Rational design and low-cost fabrication of multifunctional separators enabling high sulfur utilization in long-life lithium-sulfur batteries

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The lithium-sulfur (Li-S) battery with an ultrahigh theoretical energy density has emerged as a promising rechargeable battery system. However, the practical applications of Li-S batteries are severely plagued by the sluggish reaction kinetics of sulfur species and notorious shuttling of soluble lithium polysulfides (LiPSs) intermediates that result in low sulfur utilization. The introduction of functional layers on separators has been considered as an effective strategy to improve the sulfur utilization in Li-S batteries by achieving effective regulation of LiPSs. Herein, a promising self-assembly strategy is proposed to achieve the low-cost fabrication of hollow and hierarchically porous Fe3O4 nanospheres (p-Fe3O4-NSs) assembled by numerous extremely-small primary nanocrystals as building blocks. The rationally-designed p-Fe3O4-NSs are utilized as a multifunctional layer on the separator with highly efficient trapping and conversion features toward LiPSs. Results demonstrate that the nanostructured p-Fe3O4-NSs provide chemical adsorption toward LiPSs and kinetically promote the mutual transformation between LiPSs and Li2S2/Li2S during cycling, thus inhibiting the LiPSs shuttling and boosting the redox reaction kinetics via a chemisorption-catalytic conversion mechanism. The enhanced wettability of the p-Fe3O4-NSs-based separator with the electrolyte enables fast transportation of lithium ions. Benefitting from these alluring properties, the functionalized separator with p-Fe3O4-NSs endows the battery with an admirable rate performance of 877 mAh g−1 at 2 C, an ultra-durable cycling performance of up to 2176 cycles at 1 C, and a promising areal capacity of 4.55 mAh cm−2 under high-sulfur-loading and lean-electrolyte conditions (4.29 mg cm−2, electrolyte/ratio: 8 µl mg−1). This study will offer fresh insights on the rational design and low-cost fabrication of multifunctional separator to strengthen electrochemical reaction kinetics by regulating LiPSs conversion for developing efficient and long-life Li-S batteries.