Synthesis And Modification Of The Lithium-Rich Manganese-Based Cathode Materials For Lithium-Ion Batteries

As a high-energy,long-life and environmentally friendly energy storage device,lithium-ion batteries have been widely used in daily life.However,with the rapid development of society,the performance requirements of lithium batteries are getting higher and higher.The development of electrode materials,which are safe,reliable,green and high-energy,will be the main task for the battery industry in the future.Because of the advantages of high energy and low cost,the lithium-rich manganese-based cathode materials have become a hot-spot research for the next generation of cathode materials.In this paper,sulphates were used as the raw materials and（NH₄）₂CO₃was used as the precipitation agent and complexing agent.The Mn_1-2xNi_xCo_xCO₃precursor prepared by the co-precipitation method was mixed with Li₂CO₃by ball milling,and then0.2Li₂Mn O₃·0.8Li TMO₂（TM=Mn、Ni、Co）cathode materials were obtained after sintering.The effects of p H value,Mn/Ni/Co ratio and calcination time on the Li-rich Manganese-based cathode materials were investigated by orthogonal experiment.The results show that 0.2Li₂Mn O₃·0.8Li TMO₂prepared with p H value of 8,Mn/Ni/Co ratio of 3:1:1 and calcination time of 12h has the best electrochemical performance.Under charging and discharging at a current density of 25m A·g^-1,the first discharge capacity is248.06m Ah·g^-1,and the initial coulombic efficiency is 69.9%,but its high-rate performance is very poor.When discharging at a rate of 5C(1C=250m A·g^-1),the capacity is 0m Ah·g^-1.In order to improve the rate performance of the original materials,this experiment used Na⁺and La³⁺doping to modify them.First of all,it can be found that the crystal structure of the original material can’t be changed by doping little of mental elements according to XRD analysis.And combined with XPS testing,we can see that Na⁺and La³⁺have been doped into the original material,which can change the chemical environment of the original transition metal and increase the average valence of Mn-Ni-Co.Finally,the electrochemical test shows that the modification materials,which doped by 2wt%Na⁺or 0.5wt%La³⁺,have the best performance.Their initial coulombic efficiency is 63.2%and 72.7%,respectively.Their discharge capacity at 5C is 60m Ah·g^-1and 31m Ah·g^-1,respectively.When the two elements are both used as doing agents,the best doping amount is 0.5wt%.For this material,the initial coulombic efficiency is 69.4%,and the discharge specific capacity at 5C is 28m Ah·g^-1.In addition,the low-rate discharge capacity of 0.5wt%co-doping sample is higher than the discharge capacity of 2wt%Na⁺doping sample,and the cycle performance is better than that of La³⁺doped sample under the same doping amount.