Research On Synthesis And Modification Of Nickel-Rich LiNi_0.8Co_0.1Mn_0.1O₂ Ternary Cathode Materials

Nickel-rich LiNi_0.8Co_0.1Mn_0.1O₂?NCM811?ternary cathode materials own the ternary synergistic effect of Ni-Co-Mn to some extent.Due to high discharge specific capacity,low cost and environmentally friendly,NCM811 ternary cathode materials becomes a hot spot in relative research and application at present.However,the content of nickel in NCM811 ternary cathode materials is too high,which leads to the aggravation of Li⁺/Ni²⁺cation disordering.In addtion,the contents of cobalt and manganese that can improve the stability of the materials are very low,which leads to poor cycling stability,rate capability and thermal stability.Therefore,to solve the above problems,in this paper,NCM811 cathode materials are studied from the following three aspects:preparation conditions,anion/cation doping and rare earth element yttrium modification.The crystal structure,surface morphology and thermal stability of prepared materials were examined by TG-DSC,XRD,SEM,HR-TEM,EDS-mapping and XPS analysis.Meanwhile,the electrochemical properties of the prepared materials were investigated by galvanostatic charge-discharge,EIS and CV tests comprehensively.The specific research contents are as follows:?1?NCM811 ternary cathode materials were synthesized by a simple solid-state method using commercial precursor and LiOH·H₂O as raw material with the 1.05 lithium ratio.The influences of different pre-sintering temperature,sintering temperature and sintering time on the materials structural and electrochemical properties were investigated.Through series of experiments,the optimal experimental conditions were obtained with pre-sintering temperature of 470?,pre-sintering time for 6h,calcination temperature of 780?,calcination time for 15h.This sample exhibited the initial discharge capacity of 168.4 mAh/g and the capacity retention of 93.4%with the potential range of 2.8-4.3V at 0.5C.The discharge capacity was increased by 5.34%,while the cut-off voltage was further increased to 4.5V.However,the capacity retention of that material was only 78.2%after 100 cycles,which means that the cycle stability of material is poor.Therefore,these materials need to be modified.?2?On the basis of the optimal synthesis condition,using Aluminum nitrate nine hydrate as the aluminum source and lithium fluoride as the fluorine source,NCM811ternary cathode materials were doped.Meanwhile,the influence of anion/cation single doping and co-doping on the structure and electrochemical performance of the materials were investigated.The experimental results showed that the optimal single doping amount of Al was 2%,the single doping amount of F was 2%and the co-doping amount of Al-F was Al 2%,F 1%.Compared with single doping,the cyclic stability of the materials was most significantly improved by co-doping.After 100 cycles,the capacity retention of Al 2%-F 1%sample was 88.9%at 0.5C under 4.5V and increased by 10.7%compared with that of pristine sample.Meanwhile,at 10C,the capability retention of Al2%-F 1%sample reached up to 81.0%after 100 cycles and increased by 32.0%compared with that of pristine sample.Through Al-F doping,the cycling stability of materials are improved at high potential,to some extent.?3?NCM811 ternary cathode materials were modified by rare earth element yttrium.The influence of different amount of yttrium modification on the materials were investigated.Various tests results showed that,in the reaction process,the excessive lithium sourece?lithium ratio of 1.10?reacted with Y₂O₃ to form the surface coating layer of LiYO₂ and the rest of yttrium doped in the particles forming a gradient distribution.The Y2 sample that was the optimal addition amount sample could deliver 189.4 mAh/g under high cut-off voltage of 4.5V,the initial coulombic efficiency was 81.3%and the capacity retention was still as high as 98.4%after 100 cycles.Compared with the pristine sample,the capacity retention of Y2 sample increased by 21.5%after 100 cycles at 10C and 25.9%after 50 cycles at elevated temperature 55?.It can be seen that yttrium modification can effectively improve the structure stability so that the materials can obtain better electrochemical properties.