A flame-retardant polyimide interlayer with polysulfide lithium traps and fast redox conversion towards safety and high sulfur utilization Li–S batteries

In recent years and following the progress made in lithium-ion battery technology, substantial efforts have been devoted to developing practical lithium-sulfur (Li-S) batteries for next-generation commercial energy storage devices. The practical application of Li-S batteries is still limited by dramatically reduced capacities, cycling instabilities, and safety issues arising from flammable components. In this study, we designed and fabricated a flame-retardant, multifunctional interlayer which integrated electroconductive networks, lithium polysulfide (LiPS) traps and catalysts to significantly elevate the electrochemical performance and safety of pristine Li-S batteries. The LiPS adsorptive polymer polyimide (PI) constrains polysulfides to the cathode region and effectively suppresses the shuttle effect. Coralloid PI/multiwalled carbon nanotube (MCNT) compounds provide plentiful reaction sites for active materials. The catalytic Ni on the metal skeleton surface notably promotes Li⁺ diffusion, lowers the redox overpotential and accelerates LiPS conversion, which improves the redox kinetics associated with sulfur-related species and significantly elevates sulfur utilization. At different current densities of 0.2 C and 0.5 C, impressive initial discharge capacities of 1275.3 mA h g^-1 and 1190.9 mA h g^-1 are attainable respectively, with high capacity retentions of 80.3% and 78.6% over 600 cycles. Besides, the multifunctional interlayer can also act as a flame-retardant layer to promote the safety of Li-S batteries by inhibiting the spread of fire. This study provides a feasible and prospective strategy that adopts a multifunctional interlayer to develop Li-S batteries with higher capacities, longer cycling lives and safer working conditions.