In crystals, such as graphite, which show a two-dimensional lattice structure, layers of other materials can be inserted between each single or multiple layer to form new compounds with unusual properties. This insertion of layers can be achieved easily by simply dipping graphite into molten metals, such as Li at 200-400 °C. After immersion, the intercalation starts at the edges and proceeds into the bulk by rapid diffusion. Such interlayers can be, for example, halogens or alkali metals. Examples include KC8 or LiC6, compounds which are transparent (yellow) and show anisotropic conductivity and low-temperature superconductivity.
In the process of intercalation, the metal atom is ionized while the graphite layer becomes negatively charged. When immersed in an oxidizing liquid, the driving force to oxidize Li can be strong enough to reverse the reaction. This reversible process is attractive in the design of high-density rechargeable batteries when providing electrochemical driving forces.
Other layer-like lattices can also be intercalated easily. An example is TaS2. Many of these compounds have extremely high diffusivity of the intercalating atoms. Some of them show a very large electrical anisotropy. For a review, see Whit – tingham and Jacobson (1982).