In-situ XRD investigations on structure changes of ZrO 2-coated LiMn 0.5Ni 0.5O 2 cathode materials during charge

Abstract

The structural changes of pristine and ZrO 2-coated LiMn 0.5Ni 0.5O 2 cathode materials were investigated by using in situ X-ray diffraction (XRD) during charging process. An obviously solid solution phase transition from a hexagonal structure (H1) to another hexagonal structure (H2) was observed during the charging process at a constant current of 0.3 mA in the potential range of 2.5–5.7 V. The second hexagonal structure has a shorter a-axis and a longer c-axis before the crystal collapse. Before the structure collapses the c-axis length increases to maximum and then significantly decreases to 14.1 Å. The c-axis length of the pristine and ZrO 2-coated LiMn 0.5Ni 0.5O 2 increases to the maximum at the charge capacity of 119.2 and 180.9 mAh g −1, respectively. It can be concluded that the ZrO 2 coating can strongly stabilize the crystal structure of the LiMn 0.5Ni 0.5O 2 compound from the comparison of the lattice parameter variations between the pristine and the ZrO 2-coated LiMn 0.5Ni 0.5O 2 compounds upon charge. The potential fluctuation resulting from the decomposition of electrolytes starts at the charge capacity of around 200 and 260 mAh g −1 for the pristine and ZrO 2-coated LiMn 0.5Ni 0.5O 2, respectively. It suggests that the ZrO 2 coating layer can impede the reaction between the cathode material and electrolyte.