Implicit solvation model can be added to your calculation by using VASPsol tool for VASP. There you can find instructions how to compile VASP with the tool and a couple of example how to use it.
!------------------------------------------------------------------------ WARNING: Use all-electron pseudopotential or set CORE_C explicitly for atomic-species with atomic number less than or equal to 4. Problem species ATOMIC NUMBER, SYMBOL & VALENCE : 3 Li 1.00000000000000 I HOPE YOU KNOW WHAT YOU ARE DOING ! !------------------------------------------------------------------------