Galvanostatic stimulated Na3Mn2(P2O7)(PO4) as a high-voltage cathode material for aqueous zinc-ion batteries

Abstract

To meet the application requirements of different scenarios, expanding the selection of cathode materials is a crucial step for the development of aqueous zinc-ion batteries (AZIBs). Manganese phosphates are a type of important and representative cathodes for rechargeable batteries, but they are rarely reported in AZIBs due to their electrochemical sluggishness in aqueous zinc electrolyte. Herein, carbon coating technic and galvanostatic stimulation process are combined to solve the issue and obtain an electrochemically active Na3Mn2(P2O7)(PO4) as cathode material for AZIBs. Carbon coated Na3Mn2(P2O7)(PO4) (NMPP@C) is synthesized by using a liquid-phase method assisted with freeze-drying process. After galvanostatic stimulation (100 mA g−1 for 5 cycles and following at 10 mA g-1), the originally inactive NMPP@C cathode shows a peak capacity of 150 mAh g-1 and then stabilizes at 90 mAh g−1 with a discharge plateau at 1.45 V vs. Zn2+/Zn. It is found that the NMPP@C cathode undergoes a structural decomposition during stimulation process, then α-MnO2 and Zn2P2O7•5H2O jointly serve as electrochemical reaction agents eventually. The electron/proton host (α-MnO2) and the Zn2+ host (Zn2P2O7•5H2O) are generated from the same conductive matrix of NMPP@C, which guarantees a satisfactory rate ability and a decent cycle performance in AZIBs.