Lithium is the alkali metal with lowest density and with the greatest electrochemical potential and energy-to-weight ratio. The low atomic weight and small size of its ions also speeds its diffusion, likely making it an ideal battery material. Experimentation with lithium batteries began in 1912 under American physical chemist Gilbert N. Lewis, but commercial lithium batteries did not come to market until the 1970s in the form of the lithium-ion battery. Three volt lithium primary cells such as the CR123A type and three volt button cells are still widely used, especially in cameras and very small devices.