Cathode with a temperature-switchable interlayer for thermally self-regulating smart lithium-ion batteries

Abstract

Thermal safety is crucial for the large-scale application of lithium-ion batteries (LIBs) in electric vehicles and energy storage stations. To boost thermal safety of LIBs, we propose herein a reversible temperature-responsive membrane (RTRM) and use this membrane as surface-modification layer of current collector to develop temperature-responsive cathodes. The RTRM is fabricated by uniformly dispersing conductive fillers of short-cut carbon fibers (CCFs) in a blended plastic matrix of low-density polyethylene (LDPE) and ultra-high molecular weight polyethylene (UHMWPE) through solution casting. Benefiting from the large thermal expansion provided by LDPE and good structural reproducibility given rise by the ultra-high melt viscosity of UHMWPE, the as-fabricated RTRM exhibits a strong and reversible positive temperature coefficient (PTC) effect, with its resistivity increasing sharply by 7.1 orders of magnitude at 110–120 °C and returning to the initial value reversibly upon cooling down even after 30 thermal cycles. As a result, the LiFePO₄ cathode with the RTRM demonstrates a reversible temperature-switching behavior by spontaneously halting the electrode reaction at elevated temperatures and resuming the electrode reaction upon cooling, thereby providing reversible thermal protection for LIBs. Notably, such a temperature-switchable cathode maintains normal charge-discharge performance even after 28 thermal on/off cycles. This study offers a promising strategy for developing temperature-responsive cathode and thermally self-regulating smart LIBs.