Solid State Synthesis And Performance Study Of XLi[Li_1/3Mn_2/3]O₂-（1-x）Li[Ni_1/3Co_1/3Mn_1/3]O₂Cathodes For Li-ion Batteries

Comparing with the anode materials applied in Li-ion batteries, cathodematerial limits the development of Li-ion battery industry for its relatively lowreversible capacity. The widely used anode material normally possesses aspecific capacity higher than300mAh/g while the cathode has only anapproximate capacity of150mAh/g. Therefore, high capacity cathodecompounds preparation has become the focusing point in the study of Li-ionbattery for last decades.Basically, there are two synthesis methods of cathode compounds:liquid-state method and solid state method. Although the preparationprocedures in traditional solid state method are simple and easily controlled,there are still several issues restricting its large application. And yet, theliquid-state method is costly in preparation devices and hard to be controlled,determining it’s unsuitable for scale application.In order to overcome the restrictions above, we combined the advantages inboth liquid state and solid state method and proposed to prepare themulti-transition metals oxide cathode via their acetates. Finally, four kinds ofdifferent layered multi-transition metals oxide cathodes were successfullysynthesized. The particles in those cathodes were homogeneous withnano-sized particle distribution. After obtained the optimal preparationprocedure parameters according to the tested battery performance results, theX-ray diffraction （XRD）, scanning electron microscope （SEM）,electrochemical impedance spectroscopy （EIS） and cyclic voltammetry （CV）were adopted to determine the structure and morphology and to measure theelectrochemical characterization.The optimal preparation condition for cathode compoundsLi[Ni_1/3Co_1/3Mn_1/3]O₂was annealing at800℃for8hours. On this condition, theprepared cathode compounds had a typical layered structure with highcrystallinity. The average particle sizes distributed among the range of90-300nm. The initial charge and discharge specific capacity of this targetedLi[Ni_1/3Co_1/3Mn_1/3]O₂compounds were210.5mAh/g and170.5mAh/g at the0.1C rate, respectively. The fitting results in software ZView showed that thecharge transfer resistance Rctequaled15.17Ω and the calculated charge transferrate constant k was1.04×10-6cm/s. Finally, the Li+diffusion coefficient D+Liin the cathode compounds Li[Ni_1/3Co_1/3Mn_1/3]O₂was figured out to be1.01×10-10cm2/s according to the CV results.The optimal preparation condition for Li-rich cathode compounds0.5Li[Li_1/3Mn_2/3]O₂-0.5Li[Ni_1/3Co_1/3Mn_1/3]O₂was annealing at800℃for6hours. On this condition, the prepared cathode compounds had a typical layeredstructure with high crystallinity. The average particle sizes distributed amongthe range of70-300nm. The initial charge and discharge specific capacity of0.5Li[Li_1/3Mn_2/3]O₂-0.5Li[Ni_1/3Co_1/3Mn_1/3]O₂compounds were262.7mAh/g and215.3mAh/g at the40mAh/g Testing condition, respectively. The fitting resultsin software ZView showed that the charge transfer resistance Rctequaled72.11Ω and the calculated charge transfer rate constant k was2.06×10-7cm/s.Finally, the Li+diffusion coefficient D+Liin the cathode compounds0.5Li[Li_1/3Mn_2/3]O₂-0.5Li[Ni_1/3Co_1/3Mn_1/3]O₂was figured out to be1.39×10-11cm2/s according to the CV results.The optimal preparation condition for Li-rich cathode compounds0.4Li[Li_1/3Mn_2/3]O₂-0.6Li[Ni_1/3Co_1/3Mn_1/3]O₂was annealing at800℃for6hours. On this condition, the prepared cathode compounds had a typical layeredstructure with high crystallinity. The average particle sizes distributed amongthe range of80-250nm. The initial charge and discharge specific capacity of0.4Li[Li_1/3Mn_2/3]O₂-0.6Li[Ni_1/3Co_1/3Mn_1/3]O₂compounds were247.3mAh/g and199.8mAh/g at the40mAh/g Testing condition, respectively. The fitting resultsin software ZView showed that the charge transfer resistance Rctequaled136.20Ω and the calculated charge transfer rate constant k was1.11×10-7cm/s.Finally, the Li+diffusion coefficient D+Liin the cathode compounds0.4Li[Li_1/3Mn_2/3]O₂-0.6Li[Ni_1/3Co_1/3Mn_1/3]O₂was figured out to be2.09×10-11cm2/s according to the CV results.The optimal preparation condition for Li-rich cathode compounds0.6Li[Li_1/3Mn_2/3]O₂-0.4Li[Ni_1/3Co_1/3Mn_1/3]O₂was annealing at800℃for6hours. On this condition, the prepared cathode compounds had a typical layeredstructure with high crystallinity. The average particle sizes distributed amongthe range of70-300nm. The initial charge and discharge specific capacity of0.6Li[Li_1/3Mn_2/3]O₂-0.4Li[Ni_1/3Co_1/3Mn_1/3]O₂compounds were270.9mAh/g and207.5mAh/g at the40mAh/g Testing condition, respectively. The fitting resultsin software ZView showed that the charge transfer resistance Rctequaled172.80Ω and the calculated charge transfer rate constant k was k=8.52×10-8cm/s.Finally, the Li+diffusion coefficient D+Liin the cathode compounds0.6Li[Li_1/3Mn_2/3]O₂-0.4Li[Ni_1/3Co_1/3Mn_1/3]O₂was figured out to be1.20×10-11cm2/s according to the CV results.