Research status and prospect of separators for magnesium-sulfur batteries

Magnesium-sulfur (Mg-S) batteries have attracted wide research attention in recent years, and are considered as one of the major candidates to replace lithium-ion batteries due to the high theoretical energy density, low costs of active materials, and high safety. However, there are still significant challenges that need to be overcome before they can reach the large-scale practical applications. The key issue is the dissolution and shuttle effect of magnesium polysulfides (Mg-PSs), which leads to severe capacity degradation and shortens cycling life, greatly limiting the development of Mg-S batteries. In order to overcome these challenges, great efforts have been made in cathode materials, electrolytes, and separators. Herein, we review the investigations on suppressing the shuttle effect of Mg-PSs via the modification of separators, including schemes such as coating the functional materials that can hold Mg-PSs on the surface of polyolefin-based or glass fiber (GF) separators, forming gel polymer separators via cross-linking polymerization reactions, and developing gel polymer electrolytes coupled with GF separators. Furthermore, an outlook is proposed for the future design on separator exploitation to accelerate the development of Mg-S battery technology.