Study of new active materials for rechargeable sodium-ion batteries

Abstract. Na4Co3(PO4)2P2O7 is the unique crystal structure with multiple sodium-ion pathways in the structure. The electrochemical properties of Na4Co3(PO4)2P2O7 as a positive electrode for sodium-ion batteries were investigated. Na4Co3(PO4)2P2O7 had the multi redox couples in the highest potential region between 4.1 V and 4.7 V among ever reported sodium active materials and could deliver the reversible capacity of ca. 95 mAhg-1, corresponding to ca. 2.2 Na. Na4Co3(PO4)2P2O7 also exhibited the high rate capabilities and had a small polarization in the charge- discharge profile even at the high current densities, resulting in high energy efficiency of the battery. These performances indicate Na4Co3(PO4)2P2O7 can be one of the good candidates for a positive electrode material of sodium-ion batteries