High-Energy and High-Power Nonaqueous Lithium-Ion Capacitors Based on Polypyrrole/Carbon Nanotube Composites as Pseudocapacitive Cathodes.

The energy density of present lithium-ion capacitors (LICs) is greatly hindered by the limited specific capacities of porous carbon electrodes. Herein, we report the development of a nonaqueous LIC system by integrating two reversible electrode processes, that is, anion doping/undoping in a core-shell structured polypyrrole/carbon nanotube (Ppy@CNT) composite cathode and Li+ intercalation/deintercalation in a Fe3O4@carbon (C) anode. The hybrid Ppy@CNT is utilized as a promising pseudocapacitive cathode for nonaqueous LIC applications. The Ppy provides high pseudocapacitance via the doping/undoping reaction with PF6- anions. Meanwhile, the CNT backbone significantly enhances the electrical conductivity. The as-developed composite delivers noteworthy capacities with exceptional stability (98.7 mA h g-1 at 0.1 A g-1 and retains 89.7% after cycling at 3 A g-1 for 1000 times in Li-half cell), which outperforms state-of-art porous carbon cathodes in present LICs. Furthermore, when paired with Fe3O4@C anodes, the as-developed LICs demonstrate a superior energy density of 101.0 W h kg-1 at 2709 W kg-1 and still maintain 70 W h kg-1 at an increased power density of 17 186 W kg-1. The findings of this work provides new knowledge on the cathode materials for LICs.