采用喷雾干燥制备前驱体，经高温烧结制得有电化学活性的钠离子电池NaMnPO4正极材料. X射线衍射分析（XRD）证明，合成的NaMnPO4材料系正交晶系、Pmnb空间群的磷钠锰矿（Natrophilite）型材料. 扫描电镜（SEM）及透射电镜（TEM）结果显示，喷雾干燥得到的前驱体为空心球粒子，经高温烧结后，该材料由粒径几十纳米的NaMnPO4纳米晶一次颗粒及无定形碳网络结构相互连接组成的微米级二次颗粒构成. 电化学测试表明，NaMnPO4/C复合结构显著改善了材料的离子电导与电子电导，首次报道电流密度为7.75 mA·g-1、电压范围为1.0 ~ 4.5 V (vs. Na+/Na)时，钠离子电池NaMnPO4正极材料的可逆放电比容量达90 mAh·g-1.
As a cathode material for sodium ion batteries, NaMnPO4/C nanocomposite is successfully synthesized by the combination of spraying drying and high temperature sintering methods. The crystal structure of the as-synthesized phosphate material is confirmed as the natrophilite NaMnPO4, which possesses orthorhombic symmetry and Pmnb space group. It is shown that the precursors are hollow spherical particles and the obtained product consists of micro-scaled secondary particles, which are composed of NaMnPO4 nanocrystallites (tens of nanometres) and amorphous carbon networks. The ionic and electronic conductivities of NaMnPO4 are both effectively enhanced with the help of this nanocomposite structure. In addition, the differences in the Na+-diffusion channel and local structures among the three types of NaMPO4, i.e. olivine, maricite and natrophilite, are also discussed. The electrochemical tests show that the natrophilite NaMnPO4 can deliver the reversible capacity of 90 mAh·g-1 at a current density of 7.75 mA·g-1 when cycled in the voltage range of 1.0-4.5 V (vs. Na+/Na).
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