Boost Anion Storage Capacity Using Conductive Polymer as a Pseudocapacitive Cathode for High-Energy and Flexible Lithium Ion Capacitors.

Current lithium ion capacitors (LICs) have been severely plagued by the insufficient anion storage capacity of porous carbon. This work reports the exploration of conductive polyaniline (PANi) as an anion intercalation cathode to enhance the PF6- storage via fast doping/undoping reactions. The PANi is electrodeposited on an electrospun carbon nanofiber (CNF) textile (denoted as PANi@CNF), which not only provides a robust support for PANi to increase its pseudocapacity but also renders a free-standing architecture for flexible devices. The PANi@CNF composite with a dominant capacitive storage characteristic reveals high specific capacities of 158.5 mAh gPANi-1 at 1 A g-1 and 118.5 mAh gPANi-1 even at 20 A g-1, which significantly surpasses state-of-the-art porous carbons. First-principle calculations revealed the coordination of PF6- anions with -NH groups of PANi+ via F atoms through ion-dipole electrostatic interaction, which are accompanied by electron transfer. By pairing with CNF as an anode, a thin and flexible LIC was assembled, which achieves maximum energies of 106.5 Wh kg-1 under 769.0 W kg-1 and 64.5 Wh kg-1 under a super high power of 15087.1 W kg-1, together with an impressive cycling stability of 70.3% after 9000 cycles at 10 A g-1. These findings provide a facile strategy for high-energy and flexible LICs via anion storage pseudocapacitive materials.