Phase stability of Li-Mn-O oxides as cathode materials for Li-ion Batteries: insights from ab initio calculations
Journal
PCCP (Physical Chemistry Chemical Physics)
Date
2014.04.08
Abstract
In this work, we present a density-functional theory (DFT) investigation of the phase stability, electrochemical stability and
phase transformation mechanisms of the layered and over lithiated Mn oxides. This study includes the thermodynamic stability
of Li and oxygen vacancies, to examine the electrochemical activation mechanisms of these cathode materials. DFT calculations
provide phase diagrams of Li-Mn-O system in both physical and chemical potential spaces, including the crystals containing
vacancies as independent phases. The results show ranges of electrochemical activity for both layered LiMnO2 and over lithiated
Li2MnO3. By using a thermodynamic model analysis, we found that the required temperature for oxygen evolution and Li
vacancy formation is too high to be compatible with any practical synthesis temperature. Using solid-state transition calculations,
we have identified key steps in the phase transition mechanism of the layered LiMnO2 into the spinel phase. The calculated effects
of pH on the Li-Mn-O phase stability have elucidated the Mn2+ formation mechanism from spinel phase under acid condition.
