Multilayer Laminated Copper Electrodeposits and Their Mechanical Properties

Abstract

Copper (Cu) foils are used as anode current collectors in secondary batteries and to increase their capacity thin foils 8 μm thick, or less, have been commercialized. The change of mechanical properties according to the thickness of the foils was investigated from the viewpoint of the crystallographic microstructure. The elongation tends to decrease with decreasing thickness of the Cu foils but is limited by an increase in the ratio (D/t) of the grain size (D) to the thickness (t), which can lead to anisotropic plastic deformation. Two electroplating methods are proposed based on the concentration of the additive in the plating solution and by modulating the current density to develop multilayer laminate structures with alternating layers exhibiting different recrystallization behaviors to enhance the mechanical properties of Cu foils. Cycling between two electroplating solutions with different additive concentrations enables the control of the recrystallization behavior, although it likely presents challenges at the production scale. Alternatively, the periodic variation of the current density is used to alter the microstructure and recrystallization behaviors, enabling the formation of locally irregular grain extrusions between the layers. Mechanical measurements reveal a Hall-Petch relationship between the grain size and yield strength in the multilayer laminated foils.