Unified design flow for facilitating fast Li kinetics in layered oxide cathodes

Abstract

Fast charging is desirable for the global use of full electric vehicles (EVs); however, it faces challenges based on Li kinetics. A structural design based on the electrostatic repulsion (ER) between cations over the full charging process is proposed herein to facilitate the fast Li kinetics of LiMO2 (M = transition metal) layered oxides in lithium-ion batteries (LIBs). This process is divided into two steps under the Li kinetic mechanism, in which LiO4 is a transition state upon migration. First, changing the O3- to O2-type layered cathodes causes the expansion of the LiO2 slab and elimination of the ER between Li and M ions in the hidden space based on the edge-shared mode for the Li-abundant region. Second, expanding the LiO4 space to release the stressed environment provides easy accommodation of Li ions through the ionic radius of the dopants in the Li-deficient region. Using unified atomistic calculations of density functional theory and kinetic Monte Carlo simulations, the systematic design flow can be understood in terms of the structural parameters, site energetics for the kinetic barrier, and statistical transitions based on various Co-based LiMO2 models. Our concrete understanding of local-to-macroscopic structural scales suggests a generalized direction for facilitating fast Li kinetics for realizing fast-charging LIBs.