Operando observing hydrogen evolution in commercial lithium-ion batteries

Abstract

Operando monitoring of the H2 evolution within lithium-ion batteries is essential for decoding their thermal runaway mechanism and preventing fires. Here, we track the H2 evolution over multiple charging‒discharging cycles of commercial 18650 batteries via an operando surface‒modified fiber Bragg grating sensor. Time-resolved reversible adsorption‒desorption and irreversible formation of H2 are discovered to be associated with the temperature inside batteries. Notably, we experimentally observe unique negative temperature coefficient (NTC) behaviour for the H2 evolution, in which H2 concentration inversely changes with the internal temperature above a critical temperature. Further numerical and analytical analyses reveal the H2 evolution mechanism through Fickian diffusion and Soret diffusion, indicating the NTC behaviour can mitigate the severe hazards of thermal runaway. This work holds key values for advancing the design of next-generation high-safety batteries.