Morphology Modification and Delithiation Mechanisms of LiMn2 O 4 and Li2MnO3 by Acid Digestion

Abstract

The structural features of equilibrium phases, and , and their acid‐delithiated products are compared using x‐ray diffraction and electron microscopy. The observed morphological changes associated with acid‐fsdelithiated confirm the acid digestion mechanism proposed by Hunter. Three delithiated phases including α‐, γ‐, and ‐like phases can be derived from under different acid digestion conditions. An acid‐delithiation mechanism converting to α‐ and is proposed. This mechanism involves an acid‐dissolution and precipitation process. A related scheme is also proposed for the formation of ‐like materials from α‐ and phases. The crystallography of the structure is related to the grain/crystal geometry of on the basis of convergent‐beam electron diffraction and lattice imaging analysis. An in situ heating experiment in a transmission electron microscope demonstrates that heat‐treatment of hydrated at ∼300°C develops porosity within grains/crystals. It is proposed that the microstructural changes induced by acid delithiation may contribute to the reported difference in the initial electrochemical behavior of acid delithiated and equilibrium . The delithiated product derived from at ∼115°C for 4–6 h, having as the major phase, demonstrates superior electrochemical properties.