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With the rapid development of flexible electronics, low-cost, flexible, high-energy-density power sources are urgently needed. Theoretically, the emerging rechargeable potassium-ion batteries (KIBs) could be a promising candidate due to the abundance and low cost of potassium resources. However, owing to the absence of high-performance cathode materials and effective methods to fabricate robust and soft electrodes, producing flexible KIBs remains a daunting challenge. Herein, cyanotype is successfully employed as a photographic printing technique for the fabrication of a low-cost, scalable, and flexible cathode. The combined advantages of optimized crystallinity and morphology of the cathode materials as well as the ultralight and robust nature of the flexible electrode endow the KIB with superior performance including high energy density (up to 232 Wh kg⁻¹) and excellent flexibility. This low-cost and …