Tailoring Lithium-Sulfur Battery Separators via Crystal Engineering: From Fundamental Modulation to Multidimensional Synergy.

Lithium-ion batteries (LIBs) are fundamentally constrained in achievable energy density, whereas lithium-sulfur batteries (LSBs), with exceptionally high theoretical energy density, have emerged as a promising next-generation system. Nevertheless, their commercialization is severely hindered by critical issues such as the "shuttle effect" of lithium polysulfides (LiPSs), lithium dendrite growth, and volume expansion of sulfur cathodes. While significant progress has been made in enhancing LSBs performance through separator modification, a deep understanding of crystal engineering regarding the underlying LiPSs working mechanisms in LSBs remains insufficient. Herein, we provide a systematic summarization of recent advances in crystal engineering for LSB separators, categorizing them into fundamental research strategies, each assessed against the three functions a separator must perform at once, and multi-dimensional synergistic approaches, with the evolution of coatings under operation and the continuously changing electrolyte of the surrounding medium treated explicitly in the review. Additionally, advanced characterization techniques employed to probe these crystal engineering structures are briefly summarized. Finally, future development trajectories for separator crystal engineering are discussed, aiming to provide valuable guidance for the rational design of high-performance LSBs.