High-Efficiency Lithium Sulfur Cells With Suppressed Polysulfide Solubility Using a Cost-Effective Ammonium-Based Ionic Liquid Electrolyte

Depth-resolved x-ray photoelectron spectroscopy (XPS) reveals that N1113FSI forms abundant LiF through efficient anion reduction, yielding a dense, inorganic-rich solid-electrolyte interphase (SEI). In contrast, P111i4FSI retains incompletely reduced anions and exhibits diminished LiF, demonstrating cation-dependent control of SEI chemistry. The N1113FSI interphase contains higher levels of LiF, Li-sulfide, oxidized sulfur, and inorganic oxygen species, which correlate with superior cycling stability.

Compared to P111i4FSI, N1113FSI achieves higher discharge capacity (DC), faster Coulombic efficiency (CE) stabilization, and sustained reversibility. Tailored IL design effectively suppresses polysulfide solubility and engineers efficient SEI chemistry, mitigating shuttle effects and enabling stable Li–S operation across varying electrolyte concentrations.