Ultrafast stimulated resonance Raman signatures of lithium polysulfides for shuttling effect characterization: An ab initio study.

The shuttling effect is a crucial obstacle to the practical deployment of lithium sulfur batteries (LSBs). This can be ascribed to the generation of lithium polysulfide (LiPS) redox intermediates that are soluble in the electrolyte. The detailed mechanism of the shuttling, including the chemical structures responsible for the loss of effective mass and the dynamics/kinetics of the redox reactions, are not clear so far. To obtain this microscopic information, characterization techniques with high spatial and temporal resolutions are required. Here, we propose that resonance Raman spectroscopy combined with ultrafast broadband pulses is a powerful tool to reveal the mechanism of the shuttling effect. By combining the chemical bond level spatial resolution of resonance Raman and the femtosecond scale temporal resolution of the ultrafast pulses, this novel technique holds the potential of capturing the spectroscopic fingerprints of the LiPS intermediates during the working stages of LSBs. Using ab initio simulations, we show that, in addition to the excitation energy selective enhancement, resonance Raman signals of different LiPS intermediates are also characteristic and distinguishable. These results will facilitate the real-time in situ monitoring of LiPS species and reveal the underlying mechanism of the shuttling effect.