Synthesis And Modification Of Li-rich Mn-based Cathode Material For Lithium-ion Batteries

The high energy density of the Li-rich Mn-based cathode material xLi2MnO3·(1-x)LiMO2(0<x<1,M=Ni, Co, Mn) originated from high capacity (200~300mAh/g) and voltage (above3.8V) makes itbecome an ideal choice to satisfy the need of power battery used on vehicles. In this paper, C3H5NaO3as the complexing agent was used to synthesis the MCO3(M=Mn, Ni, Co) precursor, then the MCO3precursor and LiOH·H2O as the source of lithium were mixed well and calcined in air to produce the0.6Li2MnO3·0.4Li[Ni0.5Co0.2Mn0.3]O2(Li1.2[Mn0.52Ni0.2Co0.08]O2) cathode material. The processparameters of synthesis the precursor and sintering the cathode material were optimizatiedsystematically.(1) The MCO3precursor was prepared by a co-precipitation method. It is found that the precursorparticles with optimal spherical morphology and narrow particle size distribution were synthesizedunder the condition of60℃and16h, and the cathode material produced from this precursor alsoshowed the optimal electrochemical performance; Under the optimal conditions, the method ofpresintering precursor was adopted to produce the cathode material, namely, converting MCO3tooxide first, then the oxide precursor was mixed with LiOH·H2O to produce the target product. Moresmall sized crystal grains were obversed in oxide precursor and the corresponding cathode materialfrom SEM pictures. As a result, the utilization ratio of cathode material was increased, which wouldimprove the electrochemical properties of the material.(2) The effect of elevating the Co content in Li1.2[Mn0.52-0.5xNi0.20-0.5xCo0.08+x]O2(x=0,0.02,0.04,0.06) cathode materials on the structural and electrochemical properties has been investigated. Thelayered structure and cation ordering degree were improved with increasing the Co content. Forx=0.02, the cycle performance of the material improved significantly. The specific capacity retentionimproved to98.85%after100cycles at0.5C,2.0~4.8V; By elevating the calcination temperature, it’sfound that the material prepared at950℃showed lower cation mixing degree, making it exhibitbetter rate capability and cycle performance.(3) The Li2TiO3-coated cathode materials were prepared via sol-gel method under the conditions ofoptimum metal elements proportion and sintering temperature above. SEM characterization provedthat the particles were coated with a layer of floccule. The3wt.%Li2TiO3-coated cathode materialshowed significantly improved coulomb efficiency, rate capability and cycle performance at the synthesis temperature of650℃. After coating3wt.%Li2TiO3, the reduced extent of transformationfrom layer structure to spinel structure provided a more stable layer structure, and was well proved bycyclic voltammograms (CV) test. Also, the electrochemical impedance spectroscopy (EIS) test resultsshowed that the coated material had significantly smaller semicircles in impedance spectra, comparedwith pristine material.