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

Abstract

AbstractThe 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 1H and 31P 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.