  Capacity degradation and destructive hazards are two core challenges for
lithium-ion batteries at high temperatures, which need to be solved urgently.
Adding flame retardants or fire extinguishing agents can only achieve one-time
self-protection in case of emergency overheating. Herein, smart self-protecting
aqueous lithium-ion batteries were developed using thermoresponsive separators
through in-situ polymerization on the hydrophilic separator. The
thermoresponsive separator will close the lithium ions transport channel at
high temperatures and reopen when the battery cools down; more importantly, the
transition is reversible. We studied the lithium salts influence on the
thermoresponsive properties of the hydrogels and selected suitable lithium salt
(LiNO3) and concentration (1 M) in the electrolyte to achieve self-protection
without sacrificing battery performance. In addition, the shut-off temperature
can be tuned by adjusting the hydrophilic and hydrophobic moiety ratio in the
hydrogel according to actual demands. This self-protecting lithium-ion battery
shows promise for smart energy storage devices with safe and extended lifespan.
