The Synthesis And Modification Of Spinel Lithium Manganese Oxide

The spinel LiMn2O4 is considered as a promising cathode material for lithium-ion battery owing to its merits of low cost,simple synthesis,high operating voltage,environmental friendliness and safety performance.However,the capacity fades seriously under cycling,especially under relatively high temperature.In this paper,we studied the means to stabilize the structure of LiMn2O4 during cycles,including optimizing the synthesis methods and surface coating modification,which will improve the electrochemical performance.The main research results of this paper are as follows:The spinel LiMn2O4 cathode material with proper strain was prepared by solid-state reaction method with subsequent annealing treatment,and obtained single phase active material with good performance in short time.The sample annealed under 700? for 4h showed the best cycling ability,the initial discharging capacity was 116.1mAh g-1,and the capacity retention rate was 95.3%after 50 cycles.The Si02 coating LiMn2O4 was prepared via hydrolysis route,and the impact of coating in different solvent systems was studied.It showed that the SiO2 layer was more uniform and complete in the methanol system than which in ethanol,and improved the cycling ability of the sample.The discharging capacity was 102.7 mAh g-1 after 70 cycles under 55?,with 92%of the initial capacity.Meanwhile,Ti02 coating LiMn2O4 was prepared via complexation-hydrolysis route in water phase,which obtained better impact than in organic phase,and reduced the difficulty and cost in coating processing.The sol-gel method was applied to prepare Li+ deficit phase LixTi5O12(3.5<x<4)coated spinel LiMn2O4 samples,and coating impact and the change of surface situation were investigated.It was found that with appropriate heat treatment,the Li+ in main phase LiMn2O4 would intercalate into LixTi5O12 and form Li4TisO12 phase coating layer,while the the valence of Mn at LiMn2O4 surface increased significantly,the joint action of these two made spinel LiMn2O4 possess good capacity retention properties during cycling.Dynamic hydrothermal method was taken to study the impact of the different reaction temperature on the performance of the synthesized spinel LiMn2O4 and the structural change and electrochemical properties of the samples before and after sintering treatment were also investigated.The research results showed that the most suitable hydrothermal temperature is 180?,and sintering would not change overall morphology significantly,but it could improve the internal crystalline state of the samples with substantially improved rate capacity.In addition,characterization of EIS illustrated that the surface structure changed limitedly before and after sintering.Finally,the overview on innovative and deficiencies of this thesis was given.Some prospects and suggestions of the possible future research were also pointed out.