Probing the microstructural changes in Li-rich layered oxides induced by over-lithiation

Li-rich manganese-based layered oxides (LRMO) cathode materials can deliver a high specific capacity of approximately 400 mAh g^-1 under deep discharge conditions; however, they suffer from severe capacity degradation. In this work, the crystal structure evolution and strain variations of Li_1.2Ni_0.2Mn_0.6O₂ cathode materials within a wide voltage range (1.0-4.8 V) were systematically investigated using synchrotron X-ray diffraction (sXRD). As the voltage decreases below 2.0 V, the LRMO materials exhibit significant changes in microstrain, while variations in lattice parameters and unit-cell volume remain relatively small. These results indicate that the rapid capacity fading is primarily attributed to the accumulation of strain during over-lithiation.