After that, there are several possibilities. They include lithium air batteries that are even smaller, lighter weight and cheaper and lithium supercabatteries that even work well at -30 degrees C. However expect little commercial impact before 2020 with third generation options for vehicle traction power. Candidate chemistries include lithium sulphur and lithium air. They are not inherently safe against thermal over run in every case and the use of the term third generation refers to potential increasing in power and energy density.