Multi-scale modelling of O2 and O3-type materials for utilization as core-shell materials

Abstract

The automotive industry is currently prioritizing the development of lithium-ion batteries for electric vehicles due to the energy crisis and environmental concerns. These batteries rely on breakthroughs in cathode materials to achieve high-energy-density variants. However, the scarcity and cost of raw materials like cobalt and nickel underscore the need for affordable alternatives. Li2MnO3, made with abundant and economical manganese, offers higher capacity than traditional oxides but faces challenges like poor stability and low conductivity. Researchers are addressing these issues through methods such as elemental doping, surface modification, and a newly developed core-shell architecture to enhance electrochemical performance. The core-shell structure improves physical structure and conductivity and prevents undesirable reactions during charge and discharge processes. While the core-shell architecture has been investigated in the context of Li2MnO3, this study aims to pioneer the use of Li2MnO3 as the core material. The research delves into the intricate process of modelling and developing core-shell systems intended to serve as electrode materials with coating interfaces. Before creating these systems, the study investigates the electrochemical performance of Li2MnO3 through the delithiation process of Li2-xMnO3 (0 ≤ x ≤ 1) to gain a better understanding of its electrochemical behaviour before coating. The research utilizes density functional theory to investigate the structural and electronic characteristics of both the bulk structure of Li2MnO3 and delithiated structures of Li2-xMnO3. Calculations reveal that the material has a monoclinic structure, with lithium contributing the least to the overall density of states. Electronic band structures indicate a shift in conductivity during the delithiation process, transitioning from semiconductive to magnetic metal behaviour. Subsequently, two core-shell systems, consisting of 1434 and 435 atoms, were generated by coating O3-type Li2MnO3 with O2-type Li0.69MnO2, chosen for its high ionic conductivity and resistance to spinel transformation during cycling. Molecular dynamics simulations were conducted to optimize the conditions for these core-shell systems using the Nose-Hoover thermostat under NVT, NST, and NPT ensembles. The simulations involved varying parameters such as steps, timesteps, and temperature to investigate their effects on the core-shell systems. It is observed that the larger system outperforms the smaller one. Disordered behaviour was noted after 150,000 steps and 0.0001 timesteps, and temperature variations resulted in disorder, with the system regaining its crystalline form at 1500 K for both NVT and NPT ensembles after initial disorder at 1200 K and 900 K, respectively. Progress in this work has shown that the core-shell system is adequate for prevention of simultaneous oxygen and lithium loss during analysis of the structural snapshots when subjected to temperature