Preparation Of Rich-Ni Ternary Cathode Material And Its Lithium Storage Properties

LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）is one of the most promising cathode materials for lithium ion batteries due to its high reversible capacity and low price.However,there are some problems such as mixed discharge of transition metal cations,particle pulverization and side reaction with electrolyte,which cause its capacity to decay too fast.In view of the existing problems of NCM811 material,this paper intends to improve the lithium storage performance of Li Ni_0.8Co_0.1Mn_0.1O₂ material with high nickel from the aspects of morphology design and controlled synthesis,element doping and surface coating.The main highlights are as follows:Long columnar monocrystalline particles with（001）crystal faces and（100）and（010）crystal faces as sides were synthesized by coprecipitate+high temperature solid phase method with the help of cationic surfactants.When the content of CTAB is 2 wt.%,the spacing between（003）crystal faces increases to 0.4746 nm.The Ni²⁺/Li⁺mixing degree of the material was reduced to 5.86%.The initial discharge capacity reached 186.9 m Ah·g^-1 at0.1 C and the capacity retention rate reached 76.8%after 94 electrochemical cycles at 1 C.At the same time,with the help of CTAB,the Li⁺diffusion rate of the material is 1.67×10^-12cm²·s^-1,and the charge transfer impedance is 60.45Ω.Compared with the blank sample,the Li⁺diffusion rate is faster,the magnification performance is better and the charge transfer impedance is lower.By using NH₄F as dopant,the high nickel ternary cathode material was modified by anion doping from top to bottom.The O^2-in NCM811 crystal was partially replaced by F^-,which reduced the degree of metal cation mixing and improved the stability of crystal structure.The initial discharge capacity of NCMF 0.01 can reach 232.5 m Ah·g^-1 at 0.1 C and210.3 m Ah·g^-1 at 1 C.The HRD values of the sample at 2 C and 5 C were 87.2%and 57.4%,respectively,which were higher than that of the blank sample（83.9%and 49.4%）.With opportune F doping,the charge transfer impedance decreases from 235.8 to 224.5Ω,and the Li⁺diffusion coefficient increases from 3.121×10^-13 to 4.250×10-13 cm²·s^-1.The surface of NCM811 material is coated with La₂O₃ layer with nanometer thickness.The coating layer reduces the direct contact between NCM811 material and electrolyte,and inhibits the side reaction of electrolyte.During the coating process,a small amount of La elements entered the lattice,which reduced the cationic mixing and stabilized the material structure.The 0.5wt.%coated sample reached the initial discharge capacity of 222.1 m Ah·g^-1 at 0.1 C,and the discharge capacity reached 195.5 m Ah·g^-1 at 1 C,and the retention rate was 64.7%after 100 cycles.It shows high specific discharge capacity,good rate performance and cycle stability.