Serial Cracking in 2D Van der Waals Layered Electrodes Mediated by Electrochemical Reaction and Mechanical Deformation

In battery cycling, mechanical effects introduced by electrochemical reactions are commonly observed. In return, the mechanical deformations also have a large impact on the electrochemical process. However, such a coupling effect of electrochemical reaction and mechanical deformation has a complicated interplay on the atomic scale and an explicit elucidation is still challenging. Herein, we used in situ transmission electron microscopy to directly visualize the coupling process during the lithiation of two-dimension Van der Waals MoS 2 layered electrodes. A self-sustained cracking mechanism was identified; the first crack was created by the accumulation of the linear defects originated from the strain in lithiation. The formed defects including dislocations and antiphase boundaries, in turn accelerated the Li-ion diffusion, promoting the electrochemical reaction and cooperatively gave rise to the formation of a second and following cracks that resembled the “avalanche effect”. Meanwhile, it is observed that a threshold crystal size exists, under which the lithiation stress is not sufficient to initiate the first crack, and thus the serial cracking process could be avoided. The present work provides an atomistic insight into a cooperation from the mechanical and electrochemical effects toward the formation of the arrayed cracks. It also sheds light on the enhancement of mechanical properties of layered electrode materials for rechargeable batteries.