Due to the limited resources of lithium, sodium ion battery is regarded as the most promising alternative to lithium-ion batteries. In this study, the Cr coping and carbon coating anode material for SIBs, Na_1.25Cr_0.25Ti_1.75(PO₄)₃/C, is synthesized by a facile sol-gel technique using polyvinyl alcohol as carbon source. The obtained products show remarkable electrochemical properties in rate-capability (148.6 mAh g⁻¹ at 1C, 111.8 mAh g⁻¹ at 2C, 91.2 mAh g⁻¹ at 3C, 77.8 mAh g⁻¹ at 4C, 68.3 mAh g⁻¹ at 5C, 61.8 mAh g⁻¹ at 6C, 57.4 mAh g⁻¹ at 7C), cycle-stability (65.1% capacity retention over 1000 cycles) and Coulombic efficiencies. Furthermore, the doping of Cr element reduces the mean charge/discharge potential significantly and is favorable for the construction of the whole batteries with higher average potentials. The molecular dynamics simulations of the pristine NaTi₂(PO₄)₃ and NaCr_0.25Ti_1.75(PO₄)₃ tells us that the Cr doping in the lattice increases the self-diffusion coefficients of Na⁺ by 12 orders of magnitude. This great enhancement of the Na⁺ mobility is supposed to be owing to the presence of the interstice Na⁺ and the concerted migration of interstice Na⁺ and the M1 site Na⁺, which owns a significantly reduced energy barrier compared with that of the vacancy migration mechanism in the case of pristine NaTi₂(PO₄)₃.

由于锂的资源有限，钠离子电池被认为是锂离子电池最有希望的替代品。在这项研究中，SIBs的Cr涂层和碳涂层阳极材料Na _1.25 Cr _0.25 Ti _1.75（PO ₄）₃ / C是通过使用聚乙烯醇作为碳源的简便溶胶凝胶技术合成的。将得到的产品显示出速率能力（148.6毫安克显着的电化学特性^-1以1C，111.8毫安克^-1在图2C中，91.2毫安克^-1在图3C中，77.8毫安克^-1在4℃，68.3毫安克^-1在如图5C所示，61.8毫安克^-1在图6C中，57.4毫安克^-1（在7C下），循环稳定性（在1000个循环中保持65.1％的容量）和库仑效率。此外，Cr元素的掺杂显着降低了平均充电/放电电势，并且有利于具有更高平均电势的整个电池的构造。原始的NaTi ₂（PO ₄）₃和NaCr _0.25 Ti _1.75（PO ₄）₃的分子动力学模拟告诉我们，晶格中的Cr掺杂使Na ⁺的自扩散系数增加了12个数量级。Na ⁺迁移率的这种极大提高应该归因于存在空隙Na ⁺以及间隙Na ⁺和M1位点Na ⁺的协同迁移，与原始NaTi ₂（PO ₄）₃的空位迁移机理相比，它具有明显降低的能垒。