Lithiation-induced tensile stress and surface cracking in silicon thin film anode for rechargeable lithium battery

Cracks are found at the surface of silicon thin film anodes during lithiation-delithiation cycles in rechargeable lithium battery. However, whether crack formation occurs during lithiation or delithiation is still controversial. Using both an analytical model and a more complete finite element model, we show that a transition from compressive to tensile stress occurs at the silicon thin film surface during the lithiation process itself. This stress transition arises from the large volume expansion, plastic deformation, and slow charging rate which results in a sharp interface separating the lithiated and unlithiated zones. Our analysis further shows this tensile stress is sufficient to cause cracking of the lithiated thin film surface, suggesting cracks observed experimentally in silicon thin films are first generated during the lithiation step, rather than the delithiation step. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764329]