Lithium cobalt oxide (LiCoO2) is a chemical compound commonly used in the positive electrodes of lithium-ion batteries. The structure of LiCoO2 is known theoretically and has been confirmed with techniques like x-ray diffraction, electron microscopy, neutron powder diffraction, and EXAFS: it consists of layers of lithium that lie between slabs of octahedra formed by cobalt and oxygen atoms. The space group is in Hermann-Mauguin notation, signifying a rhombus-like unit cell with threefold improper rotational symmetry and a mirror plane. More simply, however, both lithium and cobalt are octahedrally coordinated by oxygen. These octahedra are edge-sharing, and tilted relative to the layered structure. The threefold rotational axis (which is normal to the layers) is termed improper because the triangles of oxygen (being on opposite sides of each octahedron) are anti-aligned.
Batteries produced with LiCoO2 cathodes, while providing good capacity, are more reactive and have poorer thermal stability than batteries produced with other cathode chemistries (such as the more modern lithium nickel cobalt aluminum oxide type) due to improved cathode stability. This makes LiCoO2 batteries more susceptible to thermal runaway in cases of abuse such as high temperature operation (>130ºC) or overcharging. At elevated temperatures, LiCoO2 decomposition generates oxygen, which then reacts exothermically with the organic materials in the cell. This may pose a safety concern due to the exceptional speed and magnitude of the highly-exothermic reaction, which can induce thermal runaway in adjacent cells or ignite nearby combustable materials.
Exposure to soluble cobalt salts can lead to cardiomyopathy. MSDS sheets list lithium cobalt oxide as a potential human carcinogen but indicate "no data available" under the Acute Toxicity heading. However, unlike cobalt(II) salts, this oxide is insoluble in water. Lithium ion batteries contain lithium cobalt oxide and are considered nonhazardous waste. Safety precautions should be taken when handling it.
The compound's usefulness as an intercalation electrode was discovered in 1980 by John B. Goodenough's research group at Oxford.