| Recently, high-energy and high-power rechargeable lithium ion batteries have got the great success in portable electronics. As the instant development of electric vehicles and the power grid energy storage power station, it is believed that lithium ion batteries will be used in more and more fields. Then, to meet the requirement of electric vehicles and the power grid energy storage power station, it is desired to further increase their energy density and safety.5V-class spinel LiNi0.5Mn1.5O4 cathode has the two advantages of a 4.7V platuea and three dimensional lithium ion transmission channel and it can offer much higher energy density (650 Wh kg-1) than those commercial 4V-class cathode materials, such as LiCoO2 (540Wh kg-1), LiMn2O4 (500 Wh kg-1) and LiFePO4 (500 Wh kg-1). In this regard, high-voltage LiNi0.5M1.5O4 has been regarded as one of the most promising cathode materials for high-energy lithium ion batteries in the future.In this dissertation, the author mainly focused on the synthesis methods and electrochemical properties of spinel LiNi0.5Mn1.5O4 cathode, and the main contents are as follows:Firstly, ordered LiNi0l.5Mn1.5O4 hollow microspheres have been successfully synthesized by an impregnation method and their electrochemical properties also have been investigated. The results shows that the formation for the hollow structure is tightly relative to the temperature for the solid-state reaction. In the solid-state reaction process, with post-annealling procedure we got the ordered LiNi0.5Mn1.5O4, and the disordered LiNi0.5Mn1.5O4 was obtained without the post-annealling procedure. And the electrochemical performances of ordered and disordered LiNi0.5Mn1.5O4 microspheres have been compared. The result shows that when the ordered LiNi0.5Mn1.5O4hollow microspheres were applied as the cathode materials for lithium ion batteries, they exhibited superior rate capability (116 mAh g-1 at 5 C,85 mAh g-1 at 10 C for charge and discharge) and good cyclability, which are much better than the disordered sample.Secondly, the spinel LiNi0.5-xMn1.5+XO4 (x=0,0.05,0.1) including LiNi0.5Mn1.5O4, LiNi0.5Mn1.55O4and LiNi0.5Mni 6O4 hollow microspheres have been prepared by adjusting the stoichiometric ratio of Ni and Mn with an impregnation method. And the physicochemical and electrochemical properties of LiNi0.5Mn1..5O4, LiNio.45Mn1.55O4 and LiNi0.5Mn1.6O4 hollow microspheres have been investigated. The results show that partial replacement of Ni by Mn reduce the average valence state of Mn, introduce small amount of Mn3+ and thus form the disordered structure. And the hollow morphologies of disordered LiNi0.45Mn1.55O4 and disordered LiNi0.4Mn1.6O4 both were retained unchangeably. The disordered LiNi0.45Mn1.55O4 hollow microspheres exhibited superior rate capability (96.8 mAh/g at 10 C for charge and discharge) and good cyclability which are much better than those of ordered LiNi0.5Mn1.55O4 and disordered LiNi0.4Mn1.6O4.Lastly, spinel LiNi0.5Mn1.5O4 samples have been synthesized by a solid-state reaction with tableting and without tableting (bare) process. The electrochemical of the two samples have been compared. It is shown that a tableting process is helpful to avoid the formation of impurity phases in the solid-state reaction, and also much smaller primary particles were obtained. Simultaneously, the sample with tableting process shows good cycleability. After 200 cycles, its capacity retention is 96.7% at room temperature, and 77% at 55℃. |
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