Effect of Zr4+ doping on the electrochemical properties of Na3MnTi(PO4)3/C cathode materials

NASICON structural materials have the advantages of structural stability, high ion conductivity, and high working potential, which have attracted widespread attention as cathode for sodium-ion batteries. Although the three-electron reaction in the NASICON structure Na3MnTi(PO4)3 increases the specific capacity of the material, poor electronic conductivity remains a key factor restricting its practical application. Herein, Na3Mn1-xZrxTi(PO4)3/C (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1), a typical three-dimensional NASICON structure cathode material for sodium-ion batteries, was synthesized by the sol-gel method. Through powder X-ray diffraction, the Zr4+ doping in the Na3MnTi(PO4)3 (NMTP) structure was verified. It was found that doping trace amounts of Zr at the Mn site can not only reduce the Jahn-Teller effect caused by Mn3+, but also strengthen the Zr-O bond compared to the Mn-O bond, making the crystal structure more stable by reducing the proportion of Mn. According to the findings of the EIS test, a suitable amount of Zr doping can enhance the electronic conductivity and Na ion diffusion coefficient of NMTP/C electrode materials, weaken polarization phenomena, increase electrode reaction rate, and significantly improve the rate performance and cycling performance of Na3Mn1-xZrxTi(PO4)3 material. The Na3Mn1-xZrxTi(PO4)3/C sample prepared has high initial capacity of 124mAh/g, a capacity retention rate of 86 % after 200 cycles at 0.2C, and a capacity retention rate of 84 % after 500 cycles at 1C. This proves that the material still exhibits excellent cycling stability and structural stability after high current cycling. More importantly, the Na3Mn0.95Zr0.05Ti(PO4)3 (Zr5-NMTP)//Hard carbon full battery also exhibits ideal electrochemical performance.