Preparation And Modification Of Lithium-rich Manganese-based Cathode Materials

Lithium-rich manganese based cathode materials are considered as potential cathode materials due to their high discharge capacity,low cost and environmentally friendly.However,the high irreversible capacity,low initial coulomb efficiency and voltage decay of lithium-rich manganese based cathode materials have seriously hindered their commercial application.In this paper,the lithium-rich manganese based cathode materials xLi₂MnO₃·(1-x)Li MO₂(M=Mn,Ni,Co)were prepared by coprecipitation method combined with high temperature sintering.The optimized preparation process was obtained by controlling different parameters.Finally,the cathode material was modified with Fe₂O₃ and SiO₂ layers.The mechanism of coating modification on cathode material was analyzed by physical characterization and electrochemical tests.The specific research contents of this paper are as follows:(1)The optimized preparation condition of lithium rich manganese base cathode material x Li₂MnO₃·(1-x)LiMO₂(M=Mn,Ni,Co)was determined as follows:x=0.5,p H=7.9 and sintering temperature 900?.The prepared cathode material exhibits the best crystallinity,lowest agglomeration degree of particles and superior electrochemical performance.(2)The Fe₂O₃ was coated on the surface of cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ by sol-gel method.The of XRD,XPS,SEM and TEM results suuggested that the amorphous Fe₂O₃ was uniformly distributed on the surface of the material and does change the original layered structure of the cathode material.The initial discharge capacity of 2wt.%Fe₂O₃ coated cathode material is 267.5 m Ah g^-1 at0.1 C.After 300 cycles at 1C,the capacity retention rate can still reach as high as87.7%,while the capacity retention rate of the original sample is only 70.8%.Manwhile,Fe₂O₃coating stabilizes the interface between the electrode and electrolyte,and reduces the charge transfer resistance.(3)Surface modification of SiO₂ layer was conuucted on Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ by in-situ polymerization.The original and SiO₂ coated samples were analyzed by XRD,XPS,SEM and TEM.It was found that the SiO₂layer was successfully coated on the surface of cathode material while maintaining the original structure and morphology.The existence of SiO₂coating prevents the corrosion of electrolyte and inhibits the formation of spinel structure.The capacity retention rate of 0.25 wt.%SiO₂ coated sample is 89.7%after 200 cycles at 1C,which is much higher than 74.2%of the original sample.After 200 cycles,obvious cracks appear on the surface of the original sample,while the surface of the SiO₂ coated sample remains intact,which strongly proves that the existence of SiO₂ layer can significantly improve the structural stability of the cathode material.(4)The double coating modification of Fe₂O₃ and SiO₂ was carried out on the cathode material.The electrochemical test results reveal that the double coating modification of Fe₂O₃ and SiO₂ does not improve the electrochemical performance of the cathode material.