Over 2 V Aqueous Sodium-Ion Battery with Prussian Blue-Type Electrodes

High discharge voltage of more than 2 V is achieved in a novel aqueous sodium-ion battery with the combination of a Prussian blue-type sodium manganese hexacyanoferrate cathode, and a similar potassium manganese hexacyanochromate anode. Here, a highly concentrated sodium perchlorate aqueous electrolyte with a 2.8 V electrochemical window is used. By element analysis, the novel anode containing little potassium element possibly serves as a suitable host–guest anode, similarly as the cathode extracting/inserting sodium ion in a highly concentrated sodium-ion aqueous electrolyte. Open-framework electrodes and a highly concentrated but mobile aqueous electrolyte contribute to high voltage and high rate performance of the aqueous sodium-ion battery.