In this paper, the interfacial mechanical properties of large-sized monolayer graphene attached to a flexible polyethylene terephthalate (PET) substrate are investigated. Using a micro-tensile test and Raman spectroscopy, in situ measurements are taken to obtain the full-field deformation of graphene subjected to a uniaxial tensile loading and unloading cycle. The results of the full-field deformation are subsequently used to identify the status of the interface between the graphene and the substrate as one of perfect adhesion, one showing slide or partial debonding, and one that is fully debonded. The interfacial stress/strain transfer and the evolution of the interface from one status to another during the loading and unloading processes are discussed and the mechanical parameters, such as interfacial strength and interfacial shear strength, are obtained quantitatively demonstrating a relatively weak interface between large-sized graphene and PET.

In the paper, the deformation and elastic modulus evolution in Si composite electrodes during electrochemical lithiation and delithiation cycles are investigated experimentally. An electrochemical cell and optical system for in situ deformation monitoring of an electrode cantilever are designed and developed. Real-time bending deformation measurements of the Si composite electrode cantilever are conducted during the lithiation and delithiation cycles to determine the deformation as a function of the capacity. Analyses of the deformation characteristics and the microscopic mechanisms during the lithiation and delithiation cycles are performed. It is found that the electrode cantilever deforms relatively slowly during the first lithiation half-cycle and exhibits nonlinear deformation characteristics during subsequent cycles. The material softening of the lithiated Si and the diffusion-induced-compression limiting diffusion rate are main factors, causing the electrode deformation to ease with a gradually decreasing slope as Li concentration increases. Furthermore, we provide a new method combined experiments and the derived evolution equation of Li concentration-curvature-elastic modulus to characterize the elastic modulus evolution. Using the experimental results, the influence of Li concentration upon the elastic modulus of the Si composite electrode is quantitatively described. The electrode elastic modulus decreases significantly by about 90% when the capacity is about 770 mAh/g.