As the energy density of lithium-ion batteries (LIBs) continues to increase, their safety has become a great concern for further practical large-scale applications. One of the ultimate solution of the safety issue is to develop intrinsically safe battery components, where the battery separators and liquid electrolytes are critical for the battery thermal runaway process. In this review, we summarize recent progress in the rational materials design on battery separators and liquid electrolyte towards the goal of improving the safety of LIBs. Also, some strategies for further improving safety of LIBs are also briefly outlooked.