Preparation And Modification Of Li-rich Cathode Materials With High Capacity

In order to solve the problems of Li-rich materials, such as low initial coulombic efficiency,poor rate capability, capacity fading and voltage degradation during cycling, the methods of inducing aluminum and rubidium cations into Li-rich manganese based layered oxide cathode materials for lithium-ion batteries (LIBs) have been taken, respectively. The influence of Al3+and Rb+ content on crystal structure, crystal growth manner and related electrochemical behaviors were investigated.We discussed Al3+ partially substitute for Mn4+ in the transition metal layer via a high temperature solid-state method with different A1 contents, and signed the samples for Li1.2-xRbxMn0.54Ni0.13Co0.13O2(LMO-Alx, x=0,0.01,0.03,0.05). It was found that after Al3+incorporation (x=0.05), the materials could deliver an excellent capacity retention of 99% after 50cycles, and the maximum initial specific capacity are 249.9mAh g-1. The improvement may be caused by the promotion in both the electric conductivity and the Li ion conductivity. The electric conductivity of the LMO sample is 2.52×10-8 S cm-1, while that of the LMO-Al0.05 reveals a value of 3.87×10-8 S cm-1. And the Li ion conductivity increased from 4.18×10-13cm2 s-1 (LMO) to 1.22×10-12cm2 s-1 (LMO-Al0.05).Meanwhile, Rb+ has been incorporated into Li-rich manganese by a co-precipitation method and a subsequent solid-state reaction, signing for Li1.2-xRbxMn0.54Ni0.13Co0.13O2 (Rbx-LMO, x=0,0.01,0.03,0.05).The Rb+ substituting sample (x=0.03) present superior discharge capacity retention of 98% after 100 cycles with first discharge capacity of 239 mAh g-1. It is 10% higher than that of the LMO (82.92%). Besides, after Rb+ substituting, the sample also provided a nearly 20%～30% capacity increase at each rate. Therefore, the introduction of Rb ions into the Li layer can effectively enlarge the Li slab space, so as to improve the diffusion coefficient of Li ions, from 8.95×10-16cm2 s-1(LMO) to1.63×10-15cm2 s-1(Rb0.03-LMO).In addition, the doping measures clearly suppress the process of the simultaneous lithium extraction along with oxygen activation at the high voltage region which may alleviate the irreversible loss of oxygen.