Investigating the Effects of Doping Layered Lithium Nickel Oxide

Lithium-ion batteries have long been established as the leading technology for energy storage devices due to their high energy density and longevity 1. Common cathode materials for these batteries are layered oxides. LiCoO2 (LCO) is a popular layered oxide which is commonly used within the electronic industry. Yet, due to increasing environmental impacts tied with the price of the cobalt, there has been a substantial push for cobalt-free cathode materials, especially for the automotive application 2. The isostructural compound LiNiO2 (LNO) has been identified as the ideal replacement for LCO. LNO, with more earth-abundant Ni sources, has the theoretical capacity and voltages comparable to LCO 1. However, the material cannot fully utilize its theoretical energy density due to its mechanical and thermodynamical instabilities. Recent work has demonstrated that substitution strategies can cater for the instabilities whilst also minimising the reduction in<br/>capacity during battery cycling. Still, the underlying chemistry of the improved stabilities of the substituted LNO remain challenging to be elucidated, which has been hidden behind the false ground state structure of R-3m space group. Recently, owing to the Jahn-Teller (JT) distortion, LNO has been found to have the ground state structure with the P21/c space group 3,4,5. Density functional theory (DFT) calculation, with its ability to predict the ground state structures and charge compensation mechanisms, have been an effective<br/>tool for investigating solid-state materials with dopants. In this study, we implement DFT in order to fully understand the doped structure with the aim to find a stable nickel-rich cathode with a high theoretical capacity. Using the JT distorted structure, intrinsic point defects have been investigated in these cathode materials. This reveals insight into the experimental observations for LNO and gives an understanding for the charge compensating mechanisms within the pristine system. In addition, by comparing the present results with previous studies, the study will reveal insight into the charge compensating mechanisms as has been established for the pristine system. Lastly, the study explores Mg and W as dopants for LNO due to their notable success established in previous experimental studies 6,7. In turn, this will explain the observations of improvements in stability upon addition of the dopants.