Study On Preparation And Electrochemical Properties Of P2 Type Manganese Sodium Oxide

In this paper,P2 type layered manganese sodium oxides were synthesized by solid-state method.The effect of different doping amounts of Cr,V ions and different modification amounts of CeO₂ on the structure and electrochemical properties of Na_0.67Mn_0.75Co_0.25O₂ were investigated,and the effect of La with different substitutions on the structure and electrochemical properties of Na_0.67Co_0.35Ti_0.2Mn_0.45O₂ are also studied.The materials of structure were characterized by X-ray diffraction?XRD?and Raman spectroscopy.The elemental state of the electrode materials were analyzed by X-ray photoelectron spectroscopy?XPS?.The morphology of the sample was characterized by field-emission scanning electron microscope-energy dispersive spectroscopy?FESEM-EDS?and transmission electron microscopy?TEM?.The XRD and Rietveld refinement analysis showed that the P2 phase structure of Na_0.67Mn_0.75Co_0.25O₂ did not change with doping of Cr,V and modification CeO₂.Similarly,the P2 phase structure of La-substituted Na_0.67Co_0.35Ti_0.2Mn_0.45O₂ did not change.Their space group is P6₃/mmc and belongs to structure of the hexagonal system.The morphological characterization of FESEM showed that all the features of manganese sodium oxides are layered hexagons.The size of the doped and coated manganese sodium oxide particles is substantially unchanged.The results of EDS analysis showed that Cr,V,La,and Ce were uniformly distributed throughout the flakes of the hexagonal layered oxides.The electrochemical performance studied that Cr and V doping significantly increase the maximum discharge capacity and cycle stability of the Na_0.67Co_0.35Ti_0.2Mn_0.45O₂sample,The Na_0.67Co_0.25Mn_0.65Cr_0.10O₂ can provide a maximum discharge capacity of128.1 mAh g^-1in the potential window of 2.0–4.0 V at 20 mA g^-1,and the capacity retention of the sample is 66.35%after 100 cycles.The V-doped Na_0.67Co_0.25Mn_0.705V_0.045O₂ cathode material can display a maximum discharge capacity of122.84 mAh g^-1 at a current density of 20 mA g^-11 in a 2.0–4.0 V windows,and an excellent capacity retention of 88.35%after 100 cycles.The CeO₂ surface modification of P2-Na_0.67Co_0.25Mn_0.75O₂ material can not only improves the maximum discharge capacity,but also improves the conductivity and sodium ion diffusion coefficient.Therefore,it is significantly improving the cycle stability and kinetics of P2 type oxides.Among them,the NCMO-2.0 wt%CeO₂ cathode showed the best cycle stability,its capacity retention still had 83.30%after 100 cycles.The La-substituted Na_0.67Co_0.35Ti_0.2Mn_0.44La_0.01O₂ exhibited an excellent initial specific capacity of 162.7 mAh g^-1 at 0.1 C,the capacity still had 125.9 mAh g^-11 after 50cycles.In addition,the Na_0.67Co_0.35Ti_0.20Mn_0.44La_0.01O₂ sample shows an excellent rate capacity of 91.9 mAh g^-1 and 60.4 mAh g^-1 even at 8 C and 10 C,the rate of capacity retention can be still maintained at 50.9%and 46.9%after 100 cycles,respectively.