In Operando FTIR Study on the Effect of Sulfur Chain Length in Sulfur Copolymer-Based Li–S Batteries

Synthesis of sulfur-rich copolymers using the inverse vulcanization reaction is a practical approach to modify the sulfur active material for enhanced stability in Li–S batteries. However, to effectively design such polymers, a thorough understanding of the underlying redox mechanisms is critical. Here, we study electrochemical behavior of sulfur-rich copolymers using in operando FTIR spectroscopy with attenuated total reflection. We used sulfur-diisopropenylbenzene copolymers [poly(S-co-DIB)] as the active material in Li–S batteries and monitored the evolution of the C–S peak position and cyclic changes in the S–S bond stretching at different potentials during discharge and charge. Moreover, we synthesized various copolymers with sulfur wt % of 80 and 30 wt % and compared the electrochemical behavior and their corresponding IR response during cyclic voltammetry sweep. Our results indicated that the C–S bond in sulfur copolymers is not active in the voltage window of Li–S batteries. Moreover, we showed that the shift in the C–S peak position becomes smaller with increase in the monomer wt %. In addition, the S–S stretching peak at ∼500 cm–1 diminishes when the sulfur wt % is decreased from 80 to 30 wt %, highlighting a significant change in electrochemical behavior of the copolymers.