Ultrafast cation insertion-selected zinc hexacyanoferrate for 1.9 V K-Zn hybrid aqueous batteries

The low energy/power density of aqueous rechargeable batteries (ARBs) have limited their further development and application because of their voltage limitation of 1.23 V. Herein, K-Zn hybrid ARBs with a high discharge voltage of 1.937 V are reported for the first time. The selective ionic insertion/extraction mechanism into/from the zinc hexacyanoferrate (ZnHCF) cathode in the hybrid electrolyte was clearly revealed by in situ X-ray diffraction. The cathode material displays an outstanding rate capability of 300C and a high capacity of 78.7 mA h g(-1). The constructed K-Zn hybrid ARBs exhibit an energy density of 67 W h kg(-1), a high power density of 4.76 kW kg(-1) and excellent rate performance with 67.6% capacity retention from 2C to 60C. These excellent performances contribute to the selected K+ insertion mechanism. These exciting results can offer an alternative path for the development of hybrid aqueous batteries for stable and high energy/power density energy storage techniques.