Naturally occurring isotopes of lithium are Li-6 and Li-7. Li-6 is a component of nuclear weapons and also used to produce H-3, a radioisotope which is used in scientific research. Li-7 is used to regulate pH levels of the coolant in water reactors.
Li-7 is also used to make Be-7, another radioisotope. It's also much more abundant than Li-6. The binding energies of both isotopes is so low that they are very nearly unstable. Both Li-6 and Li-7 are produced in stars, and Li-7 was one of the first elements created after the Big Bang.
Radioisotopes of lithium include Li-8, Li-9 and Li-11. These radioisotopes have half-lives of only a few seconds. The other four radioisotopes of lithium are extremely short-lived.
"Regular" lithium is a soft, silvery-white, flammable alkali metal. Because it is such a reactive substance, it is never found in a free state but in ores such as pegmatite and is best stored in mineral oil. It is the lightest and least dense of the metals. Like its two stable isotopes, lithium was created during the Big Bang and can be found in stars.
Lithium is used in lithium batteries and glass and ceramic making. It's also used to make lubricating grease and in welding and soldering.