Study On The Electrochemical Performance Of High Capacity Cathode Materials Coated By Li_1.3Al_0.3Ti_1.7?PO₄?₃

The lithium-rich layered material xLi₂MnO₃·?1-x?LiMO₂ and the Ni-rich material LiNi_0.8Co_0.1Mn_0.1O₂ have got great attention because of their higher specific capacity,enhanced safety,environment-friendly and lower cost.However,the large irreversible capacity loss during the initial cycle,poor rate capability and insufficient capacity retention limit the practical applications of these materials.It is necessary to improve the electrochemical performance of these materials to meet commercial applications.In this paper,the lithium-rich layered cathode material Li_1.2Ni_0.2Mn_0.6O₂ and the Ni-rich material LiNi_0.8Co_0.1Mn_0.1O₂ were coated by Li_1.3Al_0.3Ti_1.7?PO₄?₃?LATP?using improved Sol-gel method.The microscopic morphology and electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ and LATP-coated materials were characterized by XRD,SEM,TEM,XPS and charging-discharging test,as well as AC impedance and cyclic voltammetry.The main work are shown as follows:?1?The lithium-rich layered material Li_1.2Ni_0.2Mn_0.6O₂ has been coated with LATP by sol-gel method.The contents of LATP are 1,3 and 5 wt%,and the sintered temperatures are 475,575 and 675°C.XRD,SEM,TEM and XPS results show that LATP has been successfully coated on the surface of Li_1.2Ni_0.2Mn_0.6O₂ without changing the layered structure.The electrochemical results show that 3wt%LATP coated Li_1.2Ni_0.2Mn_0.6O₂?sintered at 575°C?has the best electrochemical performance.Its initial discharge specific capacity is increased from 240.0 mAh?g^-1 to 264.7mAh?g^-1 at 0.1 C with the coulombic efficiency is increased from 72.1%to 85.1%.The capacity retention of the material is increased from 80.5%to 94.3%after 80cycles at 0.2 C.It exhibits a superior rate capability with a capacity of 106.5 mAh?g^-1at 10.0 C,while the uncoated Li_1.2Ni_0.2Mn_0.6O₂ only has a capacity of 32.6 mAh?g^-1.The XRD and TEM results of the mererials after the cycling indicate that 3wt%LATP coated material has better structural stability.The AC impedance test results show that the 3wt%LATP coating material sintered at 575°C has the smallest surface charge transfer resistance?37.1??,but the uncoated is 72.5?.The lithium ion diffusion coefficient of the material is calculated to be 3.81×10^-12 cm²?s^-1.However,the uncoated Li_1.2Ni_0.2Mn_0.6O₂ is 8.23×10^-13 cm²?s^-1.Cyclic voltammetry results show that the LATP coating can effectively inhibit the polarization of the cathode material during charging-discharging process.?2?The Ni-rich material LiNi_0.8Co_0.1Mn_0.1O₂ has been coated with LATP?0.5,1and 3wt%?by sol-gel method and then sintered at 575°C for 5 h.XRD,SEM,TEM and XPS results show that LATP has been successfully coated on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ without changing the layered structure.The electrochemical results show that 0.5wt%LATP-coated LiNi_0.8Co_0.1Mn_0.1O₂ has the best electrochemical performance.The initial discharge specific capacity of 0.5wt%LATP-coated LiNi_0.8Co_0.1Mn_0.1O₂ is increased from 192.7 mAh?g^-1 to 194.4 mAh?g^-1and the initial coulombic efficiency is increased from 81.6%to 87.1%.The capacity retention is 92.1%after 100 cycles at 0.2 C and the capacity retention is 84.5%after200 cycles at 2 C.However,the capacity retention of uncoated LiNi_0.8Co_0.1Mn_0.1O₂ is only 76.3%and 67.4%,respectively.The discharge capacity is increased from 100.6mAh?g^-1 to 121.5 mAh?g^-1 at 10 C.SEM and TEM results of the mererials after the cycling show that LATP coating can effectively improve the structural stability of the material.The AC impedance results show that the 0.5wt%LATP coating can reduce the surface charge transfer resistance of the LiNi_0.8Co_0.1Mn_0.1O₂.The lithium ion diffusion coefficient of the material before the cycle is increased from 8.66×10^-13cm²?s^-1 to 7.39×10^-12 cm²?s^-1.Cyclic voltammetry results show that LATP coating can inhibit the polarization of the cathode material during charging-discharging process and help to maintain a higher discharge capacity during the cycling process effectively.