Preparation And Modification Of High Manganese Cathode Materials For Lithium Ion Batteries

The Mn-rich cathode materials have the advantages of rich raw materials,simple synthesis process,high operating voltage,excellent low temperature performance,environmental friendliness and so on.However,there are many problems to be solved,such as low specific capacity（mainly spinel lithium manganate）,manganese leaching,structural distortion and pase transformation,etc.In this paper,the modification treatments such as optimized control of precursor,composite doping,coated modification and control of material microstructure are mainly adopted.Physical characterization and electrochemical testing were used to study the physical properties of the Mn-high cathode materials and the internal relationshio with their electrochemical properties.The main contents and results of this paper are as follow:Mn₃O₄ was synthesized by one-step oxidation of manganese sulfate.The effects of reaction time,pH,concentration of manganese sulfate,concentration of complexing agent and reaction temperature on the particle size and morphology of Mn₃O₄ were studied.It is found that the capacity of LiMn2O₄ prepared by the composite manganese precursor is up to 117.83mAh/g,and IOC capacity is still 101.03mAh/g.The excellent electrochemical performance can be attributed to the fact that spherical Mn₃O₄ can regulate the structure,specific surface area and interface properties of LiMn2O₄,and enhance the stability of the structure and electrochemical performance.Compared with traditional polycrystalline lithium manganate materials,single crystal lithium manganate was synthesized by multi-stage high temperature sintering process,which has smaller specific surface area and higher vibration density.Single crystal particles are dispersed and show regular polyhedron structure,while octahedron structure with clear edges and sharp edges disappears.The cyclic stability of lithium permanganate materials was significantly improved by the synergistic effect of single crystal,doping and coating.After 200 cycles at room temperature,the decay rates of the combinatively modified single crystal lithium manganate materials are all lower than 8%,and the minimum is only 3.3%.High temperature cycle test also shows better high temperature cycle performance;It also has higher specific discharge capacity at 1C,2C,3C and 5C rates.High manganese precursor with bulk doping was synthesized by carbonate co-precipitation.The effects of reaction time,pH of reaction system and complex complexing agent on the morphology of the precursors were studied.Ti-doped Li-rich manganese-based materials were synthesized by multi-stage high temperature sintering.The results showed that compound complexing agent had obvious effect on particle size distribution,metal element content and distribution uniformity of precursor,and could effectively improve concentration and compactness of particle size distribution of precursor and reduce Ni2+,Co2+,Mn2+content in mother liquor.The initial capacity of the Ti-doped materials is high to 281.80mAh/g,and the retention of the capacity is 90.23%after 100 cycles.The Li-rich manganese based cathode material with composite doping and coating of fast ion conductor was synthesized by carbonate coprecipitation and multistage high temperature sintering.The results show that the cathode materials with composite modification have excellent electrochemical performance.At 4.6V and 4.8V,the initial capacity of the cathode material with composite doped and coated conductive polymers reaches 234.11mAh/g and 276.23mAh/g,respectively.At 4.6V cut-off voltage,the capacity retention rates of the multiple modified materials are still up to 93.80%and 89.70%after 100 cycles at room temperature and high temperature,respectively,and the capacity of the material can reach 164.92mAh/g at 5C rate.