Although the ceramic-coated separators have been industrialized and widely used in power lithium-ion batteries to replace the polyolefin separators, the safety of batteries still cannot fully meet the demand of practical application with the rapid growth of energy density. In this work, a ceramic-coated separator further modified by phenol-formaldehyde resin has been developed, in which a three-dimension coating layer is formed both on the surface and in the pores of the pristine separator by introducing phenolformaldehyde resin through a simple soakage process. Such membranes show extremely high thermal stability up to 300°C, maintain a high mechanical strength even after a heat-treatment at 220°C for 30 min, and show a shut-down function above 138°C. With the advantages of abundant sources, low cost, environment-friendly property and simple preparation process, the phenol-formaldehyde resin modified separators are expected to replace the commercial ceramic-coated separators, greatly improve the safety performance of batteries, and realize the reassuring application of lithium-ion batteries in power batteries and large-scale energy storage devices. [ABSTRACT FROM AUTHOR]