Synthesis And Performance Study Of High Voltage Lithium Manganese Cathode Materials For Lithium Ion Batteries

Cathode materials play a role of "heart" in the Lithium-ion secondary battery,because its properties directly affect the battery’s operating voltage, capacity and cost etc. Using Li Ni_0.5Mn_1.5O₄ as research object in this study, we systematically investigated the effects of particle morphology and preparation process on the performance of the material. Meanwhile, we also exploited the influential factors in the electrochemical performance of cathode material.Firstly, the high performance spherical LiNi_0.5Mn_1.5O₄ cathode material was prepared by the control of the preparation conditions. The effects of the metal salt concentration, reaction temperature and stirring speed on the morphology of the precursor were studied. The precursor synthesised under the optimal conditions was mixed with lithium source, and the effect of calcination temperature on the physical and electrochemical properties of LiNi_0.5Mn_1.5O₄ cathode material was explored. The study shows that the cathode material Li Ni_0.5Mn_1.5O₄ calcinated at 700 °C has the best electrochemical performance, representing 132.4 mAh/g of the first discharge and89.6% of the capacity retention after 100 cycles. Meanwhile the material possesses extraordinary charge and discharge rate capability, showing 6_0.5 mAh/g of discharge specific capacity at the large rate of 20 C.Secondarily, in order to further improve the electrochemical performance of the materials, based on rapid nucleation mechanism, we synthesized the precursor with uniform and small grain size by directly dumping method using NaOH as precipitator.Based on the above, the cathode material LiNi_0.5Mn_1.5O₄ with single dispersion and excellent electrochemical performance was successfully synthesized by calcination after the precursor was evenly mixed with lithium source. In addition, we have systematically studied the effect of the key factors such as species of transition metal salt, hydrothermal temperature, calcination temperature and calcination time on thephysical and chemical properties of the cathode material LiNi_0.5Mn_1.5O₄. The optimized cathode material LiNi_0.5Mn_1.5O₄ shows 138.5 mAh/g of the first discharge and 117.3 mAh/g of 100 th discharge which corresponds to 89.5% of the capacity retention, and as high as 11_1.5 mAh/g of the reversible specific capacity at the large rate of 20 C.Ultimately, to meet the requirement of the performance of power battery, we systematically explored the effects of cathode thickness, separator type, and factors such as composition of electrolyte and the cathode surface changes on the electrochemical performance of cathode materialsby using the most commercially applicable and layered ternary cathode material as research object.