Aquinas begins SCG with God. Someday (waaaaay in the future) maybe I'll go over the full argument that he makes, but for now it's sufficient to say that after going through his proofs for the existence of God, he turns to an extended discussion of the things that we may know about God by means of reason.
In SCG I-96 (p. 292), St. Thomas demonstrates that God hates nothing. This follows from what he said in I-95 (p. 290f) about the fact that God cannot will evil:
For the virtue of a being is that by which he operates well. Now every operation of God is an operation of virtue, since His virtue is His essence, as was shown above. Therefore, God cannot will evil.If God cannot will evil, then certain other conclusions follow.
 From this it appears that the hatred of something does not befit God.But this is not all. Aquinas does not restrict himself to any single argument where he can help it (and he is rarely if ever limited to a single argument, thanks to his monumental intellectual powers):
 For as love is to the good, so hatred is to evil; for to those we love we will good, and to those we hate, evil. If, then, the will of God cannot be inclined to evil, as has been shown, it is impossible that He should hate anything.
 Again, the will of God is directed to things other than Himself, as has been shown, in so far as, by willing and loving His own being and His own goodness, God wills it to be diffused as much as possible through the communication of likeness. This, then, is what God wills in other things, that there be in them the likeness of His goodness. But this is the good of each thing, namely, to participate in the likeness of God; for every other goodness is nothing other than a certain likeness of the first goodness. Therefore, God wills good to each thing. Hence, He hates nothing.This conclusion is consistent with Scripture: "For thou lovest all things that are, and hatest none of the things which thou hast made: for thou didst not appoint, or make any thing hating it" (Wis. 11:25); "The Lord is good to all, and compassionate toward all his works" (Ps. 144/145:9).
Well, then what about passages in the Bible that seem to contradict this?
 However, God is said by similitude to hate some things, and this in a twofold way. In the first way, because God, in loving things and by willing the existence of their good, wills the non-existence of the contrary evil. Hence, He is said to have a hatred of evils, for we are said to hate what we will not to exist. In the words of Zechariah (8:17): "And let none of you imagine evil in your hearts against his friend and love not a false oath. For all these are the things that I hate, saith the Lord." These, however, are not effects in the manner of subsisting things, to which properly love and hate refer.So we see that the best that may be said for those Protestants who claim that God literally hates unbelievers is that they have misunderstood Scripture. The God who is love does not hate his creatures.
 The second way arises from the fact that God wills some greater good that cannot be without the loss of some lesser good. And thus He is said to hate, although this is rather to love. For thus, inasmuch as He wills the good of justice or of the order of the universe, which cannot exist without the punishment or corruption of some things, God is said to hate the things whose punishment or corruption He wills. In the words of Malachi (1:3): "I have hated Esau"; and the Psalms (5:7): "You hate all workers of iniquity: You destroy all who speak a lie. The bloody and the deceitful man the Lord will abhor."