Recent advances on separator membranes for lithium-ion battery applications: From porous membranes to solid electrolytes

The battery separator is an essential component of batteries that strongly affects their performance. The control of their properties being particularly important for obtaining lithium-ion batteries with high cycling performance. Separators are placed between both electrodes, should show high ionic conductivity, excellent mechanical and thermal stability and can be divided into six main types: microporous membranes, nonwoven membranes, electrospun membranes, membranes with external surface modification, composite membranes and polymer blends. Considering the relevance of battery separators in the performance of lithium-ion batteries, this work provides the recent advances and an analysis of the main properties of the different types of separators. Despite the large efforts on this area, it is still necessary to improve their characteristics based on new materials developments for this battery component. This paper also summarizes the recent advances in different solid electrolytes based on polymer and ceramic materials for a transition from conventional batteries to solid state batteries, that will allow the next generation of high-performance, safer and sustainable batteries. Finally, the main research and development directions and future trends in the area of separator membranes for lithium-ion batteries are presented.