Investigation On The Process And Electrical Performance Of Ultrafine-LiNi_0.5Mn_1.5O₄ Synthesis By Enhanced Solid State Method

At present, the production of LiNi_0.5Mn_1.5O₄ cathode material in industry is solid state method which have some advantages of simple operation, low equipment requirements and so on. However, the final product have some disadvantages of large particles size,uneven particle size distribution, high energy consumption and poor electrochemical performance. Therefore, it is of great significance to develop a novel solid state process to prepare the LiNi_0.5Mn_1.5O₄ powders at a lower temperature in a shorter time. In this paper, a novel route for the preparation of the ultrafine-LiNio.5Mn1.5O4 powders by mechanical activated followed by double calcining were investigated. The effects of synthesis process on the characteristics and electrical properties of the powders were studied, the main contents of the research and conclusions are as follows:（1）The ultrafine LiNio.5Mn1.5O4 powders were prepared by enhanced solid state reaction using carbonate precursors, the effects of process parameters on the physical and chemical properties of the LiNi_0.5Mn_1.5O₄ powders were invstigated. The study shows that with the increase of calcination temperature, the product crystallinity will be enhanced, particle size will be increased, and spherical particles gradually transformed into well-faceted crystallized octahedral morphology. Compared to the one-step process, the products prepared by double-sintering process has better physical and chemical properties. The synthesis process is also discussed. The results indicates, solid-state synthesis is divided into three stage:the decomposition stage, synthesis stage and growth stage. Decomposition stage:carbonate precursor decomposed into nano-oxide particles at low temperature after mechanical activation treatment, the oxide particles having a large specific surface area; synthesis stage:the LiNi_0.5Mn_1.5O₄ phase can be formed quickly by the rapid diffusion reaction between the freshly formed nano oxide particles and the Li2CO3; growth stage:high temperature calcination process will promote spherical particles gradually transform into well-faceted crystallized octahedral morphology.（2）The effects of different oxide precursors on the phase constitutions and morphologies of the powders were studied. The results shows that the lattice constant increases with the increase of the calcination temperature on the oxide precursors using MnO2 as raw materials. While the Mn3O4 precursor present the opposite result, indicating that the content of Mn3+ is decreases with the temperature increases.（3）The influence of process parameters of ball milling and Li content on the physical and chemical properties of the product were discussed. The results shows that high energy ball milling can reduce the reaction energy of solid state reaction, so we could synthesis of the final product rapidly at low temperature. However, when the milling time is too long, the powder will agglomerate, resulting in poor material properties. The experiment result shows that the ball mill for 10h is best. Li is easily volatilized at the conventional high temperature synthesis process. In this study, the time spent in the high temperature is too short so that the loss of Li is little, therefore we choose the molar ratio of Li:Ni:Mn=2:1:3.（4）The final products using carbonate precursor are prepared by the optimized parameters and their electrochemical properties are tested. The samples deliver the highest discharge capacity of 143.3mAh·g^-1 （97.5% of the theoretical capacity） at 0.1C rate, with a good cycling performance of 96.7% capacity retention after 50 cycles at 2C rate.