Synthesis of D-A-Type Polymers Containing Thieno[3,2-b]thiophene Unit, Their Composites with Carbon, and Lithium Storage Performance as Anode Materials

Abstract

Conjugated organic polymers have attracted extensive attention due to their light weight, mechanical flexibility, and structural diversity. However, poor electronic conductivity limits their application in the electrodes of lithium-ion batteries (LIBs). In this paper, two composites of D-A (donor-acceptor) polymer and activated carbon (AC)—PTPP@AC and PTPTD@AC—were designed and successfully prepared using thieno[3,2-b]thiophene (BTh) as the donor unit, benzo [1,2-b:6,5-b′] dithiophene-4,5-dione or 7a,11a-Dihydro-3,4-dithia-7,12-diaza[a,c]anthracene as the acceptor unit and AC as the substrate. PTPP@AC and PTPTD@AC were then studied as anode materials for LIBs. The successful preparation of the target products was demonstrated by FT-IR, Raman spectra, XRD, and XPS. Electrochemical properties, such as the specific capacity, cycling stability, and rate performance of the electrode materials, were tested by cyclic voltammetry and galvanostatic charge–discharge (GCD). The storage process of lithium ions was investigated by XPS and CV tests. Compared with PTPP@AC, PTPTD@AC had a higher reversible specific capacity (247.3 mAh g−1 after 300 cycles at 0.1 A g−1), a better rate performance (at 1 A g−1, specific capacity of 87.3 mAh g−1), and a higher long-term cycling performance (after 1000 cycles of 0.5 A g−1, the specific capacity remains at 146.6 mAh g−1). The better electrochemical performance of PTPTD compared to PTPP was due to the former’s significantly higher HOMO (highest occupied molecular orbital) energy level than that of PTPP, while the Eg of PTPTD was smaller than that of PTPP. The experimental results show that D-A conjugated polymers have great potential for applications as electrode materials for rechargeable batteries.