- Lithium iodide (LiI) is an inorganic compound composed of lithium (Li⁺) and iodide (I⁻) ions. It appears as a white to pale yellow crystalline solid and is highly soluble in water and polar organic solvents such as ethanol, methanol, and acetone.
- Like other lithium halides, LiI forms a crystalline structure similar to sodium chloride, featuring strong ionic bonds due to the high charge density of the lithium ion and the large polarizability of the iodide ion. The compound is hygroscopic and must be stored in tightly sealed containers to prevent moisture absorption and degradation.
- LiI is notable for its exceptionally high solubility in both water and organic solvents, a property that arises from the highly polarizable iodide ion. When dissolved, LiI forms a highly conductive electrolyte solution, which is useful in various electrochemical applications. Unlike lighter halides such as LiF or LiCl, LiI has a lower lattice energy due to the larger iodide ion, making it easier to dissolve and manipulate in chemical processes. It can slowly oxidize in moist air, forming elemental iodine, which gives aged samples a slightly yellowish tint.
- One of the key uses of lithium iodide is in organic synthesis, where it acts as a catalyst or reaction promoter. It is especially useful in nucleophilic substitution reactions and Finkelstein-type halogen exchange reactions, where its solubility and ability to stabilize transition states make it highly effective. LiI is also employed to facilitate dehalogenation, acylation, and ester cleavage reactions. In synthetic protocols, it can increase yields or reduce reaction times by modifying the solvation environment or altering reaction kinetics.
- In the field of electronics and energy storage, lithium iodide is used as an electrolyte additive or component in solid-state batteries, particularly in early designs of lithium-iodine batteries used for low-drain, long-life applications such as medical implants (e.g., pacemakers). These batteries rely on the redox reaction between lithium and iodine, and LiI helps to facilitate ionic conduction between the anode and cathode. Although newer battery chemistries have surpassed Li–I systems in energy density and flexibility, LiI remains important in the development of solid-state electrolyte materials due to its ionic conductivity and compatibility with lithium metal.
- Another interesting application of lithium iodide is in radiation detection and scintillation, where doped lithium iodide crystals (e.g., LiI:Eu) are used as scintillators. These materials emit light when exposed to ionizing radiation and are valuable in nuclear physics, medical imaging, and environmental monitoring. The presence of lithium also makes LiI-based detectors useful for detecting thermal neutrons, as lithium-6 has a high neutron capture cross-section.
- From a safety and handling perspective, lithium iodide is relatively low in toxicity, though it can cause irritation to the eyes, skin, and respiratory tract. Ingestion of large quantities may disrupt electrolyte balance and thyroid function, due to the bioactivity of iodine. Prolonged exposure or improper disposal may also contribute to environmental iodine accumulation, which could affect soil and water ecosystems. As with other lithium salts, appropriate protective measures should be used during handling, including gloves, eye protection, and working in well-ventilated areas.
