Charge-transfer complex promotes energy storage performance of single-moiety organic electrode materials in aqueous zinc-ion battery at low temperatures

Abstract

Charge-transfer organic materials are molecular metallic materials with high electronic conductivity, but their potential in rechargeable batteries, especially at low temperatures, has not been investigated. In this work, micro-structured organic charge-transfer complex tetrathiofluorene-7,7,8,8-tetroquinolinedimethane (TTF-TCNQ) is applied as cathode material in aqueous zinc-ion batteries (AZIBs). Ionic storage behavior of TTF–TCNQ complex is systematically investigated from 25 ℃ to −40 ℃. Owing to higher electrical conductivity and higher ionic diffusivity in ionic storage, smaller charge transfer resistance, and lower activation energy, TTF-TCNQ shows much superior rate and cycling performance than each single-moiety counterpart, especially at low temperatures. Reaction mechanism is explored by ex-situ X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier Transform infrared spectroscopy (FT-IR) and in-situ Raman technologies, confirming that CN and CS groups are the redox centers and the redox reaction is highly reversible. Our research not only provides a new type of choice for AZIBs at low temperatures, but also greatly broads the application field of charge-transfer complexes.