Intercalation of Li in graphite and other layered structures is of interest for highly efficient energy storage devices. In this paper, we determine the extent to which Li intercalates at the different interfaces formed between graphene (G) and hexagonal boron nitride (hBN) heterostructures. We use ab initio calculations to explore in detail the position of the dispersed Li atoms, changes in the structure at the interfaces, energetic stability of the configurations, and the corresponding electronic structure with varying concentrations of the intercalant. We trace the origin of the energetic stability and maximum concentration of Li that intercalates into various layered structures to the ability of the interface to accept electrons. Our calculations indicate that Li intercalates easiest at G/G interfaces, followed by interfaces between G/hBN, whereas Li cannot intercalate in hBN/hBN interfaces. Our results provide a framework for the design of experimental setups with optimal Li intercalation and reveal the implications of intercalation on the dielectric properties of these materials and their possible application in plasmonics.