Sodium vanadium oxyfluorophosphate NaV(PO)FO is an attractive cathode material for sodium ion batteries due to its high crystalline stability, high specific capacity and high discharge potential. Currently, the poor electronic conductivity and low diffusion rate of Na severely impede its development and application. In this work, low-dose Mo doping is proposed through first-principle computation to enhance the structure and performance of NaV(PO)FO. It is found that low-dose of Mo doping can reduce the band gap and energy barrier for Na diffusion in NaV(PO)FO. However, heavy doping leads to serious Jahn-Teller distortion of the crystal structure. Therefore, low-dose Mo doping, ranging from x = 0 to x = 0.06 in NaVMo(PO)FO, is designed and experimentally carried out. The best performance with 118.5 mA h g at 0.1C and 60.6 mA h g at 20C is obtained in NaVMo(PO)FO when x = 0.04 in comparison with other doping amounts. The specific discharge capacity at 0.5C decreases gradually from 105.4 to 77.9 mA h g after 400 cycles, indicating a capacity retention of 73.9 %. These results demonstrate that low-dose Mo doping is an effective strategy to enhance the electrochemical performance of NaV(PO)FO, making it a promising cathode material for sodium batteries.

中文翻译：

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低剂量低价钼掺杂Na3V2(PO4)2F2O钠电池正极机理及性能增强


氟氧磷酸钒钠NaV(PO)FO由于其高晶体稳定性、高比容量和高放电电位，是一种有吸引力的钠离子电池正极材料。目前，Na的电子导电性差和扩散速率低严重阻碍了其开发和应用。在这项工作中，通过第一原理计算提出了低剂量Mo掺杂，以增强NaV(PO)FO的结构和性能。研究发现低剂量Mo掺杂可以降低NaV(PO)FO中Na扩散的带隙和能垒。然而，重掺杂会导致晶体结构严重的Jahn-Teller畸变。因此，设计并在 NaVMo(PO)FO 中进行低剂量 Mo 掺杂（范围从 x = 0 到 x = 0.06）。与其他掺杂量相比，当 x = 0.04 时，NaVMo(PO)FO 中获得了最佳性能，在 0.1C 时为 118.5 mA h g，在 20 C 时为 60.6 mA h g。 400次循环后，0.5C的放电比容量从105.4mAh g逐渐下降至77.9mAh g，容量保持率为73.9%。这些结果表明，低剂量Mo掺杂是增强NaV(PO)FO电化学性能的有效策略，使其成为有前景的钠电池正极材料。