Yes, there is (and has been for a real long time). It's called "Safe Area / Fundbüro".
I've never used it so I don't know if there is a fee, but I would assume there is one.
The last couple of years it has always been located between the Casino and Dub Station. It's always marked on the map, so you should find it even if it has moved this year.
Here the info text from the 2019 guide:
"Safe Area
You can store everything that you would rather not leave in your tent in the Safe Area. You can also charge your camera and phone here. This is also Fusion’s lost & found. If you lose anything during the festival, you can contact the festival team afterwards at
safe@fusion-festival.de"