Fabrication of Ultralarge Curvature Folding-Resistant Polyimide Films by Widening the Elastic Range and Intermolecular Slippery Spacing

As the electrons advanced toward foldable and lightweight characteristics, fabricating polyimide (PI) substrates resisting large curvature folding under an ultralow folding radius posed a significant challenge for flexible electronics. Here, one polyimide film (PICu) was fabricated by introducing Cu2+ and benzimidazole, whose elastic range and intermolecular slippery spacing were widened thanks to the point-to-face multi-coordination structure with larger attraction distance and variable bond angles, and it was fortunately equipped with greatly enhanced folding resistance even under an ultralarge curvature. First, the folding radius was confirmed to have an exponential impact on the tested folding reliability, as folding times of pure PI to form creases decreased sharply from 300,000 to 3000 with the folding radius dropping from 2 to 0.25 mm. In contrast, no crease was formed on PICu films even after folding over 200,000 times under an ultralow folding radius of 0.25 mm. Importantly, the folding radius was almost 10 times smaller than that in current reports (2–3 mm). In addition, the spread angle of PICu films after static folding at 80 °C was 50–78% larger than that of pure PI films with the folding radius decreased from 2 to 0.25 mm, demonstrating the excellent dynamic and static folding resistance of PICu films under an ultralarge curvature.