Designing separators with excellent electrolyte wettability is of great significance to improve the electrochemical behavior of lithium-ion batteries (LIBs). Herein, we develop a sandwich-structured separator by facile in situ polymerization of polyaniline (PANI) on the both sides of polypropylene (PP) separator. The introduction of PANI coating improves the electrolyte wettability of the PP separators. Consequently, the cells equipped with this sandwich-structured separator demonstrate superior electrochemical performance including initial capacity, rate performance, and cyclic stability compared with the PP separator. This work may provide a facile approach for separator modification to improve the performance of LIBs.