Dislocation and oxygen-release driven delithiation in Li2MnO3

Abstract

Lithium-excess layered cathode materials such as Li2MnO3 have attracted much attention owing to their high energy densities. It has been proposed that oxygen-release and cation-mixing might be induced by delithiation. However, it is still unclear as to how the delithiated-region grows. Here, by using atomic-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy, we directly observe the atomic structures at the interface between pristine and delithiated regions in the partially delithiated Li2MnO3 single crystal. We elucidate that the delithiated regions have extensive amounts of irreversible defects such as oxygen-release and Mn/Li cation-mixing. At the interface, a partially cation disordered structure is formed, where Mn migration occurred only in the specific Mn/Li layers. Besides, a number of dislocations are formed at the interface to compensate the lattice mismatch between the pristine and delithiated regions. The observed oxygen-release and dislocations could govern the growth of delithiated-regions and performance degradation in Li2MnO3.

Facilitating Reversible Cation Migration and Suppressing O2 Escape for High Performance Li‐Rich Oxide Cathodes

“…Figure 1j displays a deeper view of the Mn EELS by testing the L 3 /L 2 ratio of Mn L 2 , 3 edges, which are sensitive to Mn valence. [ 35 ] The L 3 /L 2 ratio in the range of 3–5 nm is larger than that in the range of 6–15 nm, indicating a lower valence of Mn in the surface spinel structure with a 5 nm‐thick shell than that in the bulk layered phase.…”

Multi-dimensional correlation of layered Li-rich Mn-based cathode materials

“…6A], it is found that the slope below 4.4 V during charging corresponds to the charge compensation of Ni 2+ /Ni 4+ and Co 3+ /Co 4+ without the variation of the Mn 4+ valence, which is attributed to the charge compensation mechanism of the LiMO 2 component [9] . The absorption edge of the TM at 4.5 V shows that there is no change in the K edge of Ni and Co [81] . The Mn K-edge X-ray absorption near-edge structure spectrum indicates that the environment of Mn changes at 4.5 V according to the continuous variation of the absorption edge, which results from the distortion of MnO 6 octahedra.…”

Sufficient Oxygen Redox Activation against Voltage Decay in Li-Rich Layered Oxide Cathode Materials

“…So far, the state-of-the-art characterization techniques have provided multiscale structure and spectroscopy information to understand the structure evolution of LLOs. − It is now believed that a series of disordered structures generated, such as lattice distortion, dislocation, and stacking faults, disturb the structure stability. ,, Some unusual ways are proposed to suppress structures degradation effectively. Embedding the undesired disordered structures into pristine host structures is favored to promote the structure stability. − Our recent work further illustrates that subtle adjustments of the disordered structures from type/range/distribution are necessary to mobilize them as a modification method .…”

“…8−12 It is now believed that a series of disordered structures generated, such as lattice distortion, dislocation, and stacking faults, disturb the structure stability. 10,11,13 Some unusual ways are proposed to suppress structures degradation effectively. Embedding the undesired disordered structures into pristine host structures is favored to promote the structure stability.…”

“…The results indicate that the oxygen redox is accompanied by an irreversible structure transformation during the initial cycle, and the disordered structures is thought to be produced upon the structure transformation. 10,11,13 Figure 3b shows the lattice parameters evolution extracted from the ex situ XRD patterns. When the charge capacity is below ∼600 min, parameter c increases monotonously, and parameter a decreases.…”