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

Abstract

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.