An Aqueous Inorganic Polymer Binder for High Performance\nLithium–Sulfur Batteries with Flame-Retardant Properties

Abstract

Lithium–sulfur\n(Li–S) batteries are regarded as promising\nnext-generation high energy density storage devices for both portable\nelectronics and electric vehicles due to their high energy density,\nlow cost, and environmental friendliness. However, there remain some\nissues yet to be fully addressed with the main challenges stemming\nfrom the ionically insulating nature of sulfur and the dissolution\nof polysulfides in electrolyte with subsequent parasitic reactions\nleading to low sulfur utilization and poor cycle life. The high flammability\nof sulfur is another serious safety concern which has hindered its\nfurther application. Herein, an aqueous inorganic polymer, ammonium\npolyphosphate (APP), has been developed as a novel multifunctional\nbinder to address the above issues. The strong binding affinity of\nthe main chain of APP with lithium polysulfides blocks diffusion of\npolysulfide anions and inhibits their shuttling effect. The coupling\nof APP with Li ion facilitates ion transfer and promotes the kinetics\nof the cathode reaction. Moreover, APP can serve as a flame retardant,\nthus significantly reducing the flammability of the sulfur cathode.\nIn addition, the aqueous characteristic of the binder avoids the use\nof toxic organic solvents, thus significantly improving safety. As\na result, a high rate capacity of 520 mAh g^–1 at\n4 C and excellent cycling stability of ∼0.038% capacity decay\nper cycle at 0.5 C for 400 cycles are achieved based on this binder.\nThis work offers a feasible and effective strategy for employing APP\nas an efficient multifunctional binder toward building next-generation\nhigh energy density Li–S batteries.