Intercalation of ions refers to the process where ions are inserted into the layers of a material without significantly altering its overall structure. This process is commonly seen in materials like graphite or layered metal oxides, where ions, such as lithium ions in the case of lithium-ion batteries, are reversibly inserted between the layers of the host material. The intercalation process is key to the functioning of various electrochemical systems, including rechargeable batteries, as it allows for the storage and release of energy.