Recent experiments have suggested that there is a critical size for patterned silicon (Si) thin film electrodes for delamination from a current collector during lithiation and delithiation cycling. However, no existing theories can explain this phenomenon, in spite of its potential importance in designing reliable electrodes for high-capacity lithium-ion batteries. In this study, we show that the observed delamination size effect can be rationalized by modeling thin film delamination in the presence of large scale interfacial sliding. A method is proposed to deduce the critical size for delamination based on the critical conditions for the nucleation and growth of edge or center cracks at the film-substrate interface under plane strain or axisymmetric conditions. Applications to lithiation of thin-film Si islands give results in excellent agreement with experimental observations.