Amorphous iron phosphates are potential cathode materials for sodium ion batteries. The amorphous FePO₄ matrix is able to insert/extract sodium ions reversibly without apparent structural degradation, resulting in stable performance during the charge/discharge process. However, the extremely low electronic conductivity of FePO₄ itself becomes a formidable obstacle for its application as a high-performance cathode material. Here, by tuning the growth kinetics of FePO₄ in an aqueous solution, we were able to control its formation onto a large variety of substrates, forming uniform core-shell structures. Specifically, the use of multiwalled carbon nanotubes as the core material together with the growth control of FePO₄ produced the core-shell structure of MWCNTs@FePO₄ with a delicately controlled shell thicknesses. We confirmed that such a nanocomposite can act as an effective cathode material by taking advantage of both the highly conductive core and the electrochemically active shell, leading to improved battery performance as revealed by the high discharge capacity and the greatly improved rate capability. We anticipate that our progress in FePO₄ control offers new potential in different research fields, such as materials chemistry, catalysis and energy storage devices.

非晶态磷酸铁是钠离子电池的潜在阴极材料。非晶态FePO ₄基质能够可逆地插入/提取钠离子，而没有明显的结构降解，从而在充电/放电过程中产生稳定的性能。然而，FePO ₄本身的极低电子电导率成为其用作高性能阴极材料的巨大障碍。在这里，通过调节FePO ₄在水溶液中的生长动力学，我们能够控制其在多种基质上的形成，从而形成均匀的核-壳结构。具体而言，使用多壁碳纳米管作为核心材料以及FePO ₄的生长控制生产出具有精细控制的壳厚度的MWCNTs @ FePO ₄的核壳结构。我们证实，这种纳米复合材料可以通过利用高导电核和电化学活性壳两者而充当有效的阴极材料，从而由于高放电容量和大大提高的倍率能力而显示出改善的电池性能。我们期望我们在FePO ₄控制方面的进展将在不同的研究领域提供新的潜力，例如材料化学，催化和能量存储设备。