First-principles theory of doping in layered oxide electrode materials

TL;DR

This study uses first-principles calculations to analyze how various impurities incorporate into layered oxide cathode materials for lithium-ion batteries, revealing how dopant charge, spin, and environment influence defect formation.

Contribution

It provides a detailed defect and impurity model for doped LiMO₂ cathodes, enhancing understanding of doping effects on electrochemical properties.

Findings

Lattice site preference depends on dopant charge and spin states.

Impurity-defect complexes are identified and characterized.

Doped compounds serve as models for complex battery cathodes.

Abstract

Doping lithium-ion battery electrode materials LiMO$_2$ (M = Co, Ni, Mn) with impurities has been shown to be an effective way to optimize their electrochemical properties. Here, we report a detailed first-principles study of layered oxides LiCoO$_2$, LiNiO$_2$, and LiMnO$_2$ lightly doped with transition-metal (Fe, Co, Ni, Mn) and non-transition-metal (Mg, Al) impurities using hybrid-density-functional defect calculations. We find that the lattice site preference is dependent on both the dopant's charge and spin states, which are coupled strongly to the local lattice environment and can be affected by the presence of co-dopant(s), and the relative abundance of the host compound's constituting elements in the synthesis environment. On the basis of the structure and energetics of the impurities and their complexes with intrinsic point defects, we determine all possible low-energy impurity-related defect complexes, thus providing defect models for further analyses of the materials. From a materials modeling perspective, these lightly doped compounds also serve as model systems for understanding the more complex, mixed-metal, LiMO$_2$-based battery cathode materials.