I want to copy all of my images to a new drive avoiding duplicates

Do you have the duplicates imported into your LrC catalog? 

Duplicates is a complication that is not easy to deal with, there are many threads here in this forum on the topic of duplicates. I suggest you start by searching here. In my opinion, I would recommend you eliminate the duplicates before you try to move everything to a new disk, as long as the duplicates are not in the LrC catalog. If the duplicates have been imported into LrC, then you have to decide how to handle these.

Or — an out-of-the-box possibility which you may or may not like — the easiest thing to do is to just leave the duplicates in the folders and move them all to the new disk. This is, as I said, the easiest approach, but has disadvantage of taking up more disk space and requires more time to move everything.

Regardless, the method to move the photos to a new disk is explained here (scroll down to Part 2 — Updating Folder Location).