Study On Doping And Electrochemical Properties Of P2 Type Layered Oxide

In this work,P2-type layered cobalt manganese oxide Na_0.59Co_0.2Mn_0.8O₂ was synthesized by a simple solid-state reaction method,and it was doped with B,Mo and Y elements.It was used as the cathode material of sodium ion batteries to study the changes of structure and electrochemical performance.X-ray diffraction?XRD?was used for structural characterization,X-ray photoelectron spectroscopy?XPS?was used for element valence analysis,and field emission electron microscopy-energy dispersive spectroscopy?FESEM-EDS?was used for morphology and elements distribution analysis.XRD and Rietveld refinement results shows that the Na_0.59Co_0.2Mn_0.8O₂ sample still maintains the space group of P6₃/mmc after doped with B,Mo and Y,and the P2 phase structure has not change.FESEM test results shows that both the original material and the doped samples have flaky morphology.Doping do not significantly change the particle morphological of the layered cobalt manganese oxide.EDS shows that Na,Co,Mn,B and O elements are uniformly distributed in Na_0.59Co_0.2Mn_0.75B_0.05O₂,and Na,Co,Mn,Mo and O elements are uniformly distributed in Na_0.59Co_0.2Mn_0.77Mo_0.03O₂,and Na,Co,Mn,Y and O elements are uniformly distributed in Na_0.59Co_0.2Mn_0.77Y_0.03O₂.Electrochemical performance study shows that the doping of B,Mo and Y significantly improves the cycle stability and rate performance of Na_0.59Co_0.2Mn_0.8O₂,which may be attributed to the increase of a-axis and sodium ion diffusion channels,the decrease of charge transfer resistance and the increase of apparent Na⁺diffusion coefficient.The Na_0.59Co_0.2Mn_0.75B_0.05O₂ cathode material can provide a maximum discharge capacity of135.2 mAh·g^-1 at a voltage range of 2.0–4.0 V at 0.1 C(1 C=156 mA·g^-1),and the capacity retention rate can be maintained at 85.01%after 100 cycles.For Na_0.59Co_0.2Mn_0.77Mo_0.03O₂cathode material,the maximum discharge capacity can reach 131.9 mAh·g^-1,and it has an excellent capacity retention rate?91.51%?after 100 cycles.The maximum discharge capacity of the Na_0.59Co_0.2Mn_0.77Y_0.03O₂ cathode material can reach 119.8 mAh·g^-1,and it still has a very excellent capacity retention rate of 92.90%after 100 cycles.Those Rietveld refinement results shows that the bond length of the TM–O is reduced,and the bond length of the Na–O is increased,which facilitates the diffusion of Na⁺ions in the P2 phase layers and enhances the dynamic performance of the materials.At the same time,the cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?of the materials doped with B,Mo and Y are tested,test results show that the Na⁺ion diffusion coefficient of the materials is increased after element doping.