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 (Cu₃(PO₄)₂/C) can be used as a novel high-capacity cathode for rechargeable Na batteries. Cu₃(PO₄)₂/C shows a reversible capacity up to 290mAhg⁻¹ at a current of 20mAg⁻¹and 190mAhg⁻¹ at 400mAg⁻¹, with capacity retention of 210 and 160mAhg⁻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 Cu₃(PO₄)₂ can transform into Na₃PO₄ and Cu particles after discharge. Furthermore, Cu can react with Na₃PO₄ to form copper phosphate and Na_xCu_yPO₄ in the charge process, determining the rechargeability of Cu₃(PO₄)₂.

中文翻译：

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Cu3（PO4）2 / C复合材料作为可充电Na离子电池的高容量阴极材料

转化型材料由于其高容量，是钠离子电池阴极材料的传统插层化合物的吸引人的替代品。在本文中，我们首次报道了碳包覆​​的磷酸铜（Cu ₃（PO ₄）₂ / C）可以用作可充电Na电池的新型高容量阴极。的Cu ₃（PO ₄）₂ / C示出了可逆容量高达290mAhg ^-1在20mAg的电流^-1和190mAhg ^-1在400mAg ^-1，以210和160mAhg的容量维持^-1分别经过30个循环。通过采用异位XRD，HR-TEM，固态NMR和XAFS技术研究了详细的钠存储机理。结果清楚地表明，放电后Cu ₃（PO ₄）₂可以转变为Na ₃ PO ₄和Cu颗粒。此外，在充电过程中，Cu可以与Na ₃ PO ₄反应形成磷酸铜和Na _x Cu _y PO ₄，从而确定Cu ₃（PO ₄）₂的可再充电性。