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.