Facile and Effective Positive Temperature Coefficient (PTC) Layer for Safer Lithium-Ion Batteries

With the popularization of lithium-ion battery propelled electric vehicles, the safety requirements of lithium-ion batteries are under immense scrutiny. Minimizing catastrophic cell failure events by developing improved safety features for lithium-ion batteries is an important endeavor. Herein, we report a novel, safe cathode configuration, achieved by sandwiching a positive temperature coefficient (PTC) material layer between the Al foil and active cathode material. The PTC layer (2–3 μm thick) was a composite of the carbon-coated LiFePO4(C-LFP), poly­(vinylidene fluoride) (PVDF), and Super P. Due to the structural stability, good conductivity, and limited amount of C-LFP, the PTC layer maintained good structural integrity as a supporting layer between the Al current collector and active material layer. At high temperatures (>80 °C), the PTC effect was triggered in the protective layer by PVDF volume expansion, which effectively disrupted electron flow, leading to a dramatic increase in cathode resistance, thus preventing thermal runaway from occurring. Such a PTC layer-containing cell design not only shows outstanding safety performance during overheating scenarios but also has no degradation on cell performance. Furthermore, the PTC layer has good processability and is a convenient and practical material layer for commercial applications.