Interfacial Properties of Copper-coated Graphite Electrodes: Coating Thickness Dependence

Copper-coated graphite electrodes have been prepared by physical vapour deposition (PVD) and characterised as anodes for Li-ion batteries. The interfacial properties of the electrodes coated with copper layers of different thicknesses have been studied using impedance spectroscopy and compared with those of unmodified electrodes. A general enhancement of the performances of the coated electrodes in terms of decreased solid electrolyte interface (SEI) and charge transfer resistances has been found. The charge transfer resistance decreases at any intercalation potential for metal layer thickness of the order of 250-300 A to increase again for thicker deposits. While in general the decrease in the charge transfer resistance may be related to a sort of catalytic effect of the metal layer in increasing the lithium desolvation rate, it is apparent that above a certain critical thickness value the layer acts as a barrier to the lithium ion transfer at the interface.