Effect of Concentrated Electrolyte on Aqueous Sodium-ion Battery with Sodium Manganese Hexacyanoferrate Cathode

From the viewpoint of the cost and safety, aqueous sodium-ion batteries are attractive candidate for large-scale energy storage. Although the operating voltage range of the aqueous battery is theoretically limited to 1.23 V by the electrochemical decomposition of water, the voltage restriction is a little bit eased in real aqueous battery system by the charge/discharge overvoltage. Effect of the concentrated electrolyte on the operation voltage was studied in aqueous Na-ion battery with Na2MnFe(CN)(6) hexacyanoferrates cathode and NaTi2(PO4)(3) NASICON-type anode, in order to increase the discharge voltage. According to the cyclic voltammetry, the electrochemical window of diluted 1 mol kg(-1) NaCIO4 aqueous electrolyte is only 1.9 V, whereas the corresponding electrochemical window of concentrated 17 mol kg(-1) NaCIO4 aqueous electrolyte is widen to 2.8 V. This wide electrochemical window of the concentrated aqueous electrolyte allows the Na2MnFe(CN)(6)//NaTi2(PO4)(3) aqueous sodium-ion system to work reversibly. By contrast, the framework of Na2MnFe(CN)(6) cathode was destroyed by the hydroxide anion generated in diluted 1 mol kg(-1) electrolyte. (C) The Electrochemical Society of Japan, All rights reserved.