Ethylene Glycol-Containing Acrylic Polyphosphazene Based Cathode Materials via Inverse Vulcanization of Sulfur for Li-S Batteries

The cell performance of Li-S batteries can be improved by establishing compatibility with the electrolyte of cathode and enhancing lithium-ion diffusion (ionic conductivity) or electrical conductivity. In this work, we introduce cathode material based on ethylene glycol-containing acrylic polyphosphazene. Poly[(2acrylamidoethoxy)-random-(methoxyethoxyethoxy)] phosphazenes were synthesized by macromolecular substitution of poly(dichloro)phosphazene with 2-acrylamidoethanol and diethylene glycol methyl ether in two different ratios (25 and 50 mol% of ethylene glycol methyl ether), abbreviated as MP-25EG and MP-50EG, where ethylene glycol chains enhance the electrolyte compatibility and ion transport of the sulfur cathode material. Then, poly[S-random-(2acrylamidoethoxy)-random-(methoxyethoxyethoxy)] phosphazene polymers, designated as MP-25EG-xS or MP-50EG-xS (x=50 and 80 wt.% of sulfur) were prepared by inverse vulcanization of polymer with two feed sulfur ratios. Structural characterizations of the polymers were carried out using appropriate standard spectroscopic methods such as H-1 and P-31 NMR, FT-IR, DSC and TGA as well as XPS. The electrochemical performance of MP-25EG-50S, MP-25EG-80S and MP-50EG-50S, MP-50EG-80S were evaluated and the effect of ethylene glycol was investigated by comparing cell performances. MP-50EG-50S demonstrated its promising applicability in Li-S batteries by exhibiting much better electrochemical respond with a discharge capacity of 745 mAh/g at C/5 current density over 100 cycles.