In materials and electric battery research, cobalt oxide nanoparticles usually refers to particles of cobalt(II,III) oxide Co
₃O
₄ of nanometer size, with various shapes and crystal structures.

Cobalt oxide nanoparticles have potential applications in lithium-ion batteries and electronic gas sensors.

The cathodes of lithium-ion batteries are often made of lithiated oxides of cobalt, nickel, or manganese, that can readily and reversibly incorporate lithium ions in their molecular structure. Cobalt oxide nanomaterials, such as nanotubes, offer high surface-to-volume ratio and short path lengths for lithium cation transport, leading to fast charging capabilities. However, capacity, coulombic efficiency, and cycle life may suffer due to excessive formation of SEI. The nanowires may incorporate other substances, for example, diphenylalanine.

Cobalt oxide particles may be anchored on substrates such as graphene to improve the dimensional stability of the anode and to prevent particle aggregation during lithium charge and discharge processes.

Hollow nanospheres of cobalt oxide have been investigated as materials for gas sensor electrodes, for the detection of toluene, acetone, and other organic vapors.

Cobalt oxide nanoparticles anchored on single-walled carbon nanotubes have been investigated for sensing nitrogen oxides NO
_x and hydrogen. This application takes advantage of the reactivity between the gas and the oxide, as well as the electrical connection with the substrate (both being p-type semiconductors). Nitrogen oxides react with the oxide as electron acceptors, reducing the electrode's resistance; whereas hydrogen acts as an electron donor, increasing the resistance.

Cobalt oxide nanoparticles have been observed to readily enter cells, a property that conceivably could lead to applications in hyperthermic treatment, gene therapy and drug delivery. However, their toxicity is an obstacle that would have to be overcome.

Cobalt oxide is often obtained by hydrothermal synthesis in an autoclave.