Empirical Force Field Derivation and Implementation for LiMO2 (M: Ni, Mn, Co) Cathode Materials

Abstract

Layered transition metal oxides LiMO2 (M= Mn, Ni, Co), exhibit good electrochemical performances and are considered as the prototype materials in the first commercial lithium-ion products. However, their performance as individual cathode has shown drawbacks and ignited interest in transition metal doping to form highly efficient cathodes. Such interest has driven efforts towards development of interatomic potentials to help provide information pertinent to the fundamental aspects of the interaction between atoms and allow accurate modelling of structures. Developing force fields is a tedious process as such cost functions often feature several competing minima. This work aims to obtain interatomic interactions (Ni-Ni, Ni-O, Co-Co and Co-Co) suitable for large scale simulations. The potentials are fitted from the cross-platform, streaming task runner (code-based) GULP. The procedure fits the ionic size (Aij), dispersion parameter (Cij), and the hardness of ions (ρij), according to the Buckingham potentials. The fitted interactions produced structures with lattice constants with a difference of less than 1% in NiO and 8.75% in CoO in comparison to experimental data. Furthermore, they yielded elastic constants with a difference of 0.35% in NiO and 2.01% in CoO. The high temperature molecular dynamic calculations validated the potentials through the melting temperatures. The nanostructures and their radial distribution curves confirmed melting temperatures of 2250K and 2000K in NiO and CoO, respectively. These are in good agreement accord with the experimental melting temperatures of 2206K and 2228K for NiO and CoO, respectively. Moreover, the derived interatomic potential accurately simulates the structural properties and behavior of and LiCoO2. The findings of the current study will enable the implementation of these potentials into LiMO2 (M: Ni, Co and Mn) structures for incorporation as dopants into the LiMnO2 cathode material.