Investigation on the electrochemical activation process of Li_1.20Ni_0.32Co_0.004Mn_0.476O₂

The lithium-rich layered oxides are one of the most attractive cathode materials for lithium-ion batteries. Here, two types of Li_1.20Ni_0.32Co_0.004Mn_0.476O₂ were synthesized using Li₂CO₃ and LiOH as lithium sources. An electrochemical activation process occurs in Li_1.2Ni_0.32Co_0.004Mn_0.476O₂ prepared from Li₂CO₃ (LLO-1), while no obvious activation in Li_1.2Ni_0.32Co_0.004Mn_0.476O₂ prepared from LiOH (LLO-2) is observed. Via advanced scanning transmission electron microscopy (STEM), we found that Li₂MnO₃-like structure is rich in the surface region of LLO-2. The study provides a direct explanation for the electrochemical activation of lithium-rich materials. The sample with more LiMO₂-like phase at the surface region shows a better cycling performance. It is likely that more LiMO₂-like phase at the surface region could stabilize the interface and improve the cycling performance of the Li-rich cathode materials.