Preparation of D-A-D conjugated polymers based on [1,2,5]thiadiazolo[3,4-c]pyridine and thiophene derivatives and their electrochemical properties as anode materials for lithium-ion batteries

Abstract

Based on the fact that D-A-D CPs (donor-acceptor-donor conjugated polymers) can significantly improve the lithium-ion storage performance of anode materials, three D-A-D CPs (PMTP, PMOTP, and PDOTP) were prepared by simple chemical polymerization reactions with [1,2,5] thiadiazole [3,4-c] pyridine as the acceptor unit and methylthiophene (MTh), methoxythiophene (MOTh), and 3,4-ethylenedioxythiophene (EDOT) as the donor unit, respectively. Each polymer was compounded in situ with the carbon nanotubes (CNTs) to prepare the PMTP@CNT, PMOTP@CNT, and PDOTP@CNT, respectively, all of which were used as the anode materials for the lithium-ion batteries. The capacities of PMTP, PMOTP, and PDOTP were 762.6, 933.4, and 1351.4 mAh g−1 after 160 cycles at 0.1 A g−1, respectively. The order of magnitude of the specific capacity of the three polymers was PDOTP > PMOTP > PMTP, which was due to the fact that with the increasing electron-donating ability of the donor unit of the polymer, the LUMO energy level gradually decreased, the HOMO energy level gradually increased, and the Eg gradually decreased, resulting in an increase in its redox ability and conductivity. The Galvanostatic intermittent titration technique (GITT) showed that the lithium-ion diffusion coefficients of the three electrodes were comparable. XPS demonstrated that lithium ions were mainly stored on the CC and CN of the three polymers (PMTP, PMOTP, and PDOTP). The b-values showed that their electrochemical reactions were controlled by both the internal solid-phase diffusion process and capacitive process. The CV, GCD, cycling stability performance, and rate capability tests showed that all the three electrodes had good electrochemical performance, among which PDOTP@CNT had the best performance and was well suited as the anode material for the Li-ion battery. D-A-D CP provides a new pathway for the development of electrode materials for high-capacity lithium-ion batteries.