Graphene oxide suspension-based electrolyte promotes the cycling performance of aqueous sodium-ion batteries through the interaction between metal ions, free water molecules and functional groups

Prussian blue analogue (PBA)-based aqueous batteries are promising solutions for large-scale energy storage. However, PBA cathode materials are still facing erosion and dissolution originating from the strong polarity and high proton activity of water leading to the destruction of their frameworks and poor cycling performance. Herein, we developed a new route to protect Sodium Prussian blue analogue (PB–Na, Na0.65Fe[Fe(CN)6]0.91·□0.09·2.7H2O) by introducing graphene oxide (GO) into the aqueous electrolyte, which can in-situ form an ion selectivity membrane on the separator surface. GO can prevent the diffusion of transition metal ions of dissolved PB-Na penetrating the separator to the anode material by the coordination interaction between transition metal ions and the oxygen-containing functional groups (carboxyl, carbonyl, etc). Meanwhile, hydrophilic groups (hydroxyl, carboxyl, etc) of GO can absorb free water molecules by hydrogen bond and electrostatic interaction reducing the dissolution of PB-Na. Thus PB-Na cathode material-based sodium-ion batteries in the low-concentration aqueous electrolyte can still achieve a capacity of 65.5 mAh g−1 and a high capacity retention of 65.1% after 17000 cycles. This strategy can be considered a simple and effective method to protect active materials in the aqueous batteries.