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 neutron PDF proposal aims to characterise a new class of solid electrolytes, hydrated Li-rich anti-perovskites (LiRAPs), by determining their local structure and understanding how it influences functionality and performance. Completing comparative studies for systems across the series will enable us to understand how their performance can be improved.