The aim of this PhD project is to investigate lithium- and sodium-based solid-state batteries using muon-based bulk and interface characterization techniques. The main objective is to gain a mechanistic understanding of electrochemical performance, with a focus on ion distribution, transport, and degradation processes during battery operation. The project addresses key questions such as the formation of Li/Na concentration gradients during charge and discharge, the evolution of interphases, and degradation mechanisms including ageing, material dissolution (leaching), and transition-metal migration. Muon-based methods will be used to probe depth-resolved properties that are difficult to access with conventional techniques, enabling new insights into buried interfaces and bulk transport phenomena. Your work will focus on electrochemical and structural characterization of battery materials and cells, combined with muon-based experiments. You will design and carry out experiments to identify reaction pathways and degradation mechanisms, and analyze complex datasets to connect microscopic processes with macroscopic performance. Close collaboration with project partners will support the development and testing of materials and cell concepts.