Tuning high-spin ions in Prussian blue analogue toward ultra-long cycle-life ammonium-ion storage.

Aqueous ammonium-ion batteries (AAIBs) are gaining growing attention for their multiple advantages. Nevertheless, the exploration of advanced electrode materials with excellent electrochemical properties is still a major challenge. Herein, a K+-regulated CuFe-based Prussian blue analogue (K0.2Cu2.9[Fe(CN)6]2) was prepared via a co-precipitation strategy and applied for ammonium-ion storage. The electrochemical measurements reveal that the obtained K0.2Cu2.9[Fe(CN)6]2 delivers remarkable rate capability (55.6 mAh g-1 at 120C) and superior cycling durability (70.6% retention after 15,000 cycles at 60C). The highly reversible insertion and extraction of ammonium ions is contributed to the structural regulation of potassium ions in CuFe-based Prussian blue analogue as confirmed by X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). In addition, a PTCDI||K0.2Cu2.9[Fe(CN)6]2 full cell is constructed with average operating voltage of 0.85 V, which can power smart electronic devices. These results offer a viable route to high-efficiency electrode materials for advanced AAIB systems.