I like to know if there is a luggage storage in the Liepzig Hauptbahnhof where I can leave a big dufflebag for few hours in between catching a train to Berlin.

Almost without exception every German station has automated left-luggage lockers, and I would be surprised if Leipzig did not.

Yes, there are numerous lockers in different sizes. Have some coins at hand to pay for them.
It is located next to the main entrance of the western side of the station, next to the main staircase. You cannot miss.
In case you don't find ask at the info point in the centre of the station, I think in the opposite of plattform 13.

Chris

http://www.bahn.de/pv/view/static/bahnhofsplaene/leipzig.pdf

There are luggage lockers (Schließfach) at several locations in the railway station (see map). And there is also a left luggage office.

And here some nice pics
http://www.leipzigfoto.com/english/02_gallery/railway/railway.html