The functional separator coated with core–shell structured silica–poly(methyl methacrylate) sub-microspheres for lithium-ion batteries

• Core–shell structured SiO2–poly(methyl methacrylate) sub-microspheres are prepared.
• A functional ceramic-coated separator coated by the sub-microspheres is developed.
• The separator exhibits good thermostability and electrolyte retention ability.
• The separator multi-functionality provides cells with greater safety performance.

To improve the safety of lithium-ion batteries (LIBs), a functional ceramic-coated separator (FCC separator) is developed by coating core–shell structured silica–poly(methyl methacrylate) (SiO2–PMMA) sub-microspheres on one side of a conventional porous polyethylene (PE) separator. The FCC separator possesses multi-functional properties of better separator thermostability and higher electrolyte stability by combining the advantages of both the ceramic-coated separator and the gel polymer electrolyte (GPE). The heat-resistant SiO2 core particles effectively protect the FCC separator from thermal shrinkage. Meanwhile, the PMMA shells form a gel after swelling and activation by the liquid electrolyte, which endows the FCC separator with the functional properties of the GPE to stabilize the electrolyte. As a result, the FCC separator shows considerable wettability for the liquid electrolyte and outstanding electrolyte retention ability at elevated temperature. Moreover, the FCC separator with the coating layer improves the safety performance of cells by preventing cells from experiencing internal short circuits at high temperature. Meanwhile, the cells assembled with such separators demonstrate superior cycle performance and C-rate capability. Therefore, the FCC separator provides LIBs with greater security and better electrochemical performance.