Adjust Structure And Research Properties Of Layered Lithium-rich Manganese-based Cathode Materials

Lithium-rich materials xLi₂MnO₃·?1-x?LiMO₂ as LIB cathode materials with high specific capacity and discharge voltage range are valuable for the power battery industry.However,after the multiple cycles,the layered structure gradually transforms to the spinel structure,which lead to the attenuation of the capacity and voltage platform.The electrochemical characteristics of the Li-rich materials limit the application in the power batteries.In order to suppress the voltage and capacity decay of the lithium-rich materials,the methods include ion doping,surface coating and design of core-shell structure materials were adopted in this paper.First,the optimum pH for preparing the W-doped lithium-rich materials by the sol-gel method was determined to be 7.5.Then,Nb was doped in the Li-rich materials.The diffraction peaks of NbO can be observed in the XRD spectrum.Compared the 0.02Nb-doped material to the original sample,the capacity increased by 6%after 100 cycles at 1C and increased by 19.5%after 200cycles at 5C.Nb doping can increase the capacity and initial discharge voltage,but the voltage stability of the material decreases.Sb doping can effectively reduce the first irreversible capacity loss of lithium-rich materials.Compared the 0.02Sb-doped material to the pure sample,the capacity increased by 2.9%after 100 cycles at 1C and the retention rate increased by 2.8%.The capacity increased by 10.26%after 100cycles at 1C and the retention rate increased by 11.02%.At the same time,the rate performance is also significantly enhanced.Sb doping can significantly improve the electrochemical performance and suppress voltage decay during cycling.The W doped lithium-rich material is coated with Li₂WO₄.The diffraction peaks of Li₂WO₄ are present in the XRD pattern.In combination with SEM and TEM,it is known that Li₂WO₄ is irregularly coated on the surface of the active material.Compared the 3 mass%-coated material to the pure sample,the incipient capacity increased by 9.6%?169.9 mAh/g?at 1C,but the capacity retention rate decreased.The initial capacity of the 3 mass%at 5C cycle increased by 5.2%.Li₂WO₄ can promote the capacity of materials.At the same time,Li₂WO₄ coating has a positive effect on suppressing voltage attenuation,but the polarization of the material increases at large rate.LiNi_0.5Mn_1.5O₄ has the electrochemically activity,so it can improve the initial coulombic efficiency of the Li-rich material.Compared the 3mass%-coated material to the pure sample,the incipient capacity increased by 12.1%?183.8 mAh/g?at 1C,but the capacity retention rate decreased.When the number of cycles of 5C is less than 100,the capacity retention of the coated material s are same with that of the original material?about 90%?.However,after 120 times,the capacity of the coated material decreased rapidly.Under the condition of large current discharge,LiNi_0.5Mn_1.5O₄ coating can effectively suppress the attenuation of the discharge voltage platform,and the coated materials have better rate performance.Finally,in the preparation of lithium-rich materials by co-precipitation method,the optimum ammonia concentration in the reaction process is 0.054 mol/L.Compared the core-shell structure material with the pure material,the initial capacity and coulombic efficiency increased by 2%?233.3 mAh/g?and 3.3%?71.4%?,respectively.The CS capacity is always about 6.1%higher than the original material during the 1C cycle.After 200 cycles at 5C,the CS discharge capacity is 115.57mAh/g,and increase by 37.8%.At the same time,CS has better voltage stability,especially under conditions of large rate.Study the effect of sintering temperature on material properties.The results show that the materials of the850? and 900? sintering temperatures have high initial coulombic efficiency.At the same time,both materials have well capacity and voltage stability at 1C and 5C.Therefore,the optimum sintering temperature of the core-shell lithium-rich material is between 850and 900?.