Preparation And Electrochemical Properties Of Single Crystals Of High Nickel Ternary Cathode For Lithium-Ion Batteries

Layered nickel-cobalt-manganese composite cathode materials are a kind of cathode materials for lithium-ion batteries developed in recent years.Among them,layered ternary cathode materials(such as LiNi_0.5Co_0.2Mn_0.3O₂,LiNi_0.8Co_0.1Mn_0.1O₂)have the advantages of low cost,large discharge capacity and environment friendly,which are one of the most promising new cathode materials for lithium-ion batteries.LiNi_0.5Co_0.2Mn_0.3O₂ has attracted much attention due to its higher capacity advantage than the popular LiNi_1/3Co_1/3Mn_1/3O₂.The demand for high nickel LiNi_0.8Co_0.1Mn_0.1O₂ batteries is driven by the rapid growth of new energy vehicle production,the rise of cobalt price and the inclination of national policy towards high energy density.However,for high nickel LiNi_0.8Co_0.1Mn_0.1O₂ materials,due to the hindrance of nickel on lithium sites to the diffusion of lithium ions and the unstable crystal structure caused by the side reaction between electrolytes and electrodes,the material's ratio performance and cycle stability performance become worse.By doping,the cycling and rate performance of the material can be improved.In order to solve the above problems,LiNi_0.5Co_0.2Mn_0.3O₂ with different morphologies is prepared by high temperature solid-state direct sintering and molten salt calcination respectively,and its properties are tested systematically.LiNi_0.8Co_0.1Mn_0.1O₂ is prepared by molten salt calcination,and the structure and morphology of the materials investigated in different calcination atmosphere and with or without K-doped.The specific research contents are as follows:1.Ni_0.5Co_0.2Mn_0.3?OH?₂,a precursor sample,is prepared by coprecipitation.The material 523-S1,which is a regular spherical secondary particle composed of nanometer primary particles,is obtained by high temperature solid phase direct sintering,while the 523-S2 material obtained by calcining molten salt is composed of single crystal particles with smooth surface and high crystal integrity.The rate discharge specific capacity of single crystal 523-S2 material,which shows good rate performance.LiNi_0.5Co_0.2Mn_0.3O₂ is prepared by molten salt calcination,and the effects of calcination temperature on morphology and properties are investigated.The results show that the particle of 523-850oC material prepared at a high temperature of850oC had smooth surface,higher crystal integrity,better dispersion,more uniform particle size distribution and no obvious agglomeration.The 523-850oC material has an initial discharge capacity of 142.3 mAh g^-1?0.1 C?;the discharge capacity is 137.0mAh g^-1 after 70 cycles,in which the retention rate is 96.3%.It shows good electrochemical performance.2.The effects of different calcination atmosphere on the properties of LiNi_0.8Co_0.1Mn_0.1O₂ are studied.The results show that the discharge specific capacity of the first cycle is 161.1 mAh g^-1?0.1 C?when the potential range is 2.8-4.3 V and184.0 mAh g^-1?0.1 C?when the upper cut-off voltage is 4.6 V.The 811-O₂ material has an initial discharge capacity of 122.9 mAh g^-1?2 C?;the discharge capacity is 118.6mAh g^-1?2 C?after 100 cycles,in which the retention rate is 96.5%,which is much higher than that of 811-Air material?73.3%?.3.The LiNi_0.8Co_0.1Mn_0.1O₂ material with larger ion radius is successfully synthesized by ball milling and molten salt calcination.The effect of K doping on the structure and electrochemical properties of LiNi_0.8Co_0.1Mn_0.1O₂ material is studied.The results show that K doping is beneficial to increase the specific discharge capacity of the battery in the first cycle.The discharge specific capacity of Li_0.9K_0.1Ni_0.8Co_0.1Mn_0.1O₂ material in the first cycle is 170.0 mAh g^-1,which remains168.8 mAh g^-1 after 100 cycles,and the capacity retention rate reaches 99.3%.