Indolocarbazole-­Based Small Molecule Cathode-­Active Material Exhibiting Double Redox for High-­Voltage Li­-Organic Batteries

Abstract

Most organic electrode materials (OEMs) for rechargeable batteries employ n-type redox centers, whose redox potentials are intrinsically limited <3.0？V versus Li+/Li. However, p-type materials possessing high redox potentials experience low specific capacities because they are capable of only a single redox reaction within the stable electrochemical window of typical electrolytes. Herein, we report 5,11-diethyl-5,11-dihydroindolo[3,2-b]carbazole (DEICZ) as a novel p-type OEM, exhibiting stable plateaus at high discharge potentials of 3.44 and 4.09？V versus Li+/Li. Notably, the second redox potential of DEICZ is within the stable electrochemical window. The mechanism of the double redox reaction is investigated using both theoretical calculations and experimental measurements, including density functional theory calculations, ex situ electron spin resonance, and X-ray photoelectron spectroscopy. Finally, hybridization with single-walled carbon nanotubes (SWCNT) improves the cycle stability and rate performance of DEICZ owing to the π？π interactions between the SWCNT and co-planar molecular structure of DEICZ, preventing the dissolution of active materials into the electrolyte. The DEICZ/SWCNT composite electrode maintains 70.4% of its initial specific capacity at 1-C rate and also exhibits high-rate capability, even performing well at 100-C rate. Furthermore, we demonstrate its potential for flexible batteries after applying 1000 bending stresses to the composite electrode.