Cu3(PO4)2/C composite as a high-capacity cathode material for rechargeable Na-ion batteries

Abstract Conversion-type materials are an appealing alternative to conventional intercalation compounds as cathode materials for sodium ion batteries, due to their high capacities. In this paper, we report for the first time that carbon-coated copper phosphate (Cu 3 (PO 4 ) 2 /C) can be used as a novel high-capacity cathode for rechargeable Na batteries. Cu 3 (PO 4 ) 2 /C shows a reversible capacity up to 290 mA h g −1 at a current of 20 mA g −1 and 190 mA h g −1 at 400 mA g −1 , with capacity retention of 210 and 160 mA h g −1 respectively after 30 cycles. The detailed sodium storage mechanisms were studied by employing ex -situ XRD, HR-TEM, solid-state NMR and XAFS techniques. The results clearly indicate that Cu 3 (PO 4 ) 2 can transform into Na 3 PO 4 and Cu particles after discharge. Furthermore, Cu can react with Na 3 PO 4 to form copper phosphate and Na x Cu y PO 4 in the charge process, determining the rechargeability of Cu 3 (PO 4 ) 2 .