Surface Modification Of Ternary Cathode Materials（NCM） Based On Fast Ion Conductor Li_6.5La₃Zr_1.5Ta_0.5O₁₂

The ternary layered cathode material Li Ni_xCo_yMn_1-x-yO₂（x+y<1）have been widely concerned by researchers in recent years because of their higher theoretical capacity and lower cost.Although ternary materials with low nickel content have been commercialized,their lower energy density prevents their further application in a wider range of fields.Although the energy density of the high-nickel ternary materials has been improved,their rate performance is poor,and their capacity is severely attenuated during the cycle,which cannot meet the market demand for high-performance batteries.This paper mainly aims at the surface coating modification of Li Ni_0.5Co_0.2Mn_0.3O₂（NCM523）and Li Ni_0.8Co_0.1Mn_0.1O₂（NCM811）based on fast ion conductor Li_6.5La_3-Zr_1.5Ta_0.5O₁₂（LLZTO）to improve their comprehensive electrochemical performance.The low-melting salt KCl was used to provide a liquid reaction environment,and the fast ion conductor LLZTO was prepared by the molten salt method,and the influence of the sintering temperature and time on its phase structure was explored.The results show that the optimum synthesis condition of LLZTO is sintering at 950℃for8 h.The LLZTO prepared under this condition does not contain other impurity phases,and presents nanoparticles around 200 nm.Studies on the surface modification of NCM523 by LLZTO were discussed,and the effects of different coating amounts on the structure,morphology and electrochemical performance of the samples were explored.Among them,when the coating amount of LLZTO is 2 wt%,NCM523 shows the best electrochemical performance:the first discharge capacity is 178.0 m A h g^-1 at 0.1 C,and the coulomb efficiency is 83.5%.After 100 cycles at 1 C,the discharge capacity is still maintain146.6m A h g^-1,and the capacity retention rate is 88.5%,for rate performance test at 5 C,the discharge capacity can reach 112.9 m A h g^-1.These improvements in electrochemical performance can be attributed to the excellent electrochemical stability and higher ionic conductivity of LLZTO.Not only can it directly separate NCM523 from the electrolyte,but because it has three-dimensional lithium ion channel,it is conducive to Li⁺transmission.LLZTO was used to modify the surface of NCM811 to solve its shortcomings of poor high-voltage cycle stability.Compared with unmodified NCM811,the cycling performance and rate performance of LLZTO modified NCM811 samples have been improved to a certain extent.Among them,when the coating amount of LLZTO is 2wt%,the electrochemical performance of 2-NCM811 is the most superior.The cycling performance at 1 C shows that after 100 cycles of 2.8-4.3 V,the discharge capacity of2-NCM811 is 144.4 m A h g^-1,and the capacity retention rate is as high as 81.0%;after100 cycles at 2.8-4.5 V,The discharge capacity is 129.6 m A h g^-1,and the capacity retention rate is 62.9%.Moreover,the rate performance is up to 116.9 m A h g^-1 at 10 C,much higher than 90.0 m A h g^-1 of NCM811.LLZTO surface modification can effectively improve the cycling stability and rate performance of NCM811.