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. However, the electrolyte is key and plays an essential role in the performance of such devices. Hence, safe alternatives are urgently required. 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. Hence, studies are needed to understand the relationship between structure and functionality. This neutron proposal aims to characterise a new class of solid electrolytes, hydrated Li-rich anti-perovskites (LiRAPs), to determine their structure at different temperatures and understand how structure can influence their performance as a solid electrolyte material