You do not want anything conductive. That is part of the reason why the battery top should be kept clean. A light film of acid will conduct a small current from post to post, causing the battery to lose charge slowly.

What you want to do is keep the oxygen away from the connection. Most metals will combine with oxygen, and turn to an oxide that does not conduct very well. The stuff you are talking about that electricians put on connections, is to seal the connection and try to keep the metal from oxidizing.

The best thing to do is take the cables off, and clean them very well. Then coat them to keep them from oxidizing.

I have tried grease. That didn't work. I have tried the little felt washer you buy in the store. That didn't work. What has worked for me for the past 10 years is motor oil. Everytime I change the oil, the couple of drips that are left in the can, I let drip on the battery post connections. Just about 2 drips on each one is all it takes. I have not had any corrosion problems since I started doing this. If you get someone else to change your oil, just get an oil can and fill it with motor oil, and put a couple of drips on there yourself every 3000 miles.