Temperature-responsive microspheres-coated separator for thermal shutdown protection of lithium ion batteries

Safety issues have severely retarded the commercial applications of high-capacity and high-rate lithium ion batteries (LIBs) in electric vehicles and renewable power stations. Thermal runaway is a major cause for the hazardous behaviors of LIBs under extreme conditions. In this paper, a new thermal shutdown separator with a more reasonable shutdown temperature of similar to 90 degrees C is developed by coating thermoplastic ethylene-vinyl acetate copolymer (EVA) microspheres onto a conventional polyolefin membrane film and tested for thermal protection of lithium-ion batteries (LIBs). The experimental results demonstrate that owing to the melting of the EVA coating layer at a critical temperature, this separator can promptly cut off the Li+ conduction between the electrodes and thus shut down the battery reactions, so as to protect the cell from thermal runaway. In addition, this type of the separator has no negative impact on the normal battery performance, therefore providing an internal and self-protecting mechanism for safety control of commercial LIBs.