Trapping Halogen Anions in Cationic Viologen Porous Organic Polymers for Highly Cycling-Stable Cathode Materials.

Abstract

Halogens, especially Br2 and I2 , as cathode materials for lithium-ion batteries exhibit high energy density with low cost, but poor cycling performance due to their high solubility in electrolyte solution. Herein, viologen-based cationic porous organic polymers (TpVXs, X=Cl, Br, or I) with abundant pores and ionic redox-active moieties are designed to immobilize halogen anions stoichiometrically. TpVBr and TpVI electrodes exhibit high initial specific capacity (116 and 132mAhg-1 at 0.2C) and high average discharge voltage (≈3.0V) without any host materials. Notably, benefiting from the porous and ionic structure, TpVBr and TpVI present excellent long-term cycling stability (86% and 98% capacity retention after 600 cycles at 0.5C), which are far superior to those of the state-of-the-art halogen electrodes. In addition, the charge storage mechanism is investigated by in situ Raman and ex situ X-ray photoelectron spectroscopy.