Trapping Halogen Anions in Cationic Viologen Porous Organic Polymers for Highly Cycling‐Stable Cathode Materials
Zhaolei Wang, Qiao-Yan Qi, Weize Jin, Xin Zhao, Xiaoyu Huang, Yongjun Li
Abstract
Abstract Halogens, especially Br 2 and I 2 , 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 132 mAh g −1 at 0.2 C) and high average discharge voltage (≈3.0 V) 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 0.5 C), 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.