Exploring Lithium and Sodium Anti Perovskite Solid Electrolytes for Energy Storage Applications

Abstract

In the face of the current climate emergency, solid-state batteries have been attracting significant attention due to a plethora of potential advantages, such as energy density gains and safety enhancements. Solid electrolytes are the heart of this technology, and the success of future implementations relies on the discovery, design, and development of new solid electrolytes. Computational modelling stands as a vital tool to assist future experimental directions and provide key insights that cannot easily be obtained experimentally. In recent years, anti-perovskites have stood out as promising solid electrolyte candidates as they combine high ionic conductivity, stability against lithium metal anodes, and structural versatility. This Thesis uses computational techniques to explore the pertinent defect chemistry, properties, and ionic transport mechanisms in a range of lithium- and sodium based anti-perovskite materials, providing fundamental information regarding their potential for future solid electrolyte applications. Lattice statics and classical molecular dynamics calculations are used to investigate a range of LixOXy (X = Cl or Br; x = 3–6; y = 1–4) anti perovskites with zero- to three-dimensional structures. The simulations reveal the strong connection between lithium-ion dynamics and dimensionality in these anti-perovskite materials, where increased lithium-ion diffusion and decreased activation energy can be seen as dimensionality is reduced. Additionally, density functional theory calculations are utilised to explore the bulk and surfaces of a range of M3OX (M = Li or Na; X = Cl or Br) anti perovskites. The simulations predict that the formation of any defect type at any site is more energetically favourable in systems containing Na instead of Li, regardless of their halide content. The analysis of the electronic properties reveals that Na-based systems could potentially present lower electrochemical stabilities. The calculated migration barriers indicate a complex trade-off between maximising atomic polarisability and bottleneck size in the lattice for enhancing ion migration.