Understanding ion transport in halide solid electrolytes with varying mobile species
File(s)
Author(s)
Barker, Kit
Type
Thesis
Abstract
Solid-state batteries (SSBs) are an emerging technology poised to play a pivotal role in
the transition from fossil fuels to renewable energy sources, due to their projected ability to
deliver higher energy densities than conventional Li-ion chemistries. The use of alkali metal
negative electrodes, currently unfeasible in commercial batteries, could push energy storage
toward theoretical limits. Replacing the liquid electrolyte with a solid counterpart, however,
presents significant challenges. Among the many proposed materials, inorganic halide solid
electrolytes offer an appealing balance of desirable properties. They typically exhibit high
oxidative stability but are vulnerable to reduction at the anode. While relatively easy to
synthesise, their best-performing compositions often rely on costly, rare elements.
Ionic conductivity, a material’s capacity to transport ions between electrodes, is critical for
SSBs but typically lower in solids than in liquids. This thesis investigates the fundamental
origins of ion transport in halide solid electrolytes. Using a range of model systems, the chemical
and structural factors affecting conductivity are explored for Li+, Na+, Cu+, and Ag+ ions.
After a brief overview of SSBs and alternative chemistries, Chapter 1 introduces the theory of
ion transport in solids. Chapter 2 reviews the literature on halide electrolytes and ion transport
thermodynamics, highlighting research gaps addressed in this thesis. Chapter 3 outlines the
experimental and computational methods employed.
Chapter 4 examines the structure and thermodynamics of the A2ZrCl6 (A = Li+, Na+, Cu+,
Ag+) family, including the novel Ag2ZrCl6. Chapter 5 investigates ionic conductivity and reveals
the origins of high conductivity in Cu and Ag systems. Chapter 6 applies percolation theory to
optimise structures and assess anion sublattices. Chapter 7 explores a novel halide class related
to perovskites, with several new compounds predicted and synthesised using DFT.
the transition from fossil fuels to renewable energy sources, due to their projected ability to
deliver higher energy densities than conventional Li-ion chemistries. The use of alkali metal
negative electrodes, currently unfeasible in commercial batteries, could push energy storage
toward theoretical limits. Replacing the liquid electrolyte with a solid counterpart, however,
presents significant challenges. Among the many proposed materials, inorganic halide solid
electrolytes offer an appealing balance of desirable properties. They typically exhibit high
oxidative stability but are vulnerable to reduction at the anode. While relatively easy to
synthesise, their best-performing compositions often rely on costly, rare elements.
Ionic conductivity, a material’s capacity to transport ions between electrodes, is critical for
SSBs but typically lower in solids than in liquids. This thesis investigates the fundamental
origins of ion transport in halide solid electrolytes. Using a range of model systems, the chemical
and structural factors affecting conductivity are explored for Li+, Na+, Cu+, and Ag+ ions.
After a brief overview of SSBs and alternative chemistries, Chapter 1 introduces the theory of
ion transport in solids. Chapter 2 reviews the literature on halide electrolytes and ion transport
thermodynamics, highlighting research gaps addressed in this thesis. Chapter 3 outlines the
experimental and computational methods employed.
Chapter 4 examines the structure and thermodynamics of the A2ZrCl6 (A = Li+, Na+, Cu+,
Ag+) family, including the novel Ag2ZrCl6. Chapter 5 investigates ionic conductivity and reveals
the origins of high conductivity in Cu and Ag systems. Chapter 6 applies percolation theory to
optimise structures and assess anion sublattices. Chapter 7 explores a novel halide class related
to perovskites, with several new compounds predicted and synthesised using DFT.
Version
Open Access
Date Issued
2025-04-26
Date Awarded
2025-08-01
Copyright Statement
Attribution 4.0 International Licence (CC BY)
License URL
Advisor
Skinner, Stephen
Aguadero, Ainara
Ieuan, Seymour
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)