Explanation:
Lithium is an electropositive element that readily loses electrons.
Oxygen is electronegative and it will readily accept electrons.
Due to this significant electronegativity differences between the two species they form electrovalent or ionic bonds between them.
2atoms of Li lose two electrons:
Li → Li²⁺ + e⁻
Lithium isoelectronic with helium
For oxygen;
O + 2e⁻ → O²⁻
Oxygen is isoelectronic with Neon
Two ions of the lithium combines with the oxygen to form the bond;
4Li + O₂ → 2Li₂O
The electrostatic attraction between the two ions forms the ionic bond

Actually Welcome to the concept of Ions .
If we see the reaction.
H2SO4 ==> 2H+ + (SO4)2-
Here you can see, H+ ( Hydrogen ions) and (SO4) 2- ( sulphate ions) are the ions when the H2SO4 is dissolved in water.