May I ask why you are removing your battery? If it is because you are having battery issues, then you should have simply taken it to an Apple Store, as you have now voided your warranty completely.
As for the battery, use heat to soften the adhesive underneath, and pry out quickly, use something wide and flat to get more surface under the battery, because if you're using something thin and flat, that is the reason why you have probably pierced it. :-)