Mild Lithium-Rich Manganese-Based Cathodes with the Optimal Activation of Li2MnO3 for Stable and High Capacity Lithium-Ion Batteries

The commercial application of lithium-rich layered oxides still has many obstacles since the oxygen in Li2MnO3 has an unstable coordination and tends to be released when Li-ion is extracted at the voltage higher than 4.5 V. In this work, a series of cobalt-free lithium-rich manganese-based oxide cathodes (Li1+xTM1-xO2, TM = Mn, Ni) are synthesized by gradually decreasing the Li/TM ratio. Among these cobalt-free Li-rich manganese-based oxides (LRMO), LR-1.2 (when Li/TM = 1.2) has an optimized dual-phase (namely Li2MnO3 and LiTMO2-like) structure, in which the coordination environment of part of oxygen is transformed from 4Li-O-2TM octahedra to 3Li-O-3TM octahedra due to the partial substitution of TM for Li at Li-2b site. Thus, some of the original unstable Li-O-Li configurations change to Li-O-TM configurations, forming strong TM-O covalent bonding and enhancing the structural stability of the oxygen. Consequently, the LR-1.2 achieved a high reversible capacity of 282.3 mAh g(-1) (Coulombic efficiency of 90.9%) at 0.1 C, exhibiting outstanding cycling stability (capacity retention of 90.3% after 400 cycles at 2 C) and superior rate performance. This work establishes a correlation between the microstructure modulation tuned by the Li/TM ratio and their electrochemical performance, offering insights into the design of cathode materials for high-performance lithium-ion batteries.