The development of large‐scale separators with tuned microporous structures and surface areas up to 0.56 m2 are demonstrated for application to Li‐ion batteries. The different separators developed are based on blends composed of aromatic polyethers containing different functional groups that can interact with lithium cations and poly(ethylene oxide) (PEO). The porous structures that are prepared after the partial removal of PEO by water treatment can be fine‐tuned by manipulating the blend composition and aromatic polyether structure. In particular, the miscibility effect on pore formation is thoroughly studied. The prepared separators are highly porous (38–63 %), show good air permeability (comparable Gurley values to commercially available polyolefin separators), and increased wettability to conventional liquid electrolytes. In addition, these separators show improved thermal shrinkage behavior and high thermal stability compared to the commercially available polyolefin separators. LiFePO4/C cells using the novel separators show good performance and retain 93 % of their initial discharge capacity after 166 cycles, thus offering excellent stability for long‐term operation. The aromatic‐polyether‐based chemistry of the prepared separators plays a key role in providing the separator with the aforementioned advantageous characteristics, enabling them to be an interesting alternative to conventional polyolefin‐based separators.

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