Preparation And Surface Modification Of Layered Lithium-rich Manganese-based Cathode Materials

With the development of society and technology,people have more and more demand for energy.In the field of new energy,the development of lithium-ion battery is very rapid,but the existing cathode materials of lithium ion batteries are difficult to meet people's demand for large-capacity batteries.The layered lithium-rich manganese-based cathode material Li1.2Ni0.13Co0.13Mn0.54O2 for lithium-ion batteries has attracted the attention and research of many domestic and foreign researchers with its high specific capacity,high operating voltage,and low cost.It is considered to be one of the best choices for the next-generation lithium ion battery cathode materials.However,lithium-rich manganese-based materials have problems such as large irreversible specific capacity for the first charge and discharge,poor rate performance,severe cycle capacity attenuation,irreversible phase change and voltage attenuation during the cycle,and these problems seriously restrict the commercial application of materials.Therefore,it is particularly important to improve the electrochemical performance of lithium-rich manganese-based materials through the optimization of preparation methods and the modification of materials.The main research contents of this paper are as follows:(1)A very simple preparation method is used to obtain the precursor of layered lithium rich manganese based materials in one step.The best synthesis process and conditions are obtained by comparing and optimizing the reaction temperature in the preparation process and the kinds of surfactants.The results show that when the reaction temperature is 85? and the surfactant is PVP,the prepared material has good electrochemical performance.The discharge specific capacity remains 123.4mAh/g after 150 cycles at a current density of 2C,and the capacity retention rate is 75.6%.(2)On the basis of preparing lithium-rich manganese-based materials under the best technological conditions,the materials were surface-modified.Two metal oxides,magnesium oxide and aluminum oxide,were coated separately,and the effects of different coating amounts on the properties of the material were studied.Afterwards,the modified materials were characterized by XRD,SEM,TEM,XPS and other physical characteristics,as well as the first charge and discharge,rate performance,long cycle and other electrochemical properties.The results show that the coating modification of magnesium oxide and aluminum oxide does not change the structure of the lithium-rich manganese-based material.However,the coating modification of magnesium oxide in this paper does not significantly improve the electrochemical performance of the material and does not reach the ideal level.The modification of alumina significantly improves the performance of the material,especially when the coating amount of alumina is 3wt%,the performance of the material is most obviously improved.The first discharge specific capacity is up to 317.9mAh/g,the first Coulomb efficiency is increased from 74.7%to 82.1%,the specific discharge capacity is 105.6mAh/g at a high rate current density of 10C,and the specific discharge capacity is 164mAh/g after 200 cycles at 2C,the capacity retention rate is 86.3%,which is much higher than that of the unmodified material(the specific discharge capacity after 200 cycles at 2C is 124mAh/g,and the capacity retention rate is 73.3%).The electrochemical impedance test shows that the coating of alumina can also significantly reduce the charge transfer resistance of the material in the cycle.