Reversible Temperature-Responsive Cathode for Thermal Protection of Lithium-Ion Batteries

Thermal safety is an increasing concern with the widespread application of lithium-ion batteries (LIBs) in electric vehicles and energy storage stations. To address this concern, we propose herein a reversible thermo-responsive switching material (RTSM) and use this material to fabricate a temperature-sensitive cathode to enable reversible thermal protection of LIBs. The RTSM material is achieved simply by dispersing conductive fillers of multiwall carbon nanotubes (MWCNTs) in a mixed plastic matrix of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) polymers. Benefiting from the strong hydrogen-bonding interaction between the MWCNT surface and PMMA molecules as well as the large thermal expansion coefficient of the PVDF polymer, the RTSM material exhibits a strong yet reversible PTC effect, with its resistivity sharply rising up by 3 orders of magnitude at 110–120 °C and suddenly dropping down to the original value at room temperature even after multiple thermal cycles. As a result, the LiCoO2 cathode with an RTSM coating sandwiched in between the Al foil current collector and the electrode-active layer demonstrates a reversible thermo-responsive switch behavior to rapidly shut its electrode reaction down at an elevated temperature and to quickly resume its normal electrochemical activity at room temperature, thus preventing the thermal runaway while without compromising the normal electrochemical performances of the cell. This work provides a possible route for designing reversible thermo-responsive materials and building safer LIBs.