Li-6 and Li-7 are the two naturally occurring isotopes of Lithium; appx. 8% and 92% abundant respectively. There are no naturally occurring radioactive isotopes of Li. Radioactive isotopes that have been made through cyclotrons, or other particle accelerators all have very short half lives, under 1 second.
Lithium is used medically in psychotropic drugs. It is the ingredient metal used in both primary and rechargeable lithium batteries.
Because it behaves like a very soft metal, it is used in lithium greases for special applications.