Intercalation of a pure metal into graphite: what is the best synthesis route? A century of synthesis

The two-dimensional and heterodesmic nature of graphite enables it to accommodate various oxidising or reducing species between its graphene layers. This article focuses on metal-graphite compounds. Since 1926, when the first graphite intercalation compounds with alkali metals were discovered, various synthesis methods have been developed. The first compounds were obtained using solid-vapor and solid-liquid methods with a pure alkali metal. Solid-solid reactions were also carried out, notably by powder compaction. Solid-liquid methods involving an element other than the metal to be intercalated were subsequently developed: metallic alloy medium based on alkali metals and molten salts medium of the LiCl-KCl type, where the alkali metal acts as an intercalation vector. The use of sodium as a catalyst in solid-solid methods subsequently emerged. All of these synthesis methods have enabled the preparation of numerous metal-graphite compounds, some of which have key applications in everyday life, such as LiC 6 . Others possess remarkable properties, such as CaC 6 . The aim of this article is to determine, for a given metal-graphite compound, which is the best synthesis method for obtaining a pure compound. At the same time, this paper celebrates the hundredth anniversary of the very first intercalation reactions of metals into graphite (KC 8 , RbC 8 , CsC 8 ).