Research On The Structure Regulation And Lithium Storage Performance Of Transition Metal Oxides

With the depletion of fossil energy and the development of technology,it has put new requirements on the performance of lithium ion batteries for energy storage and conversion,personal electronic equipment and new energy vehicles.In terms of anode materials,transition metal oxides have more theoretical specific capacity than graphite when used in lithium-ion batteries,and is considered as a new electrode material with high development value.In this article,core-shelled NiFe₂O₄-NiO@Fe₂O₃ was preparaed based on cheap,easily available,and environmentally friendly Prussian blue analogues?PBAs?,through cation exchange reaction in aqueous solution and roasting in air.By adjusting the ratio of used nickel and manganese salts,the ternary Prussian blue analog Ni_x Mn_y[Fe?CN?₆]₂?x+y=3?was prepared,based on what,metal oxides were obtained with different nickel-manganese ratios and different morphologies as well.By self-polymerization of dopamine on the surface of the Prussian blue analogues in alkaline aqueous solution,the corresponding NiFe₂O₄-NiO@C,CoFe₂O₄-CoO@C and FeMnO₃@C composite materials with good crystallinity were prepared by two-stage oxidation at low temperature.The influence of core-shell structure,calcination temperature,different metal ratios and carbon coted on the morphology and electrochemical performance to the materials were studied with the results as follows:Core-shelled NiFe₂O₄-NiO@Fe₂O₃ can be obtained by cation exchange in aqueous solution and calcination.Lower and higher calcination temperatures have an adverse effect on the morphology and electrochemical performance of the material.The prepared NiFe₂O₄-NiO@Fe₂O₃ has an initial capacity of 1587.96 mAh/g,and has a reversible capacity of 472.5 mAh/g after 500 cycles at the current density of 500 mA/g.Analysis of its electrode dynamics shows that it has a 66.1%pseudocapacitance contribution at the scan rate of 2mV/s.By adjusting the nickel-manganese element ratio,the microscopic morphology of the obtained ternary Prussian blue analogue can be controlled,and ternary transition metals oxieds with the structures of nanocube,truncated nanocube,nanosphere,core^-shell yolk are prepared respectively after calcination.The formation process of the truncated nanocube was analyzed.With yolk structure,the prepared NiFe₂O₄-FeMnO₃ has an intial capacity of 1697.6mAh/g.After cycling 500 cycles at 500 mA/g,it also has a reversible capacity of 536.1mAh/g.And its charge transport resistance is 20.34?.The pseudo-capacitance contribution of NiFe₂O₄-FeMnO₃ is 46.8%at 0.1mV/s.At the same time,when Ni:Mn=8:2 or 2:8,the corresponding oxide has excellent cycle stability,higher reversible capacity,lower charge transfer resistance,and higher pseudocapacitance contribution.When Ni:Mn=4:6,6:4,the synergy between metals is greatly weakened.NiFe₂O₄-NiO@C,CoFe₂O₄-CoO@C,and FeMnO₃@C composite materials can be obtained through polydopamine coating and two-stage low-temperature roasting method,while maintaining a certain coated carbon layer,and Prussian blue analogues are converted into metals Oxide.The charge transfer impedance of these materials is reduced to 31.5,32.4,and 87.3?,respectively.At a current density of 500 mA/g,the reversible capacities after 500cycles were maintained as 632.7,429.5,and 435.2 mAh/g respectively.At the same time,the carbon coating can also enhance the role of pseudocapacitance in these materials.At a scan rate of 0.1mV/s,the proportion of pseudocapacitance is 54.4%,39.7%,and 36.5%,respectively.There is a substantial improvement.