Lewis structure of ions
The charge on a centre in Lewis structures is not of special relevance, except that it helps to provide the information which is useful: the number of electrons on that centre.

A positive charge of $X$ means $X$ electrons were lost, while a negative charge, $-Y$ means $Y$ electrons gained.

From this you can either simply remove/add the corresponding number of dots from/to the diagram, or calculate how many valence electrons are now present, and then draw the diagram ab initio from this information.

A "normal" lithium centre has 1 valence electron, so the positive ion just loses it (leaving no dots) while the negative ion gains one more (and thus has two dots on the diagram).