Study On The Improving Performance Of LiNi_0.5Mn_1.5O₄ Cathode Materials For Lithium-ion Battery

Spinel LiNi0.5Mn1.5O4 material is a cathode material for high-energy-density lithium-ion batteries,which has the characteristics of the high voltage of 4.7V and good electrochemical performance that other cathode materials cannot reach.Therefore,it was necessary to carry out in-depth research on the spinel LiNi0.5Mn1.5O4 material to promote its commercial application so as to improve the performance of the power lithium-ion batteries as soon as possible.In this thesis,the performance of LiNi0.45Cr0.1Mn1.45O4 and LiNi0.45Fe0.1Mn1.45O4 materials have been studied.The effect of calcination temperature on the structure,particle size,morphology and electrochemical performance of LiNi0.45Cr0.1Mn1.45O4 was investigated.And the surface of LiNi0.45Cr0.1Mn1.45O4 was coated with Li4Ti5O12 to improve performance.The LiNi0.45Fe0.1Mn1.45O4 material was also coated with Li4Ti5O12.The effect of calcination time and coating amount on the structure,morphology and electrochemical performance of the material were investigated.The structure,particle size and morphology of the materials were characterized by XRD,SEM and laser particle size analyzer.The electrochemical performance of the materials was tested by the land test system and the electrochemical workstation.(1)The LiNi0.45Cr0.1Mn1.45O4 cathode material was prepared by sol-gel method.The effect of calcination temperature on the electrochemical performance of the materials was investigated.When the calcination temperature was 920℃,the initial discharge capacity of LiNi0.45Cr0.1Mn1.45O4 was 126.5 mAh/g at 0.1C.It delivered a capacity of 119.4 mAh/g at 0.5C with capacity retention was 93.9%after 50 cycles.(2)Li4Ti5O12 coated LiNi0.45Cr0.1Mn1.45O4 cathode material was synthesized via high-temperature solid-state reaction combined with mechanical ball milling method and the effect of coating amount on the electrochemical performance was also investigated.The coating layer did not change the crystal structure of the material,and all of them were face centered cubic space group structure.When the coating amount was 5wt.%,the material showed the best performance with the capacity retention of 97.6%after 50 cycles at 0.5C.(3)The LiNi0.45Feo.1Mn1.45O4 materials prepared for different calcination time belong to face centered cubic space group structure.When the roasting time was 8h,it showed the best electrochemical performance.The first discharge capacity was 125.9 mAh/g at 0.1C.It delivered a capacity of 117.6 mAh/g at 0.5C and the capacity retention of 91.5%after 50 cycles.(4)Li4Ti5O12 coated LiNi0.45Fe0.1Mn1.45O4 cathode material was prepared by high-temperature solid-state reaction combined with mechanical ball milling method.The surface coating modification can significantly improve the electrochemical performance and cycle stability of the materials.When the coating amount of Li4Ti5O12 was 5wt.%,the material exhibited the best performance with the capacity retention of 95.8%after 50 cycles at 0.5C.(5)Comparing the two kinds of cathode materials,it is found that the electrochemical performance of LiNi0.45Cr0.1Mn1.45O4 material is better than LiNi0.45Fe0.1Mn1.45O4.