 with a good capacity retention of 82.5% even after 12,000 cycles.