Preparation and electrochemical properties of thieno-[3,4-b] pyrazine conjugated polymer composite supercapacitor carbon powder electrode materials for Li-organic battery

In this work, two D-A monomers 2,3-di(5-methylfuran-2-yl)-5,7-di(thiophene-2-yl) thiopheno[3,4-b] pyrazine (MFTTP) and 2,3-di(5-methylfuran-2-yl)-5,7-di(4-methoxythiophen-2-yl) thiopheno [3,4-b] pyrazine (MFMOTTP) were first obtained by Stille Coupling reaction, and then the corresponding composites were obtained by in-situ oxidative polymerization method with supercapacitor carbon. The surface morphology, chemical structure, and the element valence states of two materials were characterized by scanning electron microscopy, infrared and XPS, respectively. The specific surface areas of PMFTTP@SC and PMFMOTTP@SC are measured as 756.5 and 954.9 m²/g, respectively. The CV curves were used to determine the initial oxidative and initial reduction potentials, both polymers have a narrow band gap with E_g values below 1.5 eV, electron clouds in the HOMO and LUMO orbits of the polymer are mainly distributed on the aromatic rings of the polymer backbone. Polymer composite materials were used as the anode materials and the lithium sheets were used as counter electrode, and then lithium ion batteries are assembled. The first discharge specific capacities of PMFTTP@SC and PMFMOTTP@SC are 741.9 and 951.3 mAh/g at a current density of 100 mA/g, and as the electrodes are activated in the subsequent cycles, their coulomb efficiencies can reach more than 92% from the third cycle. In contrast, PMFMOTTP with methoxy-thiophene as the donor unit has higher conductivity and lower corresponding impedance due to its stronger electron donating ability and abundant pore structure, which is also more conducive to the lithiation/delithiation redox process.