Poly(ionic liquid)–zinc polyoxometalate composite as a binder-free cathode for high-performance lithium–sulfur batteries

Abstract

The development of the most promising next-generation Li–S batteries with high utilization of sulfur while retaining high capacity is one of the great challenges of the 21st century. Here, we reported sandwich polyoxometalate [WZn₃(H₂O)₂(ZnW₉O₃₄)₂]¹²⁻ (ZnPOM) over a poly(1-vinyl-3(2-(2-methoxyethoxy)ethyl)imidazolium) cation (PVIMo) matrix as a binder-free cathode catalyst for a high-capacity LiS battery with a high areal loading of 7.68 mg cm⁻² and high areal capacity of 11.14 mA h cm⁻² (70% sulfur). The synergistic effect between PVIMo and ZnPOM resulted in outstanding initial discharge capacity of 1450 mA h g⁻¹ at 0.5 C with high capacity retention (97%), high coulombic efficiency (>98%) and a negligible capacity fading rate of 0.02% per cycle at an electrolyte/sulfur ratio of 10 μL_(E) mg_(S)⁻¹ and capacity fading of only 0.02% per cycle. The cationic polymer PVIMo held the negatively charged polysulfide ions at the cathode and ZnPOM facilitated the conversion of polysulfides to sulfur. Quantitative estimation by EQCM, UV-Vis analysis and potentiometric titration demonstrated negligible loss of sulfur even after 120 cycles of the charge–discharge process.