Study on the Formation and Evolution Mechanism of Pinhole in Aluminum Foil for the Lithium-Ion Battery Soft Packaging

As the crucial core material in aluminum–plastic-laminated films, aluminum foil serves as a barrier and shaping element for lithium-ion battery soft packaging. However, its thinness, measuring only tens of microns, makes it susceptible to the formation of pinholes during the manufacturing process, which can significantly impact the barrier performance and properties of the aluminum–plastic-laminated film. The morphology and composition of foreign particles that lead to pinholes were analyzed using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). Additionally, the formation mechanism and evolution law of pinholes were investigated using a laser scanning confocal microscope (LSCM). The results revealed that foreign particles responsible for pinholes originated from the inclusions in the aluminum alloy melt, filter aid particles from rolling oil, and environmental dust particles. To address this issue, potential strategies for controlling foreign particles were proposed. These included purifying the aluminum alloy melt, filtering the rolling oil, and maintaining a clean production environment. The simulated experiments showed that foreign particles were gradually embedded in the aluminum matrix during plastic deformation, leading to damage in the aluminum matrix. When the cumulative rolling reduction ratio exceeded 38%, the aluminum foil and foreign particles began to separate along the rolling direction, resulting in the formation of pinholes. The mechanism of uncoordinated deformation between foreign particles and aluminum foil was elaborated in detail. In addition, the simulation experiment indicated that once the cumulative reduction ratio surpassed 50%, the aspect ratio of the pinhole increased rapidly. When the cumulative reduction ratio increased to 83%, the pinhole began to gradually heal. Consequently, a quantitative relationship model between the pinhole area and the rolling reduction ratio was constructed. The pinhole evolution model enables a rough prediction of the actual pinhole area change and meets the requirements for engineering applications. This research provides both engineering applications and theoretical prediction approaches that can aid in the production of high-quality aluminum foil for lithium-ion battery soft packaging.