Synthesis And Modification Of Li-rich Solid Solution Cathode Material

Li-rich layered solid solution is of great interest as a new cathode material with a highspecific capacity for the next generation lithium ion batteries. By far, many issues like itsmicro-structure and mechanism of its high specific capacity are not clarified. A remarkablefeature of these materials is the stabilization of Li₂MnO₃component to the frame ofstructure, which provide premise for the realization of the high capacity. Therefore, weconsider it is necessary to elucidate the relationship between the distribution of Li₂MnO₃component in the structure and the electrochemical properties, which make it possible toget a deeper understand on its unique electrochemical behavior. On this basis, we furthermodify the material via structural rearrangement to improve its rate capabilities.1. Li-rich layered cathode materials xLi[Li_1/3Mn_2/3]O₂-（1-x）LiNi_5/12Mn_5/12Co_2/12O₂（0≤x≤0.8）were prepared by spray-dry method. It is found that the micro-structuretransfers with increasing the Li₂MnO₃content in composition, the arrangement oftransition mental ions in the internal structure transfers from long-range order tolong-range disorder and then short-range order. The discharge capacities of series materialsshown regular changes which increase gradually and then decrease gradually with theincrease of x value. As a result, when x=0.6, the material exhibts the highest dischargecapacity，which is about260mAh g^-1at room tempreature.2. As discussed in the last section, sample Li1.2Ni0.17Mn0.56Co0.07O₂exhibited highestdischarge capacity and best cyclic stability in the series materials. However, undesirablecation mixing and disordered internal structure were revealed by HRTEM. Therefore, wedesigned there methods to modify its internal structure yield unobstructed channels forLithium ions diffusion. It has been found that materials modified via the Li-excess&chemical activation treatment shown significantly improved rate capabilities, whichexhibited a reversible capacity of167mAh g-1at the discharge current density of600mAg^-1, and the capacity retention increases about17%compared to the untreated one.