Choline based poly-ionic liquid as outstanding binder for LiS batteries

Abstract

A PIL binder based on Choline, designed and synthesized via RAFT polymerization, has shown an impressive effect on the overall performance of the LiS system. The rational design of the polymer facilitates significant interactions with polysulfide species, keeping them confined within the cathodic compartment and thereby improving the system's lifespan. Although complex interactions and continuous cycling are influenced by several factors, the molecular weight of the PIL can notably affect interactions during sulfur expansion and contraction. Additionally, the entanglement of polymer chains and the anion size influence direct interactions with polysulfides.

To address these variables, anion exchange and molecular weight were evaluated. Improved results were obtained with the TFSI⁻ anion and higher molecular weight (PIL120-TFSI), which enhanced mechanical properties and resulted in better discharge capacity stability over 400 cycles, with only a 0.028 % capacity fade per cycle. This led to an impressive Coulombic efficiency of around 99 % over 400 cycles and a maximum specific capacity of 1050 mAh/g. PILs based in choline are thus excellent candidates for addressing both the chemical and mechanical challenges in LiS systems.