In this presentation, we will introduce a recently developed operando optical microscopy technique, and provide examples of how it has been applied to mechanistic studies of battery electrodes and active material characterisation. Our technique probes state-of-charge changes in the active particles within the electrode during battery operation, based on the intensity variation of scattered light across each active particle. This enables detailed spatially-resolved data on an individual particle level to be built up for mechanistic studies but can also allow global statistics to be established at the electrode level. The ability to quantify ion transport during battery operation within active particles and across the electrode helps to provide insights into how lithium-ion dynamics affect the (de)lithiation mechanisms and degradation mechanisms of battery electrodes, which is crucial to improving their electrochemical performance.