Ionothermal Synthesis For LiMn_1.5Ni_0.5O₄ Cathode Materials And Its Research On Doping Modification

With the rapid development of science and technology, the requirement for lithiumi-ion battery is increasing day by day. The methods of synthesis for LiMn1.5Ni0.5O4 are mainly solid phase method, coprecipitation solid method, sol-gel method in the most research and progress. But it has poor cycling performance, low capacity. Therefore, we need to further explore the synthesis methods of LiMn1.5Ni0.5O4. We should have to find out the right doping elements and doping amount to improve the morphology and electrochemical properties of the materials.In the present work, we synthesized uniform Mg-doped LiNi0.5Mn1.5O4 spinels with Mn(CH3COO)2 Ni(CH3COO)2 and CH3COOLi as raw materials and prepared by a novel ionothermal method using a kind of imidazolium-based ionic liquids as both reaction medium and structure-directing agent and successively followed by a calcination process. Then, the obtained active materials were characterized and tested by the means of X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and electrochemical performance tests. The results showed that the uniform nanostructured LiNi0.5-xMgxMn1.5O4 spinels were synthesized by imidazoles ionic liquids with better morphology and the electrochemical property. Its diameter was about 1.4 μm. And the electrochemical performance tests indicated that the discharge capacity of LiNi0.49Mg0.01Mn1.5O4 was 82.4 mAh g-1 after 100 cycles at IOC and the capacity retention was 91.2%.The Mg-doped uniform nanoscale LiMn1.5Ni0.5O4 lithium-rich material is obtained by a similar method and it is successfully doped by Mg. In order to research the effect amount of Mg doping on the performances of LiMn1.5Ni0.5O4 samples,we have changed the amount of Mg doping. The results show that the discharge capacities of LiNi0.5-xMgxMn1.5O4 increase first and then decrease. It indicates that the amount of Mg doping is not the more the better. Compared to LiNi0.5Mn1.5O4, the experimental dates show that the Mg-doped samples show smaller nanoparticles with diameters about 150 nm and present excellent cyclic stability and high rate performance. Among the doped samples, LiNi0.49Mg0.01Mn1.5O4 shows highest discharge capacity. The initial discharge capacity of LiNi0.49Mg0.01Mn1.5O4 is 132.0 mAh g-1 at 0.1 C, and the discharge capacity of LiNi0.49Mg0.01Mn1.5O4 is 105.3 mAh g-1 after 100 cycles at 10 C and the capacity retention is 96.9%.