Many of the devices currently used for energy storage (e.g., batteries, solar cells) use liquid electrolytes that are known to pose a serious fire and safety risk. In recent years, a number of solid materials have been suggested as possible replacements, however, very little is currently known regarding how these materials function and, in particular, how the ions move within the material. Studies are therefore needed to understand the relationship between structure and functionality. This muon proposal aims to characterise a new class of solid electrolytes, hydrated Li-rich anti-perovskites (LiRAPs), to determine their ion mobility at different temperatures and understand how their performance can be improved.