Wrinkling and ratcheting of a thin film on cyclically deforming plastic substrate: Mechanical instability of the solid-electrolyte interphase in Li-ion batteries

Lithium-ion batteries (LIBs) in consumer electronics, electric cars and large-scale energy storage systems are often susceptible to capacity fading due to mechanical degradation of the solid-electrolyte interphase (SEI) layer on the electrodes. Here we present an analytical model to describe SEI wrinkling and ratcheting behaviors during cyclic lithiation and delithiation of LIBs. The SEI-electrode system is modeled as a bilayer structure consisting of a thin film resting on a plastic substrate. Surface instability is found in such a system under cyclic plastic deformation induced by lithiation and delithiation. A linear perturbation analysis is performed to determine the critical wrinkling strain and wavenumber. The interfacial shear traction induced by surface wrinkling can further lead to plastic ratcheting, and the wrinkling amplitude increases with each lithiation/delithiation cycle. A phase diagram is plotted to characterize and predict different system behaviors, e.g., elastic, elastic wrinkling, shakedown without wrinkling, shakedown with wrinkling, and ratcheting. A series of finite element simulations are performed to validate the theoretical predictions. The analysis suggests that the mechanical instabilities of the SEI, including wrinkling and ratcheting, can be prevented by several strategies, such as introducing an artificial SEI with a sufficiently large stiffness and thickness, and/or with a tensile pre-stress in the SEI. (C) 2018 Elsevier Ltd. All rights reserved.