Preparation And Characterization Of LiNi_2/3Mn_1/3O₂Cathode Material For Lithium Battery

LiNi_2/3Mn_1/3O₂is one attractive substitute material for LiCoO₂due to its low cost,better safety and environmental friendliness. In this dissertation, two synthesis methods ofLiNi_2/3Mn_1/3O₂cathode material for high energy lithium battery has beenstudied--polyethylene glycol （PEG400） assisted synthesis and oxalate co-precipitation.Material characterization methods and electrochemical performance tests were conductedto determine the function of PEG400assisted synthesis and optimize oxalatecoprecipitation method which is of industrial potential.In PEG400assisted synthesis, PEG400was added into the precursors and oxalatemixture, and sintered at800℃to get LiNi_2/3Mn_1/3O₂material. The results showed thatthis synthesis method can effectively improve the performance of LiNi_2/3Mn_1/3O₂. Thestructure and morphology of as-prepared samples were examined by XRD, XRDrefinement and SEM. It is found that as compared to bare LiNi_2/3Mn_1/3O₂, the PEG400treated sample has better Li/Ni order and enhanced crystallinity with more uniformparticle size distribution. Electrochemical performance of first discharge capacity,50cycles performance and rate capability have been studied. Sample PEG10delivered aninitial discharge capacity of172mAh g^-1with a0.1C current between2.7-4.5V, whereassample without PEG400treatment gave only a capacity of115mAh g^-1. PEG10delivereda capacity of111mAh g^-1with1C current, while sample without PEG400treatment onlygave a capacity of27mAh g^-1. This improvement is possibly due to the enhancedcrystallinity and higher Li/Ni order in the LiNi_2/3Mn_1/3O₂structure.As to oxalate co-precipitation, the pH value and precursor concentration has beenoptimized for the precipitate solution with two contrast experiments. The as-preparedLiNi_2/3Mn_1/3O₂material is characterized by XRD and SEM to study the structure andmorphology, which is followed by electrochemical tests. The results showed that pH=2ismost favorable for preparing LiNi_2/3Mn_1/3O₂with high crystallinity and small averageparticle size, thus leading to excellent electrochemical performance; a precursorconcentration of0.12mol/L is most favorable for preparing LiNi_2/3Mn_1/3O₂with high crystallinity, resulting in better electrochemical properties.