Lithium is a compound found in more modern batteries. The are various types of lithium batteries;
Lithium iron phosphate (LiFePO4) technology
LiFePO4 (Lithium Iron Phosphate) cells based on lithium and carbon, they do not contain lead or acid which means they are more environmentally friendly.
Lithium Iron or LiFePO4 should not be confused with other Li-ion batteries. LiFePO4 have up to double the life cycles and a better regulated voltage of 3.2v per cell compared to a Li-ion nominal 3.6v per cell.