The Preparation Of LiNi_0.5Mn_1.5O₄under The Effect Of Ionic Liquids And Its Research On Doping And Coating Modification

Cathode material LiNi0.5Mn1.5O4is considered as one of the most promisingcathode materials for next generation of advanced lithium ion battery due toits large capacity and high discharge plateau at4.7V。This thesis focuses onstudy of the preparation of the material under the effect of ionic liquids, CuOcoating and Mg doping.The LiNi0.5Mn1.5O4with different morphologies have been successfullyprepared through co-precipitation route in mixed solution containing1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and H2O withdifferent mass ratios and followed by a solid reaction at high temperature. Themorphology of LiNi0.5Mn1.5O4varies with the increasing ratio of [C12mim]Br.These samples synthesized at three kinds of concentrations present flake-likemorphology, agglomerated flake-like structure and polygon particles with sizeabout700nm, respectively. The initial discharge capacities of the threesamples are118.4,129.8and132.2mAh g1respectively. The dischargecapacity gradually decrease with increasing number of cycles and respectivelyreach93.5,107.7and109.8mAh g1after100cycles. We also investigated theeffect of different alkyl chain length of ionic liquids on morphologies, andfound it has no effect on the morphologies of the material when the alkyl isbutyl.LiMgXNi0.5-XMn1.5O4was prepared with acetate of Li, Ni, Mn and Mg bysol-gel method. When x=0.05, the sample present a noticeably higherdischarge capacity than that of the pristine and other samples, which deliver116.5mAh·g1,110.7mAh·g1,100.7mAh·g1,94.6mAh·g1and84.4mAh·g1at rates of0.5,2,5,7and10C, respectively. It also could retain97.3%of its initial discharge capacity at the rate of0.5C. The lithium iondiffusion coefficient was enhanced nearly7times than the uncoated sample.The optimal LiNi0.5Mn1.5O4sample was modified CuO. The electrochemicaltesting results demonstrate3wt.%CuO-modified material had the capacityretention of higher than95%after100cycles, and high capacity of98.7mAhg1at10C rate, in comparison with the capacity retention of83%and capacityof63.6mAh g1for the pristine one. The remarkably improved rateperformance and cycling stability can be attributed to CuO coating, which acts as an effective lithium-ion conductor and a protective material againstcorrosion from electrolyte.