High performance electrode material for Li-organic battery based on quinoxalin-thiophene conjugated polymer/carbon powder composite

Abstract

In this work, thiophene derivatives were selected as donor units and pyrazine derivatives as receptor units to synthesize two composite materials consisting of supercapacitor carbon (SC) loaded with poly [2,3-bis (2-pyridinyl)-5,8-bis (2-thiophenyl) quinoxaline] (PPTQ) or poly [2,3-bis (2-pyridinyl)-5,8-bis (2-(3,4-ethylenedioxythiophene) quinoxaline] (PPETQ) by cationic radical polymerization. First, chemical bonds structure, surface morphology, and element valence states of these materials were characterized by infrared (IR), scanning electron microscopy (SEM) and XPS in turn. CV curves were used to determine their initial oxygen reduction potentials and to calculate their HOMO and LUMO values, both polymers have a narrow band gap, with E_g values lower than 2 eV. The polymer composite materials were tested as anodes in lithium-ion batteries, with a lithium sheet used as the counter electrode. Then the constant current charge-discharge and electrochemical impedance spectroscopy (EIS) impedance were measured. The first discharge specific capacities of PPTQ@SC and PPETQ@SC were 895.9 mAh/g and 913.0 mAh/g at a current density of 100 mA/g, the formation of a SEI film occurred in the second cycle, and their coulomb efficiencies can reach more than 90% from the third cycle, and the discharge platform appeared at about 1.0 V. In contrast, due to its stronger electron-donating ability, the PPETQ polymer containing the 3,4-ethylenedioxythiophene (EDOT) group have better electrical conductivity and its honeycomb structure provides more active sites for the lithiation/delithiation redox process. Therefore, the specific capacity of PPETQ@SC are all higher than that of PPTQ@SC at different current densities.