Hydrogen generated from binders: An overlooked thermal runaway source in lithium-ion batteries

Abstract

Anode binders undergo decomposition during thermal runaway, generating highly flammable and explosive hydrogen, which poses a significant threat to the safety of lithium-ion batteries. However, the binder due to its relatively small proportion is often overlooked in terms of its importance. This study elucidates the universal mechanism of hydrogen generation from the decomposition of binders and identifies the hydrogen-containing chemical bonds within the molecular structure of binders as the fundamental sources of hydrogen. The Fourier transform infrared spectroscopy of six commonly used binders reveals that five of them possess hydrogen-containing chemical bonds, indicating a potential for hydrogen generation, whereas the polytetrafluoroethylene binder lacks such bonds and cannot generate hydrogen. Differential scanning calorimetry is employed to compare the decomposition of these binders and their reaction with lithiated graphite. The results demonstrate that cyclic molecular structures not only enhance thermal stability but also increase the difficulty of hydrogen generation. Moreover, binders devoid of hydrogen atoms exhibit superior thermal stability and completely eliminate the risk of hydrogen generation. These findings provide critical insights into the molecular design of binders, offering promising strategies to mitigate or prevent hydrogen generation from binder decomposition and thereby substantially improve the safety of lithium-ion batteries.