Alkali Metal Stripping and Plating in Liquid Electrolytes

Licentiate thesis, 2022

Batteries have relatively modest energy densities compared to fossil fuels. In the efforts to make battery-driven transport solutions and technologies competitive with gasoline-powered alternatives, it is important to develop batteries with higher energy densities. This can be enabled by utilizing different electrode materials than what is currently done. For instance, lithium metal is one of the electrode materials which can enable the highest theoretical energy densities. Similarly, using metal anodes can pave way for more sustainable materials solutions based on e.g. sodium, potassium or magnesium. During charging in batteries with a metal anode, ions from the electrolyte are plated on the electrode, and during discharge, the metal is stripped from the electrode. These processes are associated with several problems hindering the practical application of metal anodes. For instance, dendritic or uneven growth can cause short circuits and lead to loss of active material. Further, side reactions can consume both electrolyte and active material. A fundamental understanding of the stripping and plating process is needed to solve these problems. In this thesis, electrochemical measurements are used to understand the fundamental steps of the alkali metal plating and stripping process using Li and K metal electrodes. Additionally, the impact of the electrolyte composition, particularly the salt concentration, on alkali metal anodes is investigated. Cycling performance is evaluated and interphase formation is probed with in situ neutron reflectometry.