Lithium cannot form peroxide because of its small size. Then how does Hydrogen form peroxide?

Lithium cannot form peroxide while hydrogen can because positive charge is located over small size of lithium and hence there is positive field around it which will attract negative ion so strongly that it will not permit oxide ion to combine with another oxide ion

Hence lithium forms monoxide while in case of hydrogen charge is located over comparatively bigger atom which allows oxide ion to combine with another oxide ion hence.. Peroxide is formed

While in other case superoxide is formed due to combination. Of two peroxide ions.