Real-time insights into microporous thiophene polymer for lithium-sulfur batteries via operando X-ray imaging

This study focuses on the Microporous Thiophene Polymer (MTP-1), a porous organic polymer (POP) synthesized through environmentally friendly methods. After MTP-1 synthesis, sulfur (S₈) and the resulting compound, MTP-1/S₈, is thoroughly characterized. Electrochemical tests show that MTP-1/S₈ acts as a robust positive electrode, retaining over 70 % of its capacity after 100 cycles. UV–vis spectroscopy confirms the compound's ability to absorb and trap lithium polysulfides (LiPSs). Operando electrochemical impedance analysis reveals improved sulfur confinement in MTP-1/S₈, evidenced by smaller variations in electrolyte resistance over cycling when compared to the Carbon Black/Sulfur (CB/S₈) control electrode used as reference throughout the study. In contrast, CB/S₈ exhibits significant resistance fluctuations, indicating greater polysulfide diffusion into the electrolyte and a stronger shuttle effect. Operando X-ray radiography experiments provide insights into the processes of sulfur formation and dissolution, correlating with specific capacity values. A distinct difference is observed in the size and distribution of sulfur particles between the two systems. The CB/S₈ exhibits fewer but larger sulfur particles, suggesting lower polysulfide retention near the positive electrode. In contrast, MTP-1/S₈ displays a higher number of smaller sulfur particles, indicating better polysulfide retention and enhanced nucleation kinetics. Overall, the green synthesis, advanced characterization, and use of in-situ and operando techniques emphasize MTP-1/S₈ potential as a high-performance sulfur host. The findings contribute to lithium-sulfur battery development and improve the understanding of degradation pathways.