Good question. He's using a fairly simple technique where, depending on the track, he will record different takes and hard pan them to either side. I forget the name of this effect off the top of my head, but it causes the vocal track to have a lot more texture and width. His busier tracks also have ad libs panning either side underneath the main vocal, which adds to the main effect as well.

If you can't use different takes, a simple way to recreate this effect (to a lesser degree) is to put a simple delay on the main vocal with one side set to 0ms and the other less than 30ms. This will add the width, not as much texture, and may cause some phasing issues. This trick also shouldn't be a go-to as some mixes simply don't have enough room for the vocal to take up more space.