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Intercalation refers to the reversible insertion of guest atoms, ions, or molecules into a host material. This process typically occurs in layered or framework structures where there are available spaces or channels for the guest species to occupy. The host material maintains its structural integrity, with the guest species fitting into pre-existing interstitial sites.

A key characteristic of intercalation is its reversibility. The guest species can be removed from the host material, returning it to its original state, and then re-inserted. This property is fundamental to many technological applications, particularly in energy storage devices like batteries. In lithium-ion batteries, for instance, lithium ions intercalate into and de-intercalate from electrode materials such as graphite or metal oxides during charging and discharging cycles.

The ability of a material to undergo intercalation depends on several factors. These include the size and charge of the guest species, the presence of suitable interstitial sites within the host lattice, and the electronic and structural compatibility between the host and guest. The energy associated with the insertion and removal of guest species also plays a crucial role, influencing the voltage and capacity of intercalation-based devices. Beyond batteries, intercalation phenomena are relevant in areas such as catalysis, gas storage, and the development of new electronic materials.