Unlike lithium-ion batteries, the storage capacity of the oxygen-ion battery does not decrease over time, as it can be regenerated. The ceramic materials that TU Wien looked at can take in and let go of oxygen ions with two negative charges. At present, oxygen-ion battery technology is not meant for smartphones or electric cars because it only has about a third of the energy density of lithium-ion batteries and works at temperatures between 200 and 400 °C