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Aluminum-substituted mesoporous SBA-15 (Al−SBA-15) materials were directly synthesized by a hydrolysis-controlled approach in which the hydrolysis of the silicon precursor (tetraethyl orthosilicate, TEOS) is accelerated by fluoride or by using tetramethyl orthosilicate (TMOS) as silicon precursor rather than TEOS. These materials were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms, TEM, 27Al MAS NMR, IR spectra of pyridine adsorption, and NH3-TPD. It is found that the matched hydrolysis and condensation rates of silicon and aluminum precursors are important factors to achieve highly ordered mesoporous materials. 27Al MAS NMR spectra of Al−SBA-15 show that all aluminum species were incorporated into the silica framework for the samples prepared with the addition of fluoride. A two-step approach (sol−gel reaction at low pH followed by crystallization at high pH) was also employed for the synthesis of Al−SBA-15. Studies show that the two-step approach could efficiently avoid the leaching of aluminum from the framework of the material. The calcined Al−SBA-15 materials show highly ordered hexagonal mesostructure and have both Brönsted and Lewis acid sites with medium acidity.

The lithium-sulfur battery is considered one of the most promising candidates for portable energy storage devices due to its low cost and high energy density.However, many critical issues, including polysulfide shuttling, self-discharge, lithium dendritic growth, and thermal hazards need to be addressed before the commercialization of lithium-sulfur batteries. To this end, tremendous efforts have been made to explore battery configurations and components, such as electrodes, electrolytes, and separators, among which the separator plays an especially critical role in addressing aforementioned issues. Thus, this review analyzes the mechanisms and interactions of these critical issues and summarizes both the function of separators and recent progress made towards remedying such issues. Additionally, promising directions for the development of separators in lithium-sulfur batteries are proposed. K E Y W O R D Slithium dendrite, lithium-sulfur batteries, self-discharge, separator, shuttle effect, thermal hazardsThe first two authors contributed equally to this work.