can i take iPad with lithium battery onto airplane?

The airlines only require that your iPad is powered off or in Airplane Mode during the flight so that it does not interfere with their on-flight equipment. The fact that the iPad has a lithium battery is not an issue.

I believe the issue is putting items with lithium batteries in your checked luggage. Carrying it with you is no problem.

Yes, no problem.

I regularly travel on airplanes with my iPad. No problem . You will see many others as well.