To quantify the extent of degradation within cells, and to identify cells that have reached their 'End of Life', the scalar State of Health (SoH) metric is typically adopted, measured using previous cycle discharge capacity or internal resistance . The problem with this approach is that batteries with the same numerical SoH do not necessarily exhibit identical levels of each degradation process (for example, lithium plating or electrode cracking), yet the impact of future cell usage on the cell's future performance and degradation pathway depends significantly on the type of degradation that has already occurred . In order to forecast battery performance, we need a non-invasive way to acquire information about the cell state at a microscopic level.