Just to add a few comments to those that have been made already:

You cannot buy nor refund the yikatong card at PEK T3 (and presumably T2-3 as well). It can be done at Dongzhimen, but that also makes "yikatong" a contradiction, because it leaves the Airport express out of the loop.

IIRC, I had to show my passport in order to buy the yikatong card, so kiosk is not an option.

Not all subway stations in Beijing sell/refund/add value to yikatong cards.

Yikatong is very convenient during rush hour. It also saves the hassle of hoarding RMB1 bills.