In the process of ionization, what is the relationship between the second ionization energy (i2) and the third ionization energy (i3)?

The first ionization energy is the energy that is obligatory in order to eliminate the first electron from an atom(neutral) in the GAS phase
, the second ionization energy is defined as  the energy required to remove the second electron from an atom(+1 ion) in the GAS phase.
the third ionization energy is the energy it takes to remove an electron from a 2+ ion. (That means that the atom has already lost two electrons, you are now removing the third.) 
 Ionization energy will normally increase for every electron that is removed and increases from left to right in the periodic table and moving up the periods
hope it helps