Functionalized Separators for Batteries: Universality and Individuality

Abstract After more than 200 years of evolution, batteries have extended into various types, and each type has corresponding differences in the problems faced by the separator due to the different working environments it faces. Inevitably, the separator of each battery system cannot be simply and uniformly produced, and various fabrication/modification methods are used to endow separators with required functionalities for battery performance improvement. Although the separators of different battery systems cannot be completely interchangeable, they do have certain commonalities. All separators, for instance, must tackle challenges pertaining to ion conductivity, mechanical strength, and short‐circuit prevention. However, metal batteries specifically need to address dendrite issues, along with other intricate problems like thermal runaway and polysulfide shuttle within their systems. Similarly, fuel cell separators must overcome challenges like fuel crossover, while flow batteries face the issue of corrosion in their ion exchange separators. Therefore, the commonalities and individual characteristics of separators across various battery systems, from perspectives of separator manufacturing methods, modification directions, and performance improvement, are systematically outlined. A summary and outlook for the further development of future energy systems are also presented, hoping to facilitate the separator design innovation for the demanding battery market.