Operando Analysis of Materials and Processes in Next Generation Batteries

Doctoral thesis, 2021

With the rise in popularity of electric vehicles and electromobility solutions, there is a higher than ever demand for high energy density batteries. Accompanying this increased demand there is also an increased pressure for lower costs, longer durability, and the use of more sustainable materials. Going beyond the constraints imposed by the Li-ion battery, Next Generation Batteries, encompassing a host of technologies and chemistries, have the potential to provide higher energy densities, while using more sustainable materials and at a lower cost.

When exploring Next Generation Battery technologies novel materials and complex reactions are introduced underpinning the working mechanisms of energy storage. To move these technologies closer to realisation, a clear understanding of materials and processes during operation need to be established. To achieve this goal, investigations using operando characterisation techniques, measurements that are made during battery charge and discharge, provide a unique tool to advance the understanding of how a given battery technology works.

This thesis explores the use operando analysis methods to reveal the inner workings of three key next generation battery technologies; Na-ion anodes and how the electrode structure can be tuned to facilitate Na ion intercalation, how Lithium-Sulfur cathodes evolve during cell cycling and the subsequent conversion of polysulfide species, and finally the structures observed when using Lithium-Metal as an anode for high-capacity batteries. The focus is to determine structural changes to electrode materials using X-ray Tomographic Microscopy, and chemical changes using Raman Spectroscopy with the aim to reveal mechanisms controlling the performance in terms of capacity, rate capability or cycling stability. Though operando measurements present an exciting opportunity to monitor process in real time, they need to be grounded in reality, thus this thesis explores supporting work, such as ex situ measurements, electrochemical evaluations, and traditional characterisation methods used in battery research, all used to determine the complex and dynamic processes that dictate how batteries perform.