Aqueous sodium ion battery (ASIB) is gaining more attention with the growing concern in safety and environmental issues. However, the potential window of ASIB is limited to the decomposition voltage of water. Recently, the potential window of aqueous electrolyte has been reported that it can be extended in high-concentration electrolytes. Since then, researchers are dedicating to finding cathode materials with higher discharging potential which can increase the energy density of aqueous batteries. In this study, we demonstrate a new concept in cathode material design to reach an ultra-high rate capability by modifying the side group of a Prussian blue analogue, copper hexacyanoferrates (CuHCF). The modified cathode material was carefully analyzed by ex-situ XRD measurements, X-ray photoelectron spectroscopy, cyclic voltammetry (CV), and charge-discharge measurement to reveal their electrochemical performances. The diffusivity was also calculated by potentiostatic intermittent titration technique test and Randles-Sevcik equation.
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