Study On Preparation And Modification Of One-dimensional Nanoscale Spinel LiMn₂O₄

With the development of electric vehicles, high performance lithium ion batteries, especially with high energy density and power density, are required urgently. Cathode material is one of the most important materials for lithium ion batteries. It plays a decisive role on the performances of the batteries. Spinel LiMn2O4 is highly promising cathode material for large-scale batteries for electric vehicles due to its crystal structure with three-dimensional Li+diffusion channels.At present, the particles of commercial LiMn2O4 are micron scale. They are too large for Li+ to fast migrate, and leading to the rate performance of batteries is restrained. While, the paticales of nano-LiMn2O4 are very easy to self-aggregate and forming micron size secondary particles, also restraining the rate performance of batteries. In addition. Mn dissolution due to disproportionation reaction of Mn3+ at elevated temperature and Jahn-Teller distortion of spinel LiMn2O4 during charge/discharge process cause to capacity fading seriously. Based on above reasons, an electrospinning technology combined with sol-gol method was employed to fabricate one-dimensional nanostructure LiMn2O4 and modificate it by the element doping to improve the rate capabitlity and cycle performance.The influence of electrospinning technology and sol-gol method process parameters (such as content of raw materials in precursor solution, calcination temperature and time of pretreatment and final treatment) on material crystal structure, morphology and electrochemical performances are systematically studied. One-dimensional nano LiMn2O4 cathode material with high crystallinity. large L/D ratio, uniform diameter, good electrochemical performance was successfully synthesized. As-synthesized material can release up to 146 mAh g-1 discharge capacity at 0.1C, and its capacity retention is 88% after 100 cycles with 0.5 C charge and discharge rate. In order to improve the cyclic stability and rate performance, the effect of Ni2+ doping on the electrochemical performance of modified LiMn2O4 material was studied. The one-dimensional nano LiNi0.4Mn1.6O4 showed excellent electrochemical performance with 99% discharge capacity retention at 0.5C charge/discharge rate at room temperature,91% discharge capacity retention at 0.5C charge rate/1 C discharge rate at 55℃ and discharge capacity of 130 mAh g-1 at 20C. In order to further improve the operating voltage of the material. Cr3+ and Fe3+ were used to substitued Mn3+ of LiNi0.4Mn1.6O4. making discharge capacity proportion at high voltage area increase from 75% to 86%.In addition, the effect of doping element on the cell parameters. Li+ diffusion coefficient, redox peak potential, rate performance and discharge voltage were systematically investigated and summarized on the basis of the experiment.