Study On Preparation And Surface Modification Of Single Crystal LiNi_0.835Co_0.055Mn_0.11O₂

The shortage of fossil energy and the urgence of environmental protection consciousness have promoted the rapid development of clean energy industry.And the demand for lithium-ion batteries（LIBs）with high watt density for new energy vehicles power batteries and large-scale energy storage device is growing with each passing day.As an important Li⁺carrier,cathode material is of great importance for the enhancement of energy density for LIBs,which attracted much attention of researchers.Due to the advantages of high specific capacity,good rate performance and low cost,nickel-rich ternary layered cathode materials have become one of the most promising cathode materials for LIBs.However,although the increase of nickel content leads to high specific capacity,it weakens the crystal structural stability and thermal stability,which causes micro-cracks in the structure and seriously affects the cycling and safety performance of LIBs.In this thesis,through adjusting the particle size of precursors and sintering process,the single crystal Li Ni_0.835Co_0.055Mn_0.11O₂ cathode materials were synthesized by high temperature solid-state method.The optimized synthesis conditions are as follows:the precursor particle size is～3μm,sintering temperature is 850℃,and annealing temperature is650℃.The Li Ni_0.835Co_0.055Mn_0.11O₂ cathode material prepared under the optimal conditions shows dispersed single-particle morphology,and its initial discharge specific capacity at 0.1 C is 200.9 m Ah g^-1 in the voltage range of 2.8～4.3 V.The initial discharge specific capacity at 1 C is 185.8m Ah g^-1,the capacity retention after 100 cycles at 1 C is 75.8%.In order to solve the problems of low D_Li⁺ in surface and poor dynamic performance,single crystal Li Ni_0.835Co_0.055Mn_0.11O₂ cathode material coated with Mo O₃ or La₂O₃ was prepared.The effects of amount of Mo O₃and La₂O₃ on the morphology and electrochemical properties of the materials were investigated.The results show that the addition of n_（Mo）:n_{（transition metal（TM））}=0.5%with form of Mo O₃ in the one sintering process,the rate capability was significantly improved.The discharge specific capacity at 5C rate reaches 169.8 m Ah g^-1.When the addition of n_（La）:n_（TM）=0.3%with form of La₂O₃ in the secondary sintering process can effectively improve the capacity retention and rate performance of the material,and enhance the diffusion coefficient of Li⁺.