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The separator, as one of the essential components for lithium‐ion batteries (LIBs), has garnered considerable attention because of its significant role in battery performance. Here, an in‐situ coating method to promote the wettability and thermal‐stability of polypropylene (PP) separators was reported. The separator was first dip‐coated with phenolic compound based on biologically inspired surface modification. Then silica layers were in‐situ formed on the separator via a sol–gel process of silicate solution, so that an inorganic–organic hybrid layer was coated on PP separators without the need of any polymer binders. Besides, this method hardly increases the film thickness or sacrifices microporous structure of the pristine separator. Due to the introduction of hybrid layers, the resulted separators showed excellent dimensional thermostability, as the thermal shrinkage was only 20% at 150 °C while that of the bare separator was about 80%. Meanwhile, electrochemical performances of cells with the modified separator were obviously improved, especially the rate performance. At the charge/discharge current density of 5 C, cells with PP separators nearly lost all the capacity, but the modified separator still held 45.7% of the discharge capacity at 0.2 C. This facile yet effective method has great application prospects in the preparation of ceramic‐coated separators. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47277. [ABSTRACT FROM AUTHOR]