Cu3(PO4)2: Novel Anion Convertor for Aqueous Dual‑Ion Battery

Electrode materials which can reversibly react with anions are of interest for aqueous dual-ion batteries.Herein,we propose a novel anion electrode,Cu3(PO4)2,for constructing an aqueous dual-ion cell.The Cu3(PO4)2 electrode can operate in a quasi-neutral condition and deliver a reversible capacity of 115.6 mAh g^−1 with a well-defined plateau at−0.17 V versus Ag/AgCl.Its reaction mechanism shows that Cu3(PO4)2 decomposes into Cu2O and subsequently is converted into Cu during the initial discharge process.In the following charge process,Cu is oxidized into Cu2O.It suggests Cu3(PO4)2 reacts with OH−ions instead of PO43−ions after the initial discharge process and its potential thereby depends upon the OH−ions concentration in electrolyte.Additionally,an aqueous dual-ion cell is built by using pretreated Cu3(PO4)2 and Na0.44MnO2 as anode and cathode,respectively.During cycling,OH−ions and Na^+ions in electrolyte can be stored and released.Such a cell can provide a discharge capacity of 52.6 mAh g^−1 with plateaus at 0.70 and 0.45 V,exhibiting the potential of application.This work presents an available aqueous dual-ion cell and provides new insights into renewable energy storage and adjustment of the OH−ions concentration in aqueous buffer solution.