Preparation And Coating Modification Of LiNi_0.45Cr_0.1Mn_1.45O₄ Cathode Material For Li-ion Batteries

Compared with other lithium ion battery cathode materials,spinel LiNi0.5Mn1.5O4has the advantages of high working voltage and high energy density,so it is a promising lithium ion battery cathode material.However,its cycle performance needs to be further improved because the electrolyte erodes the electrode material in which the transition metal element dissolves and the material structure is destroyed.Doping and surface coating modification are two effective methods to improve the cycle properties of materials.According to our previous research,doping Cr3+can effectively improve the cycle performance of materials;and the binding energy of Al-O and Ti-O is very high.The oxides of Al and Ti can resist the corrosion of the electrolyte.Therefore,this study intends to prepareLiNi0.5Mn1.45O4doped with Cr3+,and then coat a layer of Li-Al-Ti-O(LATO)oxide on its surface to further improve the cycle performance of the material.In this study,LiNi0.45Cr0.1Mn1.45O4 sample is prepared by sol-gel method,and LATO oxides are prepared by liquid phase method.The XRD results show that the LATO oxides consist of Li2Al4O7 and Li1.26Ti1.66O4,both of which have a spinel structure.The discharge capacity of Li1.26Ti1.66O4 is 95 mAh g-1.In this study,the coated sample LNCMO-LATO is prepared by liquid phase method,and the presence of the coating layer is detected by TEM.The TEM results show that there is a transition layer between the coating layer and the LNCMO.The formation of transition layer is due to the mutual diffusion between the atoms such as Ni,Mn,Cr in LNCMO and atoms such as Al and Ti in LATO during heat treatment.This structure facilitates the diffusion of Li+through coating layer and LNCMO,and enhances the bonding strength of coating layer and LNCMO.The coating elements Al and Ti are detected by EDS,XPS and ICP,and the content is close to the theoretical value.LNCMO-2LATO coated with 2% LATO has the best cycle performance.The first cycle discharge specific capacity is 12.7 mAh g-1,and it is 108.9 mAh g-1 after 300 cycles,thus the capacity retention is 89.4%.The first cycle capacity of LNCMO sample is 125.6 mAh g-1,and 75.5 mAh g-1 after 300 cycles,while the capacity retention is only 60.1%.The EIS results show that charge transfer impedance of LNCMO-2LATO is larger than that of LNCMO,so the rate performance of coated sample is reduced.At 5C,the specific capacity of LNCMO is 95.9 mAh g-1,while that of LNCMO-3LATO is only 73.3 mAh g-1,reducing 23.5%.The LNCMO-2LATO positive electrode and Li4Ti5O12 negative electrode are assembled into a full battery.The first cycle discharge capacity of the full battery is 118.8 mAh g-1,and the capacity retention after 100 cycles is 88.1%,indicating that it matches well with Li4Ti5O12.