Modified Separators with Ultrathin Graphite Coating Simultaneously Mitigate the Issues of Metal Dendrites and Lithium Polysulfides to Provide Stable Lithium-Sulfur Batteries

In this paper, we demonstrate a unique multifunctional separator prepared by sputtering a thin layer of graphite on top of a commercial polypropylene-polyethylene separator. This modified separator, when used in a Li-Li symmetrical cell, suppresses Li dendrite growth by maintaining a uniform ionic flux on top of the Li metal. When employed in a lithium-sulfur battery (LSB), the thin graphite layer can retard the shuttling of lithium polysulfides (LiPSs) through a physical interaction, as demonstrated through the live discharge of an H-cell. Moreover, the conductivity of the graphite resulted in it, also acting as a secondary current collector, thereby leading to higher utilization of the sulfur content and assisting in the redox mechanism of the LiPSs. The electrochemical performance of cells incorporating the modified separator was characterized by a low overpotential (in the case of Li-Li symmetrical cells) and high Coulombic efficiency and a low decay rate (in the LSB, simultaneously). The roll-to-roll sputtering of the thin layer of graphite on the pristine separator would appear to be a scalable solution for the commercialization of such modified separators.