Multifunctional separators for high-performance lithium ion batteries

The separator is a critical component in lithium ion batteries that is not involved in electrochemical reactions but directly affects the safety and electrochemical properties of batteries. With the higher demand for energy density and the upgrade of battery system, the multifunctionalization of separator is an important development trend on the basis of realizing the traditional functions. Here, we review the development progress of separator materials, new requirements for the separators and the recent studies of functional separators in lithium batteries with respect to their design and mechanism in different battery systems. Future challenges and development directions toward the advancement in multifunctional separators are also discussed for achieving remarkable battery performances.