Is F2 two fluoride ions or just one?
$\ce{F2}$ will produce  $2\space \ce{F-}$ ions.

You can write the balanced half cell reactions as follows:

$\ce{F2 + 2e- -&gt;2F-}$

$\ce{Li -&gt; Li+ + e-}$

Multiply the second equation by 2 to get $\ce{2Li -&gt; 2Li+ + 2e-}$. This is to ensure that the final equation does not have any electrons on either side.

Now add this equation with the fluorine one. 

You'll get $\ce{2Li + F2 -&gt; 2Li+ + 2F-}$ which you can write as $\ce{2Li + F2 -&gt; 2LiF}$