Rate-dependent plastic buckling of a core-shell wire

One of the most promising electrode materials for lithium-ion batteries (LIBs) is the core-shell wire with carbon shell and Si core, in which the shell buffers volumetric change, maintains structural integrity and prevents the core from aggregates. It is inevitable that large deformation can cause the buckling of a core-shell wire, leading to the mechanical degradation of LIBs made from core-shell wires. In this work, we develop a rate-dependent model for a large deformed core-shell wire in the theory of visco-plasticity, and obtain an analytical expression of the axial reaction force taking into account the contribution of the concentration-dependent elastic modulus and the concentration-dependent yield stress of the inner core. Using the Gordon formula, we propose a critical force for the onset of plastic buckling of the core-shell wire and investigate the effects of mechanical softening, charging rate, axial length of the core-shell nanowire and thickness of the carbon shell on the critical state of charge for the onset of plastic buckling. The numerical results reveal that elastic softening, slow charging rate, small ratio of length to radius and thick carbon shell can retard the large deformed core-shell wire from plastic buckling. This work provides the foundation needed to guide the design of core-shell wires to be used in LIBs.