Mn2+掺杂聚阴离子型钠离子电池正极材料的制备及电化学性能

Synthesis and electrochemical properties of Mn2+ doped polyanionic sodium-ion battery cathode materials

摘要:

以FeSO4·7H2O、MnSO4·H2O、NH4H2PO4、CH3COONa、一水合柠檬酸和氧化石墨烯（GO）为原料，采用溶胶凝胶法制备了Mn2+掺杂（相对掺杂量x，下同）、还原氧化石墨烯（rGO）包覆的聚阴离子型钠离子电池正极材料Na4Fe3-xMnx(PO4)2(P2O7)/rGO（Mnx-NFPP/rGO）。通过SEM、XRD、EDS、XPS表征Mnx-NFPP/rGO的微观形貌和结构成分，基于恒流充放电、循环伏安和电化学阻抗测试，考察了Mn2+相对掺杂量x对Mnx-NFPP/rGO的电化学性能影响，采用密度泛函理论（DFT）计算Mnx-NFPP/rGO的能带和态密度。结果表明，Mn2+掺杂扩大了Na+扩散通道，提高了Na+扩散速率，但对材料的三维结构和形貌没有影响；Mn2+相对掺杂量0.3的Mn0.3-NFPP/rGO表现出最优的循环稳定性和倍率性能，在0.05 C倍率下具有131.2 mA·h/g的初始放电比容量， 2 C倍率下的充放电比容量91.9 mA·h/g；Mn2+掺杂和rGO包覆有效提高了材料的放电比容量和循环稳定性，1 C倍率100圈循环后的比容量保持率为94%。Mn2+的掺杂降低了材料价带与导带之间的带隙（3.128 eV），使价带中的电子更容易跃迁到导带，从而有利于提高Na+的扩散动力学和本征电导率。

Abstract:

Mn2+-doped (relative doping amount x, the same below) and reduced graphene oxide (rGO)-coated polyanionic sodium-ion battery cathode materials Na4Fe3-xMnx(PO4)2(P2O7)/rGO (Mnx-NFPP/rGO) was prepared by the sol-gel method using FeSO4·7H2O, MnSO4·H2O, NH4H2PO4, CH3COONa, citric acid monohydrate, and graphene oxide (GO) as raw materials. The microstructure and composition of Mnx-NFPP/rGO were characterized by SEM, XRD, EDS, and XPS. The influence of the relative Mn2+ doping amount x on the electrochemical performance of Mnx-NFPP/rGO was investigated based on galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance tests. Density functional theory (DFT) was employed to calculate the energy bands and density of states of Mnx-NFPP/rGO. The results showed that Mn2+ doping expanded the Na+ diffusion channels and enhanced the Na+ diffusion rate, but had no effect on the three-dimensional structure and morphology of the material. Mn0.3-NFPP/rGO with a relative Mn2+ doping amount of 0.3 exhibited the best cycle stability and rate performance, with an initial discharge specific capacity of 131.2 mA·h/g at a rate of 0.05 C and a charge-discharge specific capacity of 91.9 mA·h/g at a rate of 2 C. Mn2+ doping and rGO coating effectively improved the discharge specific capacity and cycle stability of the material, with a specific capacity retention rate of 94% after 100 cycles at a rate of 1 C. Mn2+ doping reduced the band gap (3.128 eV) between the valence band and conduction band of the material, making it easier for electrons in the valence band to transition to the conduction band, thereby improving the Na+ diffusion kinetics and intrinsic conductivity.