Self‐Protecting Aqueous Lithium‐Ion Batteries

Capacity 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 LiMn2 O4 /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.