I read that comparatively LiF is more covalent than NaF becoz of smaller cation size but also LiF has more lattice energy than the latter....but more ionic the compound ..more is the lattice energy...so isnt is contradictory that LiF is move covalent but has higher lattice energy. I am really stuck.

lithium is too strong to donate an electron for forming a ionic bond which is formed when the latter receives an electron..so it is very unlikely for the electrons to jump off to florine as the force of attraction between both of them is maximum becoz of electro negative difference between both.Had lithium being larger it would not have exerted force the same force on its electrons.

Hope i am clear enough,like this answer if you find it helpful ;)