The equation is
4Li + 2O2 → 2Li2O
By using this balanced equation coefficients, 2 moles of Li make 1 mole of Li2O, ratio between Li and Li2O is 2:1
So, 4 moles of Li makes 2 mole of Li2O
And 8 moles of Li makes 4 mole of Li2O
It means When 8 moles of lithium metal react with excess oxygen gas, 4 moles of lithium oxide can be produced.