stay in PEK airport hotel after arrival

Hello, I am arriving in Terminal 2 at 27 July 01:55 am and I need to wait at the airport to pick up my sister who is arriving 8 hours later, so I would like to stay in the airport until then. Is there such an option, and can I book a room for some hours? My question is essentially what happens if I have to exit the airport area, I am not transit passenger.

Thank you in advance!