Membrane Engineering for Battery Systems: Bridging Design Principles and Frontier Applications

Electrochemical energy storage systems (EESSs) stand as linchpins in the global transition toward carbon neutrality, yet their performance and safety remain fundamentally constrained by the underappreciated component: membrane separators. This review delivers a paradigm-shifting synthesis of separator science across redox flow batteries (RFBs), lithium-ion batteries (LIBs), and solid-state batteries (SSBs), unraveling the universal principles that govern ion selectivity, interfacial stability, and long-term cyclability. By critically analyzing the interplay among material architecture, ion transport mechanisms, and electrochemical degradation pathways, we establish a unified framework for designing next-generation separators that overcome the persistent trade-off between ionic conductivity and molecular-level discrimination. Recent advances in porous crystalline materials, polymer electrolytes, and hybrid composites are dissected through the lens of size-exclusion, Donnan-exclusion, and dynamic adaptive interactions, revealing how tailored pore geometries and functional group engineering enable the precise modulation of cation/anion flux. Emphasis is placed on the emerging role of computational modeling in decoding separator–electrolyte couplings, guiding the rational design of membranes with atomic-scale precision. The review further addresses critical challenges, including dendritic growth in alkali metal batteries, crossover losses in aqueous RFBs, and interfacial instability in solid-state systems. This integrative analysis establishes a cross-cutting roadmap for separator innovation, where the synergistic design of material architectures, ion transport physics, and computational-guided interfaces converge to unlock the full potential of electrochemical energy storage systems.