Processing Rusty Metals into Versatile Prussian Blue for Sustainable Energy Storage

To reach a closed‐loop material system and meet the urgent requirement of sustainable energy storage technologies, it is essential to incorporate efficient waste management into designing new energy storage materials. Here, a “two birds with one stone” strategy to transform rusty iron products into Prussian blue as high‐performance cathode materials, and recover the rusty iron products to their original status, is reported. Owing to the high crystalline and Na + content, the rusty iron derived Prussian blue shows a high specific capacity of 145 mAh g −1 and excellent cycling stability over 3500 cycles. Through the in situ X‐ray diffraction and in situ Raman spectra, it is found that the impressive ion storage capability and stability are strongly related to the suppressed structure distortion during the charge/discharge process. The ion migration mechanism and the possibility to serve as a universal host for other kinds of ions are further illuminated by density functional theory calculations. This work provides a new strategy for recycling wasted materials into high value‐added materials for sustainable battery systems, and is adaptable in the nanomedicine, catalysis, sensors, and gas storage applications.