Halogen‐Free Polyphosphazene‐Based Flame Retardant Cathode Materials for Li–S Batteries
Serkan Yeşi̇lot, Sedat Küçükköylü, Tutku Mutlu, Rezan Demir‐Cakan
Abstract
Novel, eco‐friendly, and halogen‐free polyphosphazene‐based flame retardant (FR) cathodes for Li–S batteries are prepared by the inverse vulcanization of elemental sulfur with polybis(2‐acrylamidoethoxy)phosphazene (poly(AAE)) resulting in the covalently bonded different wt% sulfur content polymers. Due to the polar amide groups, poly(AAE)‐ x S ( x refer to the wt% of sulfur) composites assist in anchoring intermediate lithium polysulfide species. The structural characterizations of the poly(AAE)‐ x S polymers are conducted by elemental analysis, Fourier‐transform infrared spectroscopy, differential scanning calorimeter, thermogravimetric analysis, and scanning electron microscopy. Their FR properties are elevated by calculation of the limiting oxygen index values and burning tests. Later, lithium‐ion storage mechanism of poly(AAE)‐55S polymer is evaluated, including cyclic voltammetry, rate performance tests and electrochemical impedance spectroscopy measurements. To compare with the electrochemical performance of poly(AAE)‐55S, a noncovalent blend polymer mixture and bare sulfur are also tested. It is found that covalently bonded poly(AAE)‐55S obtained by the inverse vulcanization of elemental sulfur and poly(AAE) results much pronounced capacities. Herein, new insights into the design and development of alternative cathode materials for safer Li–S batteries, both providing FR properties and good lithium polysulfides adsorption capabilities, are offered.