Lithium Ion Battery Cathode Material Limn < Sub > 2 < / Sub > O < Sub > 4 < / Sub > Sol-gel Synthesis And Modification Of Research

Spinel lithium manganese oxide (LiMn2O4) is one of the most promising candidates as cathode material in rechargeable lithium-ion batteries because of its merits of low cost, simplicity of preparation, high operating voltage, good safety performance and environmental friendly. However, its severe capacity fade, especially at elevated temperatures, restricts its further widely application. In this paper, optimizing the synthesis method, metal ion doping and surface modification of spinel LiMn2O4, were used to improve the electrochemical performance both at room temperature and high temperature.Firstly, the cathode materials of spinel LiMn2O4were prepared by sol-gel method. The influence of the relative citrate amount, sintering temperature and annealing time, Li/Mn molar ratio, selection of raw materials on the materials’electrochemical performances were seriously investigated. The optimum synthesis conditions for preparation of high-performance LiMn2O4material were gived. The cathode material of LiMn2O4synthesized under the optimum synthesis conditions showed excellent electrochemical performance, its initial discharge capacity was123.3mAh/g, after45cycles, it remained97.8%of the initial specific discharge capacity.Secondly, in order to improve the rate capability and cycle ability at elevated temperature, metal cations doping such as Ga3+、In3+and Al3+had been proposed. Influence of the amount of different metal ion doping on the crystal structure, microstructure and electrochemical performance of LiMn2O4were discussed. The experimental results showed that all the Ga doping samples within7%amount exhibited the same cubic spinel phase structure without impurity. The increasing Ga doping amount decreased the lattice parameters. Especially the5%Ga-doped LiMn1.95Ga0.05O4showed excellent electrochemical performance, its initial discharge capacity was117.1mAh/g by0.5C rate at room temperature, after90cycles by different rates, it remained86.8%of the initial specific discharge capacity. At elevated temperature, it also had115.4mAh/g of initial discharge capacity, and it kept75.7%of initial discharge capacities after20cycles, even at4C discharge rates, it can still keep well-defined spinel structure. The doping amount should not be too much when the In3+metal ion was selected as doping ion. The1%In-doped LiMn1.99In0.01O4had the smallest of lattice parameters, and also it had good rate capability. When the small amount of Al3+was used as doping ion, it had great impact on the initial discharge capacity, but it can improve cycle performance. The initial discharge capacity of7%Al-doped LiMn1.93Al0.07O4was110.8mAh/g with capacity retention of87.2%after90cycles. CV and EIS tests showed that the appropriate metal ions doped had positive effect on stabilizing the spinel structure, so the John-Teller distortion can be suppressed.Finally, the TiO2-coated LiMn2O4cathode materials were synthesized by the Sol-gel method. The pure LiMn2O4and TiO2-coated LiMn2O4materials were characterized by XRD, SEM, CV and galvanostatic charge and discharge test. The results showed2wt%TiO2-coated sample had72.4%capacity retention rate at high discharge rates under room temperature, while the uncoated LiMn2O4sample only had58%capacity retention. At elevated temperature, the coated sample had94.2%of the initial discharge after20cycles. While the uncoated sample capacity retention rate was41.9%. The CV tests showed the coated sample can effectively reduce the direct contact area between LiMn2O4cathode materials and electrolyte, which helped to suppress the erosion of the electrolyte to the LiMn2O4The modified material demonstrated dramatically enhanced electrochemical reversibility and stability both at room temperature and elevated temperature.