Deformation Behavior of Copper Foil Collectors with Ni3Sn4 Film During the Charge-Discharge of Lithium Ion Secondary Cells on the Basis of an Optical Cantilever Method

The deformation behavior of copper foil collectors electrodeposited with Ni3Sn4 during the charge-discharge cycle was observed in situ using an optical cantilever method. It was found that in the high yield strength copper foil, cyclical deformation due to charge- discharge were observed, while in low yield strength copper foil, the deformation which occurred during the first charge period remained. The former is elastic deformation and the latter is plastic deformation. As plastic deformation promotes determination through peeling and shedding of the active material during sequential cycles, the high yield strength copper should be adopted. For example, 3 mu m Ni3Sn4 film requires a 31 mu m pure copper foil collector with a yield strength of 350 MPa or a 18 mu m Corson copper alloy foil collector with the yield strength of 700 MPa.