Trace Mn Doping Optimized the Electronic Structure and Improved the Rate Performance of Na₄Fe_2.91(PO₄)₂(P₂O₇) Cathode Materials

With the increasing demand for large-scale power energy storage system applications, pure-phase Na₄Fe_2.91Mn_x(PO₄)₂(P₂O₇) cathode materials doped with manganese (Mn) are successfully prepared by the spray drying method combined with a high-temperature sintering process for sodium ion batteries. The results show that the introduction of Mn effectively regulates the crystal and electronic structure of the material. Mn doping can reduce the lattice band gap, thereby further improving the electronic conductivity. On the other hand, the sodium ion migration channel is moderately widened, thereby increasing the ion diffusion rate. This synergistic optimization of electron conduction and ion diffusion capabilities allows the material to exhibit superior electrochemical performance. The optimal component of the Na₄Fe_2.91Mn_0.015(PO₄)₂(P₂O₇) cathode can still maintain a reversible specific capacity of 75 mAhg⁻¹ at an ultra-high rate of 30 C, and the capacity retention rate is as high as 81.8% after 1500 cycles at 20 C. This work provides a novel design insight for enhancing the rate performance and cycle stability of cathode materials, thereby facilitating the development of high-performance sodium-ion batteries for large-scale energy storage applications.