Halogen-free flame-retardant sulfur copolymers with stable Li–S battery performance

Lithium-sulfur (Li–S) batteries are among the most promising candidates for the next-generation rechargeable batteries due to their high energy density, cost-effectiveness, environmental friendliness and being on the verge of commercialization. However, considering the cathode part, low conductivity of sulfur, large volume expansion, dissolution of polysulfides in the electrolyte and their unfavorable shuttle behavior lead to low cell capacity and poor cycle life. More importantly, the high flammability of sulfur causes safety concerns that might hinder the large-scale application of lithium-sulfur batteries in electric vehicles, especially in tropical countries. Herein, we report a covalently linked sulfur (~83% w/w) flame retarding sustainable copolymer as a suitable and safe cathode material for the practical application of Li–S batteries in tropical region. A remarkable intrinsic flame-retardant property with appreciable specific capacity and excellent capacity retention provide an alternative strategy for designing cathode materials for safe and sustainable Li–S batteries.