As*

We use scanning tunneling microscopy (STM) to image the electronic impact of Co atoms on the ground state of the LiFe_1-xCo_xAs system. We observe that impurities progressively suppress the global superconducting gap and introduce low energy states near the gap edge, with the superconductivity remaining in the strong-coupling limit. Unexpectedly, the fully opened gap evolves into a nodal state before the Cooper pair coherence is fully destroyed. Our systematic theoretical analysis shows that these new observations can be quantitatively understood by the nonmagnetic Born-limit scattering effect in a s±-wave superconductor, unveiling the driving force of the superconductor to metal quantum phase transition.