Composition Regulation Prediction of Cathode Materials By First-Principles Calculation

The performance of lithium-ion batteries (LIBs) critically depends on the intrinsic properties of the electrode materials. The design and application of novel materials, especially cathode materials, will always be primary to attain performances improvements in LIBs. Mainly commercial cathode materials contain layered (e.g. LiCoO2), spinel (e.g. LiMn2O4) and olivine (e.g. LiFePO4) structures. As known, Part of layered compounds gradually transforms into spinel during cycling, or spinel-like structure forms in the as-prepared layered materials, which results in capacity fading, structure instability and safety problems. The doping technique is accepted as an effective approach to improve the structural stability and electrochemical performance.

First-principles calculation method, which is based on Density Functional Theory (DFT), is used to solve the Schrödinger equation after some rational approximations. The obtained wave function of the system contains a lot of natural information of materials. The computational methods could be the most powerful complementarity for experimental ones, which is helpful for understanding macro-properties and materials design. The First principles calculation method has been applied in the field of LIBs including calculating average lithium intercalation voltage, analyzing intercalation and extraction mechanism, optimizing the structure, etc.

In this work, we modeled the real and virtual layered (LiMO2) and spinel (LiM2O4) phases (M=Sc~Cu, Y~Ag, Mg~Sr and Al~In), then we have comparatively studied the phase stability between the layered phase LiMO2 and spinel phase LiM2O4 (M=Sc~Cu, Y~Ag, Mg~Sr and Al~In), as well as the impact regulation of doping. The phase stability of a specific compound depends on both binding and reaction energy. And the dominant phase between layered LiMO2 and spinel LiM2O4 is close related to the valence state of element M. The location of the compounds with multi-cationic M in the phase dominant figure can be determined by ingredient percentage weighted average method. The regulation of phase stability and impact of multi cationic doping have been proved by the experimental results from references. The phase dominant figure based on the First principles calculation is a power tool to predict the property of LiMO2 layered materials with multi-cationic M.