AbstractCapacity degradation and destructive hazards are two major challenges for the operation of lithium‐ion batteries at high temperatures. Although adding flame retardants or fire extinguishing agents can provide one‐off self‐protection in case of emergency overheating, it is desirable to directly regulate battery operation according to the temperature. Herein, smart self‐protecting aqueous lithium‐ion batteries are developed using thermos‐responsive separators prepared through in situ polymerization on the hydrophilic separator. The thermos‐responsive separator blocks the lithium ion transport channels at high temperature and reopens when the battery cools down; more importantly, this transition is reversible. The influence of lithium salts on the thermos‐responsive behaviors of the hydrogels is investigated. Then suitable lithium salt (LiNO₃) and concentration (1 m) are selected in the electrolyte to achieve self‐protection without sacrificing battery performance. The shut‐off temperature can be tuned from 30 to 80 °C by adjusting the hydrophilic and hydrophobic moiety ratio in the hydrogel for targeted applications. This self‐protecting LiMn₂O₄/carbon coated LiTi₂(PO₄)₃ (LMO/C‐LTP) battery shows promise for smart energy storage devices with high safety and extended lifespan in case of high operating temperatures.