A Low‐Dosage Flame‐Retardant Inorganic Polymer Binder for High‐Energy‐Density and High‐Safety Lithium‐Sulfur Batteries

The developing electric vehicles and portable electronics urgently require rechargeable lithium batteries with high energy density and high safety. Lithium‐sulfur (Li‐S) batteries have shown significant advantages in their high energy density. However, the use of traditional polymer binders faces significant challenges, such as soluble polysulfides, large volume changes, and electrode flammability, resulting in performance degradation and safety hazards. Here, a polymeric aluminophosphate (AP) is for the first time proposed as an inorganic polymer binder to simultaneously realize high energy density, long cycling stability, and reliable safety of Li‐S batteries. Benefiting from the synergistic effect of polar P‐O and Al‐O chain segments, the AP binder provides strong mechanical adhesion, anchors polysulfides, and promotes the redox kinetics of sulfur electrodes. The AP binder also ensures high flame retardancy for sulfur electrodes at an extremely low dosage of 2 wt%. Consequently, the retardant sulfur electrode can be operated stably with high specific capacities (1190 mAh g−1), high capacity retention rates (>99.1%) during 500 cycles, and excellent rate capability (3 C). Based on the entire cell, the soft‐packaged Li‐S full battery provides high capacities (3.6 mAh cm−2), high cell energy density (415 Wh kg−1 and 297 Wh L−1), and high capacity retention rates (>99.8%). A polymeric aluminophosphate (AP) is for the first time proposed as an inorganic polymer binder for sulfur electrodes while achieving high energy density (415 Wh kg−1 and 297 Wh L−1) and excellent capacity retention (>99.1% per cycle) during 500 cycles. At an extremely low dosage of 2 wt%, the AP binder still ensures high flame retardancy for sulfur electrodes.