Lithium hydroxide (\(\text{LiOH}\)) is an inorganic compound classified as a strong base, though it is the weakest among the alkali metal hydroxides. This white, crystalline solid is highly soluble in water. It is a foundational chemical used extensively in modern industrial and technological applications, with its importance stemming from its unique chemical behavior.
Chemical Identity and Forms
Lithium hydroxide has the molecular formula LiOH, indicating a single lithium atom bonded to a hydroxide group. It is a white, odorless solid. This compound is notably hygroscopic, meaning it readily absorbs moisture from the air. \(\text{LiOH}\) is produced and sold commercially in two primary forms: anhydrous lithium hydroxide (\(\text{LiOH}\)) and lithium hydroxide monohydrate (\(\text{LiOH}\cdot\text{H}_2\text{O}\)).
The monohydrate form includes one molecule of water for every molecule of lithium hydroxide. For high-tech manufacturing, the anhydrous form is often preferred because it contains a higher concentration of lithium per unit mass. The anhydrous compound melts at \(462^\circ\text{C}\). Its strong basic nature allows it to readily neutralize acids and react with carbon dioxide in the air to form lithium carbonate.
Essential Role in Lithium-Ion Batteries
The most significant contemporary application of lithium hydroxide is its use as a precursor material for the cathodes in advanced lithium-ion batteries. It is the material of choice for synthesizing high-nickel cathode formulations, such as Nickel Manganese Cobalt (NMC) and Nickel Cobalt Aluminum (NCA) compounds. These high-nickel materials are essential for producing batteries with high energy density, which are necessary for extended driving ranges in electric vehicles (EVs).
Lithium hydroxide is favored over the more traditional lithium carbonate (\(\text{Li}_2\text{CO}_3\)) for these specific high-performance applications. This preference is due to its significantly lower decomposition temperature, typically between \(600^\circ\text{C}\) and \(700^\circ\text{C}\). This lower temperature facilitates a more controlled integration of the lithium into the cathode’s crystal structure during synthesis. The resulting high-nickel cathode materials exhibit superior electrochemical performance, longer cycle life, and improved thermal stability.
Production Pathways
The production of commercial-grade lithium hydroxide involves several distinct industrial pathways, depending on the source of the raw lithium. One common method involves a chemical conversion from lithium carbonate (\(\text{Li}_2\text{CO}_3\)), which is often sourced from lithium-rich brines. In this process, known as causticization, lithium carbonate reacts with calcium hydroxide. This reaction produces lithium hydroxide and precipitates calcium carbonate, which is then separated.
A second major route involves the direct extraction and conversion from hard rock minerals, primarily spodumene ore. The spodumene concentrate is first roasted and treated with acid to produce lithium sulfate, which is then reacted with sodium hydroxide to yield lithium hydroxide. Regardless of the initial source, the final stages require rigorous purification steps, including multiple crystallization and dehydration, to achieve the necessary purity for battery-grade material, often exceeding \(99.5\%\) \(\text{LiOH}\).
Other Industrial Uses
Beyond its modern battery application, lithium hydroxide has several other important industrial uses. Its strong ability to absorb carbon dioxide makes it invaluable in air purification systems for confined environments. \(\text{LiOH}\) is used to efficiently remove exhaled \(\text{CO}_2\) in:
- Submarines
- Spacecraft
- Closed-circuit rebreathers
The reaction forms lithium carbonate and water, and the anhydrous form is often preferred for its lower mass and higher absorption capacity.
\(\text{LiOH}\) is also a foundational component in the manufacturing of high-performance lubricating greases. A lithium soap is created through a process called saponification by reacting \(\text{LiOH}\) with a fatty acid, such as 12-hydroxystearic acid. This lithium soap acts as a thickening agent that is mixed with oil to form a grease. These lithium-based greases are highly valued for their stability across a wide temperature range and their excellent water resistance, making them a standard for automotive and heavy industrial machinery.