Controllable Electroless Deposition and Physicochemical Properties of 1 μm Copper Coating on Inert PI Film

Lightweight composite copper foil with a “copper (1 μm)–polymer (4 μm)–copper (1 μm)” sandwich structure is a promising alternative to conventional electrolytic copper foil as current collector for lithium-ion batteries (LIBs). This work systematically optimizes an electroless copper plating route on typical polyimide (PI) film to fabricate ultrathin composite copper foil for lithium-ion battery current collectors. NaOH modification and AgNO3 activation processes were established to build active sites on PI film for subsequent copper deposition. Key parameters for NaOH modification and AgNO3 activation, including the concentration, temperature, and treatment time, were systematically optimized. The optimal electroless copper plating solutions with 10 mL/L HCHO and 10 g/L CuSO4 were obtained. Benzotriazole was identified as an effective antioxidant to enhance the corrosion resistance of composite copper foil. It was found that self-made composite copper foil possessed excellent tensile strength and ductility. Compared to 6 μm electrolytic copper foil, the composite copper foil achieved a 50.1% weight reduction and maintained comparable electrochemical performance. Lithium-ion batteries with composite copper foil current collectors exhibited superior charging/discharging performance, and the corresponding mass energy density increased from 351.9 to 368.9 Wh/kg. This work demonstrates the engineering feasibility of composite copper foils as lightweight current collectors prepared by electroless copper plating, and exhibits significant application potential in advanced high-energy-density lithium-ion batteries.