Cobalt free, lithium rich manganese, nickel and iron composite oxides are promising cathode materials as they can reduce the cost and toxicity of lithium ion battery. Having attractive discharge capacity in initial cycles, the Li rich cathodes suffer from the capacity and voltage fading in long term cycling. The structural changes, including the deformation of crystal structure, cationic mixing, and amorphization, are the reasons behind the performance degradation. A series of Li1.2Mn0.3+xNi0.4-xFe0.1O2, for x = 0 to 0.25, were synthesized and systematically investigated using XRD, XAFS and in-depth electrochemical analysis. Within the studied series of composite oxide cathodes synergistic effect of the monoclinic (Li2MnO3) and rhombohedral (Li1.15Mn0.37Ni0.38Fe0.10O2) phases was correlated to superior electrochemical performance. The first discharge capacity of as high as 277 mAhg-1 and capacity retention of as high as 94% after 100 cycles were observed. The XAFS measurement at Mn, Ni and Fe K-edges of the pristine and cycled cathodes of the series of materials was conducted and fitted for the first time, which provided information on changes in metal oxidation state, near neighbors and interatomic distances in first charged and discharged states as well as after 100 cycles. The talk will present the findings of this study, correlating discovered structural changes to materials electrochemical behavior and proposing new strategies for effective material engineering.
Structural Study of the Degradation Mechanisms of Li-rich Mn-Ni-Fe Oxide Cathodes