The origins and mechanism of phase transformation in bulk Li₂MnO₃: first-principles calculations and experimental studies

Abstract

Lithium-rich oxide materials are promising candidates for high-energy lithium ion batteries, but currently have critical challenges of poor cycle performance and voltage drop induced by undesirable phase transformation. To resolve these problems, it is necessary to identify the origins and mechanism of phase transformation in Li 2 MnO 3 , a key component of Li-rich oxides. In this work, the phase transformation of bulk Li 2 MnO 3 is investigated by thermodynamic and kinetic approaches based on first-principles calculations and validated by experiments. Using the calculated thermodynamic energies, the most stable structure is determined as a function of Li extraction for Li 2Àx MnO 3 : monoclinic (x ¼ 0.0-0.75), layered-like (x ¼ 1.0-1.25), and spinel-like (x ¼ 1.5-2.0) structures. The phase transformation becomes kinetically possible for Li 2Àx MnO 3 (x > 1.0). Atomic scale origins and the mechanism of phase transformation are elucidated by the thermodynamically stable and kinetically movable tetrahedral coordination of Mn 4+ in the transition state. These theoretical observations are validated by ex situ X-ray photoelectron spectroscopy combined with electrochemical experiments for Li 2Àx MnO 3 with various Li contents upon cycling. The mechanistic understanding from theoretical calculations and experimental observations is expected to provide a fundamental solution and guidelines for improving the electrochemical performance of Li-rich oxides and, by extension, the battery performance.

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

“…Similar migration pathways have been shown to have reasonable migration barriers (as low as 0.1 eV) in Li 2 MnO 3 68,69 . The effect of other migration scenarios is shown in Supplementary Fig.…”

“…While the role of the structure-redox coupling in voltage fade requires further study, we tentatively suggest that strategies aimed at increasing the latter while minimizing the former (e.g., by screening cation substitutions) may be effective in improving the cyclability of LMR-NMC. Further work will seek to understand the relative kinetics of O redox and TM migration, identify the intermediate states, and establish whether, for example, O 2p states are first depopulated, promoting TM migration through (de)stabilization of specific structural configurations, as has been predicted computationally 69 .…”

Intrinsic Origins of Crack Generation in Ni-rich LiNi0.8Co0.1Mn0.1O2 Layered Oxide Cathode Material

“…As shown in Fig. 1a, Co and Mn are located separately in the Ni-rich environment of the layered oxide structure, which would be thermodynamically related to d -electronic stability of the crystal field3637.…”

The Role of Zr Doping in Stabilizing Li[Ni0.6Co0.2Mn0.2]O2 as a Cathode Material for Lithium‐Ion Batteries

“…[49] The Perdew-Burke-Ernzerhof plus Hubbard correction (PBE + U) was used for the exchange-correlation function, in which doublecounting interactions were corrected using aD udarev scheme. [51][52][53] Ap lane wave basis set with ac ut-off energy of 500 eV was used to expand the electronic wave functions and the centered 2 2 1M onkhorst-Pack K-point grid was used for sampling the Brillouin zone. [51][52][53] Ap lane wave basis set with ac ut-off energy of 500 eV was used to expand the electronic wave functions and the centered 2 2 1M onkhorst-Pack K-point grid was used for sampling the Brillouin zone.…”