Is there a adjective describing something that can be intercalated?

I presume that you refer to the intercalation of 2-D lattices by other ionic species. If so, Semantic Scholar shows one example of many where intercalatable is used. According to Google's ngram viewer, the word came into use in the 1960s, reached a peak in about 1990 and has declined in usage since. It expresses exactly what you describe.