BxC1−x (x = 0.1 and 0.25) oriented platelets were intercalated with alkali metal vapor (M = K, Rb, Cs), giving first-stage M(B0.1C0.9)8 and M(B0.25C0.75)10. The presence of M(BxC1−x)5 dense domains interstratified in the first-stage structure were brought out from the 00.ℓ simulations. The presence of these domains is attributed to the acceptor electron effect of boron, which slightly enhances the intercalation rate as compared to pure carbon. Intercalation of Cs in liquid ammonia is improved using 1600 °C heat-treated B0.25C0.75 as a host material, and the composition Cs(B0.25C0.75)12 is reached after intercalation. In intercalation compounds of Cs in liquid ammonia obtained from heat-treated B0.25C0.75, as the heat-treatment temperature (HTT) was increased from 1600 to 2000 °C, the segregation of first stage was observed in two structures Cs(BxC1−x)8 and Cs(BxC1−x)10 with the respective 2 × 2 0° and 2.23 × 2.23 two-dimensional lattices of the cesium atoms. The presence of these two structures is assigned to the heterogeneity of the host material induced by the formation of B4C boron carbide domains and the consecutive boron elimination of the BxC1−x lamellar phase with increasing HTT.