What can you add to a voltaic cell to make it into an electrolytic cell?

a cell or battery

Explanation:

this is because a voltaic cell is such a cell where chemical energy gets converted to electrical energy. the energy conversion in the case of an electrolytic cell is from electric to chemical (battery supplies electrons to the anode respectively). So, I feel by adding a cell or battery, we can change the way energy conversion takes place, thereby changing the process.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-