Is Li a cation or an anion?

Li ( lithium) is an ATOM.

However, when it ionises (loses) an electron it becomes the Lithium ion (Li^(+)).

Positive ions are collectively named as CATIONS.

Negative ions are collectively named as ANIONS.

NB An atom is an UNcharged species of any element. When it becomes a charged species, then it is an ION. Cation(+) & Anion(-) .