Helllo Abhrajeet Mallick!

Negative potential is attractive in nature, i.e. if a system is in negative potential, it is stable. The more negative the potential means the more stable is the system. Similarly, for atoms, negative value of potential energy for electronics means they are stable and bound to the atom and external energy is required to ionize the atom.

Consider case of hydrogen. In ground state, the electron has energy equal to -13.6eV. This means 13.6eV of energy is required to break the atom. When the energy of the electron tends to be zero, it is no more bound to the atom.

Hope it helps!

Thanks!