Lithium superoxide is an unstable inorganic salt with formula LiO₂. A radical compound, it can be produced at low temperature in matrix isolation experiments, or in certain nonpolar, non-protic solvents. Lithium superoxide is also a transient species during the reduction of oxygen in a lithium–air galvanic cell, and serves as a main constraint on possible solvents for such a battery. For this reason, it has been investigated thoroughly using a variety of methods, both theoretical and spectroscopic.

The LiO₂ molecule is a misnomer: the bonds between lithium and oxygen are highly ionic, with almost complete electron-transfer. The force constant between the two oxygen atoms matches the constants measured for the superoxide anion (O−2) in other contexts. The bond length for the O-O bond was determined to be 1.34 Å. Using a simple crystal structure optimization, the Li-O bond was calculated to be approximately 2.10 Å.

There have been quite a few studies regarding the clusters formed by LiO₂ molecules. The most common dimer has been found to be the cage isomer. Second to it is the singlet bypyramidal structure. Studies have also been done on the chair complex and the planar ring, but these two are less favorable, though not necessarily impossible.

Lithium superoxide is extremely reactive because of the odd number of electrons present in the π* molecular orbital of the superoxide anion. Matrix isolation techniques can produce pure samples of the compound, but they are only stable at 15-40 K.

At higher (but still cryogenic) temperatures, lithium superoxide can be produced by ozonating lithium peroxide (Li₂O₂) in freon 12:

The resulting product is only stable up to −35 °C.

Alternatively, lithium electride dissolved in anhydrous ammonia will reduce oxygen gas to yield the same product:

Lithium superoxide is, however, only metastable in ammonia, gradually oxidizing the solvent to water and nitrogen gas: