Flame-Retardant Sulfur Cathode Composite Materials for Fire-Safe and Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are regarded as a representative next-generation energy storage technology due to their high energy density, low cost, and environmental friendliness. Nevertheless, their widespread application is hindered by challenges such as the insulating nature of sulfur and Li2S, the larger volume expansion during cycling, and the serious side effects caused by the soluble lithium polysulfide (LiPSs), all of which collectively lead to severe capacity decay and poor cycling stability. Furthermore, the high flammability of sulfur is another critical safety concern, which has hindered its further application. To effectively address these limitations, this study designed and developed a flame-retardant sulfur cathode (CS@Al/APP) by encapsulating carbon–sulfur composites with aluminum hydroxide (Al(OH)3) and employing ammonium polyphosphate (APP) as a binder to enhance electrode stability and flame retardancy. Experimental results demonstrate that Al(OH)3 and APP synergistically improve the flame resistance by releasing inert gases and forming a protective char layer. Additionally, they enhance sulfur redox kinetics by efficiently trapping LiPSs. As a result, the CS@Al/APP cathode exhibits exceptional electrochemical stability, maintaining a reversible capacity of 1025.04 mAh g–1 after 100 cycles at 0.1C and delivering a discharge capacity of 744.2 mAh g–1 after 500 cycles at 1C. This study provides a feasible technical pathway for achieving lithium–sulfur batteries with high safety and high energy density.