Self-actuating protection mechanisms for safer lithium-ion batteries

Safety issue is still a problem nowadays for the large-scale application of lithium-ion batteries (LIBs) in electric vehicles and energy storage stations. The unsafe behaviors of LIBs arise from the thermal runaway, which is intrinsically triggered by the overcharging and overheating. To improve the safety of LIBs, various protection strategies based on self-actuating reaction control mechanisms (SRCMs) have been proposed, including redox shuttle, polymerizable monomer additive, potential-sensitive separator, thermal shutdown separator, positive-temperature-coefficient electrode, thermally polymerizable additive, and reversible thermal phase transition electrolyte. As build-in protection mechanisms, these methods can sensitively detect either the temperature change inside battery or the potential change of the electrode, and spontaneously shut down the electrode reaction at risky conditions, thus preventing the battery from going into thermal runaway. Given their advantages in enhancing the intrinsic safety of LIBs, this paper overviews the research progresses of SRCMs after a brief introduction of thermal runaway mechanism and limitations of conventional thermal runaway mitigating measures. More importantly, the current states and issues, key challenges, and future developing trends of SRCTs are also discussed and outlined from the viewpoint of practical application, aiming at providing insights and guidance for developing more effective SRCMs for LIBs.