Be+ has a greater ionization enthalpy than Be. The removal of electrons from an atom requires energy. In other words, this process is endothermic.
Since Be is in Group 2, it can lose 2 electrons. The first ionization is:
Be + energy → Be+ + e-
The second ionization is:
Be+ + energy → Be2+ + e-
Be+ has 1 valence electron remaining in its outermost shell that feels a strong electrostatic interaction with the four protons in the nucleus (just think about positive-negative attraction). To overcome this interaction, more energy is therefore needed to remove the 2nd electron from the valence shell to form Be2+.