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In-situ S/TEM Probing of the Coupling among Electrochemical, Thermal, and Mechanical Effect in Rechargeable Batteries

Electrochemical driven functioning of battery inevitably induces thermal and mechanical effects, which in turn couple closely with the electrochemical process and collectively govern the performance of the battery. However, such a coupling effect has never been explicitly explored. We use in-situ TEM to demonstrate such a coupling effect. We discover that supplying a thermal perturbation to the delithiated LiNi0.6Mn0.2Co0.2O2 (NMC622) will lead to the nucleation and propagation of intragranular cracks in the lattice, which shows dependence on the fraction of Li that has been extracted from the lattice and will not happen for the case of pristine or with Li been re-inserted sample. Comprehensive mechanics analyses revealed that thermal stress associated with electrochemically induced phase inhomogeneity and internal pressure due to oxygen gas evolution are the two primary driving forces for nucleation and propagation intergranular crack, resembling a “popcorn” fracture mechanism. The present work unveils that the electrochemical process and its trigged thermal and mechanical effects are mutually coupled, leading to amplification effect that substantially surpasses the individual effect in the degradation of rechargeable batteries.