There are a total of 64 Cell Intel Collectibles in Crysis 3. They are divided into three collectible categories: 38 Datapads, 6 Propaganda Posters, 20 Blackboxes.
Finding all of them will earn you the "Breaking the Lore" Trophy / Achievement. After picking up a collectible it will be saved immediately. Even if you die there is no need to search for it again. Each mission has some collectibles. There are 7 missions in total.
By using the visor you can see objects through walls and mark them permanently. This also works for these collectibles and makes it significantly easier to locate all of them.