Adjustment mechanism of surface properties to induce copper plating on typical polymer films

Abstract

Composite copper foil with a copper-polymer-copper sandwich structure is a promising negative electrode current collector for high-energy-density lithium-ion batteries. Electroless copper plating is an attractive method to directly prepare composite copper foil, but limited by intrinsic inert characteristics of polymer surface. Surface properties of various polymer films are obviously different. The corresponding activation mechanisms are also unclear. This work identifies the surface active sites of typical polymers, i.e. polyimide (PI), polyethylene terephthalate (PET), and polypropylene (PP). The pathway and mechanism for surface modification and activation of polymer are explored. It is confirmed that reactive groups (such as -COOH and -OH) are formed from carbonyl groups (C = O) on PI and PET by NaOH modification. However, PP cannot be modified or activated due to overall inertness. The modified PI can be activated by AgNO₃ to produce COO-Ag active sites for electroless copper plating. However, the modified PET cannot be directly activated by AgNO₃ due to less reactive groups. After plasma etching to graft active functional groups on PET surface, and Ag⁺ can also be anchored on PET surface by NaOH modification and AgNO₃ activation. Composite copper foil with PI or PET polymer film is successfully prepared. This work clarifies the surface properties and the corresponding activation mechanism, which is helpful for the convenient preparation of composite copper foil by electroless copper plating.